Research On Instant Preparation And Parameters Control Of Ice Particles By Ice Abrasive Air Jet

The ice abrasive air jet is a clean and environmentally friendly surface treatment technology.The ice particles will melt into water when the ice abrasive air jet hits the workpiece,which greatly reduces the negative impact of the paint cleaning operation on the working environment and avoids the health hazards caused by the surface treatment operation to the operator,and the by-products after the ice abrasive air jet t paint cleaning are few,which are easier to separate,and the painted solid residues are also easier to handle and the post-processing cost is low Preparation of high-quality,low-energy ice particles is the basis for promoting the application of ice abrasive air jet,but current ice particles preparation technology suffers from high energy consumption and unregulated particle size and hardness.In this paper,a new method for real-time preparation of ice particles based on the freezing principle of heterogeneous nucleation is proposed.In order to study the principle of droplet freezing under this condition,based on repeated experiments,a geometric model of droplet freezing on the vertical lowtemperature wall was established.The droplet freezing process was analyzed by using the FLUENT melting solidification model combined with the VOF model.The influence of the droplet size,initial temperature,and wall temperature on the freezing time and the equation of freezing time was determined by coupling the relationships among the four factors,which were modified by the experimental results of droplet freezing.Based on the numerical simulation results,the freezing process of a single droplet on a lowtemperature wall was obtained.And the hardness of ice at different temperatures was graded twice,followed by the molecular dynamics software GROMACS to clarify the change pattern of intermolecular forces in ice at different temperatures.The results of this study are as follows:(1)A new method for the instant preparation of ice particles on a vertical lowtemperature wall is proposed using the principle of heterogeneous nucleation.Based on the experimental analysis of the droplet shape on a vertical low-temperature wall,a physical model for the numerical calculation of the droplet was established.The results show that the freezing time of the droplets is impacted by the droplet size,initial temperature,and wall temperature.Through the established droplet ice-forming model,it was concluded that the droplet ice-forming time(< 12 s)meets the requirements of instant preparation of ice particles.In addition,the size and temperature of ice particles can be controlled,which proves the feasibility of method.(2)Based on the results of a numerical simulation study of a single droplet on a lowtemperature wall,it was found that the liquid droplet close to the wall will freeze first,and the liquid-solid interface develops along the radial direction with time,but it does not increase linearly along the cross-section of the droplet.The boundary of the droplet freezes before the center of the droplet forming a parabolic liquid-solid boundary because the thermal conductivity of the boundary increases,resulting in an increase in the icing rate,and this trend continues.As the time and droplet size increased,the parabolic-like concavity increased.In the freezing process,the thermal conductivity of the droplet changes as the temperature and solid volume fraction constantly change.The larger the droplet size,the longer its duration in the phase change stage.The rate in the cryogenic phase is greater than that in the phase change stage,and the droplet phase change completion time and cryogenic time continue to increase.When the initial temperature of the droplet is higher,the time for the droplet to reach the phase transition point increases gradually.The higher the wall temperature,the more noticeable the influence on the iceforming time,and the longer the ice freezing time.(3)The Mohs Hardness of ice at different temperatures is roughly graded by experiment,and the second graded by the Leeb hardness.Then,the intermolecular forces of ice at different temperatures were analyzed by GROMACS molecular dynamics software,and it was found that as the temperature decreased,the hydrogen bond forces in the ice are strengthened,and the van der Waals forces also increased,leading to an increase in intermolecular forces and an increase in ice hardness.There are 49 pictures,12 tables and 106 references in this paper.