【作者】 徐爱祥；

【导师】 刘志强；

【作者基本信息】 中南大学 ， 土木工程， 2014， 博士

【摘要】 发展展冰浆动态蓄能技术是解决电网负荷的供需平衡与太阳能的高效连续开发利用的有效途径。冰浆的生成、存储及应用过程与冰晶粒径及分布密切相关。由于冰晶的微观性及其生成与存储所经历的复杂物理过程,无论是其形成过程与机理,还是在形成与演变过程中的微尺度动力学行为特点与演化规律,都缺乏相关的理论描述和定量描述。因此,本文重点研究冰浆制备与存储过程中冰晶颗粒动力学行为与粒径分布演化规律,为更深层次地揭示冰晶的形成、存储与控制的机理与规律提供理论依据与科学参考。本文首先从微观角度分析了冰晶成核的机理,并对影响成核的影响因素进行讨论；再通过建立冰层生长控制模型,从宏观角度对间接式冰浆制备过程冰层生成进行了研究,并探讨影响冰层生成的主要因素。结果表明：1)接触角与界面粗糙度的增加会降低溶液临界成核能；添加剂能够增加溶液内部临界成核能差,抑制异质成核；临界成核能差随着过冷度的增加而减小；过冷度的增加会减少临界成核能,从而增强异质成核,且过冷度对成核的影响比接触角更为明显。2)冰层生长控制模型计算结果与文献实验结果基本一致,表明模型可用于定量描述间接式冰浆制备冰层生长过程。3)乙二醇(EG)溶液比氯化钠(SC)溶液具有更强的抑制冰层生长的作用,增加添加剂浓度会降低冰层生长厚度,溶液流速过低或过高会破坏冰层形成时生长作用与剥离作用之间的平衡。搭建包含冰浆制备与冰晶图像采集的实验平台,对冰晶粒径分布规律进行实验研究。针对实验过程中发现的冰堵问题,提出间接式冰浆制备系统冰堵判定条件,并进行了实验验证。实验获取了冰晶颗粒图像,采用基于颗粒图像处理技术的数字图像测量方法,研究选取合适的数字图像处理算法,提取冰晶颗粒图像的特征参数。对冰晶颗粒图像的特征参数进行统计,并进行拟合优度检验,结果表明冰晶粒径分布的最优分布函数为Log-Normal分布函数。实验获得了冰晶粒径分布规律,为本文模拟研究中冰晶粒径分布拟合提供了可靠依据。通过冰晶动力学行为非平衡热力学分析,建立了描述冰晶动力学行为与粒径分布演化的数群平衡模型,运用改进有限容积法(IFMV)对模型进行求解,并利用文献中的实验结果对模型进行了验证。结果表明：1)通过算法比较分析发现,IFMV算法能较好的消除方程中对流项的影响,减小了生长动力学行为条件下数值解的失真,而在团聚动力学行为中,两种算法计算结果与分析解基本一致。2)冰晶粒径数量密度分布和平均粒径的模拟结果与实验结果的一致性,验证了模型的可靠性,表明该模型可用于冰晶动力学行为与粒径分布演化问题的分析研究。3)分析指出动力学行为核模型参数、冰晶粒径的初始分布、模型的边界条件、模型中冰晶粒子形状以及载流溶液与外部环境等因素是导致模型误差的主要原因。基于冰晶颗粒数群平衡模型,研究了破碎与团聚两个动力学行为对冰晶存储的影响,阐述了破碎与团聚对冰晶存储的作用机理与规律；再综合考虑冰晶的成核、生长、团聚与破碎等动力学行为,系统研究了添加剂种类与浓度、含冰率与耗损率等外因对破碎率与团聚率、冰晶粒径分布密度及平均粒径的影响。结果表明：1)团聚和破碎动力学行为是影响冰浆存储过程冰晶粒径演化的两个重要因素,两者“作用方向”相反,且破碎与团聚经历从最初的破碎与团聚“均衡作用”发展成团聚“主导”的过程。2)同浓度下,添加剂乙醇与乙二醇对冰晶粒径增长速度抑制效果比氯化钠好；减少溶液的浓度会降低冰晶粒径增长的速度；含冰率越低,冰浆溶液中冰晶粒径增长越慢；耗损率越高,冰浆溶液中冰晶粒径增长越慢。更多还原

【Abstract】 ABSTRACT:Development of ice slurry dynamic storage technology is considered as a promising way to keep the supply and demand balance of grid load and improve the efficiency and continuity of solar energy thermal utilization. Formation, storage and application of ice slurry have a close relationship with ice crystals particle size distribution and evolution. However, since the microscopic features of ice crystals and the evolution processes of complex dynamics behavior, neither the physical process of the formation and storage of ice slurry, nor the mechanism and evaluation law of dynamics behavior are lack of relevant theoretical and quantitative description. Hence, this study mainly focuses on dynamics behaviors and evolution of ice crystals during the process of ice slurry’s formation and storage. This research is expected to be a theoretical basis and scientific reference to reveal the mechanisms and laws of ice crystals formation, storage and control.Firstly, mechanisms of ice nucleation were analyzed from the microscopic point of view and influence factors of nucleation were discussed. The growth control model of ice layer was developed to studied ice layer growth of indirect ice slurry system from a macro point of view, and influence factors of ice layer growth were discussed. The results shows that the increase of contact angle and surface roughness can reduce the critical energy of nucleation, additives can increase the critical energy of nucleation, inhibiting heterogeneous nucleation; the critical energy of nucleation increases with the decreases of degree of supercooling; increase of the degree of supercooling can reduce critical to the critical energy of nucleation, thereby increasing the heterogeneous nucleation, and effect of the degree of supercooling on the nucleation is more obvious than that of the contact angle.2) The results of growth control model are consistent with experimental results, which show that this model can be used to describe the process of ice layer growth of indirect ice slurry system.3) EG solution has stronger effect on inhibiting the growth of ice layer than SC, the increase of additive concentration can reduce the thickness of ice growth, and higher or lower solution flow can break the balance of growth and stripping effect on the process of ice layer formation.Then, particle size distribution of ice crystals was experimentally studied with the experimental platform, which included systems of ice slurry production and ice crystals image acquisition. Judgment conditions for ice blockage of indirect ice slurry system was proposed and then experimentally verified. The images of the ice crystals were obtained from the experiments, and digital image processing algorithm was used to extract the characteristic parameters of ice crystals. Optimal distribution function for the ice crystal size distribution was confirmed as the Log-Normal distribution function through the analysis of the ice crystal size distribution experimental results and the test of goodness of fit, so as to provide a reliable basis for the simulation of ice particle size distribution fitting in the next chapter.Next, population balance model of ice crystals was developed to describe dynamic behavior of ice crystals as well as the distribution and evolution of particle size through analyzing the non-equilibrium thermodynamics on dynamic behaviors of ice crystals. Improved finite volume method (IFMV) was used to solve the PBM, and then the PBM was validated by using the experimental results in references. The results indicate that1) Comparative results of the algorithm shows IFMV algorithm can eliminate the influence of the equation of convective terms, and reduce the distortion of the numerical solution for the growth kinetics behavior, but in the aggregation dynamic behavior, the results of both numerical method keep consistent with the analytical solution.2) The reliability of the model was verified by the agreement of both model prediction and experimental results of number density of ice crystals and average particle size, which stated that the PBM can be used for the research of ice dynamic behaviors and the particle size distribution and evolution of ice crystals.3) Possible reasons of deviation between the model prediction and experimental results could be kernels of the dynamic behavior, the initial particle size distribution of ice crystals, the boundary condition of the model, the shape of ice particle and the carrier solution and the external environment.At last, the dynamical behaviors of breakage and aggregation influencing on the ice crystals storage were analyzed based on population balance model of ice crystals, the mechanisms and laws of breakage and aggregation dynamic behaviors were explained. The effect of additive type and concentration, ice packing factor and dissipation rate on the rate of breakage and aggregation, the number density of ice crystal size distribution and the average ice crystal size were studied under the comprehensive consideration of the ice crystal dynamic behaviors such as nucleation, growth, breakage and aggregation. The results show that:1) the dynamic behaviors of aggregation and breakage are considered to be two important factors influencing the evolution of ice crystals size during ice slurry storage. The two dynamic behaviors have opposite effect and the processes of ice slurry storage experience from "breakage-aggregation in equilibration" in the initial phase to "aggregation in dominant" at last.2) effect of EA and EG on inhibition of the ice crystal growth is stronger than SC; reducing the concentration of the solution can reduce the growth of ice crystals; the lower the rate of ice is, the slower can the growth of ice crystal be in the ice slurry solution; The higher loss rate is, the slower can the growth of ice crystals be in the ice slurry solution.更多还原