Natural Convective Heat Transfer Coefficients for Solar Dehydration of Chili

Abstract

Dried agricultural products are considered as economically important of Thailand. Most of dried agricultural products are still produced using natural sun drying method. Although, it is the cheapest method, dried products are usually contaminated by insects, birds and animals. In this research attempt has been made to evaluate the convective heat transfer coefficient during dehydration of chili in open sun drying conditions (natural convection). The convective heat transfer coefficient was correlated via the Nu-Ra relationship Nu = hCX/K = N(Ra)n. The values of the constants, N and n were obtained by linear regression analysis. The results showed that the natural convective heat transfer coefficients of red chili was 0.7199 W/m2-oC, when N and n were found to be 1.0011 and 0.0705, respectively, while the natural convective heat transfer coefficients was 0.9020 W/m2-oC, when N and n were found to be 1.0017 and 0.0871, respectively, for long red chili.