Athin electrical heater is wrapped around the outer surface of a long cylindrical tube whose inner surface is maintained at a temperature of 6°c. the tube wall has inner and outer radii of 24 and 78 mm, respectively, and a thermal conductivity of 10 w/m · k. the thermal contact resistance between the heater and the outer surface of the tube (per unit length of the tube) is r ′ t , c = 0.01 m ⋅ k / w . the outer surface of the heater is exposed to a fluid with t[infinity] = −10°c and a convection coefficient of h = 100 w/m2 · k. determine the heater power per unit length of tube required to maintain the heater at to = 25°c.

Steel is coated with a thin layer of ceramic to protect against corrosion. what do you expect to happen to the coating when the temperature of the steel is increased significantly? explain.

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?

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