B.TECH - Semester 6 heat and mass transfer Question Paper 2021 (dec)
Practice authentic previous year university questions for better exam preparation.
Sample Questions
- Enumerate the basic laws which governs the heat transfer.
- How does temperature affect thermal conductivity of solids and liquids?
- Write a note on electrical analogy of heat transfer with the help of a thermal network.
- Enumerate the importance of dimensional analysis technique.
- Define Reynold's number and explain its physical significance.
- Explain the mechanism of thermal boundary layer over a plate.
- List down the classification of heat exchangers. P.T.O.
- When do you use NTU approach for the analysis of heat exchangers?
- Differentiate pool boiling and flow boiling with a suitable sketch.
- Enumerate the various mechanisms of mass transfer. ( $10 \times 4=40$ Marks) PART - B
- (a) Derive generalised heat conduction equation and deduce it for cylindrical co-ordinate in ' $r$ ' variable.
- (b) A thermopane window consists of two 5 mm thick glass ( $\mathrm{k}=0.78 \mathrm{~W} / \mathrm{mk}$ ) sheets separated by 10 mm stagnant air gap ( $\mathrm{k}=0.025 \mathrm{~W} / \mathrm{mk}$ ). The convection heat transfer coefficient for inner a...
- (i) Determine the rate of heat loss per $/ \mathrm{m}^{2}$ of the glass surface for a temperature difference of $60^{\circ} \mathrm{C}$ between the inside and outside air. (ii) Compare the result with the heat loss if the window had only a single she...
- (a) Show that for a plane wall of thickness 2 L with uniform heat generation $\dot{q}$ per unit volume, the maximum temperature at the mid plane is given by $\mathrm{T}_{\text {max }}=\mathrm{T}_{\mathrm{w}}+\frac{\dot{q} \mathrm{~L}^{2}}{2 \mathrm{~...
- (b) A piece of chicken in the form of a rectangular block 25 mm thick is roasted in a microwave oven heating system. The centre temperature of the chicken block is $100^{\circ} \mathrm{C}$, when surrounding temperature is $30^{\circ} \mathrm{C}$. The...
- (a) It is desired to increase the temperature of water at $10^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$ flowing through a tube of 2 cm ID at a flow rate of $0.01 \mathrm{~kg} / \mathrm{s}$. Using an insulated electric heating element that produc...
- (i) The convective heat transfer co-efficient. (ii) The length of the pipe needed (iii) The inner tube surface temperature at the outlet. (iv) Friction factor.
- (b) Vertical door of a hot oven is 0.5 m high and is maintained at $200^{\circ} \mathrm{C}$. It is exposed to atmospheric air at $20^{\circ} \mathrm{C}$. Find
- (i) local heat transfer co-efficient half way up the door (ii) average heat transfer co-efficient for entire door (iii) thickness of free convection boundary layer at the top of the door. $$ 3+3+4=10 $$
- (a) Derive an expression for effectiveness of a parallel flow type heat exchanger.
- (b) A shell and tube heat exchanger is designed for heating water from $25^{\circ} \mathrm{C}$ to $50^{\circ} \mathrm{C}$ with the help of condensing steam. The water flows through tubes ( 2.5 cm ID, 2.9 cm OD and 2 m long) and the steam condenses on...
- (a) Define absorptivity, reflectivity, transmissivity and radiosity. : 10
- (b) Calculate the view factor $\mathrm{F}_{1-2}$ between a small area $\mathrm{dA}_{1}$ and a parallel circular disc $A_{2}$. The elemental area $d A_{1}$ is located at the axis of the disc $A_{2}$, at a distance L . Or
- (a) Make a note on governing laws of heat and mass transfer.
- (b) A well is 40 m deep and 9 m in diameter is exposed to atmosphere at $25^{\circ} \mathrm{C}$. The air at the top has relative humidity of $50 \%$. Calculate the rate of diffusion of water vapour through the wall. Take mass diffusivity $= 2.5 \time...