كلية الھندسة –الجامعة المستنصرية الميكـــــانيكيـــةالھندســــــــة قســــم

ــــةــــمحطــــــــــــات طاقــــــــــــــــــ     

 

CHAPTER (6) Gas Turbines & Combined Cycles 

 

د. مشعل عبد االميرأ.م.  

10‐Feb‐15 

                     

 

Chapter6

GasTurbine&CombinedCycles

The Ideal Brayton Cycle, Example (1), The Actual Simple Gas Turbine Cycle, Example (2), Splitting the Turbine, Example (3), Modification to the basic cycle: Intercooling, Reheat, Heat-Recovery Exchanger, Example (4), Combined Cycles with Heat-Recovery Boilers, Example (5), Tutorial Sheet 6.

Power Plant Engineering  TUTORIAL SHEET ‐ 6  كلية الھندسة –الجامعة المستنصرية

Gas Turbine & Combined Cycles                                                            اقةـــــــمحطات ط –قسم الميكانيك  

119  

Assume the following: 

For compression process: ‐          1.005.

, 1.4 

For combustion and expansion processes: ‐    1.15.

,  1.333 

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ 1‐ A gas turbine unit has an overall pressure ratio of (5/1) and a maximum cycle

temperatureof(550Co).Theturbinedrivesthecompressorandanelectricgenerator.Themechanicalefficiencyofthedriveis(97%).Theambienttemperatureis(20Co)andtheisentropicefficienciesofthecompressorandturbineare(80and83%)respectively.Calculate the power output in kilowatt for airflow of (15 kg/s). Also, calculate thethermal efficiency and the work ratio. Neglect changes in kinetic energy and thepressurelossesinthecombustionchamber.

2‐ Inamarinegasturbineunit,aHigh‐pressureturbinestagedrivesthecompressor,and

alow‐pressureturbinestagedrivesthepropellerthroughsuitablegearing.Theoverallpressure ratio is (4/1), and the maximum temperature is (650 Co). The isentropicefficienciesofthecompressor,HPandLPturbinesare(80,83and85%)respectively,andthemechanicalefficiencyofbothshaftsis(98%).Calculatethepressurebetweenturbinestageswhentheairintakeconditionare(1.01barand25Co).Also,calculatethethermalefficiencyandtheshaftpowerwhenthemassflowis(60kg/s).Neglectchangesinkineticenergyandthepressurelossesinthecombustionchamber.

3‐ A combined power plant consisting of a simple open cycle gas turbine unit, using air as the 

working fluid (neglect fuel mass flow rate), and a steam turbine is to be designed such that the heat rejected at the gas turbine unit is to be utilized to produce steam at the generator for the steam turbine. The exhaust air  leaving the generator  is at (200 Co). Draw a simple sketch for the plant and the (T‐s) diagram and calculate the mass flow rate of steam per (kg/s)  of  airflow,  the  total  power  output  per  (kg/s)  of  airflow  and  the  overall  thermal efficiency of the plant. Assume ideal cycles. Neglect the feed pump work of Rankine cycle.

Thedataofeachcycleareasfollows:‐ GasTurbineCycle SteamTurbineCycle

Pressure(bar)

Minimum 1 0.07Maximum 5 30

Temperature(Co)

Minimum 20 Maximum 830 300