Cavity receivers are the most usual design in solar dish concentrators in order to achieve high thermal performance. The objective of this work is the investigation of five different cavity receivers ...under different operating temperature levels and the selection of the most appropriate designs. More specifically, the examined cavities have the following shapes: cylindrical, rectangular, spherical, conical and cylindrical-conical. All the cavities are optimized in order to determine the best design which maximizes the thermal efficiency of the solar collector. The optimization variables are different for every design and they regard the cavity length, the cone angle and the distance from the concentrator base. According to the results, the best design is the novel one with cylindrical-conical shape, while the conical and the spherical are the next choices. The worst design is rectangular, while the cylindrical is the fourth design in the performance sequence. For operation at 300 °C, the cylindrical-conical design is found to have 67.95% thermal efficiency, 35.73% exergy efficiency while the optical efficiency is 85.42%. The analysis is conducted with a developed model in SolidWorks Flow Simulation which is validated with literature experimental data. Keywords: Solar dish, Cavity receiver, Conical cavity, Cylindrical cavity, Thermal analysis, Optical analysis
•A solar dish collector with spiral coil absorber is investigated parametrically.•The analysis is performed with a validated thermal model with experimental results.•The optimum exergetically inlet ...temperature and flow rate are found for many cases.•For the main case, the maximum exergetic efficiency is found 21.42%.•The optimum inlet temperature and flow rate are 212.3 °C and 314.6 L/h respectively.
The objective of this work is to investigate parametrically an innovative solar dish collector with a spiral-coil absorber and to determine its optimum operating conditions. This solar dish collector is a lightweight and low-cost technology which can operate mainly at medium temperature levels. A thermal model is developed in Engineering Equation Solver and it is validated with the experimental results. Different parameters as the inlet temperature, the flow rate, the absorber emittance, the optical efficiency, the wind velocity and the ambient temperature are investigated parametrically in order to investigate their impact on the collector performance. The analysis is performed in energetic and exergetic terms and the emphasis is given in the quantity and the quality of the useful product. In the last part of this work, the optimum inlet temperature and flow rate, which maximize the collector exergetic performance, are determined for various design cases. According to the results, the optimum fluid temperature is 212.3 °C and the optimum flow rate is 314.6 L/h with the thermal and exergetic efficiencies to be 49.83% and 21.42% respectively. The results of this work can be utilized for the improvement of the examined physical model in order to establish it as a reliable solar technology.
The efficient conversion of solar radiation into heat at high temperature levels requires the use of concentrating solar collectors. The goal of this paper is to present the optical and the thermal ...analysis of a parabolic dish concentrator with a spiral coil receiver. The parabolic dish reflector consists of 11 curvilinear trapezoidal reflective petals constructed by PMMA with silvered mirror layer and has a diameter of 3.8 m, while its focal distance is 2.26m. This collector is designed with commercial software SolidWorks and simulated, optically and thermally in its Flow Simulation Studio. The optical analysis proved that the ideal position of the absorber is at 2.1m from the reflector in order to maximize the optical efficiency and to create a relative uniform heat flux over the absorber. In thermal part of the analysis, the energetic efficiency was calculated approximately 65%, while the exergetic efficiency is varied from 4% to 15% according to the water inlet temperature. Moreover, other important parameters as the heat flux and temperature distribution over the absorber are presented. The pressure drop of the absorber coil is calculated at 0.07bar, an acceptable value.
Solar energy exploitation is one of the most promising techniques for achieving the sustainability in the energy domain. The objective of this work is to investigate the daily performance of a solar ...dish collector under different operating temperature levels. A solar dish collector with 10.28 m2 aperture and a spiral coil absorber is investigated. The analysis is performed with a developed numerical model in engineering equation solver which has been validated with experimental results. The analysis proved that the daily thermal efficiency of the collector is ranged from 67.36% to 54.65% for inlet temperatures from 50?C to 350?C, respectively. On the other hand, the exergy efficiency presents an increasing rate of the inlet tem?perature and it is found to be ranged from 8.77% up to 31.07% for the respective temperatures. The daily exergy production of the collector can reach up to 26 kWh with a respective thermal production of 50 kWh for inlet temperature equal to 350?C. The results of this work can be exploited for the suitable evaluation of the solar dish collector on a daily basis.
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This paper presents a numerical and experimental study of a heating system that consists of hot air generator driven by biomass pellet burner to drive the NH3-water absorption heat pump made by ...Robur. The aim of this work is to fully test the system of hot air generator for thermal potential, by developing a thermal field, while driving the absorption heat pump of medium capacities for residential purposes, and to make model of predicting the efficiencies of heating comparing to conveyed heat in desorber of absorption heat pump. Numerical simulations of the hot air generator were performed in the commercial software ANSYS FLUENT and CFX. The experimental part was carried out in the laboratory of the Faculty of Mechanical Engineering in Nis, where the temperature and velocity measurements were obtained and compared to numerical results. Results were obtained for mass air-flow through the hot air generator and desorber of 0.17 and 0.2552 kg/s, pellet burner power of 15 kW, 18 kW, 21 kW, 24 kW, 27 kW, and 30 kW, with air inlet temperature in desorber of around 89-140?C. The heating efficiency of the absorption heat pump goes from 1.01 to 1.37. The heat loss over the surfaces of hot air generator goes from 0.6-0.9 kW depending on ambient air and surface temperatures. The system has the potential to be applied in low temperature heating and the spare heat from combustion products and residual hot air can be used for different purposes.
The use of solar dish thermal collectors is a promising choice for designing
sustainable energy systems. The use of nanofluids is a new way for enhancing
the thermal performance of solar collectors ...because of their improved thermal
properties. The objective of this study is to investigate the use of mono and
hybrid nanofluids in a solar dish collector in order to determine which kind
of nanofluids leads to higher performance enhancements. The analysis is
conducted with a developed thermal model in Engineering Equation Solver and
the collector is studied thermally and exergetically. The examined hybrid
nanofluid has as base fluid syltherm 800 with 1% Cu and 1% TiO2. Moreover,
the examined mono nanofluids are the syltherm 800 with 2% Cu and syltherm 800
with 2% TiO2. The investigated solar dish collector has a spiral absorber and
it is examined for inlet temperatures from 25?C up to 300?C with a flow rate
of 200 L/h. According to the final results, the use of hybrid nanofluid leads
to higher thermal efficiency enhancement compared to the mono nanofluids
because of the higher increase in the Nusselt number in the flow. More
specifically, the use of the hybrid nanofluids leads to 0.99% mean thermal
efficiency enhancement compared to the pure oil case, while the use of Oil/Cu
and Oil/TiO2 lead to 0.42% and to 0.56% mean thermal efficiency enhancement,
respectively. Moreover, the exergy efficiency is found enhanced with the use
of all nanofluids. The mean exergy efficiency enhancement is 1.21% with the
hybrid nanofluid, while it is 0.73% with Oil/TiO2 and 0.53% with Oil/Cu.
Solar energy utilization is vital in order to achieve the sustainability and reduce the utilization of conventional energy sources. The use of nanofluids in concentrating solar collectors is a ...promising solution in order to achieve high performance. This paper examines the use of various nanofluids as working fluids in a solar dish collector with smooth and corrugated absorber tube. The use of Al2O3, Cu, CuO and TiO2 dispersed on thermal oil and water is presented in this work. The examined concentrations of these nanoparticles are up to 5% in this study. The solar collector is investigated exergetically in order to evaluate together the useful thermal output and pressure losses. The analysis is performed with a developed 1-D thermal model and experimental results are used for the model validation for operation with water. According to the final results, the use of oil-based nanofluids leads to higher exergetic efficiency, while the use of water-based nanofluids leads to higher thermal performance. Moreover, the use of Cu nanoparticle is the most suitable exergetically among the examined cases. Generally, the exergetic efficiency of the examined collector is maximized for Cu-oil based nanofluid with the corrugated absorber and it is about 12.29%.
•A spiral cavity receiver was experimentally investigated.•A spiral cavity receiver was modeled with smooth and corrugated absorber tube.•A spiral cavity receiver was numerically modeled using different nanofluids.•Cu, CuO, TiO2 and Al2O3 are the considered nanoparticles inside the water and oil.•The exergy analysis was investigated.
Solar energy may be practically utilized directly through transformation into heat, electrical or chemical energy. We present a procedure to design a square facet concentrator for laboratory-scale ...research on medium-temperature thermal processes. The efficient conversion of solar radiation into heat at these temperature levels requires the use of concentrating solar collectors. Large concentrating dishes generally have a reflecting surface made up of a number of individual mirror panels (facets). Optical ray tracing is used to generate a system performance model. A square facet parabolic solar concentrator with realistic specularly surface and facet positioning accuracy will deliver up to 13.604 kW of radiative power over a 250 mm radius disk (receiver diameter) located in the focal plane on the focal length of 1500mmwith average concentrating ratio exceeding 1200. The Monte Carlo ray tracing method is used for analysis of the optical performance of the concentrator and to identify the set of geometric concentrator parameters that allow for flux characteristics suitable for medium and high-temperature applications. Projekat Ministarstva nauke Republike Srbije, br. III42006: Research and development of energy and environmentally highly effective polygeneration systems based on renewable energy resources
In this study, the optical design of a solar parabolic dish concentrator is
presented. The parabolic dish concentrator consists from 11 curvilinear
trapezoidal reflective petals made of polymethyl ...methacrylate with special
reflective coating. The dish diameter is equal to 3.8 m and the theoretical
focal point distance is 2.26 m. Numerical simulations are made with the
commercial software TracePro from Lambda Research, USA, and the final optimum
position between absorber and reflector was calculated to 2.075 m; lower than
focus distance. This paper presents results for the optimum position and the
optimum diameter of the receiver. The decision for selecting these parameters
is based on the calculation of the total flux over the flat and corrugated
pipe receiver surface; in its central region and in the peripheral region.
The simulation results could be useful reference for designing and optimizing
of solar parabolic dish concentrators as for as for CFD analysis, heat
transfer and fluid flow analysis in corrugated spiral heat absorbers.
•A conical and a spiral cavity receiver are examined for a solar dish collector.•The analysis is optical, thermal and exergetic for different operating conditions.•It is found that the conical design ...is more efficient than the spiral one.•The optical efficiency of the conical design is 1.38% higher than the spiral one.•The thermal efficiency enhancement with the conical design is 5.63% at 100 °C.
The objective of this work is to compare two cavity receivers for a solar dish concentrator. The spiral and the conical cavities are investigated using a developed thermal model. The analysis is optical, thermal and exergetic for different operating temperatures and flow rates. The developed thermal model is combined with an optical tool in order to simulate properly the solar dish collector and it is validated for the case of the spiral absorber with experimental results. Every receiver is separated in the different coil and every coil is simulated separately in order to increase the model accuracy. Totally, 13 coils are used for the spiral design and 11 for the conical design. The location of the receiver in every case is optimized in order to achieve maximum optical efficiency. The results show that the conical design leads to a 1.38% increase in the optical efficiency due to the increased intercept factor. The thermal efficiency enhancement with the use of conical design is found to be 5.63% at 100 °C and 40.45% at 200 °C, while the exergy efficiency enhancement 6.67% at 100 °C and 42.06% at 200 °C.
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