Heat transfer is the subject that predicts the energy transfer which may take place between material bodies as a result of a temperature difference. The science of heat transfer seeks not merely to explain how heat energy transfers, but also to predict the rate at which exchange will take place under certain specified conditions. Thermodynamics deals with systems in equilibrium. It may be used to predict the amount of energy required to change a system from one equilibrium state to another. It may not be used to predict how fast a change will take place since the system is not in equilibrium during the process. Heat transfer supplements the first and second laws of thermodynamics by providing additional experimental rules which may be used to establish energy transfer rates.