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Heat Transfer
Question Bank
Q.1
Enumerate the basic laws which govern the heat transfer?
Q.2
Name and explain briefly the various modes of heat transfer
Q.3
Enumerate some important areas which are covered under the discipline of heat
transfer
Q.4
How is thermal conductivity of material defined? What are its units?
Q.5
What is the significance of heat transfer?
Q. 6
A furnace wall consists of 200 mm layer of refractory bricks, 6 mm layer of steel
plate and a 100 mm layer of insulation bricks. The maximum temperature of the wall
is 11500C on the furnace side and the minimum temperature is 400C on the outermost
side of the wall. An accurate energy balance over the furnace shows that the heat loss
from the wall is 400 W/m2. It is known that there is a thin layer of air between the
layers refractory bricks and steel plate. Thermal conductivities for the three layers are
1.52, 45 and 0.38 W/moC respectively. Find: i) To how many millimetres of
insulation brick is the air layer equivalent? ii) What is the temperature of the outer
surface of the steel plate.
Show that heat conduction through a composite wall consisting n numbers of slab is
𝑻 −𝑻
given by: Q = 𝟏𝒏 𝒏+𝟏
𝑳
∑𝒏=𝟏
𝑨𝑲
Q. 8
A surface at 2500C exposed to the surrounding at 1100C convects and radiates heat to
the surroundings. The convection coefficient and radiation factor are 75 W/m2 0C and
unity respectively. If the heat is conducted to the surface through a solid of
conductivity 10 W/m0C, What is the temperature gradient at the surface in solid?
Q9
Derive an expression for general heat conduction equation in Cartesian coordinates
for constant thermal conductivity.
Q. 10
Show that maximum temperature distribution in a cylindrical rod with heat
𝑞𝑔 𝑅 2
generation is given by: 𝑇𝑚𝑎𝑥 = 𝑇𝑤 +
4𝐾
Q. 11
Derive an expression for general heat conduction equation in cartesion coordinates
for constant thermal conductivity.
A wall of furnace is made up of inside layer of silica brick 120 mm thick covered
with a layer of magnesite brick 240 mm thick. The temperature at the inside surface
of silica brick wall & outside surface of magnesite brick wall are 7250C & 1100C
Q. 12
respectively. The contact thermal resistance between the two walls at the interface is
0.00350C/W per unit wall area. If the thermal conductivities of silica & magnesite
bricks are 1.7 W/m0C and 5.8 W/m0C, Calculate: i) The rate of heat loss per unit area
of wall. ii) The temperature at drop at the interface.
Q. 13
Explain briefly the terms thermal capacity and thermal diffusivity of a material?
Q. 14
Derive expressions for temperature distribution under one dimensional steady state
heat conduction for the following systems
i) Plane wall;
ii) Composite wall;
iii) Cylinder;
iv) Sphere
Q. 15
Derive expressions for temperature distribution and heat dissipation in a straight fin
of rectangular profile for the following cases:
i) infinitely long fin
ii) Fin insulated at the tip
iii) Fin losing heat at
the tip
Q. 16
Explain the following:
i) Efficiency of fin: ii) Effectiveness of fin
Q. 17
Derive an expression for heat dissociation in a straight triangular fin
Q. 18
Explain in brief critical thickness of insulation?
Q. 19
State and Explain any four laws of radiation
Q. 20
Derive Wein’s Displacement law from Planck’s law
Q. 21
Define Lambert’s law of radiation
Q. 22
700 W/m2 radient energy strikes a flat plate normally. The absorptivity is twice the
transmitivity and 2.9 times its reflectivity. Determine the rate of absorption,
transmission and reflection of energy in W/m2.
Q. 23 DDefine the following terms
i) Total Emmissive power
ii) Monochromatic emissive power
Iii) Emmissivity
iv) Intensity of radiation
Q. 24
Define geometrical or shape factor
Q. 25
What is radiation shield?
Q. 27
60 Kg of water per minute is to be heated from 300C to 500C by passing through a
pipe, 2 cm in diameter. The pipe wail is at 1000C. Find the length of the pipe
required for this purpose. Properties of water at mean temperature are- p = 992
Kg/m3, Cp= 4.174 KJ/Kg K, K= 0.634 W/mK, v = 0.659 X 10-6 m2/Sec.
Q. 28
Define the following dimensionless nos. Also discuss in brief their physical
significance.
(i) Reynolds no.
(ii) Prandtl no.
(iii) Grashoff no.
Q. 29
.
(iv) Nusselt no
Derive an energy equation for thermal boundary layer over a flat plate
Q. 30
Discuss the formation of thermal boundary layer for flow of a fluid over a hot
horizontal flat surface.
Q. 31
Differentiate between the mechanism of filmwise and dropwise condensation
Q. 32
Enumerate the applications of boiling heat transfer
Q. 33
What is Heat Exchanger?
Q. 34
How are Heat exchangers classified?
Q. 35
Define Heat exchanger effectiveness?
Q. 36
What do you mean by fouling in heat exchanger?
Q. 37
What are the applications of heat exchanger?
Q. 38
Derive an expressions for logarithmic mean temperature difference(LMTD) in cases
i) Parallel flow; ii) Counter flow heat exchanger