CrazyEngineers Archive
Old, but evergreen and popular discussions on CrazyEngineers, presented to you in read-only mode.
@raj87verma88 • 23 May, 2009
During her KYCEan interview, CEan Durga mentioned that she would like something like "How Stuff Works" on CE. The idea sounded good and I have decided to write the first "Inside It" We currently do not have a seperate section for this and each "Inside It" would be posted under the appropriate engineerig section.
Introduction
Proposed by George Brayton an American Engineer for use in the reciprocating oil-burning engine he had developed in around 1870, though some sources claim that it was originally patented by an English John Barber in 1871.
It is used for Gas turbines and to define modern aircraft engines. The Brayton Cycle is the only cycle which can be used for both External and Internal Combustion Engines.
Working
Usually it operates on an Open Cycle Fig 1(A). Fresh air at ambient conditions enters the Compressor, the temperature and pressure are raised. Air at high pressure enters the combustion chamber, where the fuel is burned at a constant pressure. The high temperature exhaust gases enter the turbine, where they expand to atmospheric pressure produckng power. The exhaust gases are then thrown out.
This cycle can be modeled into a closed cycle by assuming standard air-assumptions. It also makes the thermodynamic analysis more easy. Fig 1(B) shows the closed loop Brayton Cycle. The compression and expansion processes are the same. Combustion is replaced by constant-pressure heat addition, and exhaust by constant pressure heat rejection process to the atmosphere.
![[IMG]](proxy.php?image=http%3A%2F%2Fi40.tinypic.com%2F1zgs4te.jpg&hash=a1ab66924afe8ebb6bd3bf0f466288da)
Open and Close Loop Brayton Cycle
Image: Chris Bence.com
Brayton Cycle
(Source: Wikipedia, Thermodynamice by Yunus A. Cengel and Michael A. Boles, Thermal Engineering by P.L. Ballaney, Engineering Thermodynamics by P.K. Nag)
(Source: Wikipedia, Thermodynamice by Yunus A. Cengel and Michael A. Boles, Thermal Engineering by P.L. Ballaney, Engineering Thermodynamics by P.K. Nag)
Introduction
Proposed by George Brayton an American Engineer for use in the reciprocating oil-burning engine he had developed in around 1870, though some sources claim that it was originally patented by an English John Barber in 1871.
It is used for Gas turbines and to define modern aircraft engines. The Brayton Cycle is the only cycle which can be used for both External and Internal Combustion Engines.
Working
Usually it operates on an Open Cycle Fig 1(A). Fresh air at ambient conditions enters the Compressor, the temperature and pressure are raised. Air at high pressure enters the combustion chamber, where the fuel is burned at a constant pressure. The high temperature exhaust gases enter the turbine, where they expand to atmospheric pressure produckng power. The exhaust gases are then thrown out.
This cycle can be modeled into a closed cycle by assuming standard air-assumptions. It also makes the thermodynamic analysis more easy. Fig 1(B) shows the closed loop Brayton Cycle. The compression and expansion processes are the same. Combustion is replaced by constant-pressure heat addition, and exhaust by constant pressure heat rejection process to the atmosphere.
Open and Close Loop Brayton Cycle
Image: Chris Bence.com
@raj87verma88 • 23 May, 2009
Derivation of Equation and Cycle Efficiency
The T-S and P-V diagram of an ideal Brayton Cycle are as follows.
![[IMG]](proxy.php?image=http%3A%2F%2Fi39.tinypic.com%2Fidud53.jpg&hash=51f1cf113ad5dd47993073db243e69d6)
Image: Wikipedia
As seen the isdeal cycle is made of 4 internally reversible cycles.
1-2 Isentropic Compression (in compressor)
2-3 Constant Pressure heat addition
3-4 Isentropic Expansion (in turbine)
4-1 Constant Pressure heat rejection
Note: All four processes are executed in steady flow devices and should be analyzed as steady flow processes
When change in Kinetic and Potential Energies are neglected, energy balance equation for steady-flow process can be expressed, on a unit mass basis as:
(q in - q out) + (w in - w out) = h exit - h inlet
Therefore, heat transfer to and from working fluid are
qin = h3 - h2 = cp(T3 - T2)
qout = h4 - h1 = cp(T4 - T1)
Thermal efficiency(Neta) of ideal cycle,
Neta(thermal brayton) = wnet / qin = 1 - [qout/qin] = 1 - [cp(T4 - T1)/cp(T3 - T2)]
= 1 - [T1(T4/T1 - 1)/T2(T3/T2 - 1)]
We know 1-2 and 3-4 are isentropic. P2 = P3 and P4 = P1
T2/T1 = (P2/P1)^(k-1)/k = (P3/P4)^(k-1)/k = T3/T4
Substituting these values in the efficiency equation
Neta(Thermal Brayton) = 1 - [ 1/rp^(k-1)/k]
where rp = P1/P2, it is called pressure ratio.
k is specific heat ratio.
The efficiency equation shows that thermal efficiency of a Brayton Cycle depends upon pressure ration of Gas Turbine and specific heat ratio of working fluids.
Thermal efficiancy increases with both these factors.
The T-S and P-V diagram of an ideal Brayton Cycle are as follows.
Image: Wikipedia
As seen the isdeal cycle is made of 4 internally reversible cycles.
1-2 Isentropic Compression (in compressor)
2-3 Constant Pressure heat addition
3-4 Isentropic Expansion (in turbine)
4-1 Constant Pressure heat rejection
Note: All four processes are executed in steady flow devices and should be analyzed as steady flow processes
When change in Kinetic and Potential Energies are neglected, energy balance equation for steady-flow process can be expressed, on a unit mass basis as:
(q in - q out) + (w in - w out) = h exit - h inlet
Therefore, heat transfer to and from working fluid are
qin = h3 - h2 = cp(T3 - T2)
qout = h4 - h1 = cp(T4 - T1)
Thermal efficiency(Neta) of ideal cycle,
Neta(thermal brayton) = wnet / qin = 1 - [qout/qin] = 1 - [cp(T4 - T1)/cp(T3 - T2)]
= 1 - [T1(T4/T1 - 1)/T2(T3/T2 - 1)]
We know 1-2 and 3-4 are isentropic. P2 = P3 and P4 = P1
T2/T1 = (P2/P1)^(k-1)/k = (P3/P4)^(k-1)/k = T3/T4
Substituting these values in the efficiency equation
Neta(Thermal Brayton) = 1 - [ 1/rp^(k-1)/k]
where rp = P1/P2, it is called pressure ratio.
k is specific heat ratio.
The efficiency equation shows that thermal efficiency of a Brayton Cycle depends upon pressure ration of Gas Turbine and specific heat ratio of working fluids.
Thermal efficiancy increases with both these factors.
@raj87verma88 • 23 May, 2009
Thats it for today. The total working with all factors would be completed in a few days.
As this is the first thread under "Inside It" series, this would be a rather haphazard. I would try to co-ordinate the other posts in a more proper manner.
As this is the first thread under "Inside It" series, this would be a rather haphazard. I would try to co-ordinate the other posts in a more proper manner.
@raj87verma88 • 23 May, 2009
Function of Air in a Gas Turbine:-
That is why Gas power plant turbines are larger than those of steam power plants of same net power output.
Keep tuned for more. We have a few posts left before this cycle is complete.
- Provides oxidants for fuel combustion
- As a coolent to keep component's temperature within safe limits
- Electric Power Generation: The exhaust from the combustion chamber are at high speed. There kinetic energy is converted work i.e. rotation of the propeller connected to a shaft which is connected to a generator and produces electric power. They are also used in conjunction with Steam Power Plants. The high temperature exhaust is used as a heat source for generating steam.
- Aircraft Propulsion: Gas turbine produces just enough power to drive a small generator and provide power to small auxiliary components. The high velocity exhaust gases provide the required thrust for aircraft propulsion.
- It can also be used as a closed loop cycle in Nuclear Power Plant. Usually a gas with more desirable qualities like Helium is used as working fluid.
- Propulsion of Ships: Majority of the Naval fleets in the west use Gas-Turbine engines for propulsion and electricity generation. Some modern ships use gas turbine combined with diesel engines. Diesel provides efficient low-power and cruise operation, gas turbine is used when high speeds are needed.
That is why Gas power plant turbines are larger than those of steam power plants of same net power output.
Keep tuned for more. We have a few posts left before this cycle is complete.
@durga ch • 23 May, 2009
:shocked:
that's a looott of info for people in your field 😁 awesome !!!I scanned through it ! 😁
that's a looott of info for people in your field 😁 awesome !!!I scanned through it ! 😁
@Ashraf HZ • 24 May, 2009
This is a great initiative, patty! Honestly, the title "Inside It" took a while to accept, but I think its arlight =)
Looks like the rest of us can follow Patty's format and post their own "Inside It" articles.
Looks like the rest of us can follow Patty's format and post their own "Inside It" articles.
@silverscorpion • 24 May, 2009
Looks cool. good initiative.
I lost contact with thermodynamics years ago. So, I couldn't follow this article as well as I'd wish to. But still, I read through it. It was nice.
I'll try to post some Inside it articles of my own, of course in electronics.
I lost contact with thermodynamics years ago. So, I couldn't follow this article as well as I'd wish to. But still, I read through it. It was nice.
I'll try to post some Inside it articles of my own, of course in electronics.
@ShrinkDWorld • 24 May, 2009
I am realy thank full man you do so much work for us
You are explain in brief man!!!!! thanks.
You are explain in brief man!!!!! thanks.
@raj87verma88 • 24 May, 2009
Deviation of Actual Cycle from Ideal Cycle
Neta(compressor) = ws/wa = (h2s - h1)/(h2a - h1)
Neta(turbine) = wa/ws = (h3 - h4a)/(h3 - h4s)
2a, 4a :- actual exit states at compressor and turbine.
2s, 4s :- corresponding values for isentropic case.
Blue Line shows actual turbine diagram and black shows the ideal case
![[IMG]](proxy.php?image=http%3A%2F%2Fi41.tinypic.com%2F2u5w2vl.png&hash=0dea4428adcffbb5f3d187619a6cd533)
Picture: Wikipedia
- There is some pressure drop during heat-addition and rejection processes
- Due to irreversibilities, actual work input to compressor is more and, actual work output from turbine is less
Neta(compressor) = ws/wa = (h2s - h1)/(h2a - h1)
Neta(turbine) = wa/ws = (h3 - h4a)/(h3 - h4s)
2a, 4a :- actual exit states at compressor and turbine.
2s, 4s :- corresponding values for isentropic case.
Blue Line shows actual turbine diagram and black shows the ideal case
Picture: Wikipedia
@raj87verma88 • 24 May, 2009
Gas turbine has progressed a lot since the 1930s when it was first successfully developed. Till 1950s the single cycle efficiency was 17% because of low turbine inlet temperature due to metallurgic limitation and low compressor/turbine efficiency.
Efforts were taken to improve cycle efficiency:-
Developments in Gas Turbine
Gas turbine has progressed a lot since the 1930s when it was first successfully developed. Till 1950s the single cycle efficiency was 17% because of low turbine inlet temperature due to metallurgic limitation and low compressor/turbine efficiency.
Efforts were taken to improve cycle efficiency:-
- Increasing turbine inlet temperature This was the primary approach to increase efficiency. The inlet temperature has increased from 500 C to 1425 C. This was possible due to development of new materials and innovative cooling techniques.
- Increasing efficiencies of turbomachinery components Use of computers in manufacturing, CAD/CAM made it possible to design the components aerodynamically with less losses
- Modifications to the Cycle Efficiency was almost doubled by adding regeneration, reheating and intercooling (discussed later). The negative side was the increase in initial and operating cost. There use can not be justified unless decrease in fuel cost offsets increase in others. But 40% increase in efficiency and relatively low fuel cost was in favour of this method.
@krishthd • 24 May, 2009
very very informative
@raj87verma88 • 24 May, 2009
Thanks a lot for the appreciation, guys.
@shalini_goel14 • 25 May, 2009
Hey raj, This was good information shared but I guess it would arouse more interest of people like me (who are not of your field) if you take any real life object and can tell us how these Cycle's work in it. I mean practical knowledge sharing has chances to beat theoretical knowledge.
PS: Never mind ok. Just a feedback. 😀
PS: Never mind ok. Just a feedback. 😀
@raj87verma88 • 25 May, 2009
The application of the cycle will come up later. I was thinking something similar earlier. This thread looks more like technical paper and this is not what I had in mind. SS said that he was unable to follow as he had left Thermodynamics years ago, same may be said for others.
I am thinking of creating all "Inside It" articles in a way, that they describe the History, Anatomy, Working and Application without going into deep technical details like I did here.
This cycle is not yet complete and it will be, maximum by, day after tomorrow. I will continue this one as such but will change the format for other thread under said heading.
I am thinking of creating all "Inside It" articles in a way, that they describe the History, Anatomy, Working and Application without going into deep technical details like I did here.
This cycle is not yet complete and it will be, maximum by, day after tomorrow. I will continue this one as such but will change the format for other thread under said heading.
@raj87verma88 • 27 May, 2009
Brayton Cycle with Regeneration
![[IMG]](proxy.php?image=http%3A%2F%2Fimg21.imageshack.us%2Fimg21%2F6945%2Fimage030wwwpowerfromthe.jpg&hash=372e49cc82149a581135b0f4df6bb356)
Image: PowerFromTheSun.net
The temperature of the exhaust gases is usually very high. By incorporating a regenerator as shown, the high pressure gas from the compressor can be pre-heated via a counter flow heat exchanger called regenerator.
This increases the thermal efficiency of the cycle as the rejected heat is put to use.
Note: It should be made sure that the temperature of exhaust is greater than compressed air, otherwise the heat will flow in opposite direction and the efficiency would decrease.
![[IMG]](https://img21.imageshack.us/my.php?image=image030wwwpowerfromthe.jpg)
Image: PowerFromTheSun.net
The temperature of the exhaust gases is usually very high. By incorporating a regenerator as shown, the high pressure gas from the compressor can be pre-heated via a counter flow heat exchanger called regenerator.
This increases the thermal efficiency of the cycle as the rejected heat is put to use.
Note: It should be made sure that the temperature of exhaust is greater than compressed air, otherwise the heat will flow in opposite direction and the efficiency would decrease.
@raj87verma88 • 27 May, 2009
Brayton Cycle with Intercooling, Reheating and Regeneration
![[IMG]](proxy.php?image=http%3A%2F%2Fimg242.imageshack.us%2Fimg242%2F5819%2Fimage032wwwpowerfromthe.jpg&hash=dde6fcc34c69ef30d0274af382f61726)
Image:PowerFromTheSun.net
This is another way of increasing the efficiency of the Brayton Cycle.
The work output is increased by incorporating multistage expansion and reheating without raising the maximum temperature of the cycle.
The basic principle is: The steady flow compression or expansion work is proportional to the volume of fluid. Therefore, specific volume of fluid should be as low as possible during a compression process and as high as possible during expansion.
![[IMG]](https://img242.imageshack.us/my.php?image=image032wwwpowerfromthe.jpg)
Image:PowerFromTheSun.net
This is another way of increasing the efficiency of the Brayton Cycle.
The work output is increased by incorporating multistage expansion and reheating without raising the maximum temperature of the cycle.
The basic principle is: The steady flow compression or expansion work is proportional to the volume of fluid. Therefore, specific volume of fluid should be as low as possible during a compression process and as high as possible during expansion.
@g_rakesh2 • 27 May, 2009
raj very good information i had not studied this when I was in college..
I just dont remeber all these thanks good information...
I just dont remeber all these thanks good information...
@raj87verma88 • 12 Jun, 2009
Application of Brayton Cycle
This cycle is mos widely used in two fields
https://www.crazyengineers.com/forum...ring/24972-inside-jet-engine-2.html#post69898
This cycle is mos widely used in two fields
- Aircraft propulsion
- ElectricityGeneration
https://www.crazyengineers.com/forum...ring/24972-inside-jet-engine-2.html#post69898
@raj87verma88 • 12 Jun, 2009
Thank You.g_rakesh2raj very good information i had not studied this when I was in college..
I just dont remeber all these thanks good information...
@yadavundertaker mohit • 20 Sep, 2009
thank you very much....it will help me in my gate preparations...
@blacrobous • 21 Sep, 2009
nice that helped me to brush up my basics 😁
@4d1 • 24 Sep, 2009
nice..keep up the good work 😁
@KKOSS • 22 Jan, 2010
I need to know "rule of thumb" energy balance for gas turbine engines. I am very familiar with reciprocating engine energy balance, which is used to design a the support systems for engine testing. For example, we use on most diesel engines:
Radiated heat: 5%
Jacket Water: 24%
Dyno (Shaft): 35%
Exhaust Heat: 28%
Intercooler: 8%
So for a 100HP diesel engine, (100HP/35%) - 286HP of fuel input it required. Is there similar energy balance for typical 100-500HP turbine engines?
Radiated heat: 5%
Jacket Water: 24%
Dyno (Shaft): 35%
Exhaust Heat: 28%
Intercooler: 8%
So for a 100HP diesel engine, (100HP/35%) - 286HP of fuel input it required. Is there similar energy balance for typical 100-500HP turbine engines?
9.6k views
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