Study On The Modulation Mechanism Of Liquid Nitrogen-Ice Particle Jet

Liquid Nitrogen fracturing technology is an anhydrous fracturing technology which combines the low temperature fracturing of liquid nitrogen with the high-pressure jet technology,and LN Jet is expected to be popularized in low permeability and tight reservoirs.In order to improve the rock breaking efficiency of Liquid Nitrogen Jet,we put forward a new idea of Liquid Nitrogen-Ice particle Jet,that is to pump a proper amount of water droplets into liquid nitrogen,the water droplets quickly coagulate into ice particles,and then follow the LNJ to form abrasive jet.The key scientific problem is the modulation mechanism of liquid nitrogen ice jet based on dynamic heat transfer and parameter control.Therefore,the modulation mechanism of liquid nitrogen ice jet is studied in this paper.Firstly,the freezing characteristics of single water drop are studied by visual experiments.It is found that when a single water droplet solidifies,the ice shell is formed on the outside first,and then gradually condenses inward,which will lead to the precipitation of dissolved gas and the local rupture of ice particles;in the low temperature nitrogen environment,the freezing of water droplets can be divided into four stages,but only three stages can be measured in the liquid nitrogen environment;with the increase of the volume of water droplets,the solidification time of water droplets increases,and the effect in the liquid nitrogen is more obvious;environmental temperature The lower the degree is,the faster the water droplets solidify.4 μ L water droplets in liquid nitrogen can solidify in 0.5s.The characteristics of LN-IJ flow field and the analysis of influencing factors are studied by numerical simulation.The results show that the particle temperature can be rapidly reduced to below the freezing point,and it can be quickly sucked,mixed and accelerated by liquid nitrogen to form LN-IJ.The higher the jet pressure is,the higher the ice particle velocity at the peak value is.When the number of ice particles is small,the ice particles can be fully added in the nozzle.With the increase of ice particle size,the peak velocity of ice particle decreases.The experimental device of LN-IJ was designed and manufactured,and the LN-IJ was successfully modulated;through the target erosion experiment,it was confirmed that the impact effect of liquid nitrogen ice jet was significantly better than that of pure Liquid Nitrogen Jet;the shorter the injection distance,the greater the injection pressure,the better the impact effect of liquid nitrogen ice jet;the paint removal effect of liquid nitrogen ice jet was better on low surface roughness objects.The results of this paper can lay a foundation for the development and application of liquid nitrogen ice jet technology.