| Abstract | Drying experiments were conducted in a fluidized bed drier to study the moisture transport properties of potato and green mango of Namdokmai variety. Samples of four different shapes: bar, cylinder, semi-cylinder and prism were prepared having lengths of 10, 15 and 20 mm. Each test set consisted of eight samples and the drying was done at 50, 60 and 70 °C. Thirty six test runs were carried out for each product using the various combinations of shape, size and temperature. Diffusion coefficient, D, was determined for bar, slab and cylindrical shapes using the infinite series solutions for regular shaped bodies, based on solution of Fick's law. In case of green mango, the D value ranged between l.08x 10-9 and 3.32x 10-9 m2 /s for cylinders and between 4.90x 10-10 and l.18x 10-9 m2 /s for bars. The values ranged from 1.43x10- 9 - 3.745x10-9 m2 /s for cylindrical samples of potato, while for bars the range was from 7.55 x 10-10 - 1.395 x 10- 9 m2 /s. Increase in temperature led to an increase in D value, but change in length did not produce any statistically significant difference, other conditions being kept constant. Diffusion was higher when the volume to surface area ratio was lower, hence different ranges for different shapes. A model was developed, from simulated data, for determining D value of regular shapes. For irregular shapes, D value was estimated using two models, one developed from computer-simulated data of regular shapes and the other from experimental data of regular bodies. Simple and modified logarithmic drying models were also used to determine the drying constants, k and k' of all four shapes studied for potato and mango. Similar to the effect on diffusion coefficient, the drying constant increased with increase in temperature and was higher for a lower volume to surface area ratio. Length did not seem to have any significant effect on drying constant. Based on multiple regression, models were developed for relating drying constants of mango and potato, with temperature of drying, volume and surface area of samples. The drying constants from simple log model seemed to give better correlation as compared to modified log model. A lower correlation coefficient value obtained may be attributed to the fact that transport properties during drying depend on a number of parameters such as shrinkage which was not considered in the development of models. |