Smaller Drop Sizes Research Articles

Analysis of Cobalt Extraction by DI-(2-Ethylhexyl) Phosphoric Acid in a Continuous Flow Stirred Tank with a Laser Capillary Spectro-Photometer

Abstract A laser capillary spectrophotometric technique is used to study and quantify the dispersed phase mixing effects on the performance of a one liter continuous flow reactor for the cobalt-di-(2-ethylhexyl) phosphoric acid extraction system. Bivariate. distribution data show that, as the RPM increases, the drop size and drop concentrations change from widely to narrowly distributed, the former tending toward small drop sizes and the latter tending toward higher concentrations. Comparisons between the Monte Carlo simulation model predictions and experimental results, using an aqueous film reaction model, indicates that the simulation predicts the size distribution closely, the Sauter mean diameter within 10% error, and the extraction efficiency within 15% error.

Predicted and observed droplet deposition on tsetse flies (Glossina morsitans) following aerosol application from aircraft

AbstractA non‐toxic formulation containing fluorescent tracer was dispersed as an aerosol over savannah woodland in stable meteorological conditions, with only light wind, shortly after sunrise. Droplet deposition on wild caught tsetse flies (Glossina morsitans) was measured by means of a fluorescent tracer technique and compared with the deposit levels predicted from rotary sampler measurements using droplet collection efficiency data for samplers and flies derived from a laboratory wind tunnel study. Good correlation was found between the predicted and observed dose. An additional comparison, based only on rotary sampler data, between a typical spray (measured v.m.d. 27 μm) and a spray with smaller drop size (measured v.m.d. 21 μm) suggested that the latter might be significantly more effective as a means of control.

A fundamental study of the ultrafiltration of oil-water emulsions

Factors affecting both flux and rejection in the ultrafiltration of oil-water emulsions have been investigated. Droplet size distributions measured by laser-light scattering provided evidence of coalescence in the polarized layers which had a broader distribution and substantially larger mean drop size than the feed. The permeate had an even wider size range, including a few very large drops caused by coalescence within the membrane. However, oil rejections were high (> 99.9%) with less than 20 ppm oil in the permeate. Rejection of total organic carbon (TOC) was > 96%, equivalent to 1000 to 2000 ppm content. An increase in permeate TOC was observed resulting from release of surfactants and additives following droplet coalescence. Permeate flux generally followed gel-polarized, film model, behaviour. Reasonable agreement was obtained with flux predictions based on the smallest drop size in the gel layer. Membrane fouling was observed and most easily reversed when using cellulosic membranes.

Empirical model for estimating drop size distributions of aerosols generated by inductively coupled plasma nebulizers

Drop size distributions have been determined for two inductively coupled plasma concentric nebulizers using laser diffraction measurements. The influence on drop size distributions of (1) gas and liquid flows (2) physical properties of several solvents and gases, and (3) principal dimensions of the nebulizers are reported. An empirical equation is developed which allows the prediction of two key parameters of primary aerosols (e.g. Sauter mean diameter and span). The equation has been checked by estimating Sauter mean diameters and spans for two additional concentric nebulizers, and good agreement has been obtained between experimental and estimated values. By comparison, estimates of Sauter mean diameters obtained from the Nukiyama and Tanasawa equation have been shown to differ markedly from experimental values. From the present study it may be concluded that gas velocity is the most critical variable in nebulizer operation, and that in order to obtain aerosols with small mean drop sizes and narrow distributions, a nebulizer with small gas cross-sectional area should be used, and operated with high gas flows. Organic solvents possessing low surface tensions are shown to lead to smaller mean drop sizes than aqueous solvents under all comparable operating conditions.

Emulsion liquid membranes Part ll: Modelling mass transfer of zinc with bis(2-ethylhexyl)dithiophosphoric acid

Emulsion liquid membranes (ELMs) are liquid membranes where the membrane is the continuous phase of an emulsion. Dispersed in a third continuous phase the emulsion globules are very well suited for various concentration processes. The present work investigates the recovery of zinc from an aqueous solution with water/oil/water emulsion liquid membranes. The carrier reagent in the organic membrane is the liquid ion exchanger bis(2-ethylhexyl)dithiophosphoric acid (DTPA). A mass transfer model for carrier-facilitated transport in emulsion liquid membranes is developed which is based on the extraction and stripping reaction between the Zn 2+ ions and the carrier molecules as well as on the transient diffusion of the loaded carrier molecules into an emulsion globule. Mass transfer experiments were carried out in a single-drop apparatus to test model predictions for actual transfer rates. Results indicate that the model is well suited for describing mass transfer phenomena in emulsion globules. Experiments show that it is essential to account for both reaction kinetics and transient diffusion in an emulsion globule. The purpose of this paper was to show new developments in the modelling of complex transport effects in emulsion liquid membranes. A mass transfer model for zinc permeation with DTPA was development and critically compared to experimental results for a single-drop apparatus. It was shown that a rigorous description of diffusion and reaction desribes the experimental results well. The importance of reliable chemical kinetics of the extraction involved was demonstrated. Results show that all of the model parameters can be estimated with existing correlations, although more work has to be done to obtain correlations with better estimative capability, especially for the effective diffusivity. As a practical result for emulsion liquid membrane contacting devices, it can be concluded that it is important to achieve large surface areas and small drop sizes as the diffusion resistance inside an emulsion globule becomes very important with increasing emulsion/continous-phase contact time. Another possiblity to enhance mass transfer would be the forced coalescence of emulsion globules, thus averaging the globule concentration within an emulsion globule and reducing the fraction of the globule where equilibrium of the stripping reaction has already been established.

A Hand-Portable Single Nozzle Rainfall Simulator Designed for Use on Steep Slopes

The objective of this study was to develop a smaii plot (1 m*) rainfall simulator operational on steep terrain in the Guadalupe Mountains of New Mexico. The simuiator developed is bandportable and consists of a spray head assembly mounted on 3 adjustable legs. A 946-liter tank equipped with a gasoline powered pump was connected to the spray head assembly via rubber garden hoses. On steep slopes gravity provided sufficient pressure to operate the simulator. Site selection was limited to areas where the water tank could be located in a suitable upsiope position. The simuiator has been used for 2 years on 170 plots and has proved durable. Advantages of this device are the low cost of construction and operation, and the flexibility in plot-site selection it provides. The principal disadvantages are associated with the single stationary nozzle, such as uneven application of water at small drop sizes and low kinetic energies. An ideal rainfall simulator has yet to be developed. Those that most closely reproduce rainfall patterns and intensity are expensive and require large expenditures of manpower for setup and operation (Foster et al. 1979). However, rainfall simulators, even though imperfect, are essential tools for investigating hydrologic processes on arid and semiarid rangeland where rainfall events are sporadic. Simulator experiments can be used to estimate infiltration, interrili erosion runoff rates, and chemical water quality for given storm events. Impacts of range management practices (grazing strategy, brush control, reseeding) on the watershed can also be evaluated using rainfall simulators. Rainfall simulators can be used to collect data in a relatively short period, rather than the 10 to 20 years needed to collect sufficient information from natural rainfall events. Rainfall simulators also provide maximum control over plot conditions and rainfall characteristics. Rainfall simulators in common use by range watershed scientists are the mobile drop-forming (Blackburn et al. 1974), Rocky Mountain infiltrometer (Dortignac 1951) and versions of the Purdue type (Bertrand and Parr 1961). Ail the above provide mobility, but use of each is restricted to relatively flat terrain. Hand-portable infiltrometers have been developed (Adams et al. 1957, McQueen 1963, Seiby 1970, Munn and Huntington 1976, Malekuti and Gifford 1978) and are more suitable for rugged terrain. Munn and Huntington (1976) report the Tahoe Basin infiltrometer to be functional on slopes to 60%. Hand-portable infiltrometers, however, have not been widely used, perhaps because many are bulky, heavy, require pumps or motors, or have a limited water supply. This paper presents the construction, operation, rainfall characteristics, and limitations of a hand-portable small rainfall simulator developed for use on steep slopes in the Guadalupe Mountains of New Mexico.

Low Intensity Rainfall with a Rotating Disk Simulator

ABSTRACT THE Palouse Rainfall Simulator was designed to simulate storms of the Pacific Northwest. Such storms are characterized by their low intensities, long durations, and small drop sizes. A drop size distribution similar to that of storms with rainfall intensities of 2.5 to 10 mm/h was achieved by nozzle selection. Rainfall intensities of 6 to 46 mm/h were obtained by use of slotted rotating disks. The rotating disks had no significant effect on the drop size distribution. Application uniformity was slightly lower at the lowest intensity tested..

LIQUID DISPERSION MECHANISMS IN AGITATED TANKS: PART II. STRAIGHT BLADE AND DISC STYLE TURBINES

The dispersion of oil in water in an agitated vessel was studied for two types of radial discharge impellers, straight blade and disc style turbines. Two different dispersion mechanisms, ligament stretching and turbulent fragmentation, were observed to occur in the vortex systems of the impeller discharge. Although these two dispersion mechanisms were similar to pitched blade turbine performance, differences in the velocity magnitudes and vortex interactions were observed with the radial flow impellers. The ligament stretching mechanism was observed between the vortex formation regime and the transition to the fragmentation regime. The turbulent fragmentation mechanism was observed only in highly turbulent flow. Blade thickness was found to influence the ligament stretching mechanism. A thin blade on the straight blade turbine created higher vortex velocities and smaller drop sizes than a thick blade for the same tip speed and processing time. The consequences of this blade thickness effect could be signi...

Droplet Size and Spray Volume Influence on Control of the Bollworm1

Field experiments in cotton were conducted to determine the response of Heliothis zea (Boddie) to 3 spray drop size classes of 254, 396, and 556 μm which were applied in all combinations with 1, 2, and 3 gal/acre using a jet stream atomization system with electrostatic drop dispersion. There was no significant difference in square damage between any of the treatments. Yield data showed significantly poorer yields for the small drop size classes for all spray volume. Fiber quality characteristics indicated no differences in fineness, fiber strength, uniformity ratio, and span length that could be attributed to the treatments.

Evaluation of the Contribution of Organic Solvent Species toward Signal Enhancement in the Premixed Oxygen-Hydrogen Flame

Studies conducted in premixed oxygen-hydrogen, oxygen-acetylene, and nitrous oxide-acetylene flames utilizing a relatively small drop size aerosol generated with high frequency ultrasonic nebulization indicate that under the proper conditions emission signal enhancements observed with methanol can be attributed primarily to both increased rate of nebulization and the presence of additional reducing species. However, under the fuel-rich conditions commonly employed for analysis, solvent-supplied reducing species were found to be of primary significance only in the case of the premixed oxygen-hydrogen flame.

Atomization problems in atomic absorption spectroscopy—I. A study of the operation of a typical nebulizer, spray chamber and burner system

A study has been made of the mode of operation of the nebulizing system of a commercial atomic absorption spectrophotometer. The sensitivity of the instrument and the effect of chemical interferences in the flame are critically dependent on the construction of the nebulizer and particularly on rate of liquid uptake. An experimental determination of drop-size distribution of the spray entering the flame points to the importance of small drop size for the efficient atomization of metals which tend to form refractory compounds in the flame.

CALIFORNIA STORMS AS VIEWED BY SACRAMENTO RADAR

The WSR-57 radar at Sacramento provides an opportunity to observe mountain effects on precipitation and on radar echo patterns. Radar patterns representing a wide range of weather situations are described and interpreted in light of concurrent gage precipitation measurements. Comparisons are made between gage precipitation depth and that indicated by the radar. The frequent under-estimation by radar of rainfall on windward slopes is attributed to the small drop size and low formation level of the orographic precipitation. Overestimation on lee slopes is in part, due to evaporation before the precipitation reaches the ground.

A Rapid Method for Estimating the Atomization of Oil-Base Aerial Sprays1

The size of aerial spray drops is an important factor influencing spray coverage, distribution, evaporation, and drift. The degree of spray atomization is commonly expressed as mass median diameter (mmd). Present methods for determining mmd require the sampling and measurement of the entire drop spectrum. A simple method has been developed for estimating mass median diameter from the largest drop in the continuous spectrum (D-max). This method saves more than 90% in time with-out loss of accuracy. Drop D-max is selected from the five largest drops collected across the spray swath. It is the drop diameter with not more than 32m difference between it and the one next largest to it going from the smallest drop size up. The mmd is obtained by dividing spherical drop D-max by a conversion factor. This conversion factor is 2.2 ±.07 for slow speed (80 mph) planes and about 2.5 for medium speed (170 mph) planes.

The mechanisms of disintegration of liquid sheets in cross-current air streams

A photographic study has been made of the disintegration of thin circular liquid sheets in air streams flowing normal to the liquid sheet. The results may be summarised as follows: (1) Two principal mechanisms of disintegration have been observed: (a) Continuous atomisation proceeds through the formation of circum-ferential waves, and fragments of the sheet are subsequently torn off and atomised. (b) A vibratory system is set up between the two fluids, and the sheet breaks up by resonance between the fluids into periodic clusters of drops. (2) The occurrence of each mechanism is markedly affected by the operating conditions. The vibratory mechanism is pronounced at air/liquid momentum ratios above 18, particularly with values of air energy above 2000 ft.lbs/min. At all values of air energy wave disintegration occurs with air/liquid momentum ratios below 18. (3) A sheet undergoing wave disintegration produces smaller drops than a vibrating sheet. Since for given air flow conditions the momentum ratio can be reduced by increasing the liquid flow rate these phenomena demon-strate the surprising result that smaller drop sizes can be achieved by an increase in liquid flow rate; tha.t is to say, a decrease in air/liquid mass ratio. (4) At any level of air energy atomisation is improved when the air is distributed from a narrower annular gap, the air stream being utilised more efficiently. (5) When the sheet is atomised by a wide air stream close to the orifice, an increase of 50% in sheet thickness produces a coarser spray. When the sheet is atomised by a narrow air stream at a greater distance from the orifice, the effect of sheet thickness is less marked. (6) Spatial drop dispersion in the atmosphere is affected by the mechanism of disintegration. Wave disintegration results in a relatively well dispersed spray, whilst the vibratory mechanism produces a dense core of drops along the nozzle axis. (7) Imparting a rotary motion tothe atomising air stream improves the quality of atomisation and spatial dispersion, particularly with vibratory disintegration.

Effect of turbulence and condensation on drop‐size distribution in cloud

AbstractEquations are developed to represent the rate of change of the number of drops of a given size in a cloud owing to condensation and to coalescence respectively. Numerical computation from these equations shows that condensation has a much greater effect than coalescence on drop‐size distribution in clouds with small average drop size, with small liquid‐water content or with a large degree of super‐saturation.With the assumption that drop‐size distribution in a cloud is governed by rate of condensation on the drops in the cloud and rate of turbulent diffusion of the drops out of the cloud it is then shown that the fractional volume of water comprised by drops smaller than a specified size is expressible in terms of an Incomplete Gamma function. In this Incomplete Gamma function the argument is 1·5 and the upper limit to the integral varies as the square of the drop size and is also proportional to a quantity which depends upon the degree of turbulence and upon parameters connected with the rate of condensation. It is shown that this theoretical formula approximates closely to a simpler formula already established empirically and that reasonable values for the coefficient of turbulence and the condensation parameters lead to a mean drop size which agrees closely with measured values.

On the capillary forces in an idealized soil

1. The attraction between spheres, due to surface tension forces, in a lenticular drop between them is calculated for spheres in contact and at increasing separations up to the point of rupture of the drop. Hence the work of separation of the spheres is calculated.2. Experimental measurements confirm the validity of these calculations, down to very small drop sizes, where it is likely that the failure is in the experimental method. As predicted by Fisher, the force decreases with increasing drop size, while the work of separation increases. Since, however, it is shown that the smaller lenticels are more easily ruptured, no discrimination is provided between the differing explanations of Haines and Fisher of measurements made with the Atterberg apparatus for measurement of soil cohesion.An experimental verification of the validity of Fisher's calculation of the pressure deficiency inside the drop is also given.3. It is pointed out that these results depend on the geometry of the system; types of contact other than that of spheres will show different behaviour. Hence generalizations about the behaviour of a real soil, based on an idealized soil of packed spheres, may lead to erroneous conclusions.