Simulation Of Bubble Growth Research Articles

A new microlayer depletion model for numerical simulation of bubble growth during nucleate boiling

In this study, a new microlayer depletion model was developed to simulate bubble growth during the nucleate boiling of water and ethanol. By improving the coupled volume-of-fluid and level set model, the macro-two-phase flow was accurately tracked, eliminating velocity jumps at the interface. The proposed model was validated against pool boiling measurements in water and ethanol at atmospheric pressure. The results demonstrated that the microlayer contributed approximately 15 and 33.17 % to the growth of water and ethanol bubbles, respectively. Under the influence of the interfacial temperature, the mass accommodation coefficient of water could vary from 0.004 to 0.027. Considering the impact of the interfacial temperature on the mass accommodation coefficient could reduce the prediction error of the evaporative thermal resistance from 17.2 to 4.67 %. Furthermore, the study revealed that the evaporative thermal resistance of the water is comparable to the microlayer conductive thermal resistance, whereas the maximum evaporative thermal resistance of ethanol is less than 5 % of the microlayer conductive thermal resistance and can be neglected.

Numerical study of bubble dynamics near a solid wall with a gas-entrapping hole

Bubble dynamics with highly nonlinear interactions between an oscillating bubble and gas-liquid interface in the vicinity of a rigid wall with a gas-entrapping hole were numerically investigated in this study. The evolution of a cavitation bubble and its interactions with the gas-liquid interface were simulated using a fully compressible mixture model for three-phase flow. The solver was developed based on a dual-time preconditioning technique coupled with an interface capturing method on a general curvilinear grid. To assess the capability of the solver, validation was done with experimental data on bubble growth and collapse near a flat rigid wall (γ=2.0), and near a rigid wall with a gas-entrapping hole (γ=1.2). Good agreements in comparisons of the bubble shape and equivalent bubble radius were achieved. Numerical simulations of bubble growth and collapse in proximity to a rigid wall with a hole at different standoff distances were then conducted. The examined results showed that the gas entrapped inside the hole has considerable effects on the formation and redirection of the liquid jet, as well as on the dynamics of the cavitation bubble. Unlike the bubble collapse near a flat solid wall, the liquid jet was directed far away from the solid wall with a gas-entrapping hole, and the jet velocity was significantly smaller than that of the flat solid wall. The simulated results also revealed a potential for improving the design and production of body surfaces, which are often damaged by the impact of the liquid jet caused by bubble collapse.

Molecular dynamics simulation of bubble growth under surface of tungsten under helium irradiation

Understanding the fuzz growth mechanism on tungsten (W) surface under the helium (He) particles irradiation is an important guide for structural design of the first wall materials. In this work, molecular dynamics simulation was used to explore the process of He bubble formation, growth and rupture under irradiation to understand the initial stage of fuzz nanostructure formation. It was found that He clusters had the most movable ability at the surface temperature around 800∼1800 K and thus big bubbles were favorable to be aggregated. We simulated the growth, rupture and merging of He bubbles to reproduce the process of protrusion's formation on the surface which induced the formation of fuzz nanostructure. It was found that the shallow bubble burst led to the pinhole in surface layer. The dislocation slip in the growth process of deep bubbles was the main factor for the configurations of protrusion on surface. It mainly pushes the W above He bubble along the <111> directions, while the different surfaces have different relation with the <111> directions. Thus, the different morphology of protrusion induced by the bubble appeared on different surfaces as observed in experiments.

Extension of the Simulation Model of Bubble Growth during Phase Change Heat Transfer Using Volume of the Fluid Flow Model

Nucleate boiling is used in numerous engineering applications, such as the chemical, manufacturing, thermal, nuclear, and electronic industries. This research paper deals with the numerical analysis of bubble growth using a fluid flow model. This physical phenomenon of bubble growth has not been discussed mechanically and does not throw light on empirical models. We are discussing this phenomenon in another way to get the required results in this paper. Simulation of bubble growth is already published by measuring the volume of fluid flow; the method is known as VOFF tracking method. Lee’s model has already discussed the phase change that occurs due to evaporation and condensation of the fluid. We have used the method in which the equation terms involving energy and mass source caused by phase change are incorporated into the control equations by additional subroutines written in C language. We have mentioned in detail the results of simulating mass transfer caused by phase change and the effect of subcooling on bubble growth. The results thus obtained show that the subcooling effect prevents the growth of bubbles from growing due to the certain amount of bubble caps in the subcooled area. The effect of evaporation of the liquid increases the size of the bubbles in both the subcooled and the superheated zone.

Phase-field simulations of fission gas bubbles in high burnup UO2 during steady-state and LOCA transient conditions

To improve the economics of commercial light water reactors, increased understanding of UO2 nuclear fuel with the high burnup structure (HBS) is required in both steady-state and transient conditions. Here, a phase-field model of the fission gas bubble microstructure in nuclear fuel is developed based on the Kim-Kim-Suzuki (KKS) formulation and implemented in Idaho National Laboratory’s Marmot application for phase-field simulation of nuclear materials. The model includes the effects of gas pressure and the surface tension of the bubble-fuel matrix interface for arbitrary interfacial curvature. Simulations of bubble growth in the HBS region during steady-state conditions showed that initially overpressurized bubbles decreased in pressure during growth, but still remained above equilibrium pressure. During a loss-of-coolant accident (LOCA) transient, simulations of bubbles in the HBS region showed that bubble size did not change significantly. The bubble pressure in response to the LOCA transient was calculated for a variety of bubble sizes, initial pressures, and external restraint pressures.

NUMERICAL SIMULATION OF BUBBLE GROWTH AND COLLAPSE IN POOL BOILING: EFFECT OF BUBBLE MOTION

NUMERICAL SIMULATION OF BUBBLE GROWTH AND COLLAPSE IN POOL BOILING: EFFECT OF BUBBLE MOTION

Numerical simulation of bubble growth in a supersaturated solution

In this paper, a Volume of Fluid (VOF) based approach to simulate the growth of a pre-existing bubble in a supersaturated solution is developed and implemented in OpenFOAMⓇ. The model incorporates the Compressive Continuous Species Transfer approach to describe the transport of dissolved gas and surface tension is treated using the Sharp Surface Force method. The driving force for bubble growth is defined using Fick’s 1st law and a Sherwood number based correlation. The source terms for the governing equations are implemented by extending the work by Hardt and Wondra, J. Comp. Phys. 227 (2008) 5871–5895. The predictions of the proposed solver is compared against theoretical models for bubble growth in supersaturated solutions. The effect of spurious currents, which are generated while modelling surface tension, on bubble growth is also investigated. The proposed approach is used to model the growth of a rising bubble in the supersaturated solution.

A simulation of bubble growth on heating surface in subcooled boiling water based on the heat flows derived by experiment

Two growth processes of individual bubble on heating surface in subcooled boiling water were numerically studied based on the heat flows derived by experiment. In the experiment, a high speed camera was used to photograph the growth and condensation process of a single bubble in low subcooling degree water under normal pressure. The bulk fluid temperature and the temperature of heating wall at the nucleation point were recorded. Based on the experimental data of the bubble condensation process, the convective heat transfer formula at the bubble cap was derived and the heat flow distributions during the whole process were obtained. Then a numerical simulation of the whole process was conducted according to the heat flows. The bubble size, bubble shape and temperature fields were obtained. The simulation results can confirm the rationality and correctness of the theoretical analysis, for the bubble size is highly close to the experiment data. The results also indicated that the evaporation at the bubble base accounts for more than 45% of the total evaporation, which is mainly contributed by microlayer.

A mathematical study of bubble dynamics in superheated sodium chloride solution

A mathematical study of bubble growth in the superheated binary solution with a non-volatile solute is conducted by solving the momentum, energy and species equations around the bubble. Additionally, the two-characteristic-parameter correlation (TCPC) model is used to identify the thermodynamic conditions at the bubble-solution interface. By considering a single bubble and ignoring the interactions between the bubbles, the bubble growth characteristics in the NaCl solution are analyzed in detail, and the effects of NaCl concentration and operating conditions on bubble growth are discussed. It is observed that the non-volatile solute of NaCl slows down the bubble growth process in the entire duration of the growth period due to the extension of delay time and reduction of the driving forces with increase of solute concentration. The effects of solute concentration on bubble growth cannot be entirely eliminated by modifying the operating conditions to give the same degree of superheat by compensating the boiling point elevation (BPE). The increase of solute concentration near the bubble at moderate or high superheated conditions has non-negligible influence on bubble growth. A revised Mikic-Rohsenow-Griffith (MRG) formula by considering the solute effect and the increase in solute concentration near the bubble surface is proposed to predict the bubble growth in salt solutions. The predictions from the revised formula agree well with the complete simulations of bubble growth at various salt concentrations.

Determination of modified polyamide 6's foaming windows by bubble growth simulations based on rheological measurements

ABSTRACTReactive extrusion was used to modify virgin polyamides 6 (v‐PA6) and to prepare chain extended PA6 (CE‐PA6) and long‐chain branched PA6 (LCB‐PA6) for the melt foaming process. This was done using a twin‐screw extruder and the following modifiers: a chain extender ADR‐4368 and a branching agent maleic anhydride grafted polypropylene. A reaction mechanism was proposed to explain the chain extension and long‐chain branching reactions and was verified by the Fourier transform infrared spectroscopy data. The analysis of the gel permeation chromatography data showed that LCB‐PA6 presented a strong increase in the molecular weight and in the dispersity index. Moreover, the rheological properties of the v‐PA6 and modified PA6 resins were characterized by a dynamic shear test. The LCB‐PA6 compared with CE‐PA6 showed much higher shear viscosity and longer characteristic relaxation times, indicating the presence of an LCB structure. A uniaxial elongation test showed that the LCB‐PA6 had the highest melt viscosity and melt strength as well as most obvious strain‐hardening behavior. A high‐pressure differential scanning calorimeter under compressed CO2 was used to investigate the PA6's crystallization properties so as to analyze its minimum temperature of foaming windows. The melt foamability of the CE‐PA6 and the LCB‐PA6 was verified by batch melt foaming experiments with CO2 as the blowing agent and maximum temperature of foaming windows was also quantitatively determined by numerical simulation of bubble growth based on the rheological measurements. The results showed that the LCB‐PA6 foams had a smaller cell diameter, a larger cell density, a greater expansion ratio, and wider foaming temperature window than the CE‐PA6. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48138.

Simulation of bubble growth during the foaming process and mechanics of the solid foam

Elastomeric foams are widely used in different types of applications where different material properties are of interest in each application. All of these properties are governed by the microstructure and the properties of the material matrix. Studying the evolution of the microstructure experimentally is extremely challenging. Thus, here we use direct numerical simulations to gain an insight into the changes that happen from the creation of the gas bubbles in the liquid state, until the solidification into a cellular morphology. Furthermore, the resulting microstructure is then used directly in simulations of solid mechanical testing to determine the mechanical properties of the foam. The matrix fluid is assumed to be Newtonian and incompressible. A linear elastic isotropic material model for the solidified polymer was used to obtain the solid foam properties. The foam was described by a representative volume element (RVE), where a small number of bubbles was randomly distributed. Using this approach, the RVE can describe the bulk behavior of the foam, while remaining computationally tractable. Microstructures with volumes fraction of over 90% (2D) and 45% (3D) are accurately captured. In addition, the influence that the bubble growth rate and the initial bubble distribution of the fluid simulations have on the solid foam properties was studied.

Evaluation of a diffuse interface treatment for pressure in phase change simulations using adaptive mesh refinement

Phase change computational simulations using a diffuse interface treatment for pressure were investigated in order to quantify the spurious currents and its consequences on the interface transport in the present paper. In addition, benchmarks were conducted with a sharp interface treatment for pressure. Namely, a Delta function method (Delta) was employed for the diffuse interface treatment and a ghost fluid method (GFM) for the sharp approach. An additional force term in the non-divergent form of the momentum equation is proposed for the first time in the literature, and its impact on interface motion during simulations of bubble growth by intense phase change has been quantified. In addition, the influence of recoil force on interface position was evaluated in simulations of water bubble condensation at near critical pressure. Finally, simulations of a complex industrial application were performed using the diffuse interface treatment, namely a case of film boiling with the development of Rayleigh–Taylor instability. Both interface treatments presented excellent results for the interface evolution in time. Even with the presence of some relevant spurious currents in the Delta method, the bubble evolution in time was accurately predicted. The sharp interface treatment potential was especially evident using a mass density flux of 1.0 kg/(m2 s) or higher. Therefore, a diffuse interface treatment for pressure has been presented as an appropriate strategy for most phase change simulations since the presence of the spurious currents did not disturb the interface position, and its magnitude was low for even moderate phase change intensities. The inclusion of the source term due to the additional force in the non-divergent form of the momentum equation and the recoil force term was irrelevant in the cases tested. Lastly, the film boiling simulation using the diffuse interface treatment revealed the possibility of treating complex 3D cases for industrial applications with this method.

A numerical simulation of single bubble growth in subcooled boiling water

Water-cooling blanket is closely related to system safety in future fusion reactor for it can cooling down the reactor. The process of cooling in water-cooling blanket may involve bubble generation under subcooled boiling condition. Although many researchers have investigated bubble generation numerically, the details of bubble generation in subcooled boiling remain unclear. In this paper a two-dimensional bubble growth simulation under subcooled nucleate boiling condition has been conducted using VOF (Volume of Fluid) method in ANSYS FLUENT. A phase change model was adopted by adding extra mass source term and energy source term to the Navier-Stokes equations in the cells adjacent to vapor-liquid interface. The variations of bubble contour before bubble departure, temperature fields, velocity fields and contribution of heat flux from superheated layer and subcooled fluid can be obtained by simulation. The results were compared with existing datum of visual experiment in previous literature to verify the validity of the simulation.

Numerical simulation of bubble growth on and departure from the heated surface by an improved lattice Boltzmann model

Abstract Based on the phase change model developed by lattice Boltzmann method (LBM), an improved source term which is responsible for phase change is proposed. The computation of the latent heat is taken into consideration to avoid the error and instability caused by the equation of state (EOS). Periodic bubble growth and departure from a heated surface during the boiling process is investigated based on the newly developed lattice Boltzmann model. Effects of gravity, contact angel and superheat on bubble departure diameter and release period under constant wall temperature conditions are illustrated. The three-phase contact line movements of the vapor bubble and the wall heat flux are also described. The results reflect the dynamic features and the influencing mechanism of bubble in boiling period, and this research lays the foundation of further studies on thermal-hydraulics and safety analysis by LBM.

Evaluation of Interfacial Heat Transfer Models for Flashing Flow with Two-Fluid CFD

The complexity of flashing flows is increased vastly by the interphase heat transfer as well as its coupling with mass and momentum transfers. A reliable heat transfer coefficient is the key in the modelling of such kinds of flows with the two-fluid model. An extensive literature survey on computational modelling of flashing flows has been given in previous work. The present work is aimed at giving a brief review on available theories and correlations for the estimation of interphase heat transfer coefficient, and evaluating them quantitatively based on computational fluid dynamics simulations of bubble growth in superheated liquid. The comparison of predictions for bubble growth rate obtained by using different correlations with the experimental as well as direct numerical simulation data reveals that the performance of the correlations is dependent on the Jakob number and Reynolds number. No generally applicable correlations are available. Both conduction and convection are important in cases of bubble rising and translating in stagnant liquid at high Jakob numbers. The correlations combining the analytical solution for heat diffusion and the theoretical relation for potential flow give the best agreement.

Quantitative morphological analysis and digital modeling of polydisperse anisotropic carbon foam

Digital models of open cell carbon foam often approximate pore space by a set of overlapping spheres. In this paper, we extend this strategy to overlapping ellipsoids of varying size and anisotropy. A typical application is demonstrated: After a carbon foam sample is digitized with a computed tomography (CT) scanner, pores are analyzed with respect to polydispersity and anisotropy. Digital foam is created in two steps. First, a heuristic bubble growth simulation yields an overlapping ellipsoid packing, representing large pores. Small pores are then added to the remaining material. Finally, sample and digital model are compared by Finite Element (FE) analysis. Our results show that the foam model agrees well with the analyzed sample when considering pore statistics. However, mechanical simulations show differences, with an average effective elastic modulus of 0.341 GPa for the sample, compared to 0.153 GPa for the model. The approach of digital foam allows to assess the potential and limitation of diverse analysis techniques for CT scans of foam and hence gives respective limits. FE simulations help to identify accurateness of digital models.

Simulations of bubble growth and interaction in high viscous fluids using the lattice Boltzmann method

Phenomena of growth, coalescence and breakdown of bubbles within high viscous fluids are of great interest in the fluid dynamics of multiphase fluids because of their industrial relevance, e.g. in polymer, metal alloy and food processing fields. The dynamics of multiple bubble growth in hot viscous fluids is a complex issue governed by pressure forces, vapour diffusion, surface tension and viscous forces. Effects of water evaporation from the mixture surface are responsible for phenomena like glass transition, viscous increase and dough solidification. This article presents Lattice Boltzmann simulations of nucleating bubbles with large density ratio, that grow and interact in a hot high-viscous fluid. The work focuses on the first phases of the bubble expansion, neglecting the effects of evaporation. The simulations are performed using the Lattice Boltzmann Method (LBM). The Free Surface method is used to reduce a liquid/gas two-phase flow to a single-phase flow. The interface layer between gas and fluid is tracked using the volume of fluid (VOF) method. To avoid numerical instabilities due to the high viscosity (η=100Pas), the problem is scaled from physical to LB-units through non-dimensional quantities. The bubbles are initially punched randomly into the domain with a dimension comparable with the dimension of nucleation and are allowed to grow under an internal over-pressure. The simulated final structure of the bubbles is compared with images of a pure starch fluid, extruded under same conditions. It is shown as the final bubble distribution, matrix dimension and bubble diameters in the simulation are in good agreement with the real final conformation.

Experimental and numerical study on nucleate bubble deformation in subcooled flow boiling

Experimental and numerical study was conducted to investigate the bubble behaviors in subcooled flow nucleate boiling. The bubble behaviors in subcooled flow boiling in an upward annular channel were investigated in the range of subcooling degree 5–30K by visualization with high spatial and temporal resolutions using a high speed video camera and Cassegrain tele-microscope. Obvious deformation on the upstream side surface of the bubble during its growth process was frequently observed. This deformation phenomenon was caused by the condensation occurring at the upstream side bottom of the bubble, which results from the Marangoni flow along the bubble surface from the bubble bottom to the top. Since the Marangoni flow cannot be directly observed by the current experiments because it occurs in a very thin interface along the bubble surface, the numerical simulations of bubble growth and departure behaviors in subcooled flow boiling were carried out. As a result, it was confirmed that the bubble deformation was caused by the Marangoni flow along the bubble surface. Moreover, the phenomenon of wave propagation on the bubble surface during the condensation process was observed, and it can enhance the heat transfer between the bubble and the surrounding subcooled liquid.

Numerical simulation of bubble growth and liquid flow in a bubble jet micro actuator

Numerical models of fluid dynamics inside the micro actuator chamber and nozzle are presented. The models include ink flow from reservoir, bubble formation and growth, ejection through the nozzle, and dynamics of refill process. Since high tapered nozzle is one of the very important parameters for overall actuator performance design. The effects of variations of nozzle thickness, diameter, and taper angles are simulated and some results are compared with the experimental results. It is found that the ink droplet ejection through the thinner and high tapered nozzle is more steady, fast, and robust.

Variant of a volume-of-fluid method for surface tension-dominant two-phase flows

The capabilities of the volume-of-fluid method for the calculation of surface tension-dominant two-phase flows are explained. The accurate calculation of the interface remains a problem for the volume-of-fluid method if the density ratios of the fluids in different phases are high. The simulations of bubble growth is performed in water at near critical pressure for different degrees of superheat using combined level-set and volume-of fluid (CLSVOF) method. The effect of superheat on the frequency of bubble formation was analyzed. A deviation from the periodic bubble release is observed in the case of superheat of 20 K in water. The vapor-jet-like columnar structure is observed. Effect of heat flux on the slender vapor column has also been explained.