Bubble Growth Rate Research Articles

High stability enhanced ultrasonic microfluidic structure with flexible tip coupled bubbles

Ultrasonic microfluidic technology is a technique that couples high-frequency ultrasonic excitation to microfluidic chips. To improve the issues of poor disturbance effects with flexible tip structures and the susceptibility of bubbles to thermal deformation, we propose an enhanced ultrasonic microchannel structure that couples flexible tips with bubbles aiming to improve the disturbance effects and the stability duration. Firstly, we used finite element analysis to simulate the flow field distribution characteristics of the flexible tip, the bubble, and the coupling structure and obtained the steady-state distribution characteristics of the velocity field. Next, we fabricated ultrasonic microfluidic chips based on these three structures, employing 2.8 μm polystyrene microspheres as tracers to analyze the disturbance characteristics of the flow field. Additionally, we analyzed the bubble size and growth rate within the adhering bubbles and coupling structures. Finally, we verified the applicability of the coupling structure for biological samples using human red blood cells (RBCs). Experimental results indicated that, compared to the flexible tip and adhering bubble structures, the flow field disturbance range of the coupling structure increased by 439.53% and 133.48%, respectively; the bubble growth rate reduced from 14.4% to 3.3%. The enhanced ultrasonic microfluidic structure proposed in this study shows great potential for widespread applications in micro-scale flow field disturbance and particle manipulation.

Coupled Wall Boiling and Population Balance Model for High Void Fraction Flows Under Sub-Cooled Nucleate Boiling Regime: Model Development and Validation

Abstract The subcooled flow boiling of water in a vertical annulus channel is studied numerically at low-pressure conditions. The two-fluid model is developed with flow-regime dependent interfacial transfers for mass, momentum, and energy using the algebraic interfacial area density (AIAD) framework. A discrete population balance model is used to mechanistically determine the vapor bubble diameter in the flow channel by considering the bubble aggregation and breakup effects. Energy balance at the heated wall for the subcooled nucleate boiling is handled using a suitable wall boiling model. A coupling is achieved between the discrete population balance and the wall boiling model for the nucleation and the growth rate of the vapor bubbles along the heated wall. The developed model simulates the reference experimental cases of flow boiling in a vertical channel for various flow and thermal conditions. At low wall heat flux, the wall boiling generates vapor bubbles near the heated wall and within the bubbly flow regime. With an increase in the wall heat flux, the aggregation and evaporation cause the formation of larger bubbles, which progress toward the flow channel core region, a phase that is representative of the transitional flow regime. The model's capability to predict such flow regime transition is validated with the experimental results. The bubble aggregation is found to be dominant compared to the breakup, and thus, proper choice of the aggregation factor is important for the accurate prediction of vapor parameters for the subcooled flow boiling at low-pressure conditions.

Evaluation of hydrogen evolution activity by bubbles growth rates as descriptor

Evaluation of the electrocatalytic behavior in the high current density region is critical toward the applications in the industrial water electrolysis system. Here, we utilized the bubble growth rate as descriptor for evaluation of hydrogen evolution reaction. Ag electrode was selected as a model electrode. Pressure-controlled cell was used for the evaluation of the bubble behavior under the wider range in the overpotential. Hydrogen bubble evolution behavior was evaluated by video observation under electrochemical potential control. Even in the presence of the complex processes such as nucleation, growth and detachment of the bubbles, the hydrogen evolution behavior is evaluated with respect to the classical Tafel analyses even in high overpotential region. These analyses provide the methods for the rapid screening toward the material discovery of the green hydrogen production in high current density region.

Mechanistic impact of Stern bilayer-based electrolysis on the enhancement of pool boiling heat transfer

Pool boiling is a heat transfer method that utilizes phase change for efficient heat transfer, and enhancing its heat transfer intensity and understanding the mechanism is of great practical significance for refrigeration and microelectronics thermal management. This study employs experimental methods to innovatively use ionic surfactant modification on heating surfaces, building on the basis of strengthening heat transfer by generating hydrogen bubbles through water electrolysis to increase nucleation sites on the heating surface. The Stern double layer formed on the heating surface is utilized to control the growth rate and quantity of hydrogen bubbles, thus achieving controllable nucleation density on the heating surface. The study examines its impact on heat transfer efficiency and the onset of nucleate boiling (ONB). Results indicate that electrolysis can increase nucleation sites at low heat fluxes, thereby enhancing heat transfer. Using a CTAB solution at a concentration of 3200 ppm with an electrolytic current of 0.08A, under the Stern potential at saturated adsorption, the heat transfer coefficient increased by up to 3.16 times. Additionally, the superheat at ONB decreased from 12.6 K to 4.4 K under boiling heat flux. Therefore, utilizing electrolysis with the addition of surfactants to enhance rapid cooling of high-temperature surfaces provides a novel engineering application approach.

Two-phase closed thermosiphon with grooved the evaporator section applied for low-grade energy recovery: Thermo-hydrodynamic performance and potentials

High thermal conductivity and simple structure of two-phase closed thermosyphons (TPCTs) facilitate it extensively applied in low-grade thermal recovery, such like geothermal and solar energy exploitation. In present work, by incorporating threaded grooves into the evaporator section of the TPCTs, heat transfer performance could be significantly enhanced. Thermal transport mechanism of thermosyphons with various threaded groove structures was comprehensively investigated, and corresponding thermo-hydrodynamic performance was modelled through CFD/VOF simulations. Numerical procedures were validated well after comparison with experimental ones felled within 5.0 %. Under various heating power levels and filling ratios, heat transfer performance of thermosyphons with threaded grooves evidently surpassed that of smooth thermosyphons. Depending on delicate numerical results, critical point at 33 % filling ratio and 90 W heating power were confirmed that total thermal resistance of the grooved thermosyphon decreased almost close to 4.6 %. Furthermore, deviating from that critical point, higher heating power and lower filling ratio instead confined heat transfer performance of the threaded TPCT, which was primarily due to the rate of bubble generation and growth being significantly was slower than its detachment rate from the wall. In addition, heat and mass transfer performance of thermosyphons with threaded grooves of various pitches and apex angles were further analyzed under various conditions. Our results indicated that, when the groove apex angle turned to 90°, overall thermal transportation capability of the TPCT achieved optimal, with a decline in thermal resistance of up to 6.5 % compared to thermosyphons with smaller apex angles. Apex angle primarily affected the number of nucleation sites and the bubble detachment rate. Additionally, as the screw pitch decreased, boiling heat transfer enhancement, leading to more robust boiling heat transfer of TPCTs. Under high heating power, thermosyphons with larger screw pitch exhibited superior heat transfer performance. Overall, this innovative TPCTs with threaded grooves could be well applied in low-grade energy exploitation, particularly like as geothermal and solar energy fields.

Acoustically controlled bubble nucleation

Fundamental studies of single bubble heat transfer are crucial to improve our understanding of boiling phenomena and develop modeling and simulation tools for the design and optimization of boiling systems. However, conducting these kinds of experiments over a wide range of conditions is challenging and may involve expensive and complicated experimental techniques (e.g., lasers) to isolate and control bubble nucleation. In this work, we introduce a new technique to control nucleation with an ultrasonic beam. A low-cost and widely available piezoelectric disc driven at megahertz frequencies directed at a heated surface can increase the time-averaged pressure and suppress evaporation until the moment the transducer is turned off, allowing us to control the incipience of boiling to within 150 µs. We demonstrate this technique by measuring the physical and thermal footprint of natural and acoustically controlled bubbles with high-resolution infrared thermometry and phase detection diagnostics. We were able to raise the bubble nucleation temperature by over 30 K compared to a reference case with no acoustic control, which significantly changes bubble growth rate, microlayer formation and evaporation and departure diameter. We highlight the potential of this new low-cost and easy-to-use technique in a variety of different boiling heat transfer studies.

Rayleigh–Taylor instability in an arbitrary direction electrostatic field

Based on the potential flow theory, we carry out the nonlinear analysis for the inviscid incompressible Rayleigh–Taylor instability (RTI) in an arbitrary direction electrostatic field. The analytical expressions for the bubble amplitude and growth rate are presented. The effects of tangential and vertical electrostatic fields upon the bubble dynamics are opposite and depend on permittivity ratio. Agreements with recent simulations are found in the bubble amplitude. The direction of electrostatic field determines which (tangential or vertical) component plays the main role. The stability of the interface depends on whether the tangential and vertical components of the electrostatic field exceed the cut-off electrostatic field which is dependent of the permittivity ratio and the Atwood number. The results of this work demonstrate the importance of the direction of electrostatic field when considering the impact of electrostatic field on RTI.

Physical modeling of conjugate heat transfer for multiregion and multiphase systems with the Volume-of-Fluid method

AbstractThe Volume-of-Fluid (VOF) method is commonly used for numerical simulations of phase change phenomena, such as nucleate boiling or droplet evaporation. A key issue with the standard VOF method is the averaging of the liquid and vapor properties in interface cells, which causes non-physical conjugate heat transfer with a solid wall. Therefore, we aim at a physical model for conjugate heat transfer between a solid and a multiphase fluid. The first measure for higher quality simulations is the splitting of the single temperature field in the fluid region into separate liquid and vapor temperature fields. The second measure is the development of a new, more physical temperature boundary condition for conjugate heat transfer between a solid region and a multiphase fluid, based on experimental results, theoretical models and theoretical considerations. In interface cells, the vapor phase is excluded from the conjugate heat transfer because only heat transfer to the liquid phase occurs resp. dominates. Additionally, the conjugate heat transfer between solid and liquid in the interface cells is performed with virtual subcells, depending on the respective volume fraction of the liquid phase. This new approach (we name it distinctive approach) is successfully validated for energy conservation, and stability issues are discussed for the first time. Significant differences to simulations with averaged properties are observed due to the (now) physically correct modeling of conjugate heat transfer. In our boiling cases, the more accurate numerical simulations lead to considerably larger bubble growth rates. Higher quality simulations are also expected for nearly all applications, where there is a three-phase contact line, be it vapor bubbles in nucleate boiling or droplets impacting on a heated surface.

Nucleate pool boiling bubble dynamics for R32 and R1234yf on machined micro-structured surfaces

Efficient electronics cooling has always been a perpetual challenge, with the limits of single-phase cooling almost being reached. Two-phase cooling in the form of pool boiling is an attractive next step, with much research being devoted to it. While refrigerants operating at lower saturation temperatures are key to achieving effective cooling, surface modifications have been shown to also affect bubble dynamics and enhance nucleate pool boiling heat transfer. A simple, easy to implement fabrication method was sought, with the goal of expanding the knowledge of bubble dynamics. To this end, single bubble growth on structured surfaces that are achievable on a lathe, with an average roughness of 75 μm and differing indentation angles between 90° and 46°, was studied numerically using an OpenFOAM multiphase library. Conjugate heat transfer was applied, with heat fluxes ranging between 7.6 and 28 kW/m2 for pure refrigerants R32 and R1234yf. By comparing the bubble equivalent diameter with that of a smooth surface at a fixed heat flux, it was found that the bubble growth rates of structured surfaces were largely independent of indentation angles less than 90°, but lower than for smooth surfaces. For structured surfaces, a critical indentation angle of approximately 60° was identified which affected the bubble dynamics. For angles greater than the critical angle the bubble growth time was up to 150 % longer, which also resulted in larger departure diameters. However, the opposite trend was observed as the indentation angle was decreased below the critical angle. From a force analysis, it was found that the physical limitation imposed on the bubble growth was responsible for the critical indentation angle behaviour, with the most acute angle of 46° showing the shortest departure time. Furthermore, the bubble growth from a single cavity corresponded better with the trends of a smooth surface than a structured surface with comparable indentation angles. On a structured surface, once the bubble reached the edge of the cavity, its base diameter was limited by the physical characteristics of the surface. For the single cavity surface, however, bubble growth was uninhibited beyond the cavity, mimicking a completely smooth surface. The marked difference between results of a fully structured surface and the single cavity implies that future research will have to take the structural limitations on bubble growth imposed by a roughened surface into account.

Comprehensive experimental thermal analysis of single bubble nucleation in vertical flow boiling: Whole field temperature and microlayer dynamics

Nucleate boiling, an important heat transfer phenomenon, holds significance in the thermal management of numerous engineering applications. Understanding and predicting its heat transfer characteristics are vital for system optimization. The formation of a microlayer, resulting from rapid bubble growth on a heater substrate, subsequently facilitates further bubble growth through evaporation playing a critical role in overall bubble dynamics. This study examines the intricate relationship between bubble and microlayer dynamics and their impact on heat transfer rates. Experimental work is conducted for varying heat fluxes using rainbow schlieren deflectometry (RSD) and thin-film interferometry (TFI) in tandem for simultaneous mapping of key parameters: bubble dynamics, microlayer dynamics, and two-dimensional temperature field in vertical flow boiling. The analysis of these parameters has provided significant insights into some fundamental aspects of boiling. Firstly, this study emphasizes that the bubble growth rate models need to take into initial microlayer thickness in accurately predicting bubble growth dynamics. The iteratively obtained constant Ceff (describing the initial microlayer thickness) for bubble growth models matches well the value of Ceff obtained experimentally from thin film interferograms. Additionally, this study also validates the applicability of the kinetic theory-based model in predicting the evaporative heat transfer coefficient during the initial stage of flow boiling, while demonstrating that the accommodation coefficient is ∼0.04 for the investigated range of heat fluxes. Subsequently, using the experimentally obtained evaporative heat transfer coefficient, further insights are provided into the dry patch dynamics. Experimental dry patch dynamics were in good agreement with theoretical predictions up to the rewetting phase. The results also indicate a substantial contribution of microlayer evaporation, constituting approximately 34 % of the total heat flux.

Numerical study on the growth characteristics of bubble in a petal-shaped fuel rod channel

Based on the VOF multiphase flow model and bubble growth model, a numerical analysis model of bubble growth of subcooled flow boiling in a petal-shaped fuel rod channel was established. The growth characteristics of a single bubble and the influence of thermal parameters were analyzed. Firstly, the growth rate, shape, and trajectory of the bubble were investigated under typical working conditions. Secondly, the influences of inlet subcooling, inlet velocity, and wall superheat on the bubble growth characteristics were clarified. Finally, the existing bubble growth rate prediction correlation was evaluated based on the results of numerical calculations. The results show that the bubble growth rate is fast at the early stage of bubble growth when the evaporation heat flow from the microlayer plays a major role. With the disappearance of microlayer evaporation, the bubble diameter increases slowly. The bubble diameter decreases continuously when the evaporation heat flow in the overheating layer is less than the condensation heat flow after the bubble lift-off. Compared to the rectangular channel, the bubble diameter in a petal-shaped fuel rod channel has a larger equivalent diameter and more obvious lateral movement. With the increase of inlet flow velocity and inlet subcooling, the total evaporation heat flow of the bubble decreases, while the condensation heat flow increases, which results in the decrease of bubble diameter. The influence of increasing wall superheat on bubble diameter is opposite to that of increasing inlet flow velocity and inlet subcooling. Based on the numerical results, a new prediction correlation for bubble growth rate in a petal-shaped fuel rod channel was developed, whose prediction error is within ±20 %. The related research results help to further reveal the subcooled boiling heat transfer mechanism in a petal-shaped fuel rod channel.

Atomization behavior of burning stable emulsion droplets

We investigate the atomization behavior of burning stable water-in-oil microemulsion droplets. The microemulsion compositions are prepared by altering the dispersed phase volume fraction (ϕ) and base oils (dodecane, xylene, and surrogate (90% dodecane and 10% xylene) by weight). The combustion of base oil follows classical droplet combustion, while two-stage combustion, i.e., classical droplet combustion and atomization-dominated combustion, is observed for emulsion droplets. We reveal that vapor bubble formation occurs primarily through heterogeneous nucleation, and the mechanisms leading to bubble formation can be accurately predicted and controlled for distinct, highly stable emulsions. During the initial phase of combustion, water vapor bubbles nucleate, while the nucleation of oil vapor is more prevalent in the later phase of combustion due to the depletion of water content. In both regimes, heterogeneous nucleation ensues due to the agglomeration of surfactant inside the burning droplet. The lower volatility and viscous nature of the oil inhibit the growth rate of the nucleated oil-vapor bubble within the oil–surfactant mixtures. On the contrary, the water vapor bubble exhibits a higher growth rate within the emulsion droplet, attributed to its higher volatility and low viscosity. We show that qualitatively, the global bubble dynamics associated with the emulsion droplets remain substantially consistent regardless of ϕ and the type of base oil. However, it is observed that the onset of nucleation, bubble growth and collapse cycles, and the size of secondary droplets display a strong dependence on the ϕ and the type of base oil. The normalized diameter at the onset of nucleation increases as ϕ increases, exhibiting a logarithmic trend. The optimal dispersed phase volume fraction for effective atomization is found to be ϕ=0.2, regardless of the type of microemulsion.

Bubble departure and sliding in high-pressure flow boiling of water

Bubble growth, departure and sliding in low-pressure flow boiling has received considerable attention in the past. However, most applications of boiling heat transfer rely on high-pressure flow boiling, for which very little is known, as experimental data are scarce and very difficult to obtain. In this work, we conduct an experiment using high-resolution optical techniques. By combining backlit shadowgraphy and phase-detection imaging, we track bubble shape and physical footprint with high spatial ( $6\,\mathrm {\mu }{\rm m}$ ) and temporal ( $33\,\mathrm {\mu }{\rm s}$ ) resolutions, as well as bubble size and position as bubbles nucleate and slide on top of the heated surface. We show that at pressures above 1 MPa bubbles retain a spherical shape throughout the growth and sliding process. We analytically derive non-dimensional numbers to correlate bubble velocity and liquid velocity throughout the turbulent boundary layer and predict the sliding of bubbles on the surface, solely from physical properties and the bubble growth rate. We also show that these non-dimensional solutions can be leveraged to formulate elementary criteria that predict the effect of pressure and flow rate on bubble departure diameter and growth time.

Spontaneous Rise of Hydrogen Microbubbles in Interfacial Gas Evolution Reaction.

Liquid organic hydrogen carrier is a promising option for the transport and storage of hydrogen as a clean energy source. This study examines the stability and behavior of organic drops immobilized on a substrate during an interfacial hydrogen-evolution reaction (HER) at the drop surface and its surrounding aqueous solution. Hydrogen microbubbles form within the drop and rise to the drop apex. The growth rate of the hydrogen in-drop bubble increases with the concentration of the reactant in the surrounding medium. The drop remains stable till the buoyancy acting on the in-drop bubble is large enough to overcome the capillary force and the external viscous drag. The bubble spontaneously rises and carries a portion drop liquid to the solution surface. These spontaneous rising in-drop bubbles are detected in measurements using a high-precision sensor placed on the upper surface of the aqueous solution, reversing the settling phase from phase separation in the reactive emulsion. The finding from this work provides new insights into the behaviors of drops and bubbles in many interfacial gas evolution reactions in clean technologies.

Experimental study on generation and growth of bubbles in external flash-boiling spray regime

High-performance liquid propulsion systems, such as hypersonic scramjets and liquid rockets, utilize regenerative cooling by employing fuel as a coolant to shield components from thermal damage. The flash-boiling spray, resulting from superheated liquid injection and prevalent in regenerative cooling, has received considerable research interest for enhancing atomization and combustion efficiency. In this study, superheated water jets at various temperatures between 30 and 90 ℃ were injected into a vacuum chamber at different pressures above 5 kPa, and their spray patterns were acquired through diffusive backlight imaging. Images were analyzed to determine key parameters, such as bubble nucleation flux, bubble growth rate, and spray angle, in an external flash-boiling spray regime. The estimated nucleation flux agreed well with the predictions the model based on nucleation theory in the region of sufficiently high superheat. The dynamics of bubble growth was investigated and explained using a bubble growth model. The jet-expansion energy was computed by measuring the spray angle and compared with the available energy. By mapping the evolution of flash-boiling spray in relation to relevant nondimensional numbers, the study underscores the necessity of accounting for the pressure inside the injector to adequately model bubble generation inside the injector. Furthermore, this study substantiates the feasibility of visually recognizing and analyzing individual bubbles in the external flash-boiling regime, thereby enabling the generation of experimental data crucial for the validation of bubble nucleation and growth models.

Modeling of a liquid nitrogen droplet evaporating inside an immiscible liquid pool

Evaporation of liquid nitrogen in another immiscible liquid occurs in many industrial applications. Existing oversimplified one-dimensional (1D) quasi-steady models, although can quantitatively predict the evaporation rate by introducing an empirical fitting parameter, rely on configurations inconsistent with experimental observation so more rigorous models are required to get in-depth physical insights and improve modeling capability. This study proposes a 2D quasi-steady-state theoretical model, free of fitting parameters, that predicts the bubble growth rate and estimates the heat transfer rate for a liquid nitrogen droplet evaporating inside a liquid pool within the spherical bubble regime. The droplet's shape and position within a spherical bubble are determined by the equilibrium between the gravitational force and the upward pressure force resulting from the vapor flow between the droplet and the pool. The vapor layer thickness is calculated to be on the order of 10 microns. Notably, the primary contribution to heat transfer arises from the lower portion of the droplet, leading to local heat flux values up to approximately six times higher at the bottom compared to the top. The predicted bubble growth is quantitatively consistent with experimental data within the capillary spherical bubble regime. Furthermore, the overall heat transfer rate Q exhibits a distinct scaling relationship with the volume ratio between the bubble and droplet, yielding Q∼(Vb/Vd)−0.1.

Non-equilibrium activation dynamics of superheated phase-change contrast agents

Phase-change contrast agents, such as superheated perfluorocarbon droplets, potentially offer exciting new opportunities in diagnostic and therapeutic applications of ultrasound. An important advantage of droplets over, e.g., microbubble agents is that they can be “activated” (vaporised) by a reduction in ambient pressure, initiated by an externally applied ultrasound pulse. Controlling the timing and location of droplet activation, however, is vitally important to avoid safety concerns. Current theoretical models for droplet vaporisation assume that a critical stable bubble embryo forms that is in thermal and mechanical equilibrium. Model predictions are, however, inconsistent with some experimental observations. The aim of this study is to develop a non-equilibrium model for droplet activation wherein initial bubble growth rate and vapour pressure are dependent upon the bubble nucleus size. We demonstrate how incorporating nonequilibrium effects into theoretical models of droplet vaporisation dynamics enables better agreement of the droplet expansion with experimental data and thus provide greater insight into control of the activation process.

Bubbling triggered crystallization of xylitol phase change material for controllable heat retrieval: The subcooling effect

Towards long-term seasonal latent heat storage, the PCMs with strong supercooling are recommended as the heat storage medium. Nevertheless, the suitable techniques activating latent heat release is also of significance in the period of heat supply. The present work investigated the N2 bubbling triggered crystallization of supercooled xylitol. Special attention was paid to the subcooling effect. The N2 bubbling was identified to be a potential technique to trigger crystallization of xylitol at moderate degrees of subcooling. It was found that efficient crystallization issues were obtained with degrees of subcooling from 40 °C to 60 °C, while uncrystallization was obtained with both lower and higher subcooling. The recorded temperature history curves show that subcooling effect has strong influence on the crystallization behavior. The crystallization points tend to decline from 51.9 °C to 42.3 °C with degree of subcooling rising from 40 °C to 50 °C. The crystallization durations extend with subcooling effect enhancing. Fortunately, bubbling technique has slight influence on the properties of formed xylitol crystals. Moreover, the subcooling significantly influences the transportation behavior of bubbles. Particularly, The specific growth rates of bubbles are determined to be as low as 0.005 mm/min with the lowest degree of subcooling 10 °C, and continue to rise over 20 times when the subcooling reaches to 60 °C. The interfaces of bubbles as potential nucleation sites were deemed to be one of the important issues to activate heterogeneous nucleation, thus trigger crystallization. The present investigation is helpful to understand the fundamentals of bubbling effect on crystallization with broad range of subcooling.

Bubble nucleation and growth on microstructured surfaces under microgravity

Understanding the dynamics of surface bubble formation and growth on heated surfaces holds significant implications for diverse modern technologies. While such investigations are traditionally confined to terrestrial conditions, the expansion of space exploration and economy necessitates insights into thermal bubble phenomena in microgravity. In this work, we conduct experiments in the International Space Station to study surface bubble nucleation and growth in a microgravity environment and compare the results to those on Earth. Our findings reveal significantly accelerated bubble nucleation and growth rates, outpacing the terrestrial rates by up to ~30 times. Our thermofluidic simulations confirm the role of gravity-induced thermal convective flow, which dissipates heat from the substrate surface and thus influences bubble nucleation. In microgravity, the influence of thermal convective flow diminishes, resulting in localized heat at the substrate surface, which leads to faster temperature rise. This unique condition enables quicker bubble nucleation and growth. Moreover, we highlight the influence of surface microstructure geometries on bubble nucleation. Acting as heat-transfer fins, the geometries of the microstructures influence heat transfer from the substrate to the water. Finer microstructures, which have larger specific surface areas, enhance surface-to-liquid heat transfer and thus reduce the rate of surface temperature rise, leading to slower bubble nucleation. Our experimental and simulation results provide insights into thermal bubble dynamics in microgravity, which may help design thermal management solutions and develop bubble-based sensing technologies.

3D Simulations of Nucleate Boiling with Sharp Interface Vof and Localized Adaptive Mesh Refinement in Ansys-Fluent

Abstract The present work demonstrates the use of customized Ansys-Fluent in performing 3D numerical simulations of nucleate boiling with a sharp interface and adaptive mesh refinement. The developed simulation approach is a reliable and effective tool to investigate 3D boiling phenomena by accurately capturing the thermal and fluid dynamic interfacial vapor-liquid interaction and reducing computational time. These methods account for 3D sharp interface and thermal conditions of saturation temperature refining the mesh around the bubble edge. User-Defined-Functions (UDFs) were developed to customize the software Ansys-Fluent to preserve the interface sharpness, maintain saturation temperature conditions, and perform effective adaptive mesh refinement in a localized region around the interface. Adaptive mesh refinement is accomplished by a UDF that identifies the cells near the contact line and the liquid-vapor interface and applies the adaptive mesh refinement algorithms only at the identified cells. Validating the approach considered spherical bubble growth with an observed acceptable difference between theoretical and simulation bubble growth rates of 10%. Bubble growth simulations with water reveal an influence region of 2.7 times the departure bubble diameter, and average heat transfer coefficient of 15000 W/m2-K. In addition, the results indicate a reduced computational time of 75 hours using adaptive mesh compared to uniform mesh.