Lesson 3
Basic Vapor Compression Refrigeration System
A simple vapor compression refrigeration system consists of the following
equipment:
a) Compressor b) Condenser c) Expansion valve d) Evaporator.
Figure 3.1: Typical Compression Refrigeration System
High pressure liquid refrigerant is fed from the receiver or condenser through the
liquid line, and through the filter-drier to the metering device. It is at this point that the
high pressure side of the system is separated from the low pressure side. Various types of
control devices may be used, but for purposes of this illustration, only the thermostatic
expansion valve (TEV) will be considered.
The TEV controls the quantity of liquid refrigerant being fed into the evaporator.
The TEV’s internal orifice causes the pressure of the refrigerant to the evaporating or low
side pressure to be reduced. This reduction of the refrigerant pressure, therefore its
boiling point causes it to boil or vaporize, absorbing heat until the refrigerant is at the
saturation temperature corresponding to its pressure. As the low temperature refrigerant
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
passes through the evaporator coil, heat flows through the walls of the evaporator
tubing into the refrigerant. The boiling action continues until the refrigerant is completely
vaporized. The TEV regulates the quantity of refrigerant, (lb/min) through the evaporator
to maintain a preset temperature difference or superheat between the evaporating
refrigerant and the vapor leaving the evaporator. As the temperature of the gas leaving
the evaporator varies, the expansion valve power element bulb senses this temperature,
and acts to modulate the feed of refrigerant through the expansion valve.
The superheated refrigerant vapor leaving the evaporator travels through the
suction line to the compressor inlet. The compressor takes the low pressure vapor and
compresses it, increasing its pressure and temperature. The hot, high pressure vapor is
forced out of the compressor discharge valve(s), and into the condenser. As the high
pressure high temperature vapor passes through the condenser, it is cooled by an
external means. In air cooled systems, a fan, and fin-type condenser surface is normally
used. In water cooled systems, a refrigerant-to-water heat exchanger is employed. As
the temperature of the refrigerant vapor is lowered to the saturation temperature
corresponding to the high pressure in the condenser, the vapor condenses into a liquid
and flows back to the receiver or directly to the TEV to repeat the cycle. The refrigerating
process is continuous as long as the compressor is operating.
Figure 3.2: Schematic Diagram of Simple Compression Refrigeration System
In a vapor compression refrigeration system, the suitable refrigerants are
ammonia (NH3), R-11, R-12, R-22 and etc. This is commonly used in air conditioning, cold
storage, and ice plant.
1|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Simple Principle of Operation
The low temperature vapor from the evaporator is drawn in by the compressor
and discharge is to the condenser which cause to increase the temperature and
pressure of vapor due to mechanical compression.
In the condenser, the vapor from the compressor at the condenser pressure or
head pressure of the system is condensed by the available circulating water. After the
heat rejection has caused condensation, the liquid refrigerant may be stored in a
receiver.
If the pressure on the resulting is lowered, a portion of the liquid evaporates
immediately as the temperature drops, while the remaining liquid is vaporizing absorbs
heat from its surroundings, thereby creating refrigerating effect.
In the evaporating coils, the liquid refrigerant absorbs heat from brine or water or
directly from the space being cooled, for this reason, the leaving refrigerant in the
evaporator become saturated vapor.
The schematic diagram of the arrangement is as shown in the Figure 3.2. The low
temperature, low pressure vapor at state B is compressed by a compressor to high
temperature and pressure vapor at state C. This vapor is condensed into high pressure
vapor at state D in the condenser and then passes through the expansion valve. Here,
the vapor is throttled down to a low pressure liquid and passed on to an evaporator,
where it absorbs heat from the surroundings from the circulating fluid (being
refrigerated) and vaporizes into low pressure vapor at state B. The cycle then repeats.
The exchange of energy is as follows:
a) Compressor requires work, δw. The work is supplied to the system from the
surroundings.
b) During condensation, heat δQ1 the equivalent of latent heat of condensation etc, is
lost from the refrigerator.
c) During evaporation, heat δQ2 equivalent to latent heat of vaporization is absorbed
by the refrigerant.
d) There is no exchange of heat during throttling process through the expansion valve
as this process occurs at constant enthalpy.
2|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Figure 3.3: The T-S Diagram of a Simple Vapor Compression Cycle
The Figure 3.3 shows a simple vapor compression refrigeration cycle on T-s diagram for
different compression processes. The cycle works between temperatures T1 and T2
representing the condenser and evaporator temperatures respectively. The various
process of the cycle A-B-C-D (A-B’-C’-D and A-B”-C”-D) are as given below:
a) Process B-C (B’-C’ or B”-C”): Isentropic compression of the vapor from state B to C. If
vapor state is saturated (B), or superheated (B”), the compression is called dry
compression. If initial state is wet (B’), the compression is called wet compression as
represented by B’-C’.
b) Process C-D (C’-D or C”-D): Heat rejection in condenser at constant pressure.
c) Process D-A: An irreversible adiabatic expansion of vapor through the expansion
value. The pressure and temperature of the liquid are reduced. The process is
accompanied by partial evaporation of some liquid. The process is shown by dotted
line.
d) Process A-B (A-B’ or A-B”): Heat absorption in evaporator at constant pressure. The
final state depends on the quantity of heat absorbed and same may be wet (B’) dry (B)
or superheated (B”).
System: Evaporator
The purpose of the evaporator is to receive low-pressure, low temperature fluid
from the expansion valve and to bring it in close thermal contact with the load. The
refrigerant takes up its latent heat from the load and leaves the evaporator as dry gas.
The heat absorbed in the evaporator is commonly referred to as the refrigerating effect
(RE).
3|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
First Law: Energy Balance
QA + mrh1 = mrh4
QA = mr (h1 – h4) ; kW
Also,
RE = h1 – h4 ; kJ/kg
Also,
QA = mwCp∆t ; kW
Figure 3.4: The Evaporator section
System: Condenser
The purpose of condenser is to accept the hot, high pressure gas from the
compressor and cool it to remove first the superheat and then the latent heat, so that
the refrigerant will condense back to the liquid.
First Law: Energy Balance
QR + mrh3 = mrh2
QR = mr (h2 – h3) ; kW
Also,
QR = mwCp∆t ; kW
Figure 3.5: The Condenser section
System: Compressor
The purpose of compressor in a vapor compression cycle is to accept the lowpressure dry gas from the evaporator and raise its pressure to that of the condenser.
4|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
First Law: Energy Balance
wC + mrh1 = mrh2
wC = mr (h2 – h1) ; kW
WC = (h2 – h1) ; kJ/kg
Figure 3.6: The Compressor section
System: Expansion Valve
The purpose of expansion valve is to regulate the flow of refrigeration. This is called a
throttling or wire-drawing process. There is reduction of pressure with no change of
enthalpy.
First Law: Energy Balance
mrh3 = mrh4
h3 = h 4
Figure 3.7: The expansion valve section
where,
h1 = enthalpy of refrigerant entering the compressor.
h2 = enthalpy of refrigerant leaving the compressor.
h3 = enthalpy of refrigerant leaving the condenser.
h4 = enthalpy of refrigerant entering the evaporator.
mr = mass flow rate of the regrigerant.
Coefficient of Performance (Cop)
also,
The ratio of the useful refrigeration to the work required by the compressor.
𝑅𝐸
𝐶𝑂𝑃 =
𝑊𝑐
𝐶𝑂𝑃 =
5|Page
𝑄𝑎
𝑊𝑐
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Volumetric Efficiency (𝒆𝒗 )
The ratio of the volume flow rate entering the compressor to the displacement
rate of the compressor.
Factors influencing the volumetric efficiency are:
The effects of valve and piston ring leackage, although these are expected to be small.
The effect of surface and internal friction, 𝑒𝑖 .
The effect of superheating the refrigerant, 𝑒𝑠 .
The effect of clearance, 𝑒𝑐 .
Therefore, the actual volumetric efficiency is the product of these separate efficiencies,
or
𝑒𝑣 = 𝑒𝑖 𝑥 𝑒𝑠 x 𝑒𝑐
where,
where,
𝑒𝑠 = 1 −
𝑡2 − 𝑡1
1330
= 1−
𝑡2 − 𝑡1
738.89
𝑃2 1
𝑒𝐶 = 1 + 𝑐 − 𝑐( )𝑘 (𝑐𝑙𝑒𝑎𝑟𝑎𝑛𝑐𝑒 𝑣𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦)
𝑃1
𝑉1
= 1 − 𝑐( − 1)
𝑉2
𝑣𝑜𝑙𝑢𝑚𝑒 𝑓𝑙𝑜𝑤 𝑟𝑎𝑡𝑒 𝑒𝑛𝑡𝑒𝑟𝑖𝑛𝑔 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟
𝑒𝑉 =
𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡 𝑟𝑎𝑡𝑒 𝑜𝑓 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟
𝑉1
𝑚𝑟 𝑉1
𝑒𝑉 =
=
𝑉𝐷
𝑉𝐷
𝜋 2
𝑉𝐷 = 𝐷 𝐿𝑁𝑛
4
𝑉𝐷 = 𝑣𝑜𝑙𝑢𝑚𝑒 𝑑𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
𝑉1 = 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑟𝑒𝑓𝑟𝑖𝑔𝑒𝑟𝑎𝑛𝑡 𝑒𝑛𝑡𝑒𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟,
𝑙𝑖𝑡𝑒𝑟𝑠
𝑘𝑔
𝐷 = 𝑑𝑖𝑎𝑚𝑒𝑡𝑒𝑟 𝑜𝑓 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟 (𝑏𝑜𝑟𝑒)
𝐿 = 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑠𝑡𝑟𝑜𝑘𝑒
𝑁 = 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑡𝑟𝑜𝑘𝑒 𝑐𝑜𝑚𝑝𝑙𝑒𝑡𝑒𝑑 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑡𝑖𝑚𝑒
𝑁 = (𝑛)(1)(𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟𝑠)𝑓𝑜𝑟 𝑠𝑖𝑛𝑔𝑙𝑒 𝑎𝑐𝑡𝑖𝑛𝑔 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟
𝑁 = (𝑛)(2)(𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑐𝑦𝑙𝑖𝑛𝑑𝑒𝑟𝑠)𝑓𝑜𝑟 𝑑𝑜𝑢𝑏𝑙𝑒 𝑎𝑐𝑡𝑖𝑛𝑔 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟
𝑛 = 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑜𝑟 𝑠𝑝𝑒𝑒𝑑
𝑘 = 1.304 𝑓𝑜𝑟 𝑎𝑚𝑚𝑜𝑛𝑖𝑎
6|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
A single-acting compressor makes one complete cycle in one revolution.
A double-acting compressor makes two complete cycles in one revolution.
Mechanical efficiency
ŋ𝑚 =
𝑖𝑛𝑑𝑖𝑐𝑎𝑡𝑒𝑑 𝑤𝑜𝑟𝑘
𝑊1
=
𝑏𝑟𝑎𝑘𝑒 𝑤𝑜𝑟𝑘
𝑊𝐵
The adiabatic compression efficiency or simply compression efficiency ŋ𝑚 is defined as:
𝑖𝑠𝑒𝑛𝑡𝑟𝑜𝑝𝑖𝑐 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛
ŋ𝑚 =
𝑎𝑐𝑡𝑢𝑎𝑙 𝑤𝑜𝑟𝑘 𝑜𝑓 𝑐𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑜𝑛
Examples:
1. An NH3 vapor compression refrigeration system has a condensing temperature of
250C and an evaporating temperature of -100C. The refrigerating capacity is 7
tons. The liquid leaving the condenser is saturated and compression is isentropic.
Determine:
a. The refrigerant flow rate, kg/sec.
b. The refrigerant volumetric flow at compressor suction, liters/sec.
c. The work of compression, kJ/kg.
d. The theoretical compressor power, kW.
e. The heat rejected from the system, kW.
f. The COP.
g. Quality of refrigerant before evaporator.
2. A simple saturated refrigeration cycle for R-12 system operates at an evaporating
temperature of 260.96 kPa and condensing temperature of 400C. Determine:
a. Draw the schematic and p-h diagram
b. The refrigerant effect, kJ/kg
c. The work of compressor, kJ/kg
d. The heat rejected in the system, kJ/kg
e. The COP
CONDENSER
QR
f.
Schematic Diagram
3
2
COMPRESSOR
TXV
Wc
4
QA
EVAPORATOR
7|Page
1
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Supplementary Problems:
1. A 15-ton refrigeration system is used to make ice. The water is available at 20 C.
Refrigerant 12 is used with saturated temperature limits of –25 C and 54 C.
Determine (a) the COP, (b) the refrigerant flow rate, (c) the temperature at
discharge of the compressor, (d) the volume flow rate, and (e) the maximum kg
of ice manufactured per day.
2. An air conditioning system of a high rise building has a capacity of 350 kW of
refrigeration, uses R-12. The evaporating and condensing temperature are 00C
and 350C, respectively. Determine the following:
a. Mass of flash gas per kg of refrigerant circulated.
b. Mass of R-12 circulated per second.
c. Volumetric rate of flow under suction condition.
d. Work compression in kW.
e. COP
3. A simple vapor-compression cycle develops 13 tons of refrigeration. Using
ammonia as refrigerant and operating at a condensing temperature of 240C and
evaporating temperature of -180C and assuming that the compression are
isentropic and that the gas leaving the condenser is saturated. Find the following:
a. Draw the P-h diagram.
b. Refrigerating effect in kJ/kg.
c. Circulation flow in kg/min.
d. Power requirement
e. Volume flow in cc per minute per ton.
f. Coefficient of Performance.
g. Power per ton.
4. An ammonia refrigerating cycle operates at 247.14 kPa suction pressure and
1,230.70 kPa condenser pressure. Other data are the following:
Refrigerating capacity ……………………………………… 29 kW
Compressor capacity ………………………………………. 4kW
Compression efficiency ……………………………………. 85 %
Mechanical efficiency ……………………………………… 78 %
Actual Volumetric efficiency ………………………………. 80 %
Determine the following:
a. The clearance volumetric efficiency.
b. The ideal and actual COP.
c. The mass flow rate of ammonia.
d. The brake work.
5. A four-cylinder refrigerant 12 compressor operates between the evaporator and
condenser temperatures of 40C and 430C. It is to carry a load of 20 tons of
refrigeration at 1200 rpm. If the average piston speed is 213 m/min and the actual
volumetric efficiency is 80 per cent, what should be the bore and stroke of the
compressor?
8|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
6. A 100 x 200 mm ammonia compressor with a compressor with a compression
efficiency of 80 per cent operates with a suction pressure of 291.6 kPa and a
condenser pressure of 1204 kPa at 23 r/s. The refrigerant cools 102 kg/min of brine
by 8 degrees in the brine cooler. The specific heat of the brine is 3.14 kJ/kg-0C.
Electric input to the motor driving the compressor is 14.33 kW. Motor efficiency at
this load is 92 per cent. Assuming 5 per cent of the useful refrigerating effect is lost
by brine cooler from the room, determine the mechanical and volumetric
efficiencies of the compressor.
7. A six-cylinder, 6.70 x 5.70 - cm, refrigerant 22 compressor operating at 30 r/s
indicate a refrigerating capacity of 96.4 kW and a power requirement of 19.4 kW
at an evaporating temperature of 50C and a condensing temperature of 350C.
Compute a) the clearance volumetric efficiency if the clearance volume is 5 per
cent, b) the actual volumetric efficiency, and c) compression efficiency.
8. A manufacturing company is intending to use its water cooled condenser for its
proposed cold storage room. The name plate of the condenser gives the
following specifications:
Refrigerant
ammonia
Condenser water inlet
300C
Condenser water outlet
400C
Condenser temperature
350C
Refrigerant flow
3.84 kg/min
Circulating water flow
120 kg/min
a. If the company decided to purchase a new compressor and evaporator, find
the tonnage of the system and the temperature in the evaporator, b) what is
the COP?, c)find the theoretical hp required.
9. A standard ammonia vapor compression cycle developing 20 tons of
refrigeration operates with a condensing temperature of 320C and an
evaporating temperature of -140C. Calculate a) refrigerating effect, b)
circulating rate of refrigerant, c) theoretical power, d) COP, e) gallons per minute
of cooling water in the condenser, if change in temperature is 80C, d) quality of
the refrigerant entering the evaporator, and g) temperature of the refrigerant
leaving the compressor. ( 1 gallon contains 8.33 lb of water).
EFFECTS OF OPERATING CONDITIONS
Objectives:
1. Know effects of increasing the Vaporizing temperature
2. Know effects of increasing the Condensing temperature
3. Know effects of superheating the suction Vapor
4. Know effects of subcooling the liquid
1. Effects of Increasing the Vaporizing temperature
9|Page
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
-
A R-12 simple saturated refrigerating cycle operates at an evaporating
temperature of -100C and a condensing temperature of 400C. Show the effects
of increasing the vaporizing temperature.
Properties of refrigerants:
h3 = h4 = hf at 400C = 238.5 kJ/kg
for the -100C evaporating cycle (cycle 1-2-3-4-1)
v1 = vg at -100C = 0.07675 m3/kg
h1 = hg at -100C = 347.1 m3/kg
h2 = h at 961 kpa and s2 equals s1 = 373 kJ/kg-K
for the 50C evaporating cycle (cycle 1’-2’-3’-4’-1’)
v1 = vg at 50C = 0.04749 m3/kg
h1 = hg at 50C = 353.6 m3/kg
h2 = h at 961 kpa and s2 equals s1 = 371 kJ/kg-K
Subcooling and superheating:
In E refrigeration cycles, the temperature of the heat sink will be several degrees
lower than the condensing temperature to facilitate heat transfer. Hence it is possible
to cool the refrigerant liquid in the condenser to a few degrees lower than the
condensing temperature by adding extra area for heat transfer. In such a case, the exit
condition of the condenser will be in the subcooled liquid region. Hence this process is
known as subcooling. Similarly, the temperature of heat source will be a few degrees
higher than the evaporator temperature, hence the vapour at the exit of the
evaporator can be superheated by a few degrees. If the superheating of refrigerant
takes place due to heat transfer with the refrigerated space (low temperature heat
source) then it is called as useful superheating as it increases the refrigeration effect. On
the other hand, it is possible for the refrigerant vapour to become superheated by
exchanging heat with the surroundings as it flows through the connecting pipelines.
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Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Such a superheating is called as useless superheating as it does not increase
refrigeration effect.
Subcooling is beneficial as it increases the refrigeration effect by reducing the
throttling loss at no additional specific work input. Also subcooling ensures that only liquid
enters into the throttling device leading to its efficient operation. The Figure below shows
the VCRS cycle without and with subcooling on P-h and T-s coordinates. It can be seen
from the T-s diagram that without subcooling the throttling loss is equal to the hatched
area b-4’-4-c, whereas with subcooling the throttling loss is given by the area a-4”-4’-b.
Thus the refrigeration effect increases by an amount equal to (h4-h4’) = (h3-h3’). Another
practical advantage of subcooling is that there is less vapour at the inlet to the
evaporator which leads to lower pressure drop in the evaporator.
Figure 3.8: The P-H and T-S Diagram of the effects of sub-cooling the liquid.
Useful superheating increases both the refrigeration effect as well as the work of
compression. Hence the COP (ratio of refrigeration effect and work of compression)
may or may not increase with superheat, depending mainly upon the nature of the
working fluid. Even though useful superheating may or may not increase the COP of the
system, a minimum amount of superheat is desirable as it prevents the entry of liquid
droplets into the compressor. The figure shows the VCRS cycle with superheating on P-h
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Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
and T-s coordinates. As shown in the figure, with useful superheating, the refrigeration
effect, specific volume at the inlet to the compressor and work of compression increase.
Whether the volumic refrigeration effect (ratio of refrigeration effect by specific volume
at compressor inlet) and COP increase or not depends upon the relative increase in
refrigeration effect and work of compression, which in turn depends upon the nature of
the refrigerant used. The temperature of refrigerant at the exit of the compressor
increases with superheat as the isentropes in the vapour region gradually diverge.
Figure 3.9: The P-H and T-S Diagram of the effects of superheating the vapor.
To summarize, the following are the results of effects of different operating conditions.
1. Effects of increasing the vaporizing temperature:
12 | P a g e
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
2.
3.
4.
5.
- The refrigerating effect per unit mass increases.
- The mass flow rate per ton decreases.
- The volume flow rate per ton decreases.
- The COP increases.
- The work per ton decreases.
- The work per ton decreases.
- The heat rejected at the condenser per ton decreases.
Effects of increasing the condenser temperature.
- The refrigerating effect per unit mass decreases.
- The mass flow rate per ton increases.
- The volume flow rate per ton increases.
- The COP decreases.
- The work per ton increases.
- The heat rejected at the condenser per ton increases.
Effects of superheating the suction vapor
When superheating produces useful cooling:
- The refrigerating effect per unit mass increases.
- The mass flow rate per ton decreases.
- The volume flow rate per ton decreases.
- The COP increases.
- The work per ton decreases.
Effects of superheating the suction vapor
When superheating produces without useful cooling:
- The refrigerating effect per unit mass remains the same.
- The mass flow rate per ton remains the same.
- The volume flow rate per ton increases.
- The COP decreases.
- The work per ton increases.
- The heat rejected at the condenser per ton increases.
Effects of sub-cooling the liquid.
- The refrigerating effect per unit mass increases.
- The mass flow rate per ton remains decreases.
- The volume flow rate per ton decreases.
- The COP increases.
- The work per ton decreases.
- The heat rejected at the condenser per ton decreases.
13 | P a g e
Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Examples:
1. A R-12 simple saturated refrigerating cycle operates at an evaporating
temperature of -100C and a condensing temperature of 400C. Show the effects
of increasing the vaporizing temperature to 50C.
2. A simple saturated refrigerating cycle using R-12 as the refrigerant, operates at a
condensing temperature of 400C and an evaporating temperature of -100C.
Show the effects of increasing the condensing temperature to 500C.
Supplementary Problems:
1. A simple saturated refrigerating cycle for R-12 system operates at an evaporating
temperature of -50C and a condensing temperature of 400C. Show the effects of
superheating the suction vapor from -50C to 150C.
2. A simple saturated refrigerating cycle using R-12 as the refrigerant operates at an
evaporating temperature of -50C and a condensing temperature of 400C. Show
the effects of sub-cooling the liquid from 400C to 300C before reaching the
expansion valve.
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Romblon State University |Department of Mechanical Engineering
BS Mechanical Engineering
REFRIGERATION ENGINEERING | Second Semester | School Year 2017-2018
Reference:
A.B. Trillllana, N.C. Dela Rama, 1995, Simplified Design of Refrigeration and Air
Conditioning
C.P. Arora, 2009, McGraw-Hill International Edition, Refrigeration and Air Conditioning
H.B. Sta.Maria, Third Edition, 2001, Refrigeration and Air Conditioning
PN. Ananthanarayanan, 1999, Second Edition, Refrigeration and Air Conditioning
R.S. Alcorcon, 2005, Power Plant Engineering
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