Determination of heat transfer coefficients and drying kinetics of red chilli dried in a forced convection mixed mode solar dryer

Abstract

Solar drying is an efficient and economical way of drying of agricultural products as compared to any conventional dryers, and also in solar dryers, the products are dried under the hygienic condition in an enclosed chamber. The heat transfer coefficients play a significant role in drying operation. The temperature difference observed between the drying air and agriculture products varies with the heat transfer coefficient. Anexperimental investigation on the drying of red chilli was performed in a forced convection mixed-mode solar (FCMS) dryer integrated with an energy storage system. This paper focusses on studying the effect of moisture evaporation rate on the heat transfer coefficient of red chilli dried in the FCMS dryer. A correlation was obtained in the form of Nu = C(Rem Prn) from the experimental data with C = 1.146 and m = 0.296. The experimental drying data obtained are used to evaluate the convective heat transfer coefficient (CHTC) hc which are further used in the calculation of evaporative heat transfer coefficient (EHTC) he. The average values of CHTC and EHTC obtained were 1.63 and 49.7 W*m−2*C−1, respectively. The paper also focusses on selecting a suitable drying kinetic model for investigating the drying behaviour of red chilli in the FCMS dryer, which can be used in the design and optimization of the dryer.