Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Tomato slices drying in a liquid desiccant-assisted solar dryer coupled with a photovoltaic-thermal regeneration system Mahdiyeh Dorouzi a , Hamid Mortezapour a, ⁎ , Hamid-Reza Akhavan b , Ahmad Ghazanfari Moghaddam a a Department of Mechanical Engineering of Biosystems, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran b Department of Food Science and Technology, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Iran ARTICLE INFO Keywords: Solar fraction Energy consumption Tomato slice Surface color ABSTRACT 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 kW h. The maximum specific moisture extraction rate was around 0.275 kg/kW h. It was also re- vealed that both solar heat fraction and ratio of solar electricity to consumed electricity increased with de- creasing the drying temperature. The designed dryer was able to supply the required electricity independent of grid with drying at the temperature of 60–65 °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 °C and activation RH of 23% was recommended for tomato slices drying in this dryer. 1. Introduction Drying is the most common preservation technique used to extend the shelf-life of fresh vegetables and fruits as well as to facilitate their transportation and storage (Serhat Turgut et al., in press). Although water removal using the different drying methods inhibits microbial growth and enzymatic activity and reduces chemical changes in the dried products, but it is the most energy consuming process in food industry (Horuz et al., 2017). In this way, different designs of solar air collectors have been developed to improve the useful thermal energy gain from the solar radiations. Chamoli and Thakur (2014) and Chamoli (2015) have investigated V-down perforated baffles on the absorber plate of the solar air collectors. Bhowmik and Amin (2017) tried to improve thermal efficiency of the flat plate solar collectors using re- flectors. Gawande et al. (2016) analyzed a solar air collector equipped with reverse L-shaped ribs and achieved a maximum Nusselt number enhancement of 282% over the smooth collector duct. Sawhney et al. (2017) experimentally investigated the performance characteristics of a solar collector with delta winglets. The study reported a maximum Nusselt number enhancement of 223% over the flat plate collector and a thermo-hydraulic performance of 2.09. In hot air dryers, a large percentage of thermal energy is wasted via the exhaust air. Therefore, recycling the exhaust air can improve energy efficiency of the system. In this regard, a number of researchers have applied different methods of heat recovery to the conventional hot air dryers. Sarsavadia (2007) achieved an energy saving of 70.7% by partially recycling of the exhaust air in a solar-assisted forced-convec- tion dryer. Also, Julklang and Golman (2015) presented a spray dryer with a waste heat recovery system through which the exhaust air was supplied to an air-to-air heat exchanger to preheat the drying air. Si- milar heat recovery system was used for convective-infrared drying of kiwifruit by Özdemir et al. (2017). In dryers with the air recycling system, the hot air, after passing over the products, is re-circulated to the dryer to be heated again for contribution in drying process. The major drawback of this type of the dryers is the gradual decrease in the moisture absorption potential of the circulating air due to increase in its RH. To overcome this problem, desiccant beds (Chramsa-ard et al., 2013; De Antonellis et al., 2012; Misha et al., 2015) and heat-pumps (Aktaş et al., 2017, 2016; Ceylan and Gürel, 2016; Chapchaimoh et al., 2016) are commonly used to https://doi.org/10.1016/j.solener.2018.01.025 Received 30 September 2017; Received in revised form 10 December 2017; Accepted 9 January 2018 ⁎ Corresponding author. E-mail address: h.mortezapour@uk.ac.ir (H. Mortezapour). Solar Energy 162 (2018) 364–371 0038-092X/ © 2018 Elsevier Ltd. All rights reserved. T