subject: Heat Transfer [print this page] Heat Transfer Heat Transfer
As we know that heat is a form of energy, and heat transfer takes place between any two systems due to temperature difference.
Energy transfer occurs from a system of higher temperature to a system of lower temperature according to the second law of thermodynamics without any work transfer. But heat transfer can take place from a system of lower temperature to a system of higher temperature by adding external work. The subject dealing with the rate of heat transfer is called the "heat transfer".
The subject of heat transfer is applied in the design of boilers, heat engines, refrigerators, cold storages, air conditioners etc.
Heat transfer occurs through conduction, Convection or Radiation which are explained as follows:
Conduction
In conduction heat transfer takes place due to transfer of thermal energy from one molecule to another molecule without appreciable motion of molecules within a solid matter. Thermal conductivity is not constant.
Convection
Molecules of liquid and gases have freedom of motion and in moving, they carry over their energy. Hence heat transfer, from one region to another in fluids is due to the motion of molecules, and such a mode of heat transfer is called "heat transfer by convection". There are two types of convection: free convection and forced convection.
Radiation
All substances ( solid, liquid and gases ) at all temperature levels emit Thermal energy in the form of electromagnetic waves and absorb similar energy emerging from the neighboring substances. This kind of heat transfer is by "thermal radiation".
