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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 | |