An Investigation On The Behavior Of A Rising Ice Particle Through A Solution

Solid-liquid phase change phenomenon exists widely in the nature as well as in engineering and technical fields. In order to control and utilize the heat and mass transfer during the process of phase change, it is of great value to study the mechanism of the process. In the field of solid-liquid two-phase flow, in particular in dispersed two-phase flows, it becomes more and more important to master characteristics of the heat transfer as phase change takes place.In this thesis, the behavior of an ice particle during its rising process in a solution had been theoretically and experimentally studied, including the motion of the particle in the solution, its melting process, heat transfer on the solid-liquid interface and the melting phase morphology.Based on the previous studies, the physical phenomena of an ice particle rising in the solution had been theoretically analyzed and the mathematical model had been built, including the motion equation of the particle, equations of heat transfer on the solid-liquid interface and the controlling equations of the flow field. Furthermore, the differential equation of the motion had been numerically solved by means of the fourth-order Runge-Kutta method.In experiments, the weight method (which measures the mass difference of a particle before and after its rising process) had been used to determine the melting rate and the heat transfer coefficient on the interface. At the same time, a technique of high-speed photograph had been used to investigate the heat transfer during the process of phase change. A high-speed digital camera had been used to observe and record the rising process of a particle in the solution, the melting rate of the particle had been analyzed by means of a photograph method, through which the technique of Computer Image Processing had been attempted to utilize in the field of heat transfer analysis.The results had shown that a spherical ice particle acts a sinuous helical rising trajectory in the solution accompanied with wobbling rotation, which indicates that, in the case of different velocities of solid-liquid two phases, it's unaccepted to neglect the transverse force and movement of the solid particle while describing its movement. As for the melting rate, the result indicates that the velocity of a particle relative to fluid is as significant influence as the temperature difference of particle-fluid on the melting rate of the particle. The result of the melting rate obtained by method of photograph is very good agreement with that by weight method, which indicates that it's possible to use the technique of Computer Image Process inthe field of phase morphology investigation. The variation of Nu with Re and Pr obtained by experiments agrees well with that calculated by the correlations presented in references, but the experimental values are a little larger. It indicates that the measuring method adopted in this thesis is acceptable, and furthermore, because of their enhancement of heat transfer on the interface, the particle rotation and transverse movement should be specially paid attention to when these correlations are used to predict the heat transfer problems of moving particles in fluid. It was also found that an ice particle melts in a way of keeping itself as a sphere when it rises through the solution.