Theory of Heat Transfer — Winter 2024

Define Extended Surface. Also, write classifications of the fins.

Write a note on Fourier’s law of heat conduction.

In an air conditioned room, the wall of the house measures 2 m x 6 m. It consists of 1 cm thick wood paneling of thermal conductivity 0.06 W/mK and 20 cm thick concrete wall having the thermal conductivity of 1.2 W/mK. The inside temperature is maintained at 250C and the atmospheric temperature is 400C. Find the gain of heat transfer rate by the room and the temperature at interface of wood and concrete wall.

Define insulation? Explain economic thickness of insulation.

Write temperature profile equation and heat transfer from fin for 1) Infinite long fin 2) Tip insulated fin 3) Tip non-insulated fin

Derive general heat conduction equation in Cartesian coordinates.

The engine of an automobile can be considered as a box of length of 0.7 m, width 0.23 m and height 0.1 m. Its surface temperature is maintained at 600C. When the automobile moves at a velocity of 30 m/s, the air at 200C passes over the crankcase at relative speed. Assuming the flow to be turbulent with Nu 0.036 Re 0.8 Pr1/3, find the rate of heat transfer from L = L all sides of the crankcase. Take: ρ= 1.09 kg/m3, v = 20.1x10-6 , k = 0.07 W/mK, Pr = 0.7

Using dimensional analysis, obtain a general form of equation for forced Convective heat transfer.

Differentiate: 1. Mean film temp and bulk mean temp 2. Velocity and thermal boundary layer

Define critical thickness? Explain critical radius for cylinder?1

State and Explain: (1) Efficiency of fins (2) Effectiveness of fins

Differentiate between Natural and Forced convection heat transfer with suitable examples.

Define Nusselt Number. Explain its significance in convection heat transfer.

Explain correction factor and fouling factor?

Explain mechanism of nucleate boiling with neat sketch?

Explain NTU and Effectiveness of heat exchanger?

Write classification of heat exchanger in detail?

Explain Film and drop-wise condensation with suitable diagram?

Derive an expression for logarithmic mean temperature difference (LMTD) in the case of counter flow heat exchanger.

Explain Kirchhoff’s law of radiation?

Define following: 1) Total Emissivity 2) Emissivity 3) Radiosity 4) Absorptivity

What are the radiation surface and space resistances? How are they expressed? For what kind of surface, is radiation surface resistance zero?

Explain the following :

Solid angle

Spectral Intensity of Radiation

Black body

Define Radiation shield and Radiation geometrical factor.