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 220°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 S_L = S_T = 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

(b) Pressure drop across the tube bank. Evaluate the air properties at an assumed mean temperature of 25°C and 1 atm. Is this a good assumption?

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0°C 1 atm 4 m/s Air ST= 1.5 cm 0.8 cm 0.4 m SL 1.5 cm/ Refrigerant, -20°C