In an experiment, a sphere of crystalline sodium chloride (nacl) was suspended in a stirred tank filled with water at 20 °c. its initial mass was 100 g. in 10 min, the mass of the sphere was found to have decreased by 10%. the density of nacl is 2160 kg/m3 and its solubility in water at 20 °c is 320 kg/m3. using these results, the average value of mass transfer coefficient is

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?