Heat Transfer Phenomena and their correct sequence

Boiling:

Boiling is a phase change phenomenon where a liquid changes to vapor. It occurs when the temperature of the liquid is raised to its boiling point. Boiling is a complex phenomenon that involves the transfer of heat from the heating surface to the liquid, the generation of bubbles, and the transport of these bubbles away from the surface. The heat transfer coefficient during boiling is relatively high.

Free convection in air:

Free convection is a process where heat is transferred through a fluid due to the natural motion of the fluid. In air, this occurs due to the temperature difference between the surface and the surrounding air. As the air near the surface heats up, it becomes less dense and rises, creating a natural flow of air. The heat transfer coefficient during free convection is relatively low.

Forced convection:

Forced convection is a process where heat is transferred through a fluid due to an external force, such as a pump or a fan. This process is more efficient than free convection because it can be controlled and directed. The heat transfer coefficient during forced convection is relatively high.

Conduction in air:

Conduction is a process where heat is transferred through a material due to a temperature gradient. In air, conduction is relatively low due to the low thermal conductivity of air.

Correct sequence in increasing order of heat transfer coefficient:

Based on the above phenomena, the correct sequence in increasing order of heat transfer coefficient is:

4. Conduction in air
2. Free convection in air
3. Forced convection
1. Boiling

The heat transfer coefficient during boiling is generally higher than the other three phenomena due to the high heat transfer rate during the phase change process. Conduction in air has the lowest heat transfer coefficient due to the low thermal conductivity of air. Free convection has a relatively low heat transfer coefficient because it relies on the natural motion of the fluid. Forced convection has a higher heat transfer coefficient because it is driven by an external force.