Mid-term Exam: Gas Turbine (with solution)

Q2.  Gas Turbine Cycle  (12 points) 

 An open-cycle, externally-heated gas turbine cycle operates in a free power turbine arrangement without intercooling or regeneration but with reheat, driven by solar concentrators, as shown in the layout sketch below. The working fluid is pure air throughout the cycle.

Calculate the net electrical power output from the cycle. 

 The following parameters are given: 

Ambient air conditions                                                 1 bar, 20 °C  (p1=p6=1bar) 
Air mass flow through the cycle                                   2 kg/s 
Pressure ratio of the compressor (p2/p1)                    12     
Isentropic efficiency of the compressor                       85 % 
Specific heat ratio for compression (k_C)                      1.385 
Isentropic efficiency of each expander                        86 %
Specific heat ratio for each expander (k_T)                  1.35  
Pressure losses in each solar heater                          5 % 
Mechanical efficiency for each shaft                          96 %  
El. Generator efficiency                                             93 % 
Solar power delivered to the first air heater              1080 kW 
Solar power delivered to the second air heater        900 kW

Assume that there are no thermal losses in the cycle and that it works with simplified technical air.