| Due to the mismatch between natural gas production and demand,LNG vessels usually be used for long-distance transportation of LNG.It is necessary to carry out cooling down treatment to ensure the safety of the tank before LNG enter the tank.The cooling down of the tank is essentially the evaporation of atomized refrigerant droplets in BOG,the existing model cannot be applied.It is necessary to establish a new droplet evaporation model.A numerical simulation method was used to program the evaporation model of a stationary saturated single droplet in its vapor.Under the condition of temperature difference of10-190K,the evaporation process of four common substances such as liquid methane with a radius of 0.5-2.5mm is simulated and analyzed.At the same time,the established model was used to simulate the heat transfer process of cryogenic ball with no evaporation.The heat transfer characteristics of the two were compared,the"blow effect"was qualitatively analyzed,and the heat and mass transfer characteristics of the droplets were studied.Concluded as follow:?1?The thickness of temperature boundary layer of the cryogenic ball increases with increasing radius and becomes thinner with increasing temperature difference.The heat flux at the gas-liquid interface of the cryogenic ball decreases with increasing radius and increases with increasing temperature difference.Under the range of the study,the thickness of the temperature boundary layer of droplet evaporation was 3.88×10-20.16m,heat flux was 31.641.20×104W/m2,and heat transfer was 4.97×10-40.19W.Under the conditions of temperature difference of 190K and radius of 2.5mm,the maximum heat transfer during the evaporation of water droplets reached 0.19W.?2?Compared with the heat transfer process of the cryogenic ball,droplet evaporation has the"blow effect",which makes the temperature boundary layer thicker than the cryogenic ball under the same conditions.The thickened temperature boundary layer hinders the heat transfer,and reduce heat flux and heat transfer.Under the conditions of temperature difference of 190K and radius of 0.5mm,the"blow effect"is most obvious,which increases the thickness of temperature boundary layer of R134a Freon droplet by 38.98%,reduces heat flux and heat transfer by 36.93%,and reduces heat flux and heat transfer by2.39×103W/m2 and 3.76×10-2W.When the temperature difference is less than 20K,the"blown effect"of heat flux and heat transfer is less than 5%,which can be ignored.?3?By analyzing the relationship between mass evaporation rate,droplet radius and temperature difference,the model for calculating the droplet evaporation is proposed.The Lee model is modified by using the calculated data of mass evaporation rate to apply to the study of droplet evaporation in its vapor,and the droplet longest is calculated.The program establishes the evaporation model of static saturated single droplets in its vapor,and simulation analysis is carried out.A calculation model of droplet evaporation is proposed and the Lee model is revised.It provides a reference and has high academic value and application value in analysis of droplet evaporation. |
PDF Full Text Request