Drop Diameter Research Articles

Application of Computational Fluid Dynamics for Modeling of Hydrodynamics and Mass Transfer of Laboratory Scale Crude Palm Oil Degumming Process

In this research, computational fluid dynamics was applied to model a laboratory reactor for the degumming of crude palm oil (CPO) involving immiscible liquid-liquid mixing and being controlled by mass transfer. The fluid mixing of CPO and phosphoric acid in the reactor was simulated using multiphase mixture model and standard κ-ε turbulence model in steady state mode. The simulation predicts the distributions of the drop diameter, the dispersed-phase relative velocity, the drop Reynolds number and the interfacial area density. The mass transfer coefficient from experimental work is correlated using the model as Sherwood number Shd = 0.02576 Red0.673Sc0.431 with R2 being 0.91. Finally, the volumetric mass transfer coefficient was calculated and compared to the experiment result.

Study of the internal flow in a rotary atomizer and its influence on the properties of the resulting spray

Rotary atomizers are often used in spray drying applications because they are able to atomize complex, highly viscous, multicomponent liquids. Spray drying is widely used in the chemical and food industry and is the preferred method of drying many materials such as dairy products, foods, pharmaceuticals, polymers, etc. An important design parameter of spray dryers is the drop size distribution, since it determines the resultant powder size distribution. In this study the evolution of the rivulet thickness of the feed within the inserts of a rotary atomizer is modelled theoretically and compared to numerical and experimental data. Furthermore, the phase Doppler measurement technique has been used to analyse size and velocity of the resulting spray drops. It is shown that the average dimensionless drop diameter, scaled by the jet thickness, correlates very well with the dimensionless stretching parameter. Finally a semi-empirical model for the average diameter of drops in the spray is developed.

Influence of Raindrop Size Distribution on Throughfall Dynamics under Pine and Birch Trees at the Rainfall Event Level

Part of precipitation is intercepted by forest canopies, while the rest reaches the ground as throughfall or stemflow. This process is influenced by various meteorological variables, of which we have mainly focused on drop diameter and velocity. Rainfall in the open and throughfall under birch and pine trees have both been measured since 2014 in Ljubljana, Slovenia. The results demonstrate that the total throughfall during 3.5 years was 73% and 53% of rainfall under birch and pine trees, respectively. During the 236 analysed events, the median volume diameter was 1.8 mm (±1.7 mm), and kinetic energy between 0.01 mJ/cm2 and 23.3 mJ/cm2 was recorded. We closely analysed the effect of rainfall microstructure on throughfall under pine and birch trees during three specific rainfall events. The increase in drop diameter and fall velocity during a rainfall event instantaneously increased throughfall under pine trees between 25% and 47%, whereas no such changes were observed under birch trees. This may be the consequence of different tree properties of the two species. Additionally, in the case of a saturated canopy, throughfall under pine trees exceeded rainfall in the open after an onset of larger and faster drops.

Displacer Diameter Effect in Displacer Pulse Tube Refrigerator

Gas driving displacer pulse tube refrigerators are one of the work recovery type of pulse tube refrigerators whose theoretical efficiency is the same as Stirling refrigerators'. Its cooling power is from the displacement of the displacer. Displace diameter, rod diameter and pressure drop of the regenerator influence the displacement, which are investigated by numerical simulation. It is shown that the displacement ratio of the displacer over the piston is almost not affected by the displacer diameter at the same rod diameter ratio, or displacer with different diameters almost has the same performance.

Numerical simulation on the flow field characteristics and impact capability of liquid nitrogen jet

With the rapid progress of petroleum engineering, liquid nitrogen jet is expected to be used for perforation and jet fracturing, and then provide a new method for unconventional reservoirs efficient development. In order to research the flow field characteristics and evaluate the impact capability of liquid nitrogen jet, a computation fluid dynamic model was built by coupling the nitrogen physical property equations to simulate the flow field of liquid nitrogen jet. The results indicated that given the same simulation conditions, the impact pressure of liquid nitrogen jet was equivalent to that of water jet. The liquid nitrogen jet presented more excellent impact capability than water jet because of its higher axial and radial velocities. The impact capability of liquid nitrogen jet increased with the growth of nozzle pressure drop and nozzle diameter, decreased with the increasing of standoff distance, and was slightly influenced by fluid temperature. The confining pressure hardly affected the impact capability of liquid nitrogen jet, so it can be neglected in the engineering application. This study uncovered the flow field characteristics of liquid nitrogen jet and could provide theoretical guidance for the application of perforation and fracturing with liquid nitrogen jet.

Development and calibration of a rainfall simulator for hydrological studies

ABSTRACT Rainfall Simulators (RS) have been used as tools for researches involving the estimation of runoff and infiltration on permeable pavements as well as in evaluating storm build-up and wash-off processes on pavements and roofs. Data obtained with the use of RS allows building a database with parameters which are useful in the implementation of BMPs taking local environment conditions into consideration. The purpose of this study was to develop and calibrate a handy and low-cost RS for hydrological researches. The developed RS can reproduce rainfall with intensities from 40 mm h-1 to 182 mm h-1. The RS is able to simulate rainfall events with drops of median diameter (D50) of 2.12 mm and kinetic energy of 22.53 J mm-1m-2, which represent 90.12% of the kinetic energy produced by a natural rainfall. Spatial distribution of simulated rainfall, which is expressed by the Christiansen's Uniformity Coefficient, was considered satisfactory with a value of up to 87.80%. The developed RS can be used as an alternative for the acquisition of hydrological data in a reduced period of time, under standardized experimental conditions and independently of natural rainfall events. The RS is also capable to simulate rainfall events with varying intensity.

Microphysical processes of a stratiform precipitation event over eastern China: analysis using micro rain radar data

Data collected using the micro rain radar (MRR) situated in Jinan city, eastern China, were used to explore the altitudinal and temporal evolution of rainfall microphysical characteristics, and to analyze the bright band (BB) characteristics and hydrometeor classification. Specifically, a low-intensity and stable stratiform precipitation event that occurred from 0000 to 0550 UTC 15 February 2015 and featured a BB was studied. During this event, the rainfall intensity was less than 2 mm h−1 at a height of 300 m, which was above the radar site level, so the errors caused by the vertical air motion could be ignored. The freezing height from the radiosonde matched well with the top of the BB observed by the MRR. It was also found that the number of 0.5–1 mm diameter drops showed no noticeable variation below the BB. The maximum fall velocity and the maximum gradient fall velocity (GFV) of the raindrops appeared at the bottom of the BB. Meanwhile, a method that uses the GFV and reflectivity to identify the altitude and the thickness of the BB was established, with which the MRR can provide a reliable and real-time estimation of the 0°C isotherm. The droplet fall velocity was used to classify the types of snow crystals above the BB. In the first 20 min of the selected precipitation event, graupel prevailed above the BB; and at an altitude of 2000 m, graupel also dominated in the first 250 min. After 150 min, the existence of graupel and dendritic crystals with water droplets above the BB was inferred.

Effect of the addition of synthetic fuel on the selected physico-chemical properties of the fuel for the diesel engines

Plastics present a major threat to todays society and environment. Though mankind has awoken to this threat and responded with developments in creating degradable bio plastics, there is still no conclusive effort done to repair the damage already caused. In this regard, the catalytic depolymerization studied here presents an efficient, clean and very effective means of removing the debris that we have left behind over the last several decades. By converting plastics to fuel, we solve two issues, one of the large plastic seas, and the other of the fuel shortage. This dual benefit, though will exist only as long as the waste plastics last, but will surely provide a strong platform for us to build on a sustainable, clean and green future. The paper presents results of density, viscosity, cetane number, ignition temperature of 100% synthetic fuel and this fuels mixture with the diesel oil. The quality of the fuel-air mixture formation is best characterized by the SMD parameter – Sauters average diameter of spray drops, and its value in analytical studies depends on the physical parameters of the fuel (density, viscosity, surface tension). The results of laboratory tests will be developed in terms of the use of the measured parameters of a synthetic fuel mixture to calculate SMD values and to correct analytical equations taking into account the actual SMD values measured by laser diffraction laboratory tests.

Diffusion coefficients of water and propylene glycol in supercritical CO2 from pendant drop tensiometry

New optimized experimental setup based on pendant drop tensiometry was developed, and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. For the first time, the diffusion coefficients of propylene glycol in supercritical CO2 were determined at temperatures of 398.2 and 423.2K and at pressures from 5MPa, up to 17.5MPa.Experimental procedure was validated by a comparison of the experimental data for the mixture water-CO2 with data from the literature. For this purpose, the diffusivity of water in CO2 was measured at 298.15K in the pressure range from 5MPa, up to 60MPa. Accuracy of results was certified by measuring more than 1000 points of equivalent drop diameter. Droplet geometry was examined by using a precise computer algorithm that fits Young–Laplace equation to the axisymmetric shape of a drop.

A modified particle tracking velocimetry technique to characterize sprinkler irrigation drops

Numerous methodologies have been developed to characterize sprinkler irrigation drops with the purpose of improving irrigation efficiency and controlling soil erosion and compaction. This paper presents the laboratory characterization of the morphology and velocity of drops in their free-falling trajectory as influenced by drop diameter and wind speed. For this purpose, a particle tracking velocimetry technique with in-line volumetric illumination was implemented. Hypodermic needles were used to produce droplets of uniform size. Two needle diameters resulted in drops with average diameters of 1.94 and 2.94 mm. Drops were illuminated with a double-pulsed laser beam or an LED lamp. Drop characterization reached an elevation of 4.28 m and occasionally attained terminal velocity. Motion blur was suppressed using a deconvolution filter. Drop equivalent diameter, velocity, chord ratio, canting angle and trajectory angle were determined using an ad-hoc software. The experimental approach led to the measurement of real drop size by illuminating a volume in the capture zone; drop shape ranged from quasi-sphere to ellipsoid. Drop deformation was more intense under high wind speeds. Ballistic simulations of drop fall were performed using sphere and ellipsoid drag force models. Both models resulted in excellent agreement with measured drop velocity, with the ellipsoid model performing marginally better. The robustness of the experimental equipment, particularly in combination with the developed LED lamp, announces future outdoor applications in real sprinkler irrigated fields. Such applications will provide insight on the governing processes, and data sets for the improvement of sprinkler simulation models.

Comparative Evaluation of the OTT PARSIVEL2 Using a Collocated Two-Dimensional Video Disdrometer

AbstractThe performance of the OTT second-generation Particle Size Velocity (PARSIVEL2) laser weather sensor is evaluated by comparing it with a collocated two-dimensional video disdrometer (2DVD) and rain gauges using data collected over a total of 36 rain events. A comparison of raindrop size distributions (DSDs) between the 2DVD and two PARSIVEL2 reveals good agreement for weak rainfall rates below approximately 10 mm h−1 and for midsize drops with diameters between 0.6 and 4.0 mm irrespective of rainfall rates, whereas the PARSIVEL2 produces overestimations of large drops with diameters above 4 mm during heavy rainfall above approximately 20 mm h−1. The resultant DSD parameters of the PARSIVEL2 present overestimations of the mean diameter Dm in the normalized gamma function and the maximum drop diameter Dmax, and underestimations of the intercept parameter Nw and total number of drops NT. Furthermore, how the characteristics of DSDs from the PARSIVEL2 affect the polarimetric radar variables, such as differential reflectivity ZDR and specific differential phase KDP, is examined, as well as how these characteristics affect empirical relations required in radar hydrometeorological applications such as quantitative rainfall estimations. Based on these examinations, it can be concluded that the OTT PARSIVEL2 still produces overestimations of large drops and underestimations of small drops during heavy rainfall, similar to older models of PARSIVEL, despite significant improvements to the PARSIVEL2 system, and furthermore that the uses of PARSIVEL2 measurements can act as a source of error in radar hydrometeorological applications such as radar rainfall estimations.

Drop behaviour characteristics in different operating regimes in an L‐shaped pulsed sieve‐plate column

AbstractIn this study, the influence of different operating regimes on drop behaviour in an L‐shaped pulsed sieve‐plate column has been investigated and the effects of pulsation intensity and phase superficial velocities on drop diameters are evaluated. The toluene‐water system with 0.03 L/L (3 vol%) acetone as a mass transfer agent is used. Experimental observations reveal that with increasing pulsation intensity, drop sizes slightly decrease and by reaching to the end of mixer‐settler regime, they significantly decrease followed by a mild decrease in the dispersion regime. Moreover, it is observed that mean drop size firstly varies inversely as both phase superficial velocities change, while it slightly increases with further increase in superficial velocities. Finally, some of the most recommended correlations are compared to the experimental data. It is revealed that these correlations show the highest deviation in the lower end of the mixer‐settler regime (> 40 %), while in the dispersion regime it becomes < 15 %, indicating that they are only applicable in the region of practical regimes. Accordingly, two of these correlations are modified in order to cover different operating regimes by means of two correlations proposed to predict the transition regime in each section of the column. The AARE values of the modified correlations are found to be < 14.7 %.

New correlations for slip velocity and characteristic velocity in a rotary liquid–liquid extraction column

In this research work, the hydrodynamic behavior of a Kühni extraction column has been investigated for determination of slip velocity and characteristic velocity for three different liquid–liquid systems with and without mass transfer conditions and toluene–water system with the presence of silica nanoparticles. The effects of the agitation speed, dispersed as well as continuous phase velocity, and interfacial tension were studied. The findings revealed that an increase in agitation speed and continuous phase velocity led to the reduction of slip velocity while it increased with increasing dispersed phase velocity. More buoyancy and faster upward movement of larger drops accelerate the slip velocity in the dispersed to continuous phase mass transfer condition as compared with the case of no mass transfer. In addition, the slip velocity decreased in the experimental conditions with nanoparticles because of the decrease in Sauter mean drop diameter and the increase in the holdup. Empirical correlations for prediction of slip and characteristic velocities are recommended. The results of the proposed correlations were compared with the experimental data obtained from the literature and the present investigation. Findings of this study demonstrated that the proposed correlations gave accurate predictions for slip velocity and characteristic velocity.

Coalescence stability of water-in-oil drops: Effects of drop size and surfactant concentration

We study the effects of (1) drop size; (2) surfactant chain-length and concentration; and (3) viscosity of the oil phase on the stability of water drops, pressed by gravity towards planar oil-water interface. The experimental results show that at low surfactant concentrations (around and below the CMC) the drop lifetime is controlled by the drainage time of the oily film, viz. by the time for reaching the critical film thickness at which this film ruptures. The small drops coalesce before the formation of a planar film with the large interface and, as a consequence, their lifetime rapidly decreases with the increase of drop diameter. In contrast, the bigger drops coalesce after formation of a plane-parallel film and their lifetime increases with the drop diameter. Therefore, the drop lifetime passes through a minimum when varying the drop diameter. The obtained results at low surfactant concentrations and for small drops are described well by theoretical models, available in the literature. The lifetime of the respective larger drops is shorter, as compared to the theoretical predictions, due to the faster thinning of the oil films which are with uneven thickness. The increase of surfactant concentration above the CMC leads to a significant increase in the stability of the small drops. Interestingly, the stability of the intermediate in size drops remains low for all surfactants and oils studied. At higher surfactant concentrations, the stability of the large water drops increases significantly when Span 80 is used, while it remains rather low for drops stabilized by Span 20. The results obtained with single water drops are in a good agreement with the stability of the respective batch water-in-oil emulsions.

Motion of a spherical liquid drop in simple shear flow next to an infinite plane wall or fluid interface

The velocity of translation of a spherical liquid drop under the influence of simple shear flow near an infinite plane wall or fluid interface is computed with high accuracy using a boundary-integral method for Stokes flow based on Fourier decomposition in the absence of significant gravitational effects. Accurate results are obtained for very small gaps between the drop surface and the wall or interface, several orders of magnitude smaller than the drop diameter. As the gap decreases, a liquid drop tends to stick to a solid wall but is able to slide over an interface irrespective of the drop and ambient fluid viscosities. In the case of flow near an interface, the dependence of the drop velocity on the drop position and viscosity ratio is not necessarily monotonic. The interfacial deformation is computed to leading order with respect to the capillary number and is shown to exhibit an asymmetry due to the presence of the wall or interface. The predictions of the asymptotic analysis for nearly spherical drops are in agreement with boundary-element simulations of three-dimensional flow.

Retrieval of the raindrop size distribution from polarimetric radar data using double-moment normalisation

Abstract. A new technique for estimating the raindrop size distribution (DSD) from polarimetric radar data is proposed. Two statistical moments of the DSD are estimated from polarimetric variables, and the DSD is reconstructed using a double-moment normalisation. The technique takes advantage of the relative invariance of the double-moment normalised DSD. The method was tested using X-band radar data and networks of disdrometers in three different climatic regions. Radar-derived estimates of the DSD compare reasonably well to observations. In the three tested domains, in terms of DSD moments, rain rate, and characteristic drop diameter, the proposed method performs similarly to and often better than a state-of-the-art DSD-retrieval technique. The approach is flexible because no specific DSD model is prescribed. In addition, a method is proposed to treat noisy radar data to improve DSD-retrieval performance with radar measurements.

Computational Fluid Dynamics Simulations of Single Drops in Confined Geometries

Understanding of drop rise in confined domains is important as it influences drop rise velocity and drag coefficient. In this work, the motion of a single liquid drop rising in a quiescent channel filled with water in the presence of a wall effect is studied numerically using the combined volume of fluid and level set method. The ratio of drop diameter to column diameter is used as a parameter to quantify the presence of the wall effect. Simulations were carried out for n-butanol and toluene drops. A reduction in rise velocity is seen in all the cases. It is seen that pressure profile, strain rate, and vorticity magnitude near the drop surface have a significant effect on the evolution of a drop shape in confined geometries. Drag coefficients have been calculated from the force balance equation. The correlation for the correction factor for the drag coefficient has been developed to account for the wall effect.

Emulsification of viscous alkyd resin by catastrophic phase inversion with nonionic surfactant

The addition of water to hydrophobic alkyd resin containing a hydrophilic nonionic surfactant (polyethoxylated-20-oleyl alcohol) was used to produce the emulsion morphology change from W/O to O/W in a small thermostated reactor (50mL). The so-called catastrophic phase inversion of the water/alkyd resin system was detected by monitoring both, the viscosity by torque measurement and the electrical conductivity, until an equal weight fraction of water and resin is attained (fw=0.5). The two methods provide similar values of the phase inversion point (PIP). Although the determination of the PIP exhibits a small inaccuracy, it is clear that different torque profiles and PIP are observed depending on the resin neutralization level, the surfactant concentration and the water addition rate. For the non-neutralized resin, both, PIP and emulsion drop size, decrease with surfactant concentration increase. The completely neutralized resin could be emulsified using a minimum of 2wt% of surfactant in the final emulsion. In such a case the water fraction at which inversion occurs (fw,Inv=0.36) is independent of the surfactant concentration and a small resin drop diameter (<200nm) can be obtained. A more precise study of the reached drop size of the emulsion versus resin neutralization (0, 25, 50, 75, 100 and 125%) indicates that a minimum diameter is obtained around 90–100% neutralization, with no effect of over-neutralization. For non-neutralized resin a maximum fw,Inv (0.25) can be obtained by reducing water addition rate allowing the production of 0.5μm droplets in a longer process.

A phenomenological relationship between vertical air motion and disdrometer derived A-b coefficients

Using the well-known Z-R power law, Z=ARb, A-b parameters derived from a single disdrometer are readily found and can provide useful information to study rainfall drop size distributions (DSDs). However, large variations in values are often seen when comparing A-b sets from various researchers. Values of b typically range from 1.25 to 1.55 for both stratiform and convective events. The values of A approximately fall into three groups: 150 to 200 for convective, 200 to 400 for stratiform, and 400 to 500 for convective. Computing the A-b parameters using the gamma DSD, coupled with a modified drop terminal velocity model, vD(D)=vT(D)−w, where D is drop diameter, vT(D) is still air drop terminal velocity, and w is an estimate of vertical velocity of the air well above the disdrometer, shows an interesting result. This model predicts three regions of A, corresponding to w<0, w=0, and w>0. Additional models that incorporate a constant vertical air velocity are also investigated. A-b sets derived from a Joss-Waldvogel (JW) disdrometer and DSD data acquired near Athalassa, Cyprus, using selected 24-hour data sets from 2011 to 2014, are compared to the above models. The data is separated into two main groups: stratiform events defined by rainfall rates that did not exceed 10mmh−1 at any time during the 24-hour period, and convective events defined by rainfall rates not flagged as stratiform. The convective rainfall is further separated into two groups: A-b pairs that fall to the left of the stratiform pairs and pairs that fall to the right. This procedure is repeated with data from other researchers that corresponds to seasonal averages. In all cases, the three vertical groupings of the A-b parameter plot seem to correlate to DSD simulations where various values of positive and negative vertical velocities are used.

A Laboratory System for Nozzle Spray Analysis

Droplet spray spectrum is one of the most important factors affecting the biological efficacy of a phytosanitary treatment and water sensitive papers (WSP) are one of the most widely used tools to asses spray coverage. Aim of this study is to present a low cost laboratory test bench, suitably designed to analyse nozzle sprays according to the procedure established by ISO 5682-1 and to allow studying the correlation between spray features and WSP surface coverage. The test bench consists of a transportable trolley carrying a 70 L tank, a diaphragm pump driven by an electric motor, and a spray boom applied to a mobile support that moves along two slides placed above and parallel to the plane of the trolley, in such a way the distance between target and nozzle is 0.5 m. According to the procedure established by ISO 5682-1, the nozzle under test sprays a mixture with water-soluble dye (Poinceau Red) above Petri dishes containing silicon oil. The images of the drops trapped into the oil are acquired by using a high resolution (24 Mpixel) DSLR camera and then analysed with image analysis software. Moreover, spraying at the same time Petri dishes and WSPs, the data coming from the drops inside the Petri dishes can be correlated to those coming from the image analysis of WSPs. To better asses the WSP behaviour, this paper also reports the results of some simulations of WSPs when sprayed with drops of assigned drop size distribution (log-normal) and volume median diameter ranging from 125 µm (fine spray) to 475 µm (coarse spray). The simulations showed that the overlap between stains is independent from spray features and that the unitary deposit (µL cm−2) is highly correlated to the percentage of covered surface by means of second order equations whose coefficients depends on volume median diameter of drops.