The model consists of combining several features of heat transfer irreversibility recognized in the Bejan (1982) book, namely the bypass heat leak (Problem 2.2) and the two finite-size heat exchangers (Figure 5.14). In the simplest version of the model (Bejan, 1988a), Section 8.1, it is assumed as in Problem 2.2 that the heat leak proceeds from the heat source to the heat sink unattenuated. Section 8.2 improves the model by allowing the heat leak (the power plant insulation) to interact with the rest of the power plant (Bejan, 1995). In this way the thermodynamic performance can be optimized further, along the general course traced in the 1970s for thermal insulations (Chapter 6). With these models we continue to pursue the fundamental question considered first in Section 5.6: how to distribute a finite heat exchanger inventory over the temperature range spanned by the power plant.