Numerical Simulation Of Water Droplet Impact Characteristics And Icing Of Valve Members Of Polar Ships

Global warming caused by the burning of traditional energy is becoming more and more serious,which leads to the melting of sea ice in the Arctic region,and also raises the possibility of the development and utilization of the Arctic shipping routes.The development of the Arctic shipping route greatly shortens the voyage distance from China to ports in Europe and the United States,thus reducing waste gas emission and shipping costs.The Arctic itself stores rich natural resources such as natural gas and crude oil,etc.The advantages of the Arctic region make the Arctic increasingly attract the attention of various countries.However,due to the harsh meteorological conditions in the polar regions,such as low temperature all the year round and high moisture content in the air,polar ships will face the problem of icing when sailing.Icing of ship valves will lead to the failure of fasteners at the valve packing box and the damage of the sealing of the valve stem,resulting in safety accidents.Especially for polar LNG carriers,freezing of cryogenic valves will lead to internal media leakage,and contact with air may cause fire or explosion accidents,posing a threat to the life safety of personnel on board.At present,there are few researches on the icing of polar ship valves,and most of the calculations on the impact characteristics of water droplets before icing do not consider the existence of splash and rebound phenomenon,resulting in the accuracy of icing results.Therefore,the research on water droplet impact characteristics and icing of polar ship valves provides a theoretical basis for ice prediction and anti-icing and deicing of polar ships.The main research contents of this thesis are as follows:(1)Study on droplet impingement characteristics of polar ship valves before icing.The method of combining Euler’s multiphase flow with Euler’s wall film model was used to calculate the droplet collection coefficient,and the numerical simulation results were compared with the literature to verify the accuracy of the method.Through the analysis of the influence of different environmental factors on the droplet collection coefficient,it is concluded that the incoming air velocity and the average droplet diameter have great influence on the droplet collection coefficient,and the increase of the incoming air velocity and the average droplet diameter will increase the maximum droplet collection coefficient and the droplet impact limit range.The influence of incoming air temperature on the droplet collection coefficient is very small and can be ignored.(2)Transient temperature field of polar ship cryogenic valve.The cryogenic valve on polar LNG ship was selected as the research object,the basic theory of heat transfer of cryogenic valve was expounded,and the heat transfer analysis was carried out for the loose cooling fin and long-neck valve cover of the valve.ANSYS Workbench software was used to conduct numerical simulation research on transient temperature field of low-temperature valve,and the distribution of temperature field at different positions of low-temperature valve was obtained.Error analysis was made with literature results to verify the accuracy of the numerical simulation method of temperature field.The transient temperature field of polar ship’s cryogenic valve under different ambient temperatures is simulated to obtain its temperature distribution.(3)Numerical simulation of icing on valve components of polar ships.Euler multiphase flow method was used to calculate the formation and growth of frost layer on valve surface,and the interphase mass transfer model,interphase momentum transfer model and interphase heat transfer model were established between water vapor and ice phase in wet air.The custom function module in Fluent software was used to conduct numerical simulation of frost layer growth during valve icing.The numerical simulation results were compared with experimental results in literature to verify the accuracy of the frost growth model.(4)Sensitivity analysis of environmental factors to polar ship valve icing.The influence of inlet air velocity,inlet air relative humidity,inlet air temperature and cold surface temperature on the icing of polar ship valves is analyzed by using the control of single variable method.The conclusions are as follows: The relative humidity of incoming air and cold surface temperature have the greatest effect on valve icing.With the increase of relative humidity of incoming air and the decrease of cold surface temperature,the maximum ice phase volume fraction and the average height of frost layer on valve surface increase.With the decrease of the air temperature,the maximum ice phase volume fraction and the average height of the frost layer on the valve surface increase,but the increase amplitude is small.When the incoming air velocity increases from 1m/s to 2m/s,the maximum ice phase volume fraction and the average height of the frost layer on the valve surface increase,but when the incoming air velocity increases from 2m/s to 5m/s,the maximum ice phase volume fraction and the average height of the frost layer basically remain unchanged.Therefore,it is believed that there is a limit flow velocity between 1m/s and 2m/s,which makes the increase of volume fraction and average height of frost layer reach the maximum.