Tomato slices drying in a liquid desiccant-assisted solar dryer coupled with a photovoltaic-thermal regeneration system

摘要

A liquid desiccant-assisted solar dryer was developed for tomato slices drying. In this dryer a photovoltaic thermal solar collector was used to supply the required electrical energy and regenerate the desiccant. Experimental analysis of the dryer indicated that electrical energy needed for tomato drying was ranged from 0.65 to 1.4 kWh. The maximum specific moisture extraction rate was around 0.275 kg/kW h. It was also revealed that both solar heat fraction and ratio of solar electricity to consumed electricity increased with decreasing the drying temperature. The designed dryer was able to supply the required electricity independent of grid with drying at the temperature of 60-65 degrees C and regeneration's pump activation relative humidity (RH) of 28%. Color analysis of the dried tomato indicated that the increase in the temperature of the drying air increased the lightness (L*), and yellowness (b*) values, but the increase in the RH decreased the values of lightness and redness (a*). In addition, the hue angle values of dried tomatoes increased with increase of the activation RH and drying temperature, producing dry slices with slightly light red color. Based on the fair value of solar electricity generation and good color qualities of the final products, the temperature of 60 degrees C and activation RH of 23% was recommended for tomato slices drying in this dryer.