2. naca 2412 airfoil has a zero lift angle of -2.1 degree and a lift curve slope of 2  (if the alpha is expressed in radians). the pitching moment coefficient at the quarter chord is -0.036. compute the lift and pitching moment at quarter chord at a 4 degree angle of attack if the freestream velocity is 50 feet sec, and the chord is 2 feet. assume sea level conditions. (ans: 3.8 lb per foot of span, -0.428 ft. lb per foot of span)

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?