2.1 Shells. Seven types of shells, as classified by TEMA (1999), are shown in Fig. l.6; they are also shown in Fig. 10.3 with baffles. The E shell. the most common due to its low cost and relative simplicity, is used for single-phase shell fluid applications and for small condensers with low vapor volumes. Multiple passes on the tube side increase the heat transfer coefficient h (if corresponding more increased Ap is within allowed limits). ever. a multipass tube arrangement can reduce the exchanger effectiveness or F factor compared to that for a single-pass arrangement (due to some tube passes being in parallelflow if the increased NTU do not compensate for the parallel- flow effect. Two E shells in series (in overall count configuration) may be used to increase the exchanger effectiveness E.