采集太阳光的照明系统

提出一种采光面积大、结构简单、制作容易、维修方便的平面反光镜阵列汇聚采光，导光管传光，平面镜耦合，磨砂塑料盘散光的新型太阳光照明系统。考察了该系统的平面反光镜聚光特性，导光管的耦合方法及导光管透光率随光线入射角、导光管长度和导光管直径的关系。利用该系统，研究了透射光光强随导光管长度的变化规律、0．72m长导光管在不同集光比下的导光性能以及一天中聚光与不聚光条件下导光管透光率比较。结果表明，采用本系统汇聚阳光使进入导光管光线的入射角可以调整，入射角角度都比较小，从而使光线在导光管中的反射次数减少，光损失少，一天中光照亮度均匀。     

Experimental analysis on a 1:2 scale model of the double light pipe, an innovative technological device for daylight transmission

In this paper the authors present the double light pipe, an innovative technological device, designed as an evolution of a traditional light pipe, which distributes daylight to underground areas of a building, illuminating, at the same time, the passage areas thanks to a larger collector and a second transparent pipe attached to the first one. Unlike the traditional light pipe, thanks to this double illuminating function it can be located in the middle of a room, despite its encumbrance.In this paper the technological design of the double light pipe is presented and the results of an experimental analysis on a reduced scale (1:2) model are shown. Internal illuminance data over horizontal and vertical work-planes were measured in various sky conditions with or without direct solar radiation. Being this innovative device obtained by a light pipe integrated with a second pipe, it performs like a traditional light pipe for the final room and, at the same time, illuminates the intermediate room giving it uniform and high quality light, particularly indicated for wide plant areas, such as show-rooms or museums.     

Evaluation of dichroic material for enhancing light pipe/natural ventilation and daylighting in an integrated system

Integration of natural ventilation and daylighting in a single installation would make both technologies more attractive. One method for the integration is the use of concentric light pipe and ventilation stack. By constructing the light pipe using dichroic materials, the infrared part of the solar radiation is allowed to be transmitted to the stack but the visible light is guided by the light pipe into a room. The heat gain to the interior can be reduced and the thermal stack effect strengthened. Work presented here involved the experimental and computational evaluation of dichroic materials for enhancing both natural stack ventilation and daylighting. The transmittance of a dichroic light pipe was found to be similar to that of a light pipe with a 95% specular reflectance. The infra-red radiation transmitted through the dichroic material into a passive stack was found to enhance the natural ventilation flow by up to 14%. The effect is greater in summer than in winter, which is highly desirable as there is often a lack of driving force for natural stack ventilation in summer.     

光导管冬季采光性能的实验研究

为了优化其采光性能,并为照明工程提供设计依据,对某一光导管进行了在冬季3种典型天气情况下的测量.通过本试验工作,得到了冬季各种典型天气情况下光导管的光通量、室内照度分布值,证明了光导管对散射光的采集作用.     

Wide-angle light scattering (WALS) for soot aggregate characterization

A novel set-up for the experimental determination of aggregate morphology in combustion processes based on elastic light scattering has been designed and realized. A key feature of this wide-angle light scattering (WALS) approach is an ellipsoidal mirror which is used to collect scattered light over a wide angular range of about 10–170°. The set-up employs a cw solid-state laser as light source and an intensified CCD-camera as detector. By means of the mirror the scattered light is imaged onto the detector allowing for a simultaneous acquisition of a full scattering diagram with a high angular resolution of about 0.6°. To demonstrate the performance of the approach, measurements for various sooting flames produced by premixed combustion in a flat flame burner were carried out, where the burner was operated with different equivalence ratios and fuels. It is shown that radii of gyration of soot particles may efficiently be obtained from an analysis of the scattering diagrams.     

基于镜面积尘的线性菲涅尔系统聚光性能研究

针对线性菲涅尔反射式（LFR）聚光集热系统镜面积尘所引起的光学损失问题,建立镜面积尘的系统三维模型,利用蒙特卡洛光线追迹法进行光学仿真模拟,研究灰尘颗粒形状、粒径以及镜面积尘密度对光线路径、系统能流密度和聚光效率的影响,并利用LFR能流密度测试系统来验证仿真模拟方法的可靠性。结果表明,球体颗粒对光线有汇聚作用,入射至正方体颗粒的光线会被完全吸收,镜面积尘密度增加1 g/m²,吸热管周的平均能流密度降低625.17 W/m²,系统的聚光效率下降5.53%,且镜面积尘颗粒的粒径越小,吸热管周的能流密度下降越严重,不同积尘密度下仿真模拟与试验测试的能流密度变化趋势一致,两者之间误差为9.6%。     

A study on a ventilation stack integrated with a light pipe

A theoretical and experimental study has been conducted on the performance of a vertical light pipe that also functions as an air flow stack for night ventilation. The rectangular light pipe of height 3 m and cross-section area 0.0625 m² surrounded by an air duct of total cross-section area 0.23 m² is situated above a room of height 3.8 m and floor area 9 m². Heat transfer from the hot water in the wraparound hot water jacket to the air in the duct is assisted by stainless steel fins. The ventilation of the room, due partly to the buoyancy of the air in the duct and partly to the wind effect, amounted to nearly 10 air changes per hour which is sufficient for passive cooling during cooler night periods. The light pipe has specular reflecting walls. It was found that the transmission of daylight through the light pipe in the middle of a partly cloudy day was sufficient for illuminating the room to general illumination level.     

Transmission of mirror light pipes with triangular, rectangular, rhombic and hexagonal cross section

This paper derives expressions for the transmission of mirror light pipes (MLP) with cross sections exhibiting congruent symmetry. These include rectangular, triangular, rhombic and hexagonal cross sections. For the case of rectangular MLP the transmissions calculated by this method are the same as the transmissions calculated by integrated ray trace methods. Measurements of the transmission of rectangular and triangular MLP were made and compared with calculated transmissions. It is shown that calculated transmissions are consistent with measured transmissions provided a reflectance that varies with incidence angle on the aperture of the MLP is used. A simple expression for this variation was found from the experimental measurements.     

An internal cusp reflector for an evacuated tubular heat pipe solar thermal collector

This study involves the optical analysis of a slightly concentrating, symmetric cusp reflector inside a tubular glass envelope with a cylindrical heat pipe as the solar absorber. The basic design features of this non-tracking, evacuated, modular collector and the principles of heat removal are shown in Figs. 1 and 2. Differential equations of the cusp reflector optics, given the geometrical restrictions in Figs. 1 and 2, are derived, and solutions for the largest possible aperture inside a given diameter envelope and acceptance angle are presented.As an extension of the same study, the optical efficiency of a single collector tube has been simulated by means of a Monte Carlo Ray-Tracing Program. For a concentration ratio of 1.15, the flux distribution around the heat pipe is computed as a function of incidence angle. In addition, the impact of mirror defects and absorber misalignment on the optical performance are analyzed.     

终端供水锅炉空气预热器设计

本设计为大连旭硝子浮法玻璃有限公司节约成本资金改造项目预备提案,设计任务为利用制镜部废气焚烧装置的高温排烟为终端供水的燃气锅炉预热空气。本次设计的特点在于增设空气预热器余热回收的同时,采用较为先进的无机热管,是新型高效元件与传统技术的完美组合;布置风道及烟道时考虑相对位置,避免了多余的弯头阻力损失。     

Indoor daylight climate-comparison between light shelves and overhang performances in Madrid for hours with unit sunshine fraction and realistic values of model reflectance

In the present paper we have compared the daylighting performance at a point placed at 50 cm from a south-facing opening in 1:10 models painted for realistic reflectance values, of two light shelves and an overhang, using measurements performed during 1 year. The light shelves and the overhang produced the same shading effect, as both were designed for a vertical shade angle of 50°, adequate for south facing shading devices during the overheated period in Madrid (Spain). The comparison is performed from 06:00 to 12:00 h (true solar time), using data obtained when the hourly sunshine fraction is 1. The study of the measured illuminance provides a quantitative assessment of the advantage of using a light shelf instead of an overhang, both giving the same solar protection. A detailed study of the difference between correspondent illuminance values in the models equipped with metacrilate and mirror light shelves and the model equipped with the overhang has been performed. The difference between the daylighting performance in the model equipped with the metacrilate light shelf and the model with the mirror light shelf at the mentioned measurement point is also studied, and the period of the year when each of the light shelves performs better than the other is determined. The performance of the two light shelves is related to important differences between their mean reflectance for the specular component and after excluding the specular component, as measured with a spectrophotometer for a 4° incidence angle.     

电厂煤粉粒径、浓度和速度的在线测量技术研究

电厂煤粉管道的运行状况对电厂的安全经济运行有一定的影响,但缺少有效的在线监测手段。该文介绍了结合光脉动法和相关测速法同时在线测量煤粉粒径、浓度和速度的技术和装置。     

A novel procedure for the optical characterization of solar concentrators

A novel procedure for the optical characterization of solar concentrators is presented. The method is based on recording at night the light of a star reflected by the mirror. Images of the mirror taken from its focal region allow the reconstruction of the slope map. The application of this technique for the in situ characterization of heliostats is particularly simple and at very low cost. Results on first tests carried out with a heliostat of the CESA-I field at the Plataforma Solar de Almeria have shown the feasibility of this technique. Uncertainties in the reconstructed slopes of about 1.0 mrad have been estimated.     

Cost effective asymmetric CPC solar collectors

Low cost CPC solar collectors were designed, constructed and tested. The collectors consist of two separate absorbers, which are horizontally incorporated in a stationary asymmetric CPC mirror. The efficient operation of the proposed collectors is due to the direct absorption of a large part of the incoming solar radiation and to the thermal losses suppression by the inverted surface of both absorbers. Two collector types with the same basic design are presented. The first type has tubular absorbers which are used for direct water heating and the second has flat fin type absorbers with pipe. Test results showed that the proposed collectors operate efficiently and are suitable for hot water applications.     

High precision (1 part in 10) reflectivity measurement for the study of reflective materials used in solar collectors

A new method of reflectivity measurement for the study of reflective materials in solar energy technology is reported in this paper. The method employs a fast rotating reference mirror and certain geometry configuration to alternatively deliver the light via a sample mirror or by passing it to a photo detector. It has been proved to reach a precision of 10⁻⁴. With a good repeatability of the method, outdoor exposure tests of sample mirrors have been carried out in a relatively short period (1 month) and significant specular reflectance losses due to an aging process have been observed.     

Influence mechanism of dynamic and static liquid bridge forces on particle deposition behaviors in solar photovoltaic mirrors

Solar energy is one of the most promising forms of renewable energy for solving the energy crisis and environmental problems. Dust deposition on photovoltaic mirrors has a serious negative impact on the photoelectric conversion efficiency of solar power stations. In this paper, the influence mechanism of the dynamic and static liquid bridge forces on particle deposition behaviors on solar photovoltaic mirrors is investigated. In addition, the expression and physical meaning of the particle critical separation velocity are proposed. The research results show that the static liquid bridge force can be the primary deposition force causing dust particles to adhere to photovoltaic mirrors. However, the dynamic liquid bridge force can act as a resistance force for the particle motion process and even make dust particles roll along and finally stay on the mirror. The contact force is the primary separation force that causes dust particles to flow away from the mirror. Whether dust particles adhere to the mirror depends on the relative size of the deposition and separating forces. The particle critical separation velocity describes the relative size of the collision-rebound effect and mirror adhesion effect and is expressed in Eq. (16). These research findings can provide theoretical guidance for mirror cleaning methods in the operation process of photovoltaic mirrors.     

Thermal performance of screen mesh wick heat pipes using water-based copper nanofluids

Fairly stable surfactant free copper–distilled water nanofluids are prepared using prolonged sonication and homogenization. Thermal conductivity of the prepared nanofluid displays a maximum enhancement of ～15% for 0.5 wt% of Cu loading in distilled water at 30 °C. The wall temperature distributions and the thermal resistances between the evaporator and the condenser sections of a commercial screen mesh wick heat pipe containing nanofluids are investigated for three different angular position of the heat pipe. The results are compared with those for the same heat pipe with water as the working fluid. The wall temperatures of the heat pipes decrease along the test section from the evaporator section to the condenser section and increase with input power. The average evaporator wall temperatures of the heat pipe with nanofluids are much lower than those of the heat pipe with distilled water. The thermal resistance of the heat pipe using both distilled water and nanofluids is high at low heat loads and reduces rapidly to a minimum value as the applied heat load is increased. The thermal resistance of the vertically mounted heat pipe with 0.5 wt% of Cu–distilled water nanofluid is reduced by ～27%. The observed enhanced thermal performance is explained in light of the deposited Cu layer on the screen mesh wick in the evaporator section of the heat pipe.     

Cusp mirror—Heat pipe evacuated tubular solar thermal collector

A solar thermal collector was constructed based on an internal 1.15X cusp concentrator, thermal insulation involving a vacuum and selective absorber, and thermal transfer to a manifold via heat-pipe action. Performance of the collector was compared with that of an evacuated, selectively coated, flat-plate absorber equipped with flow-through heat transfer. It was shown that with single collector tubes, mirror losses lowered the optical efficiency of the cusp, heat-pipe collector below that of the flat plate, while the smaller absorber area of the heat pipe reduced thermal losses at absorber temperatures above ambient. Thus, a crossover in efficiency occurred such that the flat plate was more efficient at low while the cusp-heat pipe was more efficient at high . Testing of modules showed that manifold losses and gains could dominate these collector effects when the collector area approximately equaled the manifold area.     

Theoretical estimations of the efficiency of thermophotovoltaic systems using high-intensity silicon solar cells

Efficiencies have been calculated for (a) heat-mirror filter and (b) rear-mirror thermophotovoltaic systems using actual materials values for source emissivity ((λ)), mirror-filter transmissivity (τ_M(λ)) and intensity-dependent cell parameters V_oc and FF. The ratios of heat-mirror and rear-mirror efficiencies to direct sunlight impingement efficiency are estimated to be 1.6 and 1.9, respectively (2500°K thermal source), if mirror and other extraneous absorption are taken to be zero in both cases. The more realistic inclusion, for the first case, of 2 per cent light absorption in the filter/mirror and, in the second case, of 2 per cent absorption of low energy light in the cell and 8 per cent absorption at the rear mirror, plus a 2 per cent thermal loss directly from the hot source (for both), reduces the advantage of both to about a factor of 1.2.