Effects of decompression condition and temperature on drying rate in a hybrid heat pump decompression type dryer used for seafood drying

This study used a laboratory-scale prototype of a hybrid heat pump vacuum dryer to investigate its effect on the drying rate of seafood products. Although seafood products such as oysters and sea cucumbers are the target products, the initial experiments were carried out using wet sponges with the same moisture content as the oysters. The experiments were carried out for ambient pressure, two decompression pressures and three temperature conditions to study the moisture removal capability and power consumption of the dryer prototype. The moisture extraction and specific moisture extraction rate are calculated for each experiment. An optimum operating condition was obtained from the experimental analysis at −0.2 bar and 55 °C. The experiment is again carried out with oysters at the optimum condition. The time consumed for drying 100 kg of oysters decreased considerably in the optimum drying condition without degradation of its color or texture. Additionally, a CFD analysis is carried out to study the internal flow behavior inside the drying chamber. Large recirculation regions and vortices were observed in the return flow duct formed between the drying chamber and tray enclosure. Guide vanes are installed to suppress the flow instabilities. The optimum operating condition along with the stable flow is recommended for industrial-scale design.