Experiments and Simulation of Absorber on Solar Collector

• Main Authors: Cheng-HanLu, 魯承漢
• Other Authors: Ken-Chin Chang
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/33068731615615263157

碩士 === 國立成功大學 === 航空太空工程學系碩博士班 === 100 === 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