4. A U-tube with right angle bend is 305 mm wide and contains mercury that rises 229 mm in each leg when tube is at rest. At what speed must the tube be rotated about an axis 76 mm from one leg so that there will be no mercury in that leg?

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?

Acircular pipe of 30mm outside diameter is placed in an airstream at 30 c and latm pressure. the air moves in cross flow over the pipe at 20 m/s, while the outer surface of the pipe is maintained at 110 c. what is the drag force exerted on the pipe per unit length? what is the rate of heat transfer from the pipe per unit length?

Ahousehold refrigerator operating steadily and with a coefficient of performance of 2.5 removes energy from a refrigerated space at a rate of 650 kj/h. evaluating electricity at $0.06 per kw. h, determine the cost of electricity in a month when the refrigerator operates for 360 hours.