Investigation of the moisture pumping mechanism of innovative vacuum-microwave-infrared hybrid dryer

Abstract

This paper investigates the moisture pumping mechanism of an innovative vacuum-microwave-infrared hybrid dryer for Starking type apples with 3 mm thickness. The parameters marking the end of the drying process were discussed in terms of drying chamber relative humidity, average apple slice temperature, and target mass. It was found that the sequential operation of infrared and microwave heating enhanced the moisture extraction ratio and drying rate until the critical moisture content of the apple slice was reached. Below the critical moisture content, microwave heating became the dominant mechanism for moisture transport. Among the thin-film models, the Midilli and Kucuk model showed the best fit. The average energy, thermal, and drying efficiencies were determined to be 3.537%, 29.511%, and 7.535%, respectively. Additionally, moisture extraction ratio, specific energy consumption, shrinkage ratio, and effective moisture content values were calculated as 0.069 kg/h, 83.916 MJ/kg, 71.23%, and 1.005x10⁻⁷ m²/s, respectively.