scholarly journals Spreading Dynamics of Droplet Impact on a Wedge-Patterned Biphilic Surface

2019 ◽  
Vol 9 (11) ◽  
pp. 2214 ◽  
Author(s):  
Yanjie Yang ◽  
Xiaoqian Chen ◽  
Yiyong Huang
Keyword(s):  
Weber Number ◽  
Droplet Impact ◽  
Apex Angle ◽  
Experimental Results ◽  
Spreading Process ◽  
Droplet Spreading ◽  
Tilting Angle ◽  
Spreading Dynamics ◽  
Critical Weber Number ◽  
Maximum Spreading

The influence of apex angle and tilting angle on droplet spreading dynamics after impinging on wedge-patterned biphilic surface has been experimentally investigated. Once the droplet contacts the wedge-patterned biphilic surface, it spreads radially on the surface, with a tendency toward a more hydrophilic area. After reaching the maximum spreading diameter, the droplet contracts back. From the experimental results, the normalized diameter β ( β = D / D 0 ) was found to be related with the Weber number ( W e = ρ D V 2 / γ ) as β max ∼ W e 1 / 5 . during the first spreading process. Below 67.4°, a larger apex angle can help a droplet to spread on the surface more quickly. The maximum spreading diameter has a tendency to increase with the Weber number, and then decrease after the Weber number, beyond 2.7. Approximately, the critical Weber number is about 5, when the droplet lifts off the surface. Considering the effect of apex angle, the maximum normalized spreading diameter has a rough expression as β ∼ α τ

The TAR Model for Calculation of Droplet/Wall Impingement

1998 ◽  
Vol 120 (3) ◽  
pp. 593-597 ◽  
Author(s):  
Haitao Xu ◽  
Yongchang Liu ◽  
Ping He ◽  
Haiqing Wang
Keyword(s):  
Weber Number ◽  
Experimental Results ◽  
Droplet Radius ◽  
Hydrodynamic Behavior ◽  
New Model ◽  
Wall Impingement ◽  
Critical Weber Number ◽  
Wall Interaction

In this paper, we present a new model, called the TAR model, for calculation of droplet/wall impingement. Using this model, we find that the critical Weber number for rebound is not a constant. It varies with the droplet radius. For large drops, the critical Weber numbers and rebound velocities predicted by the TAR model agree with experimental results very well. Whereas, the predicted hydrodynamic behavior of small droplets is very different from that of large drops. This conclusion is significant for modeling engine spray/wall interaction.

Maximum drop radius and critical Weber number for splashing in the dynamical Leidenfrost regime

2016 ◽  
Vol 803 ◽  
pp. 516-527 ◽  
Author(s):  
Guillaume Riboux ◽  
José Manuel Gordillo
Keyword(s):  
Critical Velocity ◽  
Weber Number ◽  
Room Temperature ◽  
Liquid Velocity ◽  
Solid Substrate ◽  
Boundary Integral ◽  
Shear Stresses ◽  
Critical Weber Number ◽  
The One ◽  
Maximum Spreading

At room temperature, when a drop impacts against a smooth solid surface at a velocity above the so-called critical velocity for splashing, the drop loses its integrity and fragments into tiny droplets violently ejected radially outwards. Below this critical velocity, the drop simply spreads over the substrate. Splashing is also reported to occur for solid substrate temperatures above the Leidenfrost temperature, $T_{L}$, for which a vapour layer prevents the drop from touching the solid. In this case, the splashing morphology differs from the one reported at room temperature because, thanks to the presence of the gas layer, the shear stresses acting on the liquid can be neglected. Our purpose here is to predict, for wall temperatures above $T_{L}$, the critical Weber number for splashing as well as the maximum spreading radius. First, making use of boundary integral simulations, we calculate both the time evolution of the liquid velocity as well as the height of the sheet which is ejected tangentially to the substrate. These results are then used as boundary conditions for the one-dimensional mass and momentum equations describing the dynamics of the rim limiting the expanding liquid sheet. Our predictions for both the maximum spreading radius and for the critical Weber number for splashing are in good agreement with experimental observations.

scholarly journals DESIGNING A TEMPORARY COLD PROTECTIVE GEAR CONSTRUCTED BY FOLDING NEWSPRINT PAPER CONSIDERING HEAT-RETAINING PROPERTY AND RIGIDITY

2021 ◽  
Vol 1 ◽  
pp. 1123-1132
Author(s):  
Tatsuya Oda ◽  
Shigeru Wesugi
Keyword(s):  
Natural Disaster ◽  
Cold Season ◽  
Apex Angle ◽  
The Body ◽  
Experimental Results ◽  
Protective Gear ◽  
Significant Difference ◽  
Body Shapes

AbstractDuring the cold season, the cold protective products are often short during evacuation life after a natural disaster. If evacuees can make and wear simple cold protective gears by using materials obtainable on site, it will reduce the burden on the evacuees in emergent situation. Therefore, we investigated the structure constructed by folding newsprint paper, which can improve the heat retention effect and be applied to various body shapes. Focusing on the glide reflection structure repeating a smaller chamber, the basic size was determined by experiments with reference to the accordion shape, and the experimental results indicated that the heat retention effect was significantly greater than that of a mere air layer and those of ordinary fabrics. Next, it was found that the apex angle of structure had no significant difference in the heat retention effect. Then, the dimensions of the structure were determined to maintain the air layer under the pressure of the clothes by simulation of structural analyses. Finally, we made a temporary cold protective gear that can practically cover the trunk of the body and found that the heat retention effect was significantly higher than that of unprocessed newsprint and that of accordion shape.

Penetration Dynamics of Solid Particles into Liquids High-Speed Experimental Results and Modelling

2005 ◽  
Vol 473-474 ◽  
pp. 429-434 ◽  
Author(s):  
Olga Verezub ◽  
György Kaptay ◽  
Tomiharu Matsushita ◽  
Kusuhiro Mukai
Keyword(s):  
Contact Angle ◽  
Particle Size ◽  
Aqueous Solutions ◽  
Particle Velocity ◽  
Weber Number ◽  
High Speed ◽  
Solid Particles ◽  
Bulk Liquid ◽  
Distilled Water ◽  
Critical Weber Number

Penetration of model solid particles (polymer, teflon, nylon, alumina) into transparent model liquids (distilled water and aqueous solutions of KI) were recorded by a high speed (500 frames per second) camera, while the particles were dropped from different heights vertically on the still surface of the liquids. In all cases a cavity has been found to form behind the solid particle, penetrating into the liquid. For each particle/liquid combination the critical dropping height has been measured, above which the particle was able to penetrate into the bulk liquid. Based on this, the critical impact particle velocity, and also the critical Weber number of penetration have been established. The critical Weber number of penetration was modelled as a function of the contact angle, particle size and the ratio of the density of solid particles to the density of the liquid.

scholarly journals Cavity Detachment from a Wedge with Rounded Edges and the Surface Tension Effect

2021 ◽  
Vol 9 (11) ◽  
pp. 1253
Author(s):  
Yuriy N. Savchenko ◽  
Georgiy Y. Savchenko ◽  
Yuriy A. Semenov
Keyword(s):  
Surface Tension ◽  
Weber Number ◽  
Solution Process ◽  
Cavity Flow ◽  
Surface Tension Effect ◽  
Force Coefficient ◽  
Hodograph Method ◽  
Wide Range ◽  
Critical Weber Number ◽  
Cavity Boundary

Cavity flow around a wedge with rounded edges was studied, taking into account the surface tension effect and the Brillouin–Villat criterion of cavity detachment. The liquid compressibility and viscosity were ignored. An analytical solution was obtained in parametric form by applying the integral hodograph method. This method gives the possibility of deriving analytical expressions for complex velocity and for potential, both defined in a parameter plane. An expression for the curvature of the cavity boundary was obtained analytically. By using the dynamic boundary condition on the cavity boundary, an integral equation in the velocity modulus was derived. The particular case of zero surface tension is a special case of the solution. The surface tension effect was computed over a wide range of the Weber number for various degrees of cavitation development. Numerical results are presented for the flow configuration, the drag force coefficient, and the position of cavity detachment. It was found that for each radius of the edges, there exists a critical Weber number, below which the iterative solution process fails to converge, so a steady flow solution cannot be computed. This critical Weber number increases as the radius of the edge decreases. As the edge radius tends to zero, the critical Weber number tends to infinity, or a steady cavity flow cannot be computed at any finite Weber number in the case of sharp wedge edges. This shows some limitations of the model based on the Brillouin–Villat criterion of cavity detachment.

scholarly journals Modelling Forest Fires Using Complex Networks

2021 ◽  
Vol 26 (4) ◽  
pp. 68
Author(s):  
Sara Perestrelo ◽  
Maria C. Grácio ◽  
Nuno A. Ribeiro ◽  
Luís M. Lopes
Keyword(s):  
Forest Fires ◽  
Previous Knowledge ◽  
Time Duration ◽  
Spreading Process ◽  
Multilayer Network ◽  
Major Threat ◽  
Rate Of Spread ◽  
Spreading Dynamics ◽  
Fire Spreading ◽  
Network Of Networks

Forest fires have been a major threat to the environment throughout history. In order to mitigate its consequences, we present, in a first of a series of works, a mathematical model with the purpose of predicting fire spreading in a given land portion divided into patches, considering the area and the rate of spread of each patch as inputs. The rate of spread can be estimated from previous knowledge on fuel availability, weather and terrain conditions. We compute the time duration of the spreading process in a land patch in order to construct and parametrize a landscape network, using cellular automata simulations. We use the multilayer network model to propose a network of networks at the landscape scale, where the nodes are the local patches, each with their own spreading dynamics. We compute some respective network measures and aim, in further work, for the establishment of a fire-break structure according to increasing accuracy simulation results.

Simulation of Spreading Dynamics of a EWOD Droplet With Dynamic Contact Angle and Contact Angle Hysteresis

2009 ◽  
Author(s):  
Fangjun Hong ◽  
Ping Cheng ◽  
Zhen Sun ◽  
Huiying Wu
Keyword(s):  
Contact Angle ◽  
Contact Line ◽  
Low Voltage ◽  
Contact Angle Hysteresis ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Dielectric Surface ◽  
Contact Radius ◽  
Droplet Spreading ◽  
Spreading Dynamics

In this paper, the electrowetting dynamics of a droplet on a dielectric surface was investigated numerically by a mathematical model including dynamic contact angle and contact angle hysteresis. The fluid flow is described by laminar N-S equation, the free surface of the droplet is modeled by the Volume of Fluid (VOF) method, and the electrowetting force is incorporated by exerting an electrical force on the cells at the contact line. The Kilster’s model that can deal with both receding and advancing contact angle is adopted. Numerical results indicate that there is overshooting and oscillation of contact radius in droplet spreading process before it ceases the movement when the excitation voltage is high; while the overshooting is not observed for low voltage. The explanation for the contact line overshooting and some special characteristics of variation of contact radius with time were also conducted.

Numerical Investigation of a Liquid Droplet Impinging on a Heated Surface

2009 ◽  
Author(s):  
Andres Diaz ◽  
Alfonso Ortega ◽  
Ryan Anderson
Keyword(s):  
Heat Transfer ◽  
Numerical Investigation ◽  
Fundamental Problem ◽  
Water Drop ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Heat Removal ◽  
Droplet Spreading ◽  
Droplet Shape ◽  
Spreading Dynamics

Previous studies, most of them experimental, reveal that the cooling effectiveness of a water drop impinging on a heated surface depends on the wall temperature, droplet shape and velocity. All previous studies focus on the behavior of a droplet falling in a quiescent environment, such as still air. Evidence in the literature also shows that gas assisted droplet sprays, in which a gas phase propels the droplets, are more efficient in heat removal than sprays consisting of droplets alone. It is conjectured that this is due to an increase in the maximum droplet spreading diameter upon impact, a thinner film, and consequently an increase in the overall heat transfer coefficient. Recent experiments in the author’s group [1, 2] show that the carrier gas jet strongly influences droplet spreading dynamics by imposing normal and shear forces on the liquid surface. The heat transfer is greatly augmented in the process, compared to a free falling droplet. To date, there has been no fundamental investigation of the physics of gas assisted spray cooling. To begin to understand the complicated process, this paper reports on a fundamental problem of a single liquid droplet that impinges on a heated surface. This paper contributes a numerical investigation of the problem using the volume of fluid (VOF) technique to capture droplet spreading dynamics and heat transfer in a single drop event. The fluid mechanics is investigated and compared to the experimental data. The greatest uncertainty in the simulation is in the specification of the contact angle of the advancing or receding liquid front, and in capturing the onset of the three-dimensional fingering phenomena.

The Experimental Study of Single Droplet Impinging on an Inclined Heated Wall

2020 ◽  
Author(s):  
Wenlong Tian ◽  
Huang Zhang ◽  
Qianfeng Liu ◽  
Guang Hu ◽  
Wen He
Keyword(s):  
Inclination Angle ◽  
Wall Temperature ◽  
Weber Number ◽  
High Speed ◽  
Conservation Equation ◽  
Heated Wall ◽  
Single Droplet ◽  
Droplet Spreading ◽  
Energy Conservation Equation ◽  
Inclination Angles

Abstract We investigated a single droplet impinging on an inclined heated wall with different inclination angles. A high-speed camera was used to observe this impinging process at 10000 frames / second. The phenomena of the droplet spreading, shrinking, rebounding, boiling, break-up and splashing were observed. The effects of the wall temperature (Tw, 40–262 °C), the Weber number of the droplet (Wed, 0.66–589) and the wall inclination angle (α, 0–45.6°) on the spreading behavior of the droplet after impinging on the wall were analyzed. Energy conservation equation was used to analyze experimental results. The results show that increasing the inclination angle of the wall is beneficial to the forward spreading of the droplet along the wall, but not to the downward spreading. When α > 45.6°, the droplet will break through the flow resistance of the wall and slide down all the time. The increase of the wall temperature and the Weber number of the droplet is beneficial to the backward and forward spreading of the droplet. Increasing α, increasing Tw and decreasing Wed will promote the shrinking of the droplet after spreading. In addition, the experimental phenomenon also shows that the larger the wall inclination and the higher the wall temperature, the easier the droplet will break away from the wall.

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