To see the other types of publications on this topic, follow the link: Droplet entrainment.
Journal articles on the topic 'Droplet entrainment'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Droplet entrainment.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Sujith, R. I., G. A. Waldherr, J. I. Jagoda, and B. T. Zinn. "An Experimental Investigation of the Behavior of Droplets in Axial Acoustic Fields." Journal of Vibration and Acoustics 119, no. 3 (1997): 285–92. http://dx.doi.org/10.1115/1.2889722.
Full textAbstract:
This paper describes an experimental investigation of the behavior of water droplets in axial acoustic fields. It was motivated by the increasing interest in the use of pulsations to improve the performance of energy intensive, industrial processes. The presence of an acoustic field is believed to enhance heat and mass transfer to and from the droplets, probably because of the relative motion between the droplets and the gas phase. This relative motion is characterized by the ratio of the amplitude of the oscillatory droplet velocity to that of the acoustic velocity (entrainment factor), and by the phase between the droplet and gas phase oscillations. An experimental set-up was developed to investigate the effect of acoustic oscillations on the motion of individual droplets. In these experiments a droplet produced by a piezo-ceramic droplet generator is allowed to fall through a transparent test section in which an acoustic field has been set up using a pair of acoustic drivers. Images of the droplets in the test section acquired at consecutive instants using a high speed, intensified imaging system were used to determine the time dependent droplet trajectory and velocity. The acoustic velocity was calculated from measured acoustic pressure distributions. The entrainment factor and the phase difference were then determined from these data. The results show how the entrainment factor decreases and the phase difference increases with increasing droplet diameter and frequency, indicating that larger diameters and higher frequencies reduce the “ability” of the droplets to follow the gas phase oscillations. The measured data are in excellent agreement with the prediction of the Hjelmfelt and Mockros model. Both theoretical predictions and measured data were correlated with the Stokes number, which accounts for the effects of droplet diameter and frequency. It was also shown that acoustic oscillations decrease the mean terminal velocity of the droplets.
2
Singh, Digvijay, and Arup Kumar Das. "Predictability and benefits of coupled Eulerian-Lagrangian approach over Eulerian characterization of droplet annular flow." Fluid Dynamics Research 53, no. 6 (2021): 065501. http://dx.doi.org/10.1088/1873-7005/ac34ec.
Full textAbstract:
Abstract Wavy annular flow and subsequent droplet dispersion in air-water two-phase flow has been studied numerically using conventional Eulerian volume of fluid (VOF) solver and coupled Eulerian-Lagrangian approach. The VOF based investigation has been reported to highlights the formation of droplet swarm and its population dynamics. Coupled Eulerian-Lagrangian method has also been shown to replicate similar features with lesser computational effort. Entrainment, deposition, fragmentation and unification are traced from the numerical simulation, which ultimately predicts the volume filling behavior of the droplets inside the tube. Flow kinematics around droplet is critically assessed numerically for finding out reasons behind deposition, fragmentation and unification. A comparative behavior between different velocity ratios of gas and liquid flow rates are presented which clearly shows higher entrainment rate as shear between annular liquid and gaseous core increases. An assessment of the droplet population in coupled Eulerian-Lagrangian method shows the generation of the smaller sized spherical droplet by entrainment and fragmentation route.
3
Jauseau, Nicolas, Fernando Farelas, Marc Singer, and Srdjan Nešić. "Investigation of the Role of Droplet Transport in Mitigating Top of the Line Corrosion." Corrosion 74, no. 8 (2018): 873–85. http://dx.doi.org/10.5006/2764.
Full textAbstract:
The entrainment of liquid droplets, occurring in a limited range of gas and liquid flow conditions within the stratified flow region, could represent an effective way to transport a non-volatile liquid corrosion inhibitor through the gas phase and combat top of the line corrosion (TLC). However, such an approach is only viable if the inhibitor can reach the top of the pipe and deposit at a rate higher than the local rate of condensing water can dilute it. This work presents a combined modeling and experimental methodology to determine the onset of droplet entrainment from the bottom and deposition at the top of the line. A modeling approach predicting the droplet entrainment onset is proposed and validated against new multiphase flow data recorded in a large scale flow loop, at operating conditions similar to those encountered in gas-condensate production facilities. Additionally, TLC experiments were performed in the same flow loop under simulated water condensation conditions to measure the actual corrosion at different rates of inhibiting droplet deposition. The results confirm that the droplet entrainment/deposition can effectively mitigate TLC when operating parameters are accurately controlled.
4
Bewley, Jennifer L., and Sonia Lasher-Trapp. "Progress on Predicting the Breadth of Droplet Size Distributions Observed in Small Cumuli." Journal of the Atmospheric Sciences 68, no. 12 (2011): 2921–29. http://dx.doi.org/10.1175/jas-d-11-0153.1.
Full textAbstract:
Abstract A modeling framework representing variations in droplet growth by condensation, resulting from different saturation histories experienced as a result of entrainment and mixing, is used to predict the breadth of droplet size distributions observed at different altitudes within trade wind cumuli observed on 10 December 2004 during the Rain in Cumulus over the Ocean (RICO) field campaign. The predicted droplet size distributions are as broad as those observed, contain similar numbers of droplets, and are generally in better agreement with the observations when some degree of inhomogeneous droplet evaporation is considered, allowing activation of newly entrained cloud condensation nuclei. The variability of the droplet growth histories, resulting primarily from entrainment, appears to explain the magnitude of the observed droplet size distribution widths, without representation of other broadening mechanisms. Additional work is needed, however, as the predicted mean droplet diameter is too large relative to the observations and likely results from the model resolution limiting dilution of the simulated cloud.
5
Marchetti, J. M., and H. F. Svendsen. "REVIEW OF KERNELS FOR DROPLET-DROPLET INTERACTION, DROPLET-WALL COLLISION, ENTRAINMENT, RE-ENTRAINMENT, AND BREAKAGE." Chemical Engineering Communications 199, no. 4 (2012): 551–75. http://dx.doi.org/10.1080/00986445.2011.592453.
Full text
6
Abade, Gustavo C., Wojciech W. Grabowski, and Hanna Pawlowska. "Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Entraining Parcel Simulations." Journal of the Atmospheric Sciences 75, no. 10 (2018): 3365–79. http://dx.doi.org/10.1175/jas-d-18-0078.1.
Full textAbstract:
This paper discusses the effects of cloud turbulence, turbulent entrainment, and entrained cloud condensation nuclei (CCN) activation on the evolution of the cloud droplet size spectrum. We simulate an ensemble of idealized turbulent cloud parcels that are subject to entrainment events modeled as a random process. Entrainment events, subsequent turbulent mixing inside the parcel, supersaturation fluctuations, and the resulting stochastic droplet activation and growth by condensation are simulated using a Monte Carlo scheme. Quantities characterizing the turbulence intensity, entrainment rate, CCN concentration, and the mean fraction of environmental air entrained in an event are all specified as independent external parameters. Cloud microphysics is described by applying Lagrangian particles, the so-called superdroplets. These are either unactivated CCN or cloud droplets that grow from activated CCN. The model accounts for the addition of environmental CCN into the cloud by entraining eddies at the cloud edge. Turbulent mixing of the entrained dry air with cloudy air is described using the classical linear relaxation to the mean model. We show that turbulence plays an important role in aiding entrained CCN to activate, and thus broadening the droplet size distribution. These findings are consistent with previous large-eddy simulations (LESs) that consider the impact of variable droplet growth histories on the droplet size spectra in small cumuli. The scheme developed in this work is ready to be used as a stochastic subgrid-scale scheme in LESs of natural clouds.
7
Yang, Fan, Raymond Shaw, and Huiwen Xue. "Conditions for super-adiabatic droplet growth after entrainment mixing." Atmospheric Chemistry and Physics 16, no. 14 (2016): 9421–33. http://dx.doi.org/10.5194/acp-16-9421-2016.
Full textAbstract:
Abstract. Cloud droplet response to entrainment and mixing between a cloud and its environment is considered, accounting for subsequent droplet growth during adiabatic ascent following a mixing event. The vertical profile for liquid water mixing ratio after a mixing event is derived analytically, allowing the reduction to be predicted from the mixing fraction and from the temperature and humidity for both the cloud and environment. It is derived for the limit of homogeneous mixing. The expression leads to a critical height above the mixing level: at the critical height the cloud droplet radius is the same for both mixed and unmixed parcels, and the critical height is independent of the updraft velocity and mixing fraction. Cloud droplets in a mixed parcel are larger than in an unmixed parcel above the critical height, which we refer to as the “super-adiabatic” growth region. Analytical results are confirmed with a bin microphysics cloud model. Using the model, we explore the effects of updraft velocity, aerosol source in the environmental air, and polydisperse cloud droplets. Results show that the mixed parcel is more likely to reach the super-adiabatic growth region when the environmental air is humid and clean. It is also confirmed that the analytical predictions are matched by the volume-mean cloud droplet radius for polydisperse size distributions. The findings have implications for the origin of large cloud droplets that may contribute to onset of collision–coalescence in warm clouds.
8
Xie, Zhenqiang, and Xuewen Cao. "Effect of Entrainment on the Liquid Film Behavior in Pipe Elbows." Energies 17, no. 8 (2024): 1983. http://dx.doi.org/10.3390/en17081983.
Full textAbstract:
Multiphase flow entrainment in natural gas engineering significantly influences the safety and efficiency of oil companies since it affects both the flow and the heat transfer process, but its mechanisms are not fully understood. Additionally, current computational fluid dynamics (CFD) methodologies seldom consider entrainment behavioral changes in pipe elbows. In this article, a verified CFD method is used to study the entrainment behavior, mechanism, and changes in an elbow. The results show that droplet diameter in a developed annular flow follows a negative skewness distribution; as the radial distance (from the wall) increases, the fluctuation in the droplets becomes stronger, and the velocity difference between the gas and the droplets increases linearly. Turbulence bursts and vortices sucking near the wall jointly contribute to droplet entrainment. As the annular flow enters the elbow, the secondary flow promotes the film expansion to the upper and lower parts of the pipe. Droplets re-occur near the elbow exit intrados, and their size is much smaller than those in the upstream pipe. Vortices sucking under low gas velocity play an important role in this process. These findings provide guidelines for safety and flow assurance issues in natural gas production and transportation and bridge the gap between multiphase flow theory and natural gas engineering.
9
Shi, H., and C. Kleinstreuer. "Simulation and Analysis of High-Speed Droplet Spray Dynamics." Journal of Fluids Engineering 129, no. 5 (2006): 621–33. http://dx.doi.org/10.1115/1.2717621.
Full textAbstract:
An experimentally validated computer simulation model has been developed for the analysis of gas-phase and droplet characteristics of isothermal sprays generated by pressure jet atomizers. Employing a coupled Euler-Lagrange approach for the gas-droplet flow, secondary droplet breakup (based on the ETAB model), was assumed to be dominant and the k-ε model was selected for simulating the gas flow. Specifically, transient spray formation in terms of turbulent gas flow as well as droplet velocities and size distributions are provided for different back pressures. Clearly, two-way coupling of the phases is important because of the impact of significant gas entrainment, droplet momentum transfer, and turbulent dispersion. Several spray phenomena are discussed in light of low back-pressure (1atm) and high back-pressure (30atm) environments. At low back-pressure, sprays have long thin geometric features and penetrate faster and deeper than at high back-pressures because of the measurable change in air density and hence drag force. Away from the nozzle exit under relatively high back pressures, there is no distinct droplet size difference between peripheral and core regions because of the high droplet Weber numbers, leading to very small droplets which move randomly. In contrast to transient spray developments, under steady-state conditions droplets are subject to smaller drag forces due to the fully-developed gas entrainment velocities which reduce gas-liquid slip. Turbulent dispersion influences droplet trajectories significantly because of the impact of random gas-phase fluctuations.
10
Jia, Hailing, Xiaoyan Ma, and Yangang Liu. "Exploring aerosol–cloud interaction using VOCALS-REx aircraft measurements." Atmospheric Chemistry and Physics 19, no. 12 (2019): 7955–71. http://dx.doi.org/10.5194/acp-19-7955-2019.
Full textAbstract:
Abstract. In situ aircraft measurements obtained during the VAMOS (Variability of the American Monsoons) Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) field campaign are analyzed to study the aerosol–cloud interactions in the stratocumulus clouds over the southeastern Pacific Ocean (SEP), with a focus on three understudied topics (separation of aerosol effects from dynamic effects, dispersion effects, and turbulent entrainment-mixing processes). Our analysis suggests that an increase in aerosol concentration tends to simultaneously increase both cloud droplet number concentration (Nd) and relative dispersion (ε), while an increase in vertical velocity (w) often increases Nd but decreases ε. After constraining the differences of cloud dynamics, the positive correlation between ε and Nd becomes stronger, implying that perturbations of w could weaken the aerosol influence on ε and hence result in an underestimation of dispersion effect. A comparative analysis of the difference of cloud microphysical properties between the entrainment and non-entrainment zones suggests that the entrainment-mixing mechanism is predominantly extremely inhomogeneous in the stratocumulus that capped by a sharp inversion, whereby the variation in liquid water content (25 %) is similar to that of Nd (29 %) and the droplet size remains approximately constant. In entrainment zone, drier air entrained from the top induces fewer cloud droplets with respect to total in-cloud particles (0.56±0.22) than the case in the non-entrainment zone (0.73±0.13) by promoting cloud droplet evaporation. This study is helpful in reducing uncertainties in dispersion effects and entrainment mixing for stratocumulus, and the results of this study may benefit cloud parameterizations in global climate models to more accurately assess aerosol indirect effects.
11
Urbansky, V. A., and A. A. Petruk. "Theoretical and experimental studies of the influence of gas flow parameters on the entrainment of liquid droplets from an experimental vessel." Omsk Scientific Bulletin. Series Aviation-Rocket and Power Engineering 8, no. 3 (2024): 98–106. http://dx.doi.org/10.25206/2588-0373-2024-8-3-98-106.
Full textAbstract:
On the basis of mathematical modeling, the values of velocities above the liquid surface in the experimental vessel are obtained to ensure the condition of droplet detachment and entrainment. The program of physical experiments on the entrainment of liquid droplets from experimental vessel is developed. Physical modeling of liquid droplets entrainment from experimental vessel is carried out, which showed that the separated mass of liquid significantly depends on the parameters of the gas flow at the inlet to experimental vessel (temperature, flow velocity). At the temperature of the inlet gas flow equal to 20 °C the percentage of separation ts 62 %, at 30 ºC — 69 %, at 35 ºC — 70 %, at 40 ºC — 78 %.
12
Camacho Hernandez, Jesus, Guido Link, Markus Schubert, and Uwe Hampel. "Experimental Study of a Compact Microwave Applicator for Evaporation of Airflow-Entrained Droplets." Materials 15, no. 19 (2022): 6765. http://dx.doi.org/10.3390/ma15196765.
Full textAbstract:
In many energy and process engineering systems where fluids are processed, droplet-laden gas flows may occur. As droplets are often detrimental to the system’s operation, they need to be removed. Compact engineering solutions for the removal of entrained droplets are difficult to achieve with conventional flow control and heat transfer approaches and thus droplet removal devices are hence often costly and bulky. In this study, we analyzed the potential of a compact technology based on droplet capture and in situ evaporation by microwave heating. For that, we designed a microwave applicator containing a porous droplet separator for capturing and evaporating droplets. The application of open-cell ceramic foams as filter medium reduced 99.9% of the volumetric flow of droplets, while additional microwave exposure increases reduction to 99.99%. In addition, microwave-heated foams prevent droplet re-entrainment and structure-borne liquid accumulation within foams, thus avoiding water clogging and flooding.
13
de Lozar, Alberto, and Juan Pedro Mellado. "Reduction of the Entrainment Velocity by Cloud Droplet Sedimentation in Stratocumulus." Journal of the Atmospheric Sciences 74, no. 3 (2017): 751–65. http://dx.doi.org/10.1175/jas-d-16-0196.1.
Full textAbstract:
Abstract The effect of sedimentation on stratocumulus entrainment is investigated using direct numerical simulations of a cloud-top mixing layer driven by radiative and evaporative cooling. The simulations focus on the meter and submeter scales that are expected to be relevant for entrainment, and the finest grid spacing is Δx = 26 cm. The entrainment velocity is investigated from the analysis of the integrated-buoyancy evolution equation, which is exactly derived from the flow evolution equations. The analysis shows that sedimentation interacts with entrainment through two different mechanisms. As previously reported, sedimentation prevents droplets from evaporating in the entrainment zone, which in turn reduces the entrainment velocity. Here it is shown that sedimentation also promotes a positive buoyancy flux that directly opposes entrainment. The strengths of both mechanisms are characterized by two different settling numbers, which allow for predicting which meteorological conditions favor the reduction of entrainment by sedimentation. These new insights allow for including sedimentation in a parameterization of the entrainment velocity. The reduction of the entrainment velocity by sedimentation predicted by the parameterization and observed in the simulations is 3 times larger than previously reported in large-eddy simulations, which implies that meter- and submeter-scale turbulence plays an important role in the interaction of entrainment with sedimentation. On the whole, analysis and simulations indicate that stratocumulus entrainment is more sensitive to the cloud droplet number density due to sedimentation than previously thought.
14
Eßl, Werner, Georg Reiss, Peter Raninger, et al. "Numerical Analysis of Convective Mass Transfer during Multi-Droplet Impingement on a Structured Surface in the Presence of an Adhered Liquid Film—An Application to Spray Etching of PCBs." Fluids 8, no. 6 (2023): 180. http://dx.doi.org/10.3390/fluids8060180.
Full textAbstract:
Multi-droplet impingement is a fundamental aspect inherent to all kinds of technical spray processes which typically aim at enhancing the convective exchange of reagents or heat at the impinged surface. In this paper, the impingement of multiple droplets onto a structured surface is investigated by a comprehensive CFD model, which resolves the dynamics of the individual droplets and the film on a micro-scale level based on the Volume of Fluid (VOF) method. The considered surface topology includes cavities and is typical for protective masks used in the spray etching of Printed Circuit Boards (PCBs). The agitation of the liquid film in terms of the convective mass transfer rates across virtual horizontal evaluation planes is studied and the influence of film height and droplet impaction velocity is elaborated. Passive tracer tracking is employed to investigate the release and re-entrainment of fluid at the surface cavities. Two modes of mass exchange between the cavities and the main flow upon droplet impingement are identified, which are central inflow accompanied by lateral outflow (1) and lateral inflow with outflow at the opposing side (2). A statistical analysis of the allocation of tracer particles shows that high impaction velocities and low film heights correlate with an enhanced decay of tracer particles within the cavities. The susceptibility to re-entrainment is also reduced by high impaction velocities, whereas increased film heights are found to promote re-entrainment.
15
Cooper, William A., Sonia G. Lasher-Trapp, and Alan M. Blyth. "The Influence of Entrainment and Mixing on the Initial Formation of Rain in a Warm Cumulus Cloud." Journal of the Atmospheric Sciences 70, no. 6 (2013): 1727–43. http://dx.doi.org/10.1175/jas-d-12-0128.1.
Full textAbstract:
Abstract The objective of this study is to address the problem of the production of rain in warm cumulus clouds that has been observed to occur within about 20 min. A hybrid model approach is used where a microphysical parcel model is run along trajectories produced by a 3D cloud model, with sufficiently high resolution to allow explicit representation of the effects of entrainment and mixing. The model calculations take the next step from the previous study, which showed that entrainment and mixing can accelerate the diffusional growth of cloud droplets to the production of raindrops by collision and coalescence. The mechanism depends on the variability in droplet trajectories arriving at a given location and time in a cumulus cloud. The resulting broadening favors collisions among droplets in the main peak of the droplet size distribution, which leads to the production of raindrop embryos. However, this production and the subsequent growth of the embryos to become raindrops only occur in regions of relatively high cloud water content. The modeling framework allows an objective test of this sequence of events that explain the seemingly contradictory notions of the enhancement of cloud droplet growth as a result of entrainment and mixing and the need for substantial cloud water content for collision and coalescence growth. The results show that raindrops can be produced within 20 min in warm cumulus clouds. The rain produced is sensitive to giant aerosols, but modification of the modeling framework is required to conduct a more robust test of their relative importance.
16
Snider, Jefferson R., David Leon, and Zhien Wang. "Droplet Concentration and Spectral Broadening in Southeast Pacific Stratocumulus Clouds." Journal of the Atmospheric Sciences 74, no. 3 (2017): 719–49. http://dx.doi.org/10.1175/jas-d-16-0043.1.
Full textAbstract:
Abstract Several airborne field experiments have been conducted to verify model descriptions of cloud droplet activation. Measurements of cloud condensation nuclei and updraft are inputs to a parcel model that predicts droplet concentration and droplet size distributions (spectra). Experiments conducted within cumulus clouds have yielded the most robust agreement between model and observation. Investigations of stratocumulus clouds are more varied, in part because of the difficulty of gauging the effects of entrainment and drizzle on droplet concentration and spectra. Airborne lidar is used here to supplement the approach used in prior studies of droplet activation in stratocumulus clouds. A model verification study was conducted using data acquired during the Southern Hemispheric VAMOS Ocean–Cloud–Aerosol–Land Study Regional Experiment. Consistency between observed and modeled droplet concentrations is achieved, but only after accounting for the effects of entrainment and drizzle on concentrations produced by droplet activation. In addition, predicted spectral dispersions are 74% of the measured dispersions following correction for instrument broadening. This result is consistent with the conjecture that differential activation (at cloud base) and internal mixing (i.e., mixing without entrainment) are important drivers of true spectral broadening.
17
Beals, Matthew J., Jacob P. Fugal, Raymond A. Shaw, Jiang Lu, Scott M. Spuler, and Jeffrey L. Stith. "Holographic measurements of inhomogeneous cloud mixing at the centimeter scale." Science 350, no. 6256 (2015): 87–90. http://dx.doi.org/10.1126/science.aab0751.
Full textAbstract:
Optical properties and precipitation efficiency of atmospheric clouds are largely determined by turbulent mixing with their environment. When cloud liquid water is reduced upon mixing, droplets may evaporate uniformly across the population or, in the other extreme, a subset of droplets may evaporate completely, leaving the remaining drops unaffected. Here, we use airborne holographic imaging to visualize the spatial structure and droplet size distribution at the smallest turbulent scales, thereby observing their response to entrainment and mixing with clear air. The measurements reveal that turbulent clouds are inhomogeneous, with sharp transitions between cloud and clear air properties persisting to dissipative scales (<1 centimeter). The local droplet size distribution fluctuates strongly in number density but with a nearly unchanging mean droplet diameter.
18
Liu, Chenglong, Wei Li, Feng Guo, Patrick Wong, and Xinming Li. "Effect of Oil Dispersion on Lubricating Film Thickness Generation under Oil Droplet Supply Conditions." Lubricants 11, no. 12 (2023): 512. http://dx.doi.org/10.3390/lubricants11120512.
Full textAbstract:
Oil–air lubrication has proven to be very effective for high-speed bearings because the oil supply in the form of droplets can be precisely controlled. This work uses optical interferometry to study the mechanism of lubricating film formation in rolling point contact with oil droplet lubrication. The effect of a double oil drop pair, where two oil droplets are positioned in mirror images about the central axis of the lubricated track, is examined. The process by which pairs of oil droplets approach and lubricate a bearing contact is analysed. This study also covers the effect of multiple oil droplets supplied in a tailored or a random dispersion pattern. Additionally, the effects of oil viscosity, entrainment velocity, and droplet distribution on starvation are also investigated.
19
Cherdantsev, Andrey V. "Experimental Investigation of Mechanisms of Droplet Entrainment in Annular Gas-Liquid Flows: A Review." Water 14, no. 23 (2022): 3892. http://dx.doi.org/10.3390/w14233892.
Full textAbstract:
Entrainment of liquid from the film surface by high-velocity gas stream strongly affects mass, momentum and heat transfer in annular flow. The construction of basic assumptions for simplified physical models of the flow, as well as validation of numerical models, requires detailed experimental investigation of droplet entrainment process and the preceding stages of film surface evolution. The present paper analyzes the achievements and perspectives of application of various experimental approaches to qualitative and quantitative characterization of droplet entrainment. Optical visualization in at least two planes simultaneously may provide enough information on transitional liquid structures and detaching droplets, given that the side-view image is not obscured by the wall film. A planar LIF technique is not suitable for this purpose, since real objects are hidden by curved agitated interface and replaced by optical artifacts. To characterize the waves evolving into the transitional liquid structures, film thickness measurements in the plane of the wall are necessary. Such measurements can be achieved by intensity-based optical techniques, such as Brightness-Based LIF, near-infrared or X-ray attenuation techniques, combined with the side-view observations.
20
Kumar, Bipin, Rahul Ranjan, Man-Kong Yau, Sudarsan Bera, and Suryachandra A. Rao. "Impact of high- and low-vorticity turbulence on cloud–environment mixing and cloud microphysics processes." Atmospheric Chemistry and Physics 21, no. 16 (2021): 12317–29. http://dx.doi.org/10.5194/acp-21-12317-2021.
Full textAbstract:
Abstract. Turbulent mixing of dry air affects the evolution of the cloud droplet size spectrum via various mechanisms. In a turbulent cloud, high- and low-vorticity regions coexist, and inertial clustering of cloud droplets can occur in low-vorticity regions. The nonuniformity in the spatial distribution of the size and in the number of droplets, variable vertical velocity in vortical turbulent structures, and dilution by entrainment/mixing may result in spatial supersaturation variability, which affects the evolution of the cloud droplet size spectrum via condensation and evaporation processes. To untangle the processes involved in mixing phenomena, a 3D direct numerical simulation of turbulent mixing followed by droplet evaporation/condensation in a submeter-sized cubed domain consisting of a large number of droplets was performed in this study. The analysis focused on the thermodynamic and microphysical characteristics of the droplets and the flow in high- and low-vorticity regions. The impact of vorticity generation in turbulent flows on mixing and cloud microphysics is illustrated.
21
Uchida, J., C. S. Bretherton, and P. N. Blossey. "The sensitivity of stratocumulus-capped mixed layers to cloud droplet concentration: do LES and mixed-layer models agree?" Atmospheric Chemistry and Physics Discussions 9, no. 6 (2009): 25853–83. http://dx.doi.org/10.5194/acpd-9-25853-2009.
Full textAbstract:
Abstract. The sensitivity of a stratocumulus-capped mixed layer to a change in cloud droplet concentration is evaluated with a large-eddy simulation (LES) and a mixed layer model (MLM), to see if the two model types agree on the strength of the second aerosol indirect effect. Good agreement can be obtained if the MLM entrainment closure explicitly reduces entrainment efficiency proportional to the rate of cloud droplet sedimentation at cloud top for cases in which the LES-simulated boundary layer remains well mixed, with a single peak in the vertical profile of vertical velocity variance. To achieve this agreement, the MLM entrainment closure and the drizzle parameterization must be modified from their observationally-based defaults. This is because the LES advection scheme and microphysical parameterization significantly bias the entrainment rate and precipitation profile compared to observational best guesses. Before this modification, the MLM simulates more liquid water path and much more drizzle at a given droplet concentration than the LES and is more sensitive to droplet concentration, even undergoing a drizzle-induced boundary layer collapse at low droplet concentrations. After this modification, both models predict a similar decrease of cloud liquid water path as droplet concentration increases, cancelling 30–50% of the Twomey effect for our case. The agreement breaks down at the lowest simulated droplet concentrations, for which the boundary layer in the LES is not well mixed. Our results highlight issues with both types of model. Potential LES biases due to inadequate resolution, subgrid mixing and microphysics must be carefully considered when trying to make a quantitative inference of the second indirect effect from an LES of a stratocumulus-topped boundary layer. On the other hand, even slight internal decoupling of the boundary layer invalidates MLM-predicted sensitivity to droplet concentrations.
22
Ebner, J., M. Gerenda´s, O. Scha¨fer, and S. Wittig. "Droplet Entrainment From a Shear-Driven Liquid Wall Film in Inclined Ducts: Experimental Study and Correlation Comparison." Journal of Engineering for Gas Turbines and Power 124, no. 4 (2002): 874–80. http://dx.doi.org/10.1115/1.1476926.
Full textAbstract:
The primary objective of the present study is to clarify the droplet disintegration mechanism and the film properties of liquid oil films driven by shear stress, which is induced by a co-current gas flow. This work focuses on the flow behavior within the starting length of the complex two-phase flow and the effect of inclination on the entrainment rate. Many investigations have been performed in the past to determine the droplet entrainment in the gas core for fully developed flow conditions with respect to their relevance in pipes of power plants and various chemical engineering systems. In more recent work the effect of inclination has been studied in detail. Nevertheless, a lack of knowledge can be realized for droplet entrainment within the starting length of this complex flow type. Thus, fundamental experiments have been carried out to provide a data base for droplet entrainment of liquid disintegrated from an oil film within its starting length at several inclination angles of the flow. The experimental results have been compared with correlations from literature. Additionally, the wall film thickness has been measured to allow a fully coupled modeling of entrainment and liquid film properties depending on global flow parameters. Based on film Reynolds number, Weber number, a dimensionless film flow length, and a modified Froude number, taking into account the angle of inclination, correlations have been developed, where those from literature are not applicable.
23
Burnet, Frédéric, and Jean-Louis Brenguier. "Observational Study of the Entrainment-Mixing Process in Warm Convective Clouds." Journal of the Atmospheric Sciences 64, no. 6 (2007): 1995–2011. http://dx.doi.org/10.1175/jas3928.1.
Full textAbstract:
Thermodynamical and microphysical measurements collected in convective clouds are examined within the frame of the homogeneous/inhomogeneous mixing concept, to determine how entrainment-mixing processes affect cloud droplets, their number concentration, and their mean size. The three selected case studies—one stratocumulus layer and two cumulus clouds—exhibit very different values of the cloud updraft intensity, of the adiabatic droplet mean volume diameter, and of the saturation deficit in the environment, all three parameters that are expected to govern the microphysical response to entrainmentmixing. The results confirm that the observed microphysical features are sensitive to the droplet response time to evaporation and to the turbulent homogenization time scale, as suggested by the inhomogeneous mixing concept. They also reveal that an instrumental artifact due to the heterogeneous spatial droplet distribution may be partly responsible for the observed heterogeneous mixing features. The challenge remains, however, to understand why spatially homogeneous cloud volumes larger than the instrument resolution scale (10 m) are so rarely observed. The analysis of the buoyancy of the cloud and clear air mixtures suggests that dynamical sorting could also be efficient for the selection, among all possible mixing scenarios, of those that minimize the local buoyancy production.
24
Hohne, Thomas. "ICONE23-1413 A DROPLET ENTRAINMENT MODEL FOR HORIZONTAL GAS/LIQUID FLOWS." Proceedings of the International Conference on Nuclear Engineering (ICONE) 2015.23 (2015): _ICONE23–1—_ICONE23–1. http://dx.doi.org/10.1299/jsmeicone.2015.23._icone23-1_192.
Full text
25
Roy, Puja, Robert M. Rauber, and Larry Di Girolamo. "Evolution of cloud droplet temperature and lifetime in spatiotemporally varying subsaturated environments with implications for ice nucleation at cloud edges." Atmospheric Chemistry and Physics 24, no. 20 (2024): 11653–78. http://dx.doi.org/10.5194/acp-24-11653-2024.
Full textAbstract:
Abstract. Ice formation mechanisms in generating cells near stratiform cloud tops, where mixing and entrainment occurs in the presence of supercooled water droplets, remain poorly understood. Supercooled cloud droplet temperature and lifetime may impact heterogeneous ice nucleation through contact and immersion freezing; however, modeling studies normally assume the droplet temperature to be spatially uniform and equal to the ambient temperature. Here, we present a first-of-its-kind quantitative investigation of the temperature and lifetime of evaporating droplets, considering internal thermal gradients within the droplet, as well as thermal and vapor density gradients in the surrounding air. Our approach employs solving Navier–Stokes and continuity equations, coupled with heat and vapor transport, using an advanced numerical model. For typical ranges of cloud droplet sizes and environmental conditions, the droplet internal thermal gradients dissipate quickly (≤ 0.3 s) when droplets are introduced to new subsaturated environments. However, the magnitude of droplet cooling is much greater than estimated from past studies of droplet evaporation, especially for drier environments. For example, for an environment with 500 hPa pressure, and ambient temperature far from the droplet of −5 °C, the droplet temperature reduction can be as high as 24, 11, and 5 °C for initial ambient relative humidities of 10 %, 40 %, and 70 %, respectively. Droplet lifetimes are found to be tens of seconds longer compared to previous estimates, due to weaker evaporation rates because of lower droplet surface temperatures. Using these new end-of-lifetime droplet temperatures, the enhancement in the activation of ice-nucleating particles predicted by current ice nucleation parameterization schemes is discussed.
26
GERASHCHENKO, S., G. GOOD, and Z. WARHAFT. "Entrainment and mixing of water droplets across a shearless turbulent interface with and without gravitational effects." Journal of Fluid Mechanics 668 (January 26, 2011): 293–303. http://dx.doi.org/10.1017/s002211201000577x.
Full textAbstract:
We describe experiments of the entrainment and mixing of water (sub-Kolmogorov scale) droplets across a turbulent–non-turbulent interface (TNI) as well a turbulent–turbulent interface (TTI) in shearless grid turbulence, over a time scale in which evaporation is insignificant. The flow is produced by means of a splitter plate with an active grid and water sprays on one side and screens or an active grid on the other side. The Taylor microscale Reλ on the turbulent side is 275 and the average dissipation scale Stokes number, Stη ≈ 0.2, and based on the integral scale, Stl ≈ 0.003. By changing the orientation of the grid system, gravitational effects may be excluded or included. We show that in the absence of gravity, for the Stokes number range studied (0.06 ≤ Stη ≤ 1.33), the droplet distribution does not change across the interface. With gravity, the larger drops are selectively mixed and this is more pronounced for the TNI than for the TTI. The particle concentration distribution is an error function for the TTI but departs significantly for the TNI due to the intermittency in the flow. In terms of particle concentration, the entrainment is most efficient for the TTI with gravity. The results are related to droplet entrainment in clouds.
27
Cooper, W. A., S. G. Lasher-Trapp, and A. M. Blyth. "Initiation of coalescence in a cumulus cloud: a beneficial influence of entrainment and mixing." Atmospheric Chemistry and Physics Discussions 11, no. 4 (2011): 10557–613. http://dx.doi.org/10.5194/acpd-11-10557-2011.
Full textAbstract:
Abstract. Although rain has been observed to form in warm cumulus clouds within about twenty minutes, calculations that represent condensation and coalescence accurately in such clouds have had difficulty producing rainfall in such a short time except via processes involving giant cloud condensation nuclei (with diameters larger than 2 μm). This model-based study explores a different possible mechanism for accelerating the production of warm rain, one that depends on the variability in droplet trajectories arriving at a given location and time in a cumulus cloud. In the presence of entrainment such droplets experience different growth histories, and the result is broadening of the droplet size distribution. That broadening favours coalescence, leading to embryos that grow to raindrops. These calculations do lead to production of rain that is within the lower range of observations for clouds of Florida, USA, the location on which the input conditions were based. The process emphasized in this study, the formation of drizzle via collisions among droplets in the main peak of the droplet size distribution, complements the growth of precipitation on giant nuclei, which is also an important source of the first rain in the case studied. The results indicate that the mechanism developed here should be considered an important influence on the formation of rain in warm clouds.
28
Schmid, S. R. "Hydrodynamic Segregation, Entrainment and Rejection of Oil in Emulsion Lubrication Problems." Journal of Tribology 119, no. 2 (1997): 342–48. http://dx.doi.org/10.1115/1.2833225.
Full textAbstract:
Emulsions are widely used as metal rolling and ironing lubricants, but their application is still an art in that no widely accepted and robust models of emulsion lubrication exist. Of particular confusion to date is the mechanism through which oil particles penetrate an inlet zone and serve as a lubricant. This paper addresses hydrodynamic behavior of emulsions and addresses topics such as droplet segregation in the inlet zone and the forces acting upon individual droplets in a worst case analysis of entrainment. In segregation, a phenomenon first noted in Poiseuille tube flows, neutrally buoyant particles will cross flow streamlines to an equilibrium position a finite distance from the edge of the flow. This paper includes an analysis of segregation using the empirical results obtained elsewhere, and describes the relevance of segregation to metal forming inlet zones. If a droplet does penetrate the inlet zone to a point near the edge of contact, and it has not adhered to a roll or strip surface, hydrodynamic forces will determine whether or not the particle will become entrained. This paper analyzes the forces involved using a foil bearing analogy. The situations under which a droplet is entrained or rejected are described, and the important parameters to achieve entrainment are discussed.
29
Derksen, J. W. B., G. J. H. Roelofs, and T. Röckmann. "Influence of entrainment of CCN on microphysical properties of warm cumulus." Atmospheric Chemistry and Physics Discussions 9, no. 2 (2009): 8791–816. http://dx.doi.org/10.5194/acpd-9-8791-2009.
Full textAbstract:
Abstract. We use a 1-D cloud model with explicit microphysics and a binned representation of the aerosol size distribution to investigate the influence of entrainment of cloud condensation nuclei (CCN) on the microphysical development of warm cumulus clouds. For a more realistic representation of cloud drop spectral width, the model separates droplets that grow on aerosol that is initially present in the cloud from droplets growing on entrained aerosol. Model results are compared with observations of trade wind cumulus microphysics from the Rain in Cumulus over the Ocean experiment (RICO, 2004–2005). The results indicate that CCN are entrained throughout the entire cloud depth, and inside the cloud part of these may be activated. Compared to a simulation where entrainment of ambient CCN is neglected this leads to higher cloud droplet number concentrations (CDNC) and a continuous presence of droplets in the range smaller than ~5 μm that is consistent with the observations. Cloud dynamics are sensitive to the entrainment parameter as well as to the applied initial vertical velocity, as expressed by the liquid water content and cloud top height. However, simulated cloud drop spectra remain relatively unaffected for the specific conditions during RICO.
30
Derksen, J. W. B., G. J. H. Roelofs, and T. Röckmann. "Influence of entrainment of CCN on microphysical properties of warm cumulus." Atmospheric Chemistry and Physics 9, no. 16 (2009): 6005–15. http://dx.doi.org/10.5194/acp-9-6005-2009.
Full textAbstract:
Abstract. We use a 1-D cloud model with explicit microphysics and a binned representation of the aerosol size distribution to investigate the influence of entrainment of cloud condensation nuclei (CCN) on the microphysical development of warm cumulus clouds. For a more realistic representation of cloud drop spectral width, the model separates droplets that grow on aerosol that is initially present in the cloud from droplets growing on entrained aerosol. Model results are compared with observations of trade wind cumulus microphysics from the Rain in Cumulus over the Ocean experiment (RICO, 2004–2005). The results indicate that CCN are entrained throughout the entire cloud depth, and inside the cloud part of these may be activated. Compared to a simulation where entrainment of ambient CCN is neglected this leads to higher cloud droplet number concentrations (CDNC) and a continuous presence of droplets in the range smaller than ~5 μm that is consistent with the observations. Cloud dynamics are sensitive to the entrainment parameter as well as to the applied initial vertical velocity, as expressed by the liquid water content and cloud top height. However, simulated cloud drop spectra remain relatively unaffected for the specific conditions during RICO.
31
Liu, Yan Jun, Xiao Rong Liu, Hui Li, Yong Sheng Li, Qing Li, and Yan Liu. "Effects of Copper Extraction-Stripping Loops on Entrainment in Aqueous Raffinate." Advanced Materials Research 908 (March 2014): 18–21. http://dx.doi.org/10.4028/www.scientific.net/amr.908.18.
Full textAbstract:
Effects of extraction-stripping loops of organic phase on organic chemical entrainment in the aqueous raffinate in copper solvent extraction were studied in this paper. Results demonstrated that the total amount of organic chemicals lost in the aqueous raffinate decreased with the increase of times of extraction-stripping loops but reached largest at third loop. Entrainment was the dominate way of organic chemicals losing in the aqueous raffinate at early stage of the loops. The formation of entrainment and its stabilization mechanism was also studied. The average size of entrained droplet trended to increase with extraction-stripping loops increasing. Meanwhile, the absolute value of zeta potential trended to decrease. The surface tension of the aqueous raffinate increased after reaching the minimum value 41.3 mN/m at the 3rd loop. It showed that the formation of entrained droplets and its stability were mainly affected by the surface tension of aqueous raffinate.
32
Gao, Sinan, Chunsong Lu, Yangang Liu, et al. "Comprehensive quantification of height dependence of entrainment mixing between stratiform cloud top and environment." Atmospheric Chemistry and Physics 21, no. 14 (2021): 11225–41. http://dx.doi.org/10.5194/acp-21-11225-2021.
Full textAbstract:
Abstract. Different entrainment-mixing processes of turbulence are crucial to processes related to clouds; however, only a few qualitative studies have been concentrated on the vertical distributions of entrainment-mixing mechanisms with low vertical resolutions. To quantitatively study vertical profiles of entrainment-mixing mechanisms with a high resolution, the stratiform clouds observed in the Physics of Stratocumulus Top (POST) project are examined. The unique sawtooth flight pattern allows for an examination of the vertical distributions of entrainment-mixing mechanisms with a 5 m vertical resolution. Relative standard deviation of volume mean radius divided by relative standard deviation of liquid water content is introduced to be a new estimation of microphysical homogeneous mixing degree, to overcome difficulties of determining the adiabatic microphysical properties required in existing measures. The vertical profile of this new measure indicates that entrainment-mixing mechanisms become more homogeneous with decreasing altitudes and are consistent with the dynamical measures of Damköhler number and transition scale number. Further analysis shows that the vertical variation of entrainment-mixing mechanisms with decreasing altitudes is due to the increases of turbulent dissipation rate in cloud and relative humidity in droplet-free air and the decrease of size of droplet-free air. The results offer insights into the theoretical understanding and parameterizations of vertical variation of entrainment-mixing mechanisms.
33
Uchida, J., C. S. Bretherton, and P. N. Blossey. "The sensitivity of stratocumulus-capped mixed layers to cloud droplet concentration: do LES and mixed-layer models agree?" Atmospheric Chemistry and Physics 10, no. 9 (2010): 4097–109. http://dx.doi.org/10.5194/acp-10-4097-2010.
Full textAbstract:
Abstract. The sensitivity of a stratocumulus-capped mixed layer to a change in cloud droplet concentration is evaluated with a large-eddy simulation (LES) and a mixed layer model (MLM). The strength of the second aerosol indirect effect simulated by the two model types agrees within 50% for cases in which the LES-simulated boundary layer remains well mixed, if the MLM entrainment closure includes the effects of cloud droplet sedimentation. To achieve this agreement, parameters in the MLM entrainment closure and the drizzle parameterization must be retuned to match the LES. This is because the LES advection scheme and microphysical parameterization significantly bias the entrainment rate and precipitation profile compared to observational best guesses. Before this modification, the MLM simulates more liquid water path and much more drizzle at a given droplet concentration than the LES and is more sensitive to droplet concentration, even undergoing a drizzle-induced boundary layer collapse at low droplet concentrations. After this modification, both models predict a comparable decrease of cloud liquid water path as droplet concentration increases, cancelling 30–50% of the Twomey effect for our case. The agreement breaks down at the lowest simulated droplet concentrations, for which the boundary layer in the LES is not well mixed. Our results highlight issues with both types of model. Potential LES biases due to inadequate resolution, subgrid mixing and parameterized microphysics must be carefully considered when trying to make a quantitative inference of the second indirect effect from an LES of a stratocumulus-topped boundary layer. On the other hand, even slight internal decoupling of the boundary layer invalidates the central assumption of an MLM, substantially limiting the range of conditions that MLM-predicted sensitivities to droplet concentration are meaningful.
34
Berna, C., A. Escrivá, J. L. Muñoz-Cobo, and L. E. Herranz. "Review of droplet entrainment in annular flow: Characterization of the entrained droplets." Progress in Nuclear Energy 79 (March 2015): 64–86. http://dx.doi.org/10.1016/j.pnucene.2014.11.011.
Full text
35
Good, G. H., S. Gerashchenko, and Z. Warhaft. "Intermittency and inertial particle entrainment at a turbulent interface: the effect of the large-scale eddies." Journal of Fluid Mechanics 694 (February 3, 2012): 371–98. http://dx.doi.org/10.1017/jfm.2011.552.
Full textAbstract:
AbstractWe present measurements of mean and conditional number densities, radial distribution functions (r.d.f.s), velocities and accelerations of sub-Kolmogorov-scale water droplets entraining at a shearless turbulence–turbulence interface (TTI) and a turbulence–non-turbulence interface (TNI). We thus look at statistics of an inhomogeneous inertial particle field in both homogeneous and inhomogeneous turbulence. As in a previous communication (Gerashchenko, Good & Warhaft J. Fluid Mech., vol. 818, 2011, pp. 293–303), an active grid produces high-Reynolds number turbulence $({\mathit{Re}}_{\lambda } = 275)$ on either one or both sides of a splitter plate in a wind tunnel. Sprays seed droplets on one side of the splitter plate, while screens dampen turbulence in the adjacent flow for the TNI. Gravitational and inertial effects are isolated by turning of the apparatus with respect to gravity. We parameterize the droplets under homogeneous conditions, where it is demonstrated that both the sweeping and loitering effects on the droplet settling velocities are present. In the inhomogeneous conditions, we show that the droplets are entrained in bulk, resulting in large-scale clusters and preserving the droplet-ambient conditions of the seeded side of the flows.
36
Trabold, T. A., R. Kumar, and P. F. Vassallo. "Experimental Study of Dispersed Droplets in High-Pressure Annular Flows." Journal of Heat Transfer 121, no. 4 (1999): 924–33. http://dx.doi.org/10.1115/1.2826083.
Full textAbstract:
Local measurements were made in a droplet-laden vapor core in upward R-134a annular flow in a high aspect ratio vertical duct. These detailed measurements are unique in that they were performed at high pressures and low liquid-to-vapor density ratios. Using a gamma densitometer, hot-film anemometer and laser Doppler velocimeter, profiles of void fraction, liquid droplet frequency, and droplet velocity were acquired across the narrow test section dimension. At relatively high flows, the measured void fraction was highest near the wall, due to the thinning of the liquid film. The dip in the void fraction in the vapor core at these flows suggests significant droplet entrainment. The entrainment fractions for these refrigerant flows fall in the range measured for pressurized steam-water systems. The average drop size, calculated from direct measurements of void fraction, droplet velocity, and frequency, compares favorably with previous experimental results from the literature. These data are useful for developing an improved understanding of practical two-phase flows, and for assessment of advanced two-fluid computer codes.
37
Dunnewind, B., M. A. Bos, and W. Koops. "Entrainment of Oil from Oil Spills into the Water Column: A New Theory." International Oil Spill Conference Proceedings 2003, no. 1 (2003): 1059–66. http://dx.doi.org/10.7901/2169-3358-2003-1-1059.
Full textAbstract:
ABSTRACT Dispersion of oil into the water column is one of the oil spill response options. Under certain circumstances natural dispersion may be efficient enough. In other situations dispersant may be added to improve the dispersion efficiency. An empirical model for natural dispersion, based on laboratory results of Delvigne and Sweeney (1988), has been used for many years now, to estimate the entrainment of oil in the water column. That model, however, does not include surface rheological properties and, hence, is not sufficient to describe both natural and chemical dispersion. In the present paper we propose a new approach based on theory on emulsification processes as occurring in homogenizers. This approach includes all relevant physical characteristics of water and oil and their interface and of the turbulence of breaking waves. The deformation of oil droplets in the turbulent flow, the adsorption of surface active material to the surface of oil droplets, the encounter between oil droplets and the eddies of the turbulent flow were each described in a characteristic time. This characteristic time gives an indication of the time needed for the process to proceed. The ratios between the characteristic times of the different processes determine to what extent droplets can be broken-up. Maximum and minimum droplet sizes were estimated, from which a droplet size distribution was calculated. From the size distribution the percentage of the oil that would be present in droplets smaller than 100 μm, was estimated. The results show similarities with observations from practice. A large influence of the wave height, interfacial tension and oil viscosity was noticed. Therefore, this new approach may form the basis for a new oil spill dispersion model.
38
Sun, Bao Nan, Zhan Lian, and Yong Zeng Yang. "On Theoretical Models for Oil Droplets Size Distribution under the Influence of Surface Wave Breaking." Advanced Materials Research 998-999 (July 2014): 511–17. http://dx.doi.org/10.4028/www.scientific.net/amr.998-999.511.
Full textAbstract:
Marine oil spill often forms oil droplets in stormy conditions. Based on the dimensional analysis Rayleigh method, the relationship is established between entrainment rate of oil droplets and statistical physical quantities such as the energy dissipation rate, intrusion depth et al. An expression of size spectrum of oil droplets is derived based on theorem and relationship between the capillary number, the dimensionless intrusion time and viscosity ratio. Preliminary results show that the slope of the derived spectrum is-2.29, which agrees well with the measured slope-2.3 in laboratory. Shear rate, surface tension, droplet radius, oil and water viscosity is the main factors controlling the total number of the oil droplets.
39
Wang, H. Y., V. G. McDonell, W. A. Sowa, and G. S. Samuelsen. "Scaling of the Two-Phase Flow Downstream of a Gas Turbine Combustor Swirl Cup: Part I—Mean Quantities." Journal of Engineering for Gas Turbines and Power 115, no. 3 (1993): 453–60. http://dx.doi.org/10.1115/1.2906730.
Full textAbstract:
A production gas turbine combustor swirl cup and a 3×-scale model (both featuring co-axial, counterswirling air streams) are characterized at atmospheric pressure. Such a study provides an opportunity to assess the effect of scale on the behavior of the continuous phase (gas in the presence of spray) and droplets by comparing the continuous phase velocity, droplet size, and droplet velocity at geometrically analogous positions. Spatially resolved velocity measurements of the continuous phase, droplet size, and droplet velocity were acquired downstream of the production and 3×-scale swirl cups by using two-component phase-Doppler interferometry in the absence of reaction. While the continuous phase flow fields scale well at the exit of the swirl cup, the similarity deviates at downstream locations due to (1) differences in entrainment, and (2) a flow asymmetry in the case of the production hardware. The droplet velocities scale reasonably well with notable exceptions. More significant differences are noted in droplet size, although the presence of the swirl cup assemblies substantially reduces the differences in size that are otherwise produced by the two atomizers when operated independent of the swirl cup.
40
Dolna, Oktawia, Jarosław Mikielewicz, and Paulina Rolka. "Analytical studies on deposition and entrainment present in the Venturi nozzle two-phase flow." International Journal of Energy and Environmental Engineering 12, no. 3 (2021): 487–502. http://dx.doi.org/10.1007/s40095-021-00385-1.
Full textAbstract:
AbstractThe syngas purification is a basic problem in the gas production process through the biomass gasification. This issue is important due to the use of the Venturi scrubbers in the syngas cleaning process. As it is commonly known, syngas is an alternative for the coal and using syngas instead of the coal leads to ‘clean energy’ generation. The paper concerns the analytical research studies on two-phase fluid flow pattern in Venturi’s throat. The uniform coverage of Venturi’s cross-section with small droplets plays a significant role in the dust particles collection and chemicals removal as Venturi’s cleaning efficiency mostly depends on this operation parameter. Therefore, the analysis of the two-phase fluid flow with respect to a droplet deposition and entrainment was carried out. Based on these research studies, it is possible to determine the variation of the liquid superficial velocity in the core of the flow and within the liquid wall film, the length at which the droplet entrainment starts to occur, the liquid fraction variation with Venturi’s throat length and diameter. The obtained analytical model, which is introduced in the paper, was validated with the use of the experimental data available in the literature.
41
Jarecka, Dorota, Wojciech W. Grabowski, Hugh Morrison, and Hanna Pawlowska. "Homogeneity of the Subgrid-Scale Turbulent Mixing in Large-Eddy Simulation of Shallow Convection." Journal of the Atmospheric Sciences 70, no. 9 (2013): 2751–67. http://dx.doi.org/10.1175/jas-d-13-042.1.
Full textAbstract:
Abstract This paper presents an approach to locally predict homogeneity of the subgrid-scale turbulent mixing in large-eddy simulation of shallow clouds applying double-moment warm-rain microphysics. The homogeneity of subgrid-scale mixing refers to the partitioning of the cloud water evaporation due to parameterized entrainment between changes of the mean droplet radius and changes of the mean droplet concentration. Homogeneous and extremely inhomogeneous mixing represent two limits of possible scenarios, where the droplet concentration and the mean droplet radius remains unchanged during the microphysical adjustment, respectively. To predict the subgrid-scale mixing scenario, the double-moment microphysics scheme is merged with the approach to delay droplet evaporation resulting from entrainment. Details of the new scheme and its application in the Barbados Oceanographic and Meteorological Experiment (BOMEX) shallow convection case are discussed. The simulated homogeneity of mixing varies significantly inside small convective clouds, from close to homogeneous to close to extremely inhomogeneous. The mean mixing characteristics become more homogeneous with height, reflecting increases of the mean droplet size and the mean turbulence intensity, both favoring homogeneous mixing. Model results are consistent with microphysical effects of entrainment and mixing deduced from field observations. Mixing close to homogeneous is predicted in volumes with the highest liquid water content (LWC) and strongest updraft at a given height, whereas mixing in strongly diluted volumes is typically close to extremely inhomogeneous. The simulated homogeneity of mixing has a small impact on mean microphysical characteristics. This result agrees with the previous study applying prescribed mixing scenarios and can be explained by the high humidity of the clear air involved in the subgrid-scale mixing.
42
Freud, E., D. Rosenfeld, D. Axisa, and J. R. Kulkarni. "Resolving both entrainment-mixing and number of activated CCN in deep convective clouds." Atmospheric Chemistry and Physics Discussions 11, no. 3 (2011): 9673–703. http://dx.doi.org/10.5194/acpd-11-9673-2011.
Full textAbstract:
Abstract. The number concentration of activated CCN (Na) is the most fundamental microphysical property of a convective cloud. It determines the rate of droplet growth with cloud depth and conversion into precipitation-sized particles and affects the radiative properties of the clouds. However, measuring Na is not always possible, even in the cores of the convective clouds, because entrainment of sub-saturated ambient air deeper into the cloud lowers the concentrations by dilution and may cause partial or total droplet evaporation, depending on whether the mixing is homogeneous or extreme inhomogeneous, respectively. Here we describe a methodology to derive Na based on the rate of cloud droplet effective radius (Re) growth with cloud depth and with respect to the cloud mixing with the entrained ambient air. We use the slope of the tight linear relationship between the adiabatic water and Re3 to derive an upper limit for Na assuming extreme inhomogeneous mixing. Then we tune Na down to find the theoretical relative humidity that the entrained ambient air would have for each horizontal cloud penetration, in case of homogeneous mixing. This allows us to evaluate both the entrainment and mixing process in the vertical dimension in addition to getting a better estimation for Na. We found that the derived Na from the entire profile data is highly correlated with the independent CCN measurements from below cloud base. Moreover, it was found that mixing of sub-saturated ambient air into the cloud is inclined towards the extreme inhomogeneous limit, i.e. that the time scale of droplet evaporation is significantly smaller than that for turbulent mixing. This means that ambient air that entrains the cloud is pre-moistened by total evaporation of cloud droplets before it mixes deeper into the clouds where it can hardly change the droplet size distribution, hence Re remains close to its adiabatic value at any given cloud depth. However, the tendency towards the extreme inhomogeneous mixing appeared to slightly decrease with altitude, possibly due to enhanced turbulence and larger cloud drops aloft. Quantifying these effects, based on more examples from other projects and high resolution cloud models is essential for improving our understanding of the interactions between the cloud and its environment. These interactions may play an important role in cloud dynamics and microphysics, by affecting cloud depth and droplet size spectra, for example, and may therefore influence the cloud precipitation formation processes.
43
Hasson, D. A., and W. L. Flint. "An Investigation of the Liquid Petrol Wall Film in the Manifold of a Carburetted Spark Ignition Engine: Effect of Carburettor and Manifold Geometry on Wall Film Quantities, Engine Performance and Emissions." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 203, no. 2 (1989): 77–89. http://dx.doi.org/10.1243/pime_proc_1989_203_153_02.
Full textAbstract:
The rate of deposition on the manifold wall of liquid droplets from the multi-component, two-phase stream of fluid flowing in the inlet manifold of a carburetted petrol engine and the re-entrainment of droplets into the stream from the liquid film which flows on the walls have been investigated using a single cylinder crossflow engine. The effect of throttle opening, straight manifold length, a smooth bend and a mitre bend is reported: measurements of exhaust emissions and cycle-to-cycle pressure variation of cylinder pressure are related to wall film quantities. It was found that throttle position was important in determining the initial wall film, that the average thickness of the film decreases with length along the straight manifold and that droplet re-entrainment from a sharp bend is greater than from a smooth bend. Removal of the wall film yields a significant reduction in the emission of unburned hydrocarbons and virtually eliminates cycle-to-cycle variations of pressure in the engine cylinder.
44
Bhowmick, Taraprasad, and Michele Iovieno. "Direct Numerical Simulation of a Warm Cloud Top Model Interface: Impact of the Transient Mixing on Different Droplet Population." Fluids 4, no. 3 (2019): 144. http://dx.doi.org/10.3390/fluids4030144.
Full textAbstract:
Turbulent mixing through atmospheric cloud and clear air interface plays an important role in the life of a cloud. Entrainment and detrainment of clear air and cloudy volume result in mixing across the interface, which broadens the cloud droplet spectrum. In this study, we simulate the transient evolution of a turbulent cloud top interface with three initial mono-disperse cloud droplet population, using a pseudo-spectral Direct Numerical Simulation (DNS) along with Lagrangian droplet equations, including collision and coalescence. Transient evolution of in-cloud turbulent kinetic energy (TKE), density of water vapour and temperature is carried out as an initial value problem exhibiting transient decay. Mixing in between the clear air and cloudy volume produced turbulent fluctuations in the density of water vapour and temperature, resulting in supersaturation fluctuations. Small scale turbulence, local supersaturation conditions and gravitational forces have different weights on the droplet population depending on their sizes. Larger droplet populations, with initial 25 and 18 μ m radii, show significant growth by droplet-droplet collision and a higher rate of gravitational sedimentation. However, the smaller droplets, with an initial 6 μ m radius, did not show any collision but a large size distribution broadening due to differential condensation/evaporation induced by the mixing, without being influenced by gravity significantly.
45
Berna, C., A. Escrivá, J. L. Muñoz-Cobo, and L. E. Herranz. "Review of droplet entrainment in annular flow: Interfacial waves and onset of entrainment." Progress in Nuclear Energy 74 (July 2014): 14–43. http://dx.doi.org/10.1016/j.pnucene.2014.01.018.
Full text
46
Bai, Xing-Zhi, Zhe Zhang, Wen-Hua Wu, et al. "Fluid Dynamics of Interacting Rotor Wake with a Water Surface." Drones 8, no. 9 (2024): 469. http://dx.doi.org/10.3390/drones8090469.
Full textAbstract:
Rotor-type cross-media vehicles always induce considerably complex mixed air–water flows when approaching the water surface, resulting in relative thrust loss and structural damage on rotor. The interactions between a water surface and rotor wake bring potential risks to the cross-media process, which is known as the near-water effect of the rotor. In this paper, experimental investigations are used to explore the fluid dynamics of the near-water effect of the rotor. Qualitative droplet observation was carried out on the 0.25 m and 0.56 m diameter commercial rotor blades and the 0.07 m diameter ducted fan near the water surface first to gain a qualitative understanding of droplet characteristics. The results show that the rotor wake caused water surface deformation, droplet tearing off, splashing, and entrainment into the rotor disk. The depression formed by the rotor downwash flow impacting the water surface is named as three modes: dimpling, splashing, and penetrating, and the correlation between the depression modes and the aerodynamic characteristics of the rotor is primary analyzed. The flow mechanisms of dimpling mode were studied using the particle image velocimetry (PIV) technique. The results showed that the cavity and liquid crown obviously alter the flow direction of water surface jets, but not all rotors near water enter the vortex ring state. Two splashing mechanisms were revealed, including the direct ejection of droplets at the rim of depression and the tearing of liquid crown by the water surface jets. The blade tip vortex in the surface jet is a potential cause of entrainment into the rotor disk and secondary breakup of the droplet.
47
Duan, Yajuan, Markus D. Petters, and Ana P. Barros. "Understanding aerosol–cloud interactions through modeling the development of orographic cumulus congestus during IPHEx." Atmospheric Chemistry and Physics 19, no. 3 (2019): 1413–37. http://dx.doi.org/10.5194/acp-19-1413-2019.
Full textAbstract:
Abstract. A new cloud parcel model (CPM) including activation, condensation, collision–coalescence, and lateral entrainment processes is used to investigate aerosol–cloud interactions (ACIs) in cumulus development prior to rainfall onset. The CPM was applied with surface aerosol measurements to predict the vertical structure of cloud development at early stages, and the model results were evaluated against airborne observations of cloud microphysics and thermodynamic conditions collected during the Integrated Precipitation and Hydrology Experiment (IPHEx) in the inner region of the southern Appalachian Mountains (SAM). Sensitivity analysis was conducted to examine the model response to variations in key ACI physiochemical parameters and initial conditions. The CPM sensitivities mirror those found in parcel models without entrainment and collision–coalescence, except for the evolution of the droplet spectrum and liquid water content with height. Simulated cloud droplet number concentrations (CDNCs) exhibit high sensitivity to variations in the initial aerosol concentration at cloud base, but weak sensitivity to bulk aerosol hygroscopicity. The condensation coefficient ac plays a governing role in determining the evolution of CDNC, liquid water content (LWC), and cloud droplet spectra (CDS) in time and with height. Lower values of ac lead to higher CDNCs and broader CDS above cloud base, and higher maximum supersaturation near cloud base. Analysis of model simulations reveals that competitive interference among turbulent dispersion, activation, and droplet growth processes modulates spectral width and explains the emergence of bimodal CDS and CDNC heterogeneity in aircraft measurements from different cloud regions and at different heights. Parameterization of nonlinear interactions among entrainment, condensational growth, and collision–coalescence processes is therefore necessary to simulate the vertical structures of CDNCs and CDSs in convective clouds. Comparisons of model predictions with data suggest that the representation of lateral entrainment remains challenging due to the spatial heterogeneity of the convective boundary layer and the intricate 3-D circulations in mountainous regions.
48
Freud, E., D. Rosenfeld, and J. R. Kulkarni. "Resolving both entrainment-mixing and number of activated CCN in deep convective clouds." Atmospheric Chemistry and Physics 11, no. 24 (2011): 12887–900. http://dx.doi.org/10.5194/acp-11-12887-2011.
Full textAbstract:
Abstract. The number concentration of activated CCN (Na) is the most fundamental microphysical property of a convective cloud. It determines the rate of droplet growth with cloud depth and conversion into precipitation-sized particles and affects the radiative properties of the clouds. However, measuring Na is not always possible, even in the cores of the convective clouds, because entrainment of sub-saturated ambient air deeper into the cloud lowers the concentrations by dilution and may cause partial or total droplet evaporation, depending on whether the mixing is homogeneous or extreme inhomogeneous, respectively. Here we describe a methodology to derive Na based on the rate of cloud droplet effective radius (Re) growth with cloud depth and with respect to the cloud mixing with the entrained ambient air. We use the slope of the tight linear relationship between the adiabatic liquid water mixing ratio and Re3 (or Rv3) to derive an upper limit for Na assuming extreme inhomogeneous mixing. Then we tune Na down to find the theoretical relative humidity that the entrained ambient air would have for each horizontal cloud penetration, in case of homogeneous mixing. This allows us to evaluate both the entrainment and mixing process in the vertical dimension in addition to getting a better estimation for Na. We found that the derived Na from the entire profile data is highly correlated with the independent CCN measurements from below cloud base. Moreover, it was found that mixing of sub-saturated ambient air into the cloud at scales of ~100 m and above is inclined towards the extreme inhomogeneous limit, i.e. that the time scale of droplet evaporation is significantly smaller than that for turbulent mixing. This means that ambient air that entrains the cloud is pre-moistened by total evaporation of cloud droplets before it mixes deeper into the clouds where it can hardly change the droplet size distribution, hence Re remains close to its adiabatic value at any given cloud depth. However, the tendency towards the extreme inhomogeneous mixing appeared to slightly decrease with altitude, possibly due to enhanced turbulence and larger cloud drops aloft. Quantifying these effects, based on more examples from other projects and high resolution cloud models is essential for improving our understanding of the interactions between the cloud and its environment. These interactions may play an important role in cloud dynamics and microphysics, by affecting cloud depth and droplet size spectra, for example, and may therefore influence the cloud precipitation formation processes.
49
Ouallal, M., S. Leyer, and S. Gupta. "Literature survey of droplet entrainment from water pools." Nuclear Engineering and Design 379 (August 2021): 111188. http://dx.doi.org/10.1016/j.nucengdes.2021.111188.
Full text
50
Höhne, Thomas, and Susann Hänsch. "A droplet entrainment model for horizontal segregated flows." Nuclear Engineering and Design 286 (May 2015): 18–26. http://dx.doi.org/10.1016/j.nucengdes.2015.01.013.
Full text