Consider a nickel wall separating hydrogen gas that is maintained on one side at 5 atm and on the opposite at 3 atm. If the temperature is constant at 85°C, determine (a) the mass densities of hydrogen gas in the nickel wall on both sides and (b) the mass densities of hydrogen outside the nickel wall on both sides.

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?