In this section the cross flow of the shell-side fluid across the tube bank between two adjacent baffles or between a baffle and the adjacent tube-sheet is regarded as one pass. This usage should be distinguished from the more general one shell-side pass, which means that the fluid flows from one end of the shell to the other, with baffles treated as only a minor interruption of the basically one-dimensional flow. According to the present designation, the heat exchanger shown in Fig.1.6.1(1a) has seven shell-side passes corresponding to six segmental baffles. Figure 1 shows one of the heat exchanger cells. Leakage and bypass streams are ignored in this analysis. The following equations may be written in the steady state:

\[\label{eq1} \dot {Q}_c = \dot {C}_1 (T_1^{''}- T_1^{'} ) \tag{1}\]

\[\label{eq2} \dot {Q}_c = - \dot {C}_2 (T_2^{''} - T_2^{'} ) \tag{2}\]

\[\label{eq3} \dot {Q}_c = E_c \dot {C}_{\min} (T_2^{'} - T_1^{'}) \tag{3}\]

where E_c is the effectiveness of the cell, defined by