Heat always flows from a region of higher temperature to a region of lower temperature. It flows by conduction, convection, and radiation. Often we are interested in regulating the rate at which the thermal energy is transferred. We may want to keep an object at a temperature different from that of its surrounding for a long time by slowing down heat flow. Or we may want an object to cool down rapidly by increasing the rate at which thermal energy is transferred. In developing methods to do this effectively, we always have to consider the importance of the three different ways by which heat flows.