Optimization of heat pump fruit dryers Original Research Article

The most important factors when examining the optimum conditions of heat pump fruit dryers (HPD) and for minimizing HPD cost are recycle air ratio, evaporator bypass air ratio (BP), airflow rates, and drying air temperature. Mathematical models of papaya and mango glacé drying using HPD are developed and validated experimentally. The optimum criterion is minimum annual total cost per unit of evaporating-water. The effects of initial moisture content, cubic size, and effective diffusion coefficient of products on the optimum conditions of HPD are also investigated. The results showed that the optimum conditions of both products are not similar, especially for the optimum airflow rate and evaporator BP. For sensitivity analysis, the annual total cost per unit of evaporating-water in a HPD is linearly proportional to both interest rate and electricity price, and decreased with increasing life-time. Finally, physical properties of the product significantly affect the optimum airflow rate and evaporator bypass air ratio.