There are three 15 LCY trucks that will be used to transport the excavated soil. It takes 25 min for a truck to drive to the unloading site, unload and drive back to the excavation area. Instead of being idle till the trucks return from each truck cycle, the excavator unloads soil in a spoil bank at the same swing angle (90o). Calculate the volume of soil in the spoil bank at the end of the excavation. Total volume of excavation is 15,000 BCY.

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?