Calculate the maximum theoretical thermal efficiency of a heat engine operating between heat reservoirs at 450°C and 25°C.
4. A rigid container of 0.2 m3 volume contains a gas at a pressure of 2 bar and a temperature. 25°C.
If the characteristic constant for the gas is 0.35 kJ kg–1K–1, calculate:
(a) The mass of the gas
(b) The pressure of the gas after it is heated to 250°C
5. Air is compressed adiabatically in a closed cylinder from a pressure of 1 bar, a temperature of 20°C and volume of 0.5m3 to a pressure of 6 bar. Taking Cp = 1.004 kJ kg-1K-1 and Cv = 0.718 kJ kg-1K-1, determine:
(a) The final volume
(b) The mass of air in the cylinder
(c) The change in internal energy
6. Air flows steadily through a cooler with a mass flow rate of 5 kg min-1. The air enters the cooler at a temperature of 250°C and a pressure of 1.5 bar. The air enters the cooler through a pipe of 100mm diameter. The velocity of the air on exit from the cooler is 25 ms-1. The air is cooled with water with a mass flow rate of 7.5 kg min-1 and the temperature of the water increases by 35°C as it passes through the cooler. Assuming that the heat transfer from the air to the water is 100% efficient and that, for the air, Cp = 1.004 kJ kg-1K-1 and Cv = 0.718 kJ kg-1K-1 and the specific heat for the water = 4.187 kJ kg-1K-1, determine the temperature of the air as it leaves the cooler.
