Study On The Motion Characteristics Of Liquid-solid Two-phase Flow And Wall Abrasion In The Vertical Upward-flow Heat Exchange Tube

Heat exchangers have been widely used in various industrial field,but due to many factors,the heat transfer efficiency is generally low,and fouling occurs during the operation,and the thermal conductivity of the scaling layer is very small,which will lead to poor heat transfer in the tube.At the same time,due to the appearance of the scaling layer,the flow resistance in the tube increases,which further reduces the heat exchange efficiency.By adopting liquid-solid fluidization technology,this problem can be solved effectively.In this research,the particle motion in the heat-exchange tube and the abrasion of the particles on the tube wall are studied.The findings of this study have great significance for the design and maintenance of heat exchangers.The content of this article is as follows:(1)The development and existing problems of the liquid-solid fluidization technology were introduced.The research methods of this paper are based on the analysis and comparison of various research methods.At the same time,the analysis of the force of the particles provides theoretical guidance for the subsequent particle motion.(2)The CFD-DEM model method was used to study the particle motion characteristics of the vertical upward-flow heat exchange tube.Under 135 working conditions,the axial movement of the particles in the tube experienced from chaos to dynamic equilibrium,and ellipsoidal particles were in a relatively mild state in the movement.In terms of the axial distribution of the particle concentration,the density was high at lower part of the tube while low at the upper part.The inlet flow rate is negatively correlated with the particle concentration in the tube,and the particle size is positively correlated with the particle concentration in the tube.In terms of radial particle concentration distribution,on the whole,the particles gradually approached to the center of the tube when the inlet flow rate and particle size increased.As the inlet concentration of the particles increased,the particle tended to concentrated at the tube wall more.(3)The DPM model method and CFD-DEM model method were used to study the wall abrasion from the perspective of abrasion rate and collision force.By comparing the results obtained by the two methods,the rationality and reliability of the research results are verified.The study has shown that the order of influence of different factors on wall abrasion is: inlet flow rate > particle diameter > particle inlet concentration.After comparing the results of three types of particles(spherical particles,cylindrical particles,ellipsoidal particles),it can be seen that in the same working condition the magnitude of the collision force of the particles in the tube against the wall is: ellipsoidal particles > cylindrical particles > spherical particles.