The flux of permeate in the separation by the direct-contact membrane
distillation process as a function of membrane characteristics and ope
rating conditions was considered. The expressions describing the vapor
transfer through a hydrophobic membrane, the temperature at the surfa
ce of the membrane, and changes of temperature and concentration solut
ions along the module in the countercurrent device were derived and pr
oposed. The theoretically predicted results show about 85-90% agreemen
t with the experimental data. The utility of equations in the separati
on technology was pointed out.