Numerical Study of Bubble Growth on a Micro-Finned Surface

2011 ◽  
Author(s):  
Woorim Lee ◽  
Gihun Son
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Removal Rate ◽  
Bubble Formation ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
Finned Surface ◽  
Fin Spacing

Bubble growth on a micro-finned surface, which can be used in enhancing boiling heat transfer, is numerically investigated by solving the conservation equations of mass, momentum, and energy. The bubble deformation or the liquid-vapor interface is determined by the sharp-interface level-set method, which is modified to include the effect of phase change and to treat the contact angle and the evaporative heat flux from the liquid microlayer on an immersed solid surface of a microfin. The numerical method is applied to clarify bubble growth and heat transfer characteristics on a surface including fin and cavity during nucleate boiling which have not been provided from the previous experimental studies. The effects of single fin, fin-cavity distance, and fin-fin spacing on the bubble dynamics are investigated. The micro-fin is found to affect the activation of cavity. The fin-cavity configuration is found to determine the bubble formation in a cavity. The vapor removal rate is also observed to significantly depend on the fin-fin spacing.

Numerical Study of Lateral Merger of Vapor Bubbles During Nucleate Pool Boiling

2003 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Numerical Study ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Three Dimensions ◽  
Navier Stokes ◽  
Wall Heat Transfer ◽  
Simple Method

Nucleate boiling is one of the most efficient modes of heat transfer. At the start of nucleate boiling, isolated bubbles appear on the heating surface, the regime known as partial nucleate boiling. Transition from isolated bubbles to fully developed nucleate boiling occurs with increase in wall superheat, when bubbles begin to merge in vertical and lateral directions. The laterally merged bubbles form vapor mushrooms, which stay attached to the heater surface via numerous vapor stems. The present study is performed to numerically analyze the bubble dynamics and heat transfer associated with lateral bubble merger during transition from partial to fully developed nucleate boiling. The complete Navier-Stokes equations in three dimensions along with the continuity and energy equations are solved using the SIMPLE method. The liquid vapor interface is captured using the Level-Set technique. Calculations are carried out for multiple bubble-merger in a line and also in a plane and the bubble dynamics and wall heat transfer are compared to that for a single bubble. The results show that the merger process significantly increases the overall wall heat transfer. It is also found that the orientation of the bubbles strongly influences different heat transfer mechanisms.

A Numerical Study of Decoupled Bubble Dynamics in Nucleate Boiling

2009 ◽  
Vol 283-286 ◽  
pp. 329-334
Author(s):  
Muhammad Sajid ◽  
Rachid Bennacer
Keyword(s):  
Heat Transfer ◽  
Level Set ◽  
Bubble Dynamics ◽  
Stokes Equations ◽  
Numerical Study ◽  
Nucleate Boiling ◽  
Conservation Equation ◽  
Interface Motion ◽  
Energy Conservation Equation ◽  
Rate Of Evaporation

Nucleate boiling is an efficient mechanism of heat transfer. The rate of bubble growth and the subsequent bubble motion has a tremendous influence on heat transfer. The study of bubble dynamics is a coupled problem. The rate of evaporation controls the interface speed. One approach to study bubble dynamics is to decouple the problem from energy conservation equation and use an input value of rate of evaporation. The objective is to observe how irregular evaporation rate controls bubble dynamics and the shape of bubble and to study the local over-pressure. The level set method is used to track the liquid-vapor interface. The model consists of the Navier-Stokes equations which govern the momentum and mass balances and the level set equation which governs the interface motion due to phase change. The dynamics of a single bubble under different rates of evaporation and varying levels of gravity have been studied. The results of the numerical simulation show that this model adequately describes bubble dynamics in nucleate boiling, including conditions of microgravity.

A Numerical Study on Flow Boiling in Parallel Microchannels

2008 ◽  
Author(s):  
Jinho Jeon ◽  
Woorim Lee ◽  
Youngho Suh ◽  
Gihun Son
Keyword(s):  
Heat Transfer ◽  
Contact Angle ◽  
Bubble Dynamics ◽  
Numerical Study ◽  
Reverse Flow ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Two Phase ◽  
Flow And Heat Transfer ◽  
Parallel Microchannels

Flow boiling in parallel microchannels has received attention as an effective cooling method for high-power-density microprocessor. Despite a number of experimental studies, the bubble dynamics coupled with boiling heat transfer in microchannels is still not well understood due to the technological difficulties in obtaining detailed measurements of microscale two-phase flows. In this study, complete numerical simulation is performed to further clarify the physics of flow boiling in microchannels. The level set method for tracking the liquid-vapor interface is modified to include the effects of phase change and contact angle. The method is further extended to treat the no-slip and contact angle conditions on the immersed solid. Also, the reverse flow observed during flow boiling in parallel microchannels has been investigated. Based on the numerical results, the effects of channel shape and inlet area restriction on the bubble growth, reverse flow and heat transfer are quantified.

Nucleate Boiling Heat Transfer and Bubble Dynamics of Water-in-Polyalphaolefin Nanoemulsion

2018 ◽  
Author(s):  
Jiajun Xu ◽  
James McLaurin ◽  
Cyree Beckett
Keyword(s):  
Heat Transfer ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Pure Water ◽  
Nucleate Boiling ◽  
Temperature History ◽  
Distribution Data ◽  
Growth Data ◽  
Surrounding Water ◽  
Time Resolved

In this study, an experimental study of the nucleation heat transfer and bubble dynamics inside the Water-in-PAO nanoemulsion fluid has been performed. Synchronized highspeed video and infrared thermography are used here to capture time-resolved temperature distribution data for the boiling surface and direct visualization of the bubble cycle. Data gathered included measurements of bubble growth versus time, as well as temperature history of the heater surface underneath the bubbles. Our findings demonstrate a substantial increase in nucleate heat transfer (i.e., heat transfer coefficient), and significantly different bubble dynamics of nanoemulsion fluid compared to pure water. The bubble growth rate of the nanoemulsion lies in the diffusion-controlled regime, and the growth data fit a power law at n ≈ 0.3. This is similar to the authors’ previous study of a similar fluid and is very different from conventional fluids. While the heat transfer mechanisms behind are not completely understood yet, it is hypothesized that the interfacial structures and thermal transport between surfactant molecules surrounding water nanodroplets and the base PAO fluid at elevated temperature may contribute to that.

A Numerical Study of Quasi-Nucleate Boiling in Mini- and Micro Channels

2008 ◽  
Author(s):  
Y. Q. Zu ◽  
Y. Y. Yan
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Experimental Studies ◽  
Nucleate Boiling ◽  
Heated Wall ◽  
Channel Height ◽  
Multiphase Model ◽  
Rectangular Channels ◽  
Micro Channels ◽  
Mini Channels

In this paper, a numerical study of quasi-nucleate boiling in horizontal mini- and micro-channels is carried out. The numerical simulation which is based on the multiphase model of volume of fluid (VOF) method available in commercial CFD software (Fluent 6.1.18) aims to study the corresponding flow behaviors of nucleate bubbles generated from the tube walls in mini/micro channels so as to understand the surface dominated effect of micro/mini channels on nucleate bubbles and heat transfer. In the present simulation, water enters a 2D channels with a uniform velocity of 0.2m/s. In order to examine the effects of channels size on bubbles flow and heat transfer, numerical simulations for three types of rectangular channels which have the same length of 30mm but different channel height respectively at 5mm, 0.5mm and 0.2mm are carried out. To have the nucleate effect or a quasi-nucleation condition, bubbles are generated approximately by injecting a small vapour bubble timely through an inlet located on the heated wall as the nucleate centre; meanwhile a transient vapour mass flow, based on the boiling parameters, is applied to approximate the bubble growth. While, the boiling parameters used in the simulation, such as bubble frequency, departure diameter and so on, are obtained by the calculations of correlations available from previous experimental studies.

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