ABSTRACT
In Chapter 5, we continue our discussion of 1-D, steady-state, diffusive transport by considering systems where generation of our transported quantity within the system or on the boundaries of the system is allowed. Generation pervades the natural world, and virtually, every transport process we encounter will contain some sort of generation. The presence of generation in a system precludes our analysis of transport in that system in terms of a random walk or correlated random walk. Generation provides a force that perturbs the system and alters its course from its original random walk. This fact provides a roundabout means of de„ning what generation actually is. We de„ne generation a la Sherlock Holmes, by „rst eliminating everything we know not to be generation. Whatever remains must be the generation terms. To start, anything that «ows through the system boundaries is related to the In – Out terms not to the Gen terms. Any term involving a change in a state variable with time is related to the Acc term and also cannot be a Gen term. Finally, generation occurring within the boundaries of the system must be represented by terms that are in units of the transported quantity per unit volume (N/m3, W/m3, (mol/s)/m3, (kg/s)/m3, C/m3, etc.). Generation occurring on the boundaries of the system must be represented by terms with the units of the transported quantity per unit area (N/m2, W/m2, etc.). Generation can be positive or negative, and so we make no distinction between production and consumption. In the next few sections, we will catalog some of the more common forms generation terms take for each of our transport processes.
