透明蜂窝透过率的计算研究

透明蜂窝结构的透过率是其重要性能之一。该文的工作基于Hollands简化方法将透明蜂窝结构单元(小孔)假想为一个由不透明材料围成的腔体；再根据几何光学原理将腔体内光线的三维反射传播过程转化．为两个假想的平面在单元内不断反射传播的过程。该方法可简化透明蜂窝结构光学透过率的计算。所得计算结果与经典的Monte Carlo法相接近，而过程则大大简化。     

透明蜂窝结构太阳辐射透过率的简化分析

对透明蜂窝结构太阳辐射透过率进行理论分析，提出一个适用于工程应用的近似公式，该方法忽略了对透过率贡献极小的透明蜂窝材料的散射，漫反射和漫透射，认为进入蜂窝单元底部的太阳辐射由三部分组成：１）经壁面的多次透射，２）经本单元壁面多次反射，３）经相邻单元的多次透射与反射，其中第一部分是主要的，据此，可导出横截面为四边形的蜂窝结构的透过率随太阳辐射入射角变化的近似公式，并由实验结果得到验证。     

透明薄膜热辐射性质测定方法的研究

本文介绍了一种测定透明薄膜衰减系数K_λ的方法。其要点是:1.测定透明薄膜的有效透过率τ_λ~*;2.测定透明薄膜的有效反射率ρ_λ~*;3.利用τ_λ~*=τ_λ~*[ρ_λ,τ_λ=exp(-K_λd)]和ρ_λ~*=ρ_λ~*[ρ_λ,τ_λ=exp(-K_λd)]进行迭代求解,算出K_λ。 本方法的主要优点是,利用衰减系数K_λ,就可以用计算方法确定任意厚度d的透明薄膜的光谱和全波长热辐射性质,即:ρ_λ~*、τ_λ、τ_λ~*、ε_λ和ρ~*、τ~*、ε。 基于所述方法,作者对聚四氟乙烯透明薄膜的热辐射性质进行了论证性测定研究。结果表明,这种方法是可行的。     

太阳集热器透明盖板透过率的计算

太阳光线由空气进入太阳集热器透明盖板时,存在折射现象。设空气的折射率为１,太阳光线入射角为θ１,折射角为θ２,透明盖板材料的折射率为ξ,根据光的折射定律,入射角θ１、折射角θ２与盖板材料的折射率ξ之间存在着下列关系：ξ＝ｓｉｎθ１ｓｉｎθ２（１）对于北半球,面向正南安装的集热器,其方位角γｎ＝０°,则太阳光线入射角θ１可用下式计算：ｃｏｓθ１＝ｓｉｎ（φ－ｓ）ｓｉｎδ＋ｃｏｓ（φ－ｓ）ｃｏｓδｃｏｓω（２）式中：φ———地理纬度;ｓ———集热器倾角;γｎ———集热器方位角;δ———太阳赤纬;ω—…     

平板集热器的最佳倾角

我们知道,到达集热器透明盖板采光面上的太阳辐射量,与太阳光线和集热器表面的法线之间的夹角(入射角)有关,它可用下式表示 H_b=H_ncosθ_T (1)式中,H_b为到达集热器采光面上的太阳直接辐射量,H_n为垂直于太阳光线平面上的直接辐射量,θ_T为入射角。上式表明,太阳光线的入射角越小,到达采光面的太阳能量越大,θ_T=0°时达最大。因此,对于固定安装的集热器,为了获得最大的太阳辐射量,就必须使采光面在正午辐射最强时,与太阳光线垂直(如图1所示)。这时有下述关系:     

倾斜TIM太阳能空气集热器的数值模拟

介绍了一种新颖透明隔热材料(TIM)的蜂窝,将该种TIM蜂窝应用于太阳能空气集热器可以起到较好的集热效果.根据简化的数学模型,作者利用FLUENT软件对集热器内部流场进行了数值模拟,指出了集热器较好的运行工况,并分析了该集热器的应用前景.     

用大型积分球测定透明蜂窝结构的太阳辐射透过率

大型积分球测试系统的主体为自行研制的积分球，其直径大，试样窗口的直径也可开得较大，能测定面积和厚度较大的透明隔热材料和器件，利用该系统测定了在不同入射角下塑料透明蜂窝结构透过率，并对两各不同长度比的蜂窝单元的实测值作了比较。     

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。     

二氧化锡选择性透过涂层对平板集热器效率的影响

本文报道了水解法制备的选择性透过氧化锡涂层的特性(太阳透过率τ=0.69—0.71,红外发射率ε=0.24—0.31),研究了涂层厚度和导电性对涂层光学性能的影响。有涂层与无涂层单层玻璃盖板平板集热器相比,效率无明显提高。第二层内表面有涂层的双层玻璃盖板集热器与普通双层玻璃盖板集热器相比,效率有一定的提高,并且集热温度较高。     

蜂窝结构太阳辐射光学特性的数值计算方法

本文在简化的单层材料太阳辐射光学特性模型的基础上,讨论了用Monte Carlo方法计算圆管玻璃蜂窝结构和三角塑料蜂窝结构的太阳辐射透过率、吸收率和反射率的数学模型,并分析了各参数的影响。计算结果和实验结果基本相符,本方法可用于蜂窝结构太阳能中温集热器设计的优化。     

An evaluation of a transverse slatted flat plate collector

It is generally accepted that the insertion of a type of honeycomb structure into the air gap between the absorber plate and the transparent cover of a flat plate solar collector will suppress convection if the honeycomb dimensions are matched to the particular dimensions and operating temperatures of the collector. However relatively little research has been carried out to characterise the effectiveness of a convection suppression device under actual operating conditions.This paper surveys the experimental work carried out at the University of Melbourne, Mechanical Engineering Department, and its relationship to other experimental and theoretical research, reported in the literature. The experimental program involved the comparative testing of two collectors, identical except that one was fitted with a convection suppression device made of parallel glass slats placed laterally across the collector between the absorber plate and the cover glass. Testing was carried out in a laboratory situation with five convection suppression devices of differing aspect ratio ( ), and the most effective of these devices (aspect ratio ), was tested in the Melbourne University Solar Testing Area under a range of actual operating conditions.In the laboratory tests, the ability of the honeycomb to suppress convection was tested, whilst in the outdoor tests, the influence of the honeycomb on the transmission of solar radiation to the absorber plate was also evaluated. It was found that at high operating temperatures the convection suppression device gave rise to considerable improvement in performance. A forty percent improvement in instantaneous thermal efficiency was produced for fluid temperatures of approx. 100°C. However, if the collector is not oriented correctly the overall improvement in thermal performance will not be as large, due to the decrease in solar transmittance caused by the honeycomb. This indicates the probable need for some form of collector tilt adjustment during the year if the long-term thermal performance is to be optimised.     

Finite time thermal analysis of ground integrated‐collector‐storage solar water heater with transparent insulation cover

A transparent honeycomb insulated ground integrated‐collector‐storage system has been investigated for the engineering design and solar thermal performance. The system consists of a network of pipes embedded in a concrete slab whose surface is blackened and covered with transparent insulation materials (TIM) and the bottom is insulated by the ground. Heat may be retrieved by the flow of fluid through the pipe. A simulation model has been developed; it involves the solution of the two‐dimensional transient heat conduction equation using an explicit finite‐difference scheme. Computational results have been used to determine the effect of such governing parameters as depth as well as pitch of the pipe network and collector material on the thermal performance of the system. The pipe network depth of 10 cm and the TIM cover made of 5 cm compounded honeycomb seem suitable for the proposed system. Solar gain (solar collection efficiency of 30–50% corresponding to collection temperature of 40–60°C) and the diurnal heat storage characteristics of the system are found to be of the right order of magnitude for solar water heating applications. Copyright © 1999 John Wiley & Sons, Ltd.     

An approximate method for calculating the heat flux through a solar collector honeycomb

An approximate calculation of the radiative-conductive flux of heat from the absorber to the cover plate of a flat plate collector equipped with a convection-suppressing honeycomb is developed, using an exponential kernel approximation to the passage transmittance function of the honeycomb cells. Fluxes predicted by this method are found to be in satisfactory agreement with the results of previously reported calculations and experiments. If a selective absorber plate is used in a collector of this type, heat transport by the air in the collector eliminates the radiation slip between the honeycomb and the absorber plate, so that thermal emission by the walls of the honeycomb in close proximity to the hot absorber may largely cancel out the advantage gained by making the absorber plate selective.     

带透明蜂窝盖板和辅助反射面的整体式太阳热水器

作者对一种带透明蜂窝盖板和辅助反射面的整体式(ICS)太阳热水器进行了实验研究。该太阳热水器采用截面为三角形的水箱，水箱背面和侧面用30mm聚苯乙烯泡沫隔热，其它两个面为吸热面。底吸热面利用辅助反射面加热，而上吸热面则覆盖5cm的透明蜂窝及2mm的有机玻璃板。这种设计加大了ICS太阳热水器的吸热面积，同时也降低了吸热面向环境的热损。对实验结果的分析表明，该热水器的热效率不高，但保温性能很好。     

An approximate equation for predicting the solar transmittance of transparent honeycombs

An approximate equation is presented for predicting the solar transmittance of transparent honeycombs. The method accounts for scattering which occurs in such honeycombs by introducing diffuse components for both the reflectivity and transmissivity of the honeycomb wall. Required inputs to the equation are the optical properties of the honeycomb wall material, averaged over the solar spectrum. Methods of determining these properties are described. Although strictly applicable to a square-celled honeycomb, the equation should be approximately valid for hexagonal honeycombs as well. The equation is compared to the measured transmittance of a hexagonal-celled Lexan honeycomb with good results.     

Heat transfer across corrugated sheets and honeycomb transparent insulation

This paper describes the design of a simple guarded hot-plate apparatus for the measurement of heat transfer across transparent insulation. The apparatus is used to measure the heat transfer coefficient across a transparent corrugated (zigzag) sheet and honeycomb transparent insulation. The sheet and honeycomb are made from cellulose acetate film, which has high absorptance for long-wave thermal radiation and high transmittance for short-wave solar radiation. The corrugated sheet performs well, however, honeycomb transparent insulation of the same height and material appears to be superior due to greater thermal radiation blockage and better solar transmission characteristics. A numerical model for a honeycomb is developed which shows good agreement with the experimentally measured results.     

Experimental performance of three solar collectors

Simultaneous testing of solar collectors is important for the determination of accurate comparative performance data. Three flat-plate solar collectors were tested for over six months: a water trickle collector, a typical collector with double glazing, and a thermal trap collector. The first two collector types have been previously tested by other investigators, but the development of the thermal trap collector is unique to New Mexico State University, where in 1964 work was initiated on this type of collector. The thermal trap collector employs a transparent solid (methyl methacrylate) adjacent to the fluid cooled collector plate. It is found that by the use of this transparent solid, which has a high transmittance of short wavelengths combined with a low transmittance of long wavelengths and a small thermal conductivity, high temperatures can be achieved.

The comparative collector tests were performed for a variety of operational conditions. The collector efficiencies were experimentally determined, and analysis of the collector losses was accomplished. The thermal trap collector was found to have a higher operational efficiency than the other collector types and is capable of collecting solar energy for a longer period of time each day. At operating temperatures above 145°F, the thermal trap collector is more than twice as efficient as the water trickle collector.