Question

The open cycle continuous combustion gas turbine shown in Fig. 2 operates between pressures of 1 bar and 8 bar. The turbine takes in 15 500 kg of air per hour at a temperature of 20°C. Maximum cycle temperature is 800°C. w Fig. 2 (a) Determine the maximum efficiency possible for a constant pressure cycle operating between the above pressures. (Joule cycle efficiency.) (1 mark) (b) If actual compression and expansion occur with isentropic efficiencies of 91% (compressor) and 89% (turbine), and a heat exchanger is used to pre-heat the compressed air before combustion by recovering 60% of the available heat in the exhaust gases: (0) Sketch the actual cycle on a T-s diagram, clearly indicating state points 1-6 (refer to Fig. 2). Label all processes and show the direction of flow. (3 marks) (ii) Calculate the actual temperatures: (1) after compression (T2) (2) after expansion (T5) (3) before combustion (T3) (5 marks) (iii) Calculate the actual thermal efficiency for the cycle. (1'/2 marks) (iv) Calculate the net power output from the turbine. (1/2 marks)

Answer 1

PROBLEM:-@ Given , m= 15500 kg Ihr T= Q6L P= I borr TA = Poo'c P2 = 8 bar Pressive ratio op= op - $=8 efficiency of Joule lylle or Brayton cycle mat - 1- to Hh = 0.4479 [2=14 foras) efficiency of Joule cycle or Brayton Cylle th= 44.791.

Geiven, T-S diggaam isentropic efficiency of comperson n = 914- isentrophe efficiency of turbine m= 89), Also given, *** (Ts®-TI) foon = (T3-T29) (T3-T20) = 0.6 (TST) For process 1-2' Le 7 / 2 = ( 22 ) / Ta'= (20+273), (0,04/14 Tal=530-75k + isentropic eti Т.- Тр Ta-Ti 0.41= 530-75- 213 T2 - 299 ③ actual temperature after compression IT = 554.26 Koy 20/26'

als $ Ts'- 800+277 3004973 I is = 51234 K or 319.34°C T4 - Ts Ta-TS 1073 - Ts - 1073 – 542-3Y To Actual tempt T after expansion. U = bus.212k or 372.21°c As Condition given in the problem (T3-T2 ) = T3-554.26 = 0.6 (T5-T1) 0.6 (645.21 293) 3 Actual temperature before Combustion a T3 765.58K or 492.58ec Actual therm Wnet Osupplier (T4-Ts)- CTR-T;) T4-T3 = (1073 - 645 212 )-( 554.26 - 293) 1073-765. I Actual thermal efficiency = 0.541 = 54.16 %7

Net Power output from turbine - Whisbine - W compressor = mcp (To-Ts) - mcp1T2-T1) = mep [ (T4-TS)-(Ta-TI)] 3600 * 1:005 7(1073 - 645.2]) - ( 554,26-29 T net power output from turbine = 720:58 KW