1) The document describes the working principle of an open cycle gas turbine, which consists of a compressor, combustion chamber, and gas turbine mounted on the same shaft. 2) It then discusses the Brayton cycle, which models the open cycle gas turbine as a closed cycle using a combustion heat exchanger and chiller heat exchanger to recirculate the working fluid. 3) The document lists some advantages and disadvantages of open cycle gas turbines, such as their simplicity but also high air rate and sensitivity to changes in efficiency and temperature.

1. -:Subject:-
-:Topic:-

2. Prepared By
Name Enrollment No.
Chaudhari Saurabh S. 130420109011
Chauhan Naren J. 130420109012
Chodvadiya Kartik B. 130420109013
Desai Krunal P. 130420109014
Desai Manan B. 130420109015
Guided By:-

3.  Numerical Based On Reheat Cycle
 Brayton Cycle
 Open Cycle Gas Turbine

5. Working Principal
 Open gas turbine cycle is the most basic gas turbine unit. The working
fluid does not circulate through the system, therefore it is not a true cycle.
It consists of a compressor, a combustion chamber and a gas turbine. The
compressor and the gas turbine are mounted on the same shaft. The
compressor unit is either centrifugal or axial flow type.
 The working fluid goes through the following processes:
1-2 irreversible but approximately adiabatic compression
2-3 constant pressure heat supply in the combustion chamber
3-4 irreversible but approximately adiabatic expansion of combustion
gases
Advantages:-
 Simplicity: A simple open cycle gas turbine has only three
components,compressor ,combustion chamber turbine.The
combustion chamber is inexpensive,light weight and small with a
high rate of heat release.It can be designed to burn almost all
hydrocarbon fuels ranging from gasoline to heavy diesel oil.

6.  Low weight and size: Open cycle gas turbine has lower specific weight
and requires less space per unit power output. This property of producing
more power output in a small space and low weight is quite useful in the
field of aeronautics.
 No warm-up period: Open cycle gas turbine can accelerate from a cold
start to a full load without a warm-up period.
 Low capital cost: Since open cycle gas turbine has only minimum
components and has low weigh and size per unit power output ,the
capital cost is less compared to other plants.
Disadvantages:-
 Sensitivity: The simple open cycle gas turbine is sensitive to changes in
the component efficiencies. A reduction in the efficiencies of compressor
and turbine will rapidly lower the efficiency of the cycle. The open cycle
gas turbine is sensitive to changes in the atmospheric temperature. An
increase in atmospheric temperature lowers the thermal efficiency.
 High air rate: Simple open cycle gas turbine has a very high air rate.
This high air rate is not a disadvantage in most of the applications like a
aviation field but is a prime factor in marine applications.

7.  The Brayton cycle is a thermodynamic cycle that describes the
workings of a constant pressure heat engine. Gas turbine engines
and air breathing jet engines use the Brayton cycle.
 Although the Brayton cycle is usually run as an open system (and
indeed must be run as such if internal combustion is used), it is
conventionally assumed for the purposes
of thermodynamic analysis that the exhaust gases are reused in
the intake, enabling analysis as a closed system.
Assumption:-
 The working fluid is air and it behaves as an ideal gas
 The cycle is modeled as a closed cycle with the air cooled in
the chiller heat exchanger and recirculated to the compressor.
 The combustion chamber is replaced by combustion heat
exchanger
 All processes are internally reversible

8. Brayton cycle on (a) P-v diagram (b) T-s diagram

9. Processes: -
1-2: isentropic compression
2-3: constant pressure energy addition
3-4: isentropic expansion
4-1: constant pressure energy rejection
Efficiency:-
Energy added, Q1= mCp (T3-T2)
Energy rejected, Q2= mCp (T4-T1)
Thermal efficiency,

10. The processes 1-2 and 3-4 are isentropic. Hence
We get,
or
Therefore,
Where rp is defined as,

12.  the work required to compress in a steady flow device can be reduced by
compressing in Stages.
 cooling the gas reduces the specific volume and in turn the work
required for compression
 by itself compression with intercooling does not provide a significant
increase in the efficiency of a gas turbine because the temperature at the
combustor inlet would require additional heat transfer to achieve the
desired turbine inlet temperature
 but the lower temperature at the compressor exit enhances the potential
for regeneration i.e. a larger ΔT across the heat exchanger

14.  T3 is limited due to metallurgical constraints
 excess air is extracted and fed into a second stage combustor and turbine
 turbine outlet temperature is increased with reheat (T6 > T4), therefore
potential for regeneration is enhanced
 when reheat and regeneration are used together the thermal efficiency can
increase significantly