New chimney dryer design results in faster drying due to higher air speeds

This journal article was published in Acta Horticulturae on June 30, 2018. The authors are Angelos Deltsidis, Amrita Mukherjee, Mohd Islam, Lizanne Wheeler, Elizabeth Mitcham, James Thompson, and Michael Reid.

Abstract

Food losses in the developing world range between 30 and 50%, contributing to food insecurity and inefficient resource allocation. Many agricultural products, particularly fruit and vegetables, have production peaks when, despite high product quality, prices are typically low because supply is greater than demand. The oldest and most effective method of food preservation in resource poor environments is solar drying, which is often done in the open air where the product is exposed directly to the sun, but there is also the risk of contamination. Adding value through improved solar drying is a proven way to stabilize the product and extend postharvest life for consumption and marketing, diversify and increase income, and develop new markets. Many designs have been proposed for improved solar dryers, but few have been adopted, either because they provide little improvement in drying rates over open-air drying, or because they are too costly to use in the developing world. The most common improved solar dryer is the cabinet dryer. Although cabinet dryers are more effective than open air drying, they are inherently inefficient and can only handle relatively small quantities of product. We have designed a novel dryer that can be constructed inexpensively from local materials, has significantly higher airflow rates, and therefore greatly reduced drying times. A raised drying bed is covered with black plastic. Product on mesh drying trays is placed on the drying bed and covered with clear plastic. The plastic is connected to a chimney at one end of the drying bed. The heated air in the covered tunnel is drawn over the drying product by the draft up the chimney. The chimney dryer significantly reduced drying times in comparison to air drying or drying in a cabinet dryer. The chimney provides a measure of temperature control - as temperatures in the tunnel rise, air speed increases, moderating the temperature increase. The advantages of the dryer include a relatively high capacity, and a flexible design that can be modified to suit the needs of the product and the user.