Question 1
Consider an ideal gas turbine cycle with two stages of compression and two stages of expansion. The pressure ratio across each compressor stage and each turbine stage is 7 to 1. The pressure at the entrance to the first compressor is 100 kPa, the temperature entering each compressor is 26.3 °C (C + 273 = K), and the temperature entering each turbine is 1,026 °C. An ideal regenerator is also incorporated into the cycle. It may be assumed that Cp = 1.005 kJ/kgk, γ = 1.4. Determine the
a. compressor work (kJ/kg):
b. turbine work (kJ/kg):
c. cycle thermal efficiency (%):
Question 2
In a reheat-cycle power plant, steam enters the high-pressure turbine at 5 MPa, 450°C, and expands to 0.5 MPa, after which it is reheated to 450°C. The steam is then expanded through the low-pressure turbine to 7.5 kPa. Liquid water (vf = 0.001 m3/kg) leaves the condensor at 30°C, is pumped to 5 MPa, and returned to the steam generator. Each turbine is adiabatic, with an isentropic efficiency of 84.1 % and the pump efficiency is 80.1 %. If the total power output of the turbines is 8,500 kW, determine
a. the mass flow rate of the steam (kg/s):
b. the pump power input (kW):
c. the power plant thermal efficiency (%):
Question 3
A Diesel cycle has a compression ratio of 15.8 and cut-off ratio of 1.8. At the beginning of the isentropic-compression process, the pressure and temperature are 100 kPa and 38.9°C (C +273 = K), respectively. During the constant-pressure process, heat is added to the working fluid from a reservoir at a temperature of 1,760°C. During the constant volume process, heat is rejected to the environment, which is at 30°C and 100 kPa.
Use the air-standard assumptions (i.e specific heat ratio, γ=1.4) and calculate:
a. the temperature of the gas (in K) at the end of the isentropic compression process,
b. the pressure (in MPa) of the gas at the end of the isentropic compression process,
c. the temperature of the gas (in K) at the end of the heat addition,
d. the pressure of the gas (in MPa) at the end of the heat addition,
e. the thermal efficiency of the cycle in %.
f. the maximum thermal efficiency in % if the cycle operating between the given reservoir temperatures is reversible.
Question 4
Such a plant using ammonia as the working substance is required to provide 16.1 tonnes of refrigeration (1 tonne = 3.876 kW). To accomplish this, the Ammonia operates between pressure limits of 200 kPa and 1500 kPa. Show the cycle on either a P-h or a T-s diagram. Determine
a. the quality of ammonia entering the evaporator;
b. the mass flowrate in kg/s
c. the volume flowrate at the compressor intake in m3/s
d. the bore (D) and stroke (L) of a double-acting reciprocating compressor at 600 rpm. Assume that the fluid is completely discharged from the cylinder each revolution, and that L=D. (ans in m)
