蓄热器内高压闪蒸传热传质机理研究

Steam accumulator is widely applied to industry and military area, and the key process in the steam accumulator is the high pressure flash evaporation (HPFE). The thermodynamic and outlet boundary conditions in HPFE are different from those in atmospheric flash evaporation, so the mechanism of bubble nucleation, heat transfer and mass transfer is still not clear and required for detailed investigation to guide the design of steam accumulator.In this project, the visualization technique, laser holographic interferometer and image processing technique are applied to analysis the mechanism in the high pressure flash evaporation system. Based on the characteristic parameters of HPFE, the influences of the coupling interaction by outlet boundary and thermodynamic conditions are carefully investigated and the rank of the importance of each factor is also predicted. In order to understand the heat transfer mechanism of HPFE, the bubble nucleation, the energy transmission in the process of flash evaporation between steam-liquid, liquid-liquid and liquid-wall of HPFE chamber are carefully investigated. The mathematic model of heat transfer coefficient is expected to be built based on the mechanism of heat transfer in HPFE. The influence of interfacial effect on the mass transfer is considered by the combination of non-equilibrium thermodynamics and mass transfer theory to build the non-equilibrium theoretical model. The technique application is expected for HPFE in engineering and military based on the understanding and improving of mass transfer mechanism of HPFE.

蓄热器在工业和军事领域中得到广泛的应用，其内部工作过程是高压下工质的闪蒸过程。由于高压闪蒸的热力学和出口边界条件不同于常压闪蒸，因此高压闪蒸和常压闪蒸相比尚存在气泡成核机理不明确，相变条件下传热传质规律不清晰等问题。本项目利用前期所建的高压闪蒸实验台，结合可视化手段、激光全息干涉和图像处理技术，以研究不同热边界条件和出口边界条件下高压闪蒸特征指标的变化规律为切入点，研究出口边界条件和热力学边界条件对闪蒸的耦合作用规律，并对各个因素的重要性进行排序预测；解析高压闪蒸气泡成核机制，分析闪蒸过程中汽液之间、液液之间以及液体和闪蒸室壁面之间热量传递方式，探究高压闪蒸过程传热机理，建立传热系数数学模型；将非平衡态热力学和传质理论相结合，考虑界面效应对闪蒸过程汽液两相传质的影响，建立非平衡态传质理论模型，对闪蒸过程传质机理进行深入解析，完善高压闪蒸传热传质机理，为高压闪蒸的工程和军事应用提供技术支持。

蒸汽蓄热器在工业和军事上应用广泛，究其原因在于其内部工质发生的闪蒸现象。当前，对常压和高压闪蒸机理及传热传质规律的研究还不明确。因此，明确闪蒸机理有利于更好地指导工业生产及军事应用。本项目对闪蒸机理的研究以实验研究为主要手段，并进行了理论分析和数值模拟。采用自编程序探讨了平衡模型与非平衡模型对于模拟闪蒸过程温度与压力变化的可行性，研究发现平衡模型仅满足对闪蒸过程压力变化的模拟，而非平衡模型能同时实现对闪蒸过程压力和温度变化的模拟。在已有闪蒸实验台上利用高速摄像机进行了整个闪蒸过程的观测，发现可将闪蒸过程划分成三个阶段，并通过闪蒸图像研究了闪蒸过程中液相膨胀高度、闪蒸波传播深度及传播速度与初始水温和过热度之间的关系。而对闪蒸图像的进一步灰度分析则发现图像的平均灰度能够反映闪蒸过程的变化，建立了其与初始温度、过热度以及初始水位的关系。根据研究需求对已有测温系统进行了改进，研究了常压闪蒸过程中初始水温、过热度及初始水位对系统温度、压力及NEF变化的影响，开展了闪蒸过程气泡成核机理的分析。进而进行了高压闪蒸的研究，分析了高压闪蒸过程与常压闪蒸过程的不同及其作用机理，研究了初始温度和过热度对高压闪蒸过程的影响规律，并对高压闪蒸过程的两相流动过程进行了模拟分析。本项目的研究深化了闪蒸过程传热传质机理的研究，为高压闪蒸的工程应用提供了技术支撑。