Air is compressed adiabatically in a piston–cylinder assembly from 1 bar, 300 k to 7 bar, 600 k. the air can be modeled as an ideal gas and kinetic and potential energy effects are negligible. determine the amount of entropy produced, in kj/k per kg of air, for the compression. what is the minimum theoretical work input, in kj per kg of air, for an adiabatic compression from the given initial state to a final pressure of 7 bar? note that work is positive into the compressor.

Air is to be cooled in the evaporator section of a refrigerator by passing it over a bank of 0.8-cm-outer-diameter and 0.4-m-long tubes inside which the refrigerant is evaporating at -20°c. air approaches the tube bank in the normal direction at 0°c and 1 atm with a mean velocity of 4 m/s. the tubes are arranged in-line with longitudinal and transverse pitches of sl- st 1.5 cm. there are 30 rows in the flow direction with 15 tubes in each row. determine (a) the refrigeration capacity of this system and (b) pressure drop across the tube bank. evaluate the air properties at an assumed mean temperature of -5°c and 1 atm. is this a good assumption?