Heat transfer or flow of heat occurs when the thermal energy of a hot surface or object is transferred or flows to a cold surface or object. For example, the heat emitted by flames is transferred to cooler objects that are near to it. This occurs mainly because the kinetic energy of the hot object is transferred to the second object increasing its temperature usually until both objects or systems are in equilibrium. This is a natural process and therefore in most cases, heat flows from hot to cold rather than from cold to hot which only occurs in artificial systems such as refrigerators.
