Analysis of drying of melon in a solar-heat recovery assisted infrared dryer Mustafa Aktas ß a , Seyfi S ßevik b,⇑ , Ali Amini c , Ataollah Khanlari d a Gazi University, Technology Faculty, Energy Systems Engineering, Teknikokullar, 06500 Ankara, Turkey b Hitit University, Vocational School of Technical Sciences, Electrical and Energy, 19169 Çorum, Turkey c Atatürk University, Natural and Applied Science Institute, 25240 Erzurum, Turkey d Gazi University, Natural and Applied Science Institute, 06500 Ankara, Turkey article info Article history: Received 21 September 2015 Received in revised form 8 March 2016 Accepted 23 August 2016 Keywords: Solar energy Infrared dryer Heat and mass transfer Melon drying abstract Infrared drying systems are popular in terms of high heat and mass transfer. By using an infrared dryer, it is possible to catch fast heating and short drying time in comparison to the other drying methods. But it consumes a high amount of energy. Therefore, a new type solar air collector (SAC) and air to air heat recovery unit were added to the infrared dryer to reduce specific energy consumption. The general aim of this study is to analyze heat and mass transfer characteristics of the dryer and three- dimensional (3-D) computational fluid dynamic (CFD) simulation and to investigate drying kinetics of melon slices. Experiments were performed at 50 °C and 60 °C melon’s surface temperature and 0.5 m/s air velocity. Melon slices were dried from 9 g water/g dry matter to 0.044 g water/g dry matter moisture content. The effective moisture diffusivity (D e ) values varied from 8.25  10 10 to 1.24  10 9 m 2 /s. The average mass transfer coefficient (h m ) values increase from 8.53  10 8 m/s at 50 °C to 1.47  10 7 m/s at 60 °C. Heat recovery unit has a key role in this system and it provides 23–28% of total input energy. Average solar air collector efficiency was calculated as 50.6%. Obtained theoretical and experimental results are in line with each other. This study shows the successful and efficient combination of solar energy, infrared energy and heat recovery in food processing. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Drying is a part of the post-harvest process and it encompasses a sequence of activities and operations that can be divided into two main categories as natural and technical. Solar energy as an energy source is used in both of these methods. In drying systems, energy needed for drying is key point for evaporating the amount of mois- ture from the product. Infrared drying as one of radiation type methods is preferred since heat and mass transfer rate are high. However, it has high energy consumption. Therefore, researchers are turning to the combined dryer. Many researchers have studied on the performance of single infrared dryer or combined one. They used different techniques such as infrared drying (Nowak and Lewicki, 2004; Tog ˘rul, 2006; Nasırog ˘lu and Kocabıyık, 2009), infra- red and convective drying (Kumar et al., 2006; Jaturonglumlert and Kiatsiriroat, 2010; Supmoon and Noomhorm, 2013; Yinqiang et al., 2014). They reported that infrared dryer has important advantages to maintain product quality and to increase the drying rate. Recent studies show that infrared technology has priority over hot air dry- ing (Raksakantong et al., 2011; Yinqiang et al., 2014). Combining convective and infrared drying enhance the drying rate (Yang et al., 2010; Supmoon and Noomhorm, 2013). Solar air collector (SAC) can be used in drying applications because it is feasible and economical in drying applications. They can be used directly, indirectly or in a combination mode (S ßevik, 2014). Also, some researchers have studied different type of solar collectors (Kavak Akpinar, 2010; S ßevik, 2014; Ramani et al., 2010). Dissa et al. (2016) designed a new solar air collector with a composite absorber. Its composite absorber composed of cou- pling a non-porous absorber made of a corrugated iron sheet and a porous absorber made of a mesh of aluminum. This air collector is appropriate to use in drying applications because it can rise the air temperature between 50 °C and 75 °C. Croitoru et al. (2016) analyzed and redesigned an unglazed transpired solar collector preheat the fresh air. They increased thermal efficiency by using a new geometry with innovative perforation. This collector used as dryer in some countries. Melon (Cucumis melo L.) belongs to the cucurbitaceae family. 100 g of melon contain 8 g carbohydrate with glucose and fructose being the most predominant sugars and also contain 1 g fiber, http://dx.doi.org/10.1016/j.solener.2016.08.036 0038-092X/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: mustafaaktas@gazi.edu.tr (M. Aktas ß), seyfisvk@hotmail.com (S. S ßevik), ali82amini@gmail.com (A. Amini), ata_khanlari@yahoo.com (A. Khanlari). Solar Energy 137 (2016) 500–515 Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener