ASET/ MAE/BTM- 401 Roll No.:___________________________END SEMESTER EXAMINATION; IV – SEMESTER

JUNE - 2013HEAT & MASS TRANSFER

Time: 3 hours Max Marks: 70

SECTION - A (30 Marks) Attempt any 5 questions.All questions carry equal

Que. 1 Derive an expression for the temperature distribution and rate of heat transfer for a pin fin , when the tip of the fin is insulated.

Que.2 Explain the followingI. Kirchoff’s Law

II. Stefan Boltznman LawIII. Wien’s Displacement LawIV. Plank’s Law

Que. 3 A rod (K = 200W/mK) 5mm in diameter long has its one end maintained at 100C. The surface of the rod is exposed to ambient air at 25°C with convection heat transfer coefficient of 100 w/m2K. Assuming other end insulated, determine:

I. The temperature of the rod at 20 mm distance from the end at 100°CII. Heat dissipation rate from the surface of the rod

III. EffectivenessQue. 4The inside of a furnace wall is at 1000°C and with the existing wall of material with thermal conductivity of 1.7 W/mK looses 2.5 kW/m2 when the outside is exposed to convection to air at 30°C with h = 27 W/m2K. Determine the wall thickness. Additionally 75 mm thickness of insulation with k = 0.15 W/mK is added on the inside. The furnace wall temperature and the surrounding temperature and convection coefficient remain unchanged. Determine the reduction in heat flow and reduction in the outside surface temperature. Also find the overall heat transfer coefficient and the temperature gradient in each layer. The wall area is 3m2. Also find the temperature gradient in the flow direction.

Que. 2 A surface is at 200°C and has an area of 2m2. It exchanges heat with another surface B at 30°C by radiation. The value of factor due to the geometric location and emissivity is 0.46. Determine the heat exchange. Also find the value of thermal resistance and equivalent convection coefficient.

Que. 3: A furnace wall is of three layers, first layer of insulation brick of 12 cm thickness of conductivity 0.6W/mK. The face is exposed to gases at 870°C with a convection coefficient of 110W/m 2K. This layer is backed by a 10cm layer of firebrick of conductivity 0.8W/mK. There is a constant resistance between layers of 2.6 X 10-4 m2°C/W. The third layer is the plate backing 10mm thickness of conductivity 49W/mK. The constant resistance between the second and third layer is 1.5 X 10-4m°C/W. The plate is exposed to air at 30°C with a convection coefficient of 15 W/m2K. Determine the heat flow, surface temperatures and the overall heat transfer coefficient.