Spatial Distribution Of Drops Research Articles

Streamwise interaction of burning drops

The spatial distribution of drops and their interactions are influential parameters in spray combustion. Most available researches on this subject were about lateral spacing or were performed in micro-gravity. Studies about upstream/downstream convective interaction of burning drops are scarce. In this study, drop strings of different spacing were investigated in a high-temperature oxidizing environment for their flame transition, flame width variation and drop evaporation rate. The flame transition showed that along the flow direction, the drop flame initially located ahead of the drop, became a spherical envelope flame, then moved behind the drop, and finally burned as a wake flame. It was found that a drop string with an initial drop spacing (Si) of 2.5 or 5 was surrounded by a bulk flame tube, exhibited local group burning and soot layer. In addition, for Si=2.5, spacing instability and collision merging of the burning drops occurred; the wake flame stretched away from the drop could attach to and stabilize on the rear drop. In the experiment, for all cases, most of drops in the string were not surrounded by the flame. For Si<30, the drop evaporation rate was lower than that of a single drop. For 30<Si<75, the drop evaporation rate was higher than that of a single drop. The interaction of drops diminished if Si was more than 75.

Wall migration and shear-induced diffusion of fluid droplets in emulsions

The spatial distribution of drops in multiphase Stokes flow is derived theoretically as a function of two dimensionless parameters, accounting for wall migration, buoyancy, and shear-induced diffusion. The wall migration effect, which drives drops away from the walls and toward the center of the gap, is often significant even when droplets are 100 times smaller than the gap. By comparison with the experimental drop concentration profile, the shear-induced down-gradient diffusivity is measured and found to be approximately four to five times larger than the prediction for drop self-diffusivity. These are the first such measurements of the diffusivity of drops with clean interfaces and contrast markedly with previous measurements on surfactant-laden drops. Nonuniform concentration along the vorticity axis is also investigated briefly.

How Far does the Liquid Penetrate in a Diesel Engine: Computed Results vs. Measurements?

A multidimensional model is used to study the penetration of the liquid fuel in a constant volume chamber under normal Diesel engine conditions. Comparisons of the liquid fuel penetration as predicted by the model with results from recent experiments show inadequate agreement but, more importantly, a sensitivity to the numerical resolution. A possible origin of this sensitivity is identified through a series of systematic studies of the different components of the spray model. These studies show that the sensitivity of the liquid penetration to the numerical resolution may be related to a dependence of the computed Sauter Mean Radius (SMR) of the drops on the grid resolution. A detailed study of this dependence relates it to the non-uniformity of the spatial distribution of drops in the chamber, in particular, within about 100 diameters of the injector orifice. This non-uniformity leads to the estimate of different number densities and, hence, different collision frequencies, on different grids. The non-uniformity of drop distribution is shown to be a function of time during the transient injection process and dependent on the vaporization rate. The work also leads to a conclusion about the possible size of injected drops in the Diesel spray.

The Effect of Swirl on the Velocity and Turbulence Fields of a Liquid Spray

The work reports an experimental study of the effect of swirl on the structure of a liquid spray, i.e., on the behavior of drops and their interaction with the gaseous phase, and on the velocity and turbulence fields of the spray in the swirling flow. Three vane-type swirlers having low, medium, and high swirl numbers were used in the tests. The swirlers were placed on the liquid supply tube of a pressure atomizer and tested in the wind tunnel under specified conditions. Properties of the dispersed phase such as velocity and size distributions, particle number density, and volume flux were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. The results show that flow reversal of the drops is present at the high swirl number within the recirculation region. The spatial distribution of drops reveals a widening of the spray with increasing swirl strength while the concentration of large drops is shown to increase near the core of the swirling field with increasing swirl number. Plots of the turbulence kinetic energy, normal Reynolds stresses, and Reynolds shear stresses show double-peak radial distributions, which indicate regions in the flow where high energy content, mean velocity gradients, and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence. The significance of the turbulence measurements is that these double-peak profiles indicate a deviation of the swirling spray from isotropy. This information should be relevant to researchers modeling these complex flows.

A Research Instrument for the Study of Raindrop-Size Spectra

Abstract The photoelectric raindrop-size spectrometer, developed to meet the need in modern meteorology for detailed information about rain, is described. Operating with minimum physical disturbance of the rain field, the present instrument scans a 9.33-liter volume each second registering the size (surface area) and time of observation of each raindrop. The output of the instrument can be recorded in various stages of analysis by the use of electronic readout devices. Data obtained to date reveal interesting new information about the behavior of raindrop spectra and about the spatial distribution of drops in heavy shower rain.