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.