ng quantities for both an ideal cycle (isen- tropic compressor and turbine) and a nonideal cycle (compressor and turbine isentropic efficiencies of 82%):

3 . The net work per unit mass of air flowing (in kJ/kg) . b. The heat rejected per unit mass of air flowing (in kJ/kg) c. The cycle thermal efficiency

P8-42 An ideal air-standard Brayton cycle has a compressor pressure ratio of 10. Air enters the compressor at PI = 14.7 Ibf/in2 , T\ = 70'P, with a mass flow rate of 90,000 lbmlh. The turbine inlet temperature is 1740°F. Use an air-standard analysis with constant specific heats.

3 . Determine the net power developed (in hp and kW). b. Determine the cycle thermal efficiency.

P8-43 For the cycle in Problem P8-42, include in the analysis turbine and compressor isentropic efficiencies of 88% and 84%, respectively. For the modified cycle, determine the following:

3. The net power developed (in hp and kW) b. The cycle thennal efficiency

3 .

Using a cold-air-standard analysis, show that this ratio in an ideal Brayton cycle is equal to the absolute temperature at the compressor inlet divided by the absolute temperature at the turbine outlet.

b. Develop an expression for the back work ratio, again using a cold-air-standard analysis, but with turbine and compressor efficiencies less than 1.

P8-47 For an ideal Brayton cycle with given low temperature TI and high temperature T3, derive the expression (Eq. 8-35) for the maximum work at the optimum pressure ratio using a cold-air-standard analysis.

P8·48 For an ideal Brayton cycle with given low temperature TI and high temperature Tz, derive the expression (Eq. 8-34) for the optimum pressure ratio to produce the maximum work.

BRAYTON CYCLE WITH REGENERATION, REHEAT. ANDIOR INTERCOOLING

P8-49 (WEB) Experimental data are obtained from a regen- erative Brayton cycle. Air enters the compressor, which has an isentropic efficiency of75%, at 100 kPa, 2rC, with a flow rate of 12.4 kg/s, and exits the compressor at 1050 kPa, 400°C. The air passes through the regenerator to the combustor, where 15.21 MW of heat are added, and then the air expands in the turbine to a pressure of 100 kPa, 967°C. At the exit of the regenerator, the air temperature is 727°C.

3 . Determine the turbine isentropic efficiency. b. Determine the net power output (in

kW).c. Determine the cycle thermal efficiency.d. Determine the regenerator effectiveness.

P8-50 (WEB) The following temperatures were measured on a test of a regenerative Brayton cycle with a pressure ratio of 5.41.

392 CHAPTER 8 REFRIGERATION. HEAT PUMp, AND POWER CYCLES

T, =290.2 K T, = 629.4 K T4 = 713.7 K

T2 = 505.0 K T, = 1046.7 K Ty = 590.1 K

a. Determine the compressor isentropic efficiency. b. Determine the turbine isentropic efficiency.c. Determine the regenerator effectiveness.d. Determine the net power output (in k