Bubble Lifecycle During Heterogeneous Nucleate Boiling

2018 ◽  
Vol 140 (12) ◽  
Author(s):  
Vinod Pandey ◽  
Gautam Biswas ◽  
Amaresh Dalal ◽  
Samuel W. J. Welch
Keyword(s):  
Numerical Simulations ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Flat Surface ◽  
Nucleate Boiling ◽  
Subcooled Boiling ◽  
Subcooled Liquid ◽  
Superheat Temperature ◽  
Microlayer Evaporation ◽  
Liquid States

Heterogeneous nucleate boiling over a flat surface has been studied through complete numerical simulations. During the growth and departure of the vapor bubble, the interface is tracked following a coupled level-set and volume of fluid approach. A microlayer evaporation model similar to Sato and Niceno [“A depletable microlayer model for nucleate pool boiling,” J. Comput. Phys. 300, 20–52 (2015)] has been deployed in this investigation. A detailed study of the changes in microlayer structure as a result of different modes of boiling scenario has been performed. The departure diameter is found to increase with an increase in substrate superheat. The predicted departure diameter has been compared with the available experimental and analytical results. A power-law curve has been obtained for depicting the growth rate of bubble depending on the degree of superheat at the wall. The space–time averaged wall-heat flux at different values of superheat temperature of substrate is obtained. Bubble growth during subcooled boiling at a low and intermediate subcooled degree has been observed through direct numerical simulations. The variations in bubble dynamics after departure in saturated and subcooled liquid states have been compared.

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.

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.

Experimental Observation on Bubble Dynamics During Nucleate Boiling in Micro/Mini/Macro Tubes

2011 ◽  
Author(s):  
Di Wu ◽  
Ying Piao ◽  
Yuan-yuan Duan ◽  
Zhen Yang
Keyword(s):  
Thin Film ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Thin Liquid Film ◽  
Nucleate Boiling ◽  
Tube Diameter ◽  
Heated Wall ◽  
Growth Stages ◽  
Positive Interaction ◽  
Liquid Vapor

A series of experiments was conducted to observe nucleate boiling phenomena in horizontal tubes with inner diameters varying from 0.05 mm to 3.0 mm. Diverse behaviors of bubble growth were explored, identified by which tubes were classified into micro, mini and macro scales. In micro tubes (Di ≤ 200 μm), the liquid was emitted instantaneously with extremely fast liquid-vapor interfacial movement, referred as explosive emission boiling phenomenon. It is hard to record bubble growth process with high speed camera. In mini tubes (200 μm < Di < 2.5 mm), though liquid was also emitted outsides, the interface moves relative slow and the whole process of bubble growth can be observed. Two distinct stages, referred as spherical and oblate bubble growth stages, were divided. In macro tubes (Di ≥ 2.5 mm), only spherical bubble growth stage exists and the growth rate is much smaller than that in mini tubes. Furthermore, the mechanism of diverse bubble dynamics was analyzed. In mini/micro tubes, decreasing tube diameter can trigger a transition from spherical to oblate bubble growth and consequently establish a thin film between liquid-vapor interface and heated wall. The thin liquid film evaporates vigorously and accelerates the interfacial movement, which reversely enhances evaporation of thin film. A positive interaction between interfacial movement and thin film evaporation establishes, resulting in the interface moving faster and faster and consequently emitted liquid outsides instantaneously. In macro tubes, as tube diameter increasing, the transition and sequential positive interaction can not be raised. Hence, the bubble maintains growing spherically as that in pool boiling.

Numerical Simulation of Dynamics and Heat Transfer Associated With a Single Bubble in Subcooled Boiling and in the Presence of Noncondensables

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Jinfeng Wu ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Thermocapillary Convection ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Saturation Temperature ◽  
Subcooled Boiling ◽  
Bubble Liquid ◽  
Subcooled Liquid ◽  
Noncondensable Gases ◽  
Induced Flow

During phase change at the bubble-liquid interface, under subcooled boiling conditions, noncondensable gases dissolved in the liquid will be injected into the bubble along with vapor. Due to heat transfer into subcooled liquid, vapor will condense in the upper regions of the bubble while noncondensables will continue to accumulate. Subsequently, thermocapillary convection caused by nonuniform saturation temperature at the interface may occur. The aim of this work is to investigate the effects of noncondensables on heat transfer and bubble dynamics. The numerical results show that the effects of noncondensables on 5°C subcooled boiling of water are minor in terms of the equilibrium bubble diameter and overall Nusselt number. However, induced flow pattern around the bubble is altered, especially under reduced gravity conditions.

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.

Numerical Simulation of Bubble Dynamics in the Presence of Boron in the Liquid

2001 ◽  
Author(s):  
Qiang Bai ◽  
V. K. Dhir
Keyword(s):  
Numerical Simulation ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Thin Liquid Film ◽  
Dynamic Change ◽  
Nucleate Boiling ◽  
Reactor Power ◽  
Vapor Interface ◽  
Fuel Rod ◽  
Liquid Vapor

Abstract Deposition of boron on the fuel rod cladding during boiling of water containing boron can depress the neutron flux and lead to a decrease in nuclear reactor power output. There is practically little precise information on the temperature field, the gradients of chemical concentration and deposition of boron on the cladding surface. The objective of the present work is to simulate the nucleate boiling process along with velocity, temperature and concentration fields of aqueous boron in the vicinity of the cladding of a fuel rod. As a first step in solving the complete problem, two-dimensional numerical simulation of a bubble growth on a horizontal surface is considered. A finite difference scheme is used to solve the equations governing conservation of mass, momentum, energy and species concentration. The calculation domain is divided into macro and micro regions. In macro-region, the governing equations are used to calculate the distributions of velocity, temperature, and concentration. The Level Set method is used to capture the evolving liquid-vapor interface. For micro-region, lubrication theory is used, which includes the disjoining pressure in the thin liquid film. The solutions for micro-region and macro-region are matched at the outer edge of the micro-layer. A dilute aqueous Boron solution is considered in the simulation. From numerical simulations, the dynamic change in concentration distribution of boron during the bubble growth shows that the precipitation of boron can occur near the advancing and receding liquid-vapor interface when the ambient boron concentration level is 0.003.

Advances in Understanding of Pool Boiling Heat Transfer—From Earth on to Deep Space

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Numerical Simulations ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Pool Boiling ◽  
Space Station ◽  
Nucleate Boiling ◽  
International Space ◽  
Pool Boiling Heat Transfer ◽  
Fundamental Understanding

In this work, the effectiveness of the numerical simulations in advancing fundamental understanding of bubble dynamics and nucleate pool boiling heat transfer is discussed. The results of numerical simulations are validated with experiments on ground, in parabolic flights and on the International Space Station (ISS). As such validation is carried out when the level of gravity is varied over seven orders of magnitude. It is shown that reduced gravity stretches the length and time scales of the process and generally leads to degradation of rate of heat transfer associated with nucleate boiling.

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