Page 75 - Introduction to Transfer Phenomena in PEM Fuel Cells

64 Introduction to Transfer Phenomena in PEM Fuel Cells
This value of 83% is theoretical. The LCV is often used to calculate the
efficiency of the cell, because not only it has a high value but also it could be
compared to that of a heat engine whose efficiency is always calculated by
the LCV. In this context, the produced water is as a vapor; the yield
becomes:
228.74
=
η % 100× ≈ 94.5% [2.45]
241.98
For thermal engines, the efficiency is written as:

 T 
η= 100×  1− C  [2.46]
%
 T H   

Figure 2.2 shows the behavior of both yields with respect to temperature
[BOU 07].

Figure 2.2. Efficiency curve

The curve in Figure 2.2 shows that the theoretical efficiency of the fuel
cell is very high but, unlike thermal engines, it decreases when the
temperature increases.