PERFORMANCE MODELLING OF REFRIGERANTS
IN A VAPOR COMPRESSION REFRIGERATION CYCLE
SITI MARIAM BTE BASHARIE
This project report is submitted as a part of the
fulfilment of the requirement for the award of the
Master Degree in Mechanical Engineering
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
NOVEMBER, 2005
iii
Istimewa Buat Suami Tersayang,
Md Norrizam Mohd Jaat
“ terima kasih atas sokongan dan doronganmu”
Buat Anak-anak Yang Dikasihi,
Adam Haikal dan Aiman Syakirin
Serta Untuk
Keluarga Tercinta
iv
ACKNOWLEDGEMENT
Alhamdulillah, great thanks to Allah for giving me strength and conveniences during this
project. I would like to express my special thank to my supervisor, Dr. Normah Ghazali
for her guidance, advice and help. Also special thanks to Prof. Amer Nordin Darus,
Rahim and Mas Fawzi for their directly and indirectly contribution and helps during the
preparation of this project. Also very thankful to my parents and family for their help and
support during this course.
v
ABSTRACT
The simulation model based on the actual vapor compression cycle is performed
in order to evaluate the performance of 14 refrigerants in terms of first law and second
law efficiency. A 10% pressure drop is modelled in both the condenser and evaporator.
The refrigerants that have been evaluated include R12, R22, R502, and their alternatives
R134A, R401A, R401B, R402A, R402B, R404A, R407C, R410A, R408A, R409A, and
R507. Effects of evaporating and condensing temperature on the COP, second law
efficiency and irreversibility have been studied. The evaluation results show that R401A,
R401B, and R409A are predicted as the best replacements for R12. R410A is predicted as
the best alternative for R22, while R402B, R407C, and R408A are the best alternatives
for R502 in terms of COP and second law efficiency. The results of actual cycle model
show better predictions than that obtained with the ideal cycle model.
vi
ABSTRAK
Model simulasi berdasarkan kitar pemampatan wap sebenar telah dihasilkan bagi
tujuan menilai prestasi 14 bahan pendingin dari aspek kecekapan hukum pertama dan
kedua. Kedua-dua pemeluwap dan penyejat telah dimodelkan dengan mempunyai
kejatuhan tekanan sebanyak 10%. Bahan pendingin yang telah diuji termasuklah R12,
R22, R502, dan bahan pendingin alternatif iaitu R134A, R401A, R401B, R402A, R402B,
R404A, R407C, R410A, R408A, R409A, dan R507. Kajian kesan suhu penyejatan ke
atas pekali prestasi, kecekapan hukum kedua dan ketidakbolehbalikan juga telah
dijalankan. Hasil penilaian menunjukkan R401A, R401B, dan R409A sebagai alternatif
terbaik mengantikan R12. R410A didapati alternatif terbaik bagi R22, manakala R402B,
R407C, dan R408A untuk R502 dari aspek pekali prestasi dan kecekapan hukum kedua.
Keputusan yang diperolehi menunjukkan model kitar sebenar dapat menghasilkan
penilaian yang lebih baik berbanding model kitar unggul.
vii
TABLE OF CONTENTS
CHAPTER
CHAPTER I
CONTENTS
PAGE
TITLE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xi
LIST OF SYMBOLS
xiii
LIST OF APPENDICES
xiv
INTRODUCTION
1
1.1
Introduction
1
1.2
Refrigerants and Its Alternatives
2
1.3
Performance Evaluation of Refrigerants in
Refrigeration Cycle
1.4
3
Simulation Model of Refrigerants Performance
Evaluation
6
1.5
Objectives
12
1.6
Scopes of Project
12
viii
CHAPTER II
CHAPTER III
THEORY AND FORMULATION
13
2.1
Actual Vapor Compression Refrigeration Cycle
13
2.2
Calculating Thermodynamic Properties
15
2.3
Performance Analysis
17
RESEARCH METHODOLOGY
20
3.1
Introduction
20
3.2
Simulation Model
21
3.2.1
23
3.3
CHAPTER IV
Thermodynamics Model
Computer Programming
25
3.3.1
26
The REFTEST Simulation Program
3.4
Performance Evaluation
32
3.5
Performance Analysis
33
PERFORMANCE TEST AND ANALYSIS
4.1
COP Analysis of Refrigerants and Its
Alternatives
4.2
37
The effect of changes in evaporating temperature
on the COP
4.4
34
Second Law Efficiency of Refrigerants and Its
Alternatives
4.3
34
39
The effect of changes in condensing temperature
on the COP
40
4.5
Refrigerant with higher total irreversibility
41
4.6
Locating the primary source of irreversibility
42
4.7
The effect of changes in evaporating temperature
on the irreversibility
43
4.8
The effect of irreversibility on second law efficiency 44
4.9
Comparison between the ideal and actual cycle with
pressure drops
47
ix
CHAPTER V
CONCLUSION
47
REFERENCES
49
APPENDIX A
51
APPENDIX B
72
xiv
LIST OF APPENDICES
APPENDIX
DESCRIPTION
PAGE
A
Programming codes
51
B
Test results
72
xi
LIST OF FIGURES
FIGURE
DESCRIPTION
PAGE
1.1
Impact of critical temperature of volumetric capacity and COP
4
1.2
Vapor compression cycle simulated by Cycle 11
8
1.3
Main graphic user interface (GUI) of Cycle D
9
1.4
Welcome interface of simulation program developed by Sia
10
1.5
Input interface of simulation program developed by Sia
11
1.6
One of the output interfaces of simulation program developed
11
by Sia
2.1
T-s diagram for the ideal cycle
14
2.2
T-s diagram for the actual cycle
14
3.1
The general flow chart of methodology of the study
20
3.2
The schematic diagram of the simulation model cycle
21
3.3
The T-s diagram of the simulation model cycle
21
3.4
The general flow chart of the computer programming
26
3.5
Welcome interface of REFTEST
27
3.6
Input interface of REFTEST
28
3.7
The interface of thermodynamics property
30
3.8
Interface of first law analysis
31
3.9
Interface of second law analysis
32
4.1
COP of R12 and its alternatives
35
4.2
COP of R22 and its alternatives
36
4.3
COP of R502 and its alternatives
37
4.4
Second law efficiency of R12 and its alternatives
38
4.5
Second law efficiency of R22 and its alternatives
39
4.6
Second law efficiency of R502 and its alternatives
39
4.7
COP versus condensing temperature
40
4.8
Total irreversibility of refrigerant
41
xii
4.9
The percentage of component irreversibility of R407C and
42
R134A
4.10
Irreversibility versus evaporating temperature
43
4.11
Percentages of lost work for condenser and evaporator as a
44
function of evaporating temperature predicted by Yumrutas et
al. [19]
4.12
The effect of irreversibility on second law efficiency
45
4.13
Second law efficiency and total exergy loss in percentage
45
predicted by Yumrutas et al. [19]
xiii
LIST OF SYMBOLS
COP
Coefficient Of Performance
COPcarnot Coefficient Of Performance of a carnot cycle
COPref
Coefficient Of Performance of a refrigeration cycle
COPrev
Coefficient Of Performance of a reversible cycle
h
Specific enthalpy, h=u+Pv, kJ/kg
i
Specific irreversibility, kJ/kg
I
Irreversibility, kJ
m&
Mass flow rate, kg/s
P
Pressure, kPa
Q
Total heat transfer, kJ
Q&
Heat transfer rate, kW
Qevap
Useful refrigerating effect, kJ
s
Specific entropy, kJ/kgK
S
Total entropy, kJ/K
T
Temperature, °C or K
TO
Ambient temperature, °C or K
TR
Refrigerated space temperature, °C or K
Tsurr
Surroundings temperature, °C or K
u
Specific internal energy, kJ/kg
v
Specific volume, m3/kg
Wnet
Net work, kJ
W&
Power, kJ/kg
ηΠ
Second law efficiency
x
LIST OF TABLES
TABLE
DESCRIPTION
PAGE
3.1
The key state point refer to Figure 3.2 and Figure 3.3
22
3.2
The set values of temperature ranges of input parameters
29
3.3
The default values of input parameters
29
3.4
The units of thermodynamic properties
30
3.5
The list of refrigerants that will be evaluated and their
33
alternatives
4.1
Pressure ratio comparison between R12 and R134A
36
4.2
Component irreversibility of refrigerant R407C and R134A
42
4.3
Comparison between ideal and actual cycle of refrigerant R12
46
1
CHAPTER I
INTRODUCTION
1.1
Introduction
Chlorofluorocarbon (CFC) issues like ozone layer depletion and global warming
have brought many studies for alternative refrigerants with suitable properties to replace
the CFC and hydrochlorofluorocarbon (HCFC) refrigerants. Now, more new refrigerants
are appearing on the market. This is due to the effort that has been made to find suitable
replacements for CFC and HCFC refrigerants. R22 for example, is widely used in
refrigeration system and being the most popular replacement for R12 which has been
totally phase out by January 1, 1996 (unless for the continued use from existing and for
continued production for very limited essential uses) [1].
As the production of R22 is being totally phase out by January 1, 2030, the rush to
find its alternative continues. The study of performance evaluation of the R22 and its
possible replacement has become important especially by compressor manufacturers.
Before an experimental test in an actual system is carried out, the test through simulation
program becomes useful as a preliminary evaluation of a refrigerant performance.
Comparison and evaluation of the performance of a refrigerant and its possible
replacement, is done through the theoretical testing or testing in actual application [2].
Theoretical testing and comparison are usually made using a simulation program. Tests
enable the performance of refrigerant alternatives to be evaluated across a broad range of
operating conditions.
2
Theoretical testing would depend on refrigerant properties while an actual test
would depend more on detailed specification of the equipment. The way refrigerants
behave and perform in theory or simulation differs from which it perform in an actual
system. However, a theoretical test is very useful as a preliminary evaluation before an
extreme experimental test which involved a high cost is carried out in a full size
equipment.
1.2
Refrigerants and Its Alternatives.
CFC and HCFC have taken the leading stand in refrigerating system since 1930s
until early eighties. They became very popular and were found as the refrigerants with
good performance compared with other refrigerants. However, by the eighties, CFC was
considered as detrineutral to the environment, causing significant damage to the ozone
layer. This resulted in the phasing out of the use and manufacture of CFCs, and later of
HCFCs. It generates many studies as the search for alternative refrigerants with suitable
properties to replace the CFCs and HCFCs. Continues now, many new refrigerants have
been produced and commercialized by refrigerant manufacturers like DuPont, ICI, and
Honeywell. Most of them are hydrofluorocarbons (HFC) which do not contain chlorine
and have zero Ozone Depletion Potential (ODP).
The most common CFCs and HCFC that are being phased out are R12, R22 and
R502. R12 is used in domestic refrigerators and freezers, and in automotive air
conditioners. The most popular alternative for R12 when the CFCs phase out began is
R22. It is pure fluid and has a very good efficiency characteristic on medium temperature
range applications. But when the phase out of R22 began, the search for R12 alternatives
continues. There are several alternative refrigerants that are potential substitutes for R12
and most of them are mixtures but some are pure fluids. They include R134A, R401A,
R401B, R402B, and R409A.
R22 which is a HCFC is widely used in window air conditioners, heat pumps, air
conditioners of commercial building and in large industrial refrigeration systems. It is
considered as transitional or “interim” alternatives and has a high performance
characteristic. Its contain chlorine and will eventually be phased out but can be
3
manufactured and used until 2030. The “long-term” alternatives for R22 that have been
produced are mostly mixtures that do not contain any chlorine such as HFCs. They
include R404A, R407C, R410A, and R507. R407C was the first to replace R22, but it was
found out in recent research that new replacements R410A and R404A show better
performance compared to R407C.
Other pure fluids alternatives for R22 are ammonia (R717) and propane (R290).
Ammonia has been used for over 100 years. It is a low cost refrigerant with excellent
thermodynamic properties and zero ODP. But it is toxic and flammable. Similar to
ammonia, propane is no longer of interest because it is flammable even though it has
similar thermophysical properties as R22 [2]. Other HCFC that has been considered is
R134A which is a widely used as substitute for R22 in large chillers, as well as in
automotive air conditioners and refrigerators.
R502 which is a blend of R115 and R22 is the dominant refrigerant used in
commercial refrigeration systems such as those in supermarkets because it allows low
evaporating temperatures while operating in a single-stage compressor. One of the
replacements that have been produced for R502 is R404A. As discussed by David Wylie
and Davenport [2], the data of Alternative Refrigerants Evaluation Program (AREP)
indicates that R404A has about the same capacity as R502 at lower condensing
temperatures, but rapidly decreasing at higher condensing temperatures. For a fixed
evaporating temperature, R404A has a lower efficiency when condensing temperature
increase compared to R502. It has less efficiency when compared to R502 at high
condensing temperature. Other mixtures that have replaced R502 include R402A, R402B,
R407C, R408A and R507.
1.3
Performance Evaluation of Refrigerants in Refrigeration Cycle.
The study of refrigerant performance is very important because the behaviour of
refrigerants or refrigerant mixtures strongly influence the design of the refrigeration
system. Different refrigerants have performed differently based on their thermodynamic
properties and behavior. According to Vaisman [3], different refrigerants shows different
heat transfer ratios and pressure drops in condensors and evaporators.
4
Yana Motta and Domanski [4], reported on how the refrigerant’s critical
temperature affects the refrigerant performance in the vapor compression cycle. As shown
conceptually in Figure 1.1, differences in refrigerant’s critical temperature and the shape
of the two-phase dome on T-s diagram explain the different performance trends of the
refrigerants.
Figure 1.1 : Impact of critical temperature of volumetric capacity and COP [4].
For the same condensing and evaporating temperature, a fluid with a lower critical
temperature will tend to have a higher volumetric capacity and a lower Coefficient of
Performance (COP) while a fluid with a higher critical temperature will tend to have a
lower volumetric capacity and a higher COP. The difference in COPs is related to the
different levels of irreversibility on the superheated-horn side and at the throttling process.
These levels of irreversibility vary with operating temperatures because the slopes of the
saturated liquid and vapor lines change, particularly when approaching the critical point
[4]. These are important issues besides considerations like safety, availability, and cost.
The performance comparison which was carried out by simulation had been done
by many researchers in terms of first law and second law analysis. Yana Motta and
Domanski [4] studied the performance of refrigerant R22 and its possible replacements
which are R134a, R290, R410A and R407C in an air-cooled air conditioner system. All
5
these refrigerants have been evaluated using the NIST’s simulation program Cycle 11.
The study focuses on the COP and the effect of outdoor temperature on system capacity.
It includes performance results for the basic cycle and for the cycle with a liquid line and
suction line heat exchanger. The result shows a decreasing in system performance with
increasing outdoor temperature. It also shows that the fluids with a low critical
temperature experience a larger degradation of cooling capacity.
Vaisman [3] has presented the performance evaluation of R22 and R407C in an
air conditioner system with a rotary vane compressor. The exergy approach is applied and
performance evaluation is produced taking into account the actual system configuration
including compressor data, coil’s design, suction line, discharge line and liquid line
design, and the data from the fan and blower. The result shows that R407C is compatible
with R22 in terms of air conditioner performance.
Spatz and Yana Motta [5] evaluated the performance of R22 but in medium
temperature refrigeration systems with its potential alternatives of R410A, R404A, and
R290. The studies include thermodynamic analysis, comparison of heat transfer and
pressure drop characteristics, system performance comparisons using a validated detailed
system model, safety issues, and determination of the environmental impact of refrigerant
selection. The result shows that the R410A is an efficient and environmentally acceptable
option to replace R22 in medium temperature applications.
Stegou-Sagia and Paignigiannis [6] have focused on exergy analysis of 10
working fluids including R401B, R401C, R402A, R404A, R406A, R408A, R409A,
R410A, R401B, R410B and R507. The performances of these mixtures have been
compared with the old refrigerants they replace which are R12, R22 and R502. When
comparing the exergy efficiencies at constant evaporating temperature, the exergy losses
of old refrigerants are found lower. The compression process has been predicted as the
process which involved higher exergy losses followed by condensation process. R406A
shows the highest value of exergy efficiency, while the lowest value is belongs to the
mixture R409A.
C.K Sia [7] has developed a simulation program based on an ideal cycle to
evaluate the performance of R12 and its possible replacements R134A and R401A, R22
6
and R407C, also R502 and its replacements R402A and R402B. The performance
evaluation is focused on COP, second law efficiency, irreversibility, and discharge
temperature. The predictions show that R134A as a good replacement for R12, R407C for
R22, and R402A for R502.
1.4
Simulation Model of Refrigerants Performance Evaluation.
As described by Domanski and McLinden [8], there are a number of methods that
might be used to predict the refrigerant performance. The simulation cycle can be
modeled as a Carnot cycle, ideal, actual or actual cycle with detailed equipment
specification. Carnot cycle is the simplest cycle analysis. It represents the refrigeration
cycle which operates between two constant low and high temperatures. This cycle assume
reversible compression and expansion processes, with isothermal heat supply and heat
rejection.
An ideal cycle is modeled as a constant pressure and temperature process in the
condenser and evaporator. Refrigerant leaves the condenser as saturated liquid and leaves
the evaporator as saturated vapor. It does not consider the subcooling process at the
condenser outlet and superheating process at the compressor inlet. The compression
process is modeled as an isentropic process.
An actual cycle model normally considers at least subcooling and superheating
processes. Refrigerant leaves the condenser as liquid and enters the compressor slightly
superheated. Besides the isentropic compression process, the process in the compressor
can be modeled as having isentropic efficiency. Other components such as liquid line and
suction line heat exchanger may be included. Both the ideal and actual cycle usually
needs a complete set of thermodynamic properties data [8].
For an actual cycle with detailed equipment specifications, it needs more detailed
information on the actual system configuration. As presented by Vaisman [3], the actual
components data such as compressor performance data, design parameters of evaporator
and condenser coils, performance of fans and blowers, and, suction line, discharge line
7
and liquid line design must be taken into account. The thermodynamic cycle is defined
with actual pressure drops in condenser, evaporator and suction line.
The Alternative Refrigerant Evaluation Program (AREP), an international
cooperative program designed to identify alternative refrigerants for R22 and R502,
which is coordinated by Air Conditioning and Refrigeration Institute (ARI), established
the testing and performance evaluation methodologies. As discussed in [2], the four
phases of AREP tests that can be used as a guidelines to improved the simulation model
are ;
i.
Firstly, determine how well a given compressor operates with a particular refrigerant
by evaluates the performance of possible alternative in compressors using calorimeter
testing.
ii.
Second, the refrigerant is tested in existing refrigeration systems in “drop in” tests
without any modification to the system equipment.
iii.
Then, perform the heat transfer tests for the refrigerant under various operating
conditions during both condensing and evaporating stages. These tests measure
refrigerant-side heat transfer coefficient in “enhanced tubes”.
iv.
Finally, use the data from the three tests in system computer simulation and apply the
information to improve the computer model in order to achieve a very fair prediction
result of actual system.
The refrigerant performance evaluation and comparison can be used as a tool to
evaluate the impact of components modification on the system performance. This model
can provide very close information to the actual laboratory test. Beside the
thermodynamic properties, a complete set of the transport properties data is also needed
[8].
Many simulation programs have been developed to evaluate the performance of
refrigerant and refrigerant mixtures in the vapor compression cycle. One of them is called
Cycle 11. As reported by Domanski and McLinden [8], it is an evolution from the earlier
model, Cycle 7, which is developed by McLinden at the National Institute of Standards
and Technology (NIST), U.S.A. They called it a semi-theoretical model and the name
refers to the eleven state point of the cycle model as shown in T-s diagram in Figure 1.2.
8
Figure 1.2 : Vapor compression cycle simulated by Cycle 11 [9].
The model performs simulation for user-specified temperature profile of the heat
source and heat sink. The cycle consists of a basic cycle with an isentropic compression
process, isobaric heat transfer in liquid line and suction line heat exchangers, and an
irreversibility adiabatic expansion process. The user may specify a cross-flow, counterflow, and parallel-flow evaporator and condenser with refrigerant subcooling and
superheat, where appropriate.
The compressor model has three option type of compression process. They are
isentropic, polytropic or either of these processes with the inclusion of volumetric
efficiency and a representation of the heat transfer to the suction gas and from the
discharge gas which occurs in a hermetic compressor.
.
The output of the model includes thermodynamic properties at the key cycle
points, capacities, and the COP of heating and refrigeration. This program employs
FORTRAN subroutines from a NIST’s REFPROP database to calculate refrigerant
thermodynamic properties.
Other simulation programs that have been published is SERCLE (single
evaporator refrigerator cycle model) [9] and Cycle D which is quite similar to the Cycle
11 program. Figure 1.3 shows the interface of the Cycle D simulation program. Cycle D
is a design tools used to simulate the vapor compression refrigeration cycle produced by
NIST [10].
9
Figure 1.3 : Main graphic user interface (GUI) of Cycle D [10].
C.K Sia [7] has developed a simulation program called “Second Law Analysis of
Refrigerant”. The simulation model is based on the ideal cycle and focussed on exergy
analysis of refrigerant in a vapour compression cycle. The main interface of the program
is shown in Figure 1.4 while Figure 1.5 is input interface and Figure 1.6 is one of the
output interfaces.
10
Figure 1.4 : Welcome interface of simulation program developed by Sia [7].
As shown in Figure 1.5 and 1.6, the inputs of the simulation program include
condensing pressure, suction pressure, discharge temperature and ambient temperature.
The outputs include energy balance in compressor, condenser, and evaporator,
irreversibility and second law efficiency of each component. Other output includes
thermodynamic properties at each state point which shows in other program interface.
11
Figure 1.5 : Input interface of simulation program developed by Sia [7].
Figure 1.6 : One of the output interfaces of simulation program developed by Sia [7].
12
1.5
Objectives
This project extends the previous work done by C.K. Sia [7] which has simulated
the performance of refrigerants in an ideal cycle. The objectives of this study are;
1. To model the actual vapor compression refrigeration cycle.
2. To perform the simulation program for refrigerant performance evaluation.
3. To evaluate the performance of some common refrigerants and its alternatives.
4. To compare the results with previous results predicted by C.K. Sia [7] or published
data.
1.6
Scopes of Project
1. Literature review on the performance evaluation of refrigerants through theoretical
and actual test.
2. Performing a steady state model of actual vapor compression refrigeration cycle.
3. The computer program involved the used of set data of refrigerant thermodynamic
properties.
4. The selection of refrigerants to be tested is based on the refrigerants that have been
studied by previous researcher or that have been tested and commercialized by
manufacturers.
5. Performance evaluation of refrigerants and it alternatives is based on the drop-in
replacement evaluation.
13
CHAPTER II
THEORY AND FORMULATION
2.1
Actual Vapor Compression Refrigeration Cycle
An actual vapor compression refrigeration system operates differently from the
ideal cycle in many respects. These deviation are caused by irreversibilities which occurs
within the system. They include fluid friction between fluids and system components,
heat transfer between the refrigerant and its environment, and pressure drop which occurs
everywhere in the system except in the compression process [1]. In addition, the working
fluid is actually not a pure substance of the refrigerant but a mixture of the refrigerant and
the lubricating oil. These entire phenomenons caused the deviations from a theoretical or
ideal cycle.
The essential differences between these actual and ideal cycles on the T-s
diagram appear in the subcooling of the liquid leaving the condenser, in the superheating
of the vapour leaving the evaporator, in the pressure drops in the condenser and
evaporator, and in the compression process of compressor (Figure 2.1).
14
Figure 2.1 : T-s diagram for the ideal cycle [11].
Figure 2.2 : T-s diagram for the actual cycle [11].
In an ideal cycle, the refrigerant is assumed to leave the condenser and enters the
expansion device as saturated liquid. In an actual cycle, subcooling of the liquid in the
condenser is normally desirable to ensure that 100% liquid will enter the expansion
device. Subcooling decreases the enthalpy of the refrigerant entering the evaporator,
resulting in an increase in the cooling capacity.
For evaporator, the system is normally designed so that the refrigerant is slightly
superheated to ensure that the refrigerant is completely vaporized when entering the
compressor. This is to avoid the droplets of liquid from entering the compressor because
15
this can cause damage to the components of the compressor. This differs from the ideal
cycle, where the refrigerant that leaves the evaporator and enters the compressor is
assumed saturated vapor.
Besides these differences, the ideal cycle is assumed without pressure drop in
condenser and evaporator. However, because of fluid friction, the pressure of the
refrigerant drops in the actual cycle. The experimental data of air-conditioning system test
obtained by Abd. Rahim [12], using R134A as working fluid shows that the pressure drop
in the condenser and evaporator is about 10%.
For the compressor, the compression process is assumed reversible and adiabatic,
thus isentropic in an ideal cycle. But for the actual system, the compression process
involved friction and heat transfer from or to the surroundings. The compression process
no longer operates as an isentropic process. It might decrease or increase the entropy,
depending on the direction and on which effects dominate. It usually depends on the load
and requirements. The compression process 1-2’ (decrease in entropy) may be even more
desirable than the isentropic process since the specific volume of the refrigerant and thus
the work input requirement are smaller. For this process they have a compressor
isentropic efficiency which is equal to the ratio of the actual compression work and
isentropic compression work. For a well designed compressor, the compressor isentropic
efficiency is about 75% to 85% [11].
2.2
Calculating Thermodynamic Properties
There are several ways in calculating the thermodynamic properties for a
computer program. Tables or tabulated data that have been tabulated from experiments
data are the most popular and easy way in determining or calculating thermodynamic
properties of the refrigerant.
For a complex system analysis, equation of state may be a better approach for a
faster calculation. There are many equation of states that can be used to describe the
relationship between temperature, pressure and volume for a given substance or mixture
of substances. It depends on the requirements such as the accuracy, complexity, speed and
16
the quantity of data required [13]. The Modified Benedict-Webb-Rubin (MBWR)
equation of state is one of the more recent and very accurate equations of state. It provides
the most accurate fit of the thermodynamics data and represent the data with accuracy and
consistency throughout the entire range of temperature, pressure, and density [14]. From
McLinden [15], the form of MBWR equation of state is expressed as follows,
p=
9
⎛ −V 2
a
RT
+ ∑ n + exp⎜⎜ 2c
V
n = 2 Vn
⎝ V
⎞ 15 a n
⎟⎟ ∑ 2 n −17
⎠ n =10 V
(2.1)
where an are functions of temperature involving a total of 32 adjustable parameters.
The Martin Hou equation of state is another very popular equation of state
developed for fluorinated hydrocarbon properties. While not as accurate as the data from
the MBWR equation of state, particularly in the superheated region, data calculated using
this Martin Hou equation of state should be sufficient for most engineering calculation
[14]. The Martin Hou equation of state is expressed as follows,
RT
A + B2T + C2e
P=
+ 2
v−b
(v − b )2
A4 + B4T + C4e
(v − b )4
− kT
Tc
− kT
Tc
A + B3T + C3e
+ 3
(v − b )3
A + B5T + C5e
+ 5
(v − b )5
− kT
Tc
− kT
Tc
A + B3T + C3e
+ 3
(v − b )4
− kT
A + B T + C6e
+ 6 αv 6
e 1 + C ' eαv
(
)
− kT
Tc
+
Tc
(2.2)
where Ai, Bi, Ci, k, b, and α are constant coefficients.
As discussed earlier, the equation of state only provides the relationship between
pressure, temperature, and specific volume. Other thermodynamic properties include
internal energy, enthalpy and entropy should be calculated using other equations or
relationship.
17
2.3
Performance Analysis
The performance of a refrigeration cycle can be expressed in terms of first law or
second law analysis. The first law or energy analysis is still the most common method
used in the analysis of refrigeration system. From this first law point of view, the
performance of a refrigeration cycle is a measured by the coefficient of performance
(COP) given by,
COPref =
Qevap
Wnet
(2.3)
where Qevap is heat supplied and Wnet is the net energy supplied which is usually in the
form of mechanical and electrical work. For a vapour compression system, these may
include work to the compressor and fans or pumps [1].
However, the first law analysis only concerned with the conservation of energy
and gives no information on how, where, and how much the cycle performance is
degraded. The second law or exergy analysis gives more detail on this matter including
the information of the irreversibility. The second law may be described in several ways.
One method uses the concept of entropy flow in an open system and the irreversibility
associated with the process.
The irreversibility or degradation of energy caused by the irreversibilities can be
viewed as the wasted work potential or the lost opportunity to do work. Efforts should be
made to minimise them in order to improve the performance of the system. For this
purpose, the primary source of irreversibility in the system should be predicted and
located.
Taken from ASHRAE Handbook 2001 [1], the second law of thermodynamics can
be described in terms of entropy as,
dS system =
δQ
+ δmi s i − δme s e + dI
T
(2.4)
18
where,
dS system = total change within system in time dt during process.
δQ
T
= entropy change caused by reversible heat transfer between system and
surroundings.
δm i s i
= entropy increased caused by mass entering ( incoming).
δm e s e
= entropy decreased caused by mass leaving ( exiting).
dI
= entropy caused irreversibilities ( always positive).
Equation (2.4) accounts for all entropy changes in the system. Rearranged, this equation
becomes,
[
δQ
= T (δme s e − δmi s i ) + dS system − dI
T
]
(2.5)
In integrated form, if inlet and outlet properties, mass flow and interactions with
the surroundings do not vary with time, the general equation for the second law is,
(S
final
− S initial
)
system
=
δQ
+
T
rev
∫
∑ (ms ) − ∑ (ms )
in
out
+I
(2.6)
where,
S final
= total entropy of the system at final state.
S initial
= total entropy of the system at initial state.
In many applications the process can be considered to be operating steadily with
no change in time. The change in entropy of the system is therefore zero. The
irreversibility rate, which is the rate of entropy production caused by irreversibilities in
the process, can be determined by rearranging Equation (2.6),
i=
∑ (m& s )out
−
∑ (m& s )in − ∫
Q&
Tsurr
(2.7)
19
Based on the first law of thermodynamics, the energy balance for a steady flow
process of thermodynamic system in terms of enthalpy is given by,
∑
out
⎛
⎞
V2
m& ⎜⎜ h +
+ gz ⎟⎟ −
2
⎝
⎠
∑
in
⎛
⎞
V2
m& ⎜⎜ h +
+ gz ⎟⎟ + Q& − W& = 0
2
⎝
⎠
(2.8)
Equation (2.8) can be used to replace the heat transfer terms in Equation (2.7). Combining
Equation (2.7) and Equation (2.8), and applied to a steady state system with one mass
flow in, the same mass flow out, no work, and negligible kinetic or potential energy flows,
yields,
⎡
(h − hin )⎤
i = m& ⎢(s out − s in ) − out
⎥
Tsurrounding ⎥⎦
⎢⎣
(2.9)
Application of the second law to an entire refrigeration cycle shows that a
completely reversible cycle operating under the same conditions has the maximum
possible COP. A measure of the departure of the actual cycle from an ideal reversible
cycle is given by the second law efficiency,
η∏ =
COPref
COPrev
(2.10)
where COPrev is a COP of Carnot cycle which usually serves as an ideal reversible
refrigeration cycle. COP of a Carnot cycle is given by,
COPcarnot =
TR
TO − TR
(2.11)
where TR is the refrigerated space temperature and TO is the ambient air temperature.
20
CHAPTER III
RESEARCH METHODOLOGY
3.1 Introduction
The methodology of this study can be divided into a few sections. Figure 3.1
shows a general flow chart of methodology of the study.
Simulation Model
Computer Programming
Performance Evaluation
Performance Analysis
Yes
More Evaluation?
No
STOP
Figure 3.1 : The general flow chart of methodology of the study.
21
3.2
Simulation Model
The simulation model of an actual vapor compression cycle consists of 6
components which are compressor, condenser, liquid line, expansion device, evaporator,
and suction line. The schematic and T-s diagram of this model cycle is shown in Figures
3.2 and 3.3 respectively, while the state location is described in Table 3.1.
.
Figure 3.2 : The schematic diagram of the simulation model cycle.
Figure 3.3 : The T-s diagram of the simulation model cycle.
22
Table 3.1 : The key state point refer to Figure 3.2 and Figure 3.3.
State Point
State
1
Compressor inlet.
2
Compressor outlet, condenser inlet.
3
Condenser outlet.
4
Inlet to isenthalpic expansion device.
5
Expansion device outlet, evaporator inlet.
6
Evaporator inlet.
This model is a steady state model which considers the subcooling at the
condenser outlet and superheating at the compressor inlet. The refrigerant state at
condenser outlet (state point 3) is assumed saturated liquid while refrigerant state at
evaporator outlet (state point 6) is assumed saturated vapor.
The refrigerant enters the condenser at state 2 as superheated vapor at high
temperature. The superheated vapor is then condensed to a liquid at low pressure and
temperature during process 2-3. During this process, the heat is rejected and the state of
superheated vapor is changed to the high pressure liquid-vapor before it fully changed to
100% liquid at state 3. Because of fluid friction, the pressure drops from P2 to P3 and the
drop is assumed at about 10%. The temperature at point 3 is represented as condensing
temperature.
The saturated liquid of refrigerant exit the condenser at state 3 and it is subcooled
to state 4 to ensure that the fluid is 100% liquid before it enters the expansion device.
Then, the refrigerant liquid expands from the higher pressure to the low pressure through
the expansion device from point 4 to point 5. At this point, the refrigerant leaves the
expansion device and enters the evaporator as a low quality saturated mixture.
In evaporator, the refrigerant completely evaporates by absorbing heat from the
refrigerated space. During process 5-6, the refrigerant mixture is changed to saturated
vapor at point 6. The pressure is drop from P5 to P6 and the drop is also assumed at about
10%. The temperature at point 6 is represented as evaporating temperature.
23
The saturated vapor that leaves the evaporator is then superheated to state 1 to
ensure the fluid is 100% vapour before it enters the compressor. The refrigerant vapour is
then compressed from P1 to P2 during compression process represented by line 1-2 or line
1-2’. This model assumed that the compression process has an isentropic efficiency.
However, the process of decrease or increase in entropy depends on the discharge
temperature (T2) that will be specified by the user. The line 1-2 represents the
compression process of increase in entropy while line 1-2’ represents decrease in entropy
process.
3.2.1 Thermodynamics Model
All thermodynamics analysis of this simulation model is referred to the T-s
diagram of Figure 3.3. For this steady state analysis the changes in potential and kinetic
energy is assumed negligible. The thermodynamic model of energy balance and
irreversibility of each system component, also performance calculations are described as
follows;
Compressor (1-2) :
Energy balance, W12 = h2 − h1
Irreversibility,
i12 = (s 2 − s1 ) −
(3.1)
W12
To
(3.2)
Discharge line (2-3) :
Energy balance, Q23 = h3 − h2
Irreversibility,
i23 = (s3 − s 2 ) −
(3.3)
Q23
TO
(3.4)
Condensor (3-4) :
Energy balance, Q34 = h4 − h3
(3.5)
24
Irreversibility,
i34 = (s 4 − s3 ) −
Q34
To
(3.6)
Liquid line (4-5) :
Energy balance, Q45 = h5 − h4
Irreversibility,
i45 = (s5 − s 4 ) −
(3.7)
Q45
To
(3.8)
Expansion device (5-6) :
Energy balance, h5 = h6
(3.9)
i56 = (s 6 − s5 )
(3.10)
Energy balance, Q67 = h7 − h6
(3.11)
Irreversibility,
Evaporator (6-7) :
Irreversibility,
i67 = (s 7 − s 6 ) −
Q67
TR
(3.12)
Suction line (7-1) :
Energy balance, Q71 = h1 − h7
Irreversibility,
i71 = (s1 − s 7 ) −
(3.13)
Q71
To
(3.14)
The unit of irreversibility, i is in kJ/kgK. To obtain irreversibility, i in the unit of kJ/kg,
the result of irreversibility, i have to be multiply by To in unit Kelvin.
25
The COP of the cycle :
COP =
Q56 h6 − h5
=
W12 h2 − h1
(3.15)
COP of Carnot cycle :
COPcarnot =
TR
TO − TR
(3.16)
where TR is the refrigerated space temperature and To is the ambient air temperature.
Second law efficiency :
η∏ =
COP
COPcarnot
(3.17)
Total irreversibility:
i = i12 + i23 + i34 + i45 + i56 + i67 + i71
3.3
(3.18)
Computer Programming
The computer programming is developed using Microsoft Visual Basic 6.0. Visual
Basic provide essential graphic user interface (GUI) that enables the programmer to
create the software interface easily. Besides, it does have a high performance native code
compiler, which enables creation of applications and optimization of both client- and
server-side components. For this computer programming, the thermodynamics properties
of the refrigerants are calculated using REFPROP version 6.0 database [13], then saved in
data files. Figure 3.4 shows the general flow chart of the computer programming.
26
Start
Select Refrigerant
Input variables,
1. Tevaporating
2. Tcondensing
3. Tdischarge
4. Degree of subcool
5. Degree of superheat
6. Tambient
7. Trefrigerated space
Calculate
thermodynamic properties
(T, p, h and s) at every state
point
Data files of
Refrigerant
properties
Outputs calculation
1. COP
2. Irreversibility
3. Second Law Efficiency
End
Figure 3.4 : The general flow chart of the computer programming.
3.3.1
The REFTEST Simulation Program
The simulation program that has been performed is called REFTEST, refers to
‘Refrigerant Test’. In this simulation model, the condenser and evaporator is represented
by specifying the refrigerant condensing temperature and refrigerant evaporating
temperature in each of these components.
27
REFTEST covers 16 refrigerants which can be selected for simulation as the
working fluid. It includes 4 pure fluids which are R12, R22, R134A, and R290 (propane),
and 13 mixtures which are R401A, R401B, R402A, R402B, R404A, R407C, R408A,
R409A, R410A, R502, R507, and R507A. The thermodynamics properties of these
refrigerants are calculated using REFPROP version 6.0 database. Figure 3.5 shows the
display of welcome graphic user interface (GUI) while Figure 3.6 shows the input graphic
user interface of REFTEST. The welcome graphic user interface will appear as soon as
you activates or operates the REFTEST program.
Figure 3.5 : Welcome interface of REFTEST.
28
Figure 3.6 : Input interface of REFTEST.
In input interface, user has to select the refrigerant within the list of refrigerants.
Then he/she has to specify other inputs including discharge temperature (T2), condensing
temperature (T3), evaporating temperature (T6), degree of subcooling, degree of
superheating, ambient temperature (To), and refrigerated space temperature (TR). These
inputs have been set to the specified temperature ranges as shown in Table 3.2. The user
is only allowed to specify the inputs within the value that have been set which is based in
practical operating conditions.
29
Table 3.2 : The set values of temperature ranges of input parameters.
Parameters
Temperature ranges
Discharge temperature, (T2)
55°C to 80°C
Condensing temperature, (T3)
20°C to 50°C
Evaporating temperature, (T6)
-25°C to 25°C
Degree of subcooling
2°C to 15°C
Degree of superheating
2°C to 15°C
Ambient temperature, (TO)
20°C to 40°C
Refrigerated space temperature, (TR)
-5°C to 30°C
The input parameters also have been set to the default values as listed in Table 3.3 below.
Table 3.3 : The default values of input parameters.
Parameters
Default value (°C)
Discharge temperature, (T2)
80
Condensing temperature, (T3)
40
Evaporating temperature, (T6)
5
Degree of subcooling
5
Degree of superheating
5
Ambient temperature, (TO)
30
Refrigerated space temperature, (TR)
10
Once, the specification of the inputs have been completed, REFTEST will
calculate the thermodynamic properties and other outputs parameter including COP and
second law efficiency.
30
Figure 3.7 : The interface of thermodynamics property.
The thermodynamic property interface as shown Figure 3.7 will display the
thermodynamic properties of refrigerant at every state point. These properties include
temperature, pressure, enthalpy and entropy. Once you have selected the property,
REFTEST will also display the unit of the property. Table 3.4 shows the unit of each
property.
Table 3.4 : The units of thermodynamic properties.
Properties
Units
Temperature
°C
Pressure
kPa
Enthalpy
kJ/kg
Entropy
kJ/kg.K
31
Other information that will be displayed in this interface is the refrigerant group
and environmental effect terms of ODP and GWP value.
Figure 3.8 : Interface of first law analysis.
The interface of first law analysis as shown in Figure 3.8 contains the result of
COP of refrigerant, the value of power input and heat supply. It also displays all the
inputs or operating conditions that have been specified before and the T-s diagram of the
model cycle.
32
Figure 3.9 : Interface of second law analysis.
In the second law analysis interface, the data of irreversibility at each system
component besides the second law efficiency will be displayed. Other information
includes total irreversibility of the system and COP of carnot cycle as shown in Figure 3.9.
3.4
Performance Evaluation
The performance evaluation of refrigerants will be done in terms of first law and
second law analysis. The test on each refrigerant will be held at the same operating
conditions. The list of refrigerants and its alternatives that will be evaluated in this study
is shown in Table 3.5. It is based on those that have been evaluated and commercialized
by refrigerant manufacturers like DuPont and Honeywell, and also by previous
researchers [3], [7]. This is to provide a comparison data for this study. Comparison
between ideal and actual cycle will be made on one of any refrigerant that have been
33
tested in previous study on an ideal cycle. The test will be performed under similar
operating conditions.
Table 3.5 : The list of refrigerants and their alternatives that will be evaluated.
3.5
Refrigerant
Alternatives
R12 (CFC)
R134A, R401A, R401B, R402B, R409A.
R22 (HCFC)
R404A, R407C, R410A, R507.
R502 (CFC)
R402A, R402B, R404A, R407C, R408A.
Performance Analysis.
The performance of refrigerants and its alternatives will be evaluated in order to
predict the best replacements for them. The evaluation will be in terms of COP and
second law efficiency. The effects of changes in evaporating temperature on the COP,
second law efficiency and irreversibility will be studied. The prediction of the main
source of irreversibility will also be made. The results will be compared with the ideal
cycle [7] and other published data.
34
CHAPTER IV
PERFORMANCE TEST AND ANALYSIS
The performances of 14 refrigerants include R12, R22, R502, R134A, R401A,
R401B, R402A, R402B, R404A, R407C, R408A, R409A, R410A, and R507 have been
evaluated in terms of the first law and second law efficiency. The tests were performed to
obtain the data for COP, second law efficiency and irreversibility where each of them is
performed at the similar operating conditions. The data obtained then is plotted for
performance analysis. Some of the performance predicted by the simulation program been
compared with the result obtained by C.K Sia [7] and other published data.
4.1
COP Analysis of Refrigerants and Its Alternatives.
The COP analysis of refrigerants is carried out based on the following operating
conditions ; 40°C condensing temperature, 80°C discharge temperature, 5°C subcool, 5°C
superheat, and evaporating temperature range between -15°C to 15°C. Figure 4.1, 4.2 and
4.3 shows the plots of COP against the changes of evaporating temperature for R12, R22,
and R502 and their potential substitutes respectively.
35
5
R12
COP
4
R134A
R401A
3
R401B
2
R402B
1
R409A
0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.1 : COP of R12 and its alternatives.
The results of R12 and its alternatives show that the COP of R401A, R401B, and
R409A is higher than the COP of R12 over 15%. R402B seems to have a similar COP as
R12 except at high evaporating temperature while the COP of R134A is about 11% lower
than R12. The result for R401A and R134A does not agree with the results predicted by
Sia. In the ideal cycle, R134A is predicted to have the COP higher than R12 while R401A
shows a similar performance with R12. However, this prediction agrees with results
predicted by Xu and Clodic [16] and Chen and Prasad [17]. Xu and Clodic [16]
performed an experimental analysis while Chen and Prasad [17] evaluated the
performance of R12 and R134A using the simulation program which is based on the
actual cycle.
This shows a fair prediction of refrigerant R134A even though R134A is a well
known acceptable replacement for R12. According to thermodynamic properties, R134A
always works with a greater pressure ratio than R12 for a given temperature [16]. As
shown in Table 4.1, at 5°C evaporating temperature, R134A has a pressure ratio of 3.12
compare to R12 with pressure ratio of 2.94. For a drop-in replacement, R134A is less
efficient in the R12 system cycle. In a practical system, the modification of compressor
volumetric efficiency should be made to have a similar performance as the R12 system.
Examining the COP evaluation of R12 and its substitutes, R401A, R401B, and R409A
may be the best replacements for R12.
36
Table 4.1 : Pressure ratio comparison between R12 and R134A.
R12
R134A
P1
362
362
P2
1065
1130
Pressure ratio, P2 /P1
2.94
3.12
COP
5
4
R22
3
R404A
R407C
2
R410A
R507
1
0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.2 : COP of R22 and its alternatives.
The plots in Figure 4.2 show that R22 performs better than its alternatives. The
COP of R410A gives about 12% to 19% lower than R12 within the evaporating
temperature range. R407C has about 19% to 23% lower and both R404A and R507 give
about 48% to 51% lower than R22 in terms of COP. These predictions of COP are in
good agreement with previous result study by Sia and published data discussed by Spatz
and Yana Motta [5] and David Wylie and Davenport [2]. R22 is well known as a
refrigerant with excellent performance in vapor compression cycle.
It could be concluded that none of these alternatives match the performance
characteristics of R22 in terms of COP and second law efficiency. However, in terms of
this study, R410C could be concluded as the best replacement for R22 as it has the
highest performance compared to other alternatives.
37
5
R502
COP
4
R402A
3
R402B
2
R404A
R407C
1
R408A
0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.3 : COP of R502 and its alternatives.
In the COP analysis of R502 and its alternatives, the results of R402A and R404A
show lower performance compared to R502 with R404A giving the largest difference.
R402B and R408A perform better than R502 at about 14% to 20% while R407C shows
30% higher than R502. When compared to the results obtained by Sia, only R402A
prediction is in agreement. The result shows that R407C, R402B and R408A could be the
best replacement for R502.
4.2
Second Law Efficiency of Refrigerants and Its Alternatives.
The second law efficiency analysis also performed at 40°C condensing
temperature, 80°C discharge temperature, 5°C subcool, 5°C superheat, and evaporating
temperature range between -15°C to 15°C. The ambient temperature is assumed as 30°C
and refrigerated space temperature is assumed as 10°C. Figures 4.4, 4.5 and 4.6 shows the
plots of second law efficiency against the changes of evaporating temperature for R12,
R22, and R502 and their substitutes respectively.
As the second law efficiency was described as the ratio between the COP of actual
cycle and the COP of carnot cycle, all the plots of second law efficiency obtained give a
similar pattern with the plots of COP but at different values. Because the expression for
the second law efficiency is in terms of COP, its value cannot exceed 100%. The second
38
law efficiencies were found to have a value less than 1 compared to the value of COP
which was greater than 1. The values are between 0.1 and 0.3 between the temperature
ranges for all refrigerants tested.
This result shows that the efficiency of the refrigeration cycle based on second
law principle is smaller than the efficiency of the refrigeration cycle expressed in terms of
first law or energy analysis. To have a more realistic result, other detail analysis such as
exergy analysis should be carried out to obtain the second law efficiency of the entire
cycle or the second law efficiency of each system component.
Similar to the COP analysis, R401A, R401B, and R409A were found to performe
better than R12 at about 14% to 20%. R402B have a similar performance while R134A
have about 11% lower performance than R12. For R22, it performs better than its
alternatives. For R502 analysis, R407C, R402B and R408A each show a better
performance relative to R502 while R402A and R404A show a lower performance.
R407C with the highest different, has about 30% higher performance than R502 while
both R402B and R408A perform at about 14% to 20% higher.
Second Law Efficiency
0.35
0.3
R12
R134A
R401A
R401B
R402B
R409A
0.25
0.2
0.15
0.1
0.05
0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.4 : Second law efficiency of R12 and its alternatives
39
Second Law Efficiency
0.35
R22
0.3
0.25
R404A
0.2
R407C
0.15
R410A
0.1
R507
0.05
0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.5 : Second law efficiency of R22 and its alternatives.
Second Law Efficiency
0.3
0.25
R502
0.2
R402A
R402B
0.15
R404A
0.1
R407C
0.05
R408A
0
-20
-15
-10
-5
0
5
Evaporating Temperature (°C)
10
15
20
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.6 : Second law efficiency of R502 and its alternatives.
4.3
The effect of changes in evaporating temperature on the COP.
The effects of evaporating temperature on the COP are shown in Figures 4.1
through 4.3. The result shows that the COP of the cycle increases when evaporating
temperature increased. This could be due to the result increase in evaporating
temperature, will significantly increasing the enthalpy of the refrigerant entering the
compressor, resulting in a decrease in work input. The cooling effect slightly increases
40
due to decrease of the enthalpy of the refrigerant entering the evaporator. It results in
increasing COP.
4.4
The effect of changes in condensing temperature on the COP.
This analysis was performed at 5°C evaporating temperature, 80°C discharge
temperature, 5°C subcool, 5°C superheat, and condensing temperature range between
20°C to 40°C. Effect of changes in condensing temperature on the COP of R12 and
R134A are shown in Figure 4.7.
COP
3.5
R12
R134A
2.5
20
22
24
26
28
30
32
34
36
38
40
Condensing Temperature (°C)
Data base on 5°C evaporating temperature, 80°C discharge temperature,5°C subcool
and 5°C superheat.
Figure 4.7 : COP versus condensing temperature.
The result of R12 and R134A shows that at constant evaporating temperature, an
increase in the condensing temperature results in a decrease of COP. Increase in
condensing temperature, leads to an increase in the enthalpy of the refrigerant at the
compressor outlet, which results in an increase in the compression work needed. Besides
that, increase in condensing temperature increases the enthalpy of the refrigerant entering
the evaporator, leads in reduced the cooling effect. It results in decreasing COP.
From the result discussed in section 4.3 and 4.4, it can be concluded that, for a
maximum value of COP the cycle should operate at the maximum possible evaporating
temperature and at the lowest possible condensing temperature.
41
4.5
Refrigerant with higher total irreversibility.
This analysis is performed to predict which refrigerant has the highest total
irreversibility among all refrigerants tested. The analysis was performed at 5°C
evaporating temperature, 40°C condensing temperature, 80°C discharge temperature, 5°C
subcool, and 5°C superheat. A bar graph in Figure 4.8 gives the results of irreversibility
analysis for all refrigerants tested.
Data base on 5°C ev aporating temperature, 40°C condensing temperature,
80°C discharge temperature,5°C subcool and 5°C superheat.
60
total irreversibility
50
40
30
20
10
R408A
R402B
R402A
R502
R507
R410A
R407C
R404A
R22
R409A
R401B
R401A
R134A
R12
0
Figure 4.8 : Total irreversibility of refrigerant.
At a given operating condition, R407C is found to be the fluid that has a highest
irreversibility at about 55kJ/kg, followed by R409A and R410A. Other refrigerants which
have the total loss of more than 50 kJ/kg are R401A and R401B. R12 and R502 are
predicted to be the refrigerants with the lowest value of total losses for about 35kJ/kg.
When refers to the result in section 4.1 and 4.2, most of these fluids which have
high rate of irreversibility, have a good performance in terms of COP and second law
efficiency. Normally, their good performance is most likely to be of interest rather than
the high rate of irreversibility. This analysis also shows that the performance of
refrigerant in the theoretical study depends strongly on their thermodynamic properties.
42
4.6
Locating the primary source of irreversibility.
This test is performed to predict the component with the highest irreversibility. In
a practical refrigeration system, it helps to determine the high source of irreversibility so
that action could be taken to improve the system performance. Two refrigerants have
been chosen for this analysis, one with a higher value of total irreversibility and another
one is selected among the refrigerants with a moderate value of total irreversibility. They
are R407C and R134A. The tests were performed at the same operating conditions as
discussed in section 4.2.
Table 4.2 shows the tabulated data obtained from the test while the bar graph in
Figure 4.9 shows the percentages of irreversibility for each component of refrigeration
system of refrigerant R407C and R134A.
Table 4.2 : Component irreversibility of refrigerant R407C and R134A.
Irreversibility (kJ/kg)
Compressor
Condenser
Liquid line
Exp. valve
Evaporator
Suction line
TOTAL
R407C
33.4
12.6
0.33
3.18
5.70
0.25
55.7
R134A
27.4
11.1
0.31
2.28
3.34
0.38
44.0
Data base on 5°C evaporating temperature, 40°C condensing temperature,
80°C discharge temperature, 5°C subcool and 5°C superheat.
70
60
i / i total (%)
50
R407C
40
R134A
30
20
10
0
compressor
condenser
liquid line
exp.valve
evaporator
suction line
Figure 4.9 : The percentage of component irreversibility of R407C and R134A.
43
The result shows that the compressor is predicted as a high source of
irreversibility, followed by the condenser and evaporator at a given operating condition.
For R134A, compressor has contributed losses of about 60% of the total system
irreversibility while for R407C the percentage is more than 60%. In a practical system,
this loss or irreversibility is due to pressure drops, friction losses, mixing, motor
inefficiency, and heat transfer between compressor and the surroundings [1]. Therefore,
special attention should be considered on compressor when optimization is conducted on
a system.
For condenser, irreversibility is due to heat rejection from condenser to
surrounding and also due to the pressure drop. Similar to the condenser, the irreversibility
in evaporator is also due to the pressure drop and heat transfer. While in expansion device
the irreversibility is due to its isenthalpic processes with no work recovery.
4.7
The effect of changes in evaporating temperature on the irreversibility.
This analysis is based on R407C data under the same operating conditions as in
section 4.1. Figure 4.10 shows the effect of changes in the evaporating temperature on the
irreversibility.
100
compressor
condenser
liquid line
exp.valve
evaporator
suction line
i total
irreversibility
80
60
40
20
0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.10 : Irreversibility versus evaporating temperature.
44
The results show that the irreversibility rate decreases in most of the components
with an increase in evaporating temperature except for the condenser. These decreasing
leads to a total irreversibility decrease. Again, it is obvious that the irreversibility rate of
the compressor contributed most to the irreversibility of the system. The trend agrees with
the predictions obtained by Choong Meng [18] and Yumrutas et al. [19] (Figure 4.11).
Percentage, %
Condenser
Evaporator
Evaporating temperature, °C
Figure 4.11 : Percentages of lost work for condenser and evaporator as a
function of evaporating temperature predicted by Yumrutas et al. [19].
The irreversibility in evaporator decreasing with the evaporating temperature can
be explained by the fact that the average temperature difference between the evaporator
and the cold space area decreases with increasing evaporating temperature. The higher the
temperature difference the higher the irreversibility. Meanwhile, percent of irreversibility
in the condenser has to increase to make up the decrease in the percent losses in the
evaporator [19].
4.8
The effect of irreversibility on second law efficiency.
For this analysis, the values or percentages of irreversibility and second law
efficiency have normalized to 100% between the evaporating temperature ranges. The
analysis is based on the data of R407C and the result is shown in Figure 4.12.
45
Percentage, %
25.0
20.0
second law
efficiency
15.0
irreversibility
10.0
5.0
0.0
-20
-15
-10
-5
0
5
10
15
20
Evaporating Temperature (°C)
Data base on 40°C condensing temperature, 80°C discharge temperature,5°C subcool and 5°C superheat.
Figure 4.12 : The effect of irreversibility on second law efficiency.
It was found that the second law efficiency increases with increasing of
evaporating temperature as shown in the plot. For irreversibility, an opposite pattern
exists, as expected. The second law efficiency becomes higher when irreversibility
becomes lower. The pattern of the plot agrees with the results obtained by Yumrutas et al.
Percentage, %
[19] as shown in Figure 4.13.
Evaporating temperature, °C
Figure 4.13 : Second law efficiency and total exergy loss in percentage
predicted by Yumrutas et al. [19].
46
4.9
Comparison between the ideal and actual cycle with pressure drops.
The comparison data for this analysis is based on the data of R12 operates at 12.5°C evaporating temperature (200kPa evaporating pressure), 41.7°C condensing
temperature (1000kPa evaporating pressure) and 80°C discharge temperature. It is a
similar condensing and evaporating condition that was used by Sia. The COP of the ideal
cycle is compared with the results of the actual cycle operating at two conditions of
subcool and superheat temperatures as shown in Table 4.3.
Table 4.3 : The COP of the ideal and actual cycle of refrigerant R12.
Cycle
COP
Ideal cycle
2.65
Actual cycle with 2°C of subcool
and 2°C of superheat
Actual cycle with 5°C of subcool
and 5°C of superheat
2.25
2.40
The result shows that the COP of the actual cycle is lower than the COP of the
ideal cycle as expected. One of the factors that influence the drop of COP is
superheating in the compressor inlet. The result of superheating will increase the power
input requirements and this will results in the decrease of COP. However, the COP of
actual cycle with 5°C of subcool and superheat has drop only 9.4% compared to the
COP of actual cycle with 2°C of subcool and superheat which has drop 15%. In
refrigeration cycle, increased subcooling decreases the enthalpy of the refrigerant
entering the evaporator, resulting in an increase in the cooling effect, and an increase in
the superheat temperature decreases the work input. It results in increasing the COP.
47
CHAPTER V
CONCLUSION
A computer program for simulating the performances of refrigerants have been
completed for an actual cycle with a pressure drop of 10% in the condenser and
evaporator. The results of the COP and second law analysis show that R401A, R401B,
and R409A is found to be the best replacements for R12. R410A is predicted as the best
replacement for R22, while R402B, R407C, and R408A could be the best replacements
for R502 in terms of this study for a given operating condition.
This result also shows that the efficiency of the refrigeration cycle based on
second law analysis is smaller than the efficiency of the refrigeration cycle expressed in
terms of first law or energy analysis.
In COP analysis, the result shows that the COP is increased as evaporating
temperature increased. At constant evaporating temperature, an increase in the
condensing temperature results in a decrease of COP. It can be concluded that, for
maximum value of COP the cycle should operate at the maximum possible evaporating
temperature and at the lowest possible condensing temperature.
The irreversibility analysis shows that the irreversibility rate decreases with
increasing evaporating temperature in most of the system components except for the
condenser. It influences the performance of the system in terms of second law efficiency.
R407C, R409A, and R410A were predicted as the refrigerants that have a higher
irreversibility among refrigerants tested. However, their good performance is most likely
to be of interest rather than the high rate of irreversibility.
48
The comparison between the ideal and actual cycle using R12 as the working
fluid shows the drop in cycle performance as expected. The result of superheating in
actual cycle will increase the power input requirements and this will result in the decrease
of COP. In refrigeration cycle, increasing the subcool temperature will increase the
cooling effect and increasing the superheat temperature will decrease the work input. It
results in increasing the COP.
It could be concluded that the actual cycle model is able to make fair predictions
of refrigerant performance compared to the ideal cycle model.
49
REFERENCES
[1]
ASHRAE Handbook 2001.
[2]
David Wylie, P.E. and Davenport, J.W. (1996). “New Refrigerants For Air
Conditioning And Refrigeration System.” The Fairmont Press, Inc.
[3]
Vaisman, I.B. (1998). “Computational Comparison Of R22 And R407C Air
Conditioners With Rotary Vane Compressor.” Proceedings Of The 1998
International Refrigeration Conference at Purdue.19-24
[4]
Yana Motta, S.F. and Domanski, P.A. (2000). “Performance Of R22 And Its
Alternatives Working At High Outdoor Temperature.” Eighth International
Refrigeration Conference at Purdue University.47-54
[5]
Spatz, M.W. and Yana Motta, S.F. (2004). “An Evaluation Of Option For
Replacing HCFC22 In Medium Temperature Refrigeration Systems.”
International Journal of Refrigeration 27. 475-483
[6]
Stegou-Sagia, A., and Paigigiannis, N. (2005). “Evaluation Of Mixture
Efficiency In Refrigerating Systems.” Energy Conversion And Management
46. 2787-2802
[7]
Sia Chee Keong (2004). “Non CFC Refrigerants, First And Second Law
Effciencies.” Master dissertation. Universiti Teknologi Malaysia.
[8]
Domanski, P.A.and McLinden, M.O. (1990). “A Simplified Cycle Simulation
Model For The Performance Rating of Refrigerants and Refrigerant
Mixtures.” 1990 USNC/IIR – Purdue Refrigeration Conference.466-475
[9]
Jung, D.S. and Radermacher, R. (1990). “Performance Evaluation Of Pure
And Mixed Refrigerants In Domestic Refrigerators : Drop-in Replacement Of
R12” 1990 USNC/IIR – Purdue Refrigeration Conference. 177-189
50
[10]
http://www.nist.gov
[11]
Cengel Y. A. and Boles M.A. (2004). “ Thermodynamics An Engineering
Approach.” 4th Ed. WCB/ McGraw-Hill International.
[12]
Abd. Rahim Mat Sarip (2004). “Kajian Analitikal Dan Eksperimental
Pemampat Bilah Berputar.” Technical Report. Universiti Teknologi Malaysia.
Unpublished.
[13]
NIST REFPROP Version 6.0.
[14]
http://www.dupont.com/suva/
[15]
McLinden, M.O. (1990). “Optimum Refrigerants For Non-Ideal Cycles : An
Analysis Employing Corresponding States” 1990 USNC/IIR – Purdue
Refrigeration Conference. 69-79
[16]
Xu, X. and Clodic, D. (1992). “Exergy Analysis on a Vapor Compression
Refrigerating System Using R12, R134A and R290 as Refrigerants”
Proceedings Of The 1992 International Refrigeration Conference at Purdue.
233-240
[17]
Chen, Q.Y. and Prasad, R.C. (1999). “Simulation of a Vapor-Compression
Refrigeration Cycles using HFC134A and CFC12” Journal of International
Community Heat Mass Transfer. Vol. 26, No. 4, 513-521.
[18]
Wan Choong Meng (2003). “The Exergy Analysis of a Refrigeration Plant”
Thesis. Universiti Teknologi Malaysia.
[19]
Recep Yumrutas, Mehmet Kunduz and Mehmet Kanoglu. (2002). “Exergy
Analysis of Vapor Compression Refrigeration Systems.” Exergy, an
International Journal 2. 266–272
51
APPENDIX A
PROGRAMMING CODES
frmSplash
ption Explicit
Private Sub Form_KeyPress(KeyAscii As Integer)
frmMain.Show 'loads up the next form
Unload Me
End Sub
Private Sub Form_Load()
lblVersion.Caption = "Version " & App.Major & "." & App.Minor & "." &
App.Revision
lblProductName.Caption = "REFTEST"
End Sub
Private Sub Frame1_Click()
frmMain.Show 'loads up the next form
Timer1.Enabled = False
Unload Me
End Sub
Private Sub Timer1_Timer()
Dim SplashTime As Integer
SplashTime = SplashTime - Timer1.Interval
If SplashTime > 3000 Then
Else
frmMain.Show 'loads up the next form
Timer1.Enabled = False
Unload Me
End If
End Sub
52
frmMain
Option Explicit
'Chameleon integer
Dim i As Integer
Dim n As Integer
'Data availability boolean
Dim DataExist As Boolean
'Data export string
Dim OutputFile As String
Dim OutputData As String
'Martin-Hou coefficient
Dim R As Double
Dim b_ As Double
Dim A2 As Double
Dim B2 As Double
Dim C2 As Double
Dim A3 As Double
Dim B3 As Double
Dim C3 As Double
Dim A4 As Double
Dim B4 As Double
Dim C4 As Double
Dim A5 As Double
Dim B5 As Double
Dim C5 As Double
Dim A6 As Double
Dim B6 As Double
Dim C6 As Double
Dim alpha As Double
Dim Cprime As Double
Dim k_ As Double
Dim TC As Double
Dim a_prime As Double
Dim b_prime As Double
Dim c_prime As Double
Dim d_prime As Double
Dim f_ As Double
Dim j As Double
Dim Ln10 As Double
Dim Loge As Double
Dim x As Double
Dim Y As Double
Dim h0 As Double
Dim s0 As Double
Dim j1 As Double
Dim Pone As Double
Dim Cp1 As Double
Dim Cp2 As Double
53
Dim Cp3 As Double
Dim Cp4 As Double
Dim Cp5 As Double
'Vapor Pressure Coefficient
Dim A As Double
Dim B As Double
Dim C As Double
Dim D As Double
Dim E As Double
Dim F As Double
'Fluid Density Coefficient (R12 & R22)
Dim AL As Double
Dim BL As Double
Dim CL As Double
Dim DL As Double
Dim EL As Double
Dim FL As Double
Dim GL As Double
Dim TCR As Double
'Fluid Density Coefficient (R134)
Dim rho_c As Double
Dim TC2 As Double
Dim D1 As Double
Dim D2 As Double
Dim D3 As Double
Dim D4 As Double
'Other Variables
Dim strRef As String
Dim Tcond As Double
Dim Tevap As Double
'Refrigerant Information
Dim GRP As String
Dim ODP As String
Dim GWP As String
'Data file arrays
Dim dtx(100) As Double 'C
Dim dpf(100) As Double 'kPa
Dim dpg(100) As Double 'kPa
Dim dhf(100) As Double 'kJ/kg
Dim dhg(100) As Double 'kJ/kg
Dim dsf(100) As Double 'kJ/kgK
Dim dsg(100) As Double 'kJ/kgK
Dim dt1(100) As Double 'C
Dim dp1(100) As Double 'kPa
Dim dh1(100) As Double 'kJ/kg
Dim ds1(100) As Double 'kJ/kgK
Dim dt2(100) As Double 'C
Dim dp2(100) As Double 'kPa
Dim dh2(100) As Double 'kJ/kg
Dim ds2(100) As Double 'kJ/kgK
54
'Thermodynamics Property
Dim T1 As Double
Dim T2 As Double
Dim T3 As Double
Dim T4 As Double
Dim T5 As Double
Dim T6 As Double
Dim P1 As Double
Dim P2 As Double
Dim P3 As Double
Dim P4 As Double
Dim P5 As Double
Dim P6 As Double
Dim h1 As Double
Dim h2 As Double
Dim h3 As Double
Dim h4 As Double
Dim h5 As Double
Dim hf5 As Double
Dim hg5 As Double
Dim h6 As Double
Dim s1 As Double
Dim s2 As Double
Dim s3 As Double
Dim s4 As Double
Dim s5 As Double
Dim sf5 As Double
Dim sg5 As Double
Dim s6 As Double
'Performance analysis
Dim W12 As Double
Dim Q23 As Double
Dim Q34 As Double
Dim Q56 As Double
Dim Q61 As Double
Dim COP As Double
'Irreversibility Components
Dim T0 As Double
Dim TR As Double
Dim i12 As Double
Dim i23 As Double
Dim i34 As Double
Dim i45 As Double
Dim i56 As Double
Dim i61 As Double
Dim TI As Double
Dim COPC As Double
Dim SLE As Double
55
Private Sub GetRefInfo()
Select Case strRef
Case "R12"
GRP = "CFC"
ODP = 1
GWP = 8500
Case "R22"
GRP = "HCFC"
ODP = 0.05
GWP = 1500
Case "R134A"
GRP = "HFC"
ODP = 0
GWP = 1300
'
Case "R290"
'
strODP = 1
'
strGWP = 8500
Case "R401A"
GRP = "HCFC"
ODP = 0.03
GWP = 973
Case "R401B"
GRP = "HCFC"
ODP = 0.035
GWP = 1062
Case "R402A"
GRP = "HCFC"
ODP = 0.02
GWP = 2250
Case "R402B"
GRP = "HCFC"
ODP = 0.03
GWP = 1964
Case "R404A"
GRP = "HFC"
ODP = 0
GWP = 3260
Case "R407C"
GRP = "HFC"
ODP = 0
GWP = 1526
Case "R408A"
GRP = "HCFC"
ODP = 0.026
GWP = 2649
Case "R409A"
GRP = "HCFC"
ODP = 0.05
GWP = 1288
Case "R410A"
56
GRP = "HFC"
ODP = 0
GWP = 1725
Case "R502"
GRP = "HFC"
ODP = 0.307
GWP = 5494
Case "R507"
GRP = "HFC"
ODP = 0
GWP = 3300
'
Case "R507A"
'
ODP = 0
'
GWP = 0
Case Else
GRP = "N/A"
ODP = "N/A"
GWP = "N/A"
End Select
End Sub
Private Sub CalculateTP() 'Thermodynamics Property
Tcond = lstCT.Text
Tevap = lstET.Text
'Calculate from data file
'-----------------------'Pt. 3 - Saturated liquid
T3 = Tcond
For i = 0 To 100
If dtx(i) = T3 Then
'Get data
P3 = dpf(i)
h3 = dhf(i)
s3 = dsf(i)
Exit For
End If
If dtx(i) < T3 And dtx(i + 1) > T3 Then
'Interpolate
P3 = dpf(i) + ((dpf(i + 1) - dpf(i)) * (T3 - dtx(i)) / (dtx(i + 1) - dtx(i)))
h3 = dhf(i) + ((dhf(i + 1) - dhf(i)) * (T3 - dtx(i)) / (dtx(i + 1) - dtx(i)))
s3 = dsf(i) + ((dsf(i + 1) - dsf(i)) * (T3 - dtx(i)) / (dtx(i + 1) - dtx(i)))
Exit For
End If
Next i
'Pt. 4 - Compressed liquid
T4 = T3 - lstSC.Text
57
For i = 0 To 100
If dtx(i) = T4 Then
'Get data
P4 = dpf(i)
h4 = dhf(i)
s4 = dsf(i)
Exit For
End If
If dtx(i) < T4 And dtx(i + 1) > T4 Then
'Interpolate
P4 = dpf(i) + ((dpf(i + 1) - dpf(i)) * (T4 - dtx(i)) / (dtx(i + 1) - dtx(i)))
h4 = dhf(i) + ((dhf(i + 1) - dhf(i)) * (T4 - dtx(i)) / (dtx(i + 1) - dtx(i)))
s4 = dsf(i) + ((dsf(i + 1) - dsf(i)) * (T4 - dtx(i)) / (dtx(i + 1) - dtx(i)))
Exit For
End If
Next i
'Pt. 6 - Saturated vapor
T6 = Tevap
For i = 0 To 100
If dtx(i) = T6 Then
'Get data
P6 = dpg(i)
h6 = dhg(i)
s6 = dsg(i)
Exit For
End If
If dtx(i) < T6 And dtx(i + 1) > T6 Then
'Interpolate
P6 = dpg(i) + ((dpg(i + 1) - dpg(i)) * (T6 - dtx(i)) / (dtx(i + 1) - dtx(i)))
h6 = dhg(i) + ((dhg(i + 1) - dhg(i)) * (T6 - dtx(i)) / (dtx(i + 1) - dtx(i)))
s6 = dsg(i) + ((dsg(i + 1) - dsg(i)) * (T6 - dtx(i)) / (dtx(i + 1) - dtx(i)))
Exit For
End If
Next i
'Pt. 5 - Mixture (light vapor)
Dim x As Double
P5 = P6 / 0.9
h5 = h4
For i = 0 To 100
If dpf(i) = P5 Then
'Get data
T5 = dtx(i)
hf5 = dhf(i)
hg5 = dhg(i)
sf5 = dsf(i)
sg5 = dsg(i)
Exit For
End If
58
If dpf(i) < P5 And dpf(i + 1) > P5 Then
'Interpolate
T5 = dtx(i) + ((dtx(i + 1) - dtx(i)) * (P5 - dpg(i)) / (dpg(i + 1) - dpg(i)))
hf5 = dhf(i) + ((dhf(i + 1) - dhf(i)) * (P5 - dpg(i)) / (dpg(i + 1) - dpg(i)))
hg5 = dhg(i) + ((dhg(i + 1) - dhg(i)) * (P5 - dpg(i)) / (dpg(i + 1) - dpg(i)))
sf5 = dsf(i) + ((dsf(i + 1) - dsf(i)) * (P5 - dpg(i)) / (dpg(i + 1) - dpg(i)))
sg5 = dsg(i) + ((dsg(i + 1) - dsg(i)) * (P5 - dpg(i)) / (dpg(i + 1) - dpg(i)))
Exit For
End If
Next i
x = (h5 - hf5) / (hg5 - hf5)
s5 = sf5 + (x * (sg5 - sf5))
'Pt. 1
T1 = T6 + lstSH.Text
For i = 0 To 100
If dt1(i) = T1 Then
'Get data
P1 = dp1(i)
h1 = dh1(i)
s1 = ds1(i)
Exit For
End If
If dt1(i) < T1 And dt1(i + 1) > T1 Then
'Interpolate
P1 = dp1(i) + ((dp1(i + 1) - dp1(i)) * (T1 - dt1(i)) / (dt1(i + 1) - dt1(i)))
h1 = dh1(i) + ((dh1(i + 1) - dh1(i)) * (T1 - dt1(i)) / (dt1(i + 1) - dt1(i)))
s1 = ds1(i) + ((ds1(i + 1) - ds1(i)) * (T1 - dt1(i)) / (dt1(i + 1) - dt1(i)))
Exit For
End If
Next i
'Pt. 2
T2 = lstDT.Text
P2 = P3 / 0.9
If P2 > 999 Then
P2 = Round(P2, 0)
Else
P2 = Round(P2, 1)
End If
For i = 0 To 100
If dp2(i) = P2 Then
'Get data
h2 = dh2(i)
s2 = ds2(i)
Exit For
End If
If dp2(i) < P2 And dp2(i + 1) > P2 Then
'Interpolate
h2 = dh2(i) + ((dh2(i + 1) - dh2(i)) * (P2 - dp2(i)) / (dp2(i + 1) - dp2(i)))
59
s2 = ds2(i) + ((ds2(i + 1) - ds2(i)) * (P2 - dp2(i)) / (dp2(i + 1) - dp2(i)))
Exit For
End If
Next i
End Sub
Private Sub CalculatePA() 'Performance Analysis
'Compressor (1-2)
W12 = h2 - h1
'Condensor (2-3)
Q23 = h3 - h2
'Liquid line( 3-4)
Q34 = h4 - h3
'Evaporator (5-6)
Q56 = h6 - h5
'Suction line (6-1)
Q61 = h1 - h6
'COP
COP = Q56 / W12
End Sub
Private Sub CalculateIC() 'Irreversibility Components
T0 = lstAT.Text + 273
TR = lstRST.Text + 273
'Compressor (1-2)
i12 = T0 * ((W12 / T0) - (s2 - s1))
'Condensor (2-3)
i23 = T0 * ((s3 - s2) - (Q23 / T0))
'Liquid line (3-4)
i34 = T0 * ((s4 - s3) - (Q34 / T0))
'Expansion device (4-5)
i45 = T0 * (s5 - s4)
'Evaporator (5-6)
i56 = T0 * ((s6 - s5) - (Q56 / TR))
'Suction line (6-1)
i61 = T0 * ((s1 - s6) - (Q61 / T0))
'Total Irreversibility
TI = i12 + i23 + i34 + i45 + i56 + i61
'COP Carnot
COPC = TR / (T0 - TR)
'2nd Law Efficiency
SLE = COP / COPC
End Sub
Private Sub FillText()
60
'for debugging only
'lbl.Caption = "T3=" & T3 & ", P3=" & P3 & ", h3=" & h3 & ", s3=" & s3 & _
"; T4=" & T4 & ", P4=" & P4 & ", h4=" & h4 & ", s4=" & s4 & vbCrLf & _
"T6=" & T6 & ", P6=" & P6 & ", h6=" & h6 & ", s6=" & s6 & _
"; T5=" & Round(T5, 1) & ", P5=" & Round(P5, 1) & ", h5=" & Round(h5, 3)
& ", s5=" & Round(s5, 4) & vbCrLf & _
"T1=" & T1 & ", P1=" & P1 & ", h1=" & h1 & ", s1=" & s1 & _
"; T2=" & T2 & ", P2=" & P2 & ", h2=" & h2 & ", s2=" & s2 & _
"; COP=" & Round(COP, 2) & ", SLE=" & Round(SLE, 3)
'--- Thermo Prop --txtRef.Text = strRef
txtGRP.Text = GRP
txtODP.Text = ODP
txtGWP.Text = GWP
cblProperty.Text = "Temperature"
lblTP(1).Caption = "Unit: °C"
txtTP1.Text = Round(T1, 1)
txtTP2.Text = Round(T2, 1)
txtTP3.Text = Round(T3, 1)
txtTP4.Text = Round(T4, 1)
txtTP5.Text = Round(T5, 1)
txtTP6.Text = Round(T6, 1)
'--- 1st Law --txtRefrigerant.Text = strRef
txtDT.Text = lstDT.Text
txtCT.Text = lstCT.Text
txtET.Text = lstET.Text
txtSC.Text = lstSC.Text
txtSH.Text = lstSH.Text
txtAT.Text = lstAT.Text
txtRST.Text = lstRST.Text
txtPI.Text = Round(W12, 3)
txtHS.Text = Round(Q56, 3)
txtCOP.Text = Round(COP, 2)
'--- 2nd Law --txtI12.Text = Round(i12, 4)
txtI23.Text = Round(i23, 4)
txtI34.Text = Round(i34, 4)
txtI45.Text = Round(i45, 4)
txtI56.Text = Round(i56, 4)
txtI61.Text = Round(i61, 4)
txtTI.Text = Round(TI, 4)
txtCOPC.Text = Round(COPC, 2)
txtSLE.Text = Round(SLE, 2)
End Sub
Private Sub cblRefrigerant_Click()
cmdExportData.Enabled = False
End Sub
61
Private Sub cmdCalculate_Click()
strRef = cblRefrigerant.Text
If strRef = "" Then Exit Sub
GetCoef strRef
If DataExist = False Then
MsgBox "Data for Discharge Temperature is not available." & vbCrLf & _
"Please try other value.", vbInformation + vbOKOnly, App.Title
Exit Sub
End If
GetRefInfo 'Refrigerant Information
CalculateTP 'Thermodynamics Property
CalculatePA 'Performance Analysis
CalculateIC 'Irreversibility Components
FillText
cmdExportData.Enabled = True
End Sub
Private Sub cmdExportData_Click()
Dim fso As New FileSystemObject
Dim txtfile
OutputFile = cblRefrigerant.Text & "_" & CStr(Format(Now, "yyMMdd_HHmm"))
Set txtfile = fso.CreateTextFile(App.Path & "\Output\" & OutputFile & ".txt", True)
With txtfile
.WriteLine "+--------------------------+"
.WriteLine "| REFTEST v1.0
|"
.WriteLine "|
|"
.WriteLine "| by: Siti Mariam Basharie |"
.WriteLine "+--------------------------+"
.WriteBlankLines (2)
.WriteLine "[Input]"
.WriteLine "-------"
.WriteLine "Refg " & vbTab & cblRefrigerant.Text
.WriteLine "Tdisc" & vbTab & lstDT.Text
.WriteLine "Tcond" & vbTab & lstCT.Text
.WriteLine "Tevap" & vbTab & lstET.Text
.WriteLine "SC " & vbTab & lstSC.Text
.WriteLine "SH " & vbTab & lstSH.Text
.WriteLine "Tamb " & vbTab & lstAT.Text
.WriteLine "T0 " & vbTab & lstRST.Text
.WriteBlankLines (1)
.WriteLine "[Thermodynamics Property]"
.WriteLine "-------------------------"
.WriteLine "Point" & vbTab & "T" & vbTab & "P" & vbTab & "h" & vbTab & "s"
.WriteLine "1" & vbTab & Format(Round(T1, 1), "0.0") & vbTab &
Format(Round(P1, 1), "0.0") & vbTab & Format(Round(h1, 2), "0.00") & vbTab &
Format(Round(s1, 4), "0.0000")
.WriteLine "2" & vbTab & Format(Round(T2, 1), "0.0") & vbTab &
Format(Round(P2, 1), "0.0") & vbTab & Format(Round(h2, 2), "0.00") & vbTab &
Format(Round(s2, 4), "0.0000")
62
.WriteLine "3" & vbTab & Format(Round(T3, 1), "0.0") & vbTab &
Format(Round(P3, 1), "0.0") & vbTab & Format(Round(h3, 2), "0.00") & vbTab &
Format(Round(s3, 4), "0.0000")
.WriteLine "4" & vbTab & Format(Round(T4, 1), "0.0") & vbTab &
Format(Round(P4, 1), "0.0") & vbTab & Format(Round(h4, 2), "0.00") & vbTab &
Format(Round(s4, 4), "0.0000")
.WriteLine "5" & vbTab & Format(Round(T5, 1), "0.0") & vbTab &
Format(Round(P5, 1), "0.0") & vbTab & Format(Round(h5, 2), "0.00") & vbTab &
Format(Round(s5, 4), "0.0000")
.WriteBlankLines (1)
.WriteLine "[1st Law Analysis]"
.WriteLine "------------------"
.WriteLine "PowerInput" & vbTab & Round(W12, 3)
.WriteLine "HeatSupply" & vbTab & Round(Q56, 3)
.WriteLine "COP
" & vbTab & Round(COP, 2)
.WriteBlankLines (1)
.WriteLine "[2nd Law Analysis]"
.WriteLine "------------------"
.WriteLine "i12" & vbTab & Round(i12, 4)
.WriteLine "i23" & vbTab & Round(i23, 4)
.WriteLine "i34" & vbTab & Round(i34, 4)
.WriteLine "i45" & vbTab & Round(i45, 4)
.WriteLine "i56" & vbTab & Round(i56, 4)
.WriteLine "i61" & vbTab & Round(i61, 4)
.WriteLine "Sum(i)" & vbTab & Round(TI, 4)
.WriteLine "SLE" & vbTab & Round(SLE, 2)
.WriteBlankLines (2)
.Close
End With
MsgBox "Data exported to ..\Output\" & OutputFile & ".txt ", vbInformation +
vbOKOnly
End Sub
Private Sub cblProperty_Click()
Select Case cblProperty.Text
Case "Temperature"
lblTP(1).Caption = "Unit: °C"
txtTP1.Text = Round(T1, 1)
txtTP2.Text = Round(T2, 1)
txtTP3.Text = Round(T3, 1)
txtTP4.Text = Round(T4, 1)
txtTP5.Text = Round(T5, 1)
txtTP6.Text = Round(T6, 1)
Case "Pressure"
lblTP(1).Caption = "Unit: kPa"
txtTP1.Text = Round(P1, 3)
txtTP2.Text = Round(P2, 3)
txtTP3.Text = Round(P3, 3)
txtTP4.Text = Round(P4, 3)
txtTP5.Text = Round(P5, 3)
63
txtTP6.Text = Round(P6, 3)
Case "Enthalpy"
lblTP(1).Caption = "Unit: kJ/kg"
txtTP1.Text = Round(h1, 3)
txtTP2.Text = Round(h2, 3)
txtTP3.Text = Round(h3, 3)
txtTP4.Text = Round(h4, 3)
txtTP5.Text = Round(h5, 3)
txtTP6.Text = Round(h6, 3)
Case "Entropy"
lblTP(1).Caption = "Unit: kJ/kgK"
txtTP1.Text = Round(s1, 4)
txtTP2.Text = Round(s2, 4)
txtTP3.Text = Round(s3, 4)
txtTP4.Text = Round(s4, 4)
txtTP5.Text = Round(s5, 4)
txtTP6.Text = Round(s6, 4)
End Select
End Sub
Private Sub cmdBack_Click()
SSTab1.Tab = SSTab1.Tab - 1
End Sub
Private Sub cmdExit_Click()
Unload Me
End Sub
Private Sub cmdNext_Click()
SSTab1.Tab = SSTab1.Tab + 1
End Sub
Private Sub Form_Load()
SSTab1.Tab = 0
cmdBack.Enabled = False
cmdNext.Enabled = True
cmdExportData.Enabled = False
InitializeInput
End Sub
Private Sub InitializeInput()
With cblRefrigerant
.Clear
.AddItem "R12"
.AddItem "R22"
.AddItem "R134A"
.AddItem "R290"
.AddItem "R401A"
.AddItem "R401B"
64
.AddItem "R402A"
.AddItem "R402B"
.AddItem "R404A"
.AddItem "R407C"
.AddItem "R408A"
.AddItem "R409A"
.AddItem "R410A"
.AddItem "R502"
.AddItem "R507"
.AddItem "R507A"
.Text = "R12"
End With
'DT: Discharge Temperature
With lstDT
.Clear
.AddItem 80
.AddItem 78
.AddItem 75
.AddItem 72
.AddItem 70
.AddItem 68
.AddItem 65
.AddItem 62
.AddItem 60
.AddItem 55
.Text = 80
End With
'CT: Condensing Temperature
CreateList lstCT, 20, 50, -5
lstCT.Text = 40
'ET: Evaporating Temperature
CreateList lstET, -25, 25, -5
lstET.Text = 5
'SC: SubCooling
CreateList lstSC, 2, 15, -1
lstSC.Text = 5
'SH: SuperHeating
With lstSH
.Clear
.AddItem 15
.AddItem 10
.AddItem 5
.AddItem 3
.AddItem 2
.Text = 5
End With
'AT: Ambient Temperature
CreateList lstAT, 20, 40, -1
lstAT.Text = 30
65
'RST: Refrigerated Space Temperature
CreateList lstRST, -5, 30, -1
lstRST.Text = 10
With cblProperty
.Clear
.AddItem "Temperature"
.AddItem "Pressure"
.AddItem "Enthalpy"
.AddItem "Entropy"
End With
End Sub
Private Sub CreateList(lstObj As ListBox, minVal As Integer, maxVal As Integer, iStep
As Integer)
With lstObj
.Clear
For i = maxVal To minVal Step iStep
.AddItem i
Next i
End With
End Sub
Private Sub SSTab1_Click(PreviousTab As Integer)
Select Case SSTab1.Tab
Case 0
cmdBack.Enabled = False
cmdNext.Enabled = True
Case 1
cmdBack.Enabled = True
cmdNext.Enabled = True
Case 2
cmdBack.Enabled = True
cmdNext.Enabled = True
Case 3
cmdBack.Enabled = True
cmdNext.Enabled = False
End Select
End Sub
Private Sub GetCoef(strRef As String)
Select Case strRef
'
'
'
'
'
Case "R12" 'IP unit
'*** Martin-Hou coefficient ***
R = 0.088734
b_ = 0.0065093886
A2 = -3.40972713
66
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
B2 = 0.00159434848
C2 = -56.7827671
A3 = 0.0602394465
B3 = -0.0000187961843
C3 = 1.31139908
A4 = -0.00054873701
B4 = 0
C4 = 0
A5 = 0
B5 = 0.000000003468834
C5 = -0.0000254390678
A6 = 0
B6 = 0
C6 = 0
alpha = 0
Cprime = 0
k_ = 5.475
TC = 693.3
F = 459.7
a_prime = 0.0080945
b_prime = 0.000332662
c_prime = -0.0000002413896
d_prime = 6.72363E-11
f_ = 0
j = 0.185053
Ln10 = 2.30258509
Loge = 0.4342944819
x = 39.556551
Y = -0.01653936
'h0='s0='j1='Pone='Cp1='Cp2='Cp3='Cp4='Cp5='*** Vapor Pressure coefficient ***
A = 39.88381727
B = -3436.632228
C = -12.47152228
D = 0.00473044244
E=0
F=0
'*** Fluid Density Coefficient ***
AL = 34.84
BL = 53.341187
CL = 0
DL = 18.69137
67
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
EL = 0
FL = 21.98396
GL = -3.150994
TCR = 693.3
Case "R22" 'IP unit
'*** Martin-Hou coefficient ***
R = 0.124098
b_ = 0.002
A2 = -4.353547
B2 = 0.002407252
C2 = -44.066868
A3 = -0.017464
B3 = 0.0000762789
C3 = 1.483763
A4 = 0.002310142
B4 = -0.000003605723
C4 = 0
A5 = -0.00003724044
B5 = 0.00000005355465
C5 = -0.0001845051
A6 = 136338700
B6 = -167261.2
C6 = 0
alpha = 584.2
Cprime = 0
k_ = 4.2
TC = 664.5
F = 459.69
a_prime = 0.02812836
b_prime = 0.0002255408
c_prime = -0.00000006509607
d_prime = 0
f_ = 257.341
j = 0.185053
Ln10 = 2.30258509
Loge = 0.4342944819
x = 62.4009
Y = -0.0453335
'h0='s0='j1='Pone='Cp1='Cp2='Cp3='Cp4='Cp5='*** Vapor Pressure coefficient ***
A = 29.35754453
68
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
B = -3845.193152
C = -7.86103122
D = 0.002190939
E = 0.445746703
F = 686.1
'*** Fluid Density Coefficient ***
AL = 32.76
BL = 54.634409
CL = 36.74892
DL = -22.2925657
EL = 20.4732886
FL = 0
GL = 0
TCR = 664.5
Case "R134" 'SI unit
'*** Martin-Hou coefficient ***
R = 0.0814881629
b_ = 0.0003455467
A2 = -0.1195051
B2 = 0.000113759
C2 = -3.531592
A3 = 0.0001447797
B3 = -0.00000008942552
C3 = 0.006469248
A4 = -0.0000001049005
B4 = 0
C4 = 0
A5 = -6.953904E-12
B5 = 1.269806E-13
C5 = -0.000000002051369
A6 = 0
B6 = 0
C6 = 0
alpha = 0
Cprime = 0
k_ = 5.475
TC = 374.25
'F='a_prime='b_prime='c_prime='d_prime='f_='J=Ln10 = 2.30258509
Loge = 0.4342944819
'X='Y=h0 = 200
69
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
'
s0 = 1
j1 = 1
Pone = 101.325
Cp1 = -0.005257455
Cp2 = 0.00329657
Cp3 = -0.000002017321
Cp4 = 0
Cp5 = 15.8217
'*** Vapor Pressure coefficient ***
A = 24.8033988
B = -3980.408
C = -0.02405332
D = 0.00002245211
E = 0.1995548
F = 0.0003748473
'*** Fluid Density Coefficient ***
rho_c = 512.2
TC = 374.25
D1 = 819.6183
D2 = 1023.582
D3 = -1156.757
D4 = 789.7191
Case Else
'read strRef.txt data file
ReadDataFile strRef
ReadDataFileSH strRef
ReadDataFileT strRef
End Select
End Sub
Private Sub ReadDataFile(strRef As String)
Open App.Path & "\" & cblRefrigerant.Text & "\" & cblRefrigerant.Text & ".txt" For
Input As #1
i=0
Do While Not EOF(1)
Input #1, dtx(i), dpf(i), dpg(i), dhf(i), dhg(i), dsf(i), dsg(i)
i=i+1
Loop
Close #1
End Sub
Private Sub ReadDataFileSH(strRef As String) 'SH
Open App.Path & "\" & cblRefrigerant.Text & "\" & _
cblRefrigerant.Text & "SH" & lstSH.Text & ".txt" For Input As #2
i=0
Do While Not EOF(2)
Input #2, dt1(i), dp1(i), dh1(i), ds1(i)
70
i=i+1
Loop
Close #2
End Sub
Private Sub ReadDataFileT(strRef As String) 'T
On Error GoTo x:
Open App.Path & "\" & cblRefrigerant.Text & "\" & _
cblRefrigerant.Text & "T" & lstDT.Text & ".txt" For Input As #3
i=0
Do While Not EOF(3)
Input #3, dt2(i), dp2(i), dh2(i), ds2(i)
i=i+1
Loop
Close #3
DataExist = True
Exit Sub
x: DataExist = False
End Sub
Private Sub CalculatePoint(intPoint As Integer)
'For equation only
Dim T3, v3, h3, s3, P3
Dim rho_L As Double
Select Case intPoint
Case 3
T3 = Tcond + 273
'Eqn 2.15
rho_L = rho_c + D1 * (1 - T3 / TC) ^ (1 / 3) + D2 * (1 - T3 / TC) ^ (2 / 3) + D3 *
(1 - T3 / TC) + D4 * (1 - T3 / TC) ^ (4 / 3)
v3 = 1 / rho_L
'Eqn 2.2
'Log(P3) = A + (B / T3) + (C * T3) + (D * (T3 ^ 2)) + (E * (F - T3) * Log(F - T3)
/ T3)
P3 = Exp(A + (B / T3) + (C * T3) + (D * (T3 ^ 2)) + (E * (F - T3) * Log(F - T3) /
T3))
'Eqn 2.13
h3 = h0 + j1 * (P3 * v3 - R * T3) + Cp1 * T3 + Cp2 * T3 ^ 2 / 2 + Cp3 * T3 ^ 3 /
3 + Cp4 * T3 ^ 4 / 4 + Cp5 * Log(T3)
h3 = h3 + j1 * (A2 / (v3 - b_) + A3 / (2 * (v3 - b_)) + A4 / (3 * (v3 - b_)) + A5 / (4
* (v3 - b_)))
71
h3 = h3 + j1 * Exp(-k_ * T3 / TC) * (1 + k_ * T3 / TC) * (C2 / (v3 - b_) + C3 / (2
* (v3 - b_) ^ 2) + C4 / (3 * (v3 - b_) ^ 3) + C5 / (4 * (v3 - b_) ^ 4))
'Eqn 2.14
s3 = s0 + Cp1 * Log(T3) + Cp2 * T3 + Cp3 * ((T3 ^ 2) / 2) + Cp4 * ((T3 ^ 3) / 3)
- Cp5 / (T3)
s3 = s3 + j1 * R * Log((v3 - b_) * P1 / (R * T3))
s3 = s3 + j1 * (k_ / TC) * Exp(-k_ * T3 / TC) * (C2 / (v3 - b_) + C3 / (2 * (v3 - b_)
^ 2) + C4 / (3 * (v3 - b_) ^ 3) + C5 / (4 * (v3 - b_) ^ 4))
End Select
End Sub
72
APPENDIX B
TEST RESULTS : COP
Evaporating Temperature, ˚C
-15
-10
-5
0
5
10
15
R12
2.33
2.50
2.69
2.89
3.12
3.37
3.64
R134a
2.09
2.24
2.40
2.58
2.78
3.00
3.24
R401a
2.73
2.92
3.12
3.35
3.59
3.86
4.16
R401b
2.82
3.01
3.22
3.44
3.70
3.96
4.25
R409a
2.78
2.98
3.19
3.43
3.69
3.98
4.29
R22
3.29
3.49
3.70
3.92
4.16
4.41
4.67
R404a
1.63
1.75
1.87
2.00
2.15
2.30
2.45
R407c
2.55
2.72
2.91
3.10
3.32
3.55
3.79
R410a
2.90
3.05
3.21
3.36
3.51
3.65
3.78
R507
1.58
1.69
1.81
1.94
2.08
2.23
2.38
R502
1.94
2.08
2.22
2.39
2.56
2.74
2.92
R402a
1.89
2.03
2.17
2.32
2.48
2.65
2.83
R402b
2.34
2.49
2.66
2.83
3.03
3.22
3.42
R408a
2.32
2.47
2.62
2.79
2.97
3.15
3.34
Notes : Data based on 40˚C condensing temperature, 80˚C discharge temperature, 5˚C subcool and 5˚C
superheat.
Condensing Temperature, ˚C
20
25
30
35
40
R12
3.26
3.21
3.17
3.14
3.12
R134a
2.94
2.89
2.84
2.81
2.78
Notes : Data based on 5˚C evaporating temperature, 80˚C discharge temperature, 5˚C subcool and 5˚C
superheat.
73
TEST RESULT : SECOND LAW EFFICIENCY
Evaporating Temperature, ˚C
-15
-10
-5
0
5
10
15
R12
0.165
0.177
0.190
0.205
0.22
0.238
0.257
R134a
0.148
0.158
0.170
0.182
0.196
0.212
0.229
R401a
0.193
0.206
0.221
0.237
0.254
0.273
0.294
R401b
0.199
0.213
0.228
0.243
0.261
0.280
0.30
R409a
0.197
0.211
0.226
0.243
0.261
0.281
0.303
R22
0.233
0.247
0.261
0.277
0.294
0.312
0.33
R404a
0.115
0.123
0.132
0.142
0.152
0.162
0.173
R407c
0.180
0.192
0.205
0.219
0.235
0.251
0.268
R410a
0.205
0.216
0.227
0.237
0.248
0.258
0.267
R507
0.111
0.120
0.128
0.137
0.147
0.157
0.168
R502
0.137
0.147
0.157
0.169
0.181
0.193
0.206
R402a
0.134
0.143
0.153
0.164
0.175
0.187
0.20
R402b
0.165
0.176
0.188
0.20
0.214
0.227
0.242
R408a
0.164
0.174
0.185
0.197
0.21
0.222
0.236
Notes : Data based on 40˚C condensing temperature, 80˚C discharge temperature, 5˚C subcool and 5˚C.
74
TEST RESULT : IRREVERSIBILITY
Irreversibility (kJ/kg)
Compressor Condenser
Liquid
line
Exp.
Valve
Evaporator
Suction
line
i Total
i12
i23
i34
i45
i56
i61
I
R12
21.9
8.59
0.22
1.60
2.69
0.25
35.2
R134a
27.4
11.1
0.31
2.28
3.34
0.38
44.0
R401a
31.6
11.9
0.29
2.49
5.25
0.40
51.8
R401b
31.3
11.7
0.29
2.50
5.12
0.27
51.1
R409a
32.1
11.8
0.28
2.63
6.05
0.39
53.3
R22
28.9
10.9
0.33
2.19
3.64
0.26
46.2
R404a
24.9
10.1
0.34
2.83
2.94
0.45
41.5
R407c
33.4
12.65
0.33
3.18
5.70
0.25
55.5
R410a
32.1
12.25
0.49
3.22
3.93
0.46
52.4
R507
24.1
9.90
0.31
2.82
2.77
0.38
40.3
R502
21.6
8.57
0.34
2.16
2.53
0.31
35.5
R402a
24.1
9.52
0.33
2.65
3.10
0.36
40.0
R402b
26.3
10.2
0.34
2.57
3.43
0.38
43.1
R408a
27.8
11.0
0.34
2.67
3.37
0.37
45.5
Notes : Data based on 5˚C evaporating temperature, 40˚C 0.30condensing temperature, 80˚C discharge
temperature, 5˚C subcool and 5˚C superheat.
75
TEST RESULT : IRREVERSIBILITY OF R407C
Evaporating Temperature, ˚C
Component
-15
-10
-5
0
5
10
15
Compressor
51.83
47.01
42.19
37.77
33.35
29.44
25.63
Condenser
12.65
12.65
12.65
12.65
12.65
12.65
12.65
Liquid line
0.334
0.334
0.334
0.334
0.334
0.334
0.334
Exp. Valve
8.75
7.0
5.46
4.32
3.18
2.29
.1.52
Evaporator
18.82
15.55
12.19
8.95
5.7
2.46
0.77
Suction ine
0.75
0.75
0.65
0.45
0.25
0.3
0.32
i Total
93.14
83.3
73.48
64.47
55.47
47.48
39.69
Notes : Data based on 40˚C condensing temperature, 80˚C discharge temperature, 5˚C subcool and 5˚C
superheat.