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 performed 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 reservoir and cell as a series of well-mixed tanks is proposed. Results obtained in experiments of dissolution of a planar surface of benzoic acid to a confined water jet that impinges onto the solid surface are used to apply the model developed. Sherwood numbers calculated for experiments performed with two different volumes of liquid in the reservoir are almost the same (discrepancy of 2 %) when the increase of solute concentration in the connecting tubes was taken in account.