Simulation And Analysis On The Dispersion Behavior Of Cryogenic Vapor Cloud With Water Curtain

With the wide application of cryogenic liquids,more attention has been paid to the safety of cryogenic liquid in the processes of production,usage,storage and transportation.The accidental leakage of cryogenic liquids will form a dangerous vapor cloud,which will pose serious threat to surrounding personnel and facilities.Because of its dispersion and mitigation effects on vapor cloud,water curtain is expected to minimize the consequences caused by the dispersion of toxic or dangerous vapor cloud.Due to the lack of understanding the complex interactions between cryogenic vapor cloud and water curtain droplets,engineering guidelines are not yet available to guide the application of water curtain.Therefore,it is necessary to study the influence of water curtain on the dispersion behavior of cryogenic vapor cloud,and to understand the water curtain action mechanism and the effects of related parameters on the dispersion characteristics,which is significant for the safety protection of cryogenic liquid.Based on a comprehensive review of the relevant research,the forced dispersion of cryogenic vapor cloud with water curtain is numerically studied by using the computational fluid dynamics（CFD）model.The Euler-Lagrange method was used to simulate the energy and momentum exchange between the continuous phase（gas phase）and the discrete phase（droplets）,which realizes the unsteady simulation of vapor cloud with water curtain.The simulation results were compared with the LNG leakage experimental results of Mary Kay O’Connor Process Safety Center（MKOPSC）of USA to verify the accuracy of the model.The physical mechanism of the interaction between water curtain and vapor cloud was then studied,and elucidated the law of momentum and heat transfer between the droplets and the vapor cloud.Finally,the influences of water curtain arrangement,injection droplet velocity,leakage rate,wind speed and leakage species on the dispersion characteristics of vapor cloud are analyzed.The simulation results show that the water curtain promotes the upward movement of vapor cloud through momentum and heat transfer,which enlarges the contact area between the vapor cloud and the surrounding air to accelerates the dispersion of the vapor cloud.Better dispersion effect can be achieved if the water curtain is set closer to the leakage source.When the distance is decreased from 7 m to 2 m,the reduction ratio of separation distance increases from 26%to 49%.An increased installation angle will promote the dispersion of vapor cloud,which will even exceed the maximum downwind distance of the flammable vapor cloud without water curtain when the installation angle is greater than 45°.Therefore,the installation angle should not exceed 45°.As to the key parameters of the water curtain nozzle,it is found that increasing the nozzle flow rate can further shorten the separation distance,however,an increased nozzle flow rate cannot apparently further improve the dispersion effect when it reaches 3 kg/s.When the injection droplet velocity is increased to 12 m/s,the expansion range of the flammable vapor cloud can be greatly reduced.However,when the injection droplet velocity is further increased,the separation distance has little extra change.When the nozzle flow is kept constant,smaller droplet size can help to achieve full reaction with vapor cloud,and then to improve the dispersion effect of the water curtain.Smaller atomization angle can push the vapor cloud to a larger height while a low altitude near the ground,the vapor cloud can pass through the gap between the nozzles and travel farther.In the case of low leakage rate and high wind speed,the water curtain has higher dispersion efficiency.When the momentum rate of the nozzle is lower than 23.9 kg·m/s²,the water curtain is not enough to push the hydrogen cloud upward;and increasing the temperature of the droplet can make the hydrogen cloud obtain greater buoyancy in a short time and accelerate the dispersion of the cloud.In addition,compared with LNG spilling,the water curtain has a lower dilution efficiency for LH₂spilling,and the reduction rate of hydrogen cloud downstream penetration dimension under the action of water curtain is also lower than LNG.