双层中空玻璃盖板太阳能平板集热器集热性能实验测试研究

文章提出了一种采用双层中空玻璃盖板且吸热板表面镀有蓝钛膜的太阳能平板集热器,并在不同的工质流量和进口温度条件下对该集热器的集热性能进行实验测试,得到该集热器的瞬时集热效率曲线。研究结果表明,该集热器的集热效率曲线截距为0.83,热损系数为3.1 W/(m~2·K),该集热器的集热性能明显优于其他结构的平板集热器。此外,文章建立了该集热器的数学模型,得到该集热器的总热损系数和热迁移因子的数学表达式。     

无盖板渗透型太阳能空气集热器热性能的实验研究

无盖板渗透型太阳能空气集热器是一种易于实现建筑一体化的高效新风预热及干燥装置。为了掌握无盖板渗透型集热器在实际工况下的热性能,建造了集热面积为2.2 m2的太阳能空气加热系统实验台,并在2009年2月至2009年4月对其热性能进行了户外瞬态实验研究。实验结果表明出口空气温度随辐射强度的增加而升高,太阳辐射强度是影响集热器出口空气温度的最重要因素,而室外空气温度的影响极小。空气温升随风量的增加而减小,集热器热效率随风量的增加而增大。在三个测试日中集热器的平均热效率分别为58%、63%和72%,高于普通平板太阳能空气集热器。     

蜂窝结构太阳能集热器的性能

一、引言我国的太阳能热利用较为普及的是各种型式的太阳能热水器系统,其中的关键组件是集热器。改善平板太阳能集热器性能的方法之一,是在集热板与透明盖板之间插置一蜂窝结构。这种蜂窝结构能有效地抑制集热板和透明盖板之间的自然对流换热和辐射换热,从而显著减小集热器的热损失,提高热效率。本文论述蜂窝结构平板太阳能集热器的性能分析和实验结果。     

太阳能空气集热器(Ⅰ型)的数学模型研究

用数学模型化方法研究了太阳能空气集热器的集热传热性能,建立了基于二维假设下的流体流动和热量传递的稳定态数学模型,并用有限差分法进行数值求解,计算得到稳态下太阳能空气集热器的速度、温度分布图以及集热效率与空气流量、入口空气温度、入身太阳辐照度和表面盖板透过率的关系。结果表明,对Ｉ型太阳能空气集热器,集热效率随空气流量和表面盖板透过率的增加而增大,随入口空气温度和入射太阳辐照度的增大而减小。计算结果与     

利用条缝射流强化无盖板型太阳能集热器性能

为提升无盖板型太阳能空气集热器热性能，设计一种条缝射流型太阳能空气集热器，并利用数值模拟和实验验证对其热性能进行分析。集热器内部流动及换热特性的模拟结果表明，利用圆孔和挡片形成的条缝射流能对集热板形成有效覆盖，进而提高进气与集热板的对流换热。射流条缝存在最优结构参数，当圆孔直径为25 mm时，条缝宽度在3 mm处接近最优；集热效率则随挡片直径的增大而增大，是由于射流贴附效应在变强。实验结果表明，条缝射流型集热器的全天热效率稳定且高效。当处理气量为39 m3/h时，该集热器全天热效率稳定在约48%，优于传统的无盖板渗透型太阳能集热器。     

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。     

不同透明盖板整体式太阳能空气集热器性能研究

为了理清不同盖板形式整体式太阳能空气集热器的传热性能,建立了一维假设下的能量传递数学模型,借助MATLAB编程求解,得到了准静态条件下集热器沿程温度分布、出口温度、集热效率的数值解,对比发现数值解与实验值吻合较好。计算结果表明:采用PC中空阳光板为盖板的集热器比使用钢化玻璃为盖板性能好;两种盖板形式的集热器最佳流量相差不大;集热器存在一个最佳流道高度。     

V型多通道平板太阳能集热器的热性能研究

提出一种V型多通道平板太阳能集热器,对其建立稳态传热模型,利用Matlab软件编程进行求解,并进行实验测试验证模型的准确性.利用已验证的传热模型,模拟分析V型多通道平板太阳能集热器的结构和物性参数对其热性能的影响,结果表明当透明盖板和吸热体发射率变大时,集热器的集热效率会呈下降趋势;当V型槽顶角、吸热体长度及空气夹层厚...     

太阳能PV/T系统电热输出性能及其Matlab仿真研究

建立了太阳能PV/T(Photovoltaic/Thermal)系统的热电模型,编制了Matlab程序,采用迭代法对电热参数进行耦合求解。研究了PV/T系统在呼和浩特不同季节下的热电效率,电池温度和性能曲线的变化,通过与实验数据对比,验证了该模型具有较高的精度。实验结果显示了环境温度、风速、入射辐射量对太阳能PV/T系统热、电以及综合性能的影响:PV/T系统夏季的日平均电效率、热效率及正午组件最大功率分别为14.1%、34.5%和180.8 W,冬季的日平均电效率、热效率及正午组件最大功率分别为16.1%、24.8%和190.3 W。     

R290直膨式太阳能热泵系统工质分布和迁移特性模拟

为了研究工质R290(丙烷)在直膨式太阳能热泵系统中的分布和迁移特性,建立太阳能集热/蒸发器和冷凝器的分布参数均相流动模型、压缩机和电子膨胀阀的集中参数模型、以及系统工质充注量模型,编制以R290为工质的直膨式太阳能热泵热水器系统性能模拟程序。模拟分析环境参数和运行参数的变化对系统内部R290分布和迁移特性的影响。模拟结果表明:R290主要存在于冷凝器和太阳能集热/蒸发器内部,占系统工质充注量的80%~90%;随着太阳辐射强度和环境温度的升高,工质R290由冷凝器逐渐向太阳能集热/蒸发器迁移,系统性能系数明显增加;随着压缩机转速增快和水箱水温的增高,工质R290由太阳能集热/蒸发器逐渐向冷凝器迁移,系统性能系数明显降低;随着系统工质充注量的增加,冷凝器内工质R290质量明显增加,集热器内工质R290质量略有增加,系统性能系数先增后减,存在一个最大值;太阳能集热/蒸发器出口过热度由3℃升至8℃时,其变化对工质R290的分布和迁移特性影响很小,且对系统性能系数的影响也很小;随着环境温度、压缩机转速和工质充注量的增加,集热器集热效率不断增加;而随着太阳辐射强度、水箱水温和太阳能集热/蒸发器出口过热度的增高,集热器集热效率不断降低。     

Thermal advantages for solar heating systems with a glass cover with antireflection surfaces

Investigations elucidate how a glass cover with antireflection surfaces can improve the efficiency of a solar collector and the thermal performance of solar heating systems. The transmittances for two glass covers for a flat-plate solar collector were measured for different incidence angles. The two glasses are identical, except for the fact that one of them is equipped with antireflection surfaces by the company SunArc A/S. The transmittance was increased by 5–9%-points due to the antireflection surfaces. The increase depends on the incidence angle. The efficiency at incidence angles of 0° and the incidence angle modifier were measured for a flat-plate solar collector with the two cover plates. The collector efficiency was increased by 4–6%-points due to the antireflection surfaces, depending on the incidence angle. The thermal advantage with using a glass cover with antireflection surfaces was determined for different solar heating systems. Three systems were investigated: solar domestic hot water systems, solar heating systems for combined space heating demand and domestic hot water supply, and large solar heating plants. The yearly thermal performance of the systems was calculated by detailed simulation models with collectors with a normal glass cover and with a glass cover with antireflection surfaces. The calculations were carried out for different solar fractions and temperature levels of the solar heating systems. These parameters influence greatly the thermal performance associated with the antireflection surfaces.     

Comparative performance investigation of integrated collector‐storage solar water heaters with various heat loss reduction strategies

A detailed comparative assessment is reported on the thermal performance of integrated collector‐storage (ICS) solar water heaters with various strategies for reducing top heat losses. The objective of this investigation is to assess and compare heat loss reduction strategies. The shape of ICS solar water heater considered in present investigation is rectangular. The thermal performance of the solar water heater is evaluated and analyzed for the following cases: (1) single glass cover without night insulation; (2) single glass cover with night insulation; (3) double glass cover without night insulation; (4) transparent insulation with single glass cover; and (5) insulating baffle plate with single glass cover. Energy balances are developed for each case and solved using a finite difference technique. The numerical assessment of the system performance is performed for a typical July day in Toronto. Each strategy is observed to be beneficial, reducing top heat losses, and improving system performance. The greatest performance enhancements are observed for the water heater with a single glass cover and night insulation and for the system with a double glass cover and without night insulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of absorption of solar radiation in glass-cover(s) on heat transfer coefficients in upward heat flow in single and double glazed flat-plate collectors

Absorption of solar radiation in the glass cover(s) of a flat plate solar collector increases the temperature of cover(s) and hence changes the values of convective and radiative heat transfer coefficients. The governing equations for the case of single as well as double glazed collector have been solved for inner and outer surface temperatures of glass cover(s) with/without including the effect of absorption of solar radiation in the glass cover(s), with appropriate boundary conditions. The effects of absorption of solar radiation on inner and outer surface temperatures and consequently on convective and radiative heat transfer coefficients have been studied over a wide range of the independent variables. The values of glass cover temperatures obtained from numerical solutions of heat balance equations with and without including the effect of absorption of solar radiation in the glass cover(s) are compared. For a single glazed collector the increase in glass cover temperature due to absorption of solar radiation could be as high as 6°. The increase in temperatures of first and second glass covers of a double glazed collector could be as high as 14° and 11°, respectively. The effect on the convective heat transfer coefficient between the absorber plate and the first glass cover is substantial. The difference in the values of the convective heat transfer coefficients between the absorber plate and the first glass cover (h_cp1) of a double glazed collector for the two cases: (i) including the effect of absorption and (ii) neglecting the effect of absorption in glass cover, could be as high as 49%. Correlations for computing the temperatures of inner and outer surfaces of the glass cover(s) of single and double glazed flat plate collectors are developed. The relations developed enable incorporation of the effect of absorption of solar radiation in glass cover(s) in the relations for inner and outer surface temperatures in a simple manner. By making use of the relations developed for inner and outer surface temperatures of glass cover(s) the convective and radiative heat transfer coefficients can be calculated so close to those obtained by making use of surface temperatures of glass cover(s) obtained by numerical solutions of heat balance equations that numerical solutions of heat balance equations are not required.     

Theoretical approach of a flat plate solar collector with clear and low-iron glass covers taking into account the spectral absorption and emission within glass covers layer

Accurate modeling of solar collector system using a rigorous radiative model is applied for the glass cover which represents the most important component of the system and greatly affects the thermal performance. The glass material is analyzed as a non-gray plane-parallel medium subjected to solar and thermal irradiations in one dimensional case using the radiation element method by ray emission model (REM²). The optical constants of a clear and low-iron glass materials proposed by Rubin have been used. These optical constants, 160 values of real part n and imaginary part k of the complex refractive index of such materials, cover the range of interest for calculating the solar and thermal radiative transfer through the glass cover. The computational times for predicting the thermal behavior of solar collector were found to be prohibitively long for the non-gray calculation using 160 values of n and k for both glasses. Therefore, suitable semi-gray models have been proposed for rapid calculation. The temperature distribution within the glass cover shows a good agreement with that obtained with iterative method in case of clear glass. It has been shown that the effect of the non-linearity of the radiative heat exchange between the black plate absorber and the surroundings on the shape of the efficiency curve is important. Indeed, the thermal loss coefficient is not constant but is a function of temperature, due primarily to the radiative transfer effects. Therefore, when the heat exchange by radiation is dominant compared with the convective mode, the profile of the efficiency curve is not linear. It has been also shown that the instantaneous efficiency of the solar collector is higher in case of low-iron glass cover.     

Validation of CFD simulation for flat plate solar energy collector

The problem of flat plate solar energy collector with water flow is simulated and analyzed using computational fluid dynamics (CFD) software. The considered case includes the CFD modeling of solar irradiation and the modes of mixed convection and radiation heat transfer between tube surface, glass cover, side walls, and insulating base of the collector as well as the mixed convective heat transfer in the circulating water inside the tube and conduction between the base and tube material. The collector performance, after obtaining 3-D temperature distribution over the volume of the body of the collector, was studied with and without circulating water flow. An experimental model was built and experiments were performed to validate the CFD model. The outlet temperature of water is compared with experimental results and there is a good agreement.     

Effect of cover plate treatment on efficiency of solar collectors

Theoretical data are presented for prediction of solar collector efficiencies as the cover plates are varied by coating, de-reflecting, changing iron content, or evacuating. Tin oxide as a radiation shield appears to offer some improvement for a nonselective black with two cover plates but no improvement with a selective black with one cover plate. Low-iron and dereflected soda lime glass offer considerable improvement over regular soda lime glass over the whole range of operating temperatures. An evacuated single cover plate with a selective black performs at 50 per cent efficiency at a collector plate temperature of 430°F. An analysis is presented that shows the effect of support studs in an evacuated unit. The data show that support studs having a cross-sectional area equal to 5 per cent of the collector area will greatly lower the efficiency of the unit.Experimental data are presented for no-load (no flowing water) conditions where collector plates fabricated with either tin-oxide coated glass and low iron glass are compared to regular glass for a non-selective surface. The collector plates with the tin-oxide coated glass and low iron glass attain higher equilibrium temperatures.     

Experimental and theoretical evaluation of the overall heat loss coefficient of vacuum tubes of a solar collector

The overall heat loss coefficient (U-value) of a vacuum tube solar collector is investigated experimentally and theoretically with regard to the pressure of the remaining gas inside the evacuated glass envelope. A number of collector tubes of same geometry are randomly selected from an installation of a solar based air-conditioning system and tested individually in the laboratory for the determination of the U-value. Measurement results indicate that most of the examined collector tubes have higher overall heat loss coefficients than expected corresponding to a significant amount of gas inside the glass envelope.For the same conditions, an approximate theoretical model is developed for the evaluation of the U-value. The theoretical model is validated against the experimental results for a collector tube having air inside the glass cover at atmospheric pressure and found to be in close agreement. Then, the influence of gas pressure is studied for various gases. Possible presence of air, hydrogen, helium and argon is discussed.     

Theoretical approach of a flat-plate solar collector taking into account the absorption and emission within glass cover layer

A rigorous theoretical approach of a flat-plate solar collector with a black absorber considering the glass cover as an absorbing–emitting media is presented. The glass material is analyzed as a non-gray plane-parallel medium subjected to solar and thermal irradiations in one-dimensional case using the Radiation Element Method by Ray Emission Model (REM²). The optical constants of a clear glass window proposed by Rubin have been used. These optical constants, 160 values of real part n and imaginary part k of the complex refractive index of a clear glass, cover the range of interest for calculating the solar and thermal radiative transfer through the glass cover. The computational time for predicting the thermal behavior of solar collector was found to be prohibitively long for the non-gray calculation using 160 values of n and k. Therefore a suitable semi-gray model is proposed for rapid calculation. The profile of the efficiency curve obtained in the present study was found to be not linear in shape. Indeed, the heat loss from the collector is a combination of convection and radiation and highly non linear. The effect of the outside convective heat transfer on the efficiency curve is also studied. In fact, when the convection is the dominant heat transfer mode compared with the radiation one, the profile of the efficiency curve is more or less straight line. Consequently, the heat loss coefficient could be calculated using Klein model. It has been also shown that the effect of the wind speed on the glass cover mean temperature is very important. This effect increases with the increase of the mean absorber temperature.     

全玻璃真空太阳集热管光—热性能

从能量平衡议程导出全玻璃真空太阳集热管的3个光－热性能参数,即热损系数UTL、闷晒太阳曝辐量H和空晒性能参数Y与真空热管理的罩管玻璃的太阳透射比τ、选择性吸收表面的太阳吸收比a、发射比ε、和集热管内的气体压强p,太阳辐照度、环境温度和真空太阳集热管的几何尺寸等函数关系。理论计算的真空太阳集热管的3个热性能参数与实验的结果比较一致。上述全玻璃真空太阳集热管的光－热性能参数已经被国家标准《全玻璃真空太阳集热管》（GB／T17049－1997）采用。     

Analysis of a v-groove solar collector with a selective glass cover

The present paper describes a theoretical study of an air heating solar collector. Solar energy is collected in an absorbing triangularly corrugated plate with a selective surface. The collector also has a selective glass cover which reflects the long wavelength radiation emitted by the absorbing plate and transmits most of the short wavelength incoming solar radiation. The collector overall absorptance is further increased by the cavity effect.

Solar energy passing through the glass is incident on the selectively absorbing surface of the v-groove plate. The absorbed energy raises the temperature of the plate and heats air that is pumped through the triangular passages of the collector. The efficiency that can be obtained with the collector is determined as a function of a number of parameters of the problem.