Effect of mass on convective mass transfer coefficient during open sun and greenhouse drying of onion flakes

In this paper, an open sun and greenhouse drying of onion flakes has been performed to study the effect of mass on convective mass transfer coefficient. Three sets of experiments with total quantity of onion as 300 g, 600 g, and 900 g were done. The onion was continuously dried for 33 h both in open sun and in the roof type even span greenhouse with floor area of 1.2 × 0.78 m2. Experiments were carried out during the months of October–December 2003 at IIT Delhi (28°35′N 72°12′E). Experiments were started at 8am. The data obtained from experimentation under open sun and greenhouse conditions have been used to determine values of the constant ‘C’ and exponent ‘n’ by regression analysis and, consequently, convective mass transfer coefficient. It is observed that there is a significant effect of mass on convective mass transfer coefficient for open as well as greenhouse drying. It is also observed that the rate of moisture evaporation in case of greenhouse drying is more than that in open sun drying during the off sunshine hours due to the stored energy inside the greenhouse. The experimental observations were analyzed in terms of percentage uncertainty also.