Performance Effect and Experimental Analysis of Waste Heat Usage in a Heat Pump Dryer

Abstract

In this study, three different modes (system 1, system 2 and system 3) heat pump dryers have been designed, manufactured and stale bread slices have been dried at the different conditions. Stale breads sliced into 15 mm thickness were dried from initial dry basis moisture content 0.55 g(water) g(dry matter) (-1) to final moisture content at 0.09 g(water) g(dry matter) (-1) average 2.9 hours. Stale bread slices have been dried at 45 degrees C - 50 degrees C drying air temperatures and variable air velocities 0.2 m s(-1) - 0.7 m s(-1). Desired drying air temperature was obtained by using Proportional-Integral-Derivation (PID) controller. Also dried product surface temperature was controlled by controlling of compressor of heat pump. Six experiments were done at 45-50 degrees C drying air temperature (DAT) and 40-45 degrees C dried product surface temperature (DPST) set values. The best coefficent of performances of whole system (COP ws) were calculated as system 2 (45 degrees C DPST - 50 degrees C DAT) 5.28. The best efficient system is system 2 in all three systems. For system 2, heat of exhaust air was used as heat source of evaporator of heat pump. In this study, it is seen that heat pump systems with usage of heat of exhaust drying air are suitable and efficient applications.