Effect of shifting practices on performance of a fixed-bed convection dryer for longan

Publication Type

Contribution to conference

Authors

Gonzáles Azcárraga, J.C., M. Nagle, S. Phupaichitkun, B. Mahayothee, M. Haewsungcharern, S. Janjai, H. Leis und J. Müller

Year of publication

2007

Published in

Proceedings Tropentag 2007

Editor

University of Kassel

Conference name

Tropentag 2007: Utilisation of diversity in land use systems: Sustainable and organic approches to meet human needs

Conference location

Witzenhausen (Germany)

Conference date

09.10.2007

Longan (Dimocarpus longan Lour) is a seasonal fruit that is grown and marketed mostly in Asia. Fresh longan has high moisture content and cannot be stored extendedly. Various post-harvest treatments have been found to prolong edibility, but longan is still mainly exported in other forms. Drying reduces the longan weight by approximately 66% and adds value to the produHowever, dried longan must be undamaged and free of contaminants and have optimum color and moisture content on import. Overall, an adequate and consistent drying process is critical inachieving the standards of international markets. Thailand is currently the largest exporter of longan in the world, a third of which is dried. Production is concentrated in the north, where longan is a major component of the local economy and much of the harvest is dried for exporThe most common dryer for longan in this region is the Taiwan-type fixed bed convection dryerwhich is used for the bulk drying of unpeeled longan. However, it has been observed that the present drying procedures don’t allow for uniform quality and techniques used to remediate thare labor-intensive and damage the product. So far, little research has characterized the shifting routine used in longan drying or suggested improvements.
Experiments were conducted in Thailand using different shifting routines compared to the conventional. Drying conditions and product quality were monitored. Results showed that avelocity and temperature distributions were heterogeneous, but patterns did not correspond. Astemperature is highly influential in determining final color and moisture content of the fruits, product quality was affected. Only samples in the center positions and the side opposite the airinlet did not show significant differences when compared to a standard sample. Increased relativhumidity and convective cooling of drying air caused condensation to form on top of the bulk. It was observed that one shifting scheme was superior to the others. In order to obtain a more uniform product in the Taiwan type dryer, the main issues are to create homogeneous distributions of air and temperature in the bulk and prevent condensation.