Heat Transfer Mock Test 2

1. Dielectric heating apparatus consists of

2. A composite slab consists of 5 cm thick layer of steel (k = 146 kJ/m hr degree) on the left side and a 6 cm thick layer of brass (k = 276 kJ/m hr degree) on the right hand side. The outer surfaces of the steel and brass are maintained at 100 degree Celsius and 50 degree Celsius. The contact between the two slabs is perfect and heat is generated at the rate of 4.2 * 10 ⁵ k J/m² hr at the plane of contact. The heat thus generated is dissipated from both sides of composite slab for steady state conditions. Calculate the temperature at the interface

3. The extended surface used for the enhancement of heat dissipation is

4. The insulating material used in dielectric heating is

5. Suppose heat is conducted due to electrons
Where, i = I/A and p is the resistivity, then

6. A solid sphere of 8 cm radius has a uniform heat generation 0f 4000000 W/m³. The outside surface is exposed to a fluid at 150 degree Celsius with convective heat transfer coefficient of 750 W/m² K. If thermal conductivity of the solid material is 30 W/m K, determine maximum temperature

7. A pipe of outside diameter 20 mm is to be insulated with asbestos which has a mean thermal conductivity of 0.1 W/m degree. The local coefficient of convective heat to the surroundings is 5 W/square meter degree. Find the critical radius of insulation for optimum heat transfer from a pipe?

8. A wire of radius 3 mm and 1.25 m length is to be maintained at 60 degree Celsius by insulating it by a material of thermal conductivity 0.175 W/m K. The temperature of surrounding is 20 degree Celsius with heat transfer coefficient 8.5 W/ m² K. Find percentage increase in heat loss due to insulation?

9. A slab of 12 cm thickness and generating heat uniformly at 10 ⁶ W/m³ has thermal conductivity of 200 W/m degree. Both surfaces of the slab are maintained at 150 degree Celsius. Determine the heat flow rate at the quarter planes

10. For insulation to be properly effective in restricting heat transmission, the pipe radius r₀ will be