A simple model to obtain mass transfer coefficients from a soluble solid to a flowing fluid in closed recirculating systems

Dissolution experiments of a solid in a flowing liquid are usually performe d when correlations of mass transfer coefficients must be known for liquid- solid interfaces. Frequently, these experiments are carried out in a closed recirculation set-up where the liquid is pumped from a reservoir to a cell with the soluble solid and returns to the reservoir. In the present study, a model of the mass transfer considering the connecting tubes between rese rvoir and cell as a series of well-mixed tanks is proposed. Results obtaine d in experiments of dissolution of a planar surface of benzoic acid to a co nfined water jet that impinges onto the solid surface are used to apply the model developed. Sherwood numbers calculated for experiments performed wit h two different volumes of liquid in the reservoir are almost the same (dis crepancy of 2 %) when the increase of solute concentration in the connectin g tubes was taken in account. (C) 2001 Elsevier Science Ltd.