Heat Transfer

In the earlier chapters of this book, we considered heat to be energy in transition, and there has been only one reference to the mechanisms that must exist for this type of energy transport to occur. The limitation that was found was from the second law of thermodynamics in the Clausius statement: “Heat cannot, of itself, pass from a lower temperature to a higher temperature.” Thus, for heat transfer to occur, we can state that a temperature difference must exist between the bodies, with heat owing from the body at the higher temperature to the body at the lower temperature. For the purposes of this book, we look at only steady-state heat transfer in the system being considered. The condition for steady state is that the temperatures in the system be independent of time, and as a consequence, the rate of heat transfer out of the system must equal the rate of heat transfer to the system.