| Summary: | 博士 === 國立成功大學 === 航空太空工程學系 === 105 === Most of solar energy applications aim at beam irradiance as the main energy source, whereas there is a lack of research looking into the effect of the diffuse irradiance. However, the weather of Taiwan is not always clear and sunny, the annual averaged diffuse irradiance in Tainan, the southern part of Taiwan, is up to 52% of the global horizontal irradiance. It is therefore inevitable to study the effect of diffuse irradiance in solar energy applications.
A preliminary numerical study is first conducted. The object is a solar test stand that is operated without the working fluid, and the absorber plate is enveloped by a glass cover. The study attempts to reduce the number of filed test experiments, in which certain requirements on the weather condition have to be satisfied for the experiments to be effective. As a result, the predictions of the numerical model indicate acceptable accuracy only in a clear sunny condition, while bad result is generated on cloudy days due to high diffuse fraction. To solve this issue, the diffuse irradiance is simulated by Monte-Carlo Ray Tracing (MCRT) method by using two diffuse models: collimated and isotropic models. By taking the beam incident angle and the diffuse fraction as its input, the isotropic model can predict the absorption of the solar absorber and the glass cover with acceptable accuracy. The results are then generated to a look-up table that shows the energy absorbed by the absorber and the glass cover. The data provided by the table is further employed in other numerical simulations on a single-tube solar collector. Steady state and transient simulations are subsequently carried out according to the data from the look-up table. The predicted results are in good agreement with the experimental data.
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