Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener Experimental parametric study of a mixed-mode forced convection solar dryer equipped with a PV/T air collector M. Fterich a, ⁎ , H. Chouikhi a,b , H. Bentaher a , A. Maalej a a Laboratory of Electromechanical Systems (LASEM), National Engineering School of Sfax (ENIS), B.P. 1173, Road Soukra km 3.5, 3038 Sfax, Tunisia b Mechanical Engineering Department, College of Engineering (CoE), King Faisal University (KFU), PO Box 380, Al-Ahsa 31982, Saudi Arabia ARTICLE INFO Keywords: Solar mixed dryer PV/T air collector Drying tomatoes Relative humidity ABSTRACT This paper presents an experiment and an examination of the performance of a mixed solar dryer with forced convection, which has been used to dry tomatoes. The studied system is composed of a photovoltaic-thermal air collector (PV/T) and drying room. Actually, the air flux enters in the aluminium tubular canals located under the PV panel and spreads simultaneously into an upper gap. Consequently, it provides heat exchange in both faces of the panel PV which helps to cool the photovoltaic cells and to carry the thermal energy to the drying room. What make this prototype important and original is that it provides an economic gain for farmers who previously used natural drying techniques. It grants them the chance to conserve the dried tomatoes for longer periods and to reduce the loss of crops. Furthermore, it provides more electrical energy supplies for the rural areas. Tomatoes were divided into two trays and dried with the forced convection mixed solar dryer. After that, a comparison was established with a naturally dried sample. Using the realized prototype, product moisture content dropped from 91.94 (%) to 22.32 (%) for tray 1 and to 28.9 (%) for tray 2, by against it dropped only to 30.15 (%) for open sun dryer. It is noted that the drying temperature is improved and the quality is enhanced. The experimental tests are carried out at the Laboratory of Electromechanical Systems in the National Engineering School of Sfax in Tunisia during September 2015. 1. Introduction The sun is the major source of alternative energy. It is in fact, pre- ferred to other energy sources because it is inexhaustible and non- polluting (Kavak Akpinar, 2010). Tunisia is situated in the Mediterra- nean region. It receives between 2860 and 3200 h of sun a year (Elkahdraoui et al., 2015). This important amount of energy can be used in many different ways among which drying agricultural products. One of the main problems in Tunisian rural regions is food conservation due to electricity scarcity. Farmers mainly use drying as solution to preserve several agro-food products such as tomatoes, chilly, medicinal plants, etc. They mainly use the direct exposition of these products to the sun and that may cause their quality degradation due to dust, UV, etc. Drying is one of the most important solutions of food preservation. It has been extensively researched in the past few years. Hence, this field takes considerable importance and there is also a need to improve and develop it to the highest extent possible. There are different designs and shapes of solar dryers for agri- cultural products (Sharma et al., 2009). They are classified according to the drying methods (El-Sebaii and Shalaby, 2012): (1) open sun drying (OSD), is the oldest method, (2) direct solar drying (DSD), (3) indirect solar drying (ISD), and (4) mixed solar drying (MSD). In the OSD method, the product to be dried is spread over thin layers and directly exposed to solar radiation on the ground or on the rack (Mustayen et al., 2014). The time required to reduce the moisture content of the product in open sun is long and the product can be deteriorated by rainfall, animals and insects (Kavak Akpinar et al., 2003). Conse- quently, the final quality and quantity of the dried products are very far from the international standards and therefore, they cannot compete in the international markets. Moreover, there is a need for an extensive manpower, and much physical space occupation (Basunia and Abe, 2001). These drawbacks of OSD can be solved by using solar drying systems like DSD, ISD and MSD. The efficiency of the solar dryer systems is higher than OSD (Navalea et al., 2015). Jain and Tiwari (2003); studied the thermal performance of open sun drying by developing a mathematical model. Their results indicated that this drying method was very slow and had high loss and low quality. Since the OSD caused many problems, researchers are seeking https://doi.org/10.1016/j.solener.2018.06.051 Received 31 January 2018; Received in revised form 5 May 2018; Accepted 12 June 2018 ⁎ Corresponding author. E-mail address: mohamed.ftirichh@gmail.com (M. Fterich). Solar Energy 171 (2018) 751–760 0038-092X/ © 2018 Elsevier Ltd. All rights reserved. T