Dynamics Behaviour And Its Effect On Particle Size Distribution And Evolution Of Ice Crystals

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.