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In this study, energy and exergy analyses of the closed‐cycle infrared (IR) convective walnut drying were performed. The effects of the combined heat transfer, product–source distance, and temperature–relative humidity (RH) control on the food quality of walnuts and performance were investigated. Experiments were conducted with and without an IR lamp. The temperature and RH of the drying air were set at 40°C and 20%, respectively. The distance between the product and the IR source was changed to 20 cm and 30 cm. The coefficient of performance values of the whole system changed between 1.56 and 2.34. Exergy efficiencies varied between 60.81% and 88.19% without IR and 72.73%–78.54% with IR. Energy and time savings increased by 14.7% and 26.1%, respectively, with using IR at a 20 cm distance compared with the convective system. The fatty acid composition of walnut samples and chemical properties of walnut samples such as total phenolic content, oil, ash, color, antioxidant activity, peroxide values, free fatty acid, conjugated trienes, conjugated dienes, saponification value, and iodine number parameters were analyzed. Food analysis results of all dried walnuts were in the acceptable range. As a result, energy and time savings were achieved with the desired food quality. Novelty impact statement: This application makes it possible to achieve the desired conditions with less energy. In this study, the effects of heat transfer mechanisms, the effect of using two mechanisms together, and the effects of the variables within each mechanism on the drying of walnuts were investigated. It has been observed that the addition of an infrared heat source with the right and suitable application shortens the drying time as well as saves energy. As a result of the food quality analysis, it was determined that all products dried without deteriorating the food quality. The closed‐cycle intermittent infrared convective drying system is recommended for industrial use. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]