Droplet Dynamics on a Wettability Patterned Surface during Spray Impact

Wettability patterning of a surface is a passive method to manipulate the flow and heat transport mechanism in many physical processes and industrial applications. This paper proposes a rational wettability pattern comprised of multiple superhydrophilic wedges on a superhydrophobic background, which can continuously remove the impacted spray droplets from the horizontal surface. We observed that the spray droplets falling on the superhydrophilic wedge region spread and form a thin liquid film, which is passively transported away from the surface. However, most of the droplets falling on the superhydrophobic region move towards the wedge without any flooding. The physics of the passive transport of the liquid film on a wedge is also delved into using numerical modelling. In particular, we elucidate the different modes of droplet transport in the superhydrophobic region and the interaction of multiple droplets. The observed droplet dynamics could have profound implications in spray cooling systems and passive removal of liquid from a horizontal surface. This study’s findings will be beneficial for the optimization of efficient wettability patterned surfaces for spray cooling application.

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3-D Multiphase Flow Modeling of Bubble Growth and Burst in Spray Cooling Using Parallel Computing

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 2 ◽

10.1115/ht2007-32315 ◽

2007 ◽

Author(s):

R. Panneer Selvam ◽

Joseph Johnston ◽

Suranjan Sarkar

Keyword(s):

Heat Transfer ◽

Parallel Computing ◽

Multiphase Flow ◽

Liquid Film ◽

Convective Flow ◽

Bubble Dynamics ◽

Thin Liquid Film ◽

Spray Cooling ◽

Droplet Impact ◽

Multiphase Model

In this paper, we present an extension of the level set method from 2D into 3D for solving multiphase flow problems using distributed parallel computing. The model solves the incompressible Navier-Stokes equations to study the behavior of a bubble immersed in a thin liquid film at microscale as found in a spray cooling environment. Since modeling all aspects of spray cooling, including nucleation, bubble dynamics, droplet impact, convection and thin film evaporation is very difficult at this time; these phenomena have been divided and studied separately in order to study the heat transfer behavior of each phenomenon individually. We studied the droplet impact effect as seen in spray cooling by our 3D multiphase model in earlier studies. Through the 3D multiphase model this study simulates the dynamics of a nucleating bubble in a thin liquid film that merges with the ambient atmosphere above the film. In this study we did not consider the droplet impact effect to concentrate on the vapor bubble dynamics in thin liquid film and its effect on heat transfer. The effect of convective flow is not considered to keep the 3-D model simple. However the 2D model was modified to simulate the effect that a horizontal flow of constant velocity has on the growth and detachment of a nucleating bubble and discussed in the second part of the paper. This study illustrates the importance of considering the convective flow effect in our 3-D multiphase flow model in future with droplet impact for spray cooling modeling studies.

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The Low-Temperature Ring during Droplet Impact on a Superhydrophilic Surface

Coatings ◽

10.3390/coatings11091043 ◽

2021 ◽

Vol 11 (9) ◽

pp. 1043

Author(s):

Huixia Ma ◽

Jiang Chun ◽

Feng Zhou ◽

Kai Qiao ◽

Rui Jiang ◽

...

Keyword(s):

Heat Transfer ◽

Low Temperature ◽

Liquid Film ◽

Thin Liquid Film ◽

Film Surface ◽

Industrial Applications ◽

Droplet Impact ◽

Functional Coatings ◽

Superhydrophilic Surface ◽

The Impact

Droplet impact on the solid surfaces is widespread in nature, daily life, and industrial applications. The spreading characteristics and temperature evolution in the inertial spreading regime are critical for the heat and mass transfer process on the solid-liquid interface. This work investigated the spreading characteristics and temperature distribution of the thin liquid film in the inertial rapid spreading regime of droplet impact on the heated superhydrophilic surfaces. Driven by the inertial and capillary force, the droplet rapidly spreads on the superhydrophilic surface, resulting in a high temperature center in the impact center surrounded by a the low-temperature ring. The formation of the unique the low-temperature ring on the heated superhydrophilic surface is due to the much smaller time scale of rapid spreading than that of heat transfer from the hot solid surface to the liquid film surface. CFD numerical simulation shows that the impacting droplet spreads and congests in the front of liquid film, leading to the formation of vortex velocity distribution in the liquid film. Increasing We number and wall temperature can accelerate the heat transfer rate of liquid film and shorten the existence time of the low-temperature ring. The findings of the the low-temperature ring on the superhydrophilic surface provide the guidelines to optimization of surface structures and functional coatings for enhancing heat transfer in various energy systems.

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Direct Simulation of Spray Cooling: Effect of Multiple Droplet Impact and Latent Heat of Vaporization of Coolant Liquid on Heat Transfer

Heat Transfer: Volume 2 ◽

10.1115/ht2008-56034 ◽

2008 ◽

Author(s):

Mita Sarkar ◽

R. Panneer Selvam ◽

Rengasamy Ponnappan

Keyword(s):

Heat Transfer ◽

Liquid Film ◽

Latent Heat ◽

Stokes Equations ◽

Thin Liquid Film ◽

Spray Cooling ◽

Droplet Impact ◽

Vapor Bubbles ◽

Heat Of Vaporization ◽

Latent Heat Of Vaporization

Spray cooling is a way of efficiently removing the heat from a hot surface and considered for high power system such as advanced lasers. The heat transfer phenomenon in spray cooling is complex in nature because it occurs due to conduction, convection and phase change. The numerical model of spray cooling is done by solving the set of incompressible Navier-Stokes equations using finite difference method. Level set method is used to capture the liquid vapor interface in our multiphase flow model. Our previous 2D model which included single droplet impact on single growing vapor bubble is modified to introduce multiple droplets impact on thin liquid film with multiple growing vapor bubbles. Though the previous model was effective so far to predict the spray cooling phenomena and also the parameters for high heat removal, but the actual spray cooling phenomena consists of multiple droplets impact on multiple growing vapor bubbles at different time instances. To understand the spray cooling further and to represent it more realistically the inclusion of multiple droplets and multiple vapor bubbles is essential. In the present work, an investigation on the effect of latent heat of vaporization of coolant is conducted for the case of a thin liquid film of 44 μm in removing the heat and bubble growth when a liquid spray droplet is impacting. The flow and heat transfer details are presented for multiple droplet impacts on thin liquid film with multiple growing vapor bubbles.

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Numerical Simulation of Nucleate Spray Cooling: Effect of Droplet Impact on Bubble Growth and Heat Transfer in a Thin Liquid Film

Inaugural US-EU-China Thermophysics Conference-Renewable Energy 2009 (UECTC 2009 Proceedings) ◽

10.1115/1.802908.paper95 ◽

2009 ◽

pp. 1-7

Keyword(s):

Heat Transfer ◽

Numerical Simulation ◽

Liquid Film ◽

Bubble Growth ◽

Thin Liquid Film ◽

Spray Cooling ◽

Droplet Impact ◽

Cooling Effect

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Understanding High Heat Transfer in Spray Cooling for Different Droplet Velocities and Wall Superheats by 3D Multiphase Flow Modeling

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 1 ◽

10.1115/ht2007-32313 ◽

2007 ◽

Cited By ~ 1

Author(s):

R. Panneer Selvam ◽

Suranjan Sarkar

Keyword(s):

Heat Transfer ◽

Liquid Film ◽

Phase Change ◽

Thin Liquid Film ◽

Spray Cooling ◽

High Heat ◽

Multiphase Model ◽

High Heat Transfer ◽

Hot Surface ◽

D Model

Spray cooling with phase change has the advantage of relatively large amount of heat transfer from the hot surface of many power electronics system. In our previous works in 2-D model of spray cooling, the importance of moving the cooler liquid quickly to heated dry surface which causes the high heat flux due to transient conduction is recognized to be the main reason for high heat transfer. In reality the phenomena of spray cooling are three dimensional in nature. The major draw back in extending the 2-D model to 3-D model is huge computing time in serial computer. Here the 3-D model is developed in parallel computing environment to reduce the turn around time. The 3-D multiphase model used here considers the effect of surface tension between liquid and vapor, gravity, phase change and viscosity. The level set method is used to capture the movement of the liquid vapor interface. The governing equations of multiphase flow are solved using the finite difference method. In this work the spray cooling phenomena is studied in 3-D multiphase model where a vapor bubble is growing in a thin liquid film on a hot surface and a droplet is impacting on the thin liquid film. This study has been done for different droplet velocities and for different wall superheats with our 3-D multiphase model to understand the high heat removal mechanism in spray cooling for different velocities and wall superheat situations.

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