Single Bubble Dynamics During Flow Boiling on a Horizontal Surface at Different Gravity Levels

2005 ◽  
Author(s):  
Ding Li ◽  
Vijay K. Dhir
Keyword(s):  
Bubble Dynamics ◽  
Flow Boiling ◽  
Functional Dependence ◽  
Thin Liquid Film ◽  
Bubble Diameter ◽  
Growth Period ◽  
Contact Angles ◽  
Horizontal Surface ◽  
Level Set Function ◽  
Lift Off

Complete numerical simulations of bubble dynamics including bubble growth, sliding motion, and bubble lift-off from a horizontal surface have been carried out for different gravity levels and flow velocities. In the model, the region of interest is divided into micro and macro regions. The micro region is the ultra thin liquid film that forms between the solid and evolving vapor-liquid interface. The region occupied by vapor and liquid—excluding the micro layer—is designated as the macro region. Complete conservation equations of mass, momentum, and energy for both phases are solved in this region. The interface shape is obtained by solving for the Level-Set function. The advancing and receding contact angles obtained from experiments are used as input to the model. The predictions are compared with data from experiments. The functional dependence of bubble diameter at departure and growth period on gravity is found to weaken with the increase in flow velocity.

scholarly journals Prediction of Bubble Departure in Forced Convection Boiling with a Mechanistic Model That Considers Dynamic Contact Angle and Base Expansion

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1950 ◽  
Author(s):  
Hamed Setoodeh ◽  
Wei Ding ◽  
Dirk Lucas ◽  
Uwe Hampel
Keyword(s):  
Bubble Dynamics ◽  
Flow Boiling ◽  
Mechanistic Model ◽  
Dynamic Contact Angle ◽  
Dynamic Contact ◽  
Contact Angles ◽  
Force Balance ◽  
Heating Wall ◽  
System Pressure ◽  
Lift Off

A mechanistic model for bubble dynamics in flow boiling that is based on a force balance approach for a growing bubble is introduced. It considers the evaporation of the microlayer underneath the bubble, thermal diffusion and condensation around the bubble cap as well as dynamic inclination and contact angles between the bubble and the heating wall. It requires no recalibration of parameters to predict the bubble growth. Validation against different experimental flow boiling data was carried out with no case-dependent recalibration and yielded good agreement. The simulations confirmed the dependency of bubble departure and lift-off diameters on different parameters such as heat flux, liquid properties, subcooling temperature, system pressure, inclination angle of channel, channel geometry and mass flow rate.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

Stability Criteria of the Steady Flow of a Liquid Containing Bubbles Along a Nozzle

2001 ◽  
Vol 123 (4) ◽  
pp. 836-840 ◽  
Author(s):  
A. Crespo ◽  
J. Garcı´a ◽  
J. Jime´nez-Ferna´ndez
Keyword(s):  
Bubble Dynamics ◽  
Volume Fraction ◽  
Flow Instability ◽  
Functional Dependence ◽  
Bubble Diameter ◽  
Critical Value ◽  
Stability Criteria ◽  
Flow Through ◽  
Gas Volume Fraction ◽  
Gas Volume

The steady cavitating flow through a converging-diverging nozzle is considered. A continuum model is assumed with the Rayleigh-Plesset equation to account for the bubble dynamics. A similar problem has been studied previously by Wang and Brennen, and they found that if the upstream gas volume fraction of the bubbles exceeds a critical value there is flashing flow instability. In the present work, a perturbation analysis is made introducing a small parameter, ε, that is the ratio of the initial bubble diameter to the length scale of the nozzle. As a result of this analysis, the critical value of the upstream void fraction is calculated as a function of the several parameters appearing in the problem, and turns out to be very small and proportional to ε3. A correlation is proposed giving explicitly the functional dependence of this critical value.

Numerical Study of Single Bubble Dynamics During Flow Boiling

2007 ◽  
Vol 129 (7) ◽  
pp. 864-876 ◽  
Author(s):  
Ding Li ◽  
Vijay K. Dhir
Keyword(s):  
Bubble Dynamics ◽  
Numerical Study ◽  
Flow Boiling ◽  
Three Dimensional ◽  
Horizontal Surface ◽  
Single Bubble ◽  
Bulk Liquid ◽  
Interface Heat Transfer ◽  
Single Bubble Dynamics ◽  
Energy Equations

Three-dimensional numerical simulation of single bubble dynamics during nucleate flow boiling is performed in this work. The range of bulk liquid velocities investigated is from 0.076to0.23m∕s. The surface orientations at earth normal gravity are varied from an upward facing horizontal surface to vertical through 30, 45, and 60deg. The gravity levels on an upward facing horizontal surface are varied from 1.0ge to 0.0001ge. Continuity, momentum, and energy equations are solved by finite difference method and the level set method is used to capture the liquid-vapor interface. Heat transfer within the liquid micro layer is included in this model. The numerical results have been compared with data from experiments. The results show that the bulk flow velocity, heater surface orientation, and gravity levels influence the bubble dynamics.

Experimental Study of Effect of Nucleation Site Size on Bubble Dynamics during Nucleate Pool Boiling Heat Transfer

2014 ◽  
Vol 592-594 ◽  
pp. 1596-1600 ◽  
Author(s):  
Abdul Najim ◽  
Anil R. Aacharya
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Bubble Dynamics ◽  
Bubble Diameter ◽  
Pool Boiling ◽  
Growth Period ◽  
Nucleation Site ◽  
Hypodermic Needle ◽  
Nucleate Pool Boiling ◽  
Pool Boiling Heat Transfer

In this paper, effect of nucleation site size on bubble dynamics during nucleate pool boiling heat transfer in saturated water is studied experimentally. Single bubble was generated using right angle tip of a hypodermic needle as a nucleation site. The hypodermic needles were used of inner diameters 0.413mm, 0.514mm, and 0.603 mm with a constant depth of 25mm. The bubble dynamics was studied using SONY Cyber-shot DSC-H100 camera operating at 30 frames per second at atmospheric pressure and at a wall superheat of 5K. The results show that, bubble diameter, bubble height and bubble volume increases with increase in diameter of nucleation site. The bubble growth period is found to be dependent on nucleation site size, and it decreases with increase in diameter of nucleation site. This happens because as volume of vapor bubble increases, buoyancy force starts dominates the capillary force and bubble detaches earlier. Effect of nucleation site size on bubble departure diameter and bubble release frequency is also discussed.

Mechanistic Prediction of Nucleate Boiling Heat Transfer–Achievable or a Hopeless Task?

2005 ◽  
Vol 128 (1) ◽  
pp. 1-12 ◽  
Author(s):  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Active Sites ◽  
Bubble Dynamics ◽  
Functional Dependence ◽  
Bubble Diameter ◽  
Nucleate Boiling ◽  
Complex Nature ◽  
The Past ◽  
Nucleation Sites ◽  
Nucleate Boiling Heat Transfer

Over the last half of the twentieth century, a number of purely empirical and mechanism-based correlations have been developed for pool nucleate boiling. Empirical correlations differ from each other substantially with respect to the functional dependence of heat flux on fluid and surface properties, including gravity. The mechanism-based correlations require knowledge of the number density of active sites, bubble diameter at departure, and bubble-release frequency. However, because of the complex nature of the subprocesses involved, it has not been possible to develop comprehensive models or correlations for these parameters. This, in turn, has led to the pessimistic view that mechanistic prediction of nucleate boiling is a hopeless task. However, there is an alternative to the past approaches—complete numerical simulation of the boiling process. Value of this approach for bubble dynamics and associated heat transfer is shown through excellent agreement of predictions with data obtained on microfabricated surfaces on which active nucleation sites can be controlled.

Numerical Simulation of Bubble Growth During Nanofluid Flow Boiling in a Microchannel

2014 ◽  
Author(s):  
Arman Khalighi ◽  
Matthew Blomquist ◽  
Abhijit Mukherjee
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Contact Angles ◽  
Electronic Systems ◽  
Simulation Based ◽  
Fluid Media ◽  
Thermo Physical Properties ◽  
Current Heat

In recent years, heat dissipation in micro-electronic systems has become a significant design limitation for many component manufactures. As electronic devices become smaller, the amount of heat generation per unit area increases significantly. Current heat dissipation systems have implemented forced convection with both air and fluid media. However, nanofluids may present an advantageous and ideal cooling solution. In the present study, a model has been developed to estimate the enhancement of the heat transfer when nanoparticles are added to a base fluid, in a single microchannel. The model assumes a homogeneous nanofluid mixture, with thermo-physical properties based on previous experimental and simulation based data. The effect of nanofluid concentration on the dynamics of the bubble has been simulated. The results show the change in bubble contact angles due to deposition of the nanoparticles has more effect on the wall heat transfer compared to the effect of thermo-physical properties change by using nanofluid.

Observation and modelling of bubble dynamics in isolated bubble regime in subcooled flow boiling

2018 ◽  
Vol 335 ◽  
pp. 400-408 ◽  
Author(s):  
Tomio Okawa ◽  
Kazuhiro Kaiho ◽  
Shintaro Sakamoto ◽  
Koji Enoki
Keyword(s):  
Bubble Dynamics ◽  
Flow Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Bubble Regime
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