Theoretical approach of a flat-plate solar collector taking into account the absorption and emission within glass cover layer
Theoretical approach of a flat-plate solar collector taking into account the absorption and emission within glass cover layer
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考虑玻璃覆盖层内吸收和发射的平板太阳能集热器的理论方法
DOI：
10.1016/j.solener.2005.06.002
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发表时间：
2006
期刊：
影响因子：
6.7
通讯作者：
S. Maruyama
中科院分区：
文献类型：
--
作者：
M. Khoukhi;S. Maruyama
提出了一种考虑玻璃罩作为吸收发射介质的黑色吸收体平板太阳能集热器的严密理论方法。采用射线发射模型（REM2）的辐射单元法，分析了玻璃材料在一维情况下受太阳和热辐射的非灰色平面平行介质。采用了Rubin提出的透明玻璃窗的光学常数。这些光学常数，即透明玻璃复折射率的实部n和虚部k的160个值，涵盖了计算通过玻璃罩的太阳和热辐射传输的兴趣范围。对于使用160个n和k值的非灰色计算来说，预测太阳能集热器热行为的计算时间太长。因此，提出了一种合适的半灰色模型来进行快速计算。本研究得到的效率曲线轮廓在形状上不是线性的。实际上，集热器的热损失是对流和辐射的结合，并且是高度非线性的。研究了外对流换热对效率曲线的影响。事实上，当对流换热方式比辐射换热方式占主导地位时，效率曲线的轮廓大致为直线。因此，热损失系数可以用克莱因模型计算。研究还表明，风速对玻璃罩平均温度的影响是非常重要的。这种效应随着吸收器平均温度的增加而增加。
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.