Analysis of the suction effect on the mass transfer when using the heat and mass transfer analogy

The transport phenomenon between a fluid in movement and a wall is strongly affected by the permeability of the wall. The application of a correction factor standing for the transpiration effect will be required whenever a heat transfer model is based either on the use of heat, mass or momentum analogies or on the use of empirical correlations for the computation of the heat transfer coefficient. The suction factor commonly used when solving as a function of either mass or molar fractions is called the Bird suction factor. The validity of this factor rests on the hypothesis of the film theory or Couette flow. This paper reviews the Bird suction factor in laminar regime, extending the analysis to turbulent flow conditions and finding thereby that Bird's equation can overestimate the suction factor under turbulent condensation conditions in the gas phase. Finally, an alternative formulation for the suction factor under turbulent condensation conditions has been proposed and compared with Bird's original formulation. In doing this, both data and models developed by other authors and the UW-Madison test facility database have been used. The results show the suitability of the alternative formulation when calculating the condensation rate in turbulent natural circulation scenarios, whereas Bird's formulation seems to be more appropriate for laminar regimes. (C) 2009 Elsevier B.V. All rights reserved.