| Development and utilization of renewable energy has become one of the important ways of energy sustainable development against a background of the fossil energy face with the dual pressure of resource depletion and severe pollution. "National Guideline on Medium and Long-Term Program for Science and Technology Development (2006-2020)" present the subject of development and utilization of renewable energy with the low cost large scale mode.As one of the clean and permanent renewable energy, solar energy has great significance for conventional energy conservation, protection of natural environment, the mitigation of climate change. Based of renewable energy, solar energy will be the main energy in the next century and it will be the cornerstone of human future energy. Solar pond is brine pond which has the function of collect, store solar energy, and as low temperature heat source for external heating. Which have the advantages of universality, huge, harmless and long-term.In this paper we developed the basic research on heat collecting system experimental measurement and numerical simulation of the salt gradient solar pond. Several methods are experimentally investigated with the aim of enhancing the thermal characters of solar pond which includes changes in solar pond structure, putting porous medium to the bottom of the solar pond, covering the solar pond with a transparent plastic film, and combining a vacuum tubes solar collector with the solar pond.The main research work includes experimental measurement, numerical simulation and energy efficiency analysis etal. The specific work is as follows:(1) The experimental research of the article includes two parts:basic experiment in laboratory and outdoor experiment.Basic experiment in laboratory includes:Measure the Physical parameters of porous media experiment of the character of heat storage for different PM; the experiment of the Influence of Porous Medium (PM) on the Turbidity; the experiment of Meteorological parameter measurement, the experiment of Measure the solar radiation quantity and the experiment of evaporation pond. The results of this part can be used as boundary conditions of experiment and numerical simulation in the next step work. The rules of experiment may provide guidance for optimizing the performance of the solar pond, so as to lay a good foundation for the simulation and the experiment of study the solar pond in the next work.On the basis of improve the heat-supply temperature of the solar pond, two mini solar ponds with area of 2.4m×2.4m and depth of 1.2m are built. We conducted experiments to measure the temperature and turbidity distribution; through nonlinear fitting of experimental data to construct radiation transmission mixed regression model.We investigated the thermal performance of the solar pond by comparing the temperature distribution of the two solar ponds. Through the stages of comparative experiment explored include putting porous medium to the bottom of the solar pond, covering the solar pond with a transparent plastic film, and combining a vacuum tubes solar collector with the solar pond. Discussed three kinds of methods on the temperature characteristic and turbidity influence of solar pond, explore ways to strengthen the heat performance of the solar pond.(2) On different research focus on, numerical simulation study used of one-dimensional (1D) and two-dimensional (2D) numerical simulation respectively.ID numerical simulation focused on the pool temperature changes, heat loss analysis and var iation of thermal properties of solar pond at several strengthening measures.2D numerical simulat ion focused on the distribution of space fluid field in pond and 2D heat transfer model of trapezoid al side wall. Dynamic stability analysis of interface is also studied.Thermal performance of the solar pond was numerically simulated by one-dimension model base on the experimental data. The simulation built a thermal and salt double-diffusion model. Matlab7.0 is carried on the one-dimensional numerical simulation of solar pond with surface 2.4m×2.4m and bottom 1.0m×1.0m. Taking the local climate and solar radiation factors into consideration, a modified bottom reflection make radiation transmission model is more reasonable. A detailed heat dissipation model considering the heat loss of the surface, the wall and the soil layer, the results can be used as boundary conditions to study the stability and heat performance. It showed a good agreement on the experimental data and the simulation. And we compared of the trapezoidal and rectangular pond on the temperature distribution, heat loss, the wall temperature. On the basis of the results, a numerical simulation is conducted on enhanced solar pond performance. Established the heat balance equation of porous media model, the solar collector and the cover model, discussed the influence on the performance and stability of solar pond by different reinforce measures.Set up the one-dimensional prediction model of enhanced solar pond and analyzes the temperature profile development of enhanced solar pond.Two-dimensional model established mathematical model of double-diffusion and introduced user-defined functions of brine density?heat source?boundary condition etal. We carried out two-dimensional unsteady numerical simulation research basing on commercial software Fluent 13.0 for a trapezoidal salt gradient solar pond. By means of user-defined functions introduced brine density?heat source?boundary condition etal and salinity transport equation is established at the same time. The simulation results are compared with the experimental data and simulation results in the literature. The model was verified in two aspects through the distribution of temperature field and flow field.Compared with the one-dimensional model, the two-dimensional model focuses more on the influence of the solar pond internal stability and flow regime change caused by double diffusive convection and surface wind speed phenomenon. In the condition of heat and salt diffusion, internal temperature field, flow field and dynamic change law and boundary layer stability characteristics of trapezoidal solar pond are analyzed.(3) The solar pond efficiency analysis includes of energy efficiency and exergy efficiency analysis.The research is based on the first law of thermodynamics and the second law of thermodynamics, we combined the definition of energy efficiency and exergy efficiency and analyzed energy flux which import and export in each layers in the trapezoidal solar pond, established energy efficiency and exergy efficiency expression and then derived energy efficiency and exergy efficiency of trapezoidal solar pond. By comparing energy efficiency of the trapezoidal and rectangular pond and compared different running stage efficiency, summarizing the energy utilization efficiency of the solar pond. |
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