Evolution and heat transfer after droplet impact on heated liquid film with vapor bubbles inside

2019 ◽  
Vol 76 (5) ◽  
pp. 273-284 ◽  
Author(s):  
Yali Guo ◽  
Feng Wang ◽  
Luyuan Gong ◽  
Shengqiang Shen
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Droplet Impact ◽  
Vapor Bubbles

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

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.

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

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.

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

Coatings ◽  
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.

The Spreading Characteristics and Temperature Evolution of Droplet Impact on Cold Superhydrophilic Surface

2019 ◽  
Author(s):  
Jiang Chun ◽  
Tingting Hao ◽  
Yansong Chen ◽  
Yi Zheng ◽  
Xuehu Ma ◽  
...  
Keyword(s):  
Heat Transfer ◽  
High Temperature ◽  
Temperature Distribution ◽  
Liquid Film ◽  
Radial Direction ◽  
Heat Transfer Process ◽  
Droplet Impact ◽  
Temperature Evolution ◽  
Droplet Spreading ◽  
Superhydrophilic Surface

Abstract Droplet impact phenomena and thin liquid film flow are widespread in nature, industrial production and daily life. The spreading characteristics and temperature evolution of the liquid film after droplet impact are the key controlling factors in many industrial heat transfer processes. Constructing a thin micro-nano structured superhydrophilic surface on a metal surface is a promising approach to achieving heat transfer enhancement. Therefore, in this paper, we experimentally investigated the hydraulic characteristics and temperature distribution evolution of water droplet impact on cold superhydrophilic surface using high-speed imaging and infrared thermal imaging techniques. During the droplet spreading on superhydrophilic surface, there is an inertial-force-dominant rapid spreading regime followed by the friction-dominant slow spreading regime. It is observed that a precursor film forms in the radial direction. The results show that the droplet spreading diameter is positively correlated with the We number, increasing as the weber number becomes larger. The spreading diameter decreases as the wall temperature decreases, but the effect of temperature is not obvious compared with that of impact weber number. For temperature evolution, a low temperature center area forms at the impact center and a ring-shaped high temperature zone is observed first for droplet impact on cold superhydrophilic surfaces. Along spreading radial direction, the temperature distribution shows an uphill to downhill curve with its gradient inverted in sign near the high temperature zone. Then the high temperature ring disappears and the liquid film temperature shows a monotonically decreasing trend along the radial direction. The duration time of high temperature ring shortens with the increase of We number and decrease of wall temperature. Meanwhile, in order to reveal the reasons for the formation of special temperature distribution, CFD numerical simulation is adopted to analyze the mechanism of ring-shaped high temperature zone’s formation. CFD numerical simulation demonstrates that the temperature evolution law is in good agreement with the experiment results. The temperature distribution of high temperature ring is caused by uneven distribution of the liquid film thickness due to the superwetting properties of superhydrophilic surface. This work is of great significance for further understanding and provides new sights of the liquid film flow on superhydrophilic surface in heat transfer process. Furthermore, it has certain reference significance for the spray and heat transfer process in engineering practice.

Computer Modeling of Liquid Droplet Impact on Heat Transfer During Spray Cooling

2005 ◽  
Author(s):  
R. Panneer Selvam ◽  
Sandya Bhaskara ◽  
Juan C. Balda ◽  
Fred Barlow ◽  
Aicha Elshabini
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Vapor Bubble ◽  
Liquid Droplet ◽  
Heat Removal ◽  
Spray Cooling ◽  
Droplet Impact ◽  
System Level ◽  
High Heat Flux ◽  
Micro Level

Spray cooling is a high flux heat removal technique considered for systems dissipating high power within small areas such as advanced lasers. Recently Selvam and Ponnappan (2004 & 2005) identified the importance of modeling heat transfer in a thin liquid film on a hot surface at the micro level and illustrated how this micro level modeling could help to improve the macro level spray cooling. The goal of this research is to advance the theoretical understanding of spray cooling to enable efficient system level hardware designs. Two-phase flow modeling is done using the level set method to identify the interface of vapor and liquid. The modifications made to the incompressible Navier-Stokes equations to consider surface tension and phase change are presented. The equations are solved using the finite difference method. The effect of liquid droplet impact on a 40 μm thick liquid film containing vapor bubble and the consequent heat removal is explained with a sequence of temperature vs. time contours. From that, the importance of fast transient conduction in the liquid film leading to high heat flux in a short time is illustrated. The optimum positioning of the droplet with respect to the vapor bubble for effective heat removal is also systematically investigated. This information is expected to help in proper positioning of the droplet in three-dimensional modeling.

Sign in / Sign up

Export Citation Format

Share Document