Download GTU (Gujarat Technological University Ahmedabad) B.Tech/BE (Bachelor of Technology/ Bachelor of Engineering) 2020 Winter 4th Sem 3140503 Heat Transfer Previous Question Paper
Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE- SEMESTER?IV (NEW) EXAMINATION ? WINTER 2020
Subject Code:3140503 Date:11/02/2021
Subject Name:Heat Transfer
Time:02:30 PM TO 04:30 PM Total Marks:56
Instructions:
1. Attempt any FOUR questions out of EIGHT questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Marks
Q.1 (a) Distinguish between the conduction, convection and radiation
03
modes of heat transfer.
(b) A furnace wall is made up of steel plate 10 mm thick (k= 62.8
04
kJ/m-hr-deg) lined on inside with silica bricks 150 mm thick
(k= 7.32 kJ/m-hr-deg) and on the outside with magnesia bricks
200 mm thick (k= 18.84 kJ/m-hr-deg). The inside and outside
surfaces of the wall are at temperature 650 0C and 125 0C
respectively. Make calculations for the heat loss from unit area
of the wall.
(c) Derive equation for heat transfer by conduction through hollow
07
cylinder. Also mention assumptions made for it.
Q.2 (a) Discuss the physical significance of (i) Reynolds Number
03
(ii) Prandtl number.
(b) Set up the relationship between local heat transfer coefficient
04
and average heat transfer coefficient for flow past a stationary
flat plate.
(c) Calculate the rate of heat loss from a human body which may
07
be considered as a vertical cylinder 30 cm in diameter and 175
cm high in still air at 15 0C. The skin temperature is 35 0C and
emissivity at the skin surface is 0.4. Neglect sweating and effect
of clothing.
The thermo-physical properties of air at 25 0C are:
= 15.53 ? 10-6 m2/s; k = 0.0263 W/m-deg; Pr = 0.7
Use the following correlation
Nu 0.
13 Gr Pr0.33
Q.3 (a) Explain the concepts of critical insulation. How do you decide
03
the thickness of insulation for electric wires?
(b) Explain the terms absorptivity, reflectivity and transmissivity
04
of radiant energy. How are they related to each other for a black
body and opaque body?
(c) What is boiling and when does occurs? Explain pool boiling.
07
How does it differ from forced convection boiling?
Q.4 (a) How the thermal conductivity of metals varies with temperature
03
and pressure?
(b) State and prove Stefan Boltzman law relating to thermal
04
radiation and temperature of a radiating body.
1
(c) What is condensation and when does occurs? How does film-
07
wise condensation differ from drop-wise condensation? Which
type has a higher heat transfer film coefficient and point out the
reason thereof?
Q.5 (a) When can we consider heat exchanger as compact heat
03
exchanger?
(b) Explain the concept of NTU for heat exchangers.
04
(c) Derive equation for LMTD for parallel flow heat exchanger.
07
Also state necessary assumptions made for it.
Q.6 (a) List at least eight important parts of shell & tube heat
03
exchanger.
(b) What do you mean by "fouling" in heat exchangers? What is
04
the effect of it on performance of heat exchangers?
(c) Calculate the surface area required for a heat exchanger which
07
has to cool 55,000 kg/hr of alcohol from 66 0C to 40 0C using
40,000 kg/hr of water entering at 5 0C. Assume that U based on
the outer area is 580 W/m2 K. Specific heat of alcohol is 3.76
kJ/kg K and that of water is 4.18 kJ/kg K. Consider counter flow
tube and shell arrangement.
Q.7 (a) How does evaporation differ from distillation?
03
(b) Mention any four characteristics of solutions to be considered
04
before selecting the evaporator?
(c) What are the various types of evaporators? Draw neat sketch of
07
Calandria type evaporator and briefly explain its construction
and working.
Q.8 (a) Why evaporators generally operate under vacuum?
03
(b) When will you select plate type evaporators? Explain
04
construction & working of it.
(c) Discuss various methods of feeding in multiple effect
07
evaporators with their relative merits and demerits.
*********
2
This post was last modified on 04 March 2021