Refrigerant-134a at 600 kpa and 150°c is contained in a spring-loaded piston-cylinder device with an initial volume of 0.3m^2. the refrigerant is now cooled until its temperature is -30°c and its volume is 0.1 m3. determine the heat trans- ferred to and the work produced by the refrigerant during this process.

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?