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In order to optimize the pitaya heat pump drying process and improve the quality of dried products, the effects of drying temperature, slice thickness and relative humidity on heat pump drying characteristics and the volume ratio of pitaya were studied. The optimal shrinkage dynamic model was determined to predict the volume variation law under different heat pump drying conditions. The results demonstrated that the drying rate increased with the increase of drying temperature, the decrease of slice thickness and relative humidity. The drying temperature had the greatest effect on it while the slice thickness had the least. The volume ratio decreased with the increase of drying temperature and the decrease of slice thickness and relative humidity. Comparing and analyzing the five thin-layer drying models, the Quadratic model was determined as the most accurate to describe the volume ratio law in the pitaya heat pump drying process. The average error of the calculated value was 5.01% compared with the test value. Under the heat pump drying conditions described in this paper, the contraction activation energy of the pitaya was calculated to be 27.185 kJ/mol by Arrhenius equation. Based on the volume shrinkage model, the process parameters of heat pump drying could be optimized and the dry products with more appropriate volume could be obtained. This study could provide technical support for the volume shrinkage law of pitaya in the heat pump drying process.

In order to improve the drying efficiency and quality of potato chips, and to control the shrinkage deformation during hot air drying, the effects of temperature (45, 55, 65, 75 ℃) and slice thickness (3, 5, 7, 9 mm) on the drying characteristic curve, effective moisture diffusivity and activation energy of potato chips were studied. The results showed that the drying rate would increase with the increase of the hot air temperature or the decrease of the slice thickness of potato chips. Within the scope of the study, the effective moisture diffusivity of potato chips was between the range of 5.02×10−10~11.53×10−10 m2/s. And its value would increase with the increase of the hot air temperature and/or the decrease of slice thickness. Besides, it was found that the Weibull distribution function could describe the reduction rate stage of drying and shrinkage dynamics model of potato chips. According to Arrhenius equation, the activation energy of drying and shrinkage of potato slices were 27.35 and 46.44 kJ/mol, respectively, indicating that the activation energy of drying was less than that of shrinkage of potato slices. This work provided theoretical basis and technical support for the prediction of moisture transfer and shrinkage deformation of potato chips during hot air drying.