Heat and Mass Transfer Mechanical Engineering Online Quiz - ObjectiveBooks
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# Quiz Questions

01. The process of heat transfer from a hot body to a cold body, in a straight line, without affecting the intervening medium, is called radiation.

02. The counter-current flow heat exchanger can transfer __________ heat than parallel flow heat exchanger.

03. For a white body, absorptivity (α) = 0, reflectivity (ρ) = 1 and transmissivity (τ) = 0.

04. According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature.

05. According to Prevost's theory of exchanges, everybody irrespective of its temperature continuously emit heat radiations to the surrounding bodies and at the same time receives heat radiations from the surrounding bodies.

06. The ratio of emissive power of a body to the emissive power of a perfectly black body is called emissivity.

07. The critical thickness of insulation is the ratio of thermal conductivity of the insulating material (k) to the heat transfer coefficient at the outer surface of the insulation (h₀).

08. Emissivity of a body will be equal to its absorptivity at all temperatures.

09. Prandtl number (PN) is given by PN = μ.Cp/k.

10. The space between the two walls of a thermos flask is evacuated because vacuum is a ________ conductor of heat.

11. The ratio of actual heat transfer to the maximum possible heat transfer is known as heat exchanger effectiveness.

12. A grey body is one whose absorptivity does not vary with temperature and wave length of the incident ray.

13. The average value of thermal conductivity for water at 20° C saturate is about 0.51.

14. In a black body, all radiations are rejected.

15. A device used for transferring heat from one fluid to another is called heat exchanger.

16. The temperature below which a gas is always liquefied is known as critical temperature.

17. Logarithmic mean temperature difference is the same as the arithmetic mean temperature difference.

18. Planck's law holds good for all coloured bodies.

19. When there is an addition of water vapour to the air of enclosed space, a gain in ________ is said to occur.

20. The thermal diffusivity for solids is generally less than those for liquids and gases.

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