[2011]
I. Abstract
This report reviews the latest research in the areas of characteristics, properties,
synthesis, and current applications of carbon nanotubes. Due to the remarkable mechanical
and electronic properties carbon nanotubes boast, they have been have seen a steadily growing
interest since the early 90’s. The field has been developed rapidly, and the number of
publications per year is increasing almost exponentially. Because of this extensive research,
many technological advances have been achieved such as the fabrication of flat panel displays,
gas storage devices, toxic gas sensors, Li+ batteries, robust and lightweight composites,
conducting paints, electronic nanodevices, nano motors and many other applications. Carbon
nanotubes are a fundamental component of nanoscience and nanotechnology and because
they are so small they are difficult to test and measure. New methods must be developed for
synthesis, property characterization and fabrication. The sky is the limit with nanotubes and
research will be performed for a long time to come.
San Diego State University
Mechanical Engineering
ME 495 - Mechanical & Thermal Systems Lab
Brayton Cycle
Group D:
Emmanuel Hernandez (Project Manager)
Victor Sanchez
Rolando Herrera
Fernando Hernandez
Justin Hammerschmidt
Nick Garrett
Professor Sam Kassegne, PhD, PE
March 9th , 2011
2
Table of Contents
Objectives of the Experiment ……………………………………................................................................3
Nick Garrett
Equipment ………………………………………………….…............................................................................5
Justin Hammerschmidt
Experimental Procedure …………………………….……………………………………………………………………………5
Justin Hammerschmidt
Experimental Results and Calculations ……….…………………………………………………….……………..….....7
Victor Sanchez
Discussion of Results ...................................................................................................................13
Rolando Herrera
Conclusion ………………………..........................................................................................................16
Fernando Hernandez
References ……………………….........................................................................................................17
Fernando Hernandez
3
Objective of the Experiment
The objective of this lab was to obtain working, practical knowledge of the Brayton Cycle. An SR-30
turbojet engine (built by Turbine Technologies, LTD) was used to conduct this experiment, and empirical
readings were taken at various times and locations throughout the experiment for use in equations.
Performing a basic thermodynamic analysis will allow us to understand physically what goes on in a
Brayton cycle.
The Brayton cycle uses the cold air standard assumption that specific heats are constant at room
temperature, and all processes are internally reversible. This cycle consists of four stages.
Q in
Combustion
Chamber
2
Compressor
3
Wout
Turbine
Win
1
Atmospheric
air
1
2
3
4
2
3
4
3
: Isentropic c om pression
: Reversible c onstant pressure heat addition
: Isentropic expansion
: reversible c onstant p ressure heat rejec tion
4
Hot
exhaust
Figure 1: Standard Brayton Cycle [1]
In the first stage, atmospheric air is brought into the compressor and is compressed isentropically in
order to increase the temperature of the air (this high temperature raises the efficiency of the system).
Next, this high pressure and temperature air is mixed with fuel in the combustion chamber. This is
ignited by spark, and undergoes constant pressure heat addition. This hot gas then enters the turbine
region of the apparatus, and expands isentropically, turning the turbine. The gas then undergoes
4
constant pressure heat rejection and is relocated to the air intake from the exhaust. This last step is
theoretical; in reality there is a constant source of air intake so the exhaust does not need to be recycled
in a closed loop.
In this lab, we will calculate the overall thermal efficiency of the system, which is given by the equation:
nth,Brayton = 1 –
1
.
rP(k-1)/k
In this equation, rP is the pressure ratio, and k is the specific heat ratio of air. We will also be calculating
the thermal efficiency of the turbine and compressor at each engine speed using the standard equations
derived from the first law of thermodynamics:
nc = ( Tout,s – Tin) / ( Tout,a – Tin)
nT = (Tout,a – Tin) / ( Tout,s – Tin)
In these equations, Tin is the temperature at the inlet to the device, Tout,s is the ideal (isentropic) outlet
temperature, and Tout,a is the actual outlet temperature. We will also be calculating the back work ratio
using the following relations:
bwr = wCOMP / wTURB
- wTURB = Cp,T (Tt,out – Tt,in)
wCOMP = Cp, c (Tc, out - Tc, in)
The work in the compressor and turbine are calculated using the inlet and exit temperatures of the
device, as well as the specific heat, Cp, evaluated at the average of the inlet and exit temperatures.
5
Equipment
The equipment used in this experiment consisted of two components – the test bench and the lab
computer. The test bench is a TTL Mini-Lab manufactured by Turbine Technologies Ltd. and the lab
computer was a Dell desktop unit. The following components were used during the testing process:
SR-30 Engine
Thrust Readout Gauge
Pressure Gauges
Controls
Figure 2: TTL Mini-Lab manufactured
by Turbine Technologies Ltd. (TTL) [2]
RPM Readout Gauge
Virtual Bench Software
Hearing Protection
Thermocouples
Figure 3: SR-30 by Turbine Technologies Ltd. (TTL) [2]
Experimental Procedure
This experiment requires great concentration and awareness by the operators to ensure
safety when handling the SR-30 turbojet. The first step is to become familiar with the controls
and gauges with the turbojet. Ample time must be taken to be sure each phase of the Brayton
cycle is understood. Once the operators are familiar with the turbojet’s control the next step is
to prepare the computer to record data during the operation. From the desktop of the
6
computer, launch VirtualBench and follow the procedure listed in the lab manual for entering
the filename to which the data will be saved.
When this is complete, the experiment is ready to begin. To start the engine, turn on the
master key and the el. master key. Make sure the throttle handle is pushed all the way forward.
Then simultaneously turn on the ignition and air start switches. The compressed air will start
the engine. Once the engine has reached approximately 12,000 RPM, turn on the fuel switch.
This injects the fuel, in this case kerosene, into the engine for ignition and the increase in sound
will be an indicator that the engine has ignited. Once the engine has ignited, the air switch and
ignition can be turned off. At this point, the student designated to the computer data collection
is to be signaled to begin recording. Now, using the throttle handle, manipulate the engine until
the desired RPM is reached. When this is reached, another student should be manually
recording the temperature, engine speed, and fuel pressure to compare with the computer
data for errors, as well as for safety. If the temperature exceeds 500 degrees Celsius, the engine
must be turned of immediately. When enough data has been recorded, stop the software and
turn the engine off by cutting the fuel.
Follow the same procedure for all other desired RPMs. Make sure all the data is saved
and power down all equipment.
7
Experimental Results and Calculations
What can be observed about the turbine engine’s efficiency in relation to its RPM?
Turbine Efficiency vs RPM
Turbine Efficiency (%)
80
70
60
50
40
30
20
10
0
51000
52000
53000
54000
55000
56000
57000
58000
59000
60000
61000
RPM
Figure 3: Turbine vs RPM
There is a linear relationship between turbine efficiency and RPM. Figure 3 illustrates this relationship.
What type of relationship (constant, linear, exponential, etc.) exists between RPM and thrust?
Thrust vs RPM
16.5
Thrust (lbs)
14.5
12.5
10.5
RUN 1
8.5
RUN 2
6.5
RUN 3
4.5
44000 47000 50000 53000 56000 59000 62000 65000 68000 71000 74000
RPM (revolutions per minute)
Figure 4: Thrust vs RPM
There is a linear relationship between thrust efficiency and RPM. Figure 4 illustrates this relationship.
8
Data Reduction
Provide a T-s & P-v for the ideal and actual Brayton cycle for each test speed.
Figure 5: T-s diagram for ideal cycle at ~55000 RPM
Figure 6: P-v diagram for ideal cycle at ~55000 RPM
9
Figure 7: T-s diagram for actual cycle at ~55000 RPM
Figure 8: P-v diagram for actual cycle at ~55000 RPM
10
Figure 9: T-s diagram for ideal cycle at ~60000 RPM
Figure 10: P-v diagram for ideal cycle at ~60000 RPM
11
Figure 11: T-s diagram, for actual cycle at ~60000 RPM
Figure 12: P-v diagram for actual cycle at ~60000 RPM
12
Calculate the thermal efficiency for the Brayton cycle for each engine speed.
Engine speed = ~52000 RPM
Average turbine inlet pressure P3
= 9.2555 psig = 23.9155 psia
Average turbine outlet pressure P4 = 0.9197 psig = 15.5795 psia
rP 
P3 23.9155 psia

 1.5350
P4 15.5797 psia
 th  1 
1
rP
 k 1 / k
(100)  1 
1
(100)  11.523%
1.5350 1.41 / 1.4
Perform a first law analysis of each section of the SR-30 engine at each engine speed.
Engine speed = ~52000 RPM
Compressor
Tavg 
T1  T2 293.05K  349.28K
kJ

 321.165K  c p ,C  1.006
2
2
kg  K

kJ 
kJ
349.28K  293.05K   56.5673
wC  h2  h1  c p.C T2  T1   1.006
kg  K 
kg

Combustor
T  T3 349.28K  745.96 K
kJ
Tavg  2

 547.62 K  c p ,Q  1.04
2
2
kg  K

kJ 
kJ
745.96 K  349.28K   412.5472
qin  h3  h2  c p.Q T3  T2   1.04
kg  K 
kg

Turbine
T  T4 745.96 K  737.21K
kJ
Tavg  3

 741.59 K  c p ,T  1.08
2
2
kg  K

kJ 
kJ
745.96 K  737.21K   9.45
wT  h3  h4  c p.T T3  T4   1.08
kg  K 
kg

13
Calculate the back-work ratio for each engine speed.
Engine speed = ~52000 RPM
kJ
56.56
w
kg
rbw  C 
 5.985
kJ
wT
9.45
kg
Table 1: Summary of Efficiencies
RUN
1
RUN
2
RUN
3
RPM
Thermal
Efficiency
Compressor
Efficiency
Turbine
Efficiency
Back Work
Ration
51718.7289
11.52455612
70.65889453
28.43620087
5.992124535
55274.4547
13.21275831
77.07878092
60.90369336
1.95654517
60394.6007
13.89029374
79.91471667
70.46270178
1.459487879
14
Discussion of results
Efficiency vs RPM
Turbine Efficiency (%)
90
80
Turbine Efficiency vs RPM
70
Compressor Efficiency vs RPM
60
Thermal Efficiency vs RPM
50
Linear (Turbine Efficiency vs RPM)
40
Linear (Compressor Efficiency vs RPM)
30
Linear (Thermal Efficiency vs RPM)
20
10
0
50000
52000
54000
56000
58000
60000
62000
RPM
Figure 13: Efficiency vs RPM
Table 2: Run 1
Avg values
0.1261
rp(psia)
1.535042395
9.1734
9.2555
k
1.4
Thermal Efficiency
11.52455612
Compressor Eff
70.65889453
Turbine Eff
28.43620087
0.9197
0.6829
2.6264
7.2038 51718.729
20.0544
76.2895
472.961
464.2192
426.9823
Compressor (Tavg)
321.17195
Cp
1.006
Combustor (Tavg)
547.62525
Cp
1.04
Turbine (Tavg)
741.5901
Cp
1.08
T2-T1
56.2351
Compressor Work
56.5725106
T3-T2
396.6715
Heat in
412.53836
T3-T4
8.7418
Turbine Work
9.441144
Back Work Ratio
5.992124535
Table 3: Run 2
Avarage values
0.1776
rp(psia)
1.642118146
11.6809
k
1.4
Compressor Eff
77.07878092
11.3702
Thermal Efficiency
13.21275831
Turbine Eff
60.90369336
1.1916
0.7711
2.821
8.0164 55274.455
20.8391
92.8248
504.1006
469.8293
433.9194
Compressor (Tavg)
329.83195
Cp
1.006
Combustor (Tavg)
571.4627
Cp
1.045
Turbine (Tavg)
759.96495
Cp
1.08
T2-T1
71.9857
Compressor Work
72.4176142
T3-T2
411.2758
Heat in
429.783211
T3-T4
34.2713
Turbine Work
37.013004
Back Work Ratio
1.95654517
15
Table 4: Run 3
Avarage values
0.185
rp(psia)
1.687786943
12.6538
12.4705
k
1.4
Thermal Efficiency
13.89029374
Compressor Eff
79.91471667
Turbine Eff
70.46270178
1.4146
0.9487
3.2608
9.6465 60394.601
21.1547
103.3044
507.1288
454.6467
423.2734
Compressor (Tavg)
335.22955
Cp
1.007
Combustor (Tavg)
578.2166
Cp
1.04
Turbine (Tavg)
753.88775
Cp
1.08
T2-T1
82.1497
Compressor Work
82.7247479
T3-T2
403.8244
Heat in
419.977376
T3-T4
52.4821
Turbine Work
56.680668
Back Work Ratio
1.459487879
The data was obtained which much difficulty. Out of a total of three runs, only two were fully
acceptable for this experiment. Our group and Dr. Kessegne noted that a major pressure loss
existed somewhere in the systems that prevented an accurate compression ratio that was
needed for this experiment. Luckily, our temperature and pressure readings were within
acceptable range.
There were also other possible sources of biased experimental error in this lab. During the first
run, our thermocouple and pressure sensor for the inlet conditions of the compressor were
fluctuating very rapidly. This run skewed our results but may have helped the following runs.
We also observed how the strain gauge showed fluctuation in the thrust, even when no one
was touching it. The fluctuation was always negative. This could be due to bad hardware in the
strain gauge, or vibrations in the test bench. Fortunately, no other calculations are dependent
on thrust. Another source of random error is the fluctuation in the engine speed. The rpm was
controlled by group members via a throttle arm, and it was very hard to set the speed exactly
where we wanted it and hold it steady. Because of this change in rpm, we have data for several
ranges of rpm values, instead of data for individual speeds.
16
The data in Figure 13 show a linear relationship in both turbine efficiency versus rpm and thrust
versus rpm. Thus, at higher rpm you will have a higher efficiency as well as thrust. Compressor
and thermal efficiencies also follow a linear relationship with rpm.
Conclusion
Although there were plenty of factors present during the experiment that skewed the
experimental data, the objective of obtaining working and practical knowledge of the Brayton
cycle was still achieved. Moreover troubleshooting techniques were learned during the process
of getting the cycle up to par in order to conduct additional runs. Also, the experiment offers a
good experience to its users in the sense that concepts learned in thermodynamic classes
become tangible.
17
References
1. Kassegne, S. " ME495 Lab - Brayton Cycle Gas Turbine - Expt Number 1." Mechanical
Engineering Department. San Diego State University. Spring 2011.
2. "Turbine Technologies - Gas Turbine Lab." Turbine Technologies - Creating Educational
Laboratory Equipment For Tomorrow's Engineer. Web. 09 Mar. 2011.
<http://www.turbinetechnologies.com/gas_turbine.html>.
3. "Turbine Engine Thermodynamic Cycle - Brayton Cycle." NASA - Title... Web. 09 Mar.
2011. <http://www.grc.nasa.gov/WWW/K-12/airplane/brayton.html>.
4. "Thermodynamics EBook: Brayton Cycle." ECourses. Web. 09 Mar. 2011.
<http://www.ecourses.ou.edu/cgibin/ebook.cgi?doc=&topic=th&chap_sec=09.1&page=theory>.