Bubble Dynamics During Boiling in Polydimethylsiloxane (PDMS) Microchannels With Wire Heater

2009 ◽  
Author(s):  
Yanyan Lu ◽  
Hao Wang ◽  
Yuhui Li
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
High Speed ◽  
Bubble Dynamics ◽  
Ccd Camera ◽  
Porous Polymer ◽  
Platinum Wire ◽  
Wire Heater ◽  
Pdms Microchannel ◽  
Efficient Heat Transfer

Boiling is an important phase-change mode with efficient heat transfer and complex bubble dynamics. A microchannel fabricated using Polydimethylsiloxane (PDMS), which is a porous polymer, performed different boiling behavior and heat transfer compared to traditional glass or silica microchannels. A very fine platinum wire embedded in the PDMS microchannel served as a heater. Bubble dynamics was visualized and recorded through a high speed CCD camera equipped in a microscope. Boiling curves were concluded, and different boiling regimes were classified. The featured phenomena of droplets cycle in big bubbles were observed and analyzed.

Thermal Bubble Dynamics Under the Effect of Acoustic Vibration

2009 ◽  
Author(s):  
Xiaopeng Qu ◽  
Huihe Qiu
Keyword(s):  
Heat Transfer ◽  
Acoustic Field ◽  
Vapor Bubble ◽  
Boiling Heat Transfer ◽  
High Speed ◽  
Bubble Dynamics ◽  
Acoustic Vibration ◽  
Micro Electro Mechanical System ◽  
Mems Technology ◽  
Enhanced Boiling

The effect of acoustic field on the dynamics of micro thermal bubble is investigated in this paper. The micro thermal bubbles were generated by a micro heater which was fabricated by standard Micro-Electro-Mechanical-System (MEMS) technology and integrated into a mini chamber. The acoustic field formed in the mini chamber was generated by a piezoelectric plate which was adhered on the top side of the chamber’s wall. The dynamics and related heat transfer induced by the micro heater generated vapor bubble with and without the existing of acoustic field were characterized by a high speed photograph system and a micro temperature sensor. Through the experiments, it was found that in two different conditions, the temperature changing induced by the micro heater generated vapor bubble was significantly different. From the analysis of the high speed photograph results, the acoustic force induced micro thermal bubble movements, such as forcibly removing, collapsing and sweeping, were the main effects of acoustic enhanced boiling heat transfer. The experimental results and theoretical analysis were helpful for understanding of the mechanisms of acoustic enhanced boiling heat transfer and development of novel micro cooling devices.

Transient Thermal Characteristics for a Liquid Drop Impacting a Hot PCM Substrate

2018 ◽  
Author(s):  
Abdul Ahad Khan ◽  
Dilip Choudhary ◽  
Abhishek Basavanna ◽  
Salman Najmee ◽  
Jessica Crisantes ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
High Speed ◽  
Liquid Drop ◽  
Imaging Techniques ◽  
Thermal Characteristics ◽  
Heat Of Fusion ◽  
Performance Parameters ◽  
Transient Heating ◽  
Thermal Transients

The physics of the transient behavior of liquid drops impacting hot or cold surfaces are of significance in many different applications such as spray cooling, aircraft icing, etc. Further, the transient heating and cooling of vapor spots and liquid patches is of significance in determining the heat transfer performance parameters in phase change processes such as boiling and condensation. The thermal transients in all these processes are primarily dictated by the passive thermal properties of the solid substrate (e.g. thermal conductivity, specific heat) and by the flow conditions. An active control (or manipulation) of these thermal transients could provide a means to enhance the performance parameters in various phase change-based heat transfer processes. In this study, we experimentally explore the effect of a solid-liquid phase change material (PCM) coating on the thermal characteristics of a liquid drop impacting a hot surface. High-speed optical and infrared imaging techniques are employed for visualizing the flow and measuring the temperatures, respectively. The PCM, depending on its melting temperature and due to its latent heat of fusion, disrupts the normal process of the heating of the drop and cooling of the substrate. The insights obtained from these findings can have a significant impact on several technologies in the areas of phase change-based heat transfer and thermal management.

Effect of a High Electric Field on the Thermal and Phase Change Characteristics of an Impacting Drop

2019 ◽  
Author(s):  
Abhishek Basavanna ◽  
Prajakta Khapekar ◽  
Navdeep Singh Dhillon
Keyword(s):  
Heat Transfer ◽  
Electric Field ◽  
Phase Change ◽  
Electric Fields ◽  
High Speed ◽  
Impact Behavior ◽  
Liquid Drops ◽  
Active Interest ◽  
Post Impact ◽  
High Electric Fields

Abstract The effect of applied electric fields on the behavior of liquids and their interaction with solid surfaces has been a topic of active interest for many decades. This has important implications in phase change heat transfer processes such as evaporation, boiling, and condensation. Although the effect of low to moderate voltages has been studied, there is a need to explore the interaction of high electric fields with liquid drops and bubbles, and their effect on heat transfer and phase change. In this study, we employ a high speed optical camera to study the dynamics of a liquid drop impacting a hot substrate under the application of high electric fields. Experimental results indicate a significant change in the pre- and post-impact behavior of the drop. Prior to impact, the applied electric field elongates the drop in the direction of the electric field. Post-impact, the recoil phase of the drop is significantly affected by charging effects. Further, a significant amount of micro-droplet ejection is observed with an increase in the applied voltage.

Nucleate Boiling From Micro-Machined Surfaces

2003 ◽  
Author(s):  
Adrian M. Holland ◽  
Colin P. Garner
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Imaging System ◽  
Laser System ◽  
Ccd Camera ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Frame Rate ◽  
High Speed Imaging ◽  
Machined Surfaces

This paper discusses the production and use of laser-machined surfaces that provide enhanced nucleate boiling and heat transfer characteristics. The surface features of heated plates are known to have a significant effect on nucleate boiling heat transfer and bubble growth dynamics. Nucleate boiling starts from discrete bubbles that form on surface imperfections, such as cavities or scratches. The gas or vapours trapped in these imperfections serve as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. In this work, special heated surfaces were manufactured by laser machining cavities into polished aluminium plates. This was accomplished with a Nd:YAG laser system, which allowed drilling of cavities of a known diameter. The size range of cavities was 20 to 250 micrometers. The resulting nucleate pool boiling was analysed using a novel high-speed imaging system comprising an infrared laser and high resolution CCD camera. This system was operated up to a 2 kHz frame rate and digital image processing allowed bubbles to be analysed statistically in terms of departure diameter, departure frequency, growth rate, shape and velocity. Data was obtained for heat fluxes up to 60 kW.m−2. Bubble measurements were obtained working with water at atmospheric pressure. The surface cavity diameters were selected to control the temperature at which vapour bubbles started to grow on the surface. The selected size and spacing of the cavities was also explored to provide optimal heat transfer.

Synchronized High-Speed Video and Infrared Thermometry Study of Bubble Dynamics During Nucleate Boiling of Nanoemulsion

2017 ◽  
Author(s):  
Robert Stephenson ◽  
Jiajun Xu
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Bubble Dynamics ◽  
Nucleate Boiling ◽  
Bubble Nucleation ◽  
Heat Diffusion ◽  
Temperature History ◽  
Pure Ethanol ◽  
High Speed Video ◽  
Significant Difference

In this study, a combination of synchronized high-speed video (HSV) and infrared (IR) thermography was used to characterize the nucleation, growth and detachment of bubbles generated during nucleate boiling inside the nanoemulsion fluid. The Ethanol/Polyalphaolefin nanoemulsion fluid was formed by dispersing ethanol nanodroplets into base fluid Polyalphaolefin, in which these nanodroplets can serve as the pre-seed boiling nuclei. With this unique combination, it allows controlled nucleation, time-resolved temperature distribution data for the boiling surface and direct visualization of the bubble cycle to track bubble nucleation and growth. Data gathered included measurements of bubble growth versus time, as well as 2D temperature history of the heater surface underneath the bubbles. Our findings demonstrate a significant difference of bubble dynamics between the nanoemulsion fluid and pure ethanol, which may also account for the substantial increase in heat transfer coefficient and critical heat flux of nanoemulsion fluid. It is also observed here that the bubbles occurred inside the nanoemulsion fluid appear to be more uniform and two orders-of-magnitude larger in size. While the growth rate of the bubbles inside pure ethanol was found to be heat diffusion controlled at a coefficient around ½, which however, dropped to be around 0.3 for nanoemulsion fluid. Further study on this unique system will help reveal its heat transfer mechanisms.

A Mathematical Model of Thermal Oil Recovery in Linear Systems

1965 ◽  
Vol 5 (03) ◽  
pp. 196-210 ◽  
Author(s):  
B.S. Gottfried
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Chemical Reaction ◽  
Oil Recovery ◽  
High Speed ◽  
Thermal Recovery ◽  
Recovery Processes ◽  
Three Phase ◽  
Three Phase Flow ◽  
Thermal Oil

Gottfried, B.S., Junior Member AIME, Gulf Research and Development Co., Pittsburgh, Pa. Introduction Thermal oil recovery refers to a class of recovery processes where heat is supplied to a reservoir to provide the necessary expulsive energy. This thermal energy can be supplied externally as steam or hot water, or it can be generated in situ by forward or reverse combustion. In either case, however, thermal recovery processes are characterized by the simultaneous flow of two or three fluid phases in a variable-temperature field, accompanied by possible chemical reaction or phase-change effects. Although a physical understanding of the thermal recovery processes is far from complete, it is possible to construct mathematical models which describe approximately all of the principal physical and chemical phenomena. However, attempts to solve such models, even with high-speed computers, involve formidable mathematical difficulties. Consequently, theoretical solutions have been obtained only for idealized cases in which important physical phenomena are neglected. For example, consider the process of forward in situ combustion. All such theories which have been developed consider only certain aspects of the Process, such as heat transfer, heat transfer with phase change, heat transfer with chemical reaction, or the hydrodynamics of three-phase flow. A general theory including all of the above phenomena has not been developed to date. This paper presents a unified theory of thermal recovery processes in linear systems. A mathematical model is developed which explicitly includes conduction-convection heat transfer with convective external heat loss, chemical reaction between air and oil, aqueous phase change, and the hydrodynamics of three-phase flow. A system of equations is developed which can be solved numerically on a high-speed digital computer, resulting in predicted temperature, pressure, and saturation histories in space and time. The model allows a more detailed simulation of thermal recovery tube experiments than had previously been possible. THEORETICAL DEVELOPMENT Consider the linear flow of gas, water and oil in a homogeneous porous medium. Assume that the oil will react with gaseous oxygen, and that mass is transferred between the water and gas phase by evaporation or condensation. SPEJ P. 196ˆ

Dynamics and Breakup Regime of a Vapor Bubble Traveling Through a Heated T-Shaped Branching Microchannel

2020 ◽  
Author(s):  
Zhe Yan ◽  
Shanshan Li ◽  
Lichun Li ◽  
Bili Deng ◽  
Zhenhai Pan
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Vapor Bubble ◽  
Bubble Dynamics ◽  
Surface Force ◽  
Bubble Motion ◽  
Heat Transfer Characteristics ◽  
Bubble Breakup ◽  
Wall Superheat ◽  
Frame Method

Abstract Dynamics and breakup characteristics of a vapor bubble when traveling through the T-junction of a heated branching microchannel are numerically investigated with the Volume of Fluid-Continuum-Surface-Force (VOF-CSF) method. The moving reference frame method, which has been demonstrated to help suppressing the unphysical spurious velocity around the liquid-vapor interface (Numer. Heat Trans. 67, 1–12), is employed and coupled to the VOF-CSF model. In order to evaluate the influence of the wall heating on the growth and breakup of vapor bubble, the saturated-interface-volume phase change model is further coupled to account for the phase change on the bubble interface. The numerical model is first validated against experimental results in literature. Then the effect of wall superheat on bubble dynamics and heat transfer coefficient is investigated. Bubble motion, growth, breakup and heat transfer characteristics at different wall superheats are analyzed in detail. Four bubble breakup regimes are observed, namely non-breakup (NB), breakup with tunnel (TB), combined breakup (CB) and breakup with permanent obstruction (OB). The present study reveals the transport details around an evaporating vapor bubble and helps understanding the underlying physics of bubble behaviors when traveling through a T-shaped branching microchannel.

Boiling Heat Transfer Using Spatially-Variant and Uniform Microporous Coatings

2019 ◽  
Author(s):  
Quang N. Pham ◽  
Youngjoon Suh ◽  
Bowen Shao ◽  
Yoonjin Won
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Management ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Bubble Nucleation ◽  
Vapor Flow ◽  
Inverse Opal ◽  
Two Phase ◽  
Spatially Variant

Abstract Two-phase thermal management offers cooling performance enhancement by an order of magnitude higher than single-phase flow due to the latent heat associated with phase change. Among the modes of phase-change, boiling can effectively remove massive amounts of heat flux from the surface by employing structured or 3D microporous coatings to significantly enlarge the interfacial surface area for improved heat transfer rate as well as increase the number of potential sites for bubble nucleation and departure. The bubble dynamics during pool boiling are often considered to be essential in predicting heat transfer performance, causing it to be a field of significant interest. While prior investigations seek to modulate the bubble dynamics through either active (e.g., surfactants, electricity) or passive means (e.g., surface wettability, microstructures), the utilization of an ordered microporous architecture to instigate desirable liquid and vapor flow field has been limited. Here, we investigate the bubble dynamics using various spatial patterns of inverse opal channels to induce preferential heat and mass flow site in highly-interconnected microporous media. A fully-coated inverse opal surface demonstrates the intrinsic boiling effects of a uniform microporous coating, which exhibits 156% enhancement in heat transfer coefficient in comparison to the polished silicon surface. The boiling heat transfer performances of spatially-variant inverse opal channels significantly differ based on the pitch spacings between the microporous channels, which dictate the bubble coalescent behaviors and bubble departure characteristics. The elucidated boiling heat transfer performances will provide engineering guidance toward designing optimal two-phase thermal management devices.

Inner Phase Change Behavior of Small Liquid Droplet on Heated Solid Surface

2011 ◽  
Author(s):  
Gui Lu ◽  
Yuan-Yuan Duan ◽  
Xiao-Dong Wang
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Bubble Dynamics ◽  
Liquid Droplet ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Boiling Regime ◽  
Change Behavior ◽  
Cyclical Process ◽  
Transient Boiling

An experimental investigation was conducted to visually observe the transient boiling in an individual water droplet on different heated solid surfaces, covering the free surface evaporation, nucleate, transition and spheroidal boiling regime. Diversified bubble dynamics, phase change and heat transfer behaviors for different boiling regimes of droplet were discussed in present work. In nucleate boiling regime, plenty nucleate bubbles with uniform diameters were confined within the bottom of the droplet, enhancing the heat transfer and cooling performance. The surface properties had great effects on the bubble dynamics in this regime. In the transition boiling regime, the phase change behaviors of a droplet displayed a cyclical process, restricted, sole-bubble and metastable cyclical styles were observed in the experiments. A vapor film between the droplet and surface exists in the spheroidal boiling regime, leading to the random movement of droplet above the heated surface and prolonging the lifetime of droplet significantly.

Characteristics of Nucleation and Bubble Growth During Microscale Boiling

2005 ◽  
Author(s):  
Yong Tian ◽  
Jiang-Tao Liu ◽  
Xiao-Feng Peng
Keyword(s):  
Bubble Growth ◽  
High Speed ◽  
Bubble Dynamics ◽  
Ccd Camera ◽  
Initial Position ◽  
Length Scale ◽  
Formation Theory ◽  
Nucleus Formation ◽  
Microlayer Evaporation ◽  
Parallel Microchannels

In this paper, both nucleus formation and bubble growth during boiling in microchannels were investigated. A series of visualized experiments were conducted to observe the boiling nucleation and bubble dynamics restricted within parallel microchannels on a silicon wafer. The channels were rectangular and had selected length scale ranging from 50 to 100 microns. A high-speed CCD camera was employed together with a microscope to dynamically record the boiling images. The rates of bubble growth were measured in the channels. The phase change nucleus formation theory was used to determine the initial position of the bubble. The bubble growth rate was described by two ordinary differential equations deduced from the microlayer evaporation theory. The calculation and experimental results were reasonably coincided.

Sign in / Sign up

Export Citation Format

Share Document