Performance characteristics of spray-pyrolysed selective cobalt-oxide coated tubular absorber operated with a linear solar concentrator

Spray-pyrolysed selective cobalt-oxide (CoO_x) coatings were prepared on the surface of a bright nickel-plated copper tubular absorber (α = 0.89–0.91 and ?_100°C = 0.18) for operation in conjunction with a prototype linear Fresnel reflector solar concentrator (LFRSC). Some preliminary tests were conducted to study the optical and thermal performance characteristics of the selective cobalt-oxide coated absorber in the concentrated solar flux. The tests conducted included determination of the overall heat loss coefficient U_L of the absorber at temperatures from 50 to ～ 120°C, and the optical efficiency η_o of the concentrator-absorber system, and measurement of the stagnation temperature of the absorber with the prototype solar concentrator. Based on the results of U_L and η_o measurements, the thermal efficiency η of the concentrator-absorber system at a working temperature of 115°C has been determined for a typical beam radiation I_b of 600 W/m². Further, comparison of the results of this study with those obtained using a dimensionally identical black-painted absorber indicates that the performance of the selective cobalt-oxide coated absorber is considerably superior to that of an ordinary black-painted absorber.     

Thermal performance of linear solar concentrators with tubular absorbers

The outlet temperature, corresponding thermal efficiency and the stagnation temperature available with a linear solar concentrator using a tubular absorber have been calculated, taking into account the temperature dependence of the heat-loss coefficient. The results of some typical numerical calculations are presented graphically and discussed.     

Geometrical designs and performance analysis of a linear fresnel reflector solar concentrator with a flat horizontal absorber

Two different approaches for designing a linear Fresnel reflector solar concentrator (LFRSC) with a flat horizontal absorber are described. The performance characteristics of both the designs are studied in detail. The distribution of local concentration ratio on the surface of the absorber, for each design, is investigated using the ray trace technique. Results of some typical numerical calculations are presented graphically and discussed.     

Thermal emittance of sputter deposited infrared reflectors in spectrally selective tandem solar absorbers

The thermal emittance of infrared reflectors, deposited by DC-magnetron sputtering on glass substrates of spectrally selective solar absorbers was studied. The deposition process was optimized in order to decrease the thermal emittance of the absorber. The sputter deposition process was optimized with regard to applied power and argon pressure for nickel–vanadium, copper–nickel and copper. The results show that the thermal emittance of the infrared reflector in a tandem solar absorber can be reduced from 0.12 to 0.06 by replacing nickel–chromium by copper–nickel. The copper–nickel alloy has a higher deposition rate and is less sensitive to the sputtering conditions, which is also favorable in large-scale industrial production.     

Thermal performance simulation of a solar cavity receiver under windy conditions

Solar cavity receiver plays a dominant role in the light-heat conversion. Its performance can directly affect the efficiency of the whole power generation system. A combined calculation method for evaluating the thermal performance of the solar cavity receiver is raised in this paper. This method couples the Monte-Carlo method, the correlations of the flow boiling heat transfer, and the calculation of air flow field. And this method can ultimately figure out the surface heat flux inside the cavity, the wall temperature of the boiling tubes, and the heat loss of the solar receiver with an iterative solution. With this method, the thermal performance of a solar cavity receiver, a saturated steam receiver, is simulated under different wind environments. The highest wall temperature of the boiling tubes is about 150 °C higher than the water saturation temperature. And it appears in the upper middle parts of the absorbing panels. Changing the wind angle or velocity can obviously affect the air velocity inside the receiver. The air velocity reaches the maximum value when the wind comes from the side of the receiver (flow angle α = 90°). The heat loss of the solar cavity receiver also reaches a maximum for the side-on wind.     

A new design of nontracking seasonally adjusted plane mirror linear trough solar concentrator with a flat horizontal absorber

This paper presents an optical design based on a single-reflection criterion, and performance characteristics of an east-west aligned nontracking seasonally adjusted linear trough solar concentrator with a flat horizontal absorber, using plane mirror elements. The design procedure allows the use of any desired number of mirror elements to reflect solar energy onto the base absorber in one reflection. The angle of inclination of each mirror element with respect to the absorber surface, and the width of the mirror element, are determined so that a ray incident on the extreme upper edge of the mirror element at a specified angle to the normal to the concentrator aperture (acceptance half-angle), after reflection, strikes the extreme edge of the absorber on the opposite side of the mirror element. Other rays making angles less than the design acceptance half-angle are also reflected onto the base absorber in one reflection. Concentrator designs resulting from this approach appear to have the important characteristic of relatively smaller heights, and hence appear highly cost-effective in terms of the amount of material required for fabrication. Some numerical calculations have been carried out to illustrate the performance of concentrators for different acceptance half-angles. Results obtained are presented in graphic and tabular forms, and are discussed.     

A comprehensive model for optical and thermal characterization of a linear Fresnel solar reflector with a trapezoidal cavity receiver

In this paper, a comprehensive numerical model was developed by coupling Monte Carlo Ray Tracing (MCRT) and Finite Volume Method (FVM) for simulating the energy conversion process in the linear Fresnel reflector (LFR) with a Trapezoidal Cavity Receiver (TCR). Based on the model, firstly, the optical performance of a typical LFR was studied, followed by analyzing its heat transfer characteristics and thermal performance at various conditions. Then, the effects of key parameters were investigated. Finally, a LFR prototype was simulated to illustrate the application of the model. The results indicate that the solar fluxes on the absorber tubes exhibit non-uniform characteristics which would result in the non-uniform temperatures. The annual optical efficiency of 60.1%–44.7% from the equator to N50° and the collector efficiency of 48.3%–72.0% for the superheating section at normal incidence can be achieved, respectively. Moreover, the heat transfer characteristic study reveals that the radiation loss from the tubes is the dominant mode and contributes around 81%–87% at typical conditions. Parameter studies indicate that the energy absorbed by the glass which influences the heat loss obviously should be considered in the heat loss study of TCR. And the heat loss from the tubes increases rapidly with the coating emissivity, so the coating with low emissivity should be recommended for the TCR. In addition, the application in the realistic LFR indicates that the present model is an exercisable and useful tool for the LFR.     

Electrical and thermal performance of silicon concentrator solar cells immersed in dielectric liquids

Direct liquid-immersion cooling of concentrator solar cells was proposed as a solution for receiver thermal management of concentrating photovoltaic (CPV) and hybrid concentrating photovoltaic thermal (CPV-T) systems. De-ionized (DI) water, isopropyl alcohol (IPA), ethyl acetate, and dimethyl silicon oil were selected as potential immersion liquids based on optical transmittance measurement results. Improvements to the electrical performance of silicon CPV cells were observed under a range of concentrations in the candidate dielectric liquids, arising from improved light collection and reduced cell surface recombination losses from surface adsorption of polar molecules. Three-dimensional numerical simulations with the four candidate liquids as the working fluids, exploring the thermal performance of a silicon CPV cell array in a liquid immersion prototype receiver, have been performed. Simulation results show that the direct-immersion cooling approach can maintain low and uniform cell temperature in the designed liquid immersion receiver. The fluid inlet velocity and flow mode, along with the fluid thermal properties, all have a significant influence on the cell array temperature.     

An improved model for natural convection heat loss from modified cavity receiver of solar dish concentrator

A 2-D model has been proposed to investigate the approximate estimation of the natural convection heat loss from modified cavity receiver of without insulation (WOI) and with insulation (WI) at the bottom of the aperture plane in our previous article. In this paper, a 3-D numerical model is presented to investigate the accurate estimation of natural convection heat loss from modified cavity receiver (WOI) of fuzzy focal solar dish concentrator. A comparison of 2-D and 3-D natural convection heat loss from a modified cavity receiver is carried out. A parametric study is carried out to develop separate Nusselt number correlations for 2-D and 3-D geometries of modified cavity receiver for estimation of convective heat loss from the receiver. The results show that the 2-D and 3-D are comparable only at higher angle of inclinations (60° ? β ? 90°) of the receiver. The present 3-D numerical model is compared with other well known cavity receiver models. The 3-D model can be used for accurate estimation of heat losses from solar dish collector, when compared with other well known models.     

Thermal performance of the double-pass solar collector with and without porous media

This paper presents the thermal performance of a double-pass solar collector with and without porous media in the second or lower channel of the collector. The experimental setup has been designed to study the thermal performance over a range of design and operating conditions. Several important relationships between the design and operating conditions have been obtained. These relationships effect the thermal performance of the double-pass solar collector. The relationships include the effect of changes in upper and lower channel depth on the thermal efficiency with and without porous media. Moreover, the effects of mass flow rate, solar radiation, and temperature rises on the thermal efficiency of the double-pass solar collector have been studied. The study concluded that the presence of porous media in the second channel increases the outlet temperature, therefore increases the thermal efficiency of the systems.     

球形腔式太阳能吸热器性能的数值研究

利用蒙特卡洛光线追踪法分析了6种不同开口比(D/d)的球形腔式吸热器的光学性能,并以光学模拟所得壁面能流作为热分析的边界条件导入CFD软件中,运用CFD软件对6种不同开口比的球形腔式吸热器进行流固耦合传热计算,获得了球形腔式吸热器和内部流体的温度场分布。通过计算球形腔式吸热器的反射光损失、对流热损失和热辐射损失,得到聚光器/球形腔式吸热器系统的光热转化效率为81.9%～84.4%,球形腔式吸热器的最佳开口比1相似文献   

基于量纲分析的双轴槽式太阳能系统集热性能研究

针对影响双轴跟踪槽式太阳能系统集热效率的多种因素,文章采用量纲分析法建立了集热效率预测模型,构建了包括Re数在内的5个无量纲量。实验测试了不同工况下系统的集热性能,通过多元线性回归对集热效率预测模型进行了求解。研究结果表明:在文章研究范围内,Re对集热效率的影响较大,太阳辐照量、集热管几何参数以及传热工质物性等对集热效率影响相对较小;在集热效率预测模型复测样本范围内,集热效率计算值和实测值之间的最大相对误差不超过15%。文章建立的双轴跟踪槽式太阳能系统集热效率预测模型精度较高,可为槽式太阳能系统的工程设计和优化运行提供理论依据。     

Energy analysis of a solar air collector with rows of fins

The necessity for improving the thermal performances of the solar air collector, for some needs, encouraged us to carry out this study. Initially, to improve the efficiency factor of these solar collectors, we create an increasingly turbulent flow between the absorber and the back wooden plate. For that, we use obstacles of various forms. In this study, we chose rectangular plate fins inserted perpendicular to the flow. The fluid flows out through the interstices between fins in the same row, this allows a good distribution of the fluid and reduces the dead zones. Secondly, and for the same configuration, we undertake a study on the evaluation of the transfer coefficient. The results are compared with those obtained with a solar air collector without fins, using two types of absorbers selective (in coppersun) or not selective (black-painted aluminium).     

Theoretical and experimental study of efficiency factor,heat transfer and thermal heat loss coefficients in solar air collectors with selective and nonselective absorbers

The thermal heat performance of a solar air collector depends strongly on the thermal heat loss and the efficiency factor. In order to increase these performances, it is necessary to use a solar air collector which is well insulated and where the fluid flow is fully developed turbulent flow. It needs a high heat transfer between the absorber plate and the fluid to decrease the absorber‐plate temperature and hence the heat loss by radiation from the absorber to the ambient. This increases the efficiency factor. In the present paper, the heat loss and efficiency factor are treated for solar air collectors with selective and nonselective absorber plate. It is shown that the selectivity of the absorber plate cannot play an important role in a well‐insulated solar collector with a fanned system which permits a fully developed turbulent flow and, in consequence, high heat transfer. Copyright © 1999 John Wiley & Sons, Ltd.     

The study of the performance and efficiency of flat linear Fresnel lens collector with sun tracking system in Iraq

Two flat linear Fresnel lenses and two absorbers connected in series. Tracking system is constructed so that it tracks the sun in two directions. Thermal and optical losses are introduced. The thermal efficiency of the first lens is higher than the second lens and reaches 0.65. The FLFL all-day collector efficiency reaches 0.58 and it varies depending on weather condition.     

轻质双层纺织基太阳能空气集热器的集热性能试验研究

纺织基太阳能空气集热器作为轻质柔软的太阳能集热器,在中低温集热领域具有潜在的应用前景。文章设计了新型双层纺织基太阳能空气集热器,并进行户外试验,探究单双层结构、间隔丝密度、空气质量流量对集热器性能的影响。研究结果表明:在空气质量流量为0.023 kg/(m²·s)时,双层纺织基太阳能空气集热器热转移因子和总热损系数分别为0.97和5.87 W/(m²·℃),集热性能优于同条件下单层结构集热器;进出口空气温差和集热效率随间隔丝密度的增加而增加;集热效率随空气质量流量的增加而增加,当空气质量流量为0.037 kg/(m²·s)时,间隔丝密度为36根/cm²的集热器集热效率为0.64。     

Experimental performance of single and double pass solar air heater with fins and steel wire mesh as absorber

Thermal performance of a single and double pass solar air heater with fins attached and using a steel wire mesh as absorber plate was investigated experimentally. The effects of air mass flow rate range between 0.012 kg/s and 0.038 kg/s on the outlet temperature and thermal efficiency was studied. The bed heights were 7 cm and 3 cm for the lower and upper channels respectively.