Thermal Performance and Drying Efficiency of a Temperature- and Humidity-Controlled Chili Roasting Machine Equipped with a Thermosyphon Heat Exchanger

Abstract

This research aimed study investigated the thermal performance of a temperature- and humidity-controlled chili roasting machine equipped with a thermosyphon heat exchanger and to examine the effects of working fluid type and filling ratio on the heat transfer rate and product quality. Three working fluids, namely water, ethanol, and R134a refrigerant, were tested at filling ratios of 40%, 50%, and 60% of the evaporator volume under drying temperatures of 60, 80, and 100 °C. The results showed that the temperature, working fluid type, and filling ratio affected the heat transfer performance of the thermosyphon heat exchanger. The maximum heat transfer rates obtained using R134a refrigerant, ethanol, and water were 160.33, 154.02, and 135.02 W, respectively. The thermosyphon heat exchanger enabled waste heat to be recovered and reused in the process, resulting in a lower final moisture content of the product than that obtained without the heat exchanger under all experimental conditions. The lowest final moisture content, approximately 13% wet basis (wb), was obtained at a drying temperature of 100 °C and a filling ratio of 50%. In contrast, a drying temperature of 80 °C and a filling ratio of 50% provided the best preservation of the physical quality of the chili. The results demonstrate that integrating a thermosyphon heat exchanger with a temperature- and humidity-controlled chili roasting machine can improve heat transfer performance, recover and reuse waste heat, reduce the final moisture content of the product, and maintain the physical quality of dried chili. This approach provides a potential basis for the application of thermosyphon heat exchanger technology in industrial-scale food processing.