Test: Basic Concepts of Heat Transfer - 1 - Mechanical Engineering MCQ

Hot coffee is separated from its cooler surroundings by a plastic flask, an air space, and a plastic cover. So all modes of heat transfer.

Let's analyze each statement in relation to heat transfer processes:

1. Heat transfer is directly linked with the transport of medium itself, i.e., there is actual motion of heated particles during convection.

   • This statement is correct. Convection involves the movement of fluid (liquid or gas) particles, which carry heat from one place to another.

2. The material medium between the heat source and receiver is not affected during the process of heat transmission by radiation.

   • This statement is correct. Radiation involves the transfer of energy through electromagnetic waves, and it does not require a material medium. The medium itself is not heated or otherwise affected by the radiation passing through it.

3. Heat transfer in liquids and gases is essentially due to radiation.

   • This statement is incorrect. While radiation can occur in liquids and gases, the primary modes of heat transfer in these states are convection and conduction. Radiation is more significant in the transfer of heat through a vacuum or transparent media.

4. In gases and liquids, conduction is due to the collisions and diffusion of the molecules during their random motion.

   • This statement is correct. Conduction in gases and liquids happens due to molecular collisions and diffusion, transferring kinetic energy from hotter regions to cooler ones.

Based on this analysis, the correct answer is:

1, 2 and 4

Thermal conductivity can be defined as the rate of heat transfer through a unit thickness of material per unit area per unit temperature difference.

Thermal insulation materials have low thermal conductivity. As cork is a porous body, the trapped air in voids inhibits heat flow.