Mean Drop Velocity Research Articles

An experimental and theoretical investigation of spray characteristics of impinging jets in impact wave regime

The current study focuses on experimentally and theoretically improving the characterization of the drop size and drop velocity for like-on-like doublet impinging jets. The experimental measurements were made using phase Doppler anemometry (PDA) at jet Weber numbers We j corresponding to the impact wave regime of impinging jet atomization. A more suitable dynamic range was used for PDA measurements compared to the literature, resulting in more accurate experimental measurements for drop diameters and velocities. There is some disagreement in the literature regarding the ability of linear stability analysis to accurately predict drop diameters in the impact wave regime. This work seeks to provide some clarity. It was discovered that the assumed uniform jet velocity profile was a contributing factor for deviation between diameter predictions based on models in the literature and experimental measurements. Analytical expressions that depend on parameters based on the assumed jet velocity profile are presented in this work. Predictions based on the parabolic and 1/7th power law turbulent profiles were considered and show better agreement with the experimental measurements compared to predictions based on the previous models. Experimental mean drop velocity measurements were compared with predictions from a force balance analysis, and it was observed that the assumed jet velocity profile also influences the predicted velocities, with the turbulent profile agreeing best with the experimental mean velocity. It is concluded that the assumed jet velocity profile has a predominant effect on drop diameter and velocity predictions.

Experimental investigation of explosive vaporization of C6F14

Depressurization experiments were conducted with C6F14 for superheats between 5 °C and 90 °C in order to determine how the drop characteristics evolve with the thermodynamic disequilibrium. High-speed imaging indicates that flashing is predominant and leads to very dense sprays. Phase Doppler Interferometer (PDI) was adapted to these optically thick conditions and its ability to provide unbiased velocity and size distributions was carefully checked (even though the flux was underestimated). Experiments show that, for initial superheats above 40 °C, the mean drop velocity linearly increases with the initial superheat while the mean drop diameter remains nearly constant. Such behaviors, not reported in the literature, are tentatively related with a front boiling process in which the drop velocity is driven by the vapor velocity while the drop size is controlled by bubbles exploding at the front. In addition, phase detection optical probes used in combination with PDI data provided number density flux measurements. Global vaporization rates deduced from these local data happen to be fairly consistent with alternate techniques, and the vapor flux exhibits a somewhat weak increase with the superheat.

Effect of canopy thickness and canopy saturation on the amount and kinetic energy of throughfall: An experimental approach

To investigate how canopy thickness and canopy saturation affect the amount and kinetic energy of throughfall, we conducted indoor experiments using a 9.8‐m‐tall transplanted Japanese cypress (Chamaecyparis obtusa) and a large‐scale rainfall simulator with spray nozzles at a height of 16 m. The amount of throughfall and raindrop sizes and velocities were measured at twenty‐four points under four canopy structures generated by staged branch pruning. Decreasing the canopy thickness resulted in increases of the initial throughfall amount, volume proportion of large throughfall drops, the number of drops with high velocities, and throughfall kinetic energy. Compared to a saturated canopy, a canopy undergoing wetting had lower throughfall amounts and volume proportion of large drops, but higher mean drop velocity. Canopy thickness affected throughfall generation by affecting the processes of canopy saturation and drop generation within the canopy.

Validation of a systematic approach to modeling spray quenching of aluminum alloy extrusions, composites, and continuous castings

Optimal cooling of aluminum alloys following the high- temperature extrusion process suppresses precipitation of intermetallic compounds and results in a part capable of possessing maximum strength and hardness after the subsequent age- hardening process. Rapid quenching suppresses precipitation but can lead to large spatial temperature gradients in complex- shaped parts, causing distortion, cracking, high residual stress, and/or nonuniform mechanical properties. Conversely, slow cooling significantly reduces or eliminates these undesirable conditions but allows considerable precipitation, resulting in low strength, soft spots, and/or low corrosion resistance. This study presents a systematic method of locating and operating multiple spray nozzles for any shaped extrusion such that uniform, rapid cooling and superior mechanical and metallurgical properties are achieved. A spray nozzle data base was compiled by measuring the distribution of spray hydrodynamic parameters (volumetric spray flux, mean drop diameter, and mean drop velocity) throughout the spray field of various industrial nozzles. Spray heat transfer correlations, which link the local spray hydrodynamic parameters to the heat transfer rate in each of the boiling regimes experienced by the surface, defined the spatially nonuniform boundary conditions in a numerical model of the quenching process that also accounted for interference between adjacent spray fields. New correlations, offering increased accuracy and less computational time, were formulated for the high- temperature boiling regimes which have a critical influence on final mechanical properties. The quench factor technique related predicted thermal history to metallurgical transformations occurring within the extrusion to predict hardness distribution. The validity of this unique approach was demonstrated by comparing model predictions to the temperature response (and hardness after artificial aging) of an L- shaped Al 2024- T6 extrusion to quenches with multiple, overlapping water sprays. The validation study reported herein concludes by exploring the possibility of applying quenching technology to improving the properties of extruded metal- matrix composites such as SiCp/Al 6061 and cast alloys.

Experimental and numerical study of quenching complex-shaped metallic alloys with multiple, overlapping sprays

The present study constitutes a crucial step towards the development of a CAD based intelligent spray quenching system capable of optimizing the mechanical properties (strength, hardness) of age-hardenable aluminum alloys. The quenching of an L-shaped aluminum alloy with multiple, partially overlapping spray nozzles was successfully modeled using the finite element method. Spray heat transfer correlations, which relate the local heat transfer rate in each of the boiling regimes experienced by the surface to the local values of the spray hydrodynamic parameters (volumetric spray flux, mean drop diameter, mean drop velocity), were used as boundary conditions. The spatial distributions of the spray hydrodynamic parameters were modeled and incorporated into the finite element program. Axial non-uniformity in the heat transfer coefficient along the surfaces of long extrusions, which can lead to unwanted residual stresses, was eliminated by developing a method for optimizing the distance between adjacent nozzles. The numerical results were experimentally verified in a simulated industrial environment. This study is the first successful attempt at systematically predicting the temperature response of a quenched part from knowledge of only the part geometry and spray nozzle configuration. Integration of the finite element program with an optimization routine will yield a system capable of selecting the appropriate spray nozzle configuration for a new part prior to production; thus, achieving superior part quality without conducting costly experimental tests.

A universal approach to predicting temperature response of metallic parts to spray quenching

A new method was developed to predict the temperature response of metallic parts to spray quenching below the film boiling regime. Local heat flux measurements in surfaces subjected to full cone and hollow cone sprays revealed existing correlations based on local values of volumetric spray flux, Sauter mean diameter, and mean drop velocity are both accurate and spatially independent in the transition boiling and nucleate boiling regimes, but less accurate in the single-phase regime due to liquid run-off effects. It is shown how the instantaneous spatial distribution of the heat transfer coefficient can be predicted from a mapping of the spatial distributions of the spray hydrodynamic parameters. The validity of this approach is demonstrated by comparing numerical predictions to the temperature response of a large rectangular aluminum block subjected on one surface to a nonuniform water spray. It is shown that the new method is universally applicable to sprays having drastically different patterns.

Spray Structure from Swirl Atomizers. 3rd Report, Dimensionless Expression of Spray Characteristics.

Spray characteristics such as the spatial distributions of drop size and drop velocity are expressed by dimensionless formulae. They are dimensionless when expressed as the Sauter mean drop size and mean drop velocity in the sheath respectively. Furthermore, the Sauter mean drop size and mean drop velocity in the sheath can be derived using injection pressure, atomizer's characteristics and axial distance. The spray angle can be derived the Renolds number and Flow factor in the swirl chamber. The maximum deviations of the empirical formulae for the Sauter mean drop size, mean drop velocity and spray angle are less than 12%. On the other hand, the border lines of the spray structure model are decided quantitatively. The boundary between the main flow region and stagnated flow region are divided by the dimensionless number Sg which is defined in this paper. The boundary between the entrained flow region and sheath region are divided by the variation of the correlation coefficient for drop size and drop velocity in the radial direction.

Investigation of a novel feature for Prefilming liquid fuel Nozzels

Abstract An oscillating piezoelectric beam was used on the prefilming surface in a two-dimensional model of the prefilming-type aircraft fuel atomizer to interact with the periodic phenomena occurring inside the nozzle and just at the atomizing exit-edge of the prefilming surface. The oscillating beam was designed such thatits second mode of oscillation resonated at frequencies close to the above-mentioned periodic phenomena.It was shown that the spray Sauter Mean Diameter (SMD) and mean drop velocity profiles became more uniform at a distance of 50 mm from the nozzle for the condition tested. Cross-sectional-averaged SMD decreased slightly as a result of this novel feature.

Determination of the local quench curve for spray-cooled metallic surfaces

An experimental study of heat transfer from hot metallic surfaces to water sprays was conducted in the single-phase, nucleate boiling, and transition boiling regimes of the quench curve for surface temperatures below 400° C. Heat transfer measurements were made locally in the spray field using a heater surface area of 0.5 cm2. The hydrodynamic properties of the sprays such as drop diameters, drop velocities, and volumetric spray flux were also measured independently at a position in the spray field identical to that of the heater. The test conditions included variations in volumetric spray flux, mass mean drop diameter, and mean drop velocity of 0.6 × 10-3 to 9.96 × 10-3 m3s-1/m2, 0.434 to 2.005 mm, and 10.6 to 26.5 m/s, respectively. Correlations are presented for water temperatures from 23 to 80° C. These correlations constitute a universal approach to the development of quench curves for industrial sprays commonly employed in materials processing.