Introduction to forms of heat transfer
The science of heat transfer is concerned with the estimation of the rate at which heat is transferred, the duration of heating or cooling for a certain heat duty and the area required to accomplish that duty.
There are three different forms of heat transfer : 1. conduction 2. convection 3. radiation
Conduction form of heat transfer
It is the heat transfer between two bodies or two parts of the same body through molecules which are more or less stationary. In liquids and gases conduction results from the transport of energy by molecular motion near the wall and in solids it takes place by a combination of lattice vibrations and electron transport. The law which determines this conduction heat transfer is called as Faraday's Law. This law states that the rate of heat flux is linearly proportional to temperature gradient.
Convection Form of Heat Transfer
It is the heat transfer that occurs because of the motion of a fluid past a heated surface - the faster the motion, the greater the heat transfer. The convection heat transfer is usually assumed to be proportional to the surface area in contact with the fluid and the difference in temperature of the surface and fluid. This is also called as Newton's law of convection. When a temperature difference produces a density difference which result in mass movement, this process is called as free or natural convection. When the mass motion of fluid is caused by an external device like a pump, compressor, blower or fan, the process is called the forced convention. Here the fluid is made to flow along the hot surface and heat is transferred from the wall to the fluid.
Radiation Form of Heat Transfer
It is the heat transfer which is the result of electromagnetic radiation emitted by a surface because of the temperature of the surface. This differs from other form of electromagnetic radiation such as radio, television, X-rays, Gamma rays which are not related to the temperature.The best example of this is the heat receiving from the sun. The laws which govern this type of heat transfer are:
a. Kirchhoff's law
b. Stefan's law
c. Stefan- Boltzmann's law
The science of heat transfer is concerned with the estimation of the rate at which heat is transferred, the duration of heating or cooling for a certain heat duty and the area required to accomplish that duty.
There are three different forms of heat transfer : 1. conduction 2. convection 3. radiation
Conduction form of heat transfer
It is the heat transfer between two bodies or two parts of the same body through molecules which are more or less stationary. In liquids and gases conduction results from the transport of energy by molecular motion near the wall and in solids it takes place by a combination of lattice vibrations and electron transport. The law which determines this conduction heat transfer is called as Faraday's Law. This law states that the rate of heat flux is linearly proportional to temperature gradient.
Convection Form of Heat Transfer
It is the heat transfer that occurs because of the motion of a fluid past a heated surface - the faster the motion, the greater the heat transfer. The convection heat transfer is usually assumed to be proportional to the surface area in contact with the fluid and the difference in temperature of the surface and fluid. This is also called as Newton's law of convection. When a temperature difference produces a density difference which result in mass movement, this process is called as free or natural convection. When the mass motion of fluid is caused by an external device like a pump, compressor, blower or fan, the process is called the forced convention. Here the fluid is made to flow along the hot surface and heat is transferred from the wall to the fluid.
Radiation Form of Heat Transfer
It is the heat transfer which is the result of electromagnetic radiation emitted by a surface because of the temperature of the surface. This differs from other form of electromagnetic radiation such as radio, television, X-rays, Gamma rays which are not related to the temperature.The best example of this is the heat receiving from the sun. The laws which govern this type of heat transfer are:
a. Kirchhoff's law
b. Stefan's law
c. Stefan- Boltzmann's law
