A boundary layer solution applicable to a certain general type of mass transfer operations was developed by Baasel and Smith (1). When the solution was adapted to the systems of condensation of a vapor from noncondensing gases and absorption of a gas into a wetted wall column, the temperature and interfacial area could not be completely controlled. To overcome these difficulties, the rate of internal dissolution of a hollow cylinder of benzoic acid was experimentally measured and compared to the theoretically predicted values.

The ratios of the predicted rates to the observed rates fell, with the exception of two runs out of twenty nine, between 0.622 and 1.303. It was therefore concluded that the finite difference techniques used to obtain a mathematical solution were valid. However, it was observed that the assumption of unidirectional diffusion was possibly not valid. It was concluded that for systems in which the ratio of the total molar density of the fluid to the saturation concentration of the material being transferred was large, in the approximate range of 700 to 2,700, the boundary layer approach corresponded to the Leveque approximation of the classical Graetz solution for heat transfer for fluids with a parabolic velocity distribution.