Investigating Some Quality and Thermodynamic Parameters of Kiwifruit Thin Layer Drying in an Air Recycling Dryer Equipped with Heat Pump

Drying reduces microbial activity, increases storage time, and facilitates packaging, transportation and storage of crops by reducing weight and volume of materials. Quality indices and thermodynamic parameters are as important cases in drying food and agricultural crops. The aim of this research is investigating the effects of air recycling and heat pump on quality indices (color changes, water rehydration and pH) and thermodynamic parameters (thermal efficiency, temperature, specific power consumption, drying coefficient and convection efficiency) of kiwifruit drying. In this research, three levels of recycling (0, 50% and 100%), three drying temperatures (45, 55 and 65ºC) and two levels with and without using a heat pump were used. Results showed that by increasing recycling from 0 to 50% color changes and pH increased and from 50% to 100% both them reduced. The maximum rehydration was related to 100% recycling with heat pump. The highest temperature and specific power consumption were 73.37 and 83.57 Mj.kg-1, respectively at 45 ºC, 0% recycling and heat pump off. The lowest rate of these two parameters were 14.15 and 27.01 Mj.kg-1at 65 ºC, recycling 100% and heat pump on. Also, results showed that drying coefficient, heat efficiency and convective had an increasing trend by using heat pump and increasing air temperature and recycling.