134 Pressure drop

As the heat transfer coefficient increases, so does the pressure drop across the medium. The latter can sometimes be the limiting factor in application, because of limitations on the available pumping power. The pressure drop Ap has the general form

Ap/L = ^(1/a)[v^Pa/(1 - a)2"m]v2f~md-m (13.13)

Figure 13.3 The pressure drop per unit length of flow plotted against the exit velocity for Duocel foams, from which the power dissipated in pumping the fluid can be estimated

Present materials

Figure 13.4 The power dissipation plotted as a function of the relative density, and the dimensionless cell-edge diameter, d = d/L

Present materials

Figure 13.4 The power dissipation plotted as a function of the relative density, and the dimensionless cell-edge diameter, d = d/L

The exponent m and the coefficient f have been calibrated by experimental measurements. They are:

Some typical results are plotted in Figure 13.3. Pressure drops for other conditions can be predicted from equations (13.13) to (13.15), again with the proviso that the fluid flow scaling (13.5) retains its validity. The expected behavior is illustrated in Figure 13.4.

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