The transfer of energy in the form of heat occurs in many chemical and other types of processes. Heat transfer often occurs in combination with other separation processes, such as drying of lumber or foods, alcohol distillation, burning of fuel, and evaporation. The heat transfer occurs because of a temperature-difference driving force and heat flows from the high to the low-temperature region.
In Section 2.3 we derived an equation for a general property balance of momentum, thermal energy, or mass at unsteady state by writing Eq. (2.3-7). Writing a similar equation but specifically for heat transfer,
Assuming the rate of transfer ...