Heat Transfer Practice Test 1

1. The thermal resistance for heat conduction through a spherical wall is

2. In Cartesian coordinates the heat conduction equation is given by

3. Transmission of heat i.e. molecular is smallest in case of

4. The diffusion equations
Ɏ²t + q _g = (1/α) (d t/d r)
Governs the temperature distribution under unsteady heat flow through a homogeneous and isotropic material. The Fourier equation follows from this expression when

5. Let us say thermal conductivity of a wall is governed by the relation k = k₀ (1
+ α t). In that case the temperature at the mid-plane of the heat conducting wall would be

6. The following data pertains to a hollow cylinder and a hollow sphere made of same material and having the same temperature drop over the wall thickness
Inside radius = 0.1 m and outside surface area = 1 square meter
If the outside radius for both the geometrics is same, calculate the ratio of heat flow in the cylinder to that of sphere?

7. A composite wall is made of two layers of thickness δ₁ and δ₂ having thermal conductivities k and 2k and equal surface area normal to the direction of heat flow. The outer surface of composite wall are at 100 degree Celsius and 200 degree Celsius. The minimum surface temperature at the junction is 150 degree Celsius. What will be the ratio of wall thickness?

8. A spherical vessel of 0.5 m outside diameter is insulated with 0.2 m thickness of insulation of thermal conductivity 0.04 W/m degree. The surface temperature of the vessel is – 195 degree Celsius and outside air is at 10 degree Celsius. Determine heat flow

9. Fourier law of heat conduction is best represented by

10. An oil cooler in a high performance engine has an outside surface area 0.12 m² and a surface temperature of 65 degree Celsius. At any intermediate time air moves over the surface of the cooler at a temperature of 30 degree Celsius and gives rise to a surface coefficient equal to 45.4 W/ m ² K. Find out the heat transfer rate?