Resistance of accelerating tubes to pure air flow

On the other hand, Fig. 4.2 illustrates that the velocity of the gas flow in the accelerating tube, uQ, has an important influence on -Apac,a and such influence can also be predicted by Eq. (4.2). 

Using Eq. (4.2), the values for the friction coefficient Aa are obtained by regression of the experimental data, as shown in Fig. 4.3 and, for comparison, those obtained from Ref. [20] are also given in the same figure. As can be seen, with respect to the influence of the Reynolds number on the friction coefficient, both kinds of data exhibit the same tendency while the values obtained from Ref. [20] are higher systematically than those measured by about 50%. The reason for this is still unclear. By a linearized regression of the experimental data, we come to 

The power of 0.000118 in Eq. (4.20) implies that the effect of Rea on is very small, so that A.d can be considered to be independent of Re.d in the range of practical interest, and a constant of 0.0214 is taken for A.d. Since the pressure drop due to pure airflow passing through the accelerating tube occupies only a very small fraction of the total across the contactor while the values for A, obtained from the curves of versus Red given in Ref. [20] can also be used directly for calculation without significant error. 

---