Experimental And Numerical Investigation On The Solar Radiation Transmission And Double-Diffusion Of A Solar Pond

Due to lack of energy resource, the exploitation and utilization of renewable energy have been strategic measures in all around the world. As a clean and permanent energy resource, the solar energy has been generally recognized. Solar pond, a kind of unique saline pond, has a ability to collect and store solar energy. Research on its performance has been more and more popular at the present.Three parts of contents are included in this dissertation, namely, solar radiation transmission model, experiment on the bittern solar pond and research on its heat-salt double diffusion characteristics.Radiation transmission model, also called radiation transmission function, is the ratio of the solar radiation flux at a certain depth to that on the water surface. It has a important effect on the thermal performance of a solar pond. The bigger the radiation transmission function is, the more solar radiation flux is absorbed by the pond water, and the better the performance of a solar pond is. By choosing different water medium as research object, we measured the radiation transmission functions at different turbidities. The experiment results prove that the W.S. Model is reliable at smaller turbidities through a comparison of the measured values with W.S. Model. The radiation transmission functions is measured at bigger turbidities. Through a regression analysis, a new radiation transmission model suitable for bigger turbidity water is obtained, which extends the application range of W.S. Model. Based on W.S. Model and the big-turbidity model, and by using the reflection theory, the improved radiation transmission model is put forward, which considers both turbidity and pond bottom reflectivity. Based on numerical analysis of the improved radiation transmission model, the combined effect of water turbidity and bottom reflectivity, and affecting factors of the optimum thickness of non-convective zone and steady thermal efficiency for a solar pond are analyzed. This provides a guide for high-effective operation of a solar pond.A bittern solar pond with an area of 80m~2 is built. In the solar pond, the low part is filled up by bittern from salt production, the middle part is filled up by bittern and seawater at different ratios and the water surface is washed by fresh water. The heat storage experiment is accomplished. The profiles of temperature, density and turbidity of the solar pond aremeasured. Special experiments, such as the characteristics of bittern turbidity, bittern clarification and water sterilization were carried out. Methods for filling-up and maintenance of bittern solar pond are put forward. The research results show that the bittern solar pond is an economical heat collection and storage equipment which can find wide applications.Solar pond is a typical double diffusion system. Positive density gradient caused by concentration gradient is helpful to the stabilization of a solar pond, while negative density gradient caused by temperature gradient is harmful to the stabilization. Most early prediction models of thermal performance of solar ponds assume that the solar pond is stable, and that interfaces between each layers of the pond is steady. In those models, the pond performance does not be analyzed from the view of double diffusion. Taking account of this shortage, a turbulent entrainment model is introduced. This model includes effects of water evaporation, turbidity and environmental wind on the double diffusive system, which is more complete than the previous ones. Through analysis based on experiments and theory, the advantage and disadvantage of this model are discussed. Consequently, a simplified low Reynolds number double-diffusive turbulence model is introduced. Through comparisons between simulation and experiment, it is proved that the simplified model is suitable to describe the double diffusive system. The importance of the Soret effect in double diffusive system is demonstrated. A heat-salt double-diffusive k - e turbulence model including Soret effect for solar ponds is put forward. The double diffusion behavior and its affecting factors are predicted and analyzed by using this model. Experiment proves that this model can satisfactorily predict the double diffusive characteristics of a solar pond.