满晓兰 李龙 张宏 张永成 兰海鹏

摘要： 为了揭示热风干燥过程中核桃异质结构的水分传递特性，本研究在43 ℃热风干燥条件下，对核桃单层干燥过程中果壳、果仁及核桃的干燥特性与有效水分扩散系数进行研究。试验结果表明，果壳、果仁及核桃的干燥特性规律大致相似，干燥过程主要发生在降速干燥阶段，且没有明显恒速干燥阶段，核桃在干燥过程表现出显著的非稳态性与异质性，果壳、果仁及核桃的有效水分扩散系数与干基含水率符合三阶-多项式关系，并同时测得核桃的平均有效水分扩散系数为果壳的1.01倍和果仁的1.41倍;模型4 适合用于预测果壳、果仁及核桃43 ℃热风干燥过程中水分比的变化规律。研究结果为明晰核桃干燥过程中的水分传递机制提供了理论依据。

关键词： 核桃;热风干燥;有效水分扩散系数;数学模型

中图分类号： TS255.6 文献标识码： A 文章编号： 1000-4440（2021）03-0731-08

Hot-air drying characteristics and mathematical model of walnut based on structural heterogeneity

MAN Xiao-lan1，2， LI Long1，2， ZHANG Hong1，2， ZHANG Yong-cheng1，2， LAN Hai-peng1，2

（1.College of Mechanical and Electrical Engineering， Tarim University， Alar 843300，China;2.Key Laboratory of Modern Agricultural Engineering in Colleges and Universities of Xinjiang Uygur Autonomous Region， Alar 843300， China）

Abstract： To reveal the properties of water transfer in the heterogeneous structure of walnut during hot-air drying， the drying characteristics and effective water diffusion coefficient of the walnut shell， walnut kernel and whole walnut during single-layer drying process under hot-air drying condition of 43 ℃ were studied. The results showed that， the drying characteristics of the walnut shell， walnut kernel and whole walnut were approximately similar. The drying process mainly occurred in the speed-down drying stage， and there was no obvious drying stage with constant-speed. The walnuts showed significant instability and heterogeneity during the drying process. The effective water diffusion coefficient of the walnut shell， walnut kernel and whole walnut were in third-order polynomial relationship with water content of dry base. It was measured that the average effective water diffusion coefficient of the whole walnut was 1.01 times as large as the walnut shell and 1.41 times as large as the walnut kernel. Model four was suitable for predicting the change rule of moisture ratio of walnut shell， walnut kernel and whole walnut during drying process using 43 ℃ hot-air. The results provide theoretical basis for water transfer mechanism in the drying process of walnuts.

Key words： walnut;hot-air drying;effective water diffusion coefficient;mathematical model

核桃，是一種营养价值极高且很受欢迎的坚果[1] 。脱青皮鲜核桃含水率可达20%～45%，而安全贮藏含水率为8%，因此，干燥是核桃采后降低含水率、保持产品品质必不可少的技术过程[2-4] 。近年来，在实验室规模内研究了各种核桃高效干燥技术，如射频干燥[5] 、微波干燥[6-7] 、远红外干燥[8] 、热泵干燥[9-10] 、间歇烘箱干燥[11-12] 、组合干燥[5，13]等，但由于加工能力、工艺要求及运营成本等原因，核桃干燥处理仍主要采用43 ℃热风干燥[14-16] 。然而，核桃在热风干燥过程中，因其果壳密封且坚硬，果仁位于发达的分形木隔膜中，使干燥时间较长、干燥程度难以控制，导致大量能源浪费及果仁干燥不充分或焦化，严重制约了核桃干果品质和核桃产业的发展[17] 。……