Thermal Bubble Research Articles

A study of arc plasma energy deposition flow control on blunt-headed protuberance induced STBLI

This paper presents experimental results of flow control method using plasma energy deposition on shock wave interactions induced by blunt-headed protuberance on a flat plate at Mach 2.0. Upstream of the leading edge of the protuberance, plasma energy deposition was generated by high-frequency pulsed discharge at three streamwise locations on the flat plate. High-speed Schlieren technique was utilized to investigate the unsteadiness characteristics of shock wave/turbulent boundary layer interaction (STBLI). The visualization results reveal that thermal bubble structures formed by the pulsed discharge could attenuate the separation shock continuously, resulting in a 12.8% decrease in the maximum pressure in the interaction wall. Experimental findings disclosed the dependency of this mitigation efficacy on the average discharge power. The pulsation of the separation shock was also affected by average discharge power, while the pulsation of boundary layer and shear layer was linked to both the discharge power and frequency. The numerical results predicted flow topology under control well with experiment results, low-density plasma layer was formed by high-frequency discharge, which weakening the separation shock substantially, the “λ” shock intensity was also decreased. The flow field of numerical simulation and experiments are in good agreement. Additionally, the control of the thermal bubble structures on STBLI was very effective in terms of reducing the motion and weakening the intensity of the low-frequency separation shock, and augmenting the high frequency component in the turbulent boundary layer and shear layer.

Simulation on mass removal by recoil pressure, thermal stress, and bubble growth of concrete irradiated by a millisecond Nd: YAG pulsed laser

The present paper reports on the study of millisecond pulsed Nd: YAG laser ablation of concrete material using the finite element method simulation to elucidate the complex mass removal processes such as melt ejection by recoil pressure, spallation as a result of thermal stress and gas bubble growth which are not well documented. The simulated results showed that the mass removal of concrete by melt ejection dominates over evaporation. Effects of laser intensity and linear laser pulse overlap on mass removal of concrete were also discussed. When the laser intensity was varied over a range from 2.4×1010 W/m2 to 4.4×1010 W/m2, both the temperature and mass ablation increased, however, the ablation efficiency remained constant i.e. 0.18 mg/J indicating the mass removal process remained unchanged. The simulated results are validated with both the experimental data and analytical results.

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.

A global heat flow topology for revealing the synergistic effects of heat transfer and thermal power conversion in large scale systems: Methodology and case study

In the processes of modeling, optimization, heat transfer analysis, and thermal power conversion analysis in large-scale complex systems, challenges are encountered regarding intricate design and optimization. In this paper, a global heat flow topology is proposed that reveals the synergistic effect of heat transfer and thermal power conversion in large-scale systems. The approach involves the construction of a heat flow topology, mathematical model development, analysis of specific parameters, and multi-objective optimization. It integrates various methods and tools, including heat flow topology, numerical simulation tool, entransy transfer analysis, global thermal resistances visualization, genetic algorithm (GA), and technique for order preference by similarity to ideal solution (TOPSIS). By using the LNG cold energy recovery and regasification process in floating storage and regasification units (FSRU) as a case study, the methodology provides a comprehensive understanding of the interactions and conversions between heat transfer and thermal power within the system. The results demonstrate that the optimal configuration achieves a maximum thermal efficiency of 21.73 % and a maximum cold recovery efficiency of 58.48 %. Additionally, the interaction between LNG pressure and seawater temperature exhibits limited synergistic impact on both LNG cold exergy efficiency and entransy transfer efficiency. Similarly, the combined influence of LNG pressure and evaporator temperature shows weak synergistic effects on parameters such as supply/demand ratio, thermal efficiency, and entransy transfer efficiency. The analysis of the global thermal resistance bubble chart reveals the significant impact of evaporator temperature and seawater temperature on the evaporator resistance, as well as the notable impact of LNG pressure on the condenser resistance.

TRAM: A new non‐hydrostatic fully compressible numerical model suited for all kinds of regional atmospheric predictions

AbstractA new limited‐area numerical model (TRAM, for Triangle‐based Regional Atmospheric Model) has been built using a non‐hydrostatic and fully compressible version of the Navier–Stokes equations. Advection terms are solved using a Reconstruct–Evolve–Average (REA) strategy over the computational cells. These cells consist of equilateral triangles in the horizontal. The classical z‐coordinate is used in the vertical, allowing arbitrary stretching (e.g., higher resolution in the Planetary Boundary Layer, PBL). Proper treatment of terrain slopes in the bottom boundary conditions allows for accurately representing the orographic forcing. To gain computational efficiency, time splitting is used to integrate fast and slow terms separately and acoustic modes in the vertical are solved implicitly. For real cases on the globe, the Lambert map projection is applied, and all Coriolis and curvature terms are retained. No explicit filters are needed. The first part of the manuscript describes the dynamical core of the model and provides its thorough validation using a variety of benchmark tests (mostly in two dimensions) in the context of a dry‐adiabatic atmosphere. In the second part, TRAM is reformulated for a moist atmosphere and is completed with a proper set of physical parametrizations of cloud microphysics, cumulus convection, short and long‐wave radiation, PBL processes and surface fluxes. Various examples of the great versatility offered by this full version will be presented, with special emphasis on Mediterranean case studies. In summary, TRAM performs as well as state‐of‐the‐art numerical models and is suitable for simulating circulations ranging from small‐scale thermal bubbles (≈100 m scale) to synoptic‐scale baroclinic cyclones (>1000 km size), including orographic circulations, thermally driven flows, squall lines, supercells, all kinds of precipitation systems and medicanes. Besides opening a myriad of academic and research applications, TRAM regional forecasts at different resolutions are being disseminated in the web (see https://meteo.uib.es/tram).

Computational study of numerical flux schemes for mesoscale atmospheric flows in a Finite Volume framework

Abstract We develop, and implement in a Finite Volume environment, a density-based approach for the Euler equations written in conservative form using density, momentum, and total energy as variables. Under simplifying assumptions, these equations are used to describe non-hydrostatic atmospheric flow. The well-balancing of the approach is ensured by a local hydrostatic reconstruction updated in runtime during the simulation to keep the numerical error under control. To approximate the solution of the Riemann problem, we consider four methods: Roe-Pike, HLLC, AUSM+-up and HLLC-AUSM. We assess our density-based approach and compare the accuracy of these four approximated Riemann solvers using two classical benchmarks, namely the smooth rising thermal bubble and the density current.

Printing of liquid metal by laser-induced thermal bubble at the liquid–liquid interface

The dynamics of bubbles near a liquid–liquid interface represent a complex multiphase problem with numerous potential applications. This paper utilizes pulsed laser-induced microbubbles at the liquid–liquid interface to achieve the multi-orifice ejection of liquid metal microdroplets that are challenging to achieve with traditional inkjet printing. The study combines the expansion and collapse processes of thermal bubbles at the two-phase liquid interface with the ejection process of liquid metal droplets, unveiling the underlying mechanisms of liquid metal droplet ejection. In this work, the influence of laser parameters on the behavior of thermal bubbles at the liquid–liquid interface and the double-peak pressure effect was investigated. The impact of laser parameters on the ejection behavior of liquid metal droplets was also examined, which provides theoretical support for the wide applications of bubble dynamics at the liquid–liquid interface in the field of liquid metal inkjet printing.

GPLaSDI: Gaussian Process-based interpretable Latent Space Dynamics Identification through deep autoencoder

Numerically solving partial differential equations (PDEs) can be challenging and computationally expensive. This has led to the development of reduced-order models (ROMs) that are accurate but faster than full order models (FOMs). Recently, machine learning advances have enabled the creation of non-linear projection methods, such as Latent Space Dynamics Identification (LaSDI). LaSDI maps full-order PDE solutions to a latent space using autoencoders and learns the system of ODEs governing the latent space dynamics. By interpolating and solving the ODE system in the reduced latent space, fast and accurate ROM predictions can be made by feeding the predicted latent space dynamics into the decoder. In this paper, we introduce GPLaSDI, a novel LaSDI-based framework that relies on Gaussian process (GP) for latent space ODE interpolations. Using GPs offers two significant advantages. First, it enables the quantification of uncertainty over the ROM predictions. Second, leveraging this prediction uncertainty allows for efficient adaptive training through a greedy selection of additional training data points. This approach does not require prior knowledge of the underlying PDEs. Consequently, GPLaSDI is inherently non-intrusive and can be applied to problems without a known PDE or its residual. We demonstrate the effectiveness of our approach on the Burgers equation, Vlasov equation for plasma physics, and a rising thermal bubble problem. Our proposed method achieves between 200 and 100,000 times speed-up, with up to 7% relative error.

A Low‐Binder‐Content Ink System for 3D Printing High‐Density and Small Feature Size 316L Stainless Steel Parts

Binder ink system is the backbone of binder jet 3D printing (BJ‐3DP) technology. Compared with metal injection molding (MIM), BJ‐3DP needs much less amount of binder, which means less exhaust gas generation during the debinding process and more environmental friendliness. More than that, low content of binder is also supposed to benefit the structure properties of the printed metal parts. Herein, an ultralow‐binder‐content ethanol–water–PVP ink system is demonstrated for the BJ‐3DP 316 L stainless steel parts by applying thermal bubble inkjet technology. The PVP binder concentration is as low as 80 mg mL−1, which can achieve an ultralow solid content of 0.2 wt% in the printed green part. The two‐component solution with water and ethanol provides not only the rheology property adjustment freedom for the ink jetting and infiltration in the metal powders, but also the two boiling points for the step‐by‐step capillary bridge formation process. By applying the low‐binder‐content ink, the fully densified 316 L stainless steel parts after sintering can obtain the relative density up to 99.4%, Vickers hardness up to 185 HV, tensile strength up to 542 MPa, 25% elongation at break, and feature size as small as 200 μm.

Revise Thermal Winds of Remnant Neutron Stars in Gamma-Ray Bursts

It seems that the wealth of information revealed by the multi-messenger observations of the binary neutron star (NS) merger event, GW170817/GRB 170817A/kilonova AT2017gfo, places irreconcilable constraints to models of the prompt emission of this gamma-ray burst (GRB). The observed time delay between the merger of the two NSs and the trigger of the GRB and the thermal tail of the prompt emission can hardly be reproduced by these models simultaneously. We argue that the merger remnant should be an NS (last for, at least, a large fraction of 1 s), and that the difficulty can be alleviated by the delayed formation of the accretion disk due to the absorption of high-energy neutrinos emitted by the NS and the delayed emergence of effective viscosity in the disk. Further, we extend the consideration of the effect of the energy deposition of neutrinos emitted from the NS. If the NS is the central object of a GRB with a distance and duration similar to that of GRB 170817A, thermal emission of the thermal bubble inflated by the NS after the termination of accretion may be detectable. If our scenario is verified, it would be of interest to investigate the cooling of nascent NSs.

Thermal bubble-driven impedance-based high-throughput cell counting chip design

Cell identification and enumeration are important methods within clinical and research laboratories for rapid diagnosis of relevant diseases. However, there are still many shortcomings in the current cell counting methods. In order to improve the performance of cell counting, a novel impedance-based cell counting chip based on thermal bubble drive was designed in this study. The chip is fabricated by whole-wafer processing and provides the driving force for cells through a combination of thermal bubble nozzles and microfluidic channels, integrating 100 individual detection units on a 38 mm2 size chip. Experimental and theoretical analyses have demonstrated that the chip can achieve high throughput detection of 45 000 beads/s under extreme conditions. A fourfold difference in detection voltage was obtained for both 14 and 7 µm diameter polystyrene beads. The linear fit coefficient of determination between the cell number measured by the chip and the cell number observed in reality was above 0.999 for both polystyrene beads and 211H cells, and the counting accuracy exceeded previous studies. It turns out that the chip achieves portable, low-cost, high-throughput, and high-accuracy cell counting, which is conducive to the development of impedance cell counting.

An OpenFOAM framework to model thermal bubble-driven micro-pumps

Thermal bubble-driven micro-pumps (also known as inertial pumps) are an upcoming micro-pump technology that can be integrated directly into micro/mesofluidic channels to displace fluid without moving parts. These micro-pumps are high-power resistors that locally vaporize a thin layer of fluid above the resistor surface to form a high-pressure vapor bubble which performs mechanical work. Despite their geometric simplicity, thermal bubble-driven micro-pumps are complex to model due to the multiphysics couplings of Joule heating, thermal bubble nucleation, phase change, and multiphase flow. As such, most simulation approaches simplify the physics by neglecting Joule heating, nucleation, and phase change effects as done in this study. To date, there are no readily available, reduced physics open-source modeling tools that can resolve both pre-collapse (defined as when the bubble is expanding and collapsing) and post-collapse (defined as when the bubble has re-dissolved back into the subcooled fluid) bubble and flow dynamics. In this study, an OpenFOAM framework for modeling thermal bubble-driven micro-pumps is presented, validated, and applied. The developed OpenFOAM model agrees with both experimental data and commercial computational fluid dynamics (CFD) software, FLOW-3D. Additionally, we assess the shape of the transient velocity profile during a pump cycle for the first time and find that it varies substantially from theoretical Poiseuille flow during pre-collapse but is within 25% of the theoretical flow profile during post-collapse. We find that this deviation is due to flow never becoming fully developed during each pump cycle. We envision the developed OpenFOAM framework as an open-source CFD toolkit for microfluidic designers to simulate devices with thermal bubble-driven micro-pumps.

Validation of an OpenFOAM®-based solver for the Euler equations with benchmarks for mesoscale atmospheric modeling

Within OpenFOAM, we develop a pressure-based solver for the Euler equations written in conservative form using density, momentum, and total energy as variables. Under simplifying assumptions, these equations are used to describe non-hydrostatic atmospheric flow. For the stabilization of the Euler equations and to capture sub-grid processes, we consider two Large Eddy Simulation models: the classical Smagorinsky model and the one equation eddy-viscosity model. To achieve high computational efficiency, our solver uses a splitting scheme that decouples the computation of each variable. The numerical results obtained with our solver are validated against numerical data available in the literature for two classical benchmarks: the rising thermal bubble and the density current. Through qualitative and quantitative comparisons, we show that our approach is accurate. This paper is meant to lay the foundation for a new open-source package specifically created for the quick assessment of new computational approaches for the simulation of atmospheric flows at the mesoscale level.

Bubble nucleation at zero and nonzero temperatures

The theory of false vacuum decay in a thermal system may have a cross-over from predominantly thermal transitions to quantum transitions as the temperature is decreased. New numerical methods and results are presented here that can be used to model thermal and vacuum bubble nucleation in this regime for cosmology and for laboratory analogues of early universe phase transitions.

Processing and properties of a graphene-reinforced superhydrophobic siloxane

Three-dimensional superhydrophobic materials are characterized by a low surface energy and extremely low strength, and hence require reinforcement for viable applications. An experimental study is presented of the processing and mechanical properties of a graphene-reinforced superhydrophobic siloxane, synthesized by a sol–gel approach integrating alkali activation of metakaolin, hydrolysis of alkoxysilane, dispersion of graphene into the precursor, and co-condensation. To promote uniform dispersion and distribution of graphene, three processing techniques were used: while ultrasonication was adopted to disperse graphene nanoplatelets, accelerated condensation at 50 and 75 °C and varying the precursor’s viscosity used to prevent graphene from floating and re-aggregation. Results of nanoindentation, porosimetry, and unconfined compression show that adding 0.9 wt% graphene increases the strength of the superhydrophobic composites from ∼ 0 to 34 MPa. Slow condensation and curing at 25 °C allow graphene to re-aggregate and float upward in the sol, leading to its heterogeneous distribution. Despite its function in improving microscale dispersion, ultrasonication detrimentally decreases the composite’s strength due to acoustic cavitation. Similarly, curing at elevated temperatures accelerates co-condensation and results in a more uniform distribution of graphene, but induces thermal cavitation and bubble formation, because the threshold for acoustic and thermal cavitations is significantly reduced by superhydrophobicity.

AGN feedback in an infant galaxy cluster: LOFAR-Chandra view of the giant FRII radio galaxy J103025+052430 at z = 1.7

In the nearby universe, jets from active galactic nuclei (AGN) are observed to have a dramatic impact on their surrounding extragalactic environment. The effect of jets at high redshift (z > 1.5) is instead much more poorly constrained. However, studying the jet impact at cosmic noon, the epoch in which both star formation and AGN activity peak, is crucial for fully understanding galaxy evolution. Here we present a study of the giant (∼750 kpc) radio galaxy 103025+052430 located at the centre of a protocluster at redshift z = 1.7, with a focus on its interaction with the external medium. We present new LOFAR observations at 144 MHz, which we combine with VLA 1.4 GHz data and 0.5–7 keV Chandra archival data. The new radio map at 144 MHz confirms that the source has a complex morphology, which can possibly fit the hybrid morphology radio galaxy classification. The large size of the source enabled us to perform a resolved radio spectral index analysis, a very unique opportunity for a source at this high redshift. This revealed a tentative unexpected flattening of the radio spectral index at the edge of the backflow in the western lobe, which might be indicating plasma compression. The spatial coincidence between this region and the thermal X-ray bubble C suggests a causal connection between the two. In contrast to previous estimates for the bright X-ray component A, we find that inverse Compton scattering between the radio-emitting plasma of the eastern lobe and cosmic microwave background photons can account for a large fraction (∼45%–80%) of its total 0.5–7 keV measured flux. Finally, the X-ray bubble C, which is consistent with a thermal origin, is found to be significantly overpressurised with respect to the ambient medium. This suggests that it will tend to expand and release its energy into the surroundings, contributing to the overall intracluster medium heating. Overall, 103025+052430 enables us to investigate the interaction between AGN jets and the surrounding medium in a system that is likely the predecessor of the rich galaxy clusters we all know well at z = 0.

Single-Cell Isolation Microfluidic Chip Based on Thermal Bubble Micropump Technology

The isolation of single cells is essential for the development of single cell analysis methods, such as single-cell sequencing, monoclonal antibodies, and drug development. Traditional single-cell isolation techniques include flow cytometry (FACS), laser capture microdissection (LCM), micromanipulation, etc., but their operations are complex and have low throughput. Here, we present a microfluidic chip that can isolate individual cells from cell suspension and release them onto a well plate. It uses thermal bubble micropump technology to drive the fluid flow, and single-cell isolation is achieved by matching the flow resistance of the flow channel. Therefore, injection pumps and peristaltic pumps are not required for cell loading. Because of its small size, we can integrate hundreds of single-cell functional modules, which makes high-throughput single-cell isolation possible. For polystyrene beads, the capture rate of the single bead is close to 100%. Finally, the method has been applied to cells, and the capture rate of the single cell is also about 75%. This is a promising method for single-cell isolation.

Toward a Quantitative Understanding of Robert’s Rising Thermal Bubble as a Benchmark for 3D Atmospheric Codes

Abstract Robert’s rising thermal bubble (RRTB) is a benchmark case used to assess atmospheric models. In this paper, RRTB is further studied both using an analytical and a numerical approach, improving to a greater extent the qualitative description found in the literature. The theoretical framework used is that of buoyant thermals and scaling theory that together are able to predict part of the expected behavior of the bubble as it rises and, therefore, can be used to further validate the simulations. For the numerical experiments, we simulate both a two-dimensional and three-dimensional RRTB using a variety of convection schemes under the Boussinesq approximation and with a higher resolution. While the results are in agreement with those presented by previous authors on the same benchmark and also with the theoretical framework established, we add the quantitative measures to validate the underlying physics of the numerical model. Our results also show that, due to its completely chaotic nature when confined in a 2D plane, RRTB becomes a very challenging candidate to be used as a benchmark if only compared in a qualitative way, and when the 3D bubble is simulated, the shape changes significantly.

Visualization study of perturbations induced by plasma actuators and its effect on shock wave/boundary-layer interaction

Surface arc plasma actuator array is used to control the shock wave/boundary-layer interaction in a Ma = 2 flow. Two types of interaction are examined. The flow topology of Surface arc plasma actuator array operating at high-frequency is firstly visualized via particle laser scattering (PLS) technique. The results show that two typical flow structures are observed in the discharging process: the thermal gas bubble and the trailing vortices. The high-frame low-exposure schlieren results for flow visualization indicate a significant separation inhibition in both experiments due to an improvement in the mixture upstream of the interaction region and promoting more turbulent structure into the boundary layer. In the baseline, the separation shock oscillates in a low-frequency mode. When plasma actuation is turned on, the spectra change dramatically when compared to the baseline condition without control. There is an apparent frequency shift for separation shock.Graphical abstract

Oscillating Laser Conduction Joining of Dissimilar PET to Stainless Steel.

How to improve the bonding strength of polymers to metals has been one of the challenges in joining fields. It is generally assumed that laser transmission joining is better than laser conduction joining (LCJ) for transparent polymers, and few studies have been focused on LCJ. However, by introducing beam oscillation, an excellent result was obtained in the LCJ of transparent polyethylene terephthalate (PET) to 304 stainless steel. The interface defects of thermal decomposition and bubbles could be eliminated or reduced more efficiently in oscillating laser conduction joining (O-LCJ) rather than transmission joining. Correspondingly, the tensile shear force of joint O-LCJ could be increased by 23.8%, and the plasticity characterized by tensile displacement could be increased by seven times. The improvement mechanism was attributed to two factors by calculating the interface energy distribution and analyzing the force state at the interface. One is the homogenization of interface energy distribution caused by beam oscillation, which decreases the degradation and destruction of polymer macromolecular chains induced by high temperature. The other is the formation of interface bi-directional forces that both inhibit the porosity formation and intensify the chemical reactions. The results bring new insights and provide a new pathway to improve the joining performances of dissimilar polymers to metals.