Direct simulation of spray cooling: Effect of vapor bubble growth and liquid droplet impact on heat transfer

2006 ◽  
Vol 49 (23-24) ◽  
pp. 4265-4278 ◽  
Author(s):  
R. Panneer Selvam ◽  
Lancho Lin ◽  
Rengasamy Ponnappan
Keyword(s):  
Heat Transfer ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Liquid Droplet ◽  
Spray Cooling ◽  
Droplet Impact ◽  
Cooling Effect ◽  
Direct Simulation

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.

Numerical Analysis of Vapor Bubble Growth and Wall Heat Transfer During Flow Boiling of Water in a Microchannel

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Wall Heat Transfer ◽  
Wall Superheat

The present study is performed to analyze the wall heat transfer mechanisms during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble begins to grow at one of the walls, with liquid coming in through the channel inlet. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The average wall heat transfer at the channel walls is studied for different values of wall superheat and incoming liquid mass flux. The results show that the wall heat transfer increases with wall superheat but is almost unaffected by the liquid flow rate. The bubble growth is found to be the primary mechanism of increasing wall heat transfer as it pushes the liquid against the walls thereby influencing the thermal boundary layer development.

Experiments and Modeling of a Liquid Droplet Transported by a Gas Stream Impinging on a Heated Surface: Evaporative Regime

2009 ◽  
Author(s):  
Ryan P. Anderson ◽  
Alfonso Ortega
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Single Phase ◽  
Heat Dissipation ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Thin Liquid Film ◽  
Spray Cooling ◽  
High Speed Photography ◽  
Transfer Coefficients

Understanding the transport mechanisms involved in a single droplet impinging on a heated surface is imperative to the complete understanding of droplet and spray cooling. Evidence in the literature suggests that gas assisted sprays and mist flows are more efficient than sprays consisting only of liquid droplets. There has been few if any fundamental studies on gas-assisted droplets or spray cooling, in which a carrier gas or vapor stream propels the droplet to the target surface. The current work extends previous studies of a droplet impinging on a heated surface conducted by the same group from the single phase regime into the evaporative regime. For both regimes, understanding the transport physics due to the heat transfer from the heated surface to the droplet and then by convection and evaporation to the airflow is of fundamental importance. High-speed photography was used to capture the spreading process and yielded results that correlated well with previously published isothermal and single-phase results. The heat transfer was measured with a fitting approach by which the instantaneous temperature profile was matched to an analytic solution to determine the instantaneous value of the centerline heat transfer coefficient. A very large increase in the heat dissipation was observed when compared to previously published single-phase results. Heat transfer was optimized at Reynolds numbers that produced an optimally thin liquid film and high heat and mass transfer coefficients on the surface of the film.

A New Method for Estimating Bubble Diameter At Different Gravity Levels for Nucleate Pool Boiling

2021 ◽  
Author(s):  
Sandipan Banerjee ◽  
Yongsheng Lian ◽  
Yang Liu ◽  
Mark Sussman
Keyword(s):  
Heat Transfer ◽  
Growth Rate ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
New Method ◽  
Space Applications ◽  
Earth Gravity ◽  
Micro Gravity

Abstract Nucleate boiling has significant applications in earth gravity( in industrial cooling applications) and micro-gravity conditions (in space exploration, specifically in making space applications more compact). However, the effect of gravity on the growth rate and bubble size is not yet well understood. We perform numerical simulations of nucleate boiling using an adaptive Moment-of-Fluid (MoF) method for a single vapor bubble (water or Perfluoro-n-hexane) in saturated liquid for different gravity levels. Results concerning the growth rate of the bubble, specifically the departure diameter and departure time have been provided. The MoF method has been first validated by comparing results with a theoretical solution of vapor bubble growth in super-heated liquid without any heat-transfer from the wall. Next, bubble growth rate, bubble shape and heat transfer results under earth gravity, reduced gravity and micro-gravity conditions are reported and they are in good agreement with experiments. Finally, a new method is proposed for estimating the bubble diameter at different gravity levels. This method is based on an analysis of empirical data at different gravity values and using power-series curve fitting to obtain a generalized bubble growth curve irrespective of the gravity value. This method is shown to provide a good estimate of the bubble diameter for a specific gravity value and time.

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.

Direct Numerical Simulation of Heat Transfer in Spray Cooling Through 3D Multiphase Flow Modeling Using Parallel Computing

2009 ◽  
Vol 131 (12) ◽  
Author(s):  
Suranjan Sarkar ◽  
R. Panneer Selvam
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Parallel Computing ◽  
Phase Change ◽  
Power Electronics ◽  
Vapor Bubble ◽  
Heat Removal ◽  
Spray Cooling ◽  
Hot Surface ◽  
Liquid Vapor

Thermal management issues have become a major bottleneck for further miniaturization and increased power consumption of electronics. Power electronics require more increasing use of high heat flux cooling technologies. Spray cooling with phase change has the advantage of large amount of heat transfer from the hot surface of many power electronics. Spray cooling is a complex phenomenon due to the interaction of liquid, vapor, and phase change at small length scale. A good understanding of the underlying physics and the heat removal process in spray cooling through numerical modeling is needed to design efficient spray cooling system. A computational fluid dynamics based 3D multiphase model for spray cooling is developed here in parallel computing environment using multigrid conjugate gradient solver. This model considers the effect of surface tension, gravity, phase change, and viscosity. The level set method is used to capture the movement of the liquid-vapor interface. The governing equations are solved using finite difference method. Spray cooling is studied using this model, where a vapor bubble is growing in a thin liquid film on a hot surface and a droplet is impacting on the thin film. The symmetry boundary condition considered on four sides of the domain effectively represents a large spray made up of multiple equally sized droplets and bubbles and their interaction. Studies have also been performed for different wall superheats in the absence of vapor bubble to compare the effect of two-phase heat transfer compared to single-phase in spray cooling. The computed interface, temperature, and heat flux distributions at different times over the domain are visualized for better understanding of the heat removal mechanism.

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