Theoretical And Experimental Study On Power-law Fluid Annular Jets

The development and utilization of non-renewable energy has caused many irreversible impacts,which has made global energy and environmental problems serious.Many new alternative fuels have been developed and applied to avtual production and life,such as bio-pulp,emulsified oils,and gel fuels.Among these alternative fuels,many fuels have high combustion efficiency and low emissions,but their rheological properties exhibit very strong power-law charactertistics,and the breakup process is very different from traditional fuels.It is very far-reaching significance to research on the mechanism of these power-law fuels breakup and atomization.The commen power-law fluid fuels have high viscosity and are not easy to break in experiments.Therefore,the movement of the ambient airflow is considered to promote the atomization of power-law fluid fuels.Based on the above considerations,the process of power-law fluid annular jet breakup process with airflows has been studied by theoretical analysis and experimental exploration.Moreover,the effect of various factors on the breakup process was discussed.It is expected to find the most effective jet device,and provide reference and guidance for the design of alternative fuel engines.Based on the theory of instability analysis,the mathematical models of the powerlaw fuel cylindrical jet with gas crossflow and the power-law fuel annular jet with multiple airflows are proposed,and the dimensionless dispersion equations are derived respectively.The relationship curve between the growth rate of unstable wave and the wave number is obtained with temporal model solution.The influence of dimensionless parameters on the instability have been analyzed and discussed.Theoretical studies have shown that the liquid viscous force and the power-law characteristics will always hinder the development of the jet breakup;the liquid surface tension will promote the instability of the jet under low-speed jet condition,and will suppress the intability of the jet under high-speed jet condition.The high gas-liquid velocity ratio and high ambient gas density could effectively promoet the jet breakup process and provide a smaller primary breakup scale.Moreover,reducing the thickness of the liquid film by changing the nozzle structure parameters will make the annular jet more unstable.For the two jet processes,increasing the instensity of airflow will promote jets atomization and reduce the primary breakup scale.Based on the theoretical analysis,the global sensitivity analysis method is introduced to investigate the actual factors sensitivity of the theoretical model.The results show that,the liquid jet velocity,gas velocity and gas density are more sensitive to the instabilit,and the remaining parameters are less sensitive.That means,the jet environment,liquid jet velocity and nozzle structure parameters are the key factors to improve the power-law fluid jet breakup results,which need to be considered in the actual engineering application process.Then,a complete set of visual optical experiment platform has been designed and built.This platform could mesure the morphology of the near-field area and the droplet characteristics of the far-field area of the power-law fuel annular jet,including macroscopic morphology charateristics,core area mass distribution,droplet velocity distribution and size distribution.By using the high-speed photography technology,five different jet modes of power-law fluid annular jet are found.The characteristic parameter,the length of the first bubble,is defined,which could characterize the jet instability.Moreove,the influence of various factors is studied.By using X-ray imaging technology,the mass distribution characteristics of the annular jet core area are measured,and the influence of various influencing factors on the jet core area mass characteristics is studied.By adopting phase Doppler particle analysis technology,the distribution characteristics information of droplets velocity and size are obtained,andt the effects of diferent actual factors on the far-field droplets velocity and Sauter mean diameter are studied.The experimental results show that,for the power-law fluid annualr jet,the gasliquid velocity,inner diameter,film thichness and physical properties of the fluid all affect the jet intability.Increasing the gas-liquid two-phase velocity difference will promote the instability of the annular jet.In other words,it will make the length of the first bubble smaller,the peak of the mass distribution lower and the Sauter mean diameter smaller.Enlarging the inner diameter or reducing the film thickness also helpes the annular jet optimize atomization results.The consistency coefficient and power-law exponent could restrain the instability of power-law annular jets.Overall,the droplet velocity and SMD are both symmetrically distributed in space and gradually decrease.The change of jet conditions has no significant effect on the overall distribution of droplet velocity field and size field.The experimental results and the theoretical analysis conclusions can be mutually verified.Comprehensive analysis of the above conclusions,for the power-law fluid fuel annular jet process,increasing the ambient gas density,increasing the gas-liquid velocity,reducing the annular thickness and liquid viscosity are conducive to the instability,and obtaining better atomization results.