Theory of Heat Transfer — Summer 2023

Differentiate natural convection and forced convection.

Explain the following:

Transmissivity (ii) Emissivity (iii) Opaque body (iv) Total Emissive Power

With a neat figure, derive the expression of overall heat transfer coefficient for a sphere.

Why extended surfaces are needed in heat transfer? What are the characteristics of material of extended surfaces?

Define the following dimensionless number and write their significance in heat transfer. Prandtl number, Grashoff number, Biot number and Nusselt number.

Derive the expression of heat transfer rate in a transient heat transfer following lumped capacitance method.

Acylindrical plastic pipe (k = 0.5 W/mK) of i.d. 3 cm and o.d. 4 cm carries a fluid of average temperature 100°Cand h = 300 W/m2K. The rate of heat transfer per unit length is 500 W/m. To find: (i) The outside surface temperature of pipe, (ii) the overall heat transfer coefficient based on outside area.

What is shape factor and what is its purpose in radiation heat transfer?

State Stefan- Boltzmann law and derive the expression of the total radiant heat power emitted from a surface.

Asolid copper ball of 100 mm diameter and density = 8954 kg /m3, Cp = 383 J/kgK, k = 386 W/m Kis at a uniform temperature of 250°C. It is suddenly immersed in a well-stirred fluid which is maintained at a uniform temperature of 50°C. The heat transfer coefficient between the ball and the fluid is h = 200 W/m2 K. Estimate the temperature of the copper ball after a lapse of 5 minutes of immersion

Define thermal conductivity and convective heat transfer coefficient.

Discuss the Kirchhoff's law of thermal radiation.

Atube 5 m long is maintained at 100°Cby steam jacketing. Afluid flows through the tube at the rate of 2940 kg/h at 30°C. The diameter of the tube is 2 cm. find out average heat transfer coefficient. Take the properties at mean film temperature.

Explain the fourier’s law of conduction for solid bodies.

What is critical thickness of insulation on a small diameter wire? Explain its physical significance and derive an expression for the same for cylinder.

Derive the expression of heat exchanger effectiveness for counter flow arrangement.

What is heat exchanger? Why it is used in heat transfer applications?

What are regenerators and recuperators? Give their field applications.

State and discuss Lamberts Cosine law of radiation.1

What is a radiation shield? What are its applications?

Define following: 1) Radiosity 2) Irradiation 3) Black Body 4) Monochromotic Emissive Power

Derive the expression of temperature distribution in parallel flow heat exchangers.

Explain the Wien Displacement Law?

Define fin efficiency and fin effectiveness.

Derive the expressions for Nusselt number for forced convection.