Thermophysical Characterization of Cordyceps militaris in the Freeze-Drying Process: Focus on Primary Drying Stage

This paper presents a method for determining key thermophysical properties of Cordyceps militaris during the freeze-drying process, focusing on the variations in density, specific heat capacity, and thermal conductivity. In addition, the mass transfer characteristics of the dried region of Cordyceps militaris were investigated through the determination of the effective moisture diffusion coefficient. Experimental results revealed a significant reduction in bulk density, from 1020 kg/m3 to 277.08 kg/m3. Simultaneously, the specific heat capacity and thermal conductivity decreased from 2012 J/kg·K to 1850 J/kg·K, and from 1.073 W/m·K to 0.041 W/m·K, respectively. The effective moisture diffusion coefficient, determined based on the Knudsen diffusion mechanism, was found to be 0.00452 m2/s. These findings provide critical input parameters for modeling heat and mass transfer during freeze-drying and offer a scientific basis for the design and optimization of drying conditions for Cordyceps militaris.