太阳能热利用系统中的热浮力对流传热和掺混机理研究

针对太阳能热利用中普遍存在的热浮力传热和掺混现象，本项目提炼出与之密切相关的两个关键基础科学问题，即非均匀和非定常边界受热条件下腔体内的热浮力自然对流传热和具有非定常入射速度和温度的热浮力射流对腔体内分层流体的掺混作用。利用目前处于研究前沿的DNS和LES计算流体力学研究手段以及先进的标度分析、能量平衡以及能耗分析等理论研究方法，并配合各种实验测试研究手段对所提炼出的这两个关键基础科学问题进行全面深入的研究，并作为综合应用实例也将研究在真实的应用运行条件下全玻璃真空管太阳热水器内热浮力自然对流传热和掺混作用规律。研究结果将揭示出太阳能热利用中热浮力对流传热和掺混作用的内在规律和湍流在热浮力作用下的形成机制以及多尺度流动和复合传热传质过程的内在规律，为太阳能热利用方式优化设计和其规模化高效推广应用提供科学依据和理论基础，也为传热学和流体力学增添新的重要内容，因而具有重要的科学意义和理论价值。

This project deduces two closely relevant key fundamental problems from the heat transfer by thermal buoyant convection and mixing phenomena which are ubiquitous in solar thermal applications, that is, the heat transfer by thermal buoyant natural convection in cavities under non-uniform and unsteady heating conditions at boundaries, and the mixing caused by thermal buoyant jets of unsteady inlet velocity and temperature when they are ejected into ambient fluids. This project undertakes a thorough investigation into these two key problems by using the cutting-edge DNS and LES numerical simulation techniques, advanced scaling analysis and energy balance analysis theoretical methods, and various experimental tools, and as an example of comprehensive applications also studies the heat transfer by thermal buoyant natural convection and mixing mechanism in all-glass evacuated-tube solar collectors under real operational conditions. The outcomes of this investigation will reveal underpinning physics of hear transfer by thermal buoyant natural convection and mixing processes in solar thermal applications, the generation mechanism of turbulence under the effect of thermal buoyancy, and the multi-scale flow and composite heat and mass transfer processes, which will provide the scientific evidence and theoretical basis for optimized designs and large-scale applications and add new contents for heat transfer and fluid mechanics. Hence this investigation is of significant scientific importance and theoretical values.