Heat And Mass Transfer - Study Mode

[#146] Thermal conductivity of solid metals with rise in temperature normally
Correct Answer

(B) Decreases

Explanation

Solution: Thermal conductivity of solid metals with rise in temperature normally Decreases

[#147] The heat transfer by conduction through a thick sphere is given by
Correct Answer

(B) $${ ext{Q}} = frac{{4pi { ext{k}}{{ ext{r}}_1}{{ ext{r}}_2}left( {{{ ext{T}}_1} - {{ ext{T}}_2}} ight)}}{{{{ ext{r}}_2} - {{ ext{r}}_1}}}$$

Explanation

Solution: The heat transfer by conduction through a thick sphere is given by $${ ext{Q}} = frac{{4pi { ext{k}}{{ ext{r}}_1}{{ ext{r}}_2}left( {{{ ext{T}}_1} - {{ ext{T}}_2}}
ight)}}{{{{ ext{r}}_2} - {{ ext{r}}_1}}}.$$

[#148] The value of the wave length for maximum emissive power is given by
Correct Answer

(C) Wine’s law

Explanation

Solution: When the temperature of a blackbody radiator increases, the overall radiated energy increases and the peak of the radiation curve moves to shorter wavelengths. When the maximum is evaluated from the Planck radiation formula, the product of the peak wavelength and the temperature is found to be a constant.

[#149] The value of the wavelength for maximum emissive power is given by
Correct Answer

(A) Wien’s law

Explanation

Solution: When the temperature of a blackbody radiator increases, the overall radiated energy increases and the peak of the radiation curve moves to shorter wavelengths. When the maximum is evaluated from the Planck radiation formula, the product of the peak wavelength and the temperature is found to be a constant.

[#150] The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is
Correct Answer

(A) Equal to one

Explanation

Solution: If the Prandtl number (Pr) is 1, the two boundary layers (hydrodynamic and thermal) are the same thickness. If the Pr > 1, the thermal boundary layer is thinner than the velocity boundary layer.