ABSTRACT
Heat transfer is the science of energy transfer due to a temperature difference. We know that thermodynamics deals with energy balance in a variety of physical situations. In other words, thermodynamics deals with the amount of heat transfer as a system undergoes a process from one equilibrium state to another. Heat transfer, on the other hand, deals with the rate at which heat is transferred as well as the temperature distribution within the system as a function of time. Basically thermodynamics deals with systems in equilibrium. It may be used to predict the amount of thermal energy required to change a system from one thermal equilibrium state to another. But it cannot predict how fast this change from one equilibrium state to another will take place, because the system is not in equilibrium during the process. For example, consider the cooling of a hot metallic bar placed in a water bath. Thermodynamics may be used to predict the final equilibrium temperature of the metallic bar-water combination. But thermodynamics cannot answer the question, how long the process would take to reach this equilibrium or what would be the temperature of the bar after a certain time interval before the equilibrium is attained? Whereas, the science of heat transfer can answer these questions. That is, heat transfer can predict the temperature of both the metal bar and the water as a function of time. In other words, unlike thermodynamics, heat transfer can answer the transient energy transfer questions such as the following:
• Can heat be supplied to a system without employing high temperature difference? • How long would it take to supply a certain amount of heat energy to the
system? • How much heat energy is transferred between two specified instances of time during a process? • What sort of temperature distribution exists in the system? • How large an area is necessary to transfer the desired heat energy?
