Improving exergetic performance parameters of a rotating-tray air dryer via a simple heat exchanger

In this study, exergy analysis was applied for a rotating-tray dryer equipped with a cross-flow plate heat exchanger during drying of apple slices. Three drying air temperatures and tray rotation speeds in the range of 50-80 degrees C and 0-12 rpm, respectively, were employed. Two drying air velocities in the range of 1-2 m/s were adjusted for each drying temperature and rotation speed with and without application of the heat exchanger. The experiments were conducted to assess the effects of the experimental variables on the exergetic performance parameters of the dryer. Also, the effect of drying conditions on the quality of dried apple slices was assessed by determining rehydration ratio, apparent density, shrinkage, and surface color. In general, the exergetic performance parameters of the dryer depended profoundly on the drying air temperature and velocity. Interestingly, the exergetic efficiency of drying process was significantly improved from a minimum value of 23.0% to a maximum value of 96.1% by using the heat exchanger. Furthermore, the incorporation of heat exchanger did not negatively affect the quality of dried product. Therefore, the strategy presented herein could be a promising approach for waste energy recovery in drying without any unfavorable change in the quality of dried product. (C) 2015 Elsevier Ltd. All rights reserved.