scholarly journals Coalescence of Binary Droplets in the Transformer Oil Based on Small Amounts of Polymer: Effects of Initial Droplet Diameter and Collision Parameter

Polymers ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2054
Author(s):  
Yiting Wang ◽  
Lijuan Qian ◽  
Zhongli Chen ◽  
Fang Zhou
Keyword(s):  
Kinetic Energy ◽  
Droplet Diameter ◽  
Transformer Oil ◽  
Water Droplets ◽  
Droplet Deformation ◽  
Oil Separation ◽  
Coalescence Time ◽  
Maximum Deformation ◽  
Initial Droplet ◽  
Central Collisions

In engineering applications, the coalescence of droplets in the oil phase dominates the efficiency of water-oil separation. To improve the efficiency of water-oil separation, many studies have been devoted to exploring the process of water droplets colliding in the oil phase. In this paper, the volume of fluid (VOF) method is employed to simulate the coalescence of water droplets in the transformer oil based on small amounts of polymer. The influences of the initial diameter and collision parameter of two equal droplets on droplet deformation and coalescence time are investigated. The time evolution curves of the dimensionless maximum deformation diameter of the droplets indicate that the larger the droplet diameter, the more obvious the deformation from central collisions. As the collision parameter increases, the contact area of the two droplets, as well as the kinetic energy that is converted into surface energy, decreases, resulting in an increase in droplet deformation. Furthermore, the effects of the initial droplet diameter and collision parameter on coalescence time are also investigated and discussed. The results reveal that as the initial droplet diameter and collision parameter increase, the droplet coalescence time increases.

Consistent Theoretical Model of Mean Diameter and Size Distribution by Liquid Sheet Atomization

2012 ◽  
Author(s):  
Chihiro Inoue ◽  
Toshinori Watanabe ◽  
Takehiro Himeno ◽  
Seiji Uzawa ◽  
Mitsuo Koshi
Keyword(s):  
Theoretical Model ◽  
Kinetic Energy ◽  
Droplet Diameter ◽  
Velocity Profiles ◽  
Liquid Sheet ◽  
Estimation Methods ◽  
Liquid Jets ◽  
Injection Velocity ◽  
Size Distributions ◽  
Mean Diameter

A consistent theoretical model is proposed and validated for calculating droplet diameters and size distributions. The model is derived based on the energy conservation law including the surface free energy and the Laplace pressure. Under several hypotheses, the law derives an equation indicating that atomization results from kinetic energy loss. Thus, once the amount of loss is determined, the droplet diameter is able to be calculated without the use of experimental parameters. When the effects of ambient gas are negligible, injection velocity profiles of liquid jets are the essential cause of the reduction of kinetic energy. The minimum Sauter mean diameter produced by liquid sheet atomization is inversely proportional to the injection Weber number when the injection velocity profiles are laminar or turbulent. A non-dimensional distribution function is also derived from the mean diameter model and Nukiyama-Tanasawa’s function. The new estimation methods are favorably validated by comparing with corresponding mean diameters and the size distributions, which are experimentally measured under atmospheric pressure.

scholarly journals Comparison between sprinkler irrigation and natural rainfall based on droplet diameter

2016 ◽  
Vol 14 (1) ◽  
pp. e1201 ◽  
Author(s):  
MaoSheng Ge ◽  
Pute Wu ◽  
Delan Zhu ◽  
Daniel P. Ames
Keyword(s):  
Soil Erosion ◽  
Kinetic Energy ◽  
Droplet Diameter ◽  
Vertical Component ◽  
Radial Distance ◽  
Sprinkler Irrigation ◽  
Application Rate ◽  
Horizontal Component ◽  
Natural Rainfall ◽  
Actual Field

<p>An indoor experiment was conducted to analyze the movement characteristics of different sized droplets and their influence on water application rate distribution and kinetic energy distribution. Radial droplets emitted from a Nelson D3000 sprinkler nozzle under 66.3, 84.8, and 103.3 kPa were measured in terms of droplet velocity, landing angle, and droplet kinetic energy and results were compared to natural rainfall characteristics. Results indicate that sprinkler irrigation droplet landing velocity for all sizes of droplets is not related to nozzle pressure and the values of landing velocity are very close to that of natural rainfall. The velocity horizontal component increases with radial distance while the velocity vertical component decreases with radial distance. Additionally, landing angle of all droplet sizes decreases with radial distance. The kinetic energy is decomposed into vertical component and horizontal component due to the oblique angles of droplet impact on the surface soil, and this may aggravate soil erosion. Therefore the actual oblique angle of impact should be considered in actual field conditions and measures should be taken for remediation of soil erosion if necessary.</p>

scholarly journals Droplet Characteristics of Rotating Packed Bed in H2S Absorption: A Computational Fluid Dynamics Analysis

Processes ◽  
2019 ◽  
Vol 7 (10) ◽  
pp. 724
Author(s):  
Wang ◽  
Wu ◽  
Yang ◽  
Wang ◽  
Liu ◽  
...  
Keyword(s):  
Residence Time ◽  
Droplet Diameter ◽  
Packed Bed ◽  
Droplet Velocity ◽  
Radial Position ◽  
Selective Absorption ◽  
Rotating Speed ◽  
Initial Droplet ◽  
Rotating Packed Bed ◽  
Computational Fluid Dynamics Analysis

Rotating packed bed (RPB) has been demonstrated as a significant and emerging technology to be applied in natural gas desulfurization. However, droplet characteristics and principle in H2S selective absorption with N-methyldiethanolamine (MDEA) solution have seldom been fully investigated by experimental method. Therefore, a 3D Eulerian–Lagrangian approach has been established to investigate the droplet characteristics. The discrete phase model (DPM) is implemented to track the behavior of droplets, meanwhile the collision model and breakup model are employed to describe the coalescence and breakup of droplets. The simulation results indicate that rotating speed and radial position have a dominant impact on droplet velocity, average residence time and average diameter rather than initial droplet velocity. A short residence time of 0.039–0.085 s is credited in this study for faster mass transfer and reaction rate in RPB. The average droplet diameter decreases when the initial droplet velocity and rotating speed enhances. Restriction of minimum droplet diameter for it to be broken and an appropriate rotating speed have also been elaborated. Additional correlations on droplet velocity and diameter have been obtained mainly considering the rotating speed and radial position in RPB. This proposed formula leads to a much better understanding of droplet characteristics in RPB.

The Evaporation of Water Droplets in Superheated Steam

1968 ◽  
Vol 90 (4) ◽  
pp. 445-451 ◽  
Author(s):  
Kwan Lee ◽  
D. J. Ryley
Keyword(s):  
Reynolds Number ◽  
Glass Fiber ◽  
Water Droplet ◽  
Superheated Steam ◽  
Droplet Diameter ◽  
Steam Pressure ◽  
Water Droplets ◽  
Heating Up ◽  
Correlating Equation

The evaporation of a water droplet, diameter 230-1130μ, suspended on a 50μ diameter glass fiber was measured optically for the following range of variables: droplet Reynolds number 64-250, superheated steam pressure 14.7–29 psia, degrees of superheat 5–61 deg F; velocity 9–39 fps. The correlating equation was found to be Nu¯=2+0.74Re0.5Pr0.33 The apparatus and technique were proven using air as the evaporating medium. Calculations were made of the heating-up period at the beginning, and the drop asphericity at the end of a given test.

Numerical Analysis on Droplet Deformation and Breakup in High Gravity Field

2014 ◽  
Vol 624 ◽  
pp. 276-279 ◽  
Author(s):  
Jian Dong Li ◽  
Dian Jun Zuo ◽  
Yu Ting Zhang
Keyword(s):  
Gravity Field ◽  
Droplet Diameter ◽  
Droplet Breakup ◽  
Test Method ◽  
High Gravity ◽  
Droplet Deformation ◽  
Geotechnical Centrifuge ◽  
G Value ◽  
High Gravity Field ◽  
Breakup Time

Research slope stability under rainfall condition in geotechnical centrifuge is an ideal test method, however, the influence of high centrifugal force field produced by running geotechnical centrifuge cannot be neglected. Droplet deformation and breakup under different gravity and of different diameters were studied with VOF method, the results shows that the process of droplet deformation and breakup is similar under condition of different g-value and diameters, droplet breakup in a very short time in high gravity field, and with the increase of g-value, the breakup time of droplet became shorter, with the increase of droplet diameter, the breakup time of droplet became longer under same gravity acceleration. Studies in this paper have important significance in developing geotechnical centrifuge artificial rainfall equipment.

Acoustic Cloud Condensation Nuclei Counter

2005 ◽  
Author(s):  
Abhijit Deshpande ◽  
Marcellin Zahui
Keyword(s):  
Water Surface ◽  
Cloud Condensation Nuclei ◽  
Droplet Diameter ◽  
Bubble Formation ◽  
Maximum Velocity ◽  
Acoustic Energy ◽  
Water Droplets ◽  
Condensation Nuclei ◽  
Micro Scale ◽  
The Impact

Analysis and simulation of an acoustic cloud condensation nuclei counter is presented. The instrument is capable of accurately counting the number of micro scale water droplets impacting a water surface. The sound produced underwater by the water droplets is determined when the droplets strike the water surface with an impact velocity equal to either their terminal or maximum velocity. First, the terminal velocities of the droplets are calculated using Stoke’s law and compared to measured velocities from Gunn and Kinzer. Then the maximum velocities that these droplets can sustain without breaking are calculated as a function of droplet diameter. Second, the sound due to droplet impact is estimated. Due to their size and water surface tension, there is no bubble formation at impact when the droplets are falling with terminal velocities. However conditions for regular bubble entrainments are established and limit velocities are calculated. Assuming that the micro water droplets can be accelerated, the maximum velocities for no bubble entrainments are calculated. The results show that the level of the sound produced by individual micro scale droplet falling with terminal velocity is so small that experimental verification is not possible. However, reasonable level of acoustic energy can be obtained by increasing the impact velocities of the droplets or by measuring the sound radiated by a group of impacting droplets. Finally, the droplets counting process is simulated using a water surface of one centimeter squared and a vertical growth chamber.

The evaporation and combustion of levitated arrays of two, three and five droplets at a hot surface

1988 ◽  
Vol 418 (1855) ◽  
pp. 365-382 ◽  
Keyword(s):  
Droplet Diameter ◽  
Flame Height ◽  
Linear Arrays ◽  
Initial Droplet ◽  
Surface Temperatures ◽  
Droplet Array ◽  
Burning Rates ◽  
Hot Surface

The interactions between droplets in several geometrical arrays in Leidenfrost evaporation and combustion on a hot surface were studied. Comparisons between evaporation and burning times of isolated droplets, two- and three-droplet linear arrays, and a five-droplet array (a centre droplet surrounded by four droplets) were made. The liquids studied were water, n -heptane, and n -hexadecane at 0.101 MPa and at surface temperatures above their respective Leidenfrost values. A range of centre distance to initial droplet diameter ratios, L / d 0 , were studied (2 < L / d 0 < ∞). The evaporation or burning rates of droplets in binary arrays were found to be identical to those of isolated droplets ( L / d 0 → ∞). The flames around each droplet, however, merged as the droplets were brought closer together. In three- and five-droplet arrays more significant interactions were observed, with the edge droplets in the arrays burning faster than the centre droplets. The results are explained on the basis of flame-height measurements for the arrays. In pure evaporation, though, the droplets evaporated without regard for their neighbours.

Droplet–turbulence interactions in low-Mach-number homogeneous shear two-phase flows

1998 ◽  
Vol 367 ◽  
pp. 163-203 ◽  
Author(s):  
FARZAD MASHAYEK
Keyword(s):  
Kinetic Energy ◽  
Turbulent Flows ◽  
Carrier Phase ◽  
Mass Fraction ◽  
Turbulence Kinetic Energy ◽  
Droplet Temperature ◽  
Low Mach Number ◽  
Homogeneous Shear ◽  
Initial Droplet ◽  
The Mean

Several important issues pertaining to dispersion and polydispersity of droplets in turbulent flows are investigated via direct numerical simulation (DNS). The carrier phase is considered in the Eulerian context, the dispersed phase is tracked in the Lagrangian frame and the interactions between the phases are taken into account in a realistic two-way (coupled) formulation. The resulting scheme is applied for extensive DNS of low-Mach-number, homogeneous shear turbulent flows laden with droplets. Several cases with one- and two-way couplings are considered for both non-evaporating and evaporating droplets. The effects of the mass loading ratio, the droplet time constant, and thermodynamic parameters, such as the droplet specific heat, the droplet latent heat of evaporation, and the boiling temperature, on the turbulence and the droplets are investigated. The effects of the initial droplet temperature and the initial vapour mass fraction in the carrier phase are also studied. The gravity effects are not considered as the numerical methodology is only applicable in the absence of gravity. The evolution of the turbulence kinetic energy and the mean internal energy of both phases is studied by analysing various terms in their transport equations. The results for the non-evaporating droplets show that the presence of the droplets decreases the turbulence kinetic energy of the carrier phase while increasing the level of anisotropy of the flow. The droplet streamwise velocity variance is larger than that of the fluid, and the ratio of the two increases with the increase of the droplet time constant. Evaporation increases both the turbulence kinetic energy and the mean internal energy of the carrier phase by mass transfer. In general, evaporation is controlled by the vapour mass fraction gradient around the droplet when the initial temperature difference between the phases is negligible. In cases with small initial droplet temperature, on the other hand, the convective heat transfer is more important in the evaporation process. At long times, the evaporation rate approaches asymptotic values depending on the values of various parameters. It is shown that the evaporation rate is larger for droplets residing in high-strain-rate regions of the flow, mainly due to larger droplet Reynolds numbers in these regions. For both the evaporating and the non-evaporating droplets, the root mean square (r.m.s.) of the temperature fluctuations of both phases becomes independent of the initial droplet temperature at long times. Some issues relevant to modelling of turbulent flows laden with droplets are also discussed.

The effect of initial diameter in spherically symmetric droplet combustion of sooting fuels

1994 ◽  
Vol 446 (1927) ◽  
pp. 255-276 ◽  
Keyword(s):  
Burning Rate ◽  
Rate Constants ◽  
Soot Formation ◽  
Droplet Diameter ◽  
Droplet Surface ◽  
Spherically Symmetric ◽  
Low Gravity ◽  
Initial Droplet ◽  
Initial Diameter ◽  
Burning Rates

The effect of initial droplet diameter on the burning rate of sooting fuels – n-heptane and 1-chloro-octane – was examined experimentally at low gravity. A 1.2s drop tower provided a low gravity environment to minimize buoyancy and achieve spherically symmetric flames for stationary droplets. Free-floating and fibre-supported droplets were burned, and both techniques gave matching results for droplets of similar initial diameter. Burning rate constants for both fuels were measured for a large number of droplets ranging from 0.4 to 1.1 mm in initial diameter. Results showed that burning rate constants decreased monotonically as the initial droplet diameter was increased above 0.6 mm for both fuels. This decrease was considered to be due to the observed increase in soot formation and accumulation in a shell-like structure inside the flame of the larger droplets. The increased collection of soot inside the larger droplet flames reduced the proportional heat release from the flame and may have acted as a barrier to heat transfer from the flame to the droplet. Flame-to-droplet diameter ratio increased monotonically with time, thus suggesting that quasi-steady combustion was not achieved. The flames and soot shells for 1-chloro-octane droplets with their lower burning rates remained closer to the droplet surface than similarly sized n-heptane droplets.

Droplet Burning and Evaporation Times for Distillate and Residual Fuel Oils

1980 ◽  
Author(s):  
P. C. T. de Boer
Keyword(s):  
Gas Turbine ◽  
Constant Velocity ◽  
Droplet Diameter ◽  
Diffusion Constant ◽  
Gas Mixture ◽  
Residual Oil ◽  
Gas Turbine Combustor ◽  
Initial Droplet ◽  
Fuel Oils ◽  
Industrial Gas Turbine

Estimates are given of the burning and evaporation times of No. 2 distillate and No. 6 residual oil droplets, under conditions typical of industrial gas turbine combustors. Account is taken of the temperature dependence of the specific heat, the diffusion constant, and the thermal conductivity of the gas mixture surrounding the droplet. Detailed calculations are presented of the factor by which the droplet lifetime is reduced as a result of convection, for the case that the droplet is released in a gas moving at constant velocity. This factor is on the order of four for the conditions of interest. Using estimates of initial droplet diameter based on data reported by Jasuja, it is found that the ratio of characteristic droplet burning time to characteristic droplet residence time in a typical industrial gas turbine combustor is much smaller than 1 for distillate oil, but may be on the order of 1 for residual oil.

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