Transport mechanisms of moisture during air drying processes

A study was conducted on the transport mechanisms of Solanum tuberosum (potatoes; Pentland Dell variety) during drying. The experimental drying data indicated that the drying process consisted of no constant rate period and the drying occurred in one falling rate period In the case of potato slabs, and two falling rate periods in the case of potato cylinders. This behaviour strongly suggested an internal mass transfer-type drying with moisture diffusion as the controlling phenomenon. Hence, the effects of air temperature, velocity and sample geometry on the diffusion values were investigated. The analysis of the drying data showed that air temperature and sample thickness/radius had a pronounced effect on the diffusion values while the effect of air velocity was considered negligible in the range considered in this study. The diffusion values were found to increase considerably with the rise in temperature and decrease with the increase in sample radius/thickness. Also, the relationship between the diffusion coefficient and temperature was found to be of an Arrhenius type. Moreover, the thickness/radius dependence was of the type S proportional to L-n with n values found to be less than the theoretical value of 2 required for the satisfaction of Fick's second law of diffusion. The deviation between the experimental and the theoretical values was corrected by taking into consideration the existence of and external heat transfer resistance.