Experimental+Study+and+Analysis+on+Physical+Properties+of+Dried+Longan

Abstract

本研究的目的是在測定乾燥後帶殼龍眼之基本物性參數（包含重量、外型等）及量測乾燥後龍眼殼之力學特性，並藉此整理歸納其物理性質以提供乾燥龍眼機械剝殼之設計依據。測得整顆乾燥後帶殼龍眼平均重量約為2.87g，去殼後（含肉）籽重約占整顆重之80 %，純籽重約占整顆之40 %；完整乾燥龍眼之平均直徑介於21.34~23.47 mm，去殼後之平均直徑介於13.13~16.13 mm。除蒂部外，腰部及底部之殼厚度皆無顯著差異約0.43 mm。依據球度計算之結果與直徑、殼厚等物性，可將其簡化成厚度均勻的薄殼球體。以萬用物性試驗機，固定下壓速率為6mm/min之壓縮進行不同部位之壓縮試驗，藉由比較軸向與側向最大破裂力量及剛度值，發現軸向（蒂部）破裂力及側向（腰部）破裂力無顯著差異，最大破裂力量值界於40~60 N，平均剛度分別為18.87 N/mm 和17.19 N/mm。依據壓縮後型態發現，有裂紋產生者皆沿外力方向延伸，且裂紋出現的截面與壓縮方向一致。經由統計分析結果顯示，乾燥龍眼外殼之材料性質具有良好的等向性。藉由殼之破裂形式，推測其殼之含水率會造成材料性質的改變。進而分析在不同含水率下（乾燥、泡水1分鐘、泡水15分鐘、泡水30分鐘、泡水45分鐘），殼之破裂形態與含水率的關係。有利於龍眼殼之破裂形式的研究。The purpose of this research is to determine the basic physical parameters of the shell (includes weight, shape, and so on), and to measure the mechanical characteristics of dried longan. The measurements are summarized to provide data for dried longan which would help the machinery design of hulling. The measured average weight of the entire dried longan is about 2.87 grams, the meat-containing seed weighing about 80% of the whole weight; the pure seed, weighing 40% of the entire dried longan. The average diameter of the dried longan is between 21.34~23.38 mm wide. Besides its stem, waist and bottom shell thickness are about 0.43 mm and are in no significant difference of one another.Using material tester with a steady compression rate of 6mm/min to perform compression test on the dried longan, we observed that the axial and lateral fracture force makes no significant difference between one another to the dried longan (both between 40~60 N). And we found that the ones that produce cracks all crack along with the applied force and the cross-section of the crack align with the compression direction, producing cracks or hollow surface. We concluded that longan shell has good consistency in different directions and we are able to calculate its sphericity. Also, because of the minor difference between the average diameters and the average thickness of the shell, we can regard it as a uniformly distributed thin shell sphere. We did not observe a maximum rupture point for the hollow ones, therefore, we assume that the rupture point is associated with moisture content. We further analyze that under different moisture content, the relationship between the rupture type of the shell and moisture content can be used for researching the rupture type of the dried longan