Question

Calculate the entropy production for the piston-cylinder power producing cycle you analyzed in, problem 1.

Problem 1: A piston cylinder device has a volume of 0.04 m³ and initially contains air at 293 K and 1 bar. This device is used to perform a cycle in which the gas is heated at a constant volume until the temperature reaches 1000 K. The air is allowed to expand following an isothermal process until the volume is 3.5 times the original volume. It is then cooled at a constant volume process. The completion of the cycle is a PV^1.36 = constant process back to the original state. For the air, the specific heat is c_v =0.79 kJ/(Kg K) = constant and its gas constant is R_G=0.287 kJ/(Kg K).

The calculations should include the heat transfer systems to the source and sink temperatures. Consider that all heat flows into the system come from a constant temperature source of 1800K and that all heat flows out of the system are to a constant temperature of 250 K. Will this cycle operate? Which process or heat sink temperature should be altered in order to improve the efficiency of the system or to make it work? In doing these calculations one should begin with the differential form of the entropy balance and determine how entropy production varies throughout the process.

According to my calculations, Q12=26.56kJ, Q34=-30.203kJ, Q23=17.102kJ, Q41=-4.033kJ.

Please solve the entropy production for this problem and answer the questions given above. Thank you!

Answer 1

The entropy production is for 1 mole of gas. For actual value, multiply the calculated value by number of moles of gas.