Deformation and Rebounding Processes of a Water Droplet Impinging on a Flat Surface Above Leidenfrost Temperature

1996 ◽  
Vol 118 (1) ◽  
pp. 142-149 ◽  
Author(s):  
Hitoshi Fujimoto ◽  
Natsuo Hatta
Keyword(s):  
Surface Tension ◽  
Water Droplet ◽  
Stokes Equations ◽  
Water Film ◽  
Video Camera ◽  
Ring Structure ◽  
Point Of View ◽  
Navier Stokes ◽  
Leidenfrost Temperature ◽  
Incompressible Fluid Flows

This paper treats numerical analyses of the deformation and rebounding processes of a water droplet impinging on a flat solid surface above the Leidenfrost temperature with a speed in the order of a few [m/s], as well as the flow field inside the droplet. These calculations were performed using the MAC-type solution method to solve a finite differencing approximation of the axisymmetric Navier-Stokes equations governing incompressible fluid flows. Also, the whole dynamic process of a droplet from the moment of collision with a hot surface including the rebound from it was recorded by using a video camera equipped with a macro lens. First, the water film formed by the droplet impinging on the surface spreads radially in a fairly thin discoid-like shape until it reaches a maximum. Next, the water film begins to recoil backwards towards the center and the recoiling process continues to occur owing to the surface tension effect at the periphery. Subsequently, the center part of the liquid drop begins to elongate upwards and the liquid near the top of the drop pulls up the lower part of the remaining liquid. Finally, a vortical ring structure appearing at the bottom of the elongated droplet induces the rotative motion in such a way as to form the rising flow and the droplet rebounds from the surface as a bowling pin-shaped mass. The numerical model to predict the deformation and rebounding processes was built up by accounting for the presence of viscous and surface tension effects. The numerical results obtained by the model were compared with the experimental data and discussed from a practical point of view.

Level Set Based Modeling of Electrowetting on Dielectrics Droplet

2012 ◽  
Vol 461 ◽  
pp. 138-141
Author(s):  
Yin Xia Chang ◽  
Si Xiang Zhang ◽  
Wei Zhou ◽  
Bao Liu
Keyword(s):  
Surface Tension ◽  
Contact Angle ◽  
Level Set ◽  
Stokes Equations ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Navier Stokes ◽  
Electric Force ◽  
Electrowetting On Dielectric ◽  
Static Contact

This paper discusses the modeling of Electrowetting On Dielectric (EWOD) device that moves fluid droplets through surface tension effects and electric force. Instead of using a static contact angle as most papers did, we take the dynamic contact angle into count by using expression proposed by Voinov and Tanner. Firstly, the level set model and its initial values is present. Then the governing equations are discussed, and the diffused format is adopted for density and viscosity varies to smooth over the interface. The detailed expression for surface tension and electric force are also described for Navier–Stokes equations. After presenting the boundary conditions, the steps of numerical implementation are detailed.

scholarly journals Relaxation and breakup of a cylindrical liquid column

1970 ◽  
Vol 39 (2) ◽  
pp. 57-64 ◽  
Author(s):  
Mohammad Ali ◽  
Akira Umemura
Keyword(s):  
Surface Tension ◽  
Stokes Equations ◽  
Capillary Wave ◽  
Three Dimensional ◽  
Surface Tension Force ◽  
Surface Force ◽  
Computer Code ◽  
Vof Method ◽  
Liquid Column ◽  
Navier Stokes

Instability of capillary wave and breakup of a square cylindrical liquid column during its relaxation have been investigated numerically by simulating three-dimensional Navier-Stokes equations. For this investigation a computer code based on volume-of-fluid (VOF) method has been developed and validated with published experimental results. The result shows that the agreement of numerical simulation is quite well with the experimental data. The code is then used to study the capillary wave and breakup phenomena of the liquid column. The investigation shows the underlying physics during relaxation of the square cylindrical liquid column, illustrates the formation and propagation of capillary wave, and breakup processes. The breakup behavior for the present configuration of the liquid column shows some significant differences from those predicted by conventional jet atomization theories. The formation of capillary wave is initiated by the surface tension on the sharp edge of the square end of the cylinder and the propagation of the wave occurs due to the effect of surface tension force on the motion of the fluid. The propagation of capillary wave to the end of liquid column causes a disturbance in the system and makes the waves unstable which initiates the breakup of the liquid column. The characteristics of the capillary wave show that the amplitude of the swell grows faster than the neck of the wave and that of the tip wave grows much faster than the other waves. The velocity of the liquid particle is dominated by the pressure in the liquid column. Keywords: Instability; Continuum surface force; Liquid disintegration; Capillary wave; Surface tension; VOF method doi:10.3329/jme.v39i2.1847 Journal of Mechanical Engineering, Vol. ME39, No. 2, Dec. 2008 57-64

scholarly journals Study of Fluids Motion in a Microchannel under Heat Source

2020 ◽  
Vol 2 (SI2) ◽  
pp. First
Author(s):  
Long Thanh Le
Keyword(s):  
Contact Angle ◽  
Heat Source ◽  
Water Droplet ◽  
Stokes Equations ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Immiscible Fluids ◽  
Navier Stokes ◽  
Two Phase ◽  
Receding Contact Angle

In this study, the numerical computation is used to investigate the transient thermocapillary migration of a water droplet in a Microchannel. For tracking the evolution of the free interface between two immiscible fluids, we employed the finite element method with the two-phase level set technique to solve the Navier-Stokes equations coupled with the energy equation. Both the upper wall and the bottom wall of the microchannel are set to be an ambient temperature. The heat source is placed at the left side of a water droplet. When the heat source is turned on, a pair of asymmetric thermocapillary convection vortices is formed inside the droplet and the thermocapillary on the receding side is smaller than that on the advancing side. The temperature gradient inside the droplet increases quickly at the initial times and then decreases versus time. Therefore, the actuation velocity of the water droplet first increases significantly, and then decreases continuously. The dynamic contact angle is strongly affected by the oil flow motion and the net thermocapillary momentum inside the droplet. The advancing contact angle is always larger than the receding contact angle during actuation process.

A stationary circular hydraulic jump, the limits of its existence and its gasdynamic analogue

2008 ◽  
Vol 601 ◽  
pp. 189-198 ◽  
Author(s):  
ASLAN R. KASIMOV
Keyword(s):  
Surface Tension ◽  
Hydraulic Jump ◽  
Stokes Equations ◽  
Critical Value ◽  
Water Model ◽  
Navier Stokes ◽  
Jump Conditions ◽  
Shallow Water Model ◽  
Finite Radius ◽  
Navier Stokes Equations

We propose a theory of a steady circular hydraulic jump based on the shallow-water model obtained from the depth-averaged Navier–Stokes equations. The flow structure both upstream and downstream of the jump is determined by considering the flow over a plate of finite radius. The radius of the jump is found using the far-field conditions together with the jump conditions that include the effects of surface tension. We show that a steady circular hydraulic jump does not exist if the surface tension is above a certain critical value. The solution of the problem provides a basis for the hydrodynamic stability analysis of the hydraulic jump. An analogy between the hydraulic jump and a detonation wave is pointed out.

A new experimental set-up to study the shear strength of snow-mortar interfaces

2021 ◽  
Author(s):  
Gianmarco Vallero ◽  
Monica Barbero ◽  
Fabrizio Barpi ◽  
Mauro Borri-Brunetto ◽  
Valerio De Biagi
Keyword(s):  
Shear Strength ◽  
Progressive Failure ◽  
Failure Process ◽  
Construction Materials ◽  
Water Film ◽  
Video Camera ◽  
Point Of View ◽  
High Definition ◽  
Snow Layer ◽  
Particle Image Velocimetry Technique

<p>The progressive failure of a snow layer deposited on a stiff substrate is at the base of the comprehension of several physical processes that can be found both in natural and artificial conditions. For instance, glide avalanches often originate from the reduction of the basal friction between the snowpack and the underlying ground due to the presence of liquid water film or depth hoar at the snow-ground interface. Moreover, the interaction between snow and construction materials relates to many other applications such as the study of new and more efficient snow removal techniques, the safety of travelers along snow covered roads, the snow redistribution from roofs and buildings, etc. </p><p>Despite this large number of application fields, laboratory investigations are still limited. We performed cold room tests on artificially made snow-mortar interface specimens through a direct shear test device. The effects of confinement pressure, temperature and dry snow hardness (due to sintering times) were taken into account. The tests were carried out in displacement-controlled conditions in order to study the entire failure process at the interface and the following irreversible sliding. The results show some interesting and encouraging aspects for understanding the shear strength of the interface. From a micromechanical point of view we recorded the tests with a high-definition video camera and analyzed the data with the Particle Image Velocimetry technique to obtain the motion fields on the external side of the specimens. Here, we present and discuss some preliminary results of the experimental activity and suggest some future implementations and further developments of the studied topic.       </p>

Numerical Study on Impingement of a Droplet upon a Liquid Film

2010 ◽  
Vol 44-47 ◽  
pp. 2499-2503
Author(s):  
Hong Liu ◽  
Mao Zhao Xie ◽  
Su Chun Wang ◽  
Ming Jia
Keyword(s):  
Surface Tension ◽  
Liquid Film ◽  
Stokes Equations ◽  
Numerical Study ◽  
Surface Tension Force ◽  
Surface Force ◽  
Navier Stokes ◽  
Initial Kinetic Energy ◽  
Droplet Impingement ◽  
Fine Grid

This paper reports progress in the numerical simulations of a droplet impingement upon the wall film of the same liquid. The full Navier-Stokes equations are solved in axisymmetric formulation. The surface tension force is modeled by a continuum surface force (CSF) model. An adapting local refinement technique is used to provide the fine grid coupled by the volume-of fluid (VOF) method for tracking the interface between the gas and the droplet and liquid film. Results indicate that the motion behavior of droplet impingement upon the liquid film is dominantly influenced by the initial kinetic energy and the thickness of the film as well as the surface tension and the liquid viscosity.

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