Previous year question paper for HT (B-TECH mechanical engineering 5th)

1. Introduction

Concept of heat transfer, Difference between the subject of "Heat Transfer" and its

parent subject "Thermodynamics". Different modes of heat transfer - conditions,

convection, radiation.

2. Conduction

Fouier's law of heat conduction, coefficient of thermal conductivity, effect of

temperature and pressure on thermal conductivity of solids, liquids and gases and

its measurement.

Three-dimensional general conduction equation in rectangular, cylindrical and

spherical coordinates involving internal heat generation and unsteady state

conditions. Derivation of equations for simple one dimensional steady state heat

conduction from three dimensional equations for heat conduction though walls,

cylinders and spherical shells (simple and composite), electrical analogy of the heat

transfer phenomenon in the cases discussed above.

Equivalent areas, shape factor, conduction through edges and corners of walls and

critical thickness of insulation layers on electric wires and pipes carrying hot fluids.

Internal generation cases along with some practical cases of heat conduction like

heat transfer through underground electrical cables, simple model of heat conduction

through piston crown and case of nuclear fuel rod with cladding.

Influence of variable thermal conductivity on conduction through simple cases of

walls / cylinders and spheres. Introduction to unsteady heat transfer, Newtonian

heating and cooling of solids; definition and explanation of the term thermal diffusivity.

3. Theory of Fins

Straight rod type of fins of uniform cross-section; e.g. of circular, rectangular or any

other cross-section). Straight fins with varying cross-sectional area and having

triangular or trapezoidal profile area, circumferential find of rectangular cross-section

provided on the circumference of a cylinder.

Optimum design of straight find of rectangular and triangular profile cross-sections;

fin effectiveness and fin efficiency for straight rod fins of rectangular and circular

cross-section. Application of fins in temperature measurement of flow through pipes

and determination of error in its measurement.

4. Convection Free and forced convection, derivation of three-dimensional mass,

momentum and energy conservation equations (with introduction to Tensor

notations).

Boundary layer formation, laminar and turbulent boundary layers (simple explanation

only and no derivation).

Theory of dimensional analysis as applied to free and forced convective heat transfer.

Analytical formula for heat transfer in laminar and turbulent flow, flow over vertical

and horizontal tubes and plates.

Newton's law of cooling. Overall coefficient of heat transfer. Different design criterion

for heat exchangers. Log mean temperature difference for evaporator and condenser

tubes, and parallel and counter flow heat exchangers. Calculation of number and

length of tubes in a heat exchanger.

5. Convection with Phase Change (Boiling and Condensation)

Pool boiling, forced convection boiling, heat transfer during pool boiling of a liquid.

Nucleation and different theories of nucleation, different theories accounting for the

increased values of h.t.c. during nucleate phase of boiling of liquids; different phases

of flow boiling (theory only)

6. Radiation

Process of heat flow, definition of emissivity, absorptivity, reflectivity and 

transmissivity. Concept of black and grey bodies, Plank's law of nonchromatic

radiation. Kirchoff's law and Stefan Boltzman's law. Interchange factor. Lambert's

Cosine law and the geometric factor. Intensity of Radiation (Definition only), radiation

density, irradiation, radiosity and radiation shields.

Derivation formula for radiation exchange between two bodies using the definition of

radiosity and irradiation and its application to cases of radiation exchange between

three or four bodies (e.g. boiler or other furnaces), simplification of the formula for its

application to simple bodies like two parallel surfaces, concentric cylinders and a

body enveloped by an other body etc.

Error in Temperature measurement by a thermocouple probe due to radiation losses.