The influence of the Henry number on the conjugate mass transfer from a sphere - I. Physical mass transfer

Unsteady conjugate mass transfer between a sphere and a surrounding fluid f low has been analysed. Two sphere models, the sphere with rigid interface a nd the sphere with mobile interface and internal circulation, have been stu died. Creeping flow is assumed. The mass balance equations were solved nume rically by the ADI finite difference method. The influence of the parameter s that characterize the coupling features of the conjugate mass transfer, d iffusivity ratio (Phi (D)) and Henry number (H) (0.01 less than or equal to H (Phi (D)) less than or equal to 100), is studied at intermediate Pe numb ers. The occurrence and evolution of mass wake phenomenon is analysed. In c ontradiction with the assumptions practiced in classical theories of interf ace mass transfer, the results obtained in this work show that the Henry nu mber and the diffusivity ratio have a significant and distinct influence on the values of both overall and fractional (internal and external) Sh numbe rs. Using the additivity relation as an interpolation formula between two a symptotic solutions does not lead to accurate approximations of the numeric al results on the entire domain of variation of H and Phi (D). An analogy b etween conjugate heat and mass transfer was established.