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Mass Transfer

Mass transfer numbers (or coefficients), ki, are needed for each component i to apply of the mass transport equation presented in the Driving Force section.

For pipe geometries ki, enters into the Sherwood (Sh) number

Figure 3

dpipe is the pipe diameter, and Di is the diffusion coefficient, which in Flowasta is calculated from the Wilke-Chang (1955) correlation using the pressure-temperature correlation suggested by Rah and Eu (2002a and 2002b).

The Sh number can also be correlated through the dimensionless groups, Reynolds (Re), Schmidt (Sc) and Weber (We), as defined in e.g. Bird, Stewart and Lightfoot (2002).

Figure 4

Combining the two relations for Sh provides an expression for ki in terms of Re, Sc and We. The constants A through C are set to 0.5 (theoretical value for creeping flow around a sphere and for falling films (Bird, Steward and Lightfoot (2002)). The multiplier E is in version 1. of Flowasta set to an adjustable parameter having the default value of 1.0, but will later on be determined from flow loop data.

The applied expression for the mass transfer coefficient has been validated for stirred tank experiments carried out for methane nad ethane by Vysniauskas and Bishnoi (1983), Bishnoi (1985 and 1986) and Skovborg (1994).

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