Modes of Heat Transfer:- There are three basic modes of heat transfer; Conduction, Convection, and Radiation.

 modes of heat transfer

1. Conduction

It is a model that requires a material medium for the transfer of heat. The material medium is called a body and it could be a Solid or a Liquid or a Gas.

In Solids, if the temperature of a certain portion of the body is increased by transfer of heat then it means the internal energy of that portion of the body has increased. The molecules which are present at that location of the body vibrate to and fro and in the process they will interact and collide with neighboring molecules thus transferring energy in the process. The solids also contain free electrons, these free electrons are also responsible for the conduction of heat as they move from their location to elsewhere, get diffused, and collide with other free electrons.

The distance between the molecules in Liquids and Gases is larger as compared to solids. For conduction to happen the activity of molecules in liquids and gases is such that they donâ€™t move very far from their initial positions. Due to the large distances between molecules, the extent of conduction is relatively small as compared to solids.

The rate of heat conduction through a medium depends on the geometry of the body, temperature differential within the body, and the type of material medium itself.

2. Convection

This mode also requires a material medium for heat transfer. It results due to the bulk movement of the molecules of the medium from one part of the body to the other part due to the existence of a temperature difference between those two portions of the body. Convection occurs in Fluids.

Whenever convection takes place there is always a solid object or a solid surface in contact with the fluid or immersed in the fluid. The solid object usually transfers heat and causes the fluid to move. When there is no bulk motion in fluid the heat transfer occurs by mode of conduction. For convection to happen there should be an appreciable bulk motion in the fluid.

Convection is called Forced Convection if the fluid is forced to flow over the solid or around the solid by external means such as fans, pumps, or blowers. Convection is called Natural Convection or Free Convection if the fluid motion is caused by Buoyancy forces that are induced by density differences due to variation of temperature in the fluid.