研究題目：太陽能集熱片之集熱實驗與模擬
研 究 生：魯承漢
指導教授：張克勤
平板型太陽能集熱器是目前國內應用最為廣泛的太陽能轉換裝置。集熱板是由金屬集熱板與水流管路組成，集熱板日照面通常被玻璃罩覆蓋，可減少集熱板與外界空氣對流、輻射的熱損失。本研究目的在於建立一套實驗方法來測試噴塗不同選擇性吸收膜集熱片集熱性能好壞之方法，並利用理論分析建立玻璃熱傳過程模型。於本研究中將集熱片持續吸收太陽輻射能，並沒有水流將熱量帶走，等到集熱片達到熱平衡才停止，稱為空曬實驗。算出集熱片的溫升速率，用來比較不同選擇性吸收膜的集熱性能。集熱片集熱性能與吸收率和放射率有關，但以吸收率為主要因素。本研究中以理論方式模擬玻璃層溫度變化，此暫態溫度計算需要求解包含傳導、對流、輻射過程的熱平衡方程式。計算玻璃溫度模型考慮玻璃本身吸收太陽輻射能(波長為0.25 μm至2.5 μm)，但是忽略散射效應。玻璃在太陽光譜波段是接近透明的，但波長超過3 μm之紅外線光譜波段則會趨近於不透明。為了處理這兩種光譜區域完全不同的輻射行為，將玻璃視為輻射參與介質。計算入射太陽光時使用光學薄近似(optically thin approximation)，計算集熱片放射熱輻射被玻璃底部吸收時使用光學厚近似(optically thick approximation)。最後將計算結果與實驗值比較以驗證計算模型，發現玻璃罩上表面誤差在1.5 °C之內，但玻璃罩下表面卻有3 °C的誤差，實驗時熱電偶量測溫度的精準度為 ± 0.5 °C。整體而言，此玻璃溫度模型之預測值經由與實驗值比對後均無太大差異，可準確地估算玻璃暫態溫度的變化以及每一瞬間的溫度分布。
關鍵字：太陽熱能、輻射參與介質、熱傳

ABSTRACT
Subject：Experiments and Simulation of Absorber on Solar Collector
Student：Cheng-Han Lu
Advisor：Ken-Chin Chang
The flat-plate solar collectors are widely used in solar water heating systems in Taiwan. A flat-plate collector consists of the metallic absorbing panel and fluid piping. In addition, the absorbing panel is usually covered with glass cover. The glass cover can reduce convective and radiative heat loss to the ambient air. The purpose is (1) to build up the experimental method and facility to explore the efficiency of absorber which is coated with different selective absorbing films and (2) to establish the heat transfer modeling on the glass cover in this study. The insolation experiment is dedigned for the conditions in which the copper plate continues to absorb solar radiation and there is no flowing water to carry heat away in the test stand. The insolation experiment is stopped as the copper plate reaches thermal equilibrium. Next, the copper plate’s increasing rate of temperature is determined with the measured data for selective absorbing films. When the absorber has the larger absorptivity, the increasing rate of temperature would be larger and the collector performance would be better. In addition, we need to estimate the temperature distribution of glass layer by theoretical simulation. Transient temperature distribution of the glass layer is obtained by solving the energy balance equation with the concerns of conduction, convection, and radiation transfer processes. The glass model is considered that glass absorbs little of solar energy spectrum (wavelengths between 0.25 μm and 2.5 μm) but neglects the scattering effect. The glass is nearly transparent in the solar energy spectrum, while becomes nearly opaque at the wavelengths longer than 3 μm (Infrared subrange). To handle the different radiative behaviors in these two spectrum bands, the glass is treated as the radiative participating medium. The optically thin approximation and the optically thick approximation are respectively applied to the modelings of incoming solar energy on the glass cover and the thermal radiation energy emitted from the solar absorber surface located under the glass cover. Finally, the numerical model is validated by the experimental data with the deviations less than 1.5 °C and 3 °C at the measured points placed on the top and the bottom surfaces of glass cover. It knows that the developed glass model can accurately estimate the transient temperature distribution of the glass layer.

Keywords：Solar thermal, radiative participating medium, heat transfer

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