THE EFFECTS OF SHRINKAGE TO THIN LAYER DRYING CHARACTERISTICS OF ZEDOARY (Curcuma zedoaria, (Berg) Roscoe).

摘要

This objective of this study is to investigate the occurence of shrinkage during thin layer drying of zedoary (Curcuma zedoaria, (Berg) Roscoe) and evaluate its effect to the drying characteristics.Experiments were conducted using a laboratory scale thin-layer dryer equipped with data acquisition apparatus and machine vision system. The drying condition was controlled at a specific combination of temperature (50, 60, and 70°C) and relative humidity (20, 30, and 40%), with drying air flow rate at 0.78 – 0.95 m/s.Changes in area of the zedoary’s slices were measured continuously during the drying process, and analyzed with image processing. The results showed that drying of zedoary took place entirely in the falling rate period.Shrinkage, which was represented either by area ratio (A/A0) or by volume ratio (V/V0), indicated an almost linear relationship with moisture ratio (M/M0) of the product.total percentage of area reduction during the drying process was in the range of 67-85%, and volume reduction was in the range of 81-94%.However, it was found that drying air temperature and relative humidity had no significant effect to the shrinkage occurrence. The experiments also showed that the zedoary slice bent more at higher drying temperature (70 °C) compared to the lower temperature (50 and 60 °C). This study also evaluate the effect of shrinkage to the effective diffusivity.