Theory of Heat Transfer — Winter 2024

Define heat transfer and explain different modes of heat transfer in brief.

Write eight day to day life applications of fins.

Derive equations of temperature distribution and heat dissipation for infinite fin.

What do you understand by thermal insulation? Explain required properties of insulating materials.

Define unsteady state conduction heat transfer? Write suitable examples of transient heat conduction?

Aplane brick wall 25 cm thick, is faced with 15 cm thick concrete layer. If the temperature of exposed brick face is 700C and that of the concrete is 250C, find out heat lost per hour through a wall of 15 m x 10 m. Also, determine the interface temperature. Thermal conductivity of brick and concrete are 0.7 W/mK and 0.95 W/mK respectively.

Acopper rod 0.5 cm diameter and 50 cm long protrudes from a wall maintained at a temperature of 5000C. The surrounding temperature is 300C. Convective heat transfer coefficient is 40 W/m2K and thermal conductivity of material is 300 W/mK. Determine: (1) Total heat transfer rate from rod (2) Temperature of the rod at 20 cm from wall.

Define thermal diffusivity? Also provide significance of thermal diffusivity?

Write a short note on lumped system analysis? Also provide suitable assumptions?

Explain the significance of the following terms: (1) Prandtl Number (2) Nusselt Number (3) Grashoff Number (4) Reynolds Numbers.

Differentiate between free and forced convection.

What is thermal and hydrodynamics boundary layers with neat diagram.1

Derive the momentum equation for hydrodynamic boundary in differential form with neat sketch. Write equation for stretching factor? State its significance for solving momentum equation.

Compare parallel flow and counter flow heat exchanger.

Write the advantages of the effectiveness-NTU method over the LMTD method.

Differentiate between Film and drop-wise condensation.

State & explain Lambert’s cosine law.

Explain Effectiveness and NTU with reference to the heat exchanger.

Prove that the effectiveness of parallel flow heat exchanger is given by 1−exp [−NTU(1+C)] 𝜀 = 1+C

What do you understand by absorptivity? How can it be improved for an opaque body?

Making use of Plank’s law of distribution, establish the relation for Wien’s displacement law.

Derive the Stefan-Boltzmann law from the Plank’s law of thermal radiation. What is the value of Stefan-Boltzmann constant?

Explain fouling factor in heat exchanger.

Define a black body. Give examples of some surfaces which don’t appear black but have high value of absorptivity.

Explain boiling curve which shows all the boiling regimes in details.