Study On Freezing Of Axisymmetric Liquid Bridge

The freezing of liquid bridges has important applications in industry.Based on the research results of droplet freezing,an experimental platform is designed and constructed in this paper,and the freezing process of the vertical axisymmetric liquid bridge is experimentally studied.A theoretical model describing the freezing process of liquid bridges was established.The freezing process of the liquid bridge was simulated by using fluid simulation software,and the effects of cold surface temperature,liquid bridge height and volume on the internal temperature distribution of the liquid bridge,freezing front height and freezing time during the freezing process were studied.Main research results are as follows:(1)The theory of crystal growth during liquid bridge freezing is described,and the freezing of the liquid bridge is heterogeneous nucleation.The phase transition of the liquid bridge requires a certain degree of supercooling to overcome the energy barrier for nucleation.(2)A liquid bridge freezing experimental system is designed and constructed.The system mainly consists of two sets of upper and lower cooling systems and coaxial copper discs,which can perform liquid bridge experiments with a contact line radius of 1 mm.(3)The liquid bridge freezing experiment was performed.Liquid bridge freezing can be divided into four stages: supercooling,nucleation/recalesence,freezing and solid cooling.The freezing stage is further divided into the first and second freezing stages based on whether instability occurs.In the second stage,axisymmetric instability occurs in the liquid bridge and forms a convex shape on one side,and then the liquid gradually frozen to form a non-axisymmetric ice ring.(4)The liquid bridge melting experiment was performed,and the melting fronts were formed from the upper and lower cold surfaces.Unmelted ice was wrapped by the melted liquid phase,and suspended in the liquid bridge under the effect of surface tension at first.It didn’t float to the top of the liquid bridge under buoyancy until it was melted to a small enough size.(5)A theoretical model of liquid bridge freezing considering the effects of gravity,subcooling and volume expansion is established.This model can well describe the front height,freezing speed,profile line in the first stage of freezing and overall freezing time.(6)The liquid bridge freezing was numerically simulated with Fluent,and the simulation results were basically consistent with the experimental results.Numerical simulations were conducted to study the temperature distribution,freezing front height and freezing time during the liquid bridge freezing process.The results show that the temperature change inside the liquid bridge during the freezing process is related to the height of the position.The temperature decreases faster when the position gets closer to the cold plate.The smaller the height and volume of liquid bridge and the temperature of the cold plate surface,the bigger the rate of change of liquid bridge temperature and freezing front height.