Single-Phase Mass Transfer Inside or Outside Tubes

Single-Phase Mass Transfer Inside or Outside Tubes 

Film coefficients of mass transfer inside or outside tubes are important in membrane processes using tube-type or the so-called hollow fiber membranes. In the case where flow inside the tubes is turbulent, the dimensionless Equation 6.25a, b (analogous to Equation 5.8a, b for heat transfer) provide the film coefficients of mass transfer k [7] 

In case the flow is laminar. Equation 6.26a (analogous to Equation 5.9a for heat transfer) can be used  

In the case that the cross section of the channel is not circular, the equivalent diameter d defined by Equations 5.10 and 5.11 should be used in place of d- As with heat transfer, taking the wetted perimeter for mass transfer rather than the total wetted perimeter provides a larger value of the equivalent diameter and hence a lower value of the mass transfer coefficient. The equivalent diameter of the channel between two parallel plates or membranes is twice the distance between the plates or membranes, as noted in relation to Equation 5.11. 

In the case where the fluid flow outside the tubes is parallel to the tubes and laminar (as in some membrane devices), the film coefficient of mass transfer on the outer tube surface can be estimated using Equation 6.26a and the equivalent diameter as calculated with Equation 5.10. 

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