A Study On Droplet Morphology Evolution Under The Effect Of Gas Phase

The effect of gas-liquid separation affects the efficiency of liquefied natural gas(LNG)production.The evolution,deformation and breakup processes of LNG droplet under the action of gas phase are the primary problem in LNG gas-liquid separation process.In this work,the breakup mode,the characteristics of deformation and breakup,and the characteristics of evaporation of an LNG droplet under effect gas phase were studied by using numerical simulation.The research could provide theoretical reference for the gas-liquid separation during LNG production process.The following numerical simulations were studied about the deformation and breakup process of a single LNG droplet in the gas phase,and the evaporation process in different environments by using CLSVOF and VOF plus Lee Model,respectively.First,the influence of droplet diameter and Weber number on the deformation and breakup process for a specific relative velocity between gas and droplet,and the influence of relative velocity between gas and droplet as well as Weber number on the deformation and breakup process for a specific droplet diameter were studied.It can be concluded that as the increase in Weber number,the surface tension and viscosity for the maintenance droplet shape were not sufficient to withstand the dynamic pressure of gas,the breakup modes such as bag,multi-mode,shear and others appears on LNG droplets appeared bag,multi-mode,shear and other fragment modes.Further studies show that the critical Weber number of breakup mode is in consistent with the experimental results of reported by other researchers.Second,the parameters in the deformation and breakup were got and characterized,and the morphological characteristics and breakup modes of droplet were analyzed under the condition of different Weber number.As a result,the relationship between droplet diameter or Weber number and dimensionless deformation time or total breakup time were concluded,and the formulation about droplet diameter,relative Weber number,and total deformation time were fitted.It is indicated that the dimensionless deformation time of the droplet decrease with the increase in relative Weber number,while the total breakup time decrease first and increase with the increase in relative Weber number.Third,the dynamic characteristics of the droplet deformation and breakup process were studied,and the relationship between the velocity,acceleration and the drag coefficient of the mother droplet during droplet during the process of deformation and breakup was studied,and the time dependent pressure and velocity distribution was analyzed as well.It is shown from the result that the droplet velocity was positively correlated with time,and the change tendency of acceleration is similar to that of drag coefficient,both of which are change with the deformation and breakup of the droplet.Therefore,the drag coefficient could be used as auxiliary criterion of droplet deformation and breakup.Fourth,the evaporation process of the LNG droplet in the natural convection environment was studied.The effect of droplet diameter and ambient temperature on the evaporation process were studied,and the mass evaporation rate of droplet was obtained.In addition,the effect of Marangoni flow was analyzed.According to the results,the increase in diameter causes the results such as the increase in mass evaporation rate,the decrease in the thickness of boundary layer,and the increase in temperature gradient of boundary layer,and the enhancement in heat exchange.Besides,the Marangoni flow accelerates the evaporation process.Fifth,the evaporation process of the LNG droplet in strong convection environment was studied.The influence of the droplet diameter,ambient temperature and airflow intensity of the droplet on the evaporation process was analyzed.The characteristic of evaporation rate and the characteristic of heat and mass transfer were concluded.As it is known,the mass evaporation rate of droplet in strong convection condition is greater than that in natural convection environment.Based on the research results,the ambient temperature,droplet diameter and the relative velocity between gas and droplet affects the droplet evaporation process.However,the influence of relative velocity between gas and droplet on the droplet evaporation process was negligible.Through the research work of the deformation and breakup process of a single droplet in the gas,the deformation and breakup mechanism,the dynamic characteristics and the change tendency of temperature of an LNG droplet was obtained.The research results provide some reference for the mechanism of gas-liquid two phase flow,and provide some theoretical bases for the application of LNG industrial production and storage.