A 3m2 black surface at 140 oC is losing heat to the surrounding air at 35oC by convection with a heat transfer coefficient of 16W/m2K and by radiation to the surrounding surfaces at 15oC. What is the total rate of heat loss from the surface? (a) 1987 W
(b) 2239 W
(c) 2348 W
(d) 3451 W
(e) 3811 W

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?

Determine whether or not it is possible to compress air adiabatically from k to 140 kpa and 400 k. what is the entropy change during this process?

The higher the astm grain-size number, the coarser the grain is. a)-true b)-false