Along, cylindrical, electrical heating element of diameter ' 10 mm, thermal conductivity n 240 w/mk, density 2700 kg/m3 , and specific heat fs 900 j/kg k is installed in a duct for which air moves in cross flow over the heater at a temperature and velocity of 27c and 10 m/s, respectively. (a) neglecting radiation, estimate the steady-state surface temperature when, per unit length of the heater, electrical energy is being dissipated at a rate of 1000 w/m.

The y form of iron is known as: a) ferrite b) cementite c) perlite d) austenite

Acompressor receives the shaft work to decrease the pressure of the fluid. a)- true b)- false

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?