Effect Of Droplet Size Distribution Research Articles

Recent Developments in the Viscosity Modeling of Concentrated Monodisperse Emulsions.

Emulsions form a large group of food materials. Many foods are either partly or wholly emulsions or are in the form of emulsion at some stage of the production process. A good understanding of the rheological properties of emulsions, especially their shear viscosity, is essential in the design, formulation, and processing of food emulsions. The texture and mouthfeel of food emulsions are also largely influenced by emulsion viscosity. Therefore, it is of practical importance to be able to correlate and predict emulsion viscosity as a function of droplet concentration and other relevant variables. In this article, the recent developments made in the viscosity modeling of concentrated emulsions are reviewed. The viscosity models for concentrated emulsions published in the twenty-first century are discussed, compared, and evaluated using a large body of experimental viscosity data available on emulsions. The effects of droplet size distribution and capillary number on the viscosity of concentrated emulsions are also discussed in detail. A new generalized viscosity model is developed for concentrated emulsions that includes the effect of capillary number and is accurate with small average percent relative error (within 3%).

The effects of droplet size distribution and wave characteristics on the vertical dispersion of spilled oil due to regular non-breaking waves

The effects of droplet size distribution and wave characteristics on the vertical dispersion of spilled oil due to regular non-breaking waves

Liquid injection in a fluidised bed: Temperature uniformity

• Combination of Particle Image Velocity and Infra-Red Thermography. • Time-averaged temperature distribution for liquid injection in a fluidized bed. • Effect of droplet size distribution on the bed temperature uniformity. • Liquid agglomerates observed in the Infra-Red image as cold spots. • Solids motion affects the liquid distribution in the bed. Liquid injection in fluidized beds occurs in well-established industrial processes as fluid coking, spray fluidzed bed granulation and condensed mode gas-phase polymerisation. These processes still suffer performance issues due to their complex nature, where liquid injection adds even more complexity. In this work, the effect of liquid injection on the temperature uniformity in a pseudo-2D fluidized bed was studied using Infra-Red Thermography. The Infra-Red images were also studied to qualify the agglomeration behaviour. Injecting smaller droplets ( ∼ 90 μ m affects the uniformity of the bed more than injecting larger droplets ( ∼ 225 μ m. However, the formation of agglomerates increases with increasing droplet size. The injection velocity influences the average temperature of the bed more for the larger droplets. Additionally, increased solids motion was observed to reduce the agglomeration formation in the bed. Lastly, the particle temperature distribution does not reflect the presence of agglomerates and is thus unsuitable to quantify the agglomeration behaviour.

Lubrication and Sensory Properties of Emulsion Systems and Effects of Droplet Size Distribution.

The functional and sensory properties of food emulsion are thought to be complicated and influenced by many factors, such as the emulsifier, oil/fat mass fraction, and size of oil/fat droplets. In addition, the perceived texture of food emulsion during oral processing is mainly dominated by its rheological and tribological responses. This study investigated the effect of droplet size distribution as well as the content of oil droplets on the lubrication and sensory properties of o/w emulsion systems. Friction curves for reconstituted milk samples (composition: skimmed milk and milk cream) and Casein sodium salt (hereinafter referred to as CSS) stabilized model emulsions (olive oil as oil phase) were obtained using a soft texture analyzer tribometer with a three ball-on-disc setup combined with a soft surfaces (PDMS) tribology system. Sensory discrimination was conducted by 22 participants using an intensity scoring method. Stribeck curve analyses showed that, for reconstituted milk samples with similar rheological properties, increasing the volume fraction of oil/fat droplets in the size range of 1–10 µm will significantly enhance lubrication, while for CSS-stabilized emulsions, the size effect of oil/fat droplets reduced to around 1 µm. Surprisingly, once the size of oil/fat droplets of both systems reached nano size (d90 = 0.3 µm), increasing the oil/fat content gave no further enhancement, and the friction coefficient showed no significant difference (p > 0.05). Results from sensory analysis show that consumers are capable of discriminating emulsions, which vary in oil/fat droplet size and in oil/fat content (p < 0.01). However, it appeared that the discrimination capability of the panelist was significantly reduced for emulsions containing nano-sized droplets.

Pool boiling of a dilute emulsion: Surfactant effect on heat transfer

We report measurements of boiling heat transfer in a dilute emulsion in the presence of a surfactant on an upward facing flat surface. The emulsion comprises FC 72 droplets in water with Tween 20 as the surfactant at 0, 10, 60 and 100 ppm by volume. Boiling data for the emulsion without surfactant confirms previously observed trends, with an increase in heat transfer coefficient occurring near 80 °C. Boiling with the surfactant does not produce an enhancement of the heat transfer coefficient in both aqueous surfactant mixtures and emulsions with surfactant. Laser diffraction imaging shows that emulsions with different volume fractions of the disperse component have different particle size distributions from the same emulsification process. Mixtures with the surfactant tend to have a tighter particle size distribution with a mean diameter of 2 μm. The similarity of boiling behavior for mixtures of water with Tween 20 and the emulsion with surfactant suggests that the boiling behavior is characterized mostly by interface chemistry unique to the surfactant than to the effect of droplet size distribution.

Computational Investigation of Spray Heat Exchanger Performance (Dept.M)

Enhancement of the heat transfer coefficient is important for the design and operation of heat exchangers. In this study, a numerical model is built to investigate the performance of spray cooling heat exchanger as water is sprayed on a horizontal tube. The objectives of the study are 10 evaluate evaporation rate of the falling water film on a horizontal tube evaporator and obtaining the effect of the distance from the nozzle to the hot tube locution on the proportion rule and on heat transfer effectiveness. Moreover, the effect of droplet size distribution and the hot tube surface superheating temperature on the evaporation rate are also conducted. For a certain distance from nozzle distributor to the hot tube surface and by using the equations of mass, momentum and energy of the sprayed droplets, the change in droplet velocity, droplet size and its temperature can be evaluated. Vapor film is created around the hot tube surface. In this study, the formed vapor layer Thickness around the hot surface, evaporation rate and heat transfer effectiveness were also evaluated. The heat transfer characteristics are investigated at the considered ranges of the various spraying parameters such as: sprayed mass velocity (sprayed mass flow rate per the unit area of the lest tube) which ranged from 1.2532 101.5314 kg/m2.s, droplet size (ranged from 128.4 10 300 m), (droplet velocity (ranged from 310 7.43 m/s ) and spruce droplet size (ranged from 70 to 70 oC). The results show that the evaporation rate and the free transfer effectiveness are mainly increased by increasing the smile temperature. Also, the evaporation rule and the heat transfer effectiveness are increased by decreasing the droplet velocity. Al high initial sprayed mass velocity, hic vapored mass flow rate and the heat transfer effectiveness are inversely proportional to the droplet size. There is an optimum distance from nozzle distributor to the rube surface location of which the maximum evaporated rate will occur. The comparison between the obtained results and the results one to others shows a good agreement in which the difference between these results was ranged from 4 to15%

Quantitative characterization of the blockage effect from dispersed phase on wax molecular diffusion in water-in-oil emulsion

Molecular diffusion is the main mechanism of wax deposition, whereas the dispersed water droplets influence the wax diffusivity in water-in-oil (w/o) emulsion by restricting the diffusion path. In the present work, geometric analysis method was used to analyze the blockage effect from dispersed phase on the restricted diffusion path of wax molecules in w/o emulsion, and a correlation was proposed relating the blockage effect with water fraction, dispersed degree and nonuniformity of dispersed phase in real emulsions. Firstly, regarding water droplets as spherical particles with uniform size and arrangement pattern, the average tortuosity of different wax diffusion paths was deduced in two-dimensional (2D) and three-dimensional (3D) ideal conditions. The results showed that the blockage degree was enhanced with the increase in water fraction. Moreover, the droplet size distribution of different w/o emulsions was investigated by microscopic observation and a set of microstructure characterization parameters were summarized in statistics. A 3D microstructure model of real emulsion was established to derive the tortuosity, taking the effect of droplet size distribution into consideration. The blockage effect was enhanced by the increase in the dispersity and polydispersity of water droplets, but this influence was not significant and water fraction was still the main influencing factor. On this basis, a correlation of blockage coefficient with water fraction, number-averaged diameter and polydispersity was proposed and validated using the 1H/19F-NMR test results in literature with the average relative error being 3.17%. This will provide a support to the revealing of wax diffusion mechanism in w/o emulsions and the wax deposition prediction of multiphase flow pipelines.

Influence of Droplet Size Distribution on Liquid Dispersion in a Venturi Scrubber: Experimental Measurements and CFD Simulation

Venturi scrubbers provide highly efficient removal of particles from dust-laden gases. A uniform distribution of droplets improves the collection efficiency. Most computational models used to predict the dispersion of liquid in scrubbers employ the Boll correlation to calculate the mean droplet size. Given the lack of studies considering the effect of droplet size distribution on the liquid dispersion in Venturi scrubbers, the present work provides an experimental and numerical evaluation of this effect. Experimental measurements of droplet size distribution and liquid dispersion were made under different conditions. The fluid dynamic was simulated with ANSYS Fluent 14.0 software, using a discrete phase trajectory model. The simulations were performed with droplet size distributions measured experimentally and predicted using parameters from literature. The results for the simulated liquid dispersions were in agreement with the experimental data and indicated a strong dependence of the liquid distribution...

Effects of fuel droplet size distribution on soot formation in spray flames formed in a laminar counterflow

The effects of fuel droplet size distribution of the fuel spray on the soot formation of spray flames, which is stabilized in a laminar counterflow field, were investigated numerically and experimentally. To investigate the effects of droplet size distribution of fuel spray on soot formation, fuel sprays with quasi-mono-dispersed droplet size distribution (QM-DSD) spray and poly-dispersed droplet size distribution (P-DSD) spray were generated using a frequency-tunable vibratory orifice atomizer. The differences in the spray flame structures and soot formation characteristics between QM-DSD and P-DSD were examined in detail using an experiment with two-dimensional laser induced incandescence of soot and using three-dimensional direct numerical simulations (3D-DNS) employing a CIP method. Results showed that the soot formation area in the cases of P-DSD decreased compared to the cases of the QM-DSD under the same Sauter mean diameter (SMD) condition. This tendency was caused by differences of the flame structures. The results of the fuel and oxygen concentration and temperature obtained from the 3D-DNS indicated that the portion of the premixed-like flame structure increased in the case of P-DSD. As a result, the combustion reaction region of the spray flames is enlarged in axis direction in the case of P-DSD in the counterflow field.

Modelling pesticide flow and deposition from air-assisted orchard spraying in orchards: A new integrated CFD approach

Pesticide spray flow from air-assisted orchard sprayer through pear orchard and deposition on different environmental systems were estimated using a new integrated computational fluid dynamics (CFD) approach. The model simulated the complex interactions between wind, air and spray flow from the sprayer with target orchard canopy and the neighbouring environment. The new CFD approach involves the incorporation of the actual 3D canopy architecture into the model to simulate its effect on air and spray flow and deposition of droplets on the branches. Source–sink terms were added to the basic momentum and turbulence equations in a detailed sub-domain created around the branches to represent the effect of leaves. The spray droplets were generated from atomization model and tracked using a Lagrangian particle transport model. A new stochastic deposition model was developed and used to calculate deposition on leaves. The deposition model is a function of leaf optical porosity of the trees, leaf area density, leaf drag coefficient and droplet interception coefficient of the leaves. Two distinct nozzle setups, orchard and boom sprayer setups with ATR brown and TT blue nozzles, respectively, were compared to assess the effect of droplet size distribution on spray flow and deposition. The model results were compared with results from field measurements. For both sprayer setups, the simulation results agreed well with the measurements. The spray proportion above the tree height and behind the trees for the boom sprayer setup was 57.2% and 69.6% more than the orchard sprayer setup according to the simulations and the measurements, respectively. Such a model can be used to improve design features and the calibration of operational parameters of sprayers for better spraying efficiency and reduced environmental impact.

Study on Soot Formation in Spray Flames (Effect of Droplet Size Distribution)

Effect of the droplet size distribution of fuel spray on the soot formation process in spray flames is investigated. The vibratory orifice atomizer is used to control the droplet size distribution of fuel spray. Two-dimensional soot volume fraction and primary soot particle size are measured by the Time-Resolved Laser Induced Incandescence (Time-Resolved LII) method and direct numerical simulation. The relationship between spatial distribution of fuel droplets and soot formation area are observed by the LII method and Interferometric Laser Imaging Droplet Sizing (ILIDS) method. The results show that flame structures of spray flame and soot formation process are affected critically by the mean droplet size of fuel spray. The mean soot formation area is increased by increase of the mean droplet size of fuel spray. The primary soot particles become large at around the edge of soot formation area. This trend mainly occurs from surface growth of soot particles. The group of some droplets and its vapor forms the soot formation area, and the large droplet of liquid fuel deforms shape of the soot formation area.

Effect of droplet size distribution on reaction heat in a liquid–liquid heterogeneous reaction process

In heterogeneous liquid–liquid reaction processes, explosions have been reported. An aim of this study is to simulate the accident stories, which might be caused by inappropriate mixing conditions in the heterogeneous reaction process. The reaction of water-insoluble anhydride and water was selected as a model process. The experimental trend data of droplet size with agitation in a batch reactor were fitted to an empirical equation. The good fittings show the applicability of the equation in our reaction conditions.

The effect of droplet size distribution on gas temperature during the spray forming process

The effect of droplet size distribution on gas temperature during the spray forming process

The effect of droplet size distribution on liquid dispersion in a venturi scrubber

A three-dimensional dispersion model of our previous work was used to study liquid dispersion in a venturi type scrubber. The model in this recent work takes into account the effect of droplet size distribution on droplet dispersion in the scrubber. The results from the model are in good agreement with the experimental data.

Single-beam laser technique for measurement of droplet concentrations

An inexpensive system for measuring the concentration of micrometer-sized droplets using a single-beam laser detection system was developed. This technique allows sample volumes with dimensions on the order of a millimeter and measurements within a millimeter of surfaces and does not disturb any flow fields. Equations are derived for optical geometry, effective sample volume, and concentration calculations. Also the effects of droplet size distribution, detection threshold, and droplet concentration on measurement accuracy are described. Specific equipment and geometries are detailed for a situation where this technique was applied.

Effects of droplet-size distribution and gas-phase flow separation upon inertia collection of droplets by bluff-bodies in gas—liquid mist flow

This paper describes a trajectory analysis of the inertia collection of monodisperse- and polydisperse-droplets by a normal flat plate and a circular cylinder in gas—liquid mist flow. taking into account the far-wake displacement effect of gas-phase flow. The effects of the far-upstream droplet-size distribution and the gas-phase flow separation upon the local collection efficiency and the velocities and size distribution of droplets on impringement are examined. On the basis of these results. a new equivalent diameter of polydisperse-droplets is proposed.

Remote Determination of Cloud Liquid Water Path from Bandwidth-Limited Shortwave Measurements

A method of determining cloud liquid water path is developed using shortwave spectral measurements. The attenuation of shortwave radiant fluxes is due to scattering and absorption in the near-infrared band, but is caused only by scattering in the near-ultraviolet and visual band. The ratio of the reflectances in these two bands is defined as the reflectance ratio; the ratio of the transmittances as the transmittance ratio. Relationships between these ratios and the amount of cloud liquid water are developed. The use of reflectance ratio as a determinant of liquid water path has two advantages over the use of total shortwave reflectance alone. It minimizes the effect of droplet size distribution and the diagnostic curve is less sensitive to changes in reflectance than the curve based on total reflectance. The model is tested with data obtained by aircraft flights during the 1978 Joint Air-Sea Interaction Experiment (JASIN) and shows good agreement with measurements of liquid water path taken in the same area and with the results of other approximation formulas. Calculations show that this method could also be used to detect the extent of layering within a cloud deck.

Effect of droplet size distribution on spray drying kinetics

A comparison is made between the processes of adiabatic evaporation of a polydisperse system of droplets and a monodisperse system with droplets equal in size to the largest droplet of the polydisperse system. The process takes place in air with the same initial and final parameters in both cases.