Explore topic-wise MCQs in Heat Transfer.

This section includes 135 Mcqs, each offering curated multiple-choice questions to sharpen your Heat Transfer knowledge and support exam preparation. Choose a topic below to get started.

1.

The oven of an electric store, of total outside surface area 2.9 m2 dissipates electric energy at the rate of 600 W. The surrounding room air is at 20 degree Celsius and the surface coefficient of heat transfer between the room air and the surface of the oven is estimated to be 11.35 W/m 2 degree. Determine the average steady state temperature of the outside surface of the store

A. 38.22 degree Celsius
B. 48.22 degree Celsius
C. 58.22 degree Celsius
D. 68.22 degree Celsius
Answer» B. 48.22 degree Celsius
Discussion
2.

The following data pertains to a hollow cylinder and a hollow sphere made of same material and having the same temperature drop over the wall thicknessInside radius = 0.1 m and outside surface area = 1 square meterIf the outside radius for both the geometrics is same, calculate the ratio of heat flow in the cylinder to that of sphere?

A. 0.056
B. 2.345
C. 1.756
D. 3.543
Answer» D. 3.543
Discussion
3.

If we increase the thickness of insulation of a circular rod, heat loss to surrounding due to

A. Convection and conduction increases
B. Convection and conduction decreases
C. Convection decreases while that due to conduction increases
D. Convection increases while that due to conduction decreases
Answer» E.
Discussion
4.

A spherical vessel of 0.5 m outside diameter is insulated with 0.2 m thickness of insulation of thermal conductivity 0.04 W/m degree. The surface temperature of the vessel is – 195 degree Celsius and outside air is at 10 degree Celsius. Determine heat flow

A. – 47.93 W
B. – 57.93 W
C. – 67.93 W
D. – 77.93 W
Answer» C. – 67.93 W
Discussion
5.

A spherical vessel of 0.5 m outside diameter is insulated with 0.2 m thickness of insulation of thermal conductivity 0.04 W/m degree. The surface temperature of the vessel is – 195 degree Celsius and outside air is at 10 degree Celsius. Determine heat flow per m2 based on inside area

A. – 63.79 W/m2
B. – 73.79 W/m2
C. – 83.79 W/m2
D. – 93.79 W/m2
Answer» C. – 83.79 W/m2
Discussion
6.

The thermal resistance for heat conduction through a hollow sphere of inner radius r1 and outer radius r2 is

A. r 2 – r 1/4πk r 1r 2
B. r 2 /4πk r 1r 2
C. r 1/4πk r 1r 2
D. 4πk r 1r 2
Answer» B. r 2 /4πk r 1r 2
Discussion
7.

A bar of Cu of length 75 cm and a steel bar of 125 cm length are joined together end to end. Both the bars are having same diameter of 2 cm. The free ends of the Cu and the steel bars are maintained at 100°C and 0°C respectively. The curved surfaces of the bars are thermally insulated, what is the approximate temperature at Cu-steel junction? (consider conductivity k of Cu = 400 Js-1m-1 C-1 and k for steel 50 Js-1m-1 C-1)

A. 95°C
B. 93°C
C. 90°C
D. 89°C
Answer» C. 90°C
Discussion
8.

In a composite slab, the temperature at the interface(Tinter) between two materials is equal to the average of the temperatures at the two ends. Assuming steady one-dimensional heat conduction, which of the following statements is true about the respective thermal conductivities?

A. 2k1 = k2
B. k1 = k2
C. 2k1 = 3k2
D. k1 = 2k2
Answer» E.
Discussion
9.

Critical radius of insulation of a hollow cylinder is

A. \(\frac{2k}{h}\)
B. \(\frac{k}{2h}\)
C. \(\frac{k}{h}\)
D. \(\sqrt \frac{k}{h}\)
Answer» D. \(\sqrt \frac{k}{h}\)
Discussion
10.

Lumped heat capacity approach of transient heat conduction analysis is used:

A. When temperature variation throughout the body is very low
B. When temperature variation throughout the body is very high
C. For bodies of very high conductive resistance
D. For Biot number >10
Answer» B. When temperature variation throughout the body is very high
Discussion
11.

A composite slab has two layers of different materials having internal conductivities, k1 and k2. If each layer has the same thickness, then what is the equivalent thermal conductivity of the slab?

A. \(\frac {k_1 k_2}{k_1 + k_2}\)
B. \(\frac {k_1 k_2}{2(k_1 + k_2)}\)
C. \(\frac {2k_1 }{k_1 + k_2}\)
D. \(\frac {2k_1 k_2}{k_1 + k_2}\)
Answer» E.
Discussion
12.

A wire is plastically deformed bent by supplying a force of 40 N over a distance of 0.8 m. (The force moves in the direction in which the distance is measured). If the wire has a mass of 0.2 kg and a specific heat of 0.5 kJ/kg°C estimate the maximum increase in the average temperature of the wire

A. 0.03°C
B. 0.3°C
C. 3°C
D. 30°C
Answer» C. 3°C
Discussion
13.

A wire of 8 mm diameter at a temperature of 60°C is to be insulted by a material having k = 0.174 W/mK. The heat transfer coefficient on the outside ha = 8 W/m2 K and ambient temperature Ta = 25°C. The maximum thickness of insulation for maximum heat loss will be

A. 15.25 mm
B. 16.50 mm
C. 17.75 mm
D. 18.25 mm
Answer» D. 18.25 mm
Discussion
14.

A 2 kW resistance heater wire whose thermal conductivity is k = 15 W/mK has a diameter of D = 4 mm and a length of L = 0.5 m, and is used to boil water. If the outer surface temperature of the resistance wire is TS = 105°C, determine the temperature at the center of the wire.

A. 126°C
B. 110°C
C. 118°C
D. 130°C
Answer» B. 110°C
Discussion
15.

In descending order of magnitude, the thermal conductivity ofPure iron, Liquid water,Saturated water vapour, andPure aluminiumCan be arranged as:

A. a b c d
B. b c a d
C. d a b c
D. d c b a
Answer» D. d c b a
Discussion
16.

Determine the heat transfer through a plane of length 4 m, height 3 m and thickness 0.2 m. The temperatures of inner and outer surfaces are 150°C and 90°C respectively. Thermal conductivity of the wall is 0.5 W/mK.

A. 1800 W
B. 2000 W
C. 2200 W
D. 2400 W
Answer» B. 2000 W
Discussion
17.

An insulating material with a thermal conductivity, k = 0.12 W/mK is used for a pipe carrying steam. The local coefficient of heat transfer (h) to the surroundings is 4 W/m2K. In order to provide effective insulation, the minimum outer diameter of the pipe should be

A. 45 mm
B. 60 mm
C. 75 mm
D. 90 mm
Answer» C. 75 mm
Discussion
18.

A cylindrical uranium fuel rod of radius 5 mm in a nuclear reactor is generating heat at the rate of 4× 107 W/m3. The rod is cooled by a liquid (convective heat transfer coefficient 1000 W/m2.K) at 25°C. At steady state, the surface temperature (in K) of the rod is

A. 308
B. 398
C. 418
D. 448
Answer» C. 418
Discussion
19.

A slender rod of length L, diameter d (L >> d) and thermal conductivity k1 is joined with another rod of identical dimensions, but of thermal conductivity k2, to form a composite cylindrical rod of length 2L. The heat transfer in radial direction and contact resistance are negligible. The effective thermal conductivity of the composite rod is

A. k1 + k2
B. \(\sqrt {{k_1}{k_2}}\)
C. \(\frac{{{k_1}{k_2}}}{{{k_1} + {k_2}}}\)
D. \(\frac{{2{k_1}{k_2}}}{{{k_1} + {k_2}}}\)
Answer» E.
Discussion
20.

A hot steel sphere of diameter 40mm is immersed in oil. If the heat transfer coefficient between the sphere and oil is 300 W/m2K, then Biot Number is [Take Ksteel = 50 W/mK and Koil = 0.2 W/mK]

A. 0.04
B. 0.12
C. 10
D. 0.24
Answer» B. 0.12
Discussion
21.

On a hot summer day, surface of the concrete highway may reach 328 K. Suppose a stream of water is directed on the highway so that the surface is suddenly lowered to 308 K. Time taken in hours to cool the concrete to 318 K to a depth of 5 cm below the surface is: (Thermal diffusivity = 1.77 × 10-3 m2/hr).

A. 1.2
B. 1.4
C. 1.6
D. 1.8
Answer» C. 1.6
Discussion
22.

If R1 and R2 are the inner and outer radii of a cylinder, the heat conduction through a cylinder is proportional to

A. (R1 – R2)
B. (R1 × R2)
C. \(\frac{1}{{\left( {{R_1} - {R_2}} \right)}}\)
D. \(\frac{1}{{{{\log }_e}\left\{ {\frac{{{R_1}}}{{{R_2}}}} \right\}}}\)
Answer» E.
Discussion
23.

Heat is conducted through a 10 cm thick wall at rate of 30 W/m2. When the temperature difference across wall is 10° C. What is the thermal conductivity of wall?

A. 0.03 W/mK
B. 0.3 W/mK
C. 3 W/mK
D. 30 W/mK
Answer» C. 3 W/mK
Discussion
24.

A spherical shaped vessel of 1.4 m outer diameter is 90 mm thick. Find the rate of heat leakage, if the temperature difference between the inner and outer surfaces is 220°C. Thermal conductivity of the material of the sphere is 0.083 W/m K.

A. 0.2 kW
B. 0.5 kW
C. 1.08 kW
D. 1.6 kW
Answer» D. 1.6 kW
Discussion
25.

Four rods with different radii r and length l are connected to two reservoirs at different temperature. Which one of them will conduct most heat?

A. r = 2 cm and l = 2 m
B. r = 1 cm and l = 1 m
C. r = 2 cm and \(l = \frac{1}{2}m\)
D. \(r = \frac{1}{2}cm\;and\;l = \frac{1}{2}m\)
Answer» D. \(r = \frac{1}{2}cm\;and\;l = \frac{1}{2}m\)
Discussion
26.

In a furnace made of bricksInside heat transfer coefficient = 35 W/m2KOutside heat transfer coefficient = 25 W/m2KThermal conductivity of bricks (15 cm thick) = 0.15 W/mKThe overall heat transfer coefficient (in W/m2K) will be closer to the

A. Inside heat transfer coefficient
B. Outside heat transfer coefficient
C. Thermal conductivity of bricks
D. Heat transfer coefficient based on the thermal conductivity of the bricks alone.
Answer» E.
Discussion
27.

A spherical thermocouple junction of diameter 0.706 mm is to be used for measurement of temperature of a gas stream. The convective heat transfer coefficient on bead surface is \(400~\frac{W}{{{m^2} - K}}\). The thermo physical properties of thermocouple material are \(k = 20~\frac{W}{{m - K}},\ c = 400\frac{J}{{kg - K}},\ \rho = 8500~\frac{{kg}}{{{m^3}}}\). If the thermocouple initially at 30°C is placed in a hot stream of 300°C, the time taken by the bead to reach 298°, is

A. 2.35 sec
B. 4.9 sec
C. 14.7 sec
D. 29.4 sec
Answer» C. 14.7 sec
Discussion
28.

Minimum thermal diffusivity is of ______.

A. Aluminium
B. Rubber
C. Iron
D. Lead
Answer» C. Iron
Discussion
29.

A steam engine intakes 100 gm of steam at 100°C per minute and cools it down to 20°C. Calculate the heat rejected by the steam engine per minute, (consider Latent Heat of vaporization of steam = 540 cal/gm and cp = 1 cal/gm°C)

A. 6.2 × 104 kcal
B. 62 × 104 cal
C. 6.2 × 104 cal
D. 620 × 104 kcal
Answer» D. 620 × 104 kcal
Discussion
30.

As per Fourier law of heat conduction in one dimension, which is correct?

A. \(– kA \frac{dT}{dx}\)
B. \(kA \frac{dT}{dx}\)
C. \(– kA \frac{dx}{dT}\)
D. \(kA \frac{dx}{dT}\)
Answer» B. \(kA \frac{dT}{dx}\)
Discussion
31.

A mild steel tank of wall thickness 12 mm contains water at 100°C. The atmospheric temperature is 20°C. the thermal conductivity of mild steel is 50 W/mK, and the heat transfer co-efficients for inside and outside the tank are 2850 and 10 W/m2K, respectively. Calculate the rate of heat loss per m2 of tank surface and the temperature of the outside surface of the tank.

A. 300.5 W/m2, 45.5°C
B. 495.2 W/m2, 67.6°C
C. 602.6 W/m2, 806°C
D. 795.2 W/m2, 99.52°C
Answer» E.
Discussion
32.

A body cools from 90°C to 80°C in 5 minutes. Under the same external conditions to cool from 80°C to 70°C the body will take

A. 5 minutes
B. 4 minutes
C. 2.5 minutes
D. More than 5 minutes
Answer» E.
Discussion
33.

Critical thickness of insulation for spheres is given by _____.

A. k/h
B. k/4h
C. h/2k
D. 2k/h
Answer» E.
Discussion
34.

In a furnace, the wall thickness is 60 cm and is 100 cm wide by 150 cm height made of material with thermal conductivity 0.4 W/mK. The temperature inside and outside are 1000°C and 4°C respectively. The thermal resistance is

A. 1 K/W
B. 2 K/W
C. 18 K/W
D. 15 K/W
Answer» B. 2 K/W
Discussion
35.

In a wall of constant thermal conductivity, the temperature profile for heat conduction in the presence of a heat source inside the wall is

A. Linear
B. Logarithmic
C. Parabolic
D. Hyperbolic
Answer» D. Hyperbolic
Discussion
36.

A plane wall is 20 cm thick with an area of 1 m2 and has a thermal conductivity of 0.5 W/m. K. A temperature difference of 100°C is imposed across it. The heat flow is at:

A. 150 W
B. 180 W
C. 220 W
D. 250 W
Answer» E.
Discussion
37.

Fourier's law of heat conduction defines the rate of heat transfer through a body as

A. only dependent upon the material of the body
B. proportional to the area normal to the direction of the heat flow and the temperature gradient along the direction of the heat flow, and is dependent upon the material of the body
C. proportional only to the area normal to the direction of the heat flow
D. proportional only to the temperature gradient along the direction of the heat flow
Answer» C. proportional only to the area normal to the direction of the heat flow
Discussion
38.

Fourier’s law of heat conduction gives the heat flow for

A. Irregular surfaces
B. Non-uniform temperature surfaces
C. One dimensional cases only
D. Two dimensional cases only
Answer» D. Two dimensional cases only
Discussion
39.

A long glass cylinder of inner diameter = 0.03 m and outer diameter = 0.05 m carries hot fluid inside. If the thermal conductivity of glass = 1.05 W/mK, the thermal resistance (K/W) per unit length of the cylinder is

A. 0.031
B. 0.077
C. 0.17
D. 0.34
Answer» C. 0.17
Discussion
40.

A brick wall \(\left( {k = 0.9\frac{W}{{mk}}} \right)\) of thickness 0.18 m separates the warm air in a room from the cold ambient air. On a particular winter day, the outside air temperature is -5°C and the room needs to be maintained at 27°C. The heat transfer coefficient associated with outside air is \(20\frac{W}{{{m^2}K'}}\). Neglecting the convective resistance of the air inside the room, the heat loss, in (W/m2), is

A. 88
B. 110
C. 128
D. 160
Answer» D. 160
Discussion
41.

A pipe of 25 mm outer diameter carries steam. The heat transfer coefficient between the cylinder and surroundings is 5 W/m2K . It is proposed to reduce the heat loss from the pipe by adding insulation having a thermal conductivity of 0.05 W/mK. Which one of the following statements is TRUE?

A. The outer radius of the pipe is equal to the critical radius
B. The outer radius of the pipe is less than the critical radius
C. Adding the insulation will reduce the heat loss
D. Adding the insulation will increase the heat loss
Answer» D. Adding the insulation will increase the heat loss
Discussion
42.

A composite wall of surface area 1 m2 has three layers of thickness 0.3 m, 0.2 m, and 0.1 m and has thermal conductivities 0.6, 0.4, and 0.1 W/m°C, respectively. There is no generation of thermal energy within the wall. If the inner and outer temperatures of the composite wall are 1840°C and 340°C, respectively, the rate of heat transfer through this wall is:

A. 0.75 kW
B. 0.150 kW
C. 7.5 kW
D. 1.5 kW
Answer» B. 0.150 kW
Discussion
43.

Consider steady-state heat conduction across the thickness in a plane wall of thickness 0.6 m. The wall has a normal area 1.5 m2 and is made up of material of thermal couductivity 0.4 W/m°C. There is no generation of thermal energy within the wall. The temperatures on the two sides are 800°C and 300°C. The thermal resistance of the wall is:

A. 1.5 W/°C
B. 1 W/°C
C. 1.5 °C/W
D. 1 °C/W
Answer» E.
Discussion
44.

For a given amount of heat transfer rate during steady state one-dimensional heat conduction through a plane wall – with constant thermal conductivity and no internal heat generation – the higher the value of thermal conductivity of the wall, the temperature gradient within the wall will be:

A. higher
B. lower
C. same
D. dependent on ambient conditions
Answer» C. same
Discussion
45.

Heat is generated uniformly in a 4 cm diameter, 16 cm long solid bar [k = 24 W/m°c]. The temperatures at the centre and the surface of the bar are measured to be 210°C and 45°C respectively. The rate of heat generation within the bar is,

A. 240 W
B. 1013 W
C. 7962 W
D. 3.96 × 106 W
Answer» D. 3.96 × 106 W
Discussion
46.

A steam pipe is to be insulated by two insulating materials put over each other. For best result

A. Better insulation should be put over pipe and inferior one over it.
B. Inferior insulation should be put over pipe and better one over it.
C. Both may be put in any order.
D. Whether to put inferior one over pipe or the better one would depend on steam temperature.
Answer» B. Inferior insulation should be put over pipe and better one over it.
Discussion
47.

In which of the following mechanisms, is heat conducted in liquid and gas

A. Lattice vibration
B. Transportation of free electrons
C. Collisions and diffusion
D. No heat conducted
Answer» D. No heat conducted
Discussion
48.

A steam pipe is to be insulated by 2 insulating materials put over each other. For best results

A. better insulation should be put over pipe and inferior one over it
B. inferior insulation should be put over pipe and better one over it
C. both may put in any order
D. unpredictable
Answer» B. inferior insulation should be put over pipe and better one over it
Discussion
49.

Consider the following statements with regard to heat transfer:1. The temperature variations in lumped heat capacity analysis is exponential with time2. In situations involving simultaneous heat and mass transfer, the ratio of convective heat transfer to convective mass transfer varies with Lewis number, Le, as (Le)1/3Which of the above statements are correct?

A. Both 1 and 2
B. Neither 1 nor 2
C. 1 only
D. 2 only
Answer» D. 2 only
Discussion
50.

A composite slab has two layers of different materials having thermal conductivities k ad 2k. If each layer has the same thickness, the equivalent thermal conductivity of the slab is

A. 3k
B. \(\frac{k}{2}\)
C. \(\frac{3}{2k}\)
D. \(\frac{4k}{3}\)
Answer» E.
Discussion