Design and experiment of a box-type heat-pump dryer with side-ventilating and rack moving

Abstract

A box-type hot-air convection dryer integrated with parallel vertical fans, multiple air deflectors, a rack moving mechanism, and an opening heat pump system was designed and used. The airflow distributions in the inlet surface of the air-inlet chamber and drying chamber under empty-loading conditions were measured and the results showed excellent uniformities. The air temperature distributions at the inlet and outlet surfaces of the drying chamber, wet basis moisture content of the materials, energy consumption, product loss rate, and processing capacity were measured and analyzed as well under the loading of longans, lychees, and shiitake mushrooms. The results indicated that the maximum temperature difference at air-inlet surface of drying chamber was 4 °C. The dehydration rate was fast, and the moisture content of the wet basis decreased slowly in the earlier half stage of drying. However, the dehydration rate was slow, and the moisture content decreased at an accelerated rate in the latter half stage of drying. The higher the initial moisture of the material, the more obvious the above phenomenon. Further, the moisture uniformity of dried products reached 90%, with no products of mildewing and obviously insufficient drying found, which would support technique for the drying of fruits and vegetables.