1,720,981 research outputs found
PLACEMENT AND ACCELERATION OF LIQUID JETS IN PRESSURIZED CROSS-FLOWS
No full textDetermination of velocities and locations of liquid droplets formed during the atomization process of a liquid jet injected in a high-pressure air cross flow represents an essential step in the definition of appropriate boundary conditions for the elaboration and validation of reliable numerical models. In this paper, three test cases relative to different air-to-liquid velocity ratios and air temperatures are analyzed by means of elastic scattering imaging and particle image velocimetry (PIV). The significance of the PIV measurements, evaluated as a function of spatial position and operating conditions, was adequately high with the exception of the nearest field to the injection point, where the spray is too dense. Velocity data, measured in the axial and transversal planes, are presented along with corresponding velocity components' profiles at selected positions. Results show the rapid alignment of droplet trajectories to the airflow and the dominant role played by the airflow in determining final droplet velocities and, hence, their placement in the spray plume. The droplets close to the windward profile move parallel to the jet leading edge, whereas in the leeward region they cross the scattering intensities' isocontours. On the grounds of these results, a synthetic description of liquid droplet velocities' behavior in the different regions of the spray plume is given that represents a useful conceptual tool in the attempt to correlate physical mechanisms, underpinning atomization processes, to the observed phenomenologies
POLARITY INVERSION IN ELECTROHYDRODYNAMICS SPRAYING
No full textAn experimental study of polarity inversion effects in electrohydrodynamic spraying is developed by characterizing the several atomization regimes that can be observed by varying liquid flow rate and applied voltage. n -Heptane, doped with an antistatic additive, is atomized in a classical needle-to-plate system. The study allows for the determination of two-dimensional maps of the stability regimes occurring by varying the controlling parameters. These maps have been obtained by comparison of results of direct visualization, by means of a digital camera, and Particle Dynamics Analyzer (PDA) measurements of droplet size and velocity components. Results show that occurrence of the regimes is not qualitatively influenced by polarity inversion, but in the negative polarity case any modification on spraying modes needs higher variation in applied voltage, and so the regimes are stable in larger voltage ranges
SEQUENTIAL ENLARGEMENT COMBINATION OF SEPARETED EFFECT CONTRIBUTIONS FOR THE ANAL. OF LIQ. JET ATOMIZ.IN CROSS-FLOW COND.
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Air density effect on the atomization of liquid jets in crossflow
No full textAn experimental study of liquid injection in a transverse airflow at high pressure and temperature was performed. Collected shadowgraphs were processed by image statistical analysis tools. The breakdown point location was correlated to liquid-to-gas momentum ratio, gas Reynolds number and aerodynamic Weber number. The substantial uniformity of behavior of the normalized jet trajectories allowed providing an empirical correlation validated in a range of operating conditions of interest for LPP gas turbines. Liquid dispersion in the gas phase, atomization and evaporation were qualitatively investigated by means of statistical parameters related to the behavior of the spray plume. For liquid spraying and spreading, the relevance of the interaction between aerodynamic and capillary pressure was underscored, whereas in the range of operating conditions studied, both experimental evidence and theoretical estimation indicate that even at 600K temperature the evaporation of water drops is not significant within 100 diameters downstream the injection point
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