Water Object Study Of Salt Gradient Solar Pond And Effect Of Surface Ice On Solar Pond Performance

Salt-Gradient Solar Pond is a brine pond with an increasing salinity from above to below, which is able to collect and store solar energy for utilization as a heat source. The solar pond has been more and more recognized by new energy researchers both at home and abroad because of its advantages such as simple configuration, low cost, little pollution and so on. With the background of solar pond, in this thesis, influencing factors of the solar pond performance have been studied through experiments measurement, theoretic analysis and numerical simulations. Further theoretical bases have been suggested for the future practicality of solar pond. The main works and conclusions are summarized as follows:Firstly, salinity and turbidity studies have been performed on perfusion and maintenance for the actual solar pond. For salinity side, the ratio of evaporation rate of brine has been measured and evaporation equation has been fitted. The areas and time needed for high salinity brine, which is obtained from evaporation pond, have been simulated. For the actual solar pond in this subject, the best value of evaporation pond is 10-15cm in water depth and 100m2 in pond area. A new method for high salinity brine supplying has been suggested: pumping solution from LCZ and dissolving some salt, then the new brine with high salinity was pumped to the LCZ again. To be ensuring the stability of NCZ, the solution flux should be under 0.15×10-3m3/s when pumping out and less than 0.1×10-3m3/s when pumping in. For turbidity side, different turbidity reduction methods have been adopted for seawater, concentrated residual brine left after desalination and bittern left after the production of salt. Based on turbidity characteristic, the perfusion solution of LCZ is bittern and NCZ is concentrated residual brine left after desalination. The experiment result shows that algae and bacteria have been reduced obviously when the solar pond is isolated with air for 72 hours. The experiment also shows that salinity diffusion of LCZ is depressed and the change of turbidity is restrained when brine supplying according to adding cobblestone layer at bottom of the solar pond.Secondly, the reliability of W.S. model at small turbidity range (0<θ< 5.0ntu) has been validated basing on experiment data. A calculation describes the solar radiation transmission functions in different turbidities distributing, and the results have been analyzed through optics and thermodynamics. Thermal performances of LCZ and thermal efficiencies for each layer of a solar pond have been simulated in different turbidities distributing. It is shown that when there is an equal average turbidity in vertical direction, the solar radiation transmission functions, maximal temperature and thermal efficiency in the case of turbidity increases by degrees for a linear distribution from the top down is better. In addition, raining possibly cause high turbidity in ponds. In this paper, new ideas and methodologies have been suggested for preventing rainwater dropping into the solar pond directly and reusing the treated rainwater to supply the solar pond as freshwater.Additionally, small experiment solar ponds have been built in the seaside in order to study the thermal performance of LCZ. The flood tide and ebb tide can erode the bottom and take heat from pond. The heat losing of LCZ can be decreased according to add cobblestone layer at bottom of pond. The sides wall of the solar pond in the seaside have been embed into the sea-sand, which can not be destroyed by seawater, and also there is no exchange between pond water and seawater. So the stability and safety of pond are feasible. Moreover, building solar pond in the seaside can save more soil, it is economical than ordinary solar pond.Finally, surface freezing of solar pond is usual in winter, but the study is fewer both home and abroad. Some small-scale experiments have been accomplished to measure the salt distributing after the brine freezing and the solar radiation transmission under the ice layer. Ice subroutine has been considered when the solar pond is simulated, which makes the continuous study of the solar pond in a long term is more authentic. The salt of surface brine is excreted adown in the course of freezing and melting. This provides a positive influence on keeping stability of NCZ. In addition, the solar radiation transmission of pond is debased and radiant energy reaching the down layer is reduced because of surface ice, but the surface thermal resistance is increased and latent heat of phase change is released in the freezing. In the case of taking into account of ice or not, the simulation results show that maximal difference in temperature of LCZ has been found in the period of heat losing in winter and the max-value is 5℃. In the case of dust and snow accumulation on existing ice cover is not considered, the surface ice is beneficial for the temperature keeping of solar pond in winter.