Q. 1 A 50 cm diameter pipeline in the Arctic Carries hot oil at 30 0C and exposed to a coefficient surrounding temperature of -20 0C. Special powder insulation 5 cm thick surrounds the pipe and has a thermal conductivity of 7 mW/m. 0C. The Convective heat transfer on the outside of the pipe is 9 W/m2. 0C. Estimate the energy loss from the pipe per meter of length. (1.7, pp. 19) [5M]
Q. 2 A house wall may be approximated as two 1.2 cm layers of fiber insulating board, a 8 cm ive heat transfer coefficient 12 W/m2. 0C on both side of the wall. Calculate the overall heat transfer for this arrangement. (2.26, pp. 58) [5M]
layer of loosely packed asbestos, and 10 cm layer of common brick. Assuming convect
Q. 3 Heat generated uniformly in Stainless steel plate having k=20 W/m.0C. The thickness of the plate is 1cm and the heat generation rate is 500 MW/m3. If the two sides of the plate are maintained at 100 and 200 0C respectively, calculate the temperature at the center of the pipe? (2.42, pp.59) [10M]
Q. 4 A circumferential fin rectangular profile is constructed of Cu and surrounds a tube having a diameter of 1.25 cm. The fin length is 6 mm and its thickness is 0.3 mm. The fin is exposed to a convection environment a 20 0C with h= 55 W/m2.0C base temperature. (2.92, pp. 63) [10M]
Q. 5 A tube assembly constructed of Cu with an inside diameter of 1.25 cm, wall thickness of 0.8 mm and circumferential fins around the periphery. The fins have thickness of 3 mm, and are spaced 6 mm apart. If the convective heat transfer coefficient from the tube and the fins to the surrounding air is 50 W/m2. 0C, calculate the thermal resistance for a 30 cm length of the tube fin combination. What is the fin efficiency for this arrangement? If the inside tube temperature is 100 0C and surrounding temperature is 20 0C, what is the heat loss per meter length of the tube? What fraction of heat loss by the fin? (2.118, pp. 66) [15M]
Q. 6 A piece of Al weighing 6 kg and initially at a temperature of 300OC is suddenly immersed in a fluid at a temperature of 20OC. The convectice heat transfer coefficient is 58 W/m2. 0C. Taking the Aluminum as a sphere having the same weight as that given, estimate the time require to cool the aluminum to 90 0C using the lumped-capacity method of analysis. (4.6, pp. 188) [10M]
Q. 7 A 4 cm diameter Cu sphere is initially at uniform temperature of 400 0C. it is suddenly exposed to a convection environment at 30 0C with h= 20 W/m2.0C. Calculate time necessary for the center of the sphere to reach a temperature 80 0C. (4.17, pp. 189)
[10M]
Q. 8 A steel cylinder 10 cm in diameter and 10 cm long is initially at 300 0C. it is immersed in an oil bath which is maintained at 40 0C, with h= 280 W/m2. 0C. Find the temperature at the center of solid after 2 min. (4.39, pp. 191). [10M]
Q. 9 Air at 1 atm, 300K, and Re = 50,000:
a. Flow across the cylinder with a diameter of 10 cm.
b. Flow inside a tube with a diameter of 10 cm.
c. flow along the flat plate of length 10 cm.
Calculate the Average Heat transfer coefficient for each of above cases and comment on result. (6.92, pp. 312). [10M]
Q.10 A smooth glass plate is coated with a special electrically conductive film that may be used to produce a constant heat flux on the plate. Estimate the air flow velocity which must be used to remove 850 W from a 0.5-m-square plate, maintained at an average temperature of 65 0C and dissipating heat to air at 1 atm and 20 0C. Suppose the plate also radiated like black surface to the surrounding 20 0C. what flow velocity would be necessary to dissipate the 850 W under these condition. (6.116, pp. 314)
[15M]