DESIGN, DEVELOPMENT AND MODELING OF A SOLAR ASSISTED PADDY DRYER FOR ON-FARM PROCESSING

Abstract

Drying is an important process used all over the world for the preservation of agricultural produce. Different types of dryers are available for drying purpose; however batch type dryers are the most favorite equipment used for drying purpose at farm level. These dryers are simple in design and construction, cheaper and easy to operate and offers possibility to be used under different environmental and climatic conditions. Un-even air distribution is a major drawback of batch type dryers. Over and under dried zones developed when air is introduce in the drying chamber, and this heterogeneity of the drying air reduces the dryer efficiency by increasing the drying time and energy consumption. To overcome this problem, a new batch type dryer with central air distribution model (along the length of the drying chamber) has been developed and evaluated in the Workshop of Farm Machinery and Power, University of Agriculture, Faisalabad. The dryer consists of drying chamber, air distribution model, flat plat solar air collector and blower. The prediction of air distribution pattern with in the drying chamber has analyzed using ANSYS-Fluent software. The simulations showed that air uniformly distributed within the drying chamber. The simulation results have been validated using experimental trials performed on freshly harvested paddy. A good distribution of air was found both numerically and experimentally within the drying chamber and this was due to the distinct feature (central air distribution model) of this dryer. The quality parameters of dryer have also been evaluated. Response surface methodology was used to determine the effect of independent variables like air velocity, depth of grain and desired moisture content on the head rice yield, whiteness and drying time of the dried paddy. It was observed that head rice yield and whiteness of the dried paddy decreases when moisture content decreases from 14 to 9%. Results showed that maximum head rice yield of 51.2% and maximum whiteness of 38% were achieved at moisture content of 14%. Drying time was increased when depth of grain and desired moisture content increased and vice versa. Quality of paddy dried with solar assisted dryer was also compared with conventional sun drying method. Results showed that the head rice yield and whiteness of the dried paddy with solar assisted paddy dryer was 14 and 13 times higher respectively, as compared with the open sun drying method. Solar assisted paddy dryer also cuts the 50% drying time as compared with the conventional open sun drying method. 100 kg of paddy can be dried in 10 hours to reduce its moisture to 14 % using solar assisted paddy dryers compared with 26 xiv hours in case of open sun drying method. Results of performance evaluation showed that the mean drying rate of the solar assisted paddy dryer was 0.87 kg/hr per 100 kg, whereas 0.46 kg/hr was the sun drying rate comparatively. Economic analysis was also performed to check the suitability of the dryer for our local farmers. Cost of drying with solar assisted paddy dryer was found to be 1.2 Rs/kg, whereas, the cost of drying with open sun drying method ranges 2 to 3 Rs/kg. Therefore, it could be concluded that using solar assisted paddy dryer, a good quality paddy can be dried at lower costs.