The most common baffle cut is about 25 percent of the diameter. This means that the height of the baffle window is 25 percent of the shell diameter. Figure 6-3 shows the effects in the shell fluid streamlines corresponding to different baffle cuts. For low baffle cuts (Fig. 6-3a), the velocity of the fluid at the window is high, with further reconversion in pressure with high turbulence and eddy formation. A large amount of
the fluid energy is spent in the window area, where there are few tubes, resulting in an inefficient conversion of pressure drop in heat transfer. If, on the other hand, the baffle cut is high, there may be short circuits between the baffle tips, as shown in Fig. 6-3c, and there will be important zones of the fluid with low and erratic velocities and low heat transfer coefficients.6 The optimum seems to be in an intermediate situation
such as that illustrated in Fig. 6-3b.