Infrared convective drying of walnut with energy-exergy perspective

Abstract

Walnut drying is a time-consuming and an energy-intensive process. To decrease energy consumption a new type drying system was designed. Effect of heat transfer mechanism and bi-directional penetration of the heat to the product were investigated according to energy-exergy analysis. In this study, walnuts were dried with a heat pump dryer with heat recovery (HP) and an infrared assisted heat pump dryer with heat recovery (IRAHP). Energy efficiencies varied between 0.29-7.94% and 0.28–6.54% in IRAHP and HP, respectively. Exergy efficiencies varied between 59.54 and 68.39% in IRAHP and 54.76–59.92% in HP. The average COP values of the heat pump were calculated as 4.10 in IRAHP and 3.97 in HP. The average COP values of the whole system were determined as 3.14 for IRAHP and 3.34 for HP. It was seen that IRAHP provides 10% energy saving and 20% time saving compared to HP. • Walnut was dried with convection and combined radiation & convection. • A vertical tray was used for bi-directional penetration of the heat to the product. • Energy and exergy analyses were performed for two heat transfer mechanism. • Drying time was reduced by 20% and energy consumption was reduced by 10%. • Drying kinetics of walnut and performance analysis of system were investigated.