A. Allocation of finite heat exchanger inventory in a power plant

In this section we illustrate how the EGM method can be used to determine the optimal way in which a finite heat exchanger inventory (e.g. finite area) can be distributed among the heat exchangers of a power plant. In power plants, the optimization can be performed by maximizing the power output (the course chosen here), or by minimizing the total entropy generation rate Bejan (1996).

The simplest illustration of this thermodynamic optimization principle is made possibly by the power plant model (ref. Bejan (1982), p. 146) shown in Figure 1. The heat input \(\dot {Q}_{H}\) is fixed,i.e. the optimization is carried out on a per unit of fuel basis. The power plant operates irreversibly between the heat source temperature T_H and the ambient, T _L. The model is based on the assumption that the power plant irreversibility is due to the two heat transfer rates. The simplest heat exchanger models are

\[\label{eq1} \dot {Q}_{H} = U_{H}A_{H}(T_{H} - T_{HC})\tag{1}\]

\[\label{eq2} \dot {Q}_{L} = U_{L}A_{L}(T_{LC} - T_{L})\tag{2}\]