The Light Of The Surface Of Porous Materials - Heat Transfer Performance

The solar-collecting plate with porous surface has enhanced light-heat absorptivity, can be applicated prospectivly in solar-collecting settings. To fill up the insufficiency of system study in a certain degree and settles a certain foundation for porous material on light-heat property of surface porous material, the basic theory and experimental study for light-heat properties of the surface porous material were carried through in this paper.In this paper, the theories study and experiments study are provided respectively. On the aspect of theories studies, mathematical model of equivalent heat-absorptivity, equivalent heat-radiance and equivalent solar-collecting efficiency of the porous surface material are established respectively. Also the effects of porous structure parameter on light-heat property are analyzed. On the aspect of experiment study, the porous plates with different porosity and cell-diameter are prepared, the relevant experiment equipments are designed, which are used to measure the equivalent absorptivity> heat radiance and heat-collecting efficiency of these material. The theories conclusions of light-heat property of porous surface material are verified by experiment.In order to obtain the equivalent absorptivity of porous surface, light-track method is used. Firstly, porous surface structure parameters are simplified; then, the reflection rules of light on the semicircle, hemisphere and porous surface plate are analyzed respectively; finally, a mathematical model of equivalent light-heat absorptivity is established as below:Analyses of the mathematical model of equivalent light-heat absorptivity show that: the equivalent absorptivity is effected by the porosity, ray angle of incidence and material inherent light-heat absorptivity, and is independent of suface cell diameter; equivalent light-heat absorptivity increases along with porosity as a function of a straight line. When the angle of incidence is 40° ~ 60° and theabsorptivity is 0.4~0. 5, the effect of porosity on equivalent light-heat absorptivit) is most obvious ; even the material inherent light-heat absorptivity is as high as 0.9. equivalent light-heat absorptivity of porous surface can still raise remarkably, up tc 4%. 40° and 75° are two boundary points influencing equivalent absorptivity, equivalent absorptivity increases soonly with angle of incidence in the zone [40°,75 °],while equivalent absorptivity increases slowly with angle of incidence less than 40 "or more than 75° .The mathematics model of heat radiance on porous surface and heat-collecting efficiency are also established via theory analysis in this paper:It is shown that: the heat radiance and beat-collecting efficiency are independent of cell-diameter; equivalent heat radiance increases along with the increasing of porosity directly. The effect on porosity to solar-collecting efficiency will be strengthened with the increase of material self light-heat absorptivity and the angle of incidence. The effect of angle of incidence on equivalent solar-collecting efficiency lies in: 40° and 80° are two effect points, along with increasing of angle of incidence, equivalent solar-collecting efficiency of the aluminum plate with porous surface increases soonly with angle of incidence in the zone [30° ,80° ],while equivalent solar-collecting efficiency increases slowly with angle of incidence less than 40° or more than 80° .The design and preparations of experiment equipment are introduced in the experiment and the light-heat properties of porous surface aluminum plates are tested. Also the relationship between equivalent absorptivity and solar-collecting and each effect factors is discussed. The tested result show that: the theories calculation model curve is near to experiment curve, which illuminates that the theories calculation model is reasonable as the error is acceptable, the tested result confirms that light-heat properties are dependent of incidence angle and porosity but independentof cell-diameter, which is consistent with theoretical model analysis conclusion. Thus the content of this study can provide certain theories foundation on analyzing light-heat property of porous surface materials and certain technique reference on development of porous surface material.