Heat And Mass Transfer - Study Mode

[#66] Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
Correct Answer

(B) Radiation

Explanation

Solution: Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by Radiation

[#67] According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
Correct Answer

(C) Fourth power of absolute temperature

Explanation

Solution: Stefan-Boltzmann law is applicable for radiation it states that the total radiant heat power emitted from a surface is proportional to the fourth power of its absolute temperature. The law applies only to blackbodies, theoretical surfaces that absorb all incident heat radiation.

[#68] The critical radius is the insulation radius at which the resistance to heat flow is
Correct Answer

(B) Minimum

Explanation

Solution: It is the radius of insulation before heat transfer increases and after heat transfer decreases. The critical radius is the insulation radius at which the resistance to heat flow is Minimum

[#69] Unit of thermal diffusivity is
Correct Answer

(A) m 2 /hr

Explanation

Solution: Thermal diffusivity. In heat transfer analysis, thermal diffusivity is the thermal conductivity divided by density and specific heat capacity at constant pressure. It measures the rate of transfer of heat of a material from the hot end to the cold end. It has the SI derived unit of m 2 /hr.

[#70] Temperature of steam at around 540°C can be measured by
Correct Answer

(C) Thermocouple

Explanation

Solution: Thermocouple can easily sense temperature of 540°C or even upto 1200°C. For measuring any temperature above 1200°C a radiation pyrometer type thermometer is generally used because this type of temperature sensors is not required to be brought in touch with the object whose temperature to be measured.