5.1. DERIVATION OF BASIC EQUATION

5.1A. Introduction

In Chapter 4 we considered various heat-transfer systems in which the temperature at any given point and the heat flux were always constant over time, that is, in steady state. In the present chapter we will study processes in which the temperature at any given point in the system changes with time, that is, heat transfer is unsteady state or transient.

Before steady-state conditions can be reached in a process, some time must elapse after the heat-transfer process is initiated to allow the unsteady-state conditions to disappear. For example, in Section 4.2A we determined the heat flux through a wall at steady state. We did not consider the period during which one side of the wall was being ...

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