Athick steel slab (rho= 7800 kg/m3 , cp= 480 j/kg k, k= 50 w/m k) is initially at 300 °c and is cooled by water jets impinging on one of its surfaces. the temperature of the water is 25 °c, and the jets maintain an extremely large, approximately uniform convection coefficient at the surface. assuming that the surface is maintained at the temperature of the water throughout the cooling, how long will it take for the temperature to reach 50 °c at a distance of 25 mm from the surface?

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?

Afluid flows with a velocity field given by v=(x/t)i.. determine the local and convective accelerations when x=3 and t=1.

Give heat transfer applications for the following, (i) gas turbines (propulsion) ) gas turbines (power generation). (iii) steam turbines. (iv) combined heat and power (chp). (v) automotive engines