| Amounts of ice floating on polar sea and tiny ice particles will flow into seawater system of polar ship during icebreaking,they then take part in heat transfer with high temperature water in central cooling system.The seawater-ice two-phase flow has been formed when ice particles mixed with seawater,ice particles exist dynamic behaviors during its transportation,these behaviors can be divided into nucleation,breakage,growth and aggregation based on physical characteristics.The increasing of ice particle diameter can be harmful to transportation and heat transfer of seawater-ice flow,larger ice particles may cause inefficient heat transfer or block flow channel in heat exchanger.So the diameter variation of ice particles is main factor affects heat transfer quality of ice slurry.The initial mean diameter of ice particle is 125μm in this study which is measured through ice slurry flow experiment,the diameter distribution of ice particles is Log-Normal measured by fitting goodness experiment.Result shows that mean diameter of ice particles becomes larger after the whole flow experiment.Then a numerical calculation model CFD-PBM is established and its dynamics UDF is compiled to calculate on Fluent respectively in two models of straight seawater pipe and valve-pipe,in order to study diameter evolution of ice particle of seawater-ice flow.（1）The calculation of straight pipe and valve-pipe shows that ice particle diameter increases with flow distance and nucleation is more evident than breakage.Velocity gradient change is main reason for diameter variation of ice particles,it includes velocity magnitude which facilitates nucleation and velocity direction which facilitates breakage.Besides,increase velocity of ice slurry can reduce growth speed of ice particle diameter.（2）For the condition of ice packing factor（IPF）increasing in ice slurry,velocity gradient dominates diameter variation of ice particles when velocity gradient and ice particles concentration both have great change.On the contrary,increasing of ice particles concentration dominates diameter growth of ice particles when velocity gradient change is small but the change of ice particles concentration is great.Also,velocity gradient change has greater influence to particle diameter more than IPF.（3）The calculation of vertical pipe shows that growth rate of ice particles diameter along antigravity flow direction is larger than that along gravity flow direction.Variation gradient of particle diameter is influenced by velocity gradient near the pipe wall.Moreover,the flow of ice slurry in vertical pipe is uniform and it is beneficial to safe transportation of ice slurry.（4）The flow variation before valve in valve-pipe model is same to that in straight pipe.Negative pressure area exists behind valve in every working condition,diameter and concentration of ice particle in this area are biggest in the whole flow field.Besides,the flow behind valve is irregular and particle diameter distribution of outlet near valve is larger than that away from valve.The mean diameter of ice particles and growth speed of particle diameter are increasing with increasing of IPF,but the increasing of IPF has low impact on growth rate of particle diameter.（5）Vortex becomes larger with valve opening degree decreasing,also the irregularity of flow velocity and concentration distribution are more evident.Besides,velocity gradient and growth speed of particle diameter are increasing with valve opening degree decreasing.In conclusion,increase velocity of ice slurry and reduce valve working time under small opening degree,or reasonable layout of seawater pipe can slow down the growth speed of particle diameter.The evolution laws of ice particle diameter in this study will have instructional significance for the design of central cooling system in polar ships. |
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