[Rao, 3(7): July, 2014] ISSN: 2277-9655 Scientific Journal Impact Factor: 3.449 (ISRA), Impact Factor: 1.852 http: // www.ijesrt.com (C)International Journal of Engineering Sciences & Research Technology [425-437] IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Drying Characteristics of Red Chillies: Mathematical Modelling and Drying Experiments D.Kamalakar 1 , Dr.L.Nageswara Rao * 2 , P.Rohini Kumar 3 & Dr. M.Venkateswara Rao 4 1,3 Assistant Professor, Department of Chemical Engineering, R.V.R. & J.C.College of Engineering (A), Guntur-19, A.P, India 2 Associate Professor, Department of Chemical Engineering, R.V.R. & J.C.College of Engineering (A), Guntur-19, A.P, India 4 Professor, Department of Chemical Engineering, R.V.R. & J.C.College of Engineering (A), Guntur- 19,A.P, India lnrao1978@gmail.com Abstract The effects of drying conditions on the drying behaviour of Red Chillies (Capsicum annum) and the applicability of drying models to predict the drying curves of Red Chillies were studied. The experiments were conducted at different temperatures (90, 120, 140,160,180 and 200°C) with varying air velocities. Drying air temperature was found to be the main factor affecting the drying kinetics of Red Chillies; raising the drying temperature from 90°C to 200°C dramatically reduced the drying times. The effect of the relative humidity was lower than that of temperature; increasing the relative humidity resulted on longer drying times. Higher equilibrium moisture contents were obtained with high relative humidity’s and low temperatures. Furthermore, drying was observed only in the falling-rate period. Statistical analysis was carried out and comparison among drying models was made to select the best-fitted model for the drying curves. Keywords: Capsicum annum, air drying, mathematical models, kinetics. Introduction The Drying is one of the most common methods used to improve food stability, it is a complex process involving simultaneous coupled heat and mass transfer phenomena. However, the theoretical application of these phenomena to food products becomes difficult due to the complex structure and to the physical and chemical changes that occur during drying. Drying is one of the oldest methods of food preservation and it is a complex process. The temperature, drying time, moisture diffusivity and drying rate are vital parameters in the design of process like for instance drying, storage, aeration and ventilation, etc. Different conventional thermal treatments are used in the drying of biological products such as, hot-air drying, vacuum drying, sun-drying and freeze drying result in low drying rates in the falling rate period which leads to undesirable thermal degradation of the finished products [1, 2]. Drying is one of the most important unit operations in the food process engineering, and represents a feasible way in order to extend the shelf life of foods with high moisture contents, especially fruits and vegetables, by reducing their water content to an extension at which the microbial spoilage and undesirable reactions are minimized. Additionally, drying of foodstuffs is intended to improve product stability, decrease shipping weights and costs and minimize packaging requirements. Because drying is an energy intensive operation, a better understanding of the drying mechanisms is important to optimize both the quality of the product and the efficiency of the process. Several models have been formulated to describe the heat and mass transfer processes during fixed bed drying. These models include either simplified or rigorous models. In some products having a relatively high initial moisture content, an initial linear reduction of the average product moisture content as a function of time may be observed for a limited time, often known as a "constant drying rate period". Usually, in this period, it is surface moisture outside individual particles that is being removed. The drying rate during this period is dependent on the rate of heat