Heat Transfer Mock Test 2

1. 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?

2. With respect to the equation k = k₀ (1 +β t) which is true if we put β = 0?

3. For a cylindrical rod with uniformly distributed heat sources, the thermal gradient at half the radius location will be

4. The value of critical radius in case of a cylindrical hollow object is

5. 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

6. In case when both the surfaces of plane wall are at different temperature, we get an expression i.e.
T _MAX – T _W2 /T _W1 – T_W2 = (B + 1)²/4B
What is the value of B?

7. For the same amount of fabrication material and same inside capacity, the heat loss is lowest in

8. For steady flow of heat along a rod, the general equation is
d²α/dx ² – m ² α = 0
The value of constant m is

9. A cable of 10 mm outside is to be laid in an atmosphere of 25 degree Celsius (h = 12.5 W/m² degree) and its surface temperature is likely to be 75 degree Celsius due to heat generated within it. How would the heat flow from the cable be affected if it is insulated with rubber having thermal conductivity k = 0.15 W/m degree?

10. The accompanying sketch shows the schematic arrangement for measuring the thermal conductivity by the guarded hot plate method. Two similar 1 cm thick specimens receive heat from a 6.5 cm by 6.5 cm guard heater. When the power dissipation by the wattmeter was 15 W, the thermocouples inserted at the hot and cold surfaces indicated temperatures as 325 K and 300 K. What is the thermal conductivity of the test specimen material?