Access and Discuss Multiple choice questions for various competitive Exams and Interviews.

1. The diagram shows heat conduction through a plane wall. The surface temperature is 475 K and it radiates heat to the surroundings at 335 K. If thermal conductivity of the material is 12.5 W/m degree, find the temperature gradient. Let convective coefficient be 80 W/m² degree and radiation factor is 0.9
a. – 1052.4 degree celsius
b. – 2052.4 degree celsius
c. – 3052.4 degree celsius
d. – 4052.4 degree celsius
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Answer: (a).– 1052.4 degree celsius

2. From the concept of kinetic theory, mean travel velocity of the gas molecules is prescribed by the relation
(Where,
G = Universal gas constant
M = Molecular weight of the gas
T = Absolute temperature)
a. V = (3M/GT)⅟₂
b. V = (3GT/M)⅟₂
c. V = (6T/GM)⅟₂
d. V = (3GT/2M)⅟₂
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Answer: (b).V = (3GT/M)⅟₂

3. Low temperature insulation are used when the enclosure is at a temperature lower than the ambient temperature. Which one of the following is not a low temperature insulation?
a. Asbestos
b. Cork
c. Cattle hair
d. Slag wool
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Answer: (a).Asbestos

4. The value of Lorenz number in 10¯⁸ W ohms/K² is
a. 2.02
b. 2.35
c. 2.56
d. 2.45
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Answer: (d).2.45

5. Consider the following parameters
(i) Composition
(ii) Density
(iii) Porosity
(iv) Structure
Then, thermal conductivity of glass wool varies from sample to sample because of variation is
a. 1 and 2
b. 1, 2, 3 and 4
c. 1 and 3
d. 1, 2 and 3
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Answer: (b).1, 2, 3 and 4

6. The thermal conductivity and the electrical conductivity of a metal at absolute temperature are related as
a. k/σ T
b. k/σ
c. k σ/T
d. k/T
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Answer: (a).k/σ T

7. The relation Ϫ² t =0 is referred to as
a. Poisson’s equation
b. Fourier heat conduction equation
c. Solution for transient conduction
d. Laplace equation
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Answer: (d).Laplace equation

8. The unit of thermal diffusivity is
a. m²/hr-K
b. kcal/m²-hr
c. m²/hr
d. m/hr-K
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Answer: (c).m²/hr

9. To effect a bond between two metal plates, 2.5 cm and 15 cm thick, heat is uniformly applied through the thinner plate by a radiant heat source. The bonding must be held at 320 K for a short time. When the heat source is adjusted to have a steady value of 43.5 k W/m², a thermocouple installed on the side of the thinner plate next to source indicates a temperature of 345 K. Calculate the temperature gradient for heat conduction through thinner plate. In the diagram, the upper plate is 2.5 cm thick while the lower is 15 cm thick.
a. – 1000 degree Celsius/m
b. – 2000 degree Celsius/m
c. – 3000 degree Celsius/m
d. – 4000 degree Celsius/m
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Answer: (a).– 1000 degree Celsius/m

10. The diffusion equations
Ɏ²t + q g = (1/α) (d t/d r)
Governs the temperature distribution under unsteady heat flow through a homogenous and isotropic material. The Fourier equation follows from this expression when
a. Temperature doesn’t depends on time
b. There is no internal heat generation
c. Steady state conditions prevail
d. There is no internal heat generation but unsteady state condition prevails
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Answer: (d).There is no internal heat generation but unsteady state condition prevails

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