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This paper proposes the design and optical evaluation of a solar dish collector with changeable structure using TracePro software with native conditions of Iran for solar dryers. The designed dish concentrator has a diameter of 1.5m. TracePro's goal is to design and evaluate complex optical systems. Modeling a parabolic concentrator in TracePro can be achieved using several methods. All segments of dish collectors are made of glass (perfect parabolic mirror with a reflection coefficient of 95%). In the ray-tracing simulations, the two cavity receiver model (cylindrical and semi-sphere) is added to study the influence of physical parameters of the cavity. The simulation result shows that semi-spherical receiver is better and it has got better optical performance. Thereby it is highly recommended for various types of solar dryers such as direct drying (solar box dryer), or indirect drying (solar cabinet dryer). هدیکچ : رازفا مرن زا هدفتسا اب ار ریغتم راتخاس اب یدیشروخ یباقشب روتکلک کی یکیتپا یزاس هیبش و یحارط هلاقم نیا TracePro طیراش یارب دیامن یم هئارا یدیشروخ یاه نک کشخ رد هدافتسا یارب ناریا یموب . هدش یسررب باقشب رطق 1.5 دشاب یم رتم . رازفا مرن فده TracePro لدم دشاب یم اهنآ یرون سزیلانآو یدیشروخ یاه هناماس یارب هدیچیپ یاه متسیس یکیتپا یزاس . یباقشب روتکلک یزاس لدم یارب ناوت یم یفلتخم یاهشور رازفا مرن رد TrcePro درک هدافتسا . یبایدر یوترپ رازفا مرن زا هدافتسا اب کیلوباراپ یباقشب روتکلک دحاو یرون یاه یزاس هیبش هلاقم نیا رد TracePro تسا هدش هئارا . دنا هدش هتخاس هشیش زا کیلوباراپ یباقشب روتکلک زا یکچوک یاه شخب ( باتزاب بیرض اب لماک کیلوباراپ هنیآ 95 ٪ ) . هدنریگ لدم ود ( یورک همین و یا هناوتسا ) تسا هدش هفاضا ییوترپ یبایدر یاه یزاس هیبش رد هرفح یکیزیف یاهرتماراپ ریثأت یسررب روظنم هب . دراد یرتهب یرون درکلمع و تسا رتهب یورک همین هدنریگ هکدشاب یم نیا زا یکاح هیبش هجیتن . یاه نک کشخ زا یفلتخم عاونا یارب بیترت نیدب میقتسم ندرک کشخ دننام یدیشروخ ( یدیشروخ هبعج نک کشخ ) میقتسمریغ ندرک کشخ ، ( یدیشروخ نیباک نک کشخ ) دوش یم هیصوت رایسب . INTRODUCTION As the primary source of energy, solar energy is one of the best alternatives to fossil fuels because it is green, it is environmentally-friendly and it can be used in systems requiring minimal maintenance and operating costs. Solar energy use is critical to tackle recent energy problems such as global warming, the fossil fuel depletion and high electricity prices (Stijepovic M.Z., Papadopoulos A.I. et al., 2017). The abundance is the key advantages of solar energy (Jamil and Akhtar, 2017) and possibility of direct heat conversion (Kasaeian A., Daneshazarian R. et al., 2017). The production of solar thermal energy can be carried out with concentrating technologies such as parabolic trough collectors, linear Fresnel reflectors, solar plates and solar towers (Kaushika N. and Reddy K., 2000). In tropical and semi-tropical areas, the use of solar energy for thermal applications such as cooking, heating and drying is well established (Bal L.M., Satya S. et al., 2010). In Iran, conventionally, open sun drying (OSD) is used to dry agricultural products. The disadvantage of OSD is the uncontrolled heat transfer to the product and slow drying rate. As a result, the quality of the products is very poor and they aren’t able to compete on the international market. 1 Hosseinzadeh J., Ph.D. Stud. Eng.; Mohhebi A., Lect. Ph.D. Eng.; Loni R., Lect. Ph.D. Vol. 59, No. 3 / 2019 INMATEH – 198 To improve the product quality, drying should be performed in controlled conditions in order to maintain a constant temperature and a low relative humidity. It can be done by means of hot air (produced either using electric energy or biomass), or by means of infrared radiation. Such methods, however, require a lot of investment and also consume a lot of energy. One of the cleanest and simplest options is to dry using renewable energy sources. Karthikeyan and Murugavelh have developed a solar tunnel dryer for turmeric drying integrated with a solar flat plate collector. They conducted drying kinetics experiments and found that the Verma model is best suited to represent the drying behaviour of turmeric (Karthikeyan A. and Murugavelh S., 2018). José Vásquez et al., proposed a novel solar dryer for agricultural products with thermal energy storage system. The dryer's mathematical model included three stages: a solar panel, a solar accumulator and a drying chamber (Vásquez J, Reyes R. et al., 2019). Kumar et al. modeled a greenhouse dryer with modifications to define temperature distribution with wind speed variability. They reported a better drying rate for forced circulation compared to natural convection in accordance with the available experimental results (Kumar R., Gupta V. et al. 2017). Compared to linear technologies, solar dishes have high concentration ratios and are therefore promising for high-temperature applications. In recent years, substantial theoretical and experimental work has been carried out on solar dish concentrators for a wide range of industrial applications (Reddy K. and Kumar N.S., 2009; Wang M. and Siddiqui K., 2010; Wu Xiao et al., 2010; Wu Xiao et al., 2010; Wu Z., Caliot C et al., 2010; Li Tang et al., 2011; Lovegrove K., Burgess G. et al., 2011). In solar collectors, the receiver plays the most important role in improving the efficiency of the solar system and it must be designed to result in high optical efficiency and low heat loss. In the literature, the shape and dimensions of the receivers have been investigated to achieve a design that absorbs as much solar energy as possible while having a low external area to reduce heat loss. In past years, a lot of research has centered on solar collectors as compact technologies that can generate heat at high temperatures and also different absorber shapes, such as conical, cylindrical and rectangular, have been investigated. Roux et al. designed a rectangular absorber for solar thermal Brayton cycle in which the air was used as working fluid. They suggested a method for determining temperatures of the receiver surface and performance of various cavity receiver (Le Roux W.G., Bello-Ochende T. et al. 2014). Thirunavukkarasu and Venkatachalam performed an experimental analysis on the thermal efficiency of the cavity receiver with specific aspect ratios. They found that the temperature of the receiver's surface was decreased by increasing the aspect ratio (Venkatachalam T. and Cheralathan M., 2019). Evangelos Bellos et al. investigated different cavity receivers (cylindrical, rectangular, spherical, conical and cylindrical-conical) under different operating temperature levels. They reported that cylindricalconical shape receiver has the best optical, thermal and exergy efficiency (Bellos E., Bousi E. et al., 2019). Song Yang et al. suggested a new model of a heat-pipe cavity receiver for a two-stage dish concentrator. They found that improved dish concentrator configuration shows superior performance compared to the conventional one, especially in terms of compact structure, flux and temperature distribution uniformity, and solar to thermal efficiency. Moreover they stated that there are fewer scale limitations such as weight and volume on the new receiver with overlapped configuration (Yang S., Wang J. et al., 2018). ZhouSi-Quan et al., created a three-dimensional model to investigate the spherical cavity receiver's optical and thermodynamic performance. They found that when the spherical receiver moves away either positively or negatively from the focal plane, the distribution of the radiation flux is more uniform (Si-Quan Z., Xin-Feng L. et al., 2019). Sara Soltani et al. experimentally and theoretically studied a helically baffled cylindrical cavity receiver and they investigated the effect of certain mathematical, structural and functional parameters on the thermal performance of the system. Their results showed that the optimal selection of the above parameters could improve the system's thermal performance by up to 65% (Soltani S., Bonyadi M. et al. 2019). Huang et al., suggested a novel method to optimize the system to provide maximum solar energy for net heat output under typical conditions for specific optical errors (Huang W., Huang F. et al. 2013). A revised hybrid computational approach was proposed by Li Zhang et al. to investigate the thermal performance of the steady-state three-dimensional molten salt cavity models. They found that when only the lengths of the back walls next to the side walls were raised, the thermal efficiency first decreased and then increased as the depth decreased (Zhang L., Fang J. et al., 2017). Huairui Li et al. suggested an experimental approach for predicting the performance of a solar concentrator with a cavity receiver. They found that a non-window cavity receiver is favoured if the optical error is less than 4 mrad and the ideal geometric concentration ratio is more than 3000 and if the optical error Vol. 59, No. 3 / 2019 INMATEH – 199 is larger than 4 mrad, a windowed cavity receiver with an optimal geometric concentration below 1200 is preferred (Li H, Huang W. et al. 2013). Steinfeld and Schubnell described a semi-empirical method for determining the optimum aperture size and the optimum operating temperature of a solar cavity receiver with maximum energy conversion efficiency (Steinfeld A. and Schubnell M., 1993). Wu et al. performed a three-dimensional numerical analysis to determine the cumulative heat loss from the cavity receiver under various inclinations of the receiver. Results showed that natural convection heat loss Nusselt number is sensitive to the tilt angle and aperture size, except at 90° tilt angle, no matter how other parameters change at this point, the natural convection heat loss Nusselt number always fluctuates in a small value (Wu S., Guo et al., 2014). Qiu et al., studied numerically and experimentally a cavity receiver dish collector. They found that the cavity receiver's performance is better with up-flows than d

inmateh - agricultural engineering

OPTICAL SIMULATION OF A SOLAR PARABOLIC COLLECTOR AND CAVITY RECEIVERS USING RAY-TRACING SOFTWARE TRACEPRO WITH NATIVE CONDITIONS OF IRAN FOR SOLAR DRYERS