Performance Effect and Experimental Analysis of Waste Heat Usage ina Heat Pump Dryer

In this study, three different modes (system 1, system 2 and system 3) heat pump dryers have been designed, manufacturedand stale bread slices have been dried at the different conditions. Stale breads sliced into 15 mm thickness were driedfrom 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 2.9waterdry matterwaterdry matterhours. Stale bread slices have been dried at 45 °C – 50 °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 oC drying air temperature (DAT) and 40-45 oC dried product surface temperature (DPST) set values. Thebest coefficent of performances of whole system (COP) were calculated as system 2 (45 °C DPST - 50 °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 aresuitable and efficient applications.