Heat And Mass Transfer - Study Mode

[#86] In case of liquids and gases, the heat transfer takes place according to
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.

[#87] Depending on the radiating properties, a body will be opaque when
Correct Answer

(D) x = 0, a + p = 1

Explanation

Solution: Opaque body are those body where the atoms are closely packed and the light cannot pass through. Whereas a light may or may not pass through a black body depending whether it is opaque or transparent. Depending on the radiating properties, a body will be opaque when x = 0, a + p = 1.

[#88] Log mean temperature difference in case of counter flow compared to parallel flow will be
Correct Answer

(B) More

Explanation

Solution: The larger the LMTD more heat is transferred. In parallel flow heat exchangers both hot fluid and cold fluid flow in same direction. Counter flow heat exchanger: In counter flow heat exchangers both hot fluid and cold fluid flow in opposite direction.

[#89] Absorptivity of a body will be equal to its emissivity
Correct Answer

(C) When system is under thermal equilibrium

Explanation

Solution: Kirchhoff's law states that For an arbitrary body emitting and absorbing thermal radiation in thermodynamic equilibrium, the emissivity is equal to the absorptivity.

[#90] In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
Correct Answer

(D) All of these

Explanation

Solution: In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
-Parallel flow
- Counter flow
- Cross flow