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.

101.

Liquid metal having highest thermal conductivity is of _______.

A. Sodium
B. Potassium
C. Lead
D. Mercury
Answer» B. Potassium
102.

Fouling factor is used

A. In heat exchanger design as a safety factor
B. In case of Newtonian fluids
C. When a liquid exchanges heat with a gas
D. None of the above
Answer» B. In case of Newtonian fluids
103.

If two ends of rods of length L and radius r, made up of same material are kept at the same temperature difference, which of the following rods conduct most heat per unit time?

A. L = 50 cm, r = 1 cm
B. L = 2 cm, r = 0.5 cm
C. L = 100 cm, r = 2 cm
D. L = 3 cm, r = 1 cm
Answer» E.
104.

A flat wall with a thermal conductivity of 0.2 kW/mK has its inner and outer surface temperatures 600°C and 200°C respectively, If the heat flux through the wall is 200 kW/m2, what is the thickness off the wall?

A. 10 cm
B. 20 cm
C. 30 cm
D. 40 cm
Answer» E.
105.

It is proposed to coat a 1 mm diameter wire with enamel paint (k = 0.1 W/mK) to increase the heat transfer with air. If the air side heat transfer coefficient is 100 W/m2K, the optimum thickness of enamel paint should be

A. 0.25 mm
B. 0.5 mm
C. 1 mm
D. 2 mm
Answer» C. 1 mm
106.

Consider steady-state heat conduction across the thickness in a plane composite wall (as shown in the figure) exposed to convection conditions on both sides.Givenhi = 20 W / m2K; h0 = 50 W / m2K; T∞,i = 20°C; T∞,0 = - 2°C ; k1 = 20 W / mk; k2 = 50 W / mk; L1 = 0.30 m and L2 = 0.15 mAssuming negligible contact resistance between the wall surfaces, the interface temperature, T (in °C), of the two walls will be

A. -0.50
B. 2.75
C. 3.76
D. 4.50
Answer» D. 4.50
107.

Consider one-dimensional steady state heat conduction along x-axis (0 ≤ x ≤ L) , through a plane wall with the boundary surfaces (x = 0 and x = L) maintained at temperatures 0°C and 100°C. Heat is generated uniformly throughout the wall. Choose the CORRECT statement.

A. The direction of heat transfer will be from the surface at 100°C to surface at 0°C.
B. The maximum temperature inside the wall must be greater than 100°C
C. The temperature distribution is linear within the wall
D. The temperature distribution is symmetric about the mid-plane of the wall
E. None of the above
Answer» C. The temperature distribution is linear within the wall
108.

For the three-dimensional object shown in the figure below, five faces are insulated. The sixth face (PQRS), which is not insulated, interacts thermally with the ambient, with a convective heat transfer coefficient of 10 W/m2.K. The ambient temperature is 30°C. Heat is uniformly generated inside the object at the rate of 100 W/m3. Assuming the face PQRS to be at uniform temperature, its steady state temperature is

A. 10°C
B. 20°C
C. 30°C
D. 40°C
Answer» E.
109.

A hollow cylinder has length L, inner radius r1, outer radius r2, and thermal conductivity k. The thermal resistance of the cylinder for radius conduction is

A. \(\frac{{\ln\;\left( {{r_2}/r_1} \right)}}{{2\pi kL}}\)
B. \(\frac{{\ln\;\left( {{r_1}/{r_2}} \right)}}{{2\pi kL}}\)
C. \(\frac{{2\pi kL}}{{\ln\;\left( {{r_2}/{r_1}} \right)}}\)
D. \(\frac{{2\pi kL}}{{\ln\;\left( {{r_1}/{r_2}} \right)}}\)
Answer» B. \(\frac{{\ln\;\left( {{r_1}/{r_2}} \right)}}{{2\pi kL}}\)
110.

According to Fourier’s law, amount of heat flow (Q) through the body in unit time is equal to

A. \(kA\frac{{dT}}{{dx}}\)
B. \(kA\frac{{d{T^2}}}{{d{x^2}}}\)
C. \(k\frac{{dx}}{{dT}}\)
D. \(kA\frac{{dx}}{{dT}}\)
Answer» B. \(kA\frac{{d{T^2}}}{{d{x^2}}}\)
111.

A chromel – alumel thermocouple of diameter 0.7 mm is used to measure the temperature of a gas stream for which h = 600 W/sqm K. Acceptable reading of the temperature can be taken after (specific heat = 400 J/kg K, Density = 8600 kg/cum)

A. 1 second
B. 4 seconds
C. 2 seconds
D. 3 seconds
Answer» B. 4 seconds
112.

It is required to insulate a kitchen oven with corkboard (k = 0.043 W/(m K)) so that the heat losses from the oven does not exceed 400 W/m2 when the outer surface of the oven is at 225°C and the outer surface of the insulation is at 40°C. The thickness of insulation required is nearly

A. 1 cm
B. 2 cm
C. 3 cm
D. 4 cm
Answer» C. 3 cm
113.

In case of one dimensional heat conduction in a medium with constant properties, T is a temperature at position x, at time t. then \(\frac{\partial T}{\partial t}\) is proportional to

A. \(\frac{T}{x}\)
B. \(\frac{\partial T}{\partial x}\)
C. \(\frac{\partial^2 T}{\partial x\partial t}\)
D. \(\frac{\partial^2 T}{\partial x^2}\)
Answer» E.
114.

For heat transfer across a composite slab with materials having different thermal conductivity, study the following statements.I. Temperature is continuous always.II. The temperature gradient is not continuous.III. Heat flow is not continuous.

A. Statement I alone is correct
B. Statement I and II are correct
C. Statement II alone is correct
D. All the statements are correct
Answer» C. Statement II alone is correct
115.

A 10 mm diameter electrical conductor is covered by an insulation of 2 mm thickness. The conductivity of the insulation is 0.08 W/m-K and the convection coefficient at the insulation surface is 10 W/m2-K. Addition of further insulation of the same material will

A. increase heat loss continuously
B. decrease heat loss continuously
C. increase heat loss to a maximum and then decrease heat loss
D. decrease heat loss to a minimum and then increase heat loss
Answer» D. decrease heat loss to a minimum and then increase heat loss
116.

An electric heater is sandwiched between two plates each 0.3 m long and 0.1 m wide with a thickness of 30 mm. At steady-state condition, the heater is maintained at a temperature of 100°C, with a current of 0.25 A and voltage of 200 V. Assume the plates are perfectly insulated at the edges, and the heater is having perfect contact with the plates to give a temperature of 50°C on the outside of the plate surface. What is the thermal conductivity of the plate material?

A. 1.0 W/m-K
B. 0.5 W/m-K
C. 0.015 W/m-k
D. 0.3 W/m-K
Answer» C. 0.015 W/m-k
117.

If thermal conductivity of a material of wall varies as k0 (1 + αT), then the temperature at the centre of the wall as compared to that in case of constant thermal conductivity, will be ______. (​α > 0)

A. More
B. Less
C. Same
D. Depend on other factors
Answer» B. Less
118.

In the figure given below, curve A will be applicable when thermal conductivity of the material.

A. Increases with increase in temperature
B. Decreases with increase in temperature
C. Is very large
D. Is constant at all the temperatures
Answer» B. Decreases with increase in temperature
119.

In an equation of Fourier law of heat conduction, heat flow through a body per unit time is \(Q = - kA\frac{{dT}}{{dx}}\), the negative sign of k in this equation is to take care of

A. Decreasing temperature along the direction of increasing thickness
B. Increasing temperature along the direction of increasing thickness
C. Constant temperature along the direction with constant thickness
D. All of the above
Answer» B. Increasing temperature along the direction of increasing thickness
120.

Critical radius of a hollow cylinder is defined as _______.

A. Outer radius which gives maximum heat flow
B. Outer radius which gives minimum heat flow
C. Inner radius which gives minimum heat flow
D. Inner radius which gives maximum heat flow
Answer» B. Outer radius which gives minimum heat flow
121.

Consider a long cylindrical tube of inner and outer radii, ri and ro, respectively, length, L and thermal conductivity, k. its inner and outer surfaces are maintained at Ti and To respectively (Ti > To) . Assuming one-dimensional steady-state heat conduction in the radial direction, the thermal resistance in the wall of the tube is

A. \(\frac{1}{{2\pi kL}}\ln \left( {\frac{{{r_i}}}{{{r_o}}}} \right)\)
B. \(\frac{L}{{2\pi {r_i}k}}\)
C. \(\frac{1}{{2\pi kL}}\ln \left( {\frac{{{r_o}}}{{{r_i}}}} \right)\)
D. \(\frac{1}{{4\pi kL}}\ln \left( {\frac{{{r_o}}}{{{r_i}}}} \right)\)
Answer» D. \(\frac{1}{{4\pi kL}}\ln \left( {\frac{{{r_o}}}{{{r_i}}}} \right)\)
122.

For steady state one-dimensional heat conduction through a plane wall with constant thermal conductivity and no internal heat generation, the temperature distribution within the wall will be:

A. hyperbolic
B. ​elliptic
C. linear
D. non-linear
Answer» D. non-linear
123.

If the inner and outer surfaces of a hollow cylinder (having radii r1 and r2 and length L) are at temperatures t1 and t2 then rate of radial heat flow will be

A. \(\frac{k}{{2\pi L}}\;\frac{{{t_1} - {t_2}}}{{\log \frac{{{r_2}}}{{{r_1}}}}}\)
B. \(\frac{1}{{2\pi Lk}}\;\frac{{{t_1} - {t_2}}}{{\log \frac{{{r_2}}}{{{r_1}}}}}\)
C. \(\frac{{2\pi L}}{k}\frac{{{t_1} - {t_2}}}{{\log \frac{{{r_2}}}{{{r_1}}}}}\)
D. \(2\pi Lk\frac{{{t_1} - {t_2}}}{{\log \frac{{{r_2}}}{{{r_1}}}}}\)
E. None of the above
Answer» E. None of the above
124.

A large concrete slab 1 m thick has one-dimensional temperature distribution: T = 4 - 10x + 20x2 + 10x3, where T is temperature and x is the distance from one face towards the other face of the wall. If the slab has a thermal diffusivity of 2 × 10-3 m2/hr, what is the rate of change of temperature at the other face of the wall?

A. 0.1°C/h
B. 0.2°C/h
C. 0.3°C/h
D. 0.4°C/h
Answer» C. 0.3°C/h
125.

A steel ball of diameter 60 mm is initially in thermal equilibrium at 1030°C in a furnace. It is suddenly removed from the furnace and cooled in ambient air at 30°C, with convective heat transfer coefficient h = 20 W/m2K. The thermophysical properties of steel are: density ρ = 7800 kg/m3, conductivity k = 40 W/mK and specific heat c = 600 J/kgK. The time required in seconds to cool the steel ball in the air from 1030°C to 430°C is

A. 519
B. 931
C. 1195
D. 2144
Answer» E.
126.

Log mean area ‘A’ of cylinder can be given as

A. \(\frac{{\log A_2 - \log A_1}}{{A_2 - A_1}}\)
B. \(\frac{{A_2 - A_1}}{{\log A_2 - \log A_1}}\)
C. \(\frac{{\log A_2 - \log A_1}}{{\log \left( {\frac{{A_2}}{{A_1}}} \right)}}\)
D. None
Answer» C. \(\frac{{\log A_2 - \log A_1}}{{\log \left( {\frac{{A_2}}{{A_1}}} \right)}}\)
127.

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

A. 0.10 kW
B. 0.15 kW
C. 0.20 kW
D. 0.25 kW
Answer» E.
128.

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_THICKNESS?$

A.
B.
Answer» B.
129.

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

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» D. Convection increases while that due to conduction decreases
130.

The quantity d t/Q for conduction of heat through a body i.e. spherical in shape is

A. ln (r<sub>2</sub>/r<sub>1</sub>)/2πLk
B. ln (r<sub>2</sub>/r<sub>1</sub>)/πLk
C. ln (r<sub>2</sub>/r<sub>1</sub>)/2Lk
D. ln (r<sub>2</sub>/r<sub>1</sub>)/2πk
Answer» C. ln (r<sub>2</sub>/r<sub>1</sub>)/2Lk
131.

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/m<sup>2</sup>
B. – 73.79 W/m<sup>2</sup>
C. – 83.79 W/m<sup>2</sup>
D. – 93.79 W/m<sup>2</sup>
Answer» B. ‚Äö√Ñ√∂‚àö√ë‚àö¬® 73.79 W/m<sup>2</sup>
132.

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

A. r <sub>2</sub> – r <sub>1</sub>/4πk<sub> </sub>r <sub>1</sub>r <sub>2</sub>
B. r <sub>2 </sub>/4πk<sub> </sub>r <sub>1</sub>r <sub>2</sub>
C. r <sub>1</sub>/4πk<sub> </sub>r <sub>1</sub>r <sub>2</sub>
D. 4πk<sub> </sub>r <sub>1</sub>r <sub>2</sub>
Answer» B. r <sub>2 </sub>/4‚âà√¨‚àö√ëk<sub> </sub>r <sub>1</sub>r <sub>2</sub>
133.

The rate of conduction heat flow in case of a composite sphere is given by

A. Q = t<sub>1 </sub>– t<sub>2</sub>/ (r<sub>2</sub> – r<sub>1</sub>)/4πk<sub>1</sub>r<sub>1</sub>r<sub>2 </sub>+<sub> </sub>(r<sub>3</sub> – r<sub>2</sub> )/4πk<sub>2</sub>r<sub>2</sub>r<sub>3</sub>
B. Q = t<sub>1 </sub>– t<sub>2</sub>/ (r<sub>2</sub> – r<sub>1</sub>)/4πk<sub>1</sub>r<sub>1</sub>r<sub>2 </sub>+<sub> </sub>(r<sub>3</sub> – r<sub>2</sub> )/4πk<sub>2</sub>r<sub>2</sub>r<sub>3</sub>
C. Q = t<sub>1 </sub>– t<sub>2</sub>/ (r<sub>2</sub> – r<sub>1</sub>)/4πk<sub>1</sub>r<sub>1</sub>r<sub>2 </sub>+<sub> </sub>(r<sub>3</sub> – r<sub>2</sub> )/4πk<sub>2</sub>r<sub>2</sub>r<sub>3</sub>
D. Q = t<sub>1 </sub>– t<sub>2</sub>/ (r<sub>2</sub> – r<sub>1</sub>)/4πk<sub>1</sub>r<sub>1</sub>r<sub>2 </sub>+<sub> </sub>(r<sub>3</sub> – r<sub>2</sub> )/4πk<sub>2</sub>r<sub>2</sub>r<sub>3</sub>
Answer» D. Q = t<sub>1 </sub>‚Äö√Ñ√∂‚àö√ë‚àö¬® t<sub>2</sub>/ (r<sub>2</sub> ‚Äö√Ñ√∂‚àö√ë‚àö¬® r<sub>1</sub>)/4‚âà√¨‚àö√ëk<sub>1</sub>r<sub>1</sub>r<sub>2 </sub>+<sub> </sub>(r<sub>3</sub> ‚Äö√Ñ√∂‚àö√ë‚àö¬® r<sub>2</sub> )/4‚âà√¨‚àö√ëk<sub>2</sub>r<sub>2</sub>r<sub>3</sub>
134.

The thermal resistance for heat conduction through a spherical wall is

A. (r<sub>2</sub>-r<sub>1</sub>)/2πkr<sub>1</sub>r<sub>2</sub>
B. (r<sub>2</sub>-r<sub>1</sub>)/3πkr<sub>1</sub>r<sub>2</sub>
C. (r<sub>2</sub>-r<sub>1</sub>)/πkr<sub>1</sub>r<sub>2</sub>
D. (r<sub>2</sub>-r<sub>1</sub>)/4πkr<sub>1</sub>r<sub>2</sub>
Answer» E.
135.

The temperature distribution associated with radial conduction through a sphere is represented by

A. Parabola
B. Hyperbola
C. Linear
D. Ellipse
Answer» C. Linear