Two theoretical and two semi-empirical models were analyzed and the following conclusions were drawn from the investigation: ail the models assume temperature equilibrium; the Sherwood and the Newman models are distributed parameter ones, the Lewis and the Page models are lumped parameter ones; the Sherwood model neglects the external mass transfer resistance and can be used if Bi-M is above 100; the Newman model takes into account both mass transfer resistances but the surface emissivity was found not to be a constant; the Lewis model is the approximation of the Sherwood model, consequently it does not neglect the internal mass transfer resistance as generally stated in literature; the Lewis model can be applied if BiM is above 100 and Fo(M) is above 0.1, but there is no drying coefficient by which it can describe the whole drying process equally well; the Page model, because of the decreasing drying coefficient, can more closely approximate the Sherwood model and the experiments.