Show, by calculating net work and heat supplied, that for a carnot heat engine using air as a working medium, the carnot efficiency is \eta _{c}=1-t_{l}/t_{h} . a carnot heat engine cycle is executed in a closed system using 0.5 kg as a working fluid. initially the air is at a pressure of 100 kpa and a specific volume of 1 m3/kg and the maximum pressure in the cycle is 2,500 kpa. determinea) the carnot efficiencyb) the amount of work output if the specific volume increases during heat addition by a factor of 5.

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?