Heat And Mass Transfer - Study Mode
[#81] Heat transfer by radiation mainly depends upon
Correct Answer
(D) All of the above
Explanation
Solution: Heat transfer through radiation takes place in form of electromagnetic waves mainly in the infrared region. It depends on nature of the body, its temperature and kind & extent of its surface.
[#82] The transfer of heat by molecular collision is known as
Correct Answer
(B) Convection
Explanation
Solution: When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along. This type of heat transfer is called convection.
[#83] According to Kirchoff's law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
Correct Answer
(D) Black body
Explanation
Solution: Kirchhoff's law states that the emissivity and the absorptivity of a surface at a given temperature and wavelength are equal. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as Kirchhoff's law.
[#84] 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
Correct Answer
(A) 0.45
Explanation
Solution: a + p + T = 1 a + 0.40 + 0.15 = 1 (p = 0.40, T = 0.15) a = 1 - 0.55 a = 0.45
[#85] The heat transfer takes place according to
Correct Answer
(C) Second law of thermodynamics
Explanation
Solution: Heat transfer takes place as per Second law of the thermodynamics it states that Heat transfer occurs spontaneously from higher- to lower-temperature bodies but never spontaneously in the reverse direction.