Drop Diameter Research Articles

Experimental determination of forces applied by liquid water drops at high drop velocities impacting a glass plate with and without a shallow water layer using wavelet deconvolution

Time-dependent forces applied by 2 and 4.5 mm diameter drops of water (with velocities up to terminal velocity) impacting upon a glass plate with or without a water layer (up to 10 mm depth) have been measured using two different approaches, force transduction and wavelet deconvolution. Both approaches are in close agreement for drops falling on dry glass. However, only the wavelet approach is able to measure natural features of the splash on shallow water layers that impart forces to the plate after the initial impact. At relatively high velocities (including terminal velocity) the measured peak force from the initial impact is significantly higher than that predicted by idealised drop shape models and models from Roisman et al. and Marengo et al. Hence empirical formulae are developed for the initial time-dependent impact force from drops falling at (a) different velocities up to and including terminal velocity onto a dry glass surface, (b) terminal velocity onto dry glass or glass with a water layer and (c) different velocities below terminal velocity onto dry glass or glass with a water layer. For drops on dry glass, the empirical formulae are applicable to a glass plate or a composite layered plate with a glass surface, although they apply to other plate thicknesses and are applicable to any plate material with a similar surface roughness and wettability. The measurements also indicate that after the initial impact there can be high level forces when bubbles are entrained in the water layer.

Experimental investigations of fuel preparation in a swirling airflow under realistic conditions without reaction in a combustor model with a point fuel source

This paper presents quantitative experimental results of non-reacting spray analysis inside a model combustor at realistic jet engine conditions based on a point fuel source and with using kerosene Jet A-1 for the first time. Therefore, two test conditions with combustor pressures of 0.4 and 1.2 MPa, air preheat temperatures of 440 and 740 K and fuel preheating temperatures of 358 and 467 K were investigated. The basis for this investigation was a specially made combustor model in combination with a burner model similar to a fuel-staged lean burner. The focus was on the main stage with a single decentralised point fuel source. This fuel entry is a liquid jet in cross flow (LJICF) with the jet direction normal to the main air flow. The velocity of the air flow was measured by Laser Doppler Anemometry (LDA). Phase Doppler Anemometry (PDA) was used for the simultaneous measurements of fuel drop size and velocity. Sauter mean diameter (SMD) distributions and drop size dependent velocities were shown for the different axial distances inside the model combustor and were discussed with respect to the distributions and the ability of fuel droplets to follow the airflow. The consequent findings of the drop dispersion were verified by Stokes numbers. The drop diameters, and therefore the Stokes numbers, are heavily dependent on test conditions. With values of 8 < SMD [μm] < 20, the drop sizes were accordingly small. For validating the liquid fuel combustion codes, the dataset is completed by histograms of drop size and the determined Rosin–Rammler (RR) parameters.

Deuterium absorption in reduced activation ferritic/martensitic steel F82H under exposure to D2O vapor/water at room temperature

Eight samples of F82H ferritic/martensitic steel were irradiated at 300 K with 20 MeV W ions to the damage level of 0.54 displacements per atom at the damage peak. Three samples were afterwards annealed in vacuum at 423 K for 72 h and then at 373 K for 106 h. Three other samples were annealed in H2 atmosphere at 100 kPa at the same annealing temperatures and durations. All samples were exposed at room temperature to D2O vapor at the partial pressures in the range from 3 to 6 kPa for 365 to 1181 days. After termination of the D2O vapor exposure, the surfaces of the samples were partly covered by small (≤1 mm in diameter) drops of D2O water. Thus, the damaged samples were exposed to a mixture of D2O vapor and water. Trapping of deuterium at the ion-induced defects in the damage zone was examined by the D(3He, p)4He nuclear reaction. It has been found that the W-ion-induced defects generated in the F82H samples are decorated by deuterium diffusing from the surface.

Effect of Gas Diffusion Layer Surface Wettability Gradient on Water Behavior in a Serpentine Gas Flow Channel of Proton Exchange Membrane Fuel Cell

Water removal and behavior, in proton exchange membrane fuel cell (PEMFC) gas flow channel has been investigated in this work. Single serpentine gas flow channel has been simulated. Hydrodynamics of water drops in a serpentine channel are studied as a function of nature of gas diffusion layer (GDL) surface wettability. In one case, the surface becomes gradually hydrophobic starting from 90 deg to 170 deg. In this second case, the value of contact angle reduces to 10 deg. A three-dimensional model has been developed by using cfd software. Two different drop of diameter 0.2 mm and 0.4 mm are simulated for all the cases. It is observed that, water coverage is always lesser for a gradual hydrophobic surface. Also at low air velocity and gradual hydrophobic GDL surface results in lesser pressure drop as well as water coverage.

Drop behavior in a pilot plant asymmetric rotating disc extraction column for three various liquid–liquid systems

Among the liquid dispersion properties affecting the ARDC column behavior, the drop size distribution is one of the important parameters. Its control could positively contribute to optimize the column performance. The experimental works were carried out in a pilot plant ARDC column with three different systems. The effect of operating parameters on the Sauter mean drop diameters and drop size distributions were investigated. The drop size distribution is largely dependent on the agitation conditions in the column, but, the effect of phase flow rates is not significant. The empirical drop size distributions in the ARDC column are compared with the five common theoretical distribution functions (normal, log-normal, Gamma, Inverse Gaussian, Weibull).The constant parameters in these functions were correlated with operating conditions and physical properties of three systems. The Weibull is found to perform adequately and accurately in fitting the drop size distributions. Except for these findings, an empirical correlation is proposed for estimation of the Sauter mean drop diameter in terms of operating variables, column geometry and physical properties.

Drop bouncing by micro-grooves

Micro-textures are a well-known measure to increase surface hydrophobicity. Here, we experimentally investigate the impact of falling water droplets (diameter 2.1 mm, impact speed 0.62 m/s) on flat and structured surfaces made of the same hydrophobic material. While on the flat surface the drop settles with deposition, it bounces from the micro-grooved surface. Numerical simulations with a phase-field method mimicking the experiments do reproduce the different impact outcomes (deposition vs. bouncing) observed on both substrates. The axisymmetric simulation for the flat surface and the three-dimensional simulation for the structured surface employ the same grid size. In addition, the values for capillary width (chosen to be about 1% of the drop diameter) and mobility are the same in both simulations, where in the wetting boundary condition the static contact angle on the flat surface (100.3°) is identically used. Recovering the distinct experimental impingement outcomes in the simulation, though limited to one specific combination of drop diameter and impact speed, highlights the potential of the phase-field method for correctly predicting drop impact phenomena on flat and micro-structured surfaces under adequate resolution. Concerning the instantaneous droplet shape, the agreement between computations and experiments on both substrates is, however, only good till the beginning of the receding phases, whereas thereafter, significant differences are obtained.

The influence of the drop formation rate at spreading over a microstructured surface on the contact angle

The article presents the experimental dependences of a macro-contact angle and the diameter of a distilled water drop spreading over solid microstructured surface on surface average roughness (Ra) and fluid flow rate (G). It has been found that at changing G from 0.005 to 0.02 ml/s, the contact angle decreases, and at a liquid flow rate over 0.02 ml/s, it increases. With small values of G (0.005−0.01 ml/s), the drop diameter grows throughout the spreading process. In the range of G from 0.02 to 0.16 ml/s at the final stage of spreading, the contact line pinning, i.e., the diam-eter constancy, has been detected. The hypothesis about the mechanism of the pinning process has been formulated: it is due to the zero sum of all forces acting on the drop (inertia, viscosity, friction, gravity, and surface tension).

Study on viscosity and surface tension properties of biodiesel-diesel blends and their effects on spray parameters for CI engines

Biodiesels, prepared from different vegetable oils, have the potential to substitute the petro-diesel fuel in engines for global sustainability. In this work, the biodiesels of castor oil, neem oil and sunflower oil, have been produced in the laboratory by transesterification process and the properties of the prepared fuels are measured and compared against those of diesel. We have focused on the fuel properties that influence the spray formation in the engine cylinder following injection, viz. viscosity and surface tension, at various temperatures. The viscosity and surface tension properties are also measured for blends of diesel and biodiesels at different temperatures and blend ratios. Different correlation functions, both from the literature and newly developed, are used to evaluate the viscosity and surface tension of pure fuels and blends. The properties of the blends predicted from the correlations are compared against the measured values. The deviations in the predicted and measured values are statistically obtained to identify the most suitable correlation for the fuels under consideration. The effects of the variation in the properties of the pure and blended fuels on the spray characteristics, like mean drop diameter and spray cone angle, for compression ignition engines are studied using suitable correlations. The results are used to determine the preheating required in the biodiesel and blended fuels to achieve the identical spray parameters in the engine cylinder as with diesel fuel following injection.

Dropwise condensation patterns of bismuth formed on horizontal and vertical surfaces

Simulation of dropwise condensation of bismuth vapor on a subcooled hydrophobic surface is discussed in the present study. The process starts from nucleation of drops, followed by their growth and coalescence, resulting in drop instability that removes them from the surface. Fresh nucleation occurs at the exposed nucleation sites, thus creating a cycle of vapor condensation and liquid removal. The drop size distribution over the surface determines the instantaneous surface averaged wall heat flux. Wall shear stresses are generated during coalescence process and also when large drops start moving due to instability, which is gravitational in origin; hence, the largest drop diameter achieved depends on the surface orientation. Near-horizontal and vertical surfaces have been studied in the present work. Drop instability affects the periodicity of the condensation process and the average drop size and thus, the wall heat flux and wall shear stress. Coalescence of adjacent drops is a momentary step with a timescale of milliseconds, but the velocities generated are substantial. Coalescence velocities and time intervals have been determined by scale analysis, and the sensitivity of wall heat flux and wall shear stress to these ensuing velocities are delineated. The multiscale model developed is computationally intensive and has been simulated on large condensing surface areas using MPI on a parallel architecture. Bismuth condensation properties have been compared with water. Large heat fluxes and shear stresses are seen to be attained sporadically during coalescence for short time instants and do not contribute significantly to the surface-averaged values. On the other hand, wall shear stresses are found to be large enough to damage the hydrophobic coatings and degrade surface wettability, thereby hindering dropwise mode of condensation.

English

This study screened four Rhizopus species as biosurfactant producers using different markers. First of all, Rhizopus spp. UCP 1607 was identified as Rhizopus arrhizus by morphological and molecular methods. The production of biosurfactant/bioemulsifier was investigated by submerged fermentation using soybean post-frying oil (5% v/v) and sodium glutamate (1% w/v) medium. The primary markers’ hemolysis and parafilm M tests showed that R. arrhizus UCP1607 strain exhibited higher hemolytic activity (49 mm of clear zone) on sheep blood agar and a larger drop diameter (12 mm) on parafilm hydrophobic surface. The experimental results showed the most promising biosurfactant production by R. arrhizus UCP 1607 strain led to a reduction of surface tension (31.8 mN/m) and the diameter of the oil-spreading covered an area of 66.4 cm2. The strains Rhizopus microsporus var. chinensis UCP1296, R. microsporus var. microsporus UCP1304, and R. arrhizus UCP1607 were capable of forming stable emulsions corresponding to 91.7, 94.8, and 82.6%, respectively in crude oil. Key words: Tensio-active agent, bioemulsifier, screening of Rhizopus strains, submerged fermentation.

Ozone assisted cool flame combustion of sub-millimeter sized n-alkane droplets at atmospheric and higher pressure

Cool flame combustion of individual and isolated sub-millimeter sized n-heptane (n-C7H16) and n-decane (n-C10H22) droplets are computationally investigated for atmospheric and higher operating pressure (25 atm) conditions with varying levels of ozone (O3) mole fractions in the surroundings. A sphero-symmetric, one-dimensional, transient, droplet combustion model is utilized, employing reduced versions of detailed chemical kinetic models for the fuel species and an appended ozone reaction subset. Comprehensive parametric computations show that the regime of the cool flame burning mode and the transition from cool to hot flames are sensitive to the changes of O3 loading, pressure, diluent variation, the strength of initiation source, and the influence of fuel vapor pressure at the ambient condition. For both fuels and over a range of O3 concentrations in the ambient, sustained cool flame burning can be directly produced, even for sub-millimeter sized droplets. Over some range of O3 concentrations, operating pressure, and drop diameter, a self-sustaining, continuous cool flame burn can be produced without incurring a hot flame transition. For sufficiently high O3 concentrations, combustion initiation is always followed by a hot flame transition. Fuel volatility is also shown to be important for initiation and transition to cool flame and hot flame initiation. For fuels having a flash point lower than the ambient temperature (e.g. n-heptane), atomic O radicals formed by O3 decomposition react with the partially premixed, flammable gas phase near the droplet surface, leading to OH radicals, water production, and heat that auto-thermally accelerates the combustion initiation process. For fuels with flashpoints higher than the ambient temperature (e.g. n-decane), the reaction progress is limited by the local fuel vapor concentration and the necessity to heat the droplet surface to sufficiently high temperatures to produce locally flammable conditions. As a result, the initial transient for establishing either cool flame or hot flame transition is significantly longer for high flash point fuels. The transition of locally partially premixed reaction to diffusive burning conditions is more evident for high flash point conditions.

Influence of meteorological variables on rainfall partitioning for deciduous and coniferous tree species in urban area

Rainfall partitioning is an important part of the ecohydrological cycle, influenced by numerous variables. Rainfall partitioning for pine (Pinus nigra Arnold) and birch (Betula pendula Roth.) trees was measured from January 2014 to June 2017 in an urban area of Ljubljana, Slovenia. 180 events from more than three years of observations were analyzed, focusing on 13 meteorological variables, including the number of raindrops, their diameter, and velocity. Regression tree and boosted regression tree analyses were performed to evaluate the influence of the variables on rainfall interception loss, throughfall, and stemflow in different phenoseasons. The amount of rainfall was recognized as the most influential variable, followed by rainfall intensity and the number of raindrops. Higher rainfall amount, intensity, and the number of drops decreased percentage of rainfall interception loss. Rainfall amount and intensity were the most influential on interception loss by birch and pine trees during the leafed and leafless periods, respectively. Lower wind speed was found to increase throughfall, whereas wind direction had no significant influence. Consideration of drop size spectrum properties proved to be important, since the number of drops, drop diameter, and median volume diameter were often recognized as important influential variables.

Experimental Study of Drop Impact on Deep-Water Surface in the Presence of Wind

AbstractThe effects of wind on the impact of a single water drop on a deep-water surface are studied experimentally in a wind tunnel. Experiments are performed by varying impacting drop diameters, ranging from 2.5 to 4.1 mm and wind speeds up to 6.7 m s−1. The sequence of splashing events that occurred during drop impacts is recorded with a backlit, cinematic shadowgraph technique. The experimental results show that for low wind speeds, an asymmetrical crown forms on the leeward of the periphery of the colliding region after the drop hits the water surface, while a wave swell forms on the windward. Secondary droplets are generated from the crown rim. For high wind speeds with large drop diameters, ligaments are generated from the crown rim on the leeward of the drop impact site. The ligaments grow, coalesce, and fragment into secondary droplets. It is found that both the drag force and surface tension play important roles in the evolution process of the ligaments. The nondimensional K number (K = WeOh−0.4, where We is the Webber number and Oh is the Ohnesorge number) is used to describe the splashing-deposition limit of drop impact. The threshold value of this K number changes with the wind velocity and/or drop impact angle.

Experimental study of a drop “evolution” under conditions of its free fall on a heated surface

Time dependences of distilled water drop diameter were obtained experimentally after its falling on a heated copper substrate from a height of 0.09 m. The temperature of the solid surface ( Tw ) varied from 333 to 413 K in steps of 20 K. The effect on the drop dynamics after falling and the maximum ratio of the spreading diameter to the drop diameter in flight ( βmax ) were determined.

Application of response surface methodology to optimize the performance of cyclone separator using mathematical models and CFD simulations

The present study aims at optimizing the cyclone performance for a fixed total cyclone height. The objectives include reducing both pressure drop and cut-off diameter. Response surface methodology (RSM) based on the desirability approach is used to optimize the cyclone performance. Table of runs is constructed using Box-Behnken design method for five independent variables viz. vortex finder diameter and its insertion length, cylinder diameter and its height, and cone tip diameter of cyclone. Muschelknautz method (MM) of modeling is used to predict the values of dependent variables to fill the spread-sheet. The cyclone model with a new set of optimized geometrical values is analysed using numerical simulations and comparison of the results against the standard model shows significant improvement in the cyclone performance.

Evaluation of Operational and Experimental Precipitation Algorithms and Microphysical Insights during IPHEx

Abstract During May and June 2014, NOAA X-Pol (NOXP), the National Severe Storms Laboratory’s dual-polarized X-band mobile radar, was deployed to the Pigeon River basin in the Great Smoky Mountains of North Carolina as part of the NASA Integrated Precipitation and Hydrology Experiment. Rain gauges and disdrometers were positioned within the basin to verify precipitation estimates from various radar and satellite precipitation algorithms. First, the performance of the Self-Consistent Optimal Parameterization–Microphysics Estimation (SCOP-ME) algorithm for NOXP was examined using ground instrumentation as validation and was found to perform similarly to or slightly outperform other precipitation algorithms over the course of the intensive observation period (IOP). Radar data were also used to examine ridge–valley differences in radar and microphysical parameters for a case of stratiform precipitation passing over the mountains. Inferred coalescence microphysical processes were found to dominate within the upslope region, while a combination of processes were present as the system propagated over the valley. This suggests that enhanced updrafts aided by orographic lift sustain convection over the upslope regions, leading to larger median drop diameters.

Unforced Rayleigh instability of an immersed liquid jet

Motivated by the occurrence of the injection of liquids in various technical processes, we study the capillary instability of a liquid jet surrounded by another liquid. The study focuses on the natural developing Rayleigh instability, hence without an imposed perturbation. We also point out the influence of viscosity on the main drop diameter, resulted after jet breakup, and on the breakup length itself. Modifications brought by a decrease of the capillary nozzle are also emphasized for a particular case.

Spatio-temporal prediction of spill crude-base contaminant transport through selected porous soil matrix

Based on petroleum resource annual report of 1997, there has been occurrence of over 60,000 oil spills since the 40 years of oil exploration in Nigeria. The transport of contaminants has been a problematic issue for many years, mainly due to the adverse impact of the contaminants on the quality of groundwater. Predicting the effect and movement of the contaminant in soils and groundwater is essential to access and reduce the risk of soil contamination and groundwater pollution. We investigated contamination transport by modelling the flow of contaminants in the soil matrix. Darcy's law was employed to predict the permeability, porosity and hydraulic conductivity of the soil for different soil conditions. We developed 2D Numerical model for transport of diluted species under time-variant conditions was developed using advection-diffusion equation implemented using finite element technique over 2D computation domain with oil spill assumed drop diameter of 30 cm. The results presented in this report could be employed for developing enduring remediation strategies in reclaiming crude devastated soil.

MODELING OF LIQUID DROP HEATING AND EVAPORATION: THE EFFECT OF DROP SHRINKING

The process of heat and mass transfer from a spherical mono-component liquid drop evaporating into a gas environment is investigated, relaxing the commonly adopted quasi-steady approximation and accounting for the inherent unsteadiness caused by the sudden immersion of a liquid drop in a gaseous environment. The drop radius shrinking due to evaporation settles a moving boundary problem, which is transposed to a fixed boundary one by a proper coordinate transformation. The heat and evaporation rates and the drop diameter evolution are quantified by numerical solution of the species and energy conservation equations and the overall mass and energy balances over the drop for different species (water, n-octane, n-dodecane, ethanol).

Icing distribution of rotating blade of horizontal axis wind turbine based on Quasi-3D numerical simulation

For researching on the rules of icing distribution on rotating blade of horizontal axis wind turbine, a Quasi-3-D method is proposed to research on icing on rotating blades of horizontal axis wind turbine by numerical simulation. A 2-D and 3-D method of evaluating the irregular shape of ice has been established. The model of rotating blade from a 1.5 MW horizontal axis wind turbine is used to simulate the process and shape of icing on blade. The simulation is carried out under the conditions with four important parameters including ambient temperature, liquid water content, medium volume drop diameter, and icing time. The results reveal that icing mainly happens on 50% ~ 70% of the blade surface along wingspan from tip to root of blade. There are two kinds of icing shapes including horn shape icing and streamline shape icing. The study can provide theoretical basis and numerical reference to development of anti and deicing strategy for wind turbine blades.