Page 127 - Modelling in Transport Phenomena A Conceptual Approach

4.5. FLOW IN CIRCULAR PIPES 107

Comment: The increase in surface roughness increases the friction factor and
hence power consumption. On the other hand, the increase in surface roughness
causes an increase in the heat tmnsfer coefficient with a concomitant decrease in
pipe length.

4.5.3 Mass Transfer Correlations

Mass transfer in cylindrical tubes is encountered in a variety of operations such as
wetted wall columns, reverse osmosis, and cross-flow ultrafiltration. As in the case
of heat transfer, mass transfer correlations depend on whether the flow is laminar
or turbulent.

4.5.3.1 Laminar flow correlation
For laminar flow mass transfer in a circular tube with a constant wall concentration,
an analogous expression to Eq. (4.5-25) is given by
I Sh = 1.86 [ReSc (D/L)p3 I (4.5-31)

Equation (4.531) is valid for

[ReSc (D/L)]1’3 2 2
4.5.3.2 Turbulent flow correlations

Gilliland-Sherwood correlation
Gilliland and Sherwood (1934) correlated the experimental results obtained from
wetted wall columns in the form
I Sh = 0.023 I (4.532)

which is valid for
2,000 I Re 5 35,000
0.6 5 Sc 5 2.5
Linton-Sherwood correlation

The correlation proposed by Linton and Sherwood (1950) is given by
Sc1l3 1
I Sh = 0.023 (4.533)

Equation (4.5-33) is valid for
2,000 5 Re 5 70,000
0.6 5 Sc 5 2,500