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) [1].

The simplest illustration of this thermodynamic optimization principle is made possibly by the power plant model (ref. Bejan (1982) [2], 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

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

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