Experimental Performance Investigation of Double Pass Solar Air Heater with Baffles for Red Chilli Drying

Abstract

Drying is an important form of food preservation method used to remove the excess moisture content from products for long-term storage without compromising quality. Food preservation by solar drying has become a widespread practice in developing countries to overcome the drawbacks associated with traditional open air drying but developing cheap and energy-efficient solar dryers is still a challenge hence studying a way to improve the efficiency of solar dryers are becoming increasingly important. The main aim of this thesis is to design, develop and experimentally investigate the performance of solar dryer using double pass solar air heater (DPSAH) integrated with baffles and thermal energy storage inside the drying chamber by drying red chilli. The dryer is designed based on requirements to dry 5kg of red chilli and has a double pass solar air heater integrated with baffles to enhance the efficiency of the solar air heater, drying chamber with latent heat storage unit, and a blower. A comparative study of the performance of a DPSAH with and without baffles was conducted, and the result shows that integrating the baffles increases change in air temperature, thermal and exergy efficiency of the solar air heaters by an average value of 6 ℃, 7% and 0.53%, respectively. The effects of mass flow rate on the performance of the enhanced DPSAH is also studied and maximum change in air temperature of 35.8 ℃, 26.7 ℃ and 21.2 ℃ and an average thermal efficiency of 34.80%, 46.99%, and 56.97% were obtained for a mass flow rate of 0.0186 kg/s, 0.037 kg/s and 0.056 kg/s, respectively. The addition of PCM in the drying chamber reduces the air temperature fluctuation and the air is supplied at nearly constant temperature to the drying chamber. Red chilli was dried within 29 h and 56 h, reducing the moisture content from an initial value of 81% (w.b.) to a final value of 11.7% (w.b.) and 14.32%, in the solar dryer and open-air sun drying, respectively. The specific energy consumption of the dryer was 7.52 kWh per kilogram of moisture removed, while the electrical energy consumption of the blower was 7.4% of the total energy. The overall efficiency of the drying system was 8.75%. Finally, an economic analysis was carried out and the pay-back period of the dryer was found to be 2.04 years.