HEAT AND MASS TRANSFER IN CONTINUOUS INFRARED DRYING OF A SPHERICAL BODY

Heat and mass transfer of a wet spherical body with an external gas medium under electromagnetic energy supply in the infrared frequency range is considered. The linear problem (constancy of process parameters) of infrared heating of a body at convective heat and mass exchange of its surface with external gas medium is formulated and analytically solved both for the general case of drying process and for drying in the first period. In formulating the heat conduction problem, it is assumed that the internal heat source caused by absorption of radiant energy is exponentially distributed over the thickness of the ball and that the phase transformations during moisture evaporation occur near the surface of the body. The drying intensity is described on the basis of the analytical solution of the linear (constant mass-conductivity coefficient) mass-conductivity (moisture diffusion) problem for the ball under the boundary condition of mass transfer of the third kind. The solutions of heating problems are obtained with respect to the local and average body volume temperature. On their basis, numerical modeling of the ball heating process with regard to its drying is carried out: the influence of the radiant flux density on the ball heating dynamics is shown. For the first period of drying it is shown that the partial solution of the problem obtained for this case allows to calculate the temperature of the body surface and further the intensity of drying in conditions of infrared energy supply (in which the temperature of the body surface is not equal to the temperature of the wet thermometer). To calculate the body surface temperature in this case, a method of successive approximations is proposed, in which the desired temperature is set first, and then it is calculated using the obtained solution and Antoine's equation expressing the dependence of saturated vapor pressure on temperature. For this case, numerical calculations have been performed, showing the performance of the mathematical model and illustrating the influence of additional (to convective) infrared energy supply on the drying intensity. A zonal piecewise stepwise method is recommended to account for the change of thermophysical characteristics during the process.