There is a number of methods known in the literature, which may be used to evaluate the thermal performance of heat exchangers. These methods relate different dimensionless parameters of the heat exchanger. The most common parameters are: correction factor F, number of transfer units NTU, heat capacity ratio R, heat exchanger effectiveness E and flow configuration. A detailed review is given in Section 97. The relationships between the parameters for shell-and-tube heat exchangers with different flow configurations (e.g. different number of tube-side passes) are presented in the different methods mostly in a graphical form. These graphical presentations differ from one another. However, the different methods present basically the same information and they have a common assumption: i.e. the influence of the shell-side baffle induced flow on the heat exchanger effectiveness is negligible. Because of that they are considered in this section as one category with the designation “conventional method”. A representative for the conventional method is the E-NTU method, or

\[\label{eq1} E=f (\mbox{NTU}, R,\,\mbox{flow configuration}) \tag{1}\]

The cell method differs basically from the conventional method in one point: It takes into consideration the influence of the shell-side baffle induced flow on the thermal performance of the heat exchanger. The following questions may arise in this context:

• - Are the differences between the conventional method and the cell method under all operating conditions significant?

• - If the differences between the conventional method and the cell method are significant only in a certain range, which range is that?

The purpose of this section is to answer the above mentioned questions and to give the designer some guide to the conditions under which the use of the cell method is justified. A comparison is made hereafter between the conventional method and the cell method under simplified conditions.