澳洲坚果热风干燥过程中果壳收缩特性

该文以澳洲坚果为对象,研究了热风干燥过程中果壳的收缩特性。利用试验方法获得了果壳在不同含水率、不同方向下的收缩曲线、线应变和湿线膨胀系数。并推导了果壳内部各单元层边界的收缩方程,通过收缩方程计算出任一含水率、任一单元层的外径和收缩量。结果显示:果壳的收缩在宽度向、种脐向、水平向存在差异,线应变为宽度向最小,其次为种脐向,水平向最大,且随含水率的减小而呈非线性增长趋势。计算数据还表明:果壳收缩量由内至外逐渐增大,收缩不均匀;且收缩量随含水率的降低呈非线性增长趋势。由收缩方程计算出最外单元层的外径值,与试验值进行比较,最大误差为5.83%,证明收缩方程的预测性较好。研究结果可为澳洲坚果深加工提供一定的参考。

Shrinkage characteristics of macadamia nuts shell during hot-air drying

The shrinkage characteristics of macadamia nuts shell were studied in this paper. The shrinkage curve, linear strain and linear moisture expansion coefficient of shell were obtained by experiments. The shrinkage equation to calculate the outer diameter and shrinkage of every element layer in different drying periods was established. The results show that the shrinkage of each direction is different. The linear strain in width direction is smallest, while the ones in horizontal direction are largest. Furthermore, the linear strain of shell increase with decrease of the moisture content. The external shrinkage is greater than the internal one. The shrinkage increases nonlinearly with decrease of the moisture content. The shrinkage equation was verified by comparison of outer diameters of macadamia nuts shell computed by shrinkage equation with experimental data, which maximum error was 5.83%. The results can provide a reference for processing of macadamia nuts.