Nghiên cứu sự biến đổi các tính chất nhiệt vật lý của cá thu fillet trong quá trình sấy thăng hoa

Abstract

This study investigates the variation in the thermophysical properties of mackerel fillets during the freezing and freeze-drying processes. The investigated properties include density, specific heat capacity, thermal conductivity, thermal diffusivity, enthalpy, and initial freezing point over a temperature range from −40,0 to 25,0°C. The combination of mathematical modeling and experimental measurements indicated that the initial freezing point of mackerel was approximately −1,1°C, while the fraction of frozen water reached about 0,93 at −40,0°C. During the freezing stage, the thermophysical properties changed significantly, particularly in the vicinity of the freezing point due to phase transition effects. Upon entering the freeze-drying stage, the formation of a porous dried layer substantially altered the material properties. The moisture content decreased from 74,86% to 7,00% after 14 h, accompanied by a reduction in density from 1087,00 to 371,56 kg/m³ and an increase in porosity to 0,726. The thermal conductivity and thermal diffusivity of the dried layer decreased to average values of approximately 0,052 W/m·K and 7,286×10⁻⁸ m²/s, respectively, indicating poor heat transfer capability of the dried porous structure. Meanwhile, the enthalpy of the dried layer varied within the range of 216,815–288,131 kJ/kg depending on material temperature and residual moisture conditions. The obtained results provide essential thermophysical data for modeling and optimization of the freeze-drying process of mackerel fillets.