Accumulation Of Bubbles Research Articles

Experimental study of pool boiling characteristics for non-azeotropic mixtures n-pentane / n-hexane on microstructure surfaces

Mixed alkanes are widely used as refrigerants in applications such as natural gas liquefaction, especially in the Floating Liquefied Natural Gas (FLNG) process. To elucidate the mechanisms underlying the weakening of phase transition in mixed refrigerants and to develop enhanced heat transfer methods, a pool boiling experimental setup is established in this study to investigate the boiling heat transfer characteristics of n-pentane/n-hexane mixtures on three different microstructure surfaces. By combining visual observation of bubble dynamics with analysis of the effects of composition conditions, micro-surface geometry, and wall heat flux conditions on the boiling heat transfer characteristics, it is revealed that the heat transfer coefficient (HTC) on the pyramid surface and the cylindrical surface, compared to the smooth surface, maximum increase by up to 345 % and 203 %, respectively. Compared with pure components, the mixture with a mass fraction of 0.5 n-pentane shows the greatest heat transfer deterioration. Microstructure surfaces significantly enhanced the HTC of the mixed refrigerants. Additionally, the microstructures activate more nucleation sites and higher bubble departure frequency. The guiding effect of the pyramid surface effectively decreases the possibility of bubble aggregation under high Eo and Ga numbers, thereby delaying the formation of mushroom bubbles. Therefore, the pyramid surface shows its advantages at different component ratios. The HTC correlations for pure and mixed refrigerants are developed. The predictions for pure and mixed refrigerants HTCs agree with most of the experimental data with a deviation of ±10 % and ±25 %, respectively.

Enhanced Impeller Gas-Liquid Flow Using Ribs for High Performance of Centrifugal Pump

Transporting two-phase fluids presents a challenge due to their negative effects on centrifugal pump performance. The accumulation of gas bubbles in the pump impeller forms large gas pockets, reducing efficiency. This work aims to improve the performance of a two-phase flow centrifugal pump by modifying the pump impeller through the addition of ribs. These ribs are positioned near gas bubble accumulation. The modified impeller helps to disperse this accumulation, thereby enhancing pump performance. A study was conducted to evaluate the effect of ribs on the pump efficiency. The results showed a negative effect in low (GVF) and single-phase flows. However, at high GVF, the ribs significantly improved head up to 9%. Moreover, rib characteristics, such as diameter and radial position, were key parameters affecting the pump's efficiency. The ribs with a diameter of 1 mm and a radial position of 33 mm showed the best performance.

Experimental Simulation Studies on Non-Uniform Fluidization Characteristics of Two-Component Particles in a Bubbling Fluidized Bed

Taking the fluidized pre-reduction process of iron ore powder bubbling fluidized bed as the background, for the problem of non-uniform structure in the bed of gas-solid fluidization process, the non-uniform fluidization characteristics of bicomponent particles are investigated in a cold two-dimensional bubbling fluidized bed by using a combination of physical experiments and mathematical simulations. Fluidization experiments were carried out under typical working conditions by using glass beads to study the effects of apparent gas velocity, mass ratio, and other factors on the non-uniform structure in the bed. Through the experimental observation of the bubble behavior, the effect of the cyclic change in bubble formation, rise and growth to rupture on the bed uniformity were analyzed. The experiments showed that the fluidized bed of two-component particles would be stratified, and the non-uniformity was strong in the upper part and weak in the lower part, and the apparent gas velocity and particle size were the main influencing factors. Based on the Euler-Lagrange reference frame modeling, the fluidization process of the two-dimensional bubble bed was simulated by the CFD-DEM method. The simulations of typical experimental conditions were carried out to further analyze the velocity distribution and the volume ratio of each phase in the bed from the gas-solid interaction level, revealing that the velocity distribution in the upper part of the bed is not uniform, and the gas flow is strongly perturbed, with intense bubble aggregation. The results reveal the reasons for the non-uniform phenomenon of gas-solid fluidization, which can provide a theoretical basis for the regulation of the non-uniform structure of the fluidization process.

High Mass Transfer Rate in Electrocatalytic Hydrogen Evolution Achieved with Efficient Quasi‐Gas Phase System

AbstractThe adhesion of H2 bubbles on the electrode surface is one of the main factors limiting the performance of H2 evolution of electrolytic water, especially at high current density. To overcome this problem, here a “quasi‐gas phase” electrolytic water reaction system based on capillary effect is proposed for the first time to improve the mass transfer efficiency of H2. The typical feature of this reaction system is that the main site of H2 evolution reaction is transferred from the bulk aqueous solution to the gas phase environment above the bulk aqueous solution, thus effectively inhibiting the aggregation of H2 bubbles and reducing the resistance of their diffusion away. Electrochemical test results show that the proposed quasi‐gas phase system can significantly reduce the potential required in H2 evolution reaction process at high current density compared with the conventional electrolytic reaction system. Specifically, the overpotential potential is reduced by 0.31 V when the H2 evolution current density of 250 mA cm−2 is achieved.

High Mass Transfer Rate in Electrocatalytic Hydrogen Evolution Achieved with Efficient Quasi-Gas Phase System.

The adhesion of H2 bubbles on the electrode surface is one of the main factors limiting the performance of H2 evolution of electrolytic water, especially at high current density. To overcome this problem, here a "quasi-gas phase" electrolytic water reaction system based on capillary effect is proposed for the first time to improve the mass transfer efficiency of H2. The typical feature of this reaction system is that the main site of H2 evolution reaction is transferred from the bulk aqueous solution to the gas phase environment above the bulk aqueous solution, thus effectively inhibiting the aggregation of H2 bubbles and reducing the resistance of their diffusion away. Electrochemical test results show that the proposed quasi-gas phase system can significantly reduce the potential required in H2 evolution reaction process at high current density compared with the conventional electrolytic reaction system. Specifically, the overpotential potential is reduced by 0.31 V when the H2 evolution current density of 250 mA cm-2 is achieved.

Comparison of subcooled flow boiling in concentric annuli with bare and finned surfaces

In this study, the hydrodynamic and thermal characteristics of subcooled flow boiling in concentric annuli with inner heating wires, featuring bare and finned surfaces designed for heat transfer enhancement, were experimentally investigated, with a focus on cooling technology for EV charging cables. The bare wire test module consisted of a 300 mm long wire, with a 290 mm long inner heating surface and a diameter of 10 mm. The outer tube was constructed from transparent polycarbonate with a 22 mm diameter, allowing optical access to observe the flow. The finned wire test module has an identical construction, except for the addition of six longitudinally extruded fins with cross-sectional dimensions of 2 × 5 mm2. Experiments and flow visualizations, aided by high speed imaging, were conducted using HFE-7100 as the working fluid at mass velocities, G, 463.7 to 1,309.6 kg/m2s and heat fluxes from 0.90 to 9.93 W/cm2, under inlet pressures between 120 and 240 kPa. The study investigated thermal non-equilibrium phenomena, driven by asymmetric bubble accumulation, and their effects on circumferential temperature distribution, which showed opposing trends between the bare and finned surfaces. An evaluation of previous empirical correlations for predicting subcooled flow boiling heat transfer coefficients was performed, followed by an assessment of fin performance in enhancing heat transfer. A comparative analysis with the bare surface module of the same dimensions confirmed that the longitudinal fins provided superior thermal management, maintaining the surface temperature below the safety threshold, Ts,safe. The longitudinal fins demonstrated a 54.5 % reduction in charging time and a 183.7 % increase in charging current for charging up to 80 % state of charge (SOC) of a 77.4 kWh battery, compared to the bare wire.

Reducing the overpotential of overall water spitting by micro-pump-like electrode engineering

Electrolyzing water for hydrogen generation consumes a significant amount of electricity. Minimizing bubble accumulation on the electrodes can reduce the overpotential, thereby enhancing the efficiency of water electrolysis. In this work, Co1.8Mn1.2S4 as the catalyst for oxygen evolution reaction (OER) was optimized from 54 compounds of oxides and sulfides of Ni, Co, and Mn, then designed a three-dimensional electrode with a pump-like function to expel bubbles from the electrodes. Using laser-assisted curing 3D printing technology, a capillary array with side holes was fabricated and utilized as a support structure for the Co1.8Mn1.2S catalyst. During water electrolysis, the electrolyte enters the interior of the capillary through the side holes, and the bubbles inside the capillary are released from both ends of the capillary. The optimized electrode achieved 10 mA cm−2 at an overpotential of 345 mV during the OER, and reached 100 mA cm−2 at an overpotential of 435 mV. In-situ optical microscopy observations and fluid dynamics simulations demonstrated that bubbles were effectively released through the main outlet of the capillary. In overall water splitting, the current density reached 10 mA cm−2 at 1.646 V, without significant current decay after 60 h continuous operation. The electrode design presented holds promise for broader applications in catalytic reactions, such as CO2 reduction, electrochemical ammonia synthesis, and electrochemical treatment of water pollutants.

Experimental and numerical study of characteristic parameters of Taylor bubble in vertical pipe under short-time gas injection

Purpose This study aims to investigate the formation and characteristics of Taylor bubbles resulting from short-time gas injection in liquid-conveying pipelines. Understanding these characteristics is crucial for optimizing pipeline efficiency and enhancing production safety. Design/methodology/approach The authors conducted short-time gas injection experiments in a vertical rectangular pipe, focusing on Taylor bubble formation time and stable length. Computational fluid dynamics simulations using large eddy simulation and volume of fluid models were used to complement the experiments. Findings Results reveal that the stable length of Taylor bubbles is significantly influenced by gas injection velocity and duration. Specifically, high injection velocity and duration lead to increased bubble aggregation and recirculation region capture, extending the stable length. Additionally, a higher injection velocity accelerates reaching the critical local gas volume fraction, thereby reducing formation time. The developed fitting formulas for stable length and formation time show good agreement with experimental data, with average errors of 6.5% and 7.39%, respectively. The predicted values of the formulas in glycerol-water and ethanol solutions are also in good agreement with the simulation results. Originality/value This research provides new insights into Taylor bubble dynamics under short-time gas injection, offering predictive formulas for bubble formation time and stable length. These findings are valuable for optimizing industrial pipeline designs and mitigating potential safety issues.

Numerical investigation of dynamic gas–liquid separator by population balance model

Dynamic gas–liquid separator (DGLS) can efficiently separate gas and liquid phases and are widely used in aerospace, chemical, and petroleum engineering. The energy loss and separation efficiency within the DGLS are studied through the combination of numerical simulations and experiments. Three-dimensional transient Reynolds-Averaged Navier–Stokes equations were solved to analyze the fluid dynamics within the DGLS. The bubble aggregation and breakup in oil were simulated by using the population balance model. Experimental data were meticulously compared with numerical results to validate the accuracy and reliability of the numerical methods. The findings revealed a direct correlation between the inlet flow rate and various performance metrics of the DGLS. Specifically, as the inlet flow rate increased, the energy loss within the DGLS escalated, resulting in higher power consumption. The degassing rate of the DGLS exhibited a decreasing trend with increasing inlet flow rate, while the de-oiling rate showed an inverse relationship. The optimal performance of the separator was observed at an inlet flow rate of 140 m3·d−1, with ηg* and ηl* reaching 0.94 and 0.99, respectively. The relationship between the Qo and the η* and Po was fitted by a second-order polynomial. Moreover, the rotational speed of the DGLS demonstrated a positive correlation with energy consumption, accompanied by an increase in power output. However, the separation efficiency of the DGLS exhibited a non-linear relationship with rotational speed, peaking at a specific value before marginally declining. The optimization of degassing and dewatering rates occurred at a rotational speed of 2500 r·min−1. These findings underscore the importance of carefully adjusting operational parameters to achieve optimal performance and energy efficiency within DGLS.

Bubble Migration and Accumulation in Oil-Paper Insulation: Interfacial Forces Modeling

Bubble Migration and Accumulation in Oil-Paper Insulation: Interfacial Forces Modeling

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.

Foam Stabilization Process for Nano-Al2O3 and Its Effect on Mechanical Properties of Foamed Concrete.

Foamed concrete is increasingly utilized in engineering due to its light weight, excellent thermal insulation, fire resistance, etc. However, its low strength has always been the most crucial factor limiting its large-scale application. This study introduced an innovative method to enhance the strength of foamed concrete by using nano-Al2O3 (NA) as a foam stabilizer. NA was introduced into a foaming agent containing sodium dodecyl sulfate (SDS) and hydroxypropyl methylcellulose (HPMC) to prepare a highly stable foam. This approach significantly improved the foam stability and the strength of foamed concrete. Its drainage volume, settlement distance, microstructure, and stabilizing action were investigated, along with the strength, microstructure, and hydration products of foamed concrete. The presence of NA effectively reduced the drainage volume and settlement distance of the foam. NA is distributed at the gas-liquid interface and within the liquid film to play a hindering role, increasing the thickness of the liquid film, delaying the liquid discharge rate from the liquid film, and hindering bubble aggregation, thereby enhancing foam stability. Additionally, due to the stabilizing effect of NA on the foam, the precast foam forms a fine and uniform pore structure in the hardened foamed concrete. At 28 d, the compressive strength of FC0 (0% NAs in foam) is 2.18 MPa, while that of FC3 (0.18% NAs in foam) is 3.90 MPa, increased by 79%. The reason for this is that NA promotes the formation of AFt, and its secondary hydration leads to the continuous consumption of Ca(OH)2, resulting in a more complete hydration reaction. This study presents a novel method for significantly improving the performance of foamed concrete by incorporating NA.

Superaerophobic Ni3N/Ni@W2N3 multi-heterointerfacial nanoarrays for efficient alkaline electrocatalytic hydrogen evolution reaction

The hydrogen evolution performances of electrocatalysts are greatly restricted by their unfavorable hydrogen evolution kinetics and the undesirable accumulation of as-evolved gas bubbles on the electrocatalysts surface. Herein, we present the fabrication of self-supporting multi-heterointerfacial nanoarrays electrode toward addressing these challenges simultaneously. A monolith Ni3N/Ni@W2N3 electrode is prepared, which exhibits a multi-heterojunction interface between the different components. The construction of this multi-heterojunction interface allows for the redistribution of the electrons, thus alleviating the strong Ni-H bond and optimizing the hydrogen adsorption free energy toward more efficient HER catalysis. Moreover, by virtue of the distinct nanoarray structure, the Ni3N/Ni@W2N3 nanoarrays exhibit improved hydrophilicity and superaerophobicity compared with Ni/Ni3N, facilitating water contact and enabling more efficient detachment of the as-evolved H2 bubbles from the surface. Benefiting from these attractive features, the Ni3N/Ni@W2N3 nanoarrays deliver an attractive alkaline HER catalytic activity with a low overpotential of 66 mV to achieve a current density of 10 mA cm−2, which is comparable with that of the benchmark Pt/C electrode. Moreover, the electrode exhibits remarkable stability during long-term electrolysis. The simultaneous interface and nanostructure engineering provide a feasible pathway for obtaining high-performance electrodes and beyond for various electrochemical reactions.

Effect of turbulence intensity on bubble-particle detachment mechanism in a confined vortex

Bubble-particle detachment induced by turbulence is the primary factor for the low recovery of coarse particles, which has attracted much attention in recent years. The prevailing centrifugal detachment theory has achieved broad consensus. However, due to the complexity of bubble-particle aggregate motion in the turbulent field, the influence of turbulence intensity on bubble-particle detachment mechanism remains unclear. In this study, a controlled rotating vortex was generated using a custom-made fluid channel to systematically investigate the effect of turbulence intensity on bubble-particle centrifugal detachment. Firstly, detachment behaviours of bubble-particle aggregates were captured using high-speed cameras, followed by flow field visualization of bubble-particle detachment processes using Computational Fluid Dynamics (CFD). Experimental results reveal three typical detachment modes of bubble-particle aggregates in the confined vortex: fluid shear, bubble oscillation, and particle centrifugal motion, with particle centrifugal detachment becoming dominant with increasing turbulence intensity. This shift is attributed to changes in turbulence intensity directly affecting the trajectories of bubble/aggregates and indirectly influencing the detachment mode of bubble-particle. Compared to low turbulence intensity, bubble-particle aggregates exhibit smaller rotational radii under high turbulence intensity, reducing the probability of fluid shear and bubble oscillation detachment by mitigating the influence of high-speed shear zones at the top of the cavity. Conversely, particles located at the edge of aggregates are more susceptible to acceleration by sidewall flow fields, favouring detachment through particle centrifugal motion. Moreover, unlike traditional centrifugal detachment theories, particles do not merely undergo independent circumferential motion on the bubble surface but participate as a whole with bubbles in centrifugal motion governed by vortices. These findings are expected to provide fundamental insights into the bubble-particle detachment mechanism in turbulent fields.

Mesenchymal Stem Cell and Hematopoietic Stem and Progenitor Cell Co-Culture in a Bone-Marrow-on-a-Chip Device toward the Generation and Maintenance of the Hematopoietic Niche.

Bone marrow has raised a great deal of scientific interest, since it is responsible for the vital process of hematopoiesis and is affiliated with many normal and pathological conditions of the human body. In recent years, organs-on-chips (OoCs) have emerged as the epitome of biomimetic systems, combining the advantages of microfluidic technology with cellular biology to surpass conventional 2D/3D cell culture techniques and animal testing. Bone-marrow-on-a-chip (BMoC) devices are usually focused only on the maintenance of the hematopoietic niche; otherwise, they incorporate at least three types of cells for on-chip generation. We, thereby, introduce a BMoC device that aspires to the purely in vitro generation and maintenance of the hematopoietic niche, using solely mesenchymal stem cells (MSCs) and hematopoietic stem and progenitor cells (HSPCs), and relying on the spontaneous formation of the niche without the inclusion of gels or scaffolds. The fabrication process of this poly(dimethylsiloxane) (PDMS)-based device, based on replica molding, is presented, and two membranes, a perforated, in-house-fabricated PDMS membrane and a commercial poly(ethylene terephthalate) (PET) one, were tested and their performances were compared. The device was submerged in a culture dish filled with medium for passive perfusion via diffusion in order to prevent on-chip bubble accumulation. The passively perfused BMoC device, having incorporated a commercial poly(ethylene terephthalate) (PET) membrane, allows for a sustainable MSC and HSPC co-culture and proliferation for three days, a promising indication for the future creation of a hematopoietic bone marrow organoid.

Bubble desorption enhanced superareophilic cooperative electrode for hydrogen evolution reaction

The efficiency of the hydrogen evolution reaction (HER) is significantly influenced by the accumulation of the H2 bubbles at the electrode reaction interface. Superhydrophobic/underwater superaerophilic materials can expedite bubble desorption on board. Therefore, in this study, a superaerophilic titanium felt (SALTF) is fabricated and positioned opposite to the working electrode (Pt). The cooperative electrode is referred to as the Pt//SALTF electrode. With adjustable distance between the flat Pt and the SALTF, bubble transfer from the flat Pt to the SALTF can be observed between them. Due to the enhanced bubble escape process, the overpotential for the Pt//SALTF cooperative electrode is reduced by 20 mV at −10 mA cm−2 and reduced by 92 mV at −100 mA cm−2 compared to that of the flat Pt electrode. At an overpotential of −500 mV, the current density for the flat Pt electrode is −146 mA cm−2, which increases to −209 mA cm−2 after assembling the Pt//SALTF. This mode of assembly greatly enhances HER performance through mass transfer enhancement.

Subcooled flow boiling characteristics and CHF in an eccentric annulus at low pressure conditions

Controlled flow boiling conditions enhance the heat transfer rate in various industrial applications such as heat exchangers, fuel rod bundles etc. In nuclear industry, the presence of mixing vanes, spacers, channel creep deformation etc., may lead to the formation of narrow and wide zones around the fuel rods. The asymmetry in the cross-sectional flow area around the fuel rod can be modelled as eccentricity which may cause an irregular coolant flow distribution affecting the heat transfer rate. In the present study, the eccentricity (e) is defined as the ratio of offset (s) to the difference in radii of inner and outer cylinders (Ro−Ri). The current study introduces a framework that involves calibrating the departure size of vapour bubble (D) in the EMF model framework which enables the accurate prediction of subcooled flow boiling characteristics and CHF power in an annulus (0.0≤e≤0.50) at low operating pressure conditions. The developed framework is validated with experimental data and a very good match is noticed. It is observed that eccentricity causes a decrease in coolant peak velocity magnitude by 12.8% in the narrow zone for e=0.50. In the subcooled region, the accumulation of vapour bubbles impedes further heat transfer to the liquid coolant, and thus the peak heated wall temperature (≈380.88K) is observed in the narrow zone for e=0.50. Eccentricity causes early coolant phase change which in turn results in early occurrence of CHF (q=522KWm−2) in the narrow zone of e=0.50. A quadratic relationship is also established to predict the CHF power in terms of eccentricity (e) within 5% variation.

Alkaline water electrolysis: Ultrasonic field and hydrogen bubble formation

In alkaline water electrolysis, gas bubble coverage of the electrode surface is directly linked with an increase in cell potential. Ultrasonic field presence in water electrolysis has been proven effective in removing gas bubbles from the electrode and enhancing mass transfer and bubble removal. Most studies regarding water electrolysis under sonification focused on low-concentration NaOH electrolyte solutions so there is a lack of information regarding operating conditions similar to commercial solutions. This work focused on an experimental evaluation of the effect of an ultrasonic field with a 40 kHz frequency on water electrolysis using a lab-scale electrolyser with three different KOH solutions varying in concentration (15, 25, 35% (w/w)) at 30, 40, 50, 60 °C. A reduction in cell potential was registered across all test conditions and it was maximum for 15 and 25% KOH solutions at 30 °C with 52 and 34 mV, respectively, and decreased with an increase in temperature. For a 35% KOH solution, the cell potential reduction stayed constant across all temperatures (16–19 mV). This difference was thought to be caused by the ultrasonic frequency and power and therefore required further testing. To further investigate the effect of gas bubble accumulation on the electrode surface, measurements of hydrogen bubbles’ critical diameter were taken. It was found that a higher electrolyte concentration results in a lower critical diameter (0.404, 0.356, and 0.293 mm with a 15, 25, and 35% KOH, respectively) assumed to be a consequence of higher viscosity and gas formation rate at higher concentrations.

Numerical simulation and model development of drag coefficient of bubbles in gas-liquid metal two-phase flow

The occurrence of a steam generator tube rupture (SGTR) accident in a lead-bismuth cooled fast reactor results in the formation of steam bubbles in the liquid lead-bismuth eutectic (LBE). This may degrade heat transfer and power transients in the reactor core due to the migration and accumulation of steam bubbles. To investigate the dynamics of steam bubbles flowing in liquid LBE, it is essential to develop an accurate model for the bubble drag coefficient. In this paper, a three-dimensional numerical model is first established to simulate the injection of high-pressure steam bubbles into a high-temperature LBE molten pool. The model is based on the CLSVOF method. By analyzing the trajectory, velocity, and diameter of bubbles, and combining them with the force equilibrium equation for bubbles, the values of the drag coefficient for bubbles are determined. On this basis, the suitability of current empirical drag models for bubble migration in LBE is evaluated. Finally, the optimal drag coefficient model is selected and further improved. Results reveal that the prediction error of the optimized model for the bubble drag coefficient in liquid LBE is within ±15 %.

Numerical Study on the Local Aggregation of Helium Bubbles in Liquid Lithium and Its Thermal Analysis

Abstract Liquid lithium is widely regarded as an optimal cooling medium for space nuclear reactors due to its exceptional heat transfer properties and low density. However, the helium bubbles generated by liquid lithium under space irradiation pose significant hazards to the safe and stable operation of nuclear reactions. This study employs the COMSOL finite element software to construct the level-set two-phase flow models and bubble stream model separately to investigate the local accumulation of helium bubbles and the overall flow of low-concentration gas–liquid mixtures. The main focus is on examining the different distributions of multiple helium bubbles randomly generated in local liquid lithium and the influence of boundary conditions on their accumulation morphology, as well as the impact of low-concentration bubble stream on their overall heat transfer performance. Agglomerated bubbles with radii between 5 μm and 150 μm are classified into three categories based on local concentrations: circular (≤20.37%), irregular elongated (up to 30.44%), and banded (up to 36.31%).The interconnected banded bubbles can be up to 8 times larger than irregularly elongated ones, and they have a positive effect on the distribution of physical quantities and wall temperature perturbations in the pipeline. The increase in inlet velocity triggers bubble impacts and fragmentation, further reducing thermal resistance and enhancing heat transfer performance. When the bubble diameter is less than 15 μm and the bubble concentration is within 1%, the influence of the mixed flow on overall heat transfer is not significant. This study provides insights for manipulating bubble structure and guiding localized and comprehensive thermal analyses.