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Effect of air recirculation and heat pump on mass transfer and energy parameters in drying of kiwifruit slices
- Mohammadi, Iman, Tabatabaekoloor, Reza, Motevali, Ali
- Energy 2019 v.170 pp. 149-158
- activation energy, air, diffusivity, drying, energy, heat, heat pumps, kiwifruit, mass transfer, models, specific energy, temperature
- The simultaneous transfer of mass and heat in the drying process has turned it into a complicated process with respect to mass transfer and moisture removal. A hot-air dryer equipped with an auxiliary heat pump and air recirculation system was used to dry kiwifruit slices at three different temperatures (45, 55 and 65 °C) to determine mass transfer and activation energy using two different models, namely Dincer-Dost and Crank's models. When the heat pump was on, compared with 45 °C and air recirculation rate (0%) at higher temperature (65 °C) and higher air recirculation rate (100%) the drying rate constant increased from 1.113 × 10−4 s−1 to 2.357 × 10−4 s−1and the effective moisture diffusion coefficient increased from 1.94 × 10−9 m2/s to 7.12 × 10−9 m2/s. When the heat pump was off, both parameters decreased with increasing recirculation (from 0 to 100%) and increased with rising the temperature (from 45 to 65 °C). When the heat pump was turn off and on, at 65 °C and 100% recirculation the change in the range of activation energy, convective mass transfer coefficient, specific energy consumption, drying efficiency and specific moisture extraction rate (SMER) were 14.04–20.39 kJ/mol, 4.12–8.55 × 10−7 m/s, 1.08–1.49 kWh/kg, 9.84–12.15% and 0.11–0.15 kg/kWh, respectively.