Thermo-mathematical modeling of parabolic trough collector _ Ibrahim Halil Yılmaz ⇑ , Mehmet Sait Söylemez 1 Department of Mechanical Engineering, University of Gaziantep, 27310 Gaziantep, Turkey article info Article history: Received 24 July 2014 Accepted 9 September 2014 Keywords: Parabolic trough collector Optical analysis Thermal analysis Thermo-mathematical modeling abstract A comprehensive thermo-mathematical analysis for parabolic trough solar collector (PTSC) was completely performed in this study. Based on actual system parameters, solar, optical and thermal mod- els were developed by using differential and non-linear algebraic correlations. Obtained solutions for the differential equations were integrated into Engineering Equation Solver (EES) and solved simultaneously with the all model equations. The developed model was compared to the experimental data of Sandia National Laboratory (SNL) and yielded satisfactory results showing a pretty good consistency with respect to the other model studies. Finally, the current model was applied to an existing PTSC module to analyze the performance characteristics under different operating conditions. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction In recent years parabolic trough solar collectors have gathered much more interest since they have remarkable advantages with respect to the stationary solar thermal technologies such as rela- tively high thermal performance and operating temperature. Such typical characteristics put them forward to be used in industrial process heat (IPH) and concentrating solar power (CSP) applica- tions. There are currently several commercial PTSCs for CSP plants that have been successfully tested in a temperature range of 300– 400 °C. A number of projects for solar electric generating systems (SEGS) are currently under development or construction world- wide. Up to date, there are 20 active parabolic trough power plants, and 27 parabolic trough power plants are being constructed [1]. New SEGS plants concentrate on substantial technological progress in vacuum technology, selective surfaces, manufacturing pro- cesses, and improved materials. Additionally; a number of works have been carried out for reducing the cost of energy using advanced thermal energy storage techniques (such as storage in concrete medium and thermocline tanks), and for overwhelming the limitations originated from the heat transfer fluid used. The heat transfer fluid is usually synthetic oil or molten salts. The syn- thetic oil is the most common solution in spite of its flammability, toxicity, and chemical instability characteristics, as well as its relatively low operating temperature (<400 °C). On the other hand, the molten salts allow increasing the maximum working temperature up to 550 °C however they require anti-freezing sys- tems due to their solidification temperature of about 250 °C. Recent works on transparent receivers combined with gas-based nanofluids are investigated for high temperature applications i.e. 650 °C to overcome the above-described limitations [2]. Although most of the PTSC applications focus on CSP, IPH applications have also been gaining momentum in the course of time. In 2007, there were about 90 number of operating IPH solar thermal plants worldwide (China and Japan not included) with a total capacity of about 25 MWth [3]. Approximately 45–65% of the total energy is used for direct application of industrial process heat in the prep- aration and treatment of goods. The thermal energy demand for IPH is below 300 °C, and 37.2% of the total demand is in the range of 92–204 °C. According to the ECOHEATCOOL study done in 32 countries, 27% of the thermal energy demand for IPH is between 100 and 400 °C [4]. Along with increasing IPH and CSP applications, necessarily have increased the researches on the PTSCs and their analyses. However, the thermal and/or mathematical analyses have been developed with either simplified approaches for a specified system [5,6] or more detailed ones. Simplified approaches save consider- able time of the analyst but they may not provide constantly to get consistent solutions particularly when the number of variables is high. On the contrary, more comprehensive and realistic analyses make possible to obtain more accurate results reflecting the nearest system characteristics of the PTSC. Thus making a detailed analysis shows the effective system parameters on the performance of the PTSC and provides us to apply it to the fronting studies relevant with thermal system design. Many researchers presented energy models on parabolic trough collectors. When the studies conducted on detailed modeling of http://dx.doi.org/10.1016/j.enconman.2014.09.031 0196-8904/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +90 342 317 2536; fax: +90 342 360 1104. E-mail addresses: iyilmaz@gantep.edu.tr ( _ I.H. Yılmaz), sait@gantep.edu.tr (M.S. Söylemez). 1 Tel.: +90 342 317 2504; fax: +90 342 360 1104. Energy Conversion and Management 88 (2014) 768–784 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman