Eco-Thermal analysis and response surface optimization of the drying rate of potato slices in a mix-mode solar dryer

Onyenwigwi D.I, M.C. Ndukwu, F.I. Abam, Ibeh Mathew, Ugwu Elijah, Hongwei Wu, Dirioha Cyprian, Lyes Bennamoun

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Abstract

This research aims to establish the interconnectivity between mix-mode solar dryer designs with carbon and energy cost mitigation using different energy scenarios and study the drying kinetics to obtain the optimal drying rates for drying blanched potato slices. This will help the policy makers in the establishment of design standard for solar dryer fabricators and also assist them in making the right choice for carbon emission management for environmental sustainability and determining the end point of drying potato slices for energy conservation. Hence, a mix–mode solar dryer was deployed with sun-drying using blanched potato as a case study. The potato slices were spread on the drying tray to form a thin layer. Mass loss data and temperature and relative humidity data were recorded at 1 h intervals until the desired moisture content was achieved. The dryer utilized 4.562 M J to dry the potato slices from 64% w.b initial moisture content to 7.56% w.b final moisture content. The percentage of the energy utilization ratio (EUR) ranged from 4.19 to 82.68% with an average value of 39.46%, while the thermal efficiency of the solar dry varied from 0.6 to 34% with an average value of 17%. The dryer can save from $74.22 to $741.22 per year at a 10 to 100% rate of usage with an indicative payback period of 0.17–1.64 years at the same rate of usage. The decarbonization potential of the solar dryer was high when compared to coal, diesel or grid electricity-powered dryers as an energy case scenario with the values ranging from 2.9 to 237.71 tonnes of CO 2 per year with earned carbon credit ranging from $41.98 to $ 3446.85 per year. Blanching time affected the drying rate and effective moisture diffusivity of the potato slices with effective moisture diffusivity varying from 6.35 × 10 −11 to 7.07 × 10 −10m 2/s for sun-dried potato slices and 9.86 × 10 −11 to 1.24 × 10 −9m 2/s for solar drying potato slices. Using the solar dryer reduced the drying time by 25.81 to 34.48% compared to open sun drying. The optimum drying rate for the solar-dried untreated potato slices was 0.0239665 kg/h at a collector temperature of 40.93 °C and thermal efficiency of 17.30%, while blanching for 3, 6 and 9 min gave optimum drying rate of 0.0177959 kg/h, collector temperature (T) of 40.9 °C and thermal efficiency(η) of 17.30% for the three pre-treatments.

Keywords

  • Blanching
  • Decarbonization
  • Drying rate
  • Energy efficiency
  • Optimization

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