ABSTRACT
We know that the temperature of a solid body subjected to a sudden change of environment takes some time to attain an equilibrium. For example, if the surface temperature of a system is altered, the temperature at each point in the system will also begin to change. The changes will continue till a steadystate temperature distribution is reached. Consider a hot metal billet that is removed from a furnace and exposed to a cool air stream. Energy is transferred by convection and radiation from the billet surface to its surroundings. Energy transfer by conduction also occurs from the interior of the metal to the surface, and the temperature of each point in the billet decreases until a steady-state condition is reached. Such time-dependent effects occur in many industrial heating and cooling processes.
