In water electrolysis, achieving smaller bubble detachment diameters and shorter detachment times could enhances the efficiency of the electrolysis process. This study investigates the impact of H2SO4 and HNO3 electrolytes on the detachment of both oxygen and hydrogen bubbles from a platinum microelectrode with a diameter of 50 um, using high-speed photography and electrochemical measurements. The experiments show that oxygen bubbles exhibit shorter lifetimes and smaller detachment diameters than hydrogen bubbles in 1 mol/L H2SO4 electrolytes. Conversely, in 1 mol/L HNO3 electrolytes, hydrogen bubbles have shorter lifetimes and smaller detachment diameters than oxygen bubbles. The results indicate that Marangoni convection plays a critical role in the detachment of bubbles. These insights provide a new approach to accelerating bubble detachment from electrode surfaces during electrochemical bubble formation.

Understanding the dynamics of interacting gas bubbles is crucial for optimizing the efficiency of water electrolysis. This study systematically investigates the evolution behavior of dual hydrogen and oxygen bubbles and their impact on electrolysis performance using dual Pt microelectrodes with a fixed interelectrode distance of 1 mm in 1 mol/L H2SO4 and HNO3 solutions. Using high-speed imaging and electrochemical analysis, three distinct dual-bubble detachment modes are identified under different applied potentials: Mode I (buoyancy-driven detachment), Mode II (buoyancy- and wake effect-driven detachment), and Mode III (coalescence-driven detachment). The results show that the production rates of both H-2 and O-2 exhibit a nonlinear dependence on the applied potential, with an optimal potential observed for each system. Notably, simultaneous dual-electrode operation does not always enhance efficiency: compared to two independent single electrodes, the efficiency of dual hydrogen bubbles increases by 18% at -3 V in H2SO4 but decreases by 21.1% at -8 V in H2SO4, while that of dual oxygen bubbles decreases by up to 57.6% at 3 V in HNO3. With a fixed interelectrode distance, the performance of the dual-bubble system is governed by two factors: the operating potential, which primarily determines the plateau current magnitude, and the electrolyte type, which influences both the magnitude and direction of the solutal Marangoni force. These findings provide valuable insights into electrolyte selection and operational parameters aimed at enhancing the efficiency of water electrolysis.

The microlayer at the bottom of the bubble in nucleate boiling plays an important role in heat transfer. In this paper, the characteristics of microlayer under high heat flux are studied by laser interferometry. The thickness of the microlayer, the temperature distribution of the microlayer at the bottom of the bubble, the micro-contact angle, and the heat flux of the microlayer were studied. The results show that the uneven temperature distribution at the bottom of the bubble causes the deformation of the microlayer. The increase of evaporative heat flux of early stage the microlayer results in the bending of the thickness distribution of the microlayer.

Bubble coverage on the electrode surface significantly reduces the efficiency of water electrolysis. This study investigates the effects of current density and microelectrode size on the growth and detachment dynamics of hydrogen and oxygen bubbles during water electrolysis. A high-speed camera is used to capture the dynamic behavior of bubble evolution and electrochemical measurements are conducted to record the instantaneous potential fluctuations. The results reveal that the bubble detachment size depends on the electrode size. At identical current densities, as the diameter of microelectrodes decreases, the generated hydrogen and oxygen bubbles exhibit smaller detachment diameters. Moreover, as the current density increases, the detachment diameter of bubbles increases. The results indicate that solutal Marangoni convection plays a critical role in the detachment of bubbles. These findings provide critical insights into bubble dynamics for optimizing electrolysis efficiency.

This study was devoted to the theory of microlayer evaporation and bubble dynamics. In subcooled flowing boiling, a theoretical study of the mechanism of heat and mass transfer in vapor bubbles during boiling heat transfer has been carried out. The forces on mononuclear boiling bubbles during subcooled flow boiling are analyzed. In addition, the effect of microlayer evaporation was considered, and microlayer evaporation force has been introduced. Evaporation of the microlayers as between the bottom of a bubble and the heated wall, evaporation of the layer of superheated liquid around the bubble, the condensation of the vapors at the top of a bubble are taken into account on the basis of the bubble dynamics. The prediction models for bubble forces, departure and lift-off diameters were improved. The influence of force on the bubble under the same working conditions was also investigated. Compared with previous experimental results, it was found that the improved model could forecast the diameters of the bubble departure and bubble lift-off well.

In the process of boiling heat transfer, the microlayer is not only a crucial medium for enhancing heat transfer but also directly determines the heat flux distribution, dry zone expansion, and overall heat transfer efficiency through its morphological evolution and evaporation behavior. Building on this, this study employs the Lattice Boltzmann Method (LBM) with a single-component multiphase model to numerically simulate the evaporation process of microlayers on non-isothermal walls. The results show that, due to the uneven velocity distribution in the flow field, the microlayer exhibits significant contraction behavior during evaporation, particularly at the three-phase contact point, where velocity differences lead to fluid accumulation and the formation of a “cap-like” structure. The initial growth of the dry zone follows a linear trend, but its growth rate gradually decreases as the microlayer thickness increases, while near-wall density effects result in residual thickness within the dry zone. Additionally, the microlayer height first increases and then decreases over time, accompanied by a noticeable time lag. Heat flux analysis reveals that, during the formation of the dry spot, the lowest heat flux occurs at the three-phase contact point, followed by a sudden increase. A cold air ring forms above the dry zone, expanding and splitting as it moves with the dry spot. Higher temperatures promote microlayer evaporation, with the evaporation volume exhibiting nearly linear growth and the total fluid mass decreasing linearly.

In water electrolysis, achieving smaller bubble detachment diameters and shorter detachment times could enhances the efficiency of the electrolysis process. This study investigates the impact of H2SO4 and HNO3 electrolytes on the detachment of both oxygen and hydrogen bubbles from a platinum microelectrode with a diameter of 50 μm, using high-speed photography and electrochemical measurements. The experiments show that oxygen bubbles exhibit shorter lifetimes and smaller detachment diameters than hydrogen bubbles in 1 M H₂SO₄ electrolytes. Conversely, in 1 M HNO₃ electrolytes, hydrogen bubbles have shorter lifetimes and smaller detachment diameters than oxygen bubbles. The results indicate that Marangoni convection plays a critical role in the detachment of bubbles. These insights provide a new approach to accelerating bubble detachment from electrode surfaces during electrochemical bubble formation.

Imposing uniform electric field is an effective method to enhance boiling heat transfer with the critical density flux (CHF) or/and heat transfer performance being increased. Contact angle hysteresis (CAH) is an inherently inevitable phenomenon for a nonideal real surface. In this work, we study the coupling effects of a uniform electric field and the contact angle hysteresis on pool boiling in FC-72, exploring the mechanisms that improve the boiling heat transfer of dielectric fluids on nonideal real surfaces in the presence of an electric field force. According to the numerical analysis, the electric field always promotes boiling heat transfer at high wall superheats and suppresses it at low wall superheats. This phenomenon is related to bubble dynamics under various wall superheats. Both the bubble size and nucleation site number reduce under a low wall superheat. At high wall superheats, the electric field prevents bubbles from merging and increases the wetted area. The effect of an electric field on the CHF, however, relies on the properties of the heater surface. The CHF rises as the electric field intensifies on the ideal hydrophilic and hydrophobic surfaces. If the width of the CAH is modest, the CHF grows with the increase in the electric field strength on nonideal hydrophilic surfaces. The relationship among the electric field strength, hysteresis windows, and CHF becomes more complicated in the case of a large hydrophilic hysteresis window and a minimal electric field strength. In addition, the CHF drops as the contact angle hysteresis rises on both the hydrophilic and hydrophobic surfaces.

For the study of sessile droplets evaporating on heated (non-isothermal) walls by the single-component Lattice Boltzmann method, it is necessary to apply a ghost fluid layer near the border to calculate the adhesive force between the liquid particles and the solid wall. In this paper, we apply three commonly used fluid-solid interaction schemes, combined with four methods for constructing ghost fluid layers, and specifically investigate the effects of using different combinations of schemes on the results of maximum spurious velocity and near-wall fluid density deviation of heated droplets, respectively. Finally, the most suitable schemes was found in the normal range contact angle, hydrophobic contact angle, and more hydrophilic contact angle. And the reasons why some contact angle schemes can't be realized are analyzed. In addition, the temperature and velocity fields of the heated droplet formed under different schemes were analyzed, and the conclusions are in agreement with the previous theoretical analysis.

The problem of droplets impacting rough wall has always been a hot spot in the engineering field. In this paper, the single-component multiphase lattice Boltzmann method is used to construct the wall microstructure, and the dynamic behavior characteristics of droplets impacting rough walls are simulated. The results show that the final state of a droplet impacting rectangular microstructure shows that the hydrophilic surface is more hydrophilic and the hydrophobic surface is more hydrophobic, and compared with the smooth surface, the microstructure surface hinders the rebound of the droplet, and the application of microstructure on the wall can promote the spreading of a droplet on the wall.

Various numerical schemes of contact angle are widely used in pseudopotential lattice Boltzmann model to simulate substrate contact angle in condensation. In this study, effects of numerical schemes of contact angle on condensation nucleation and heat transfer simulation are clarified for the first time. The three numerical schemes are pseudopotential-based contact angle scheme, pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate with weighted average density of surrounding fluid nodes, and the geometric formulation scheme. It is found that the subcooling condition destabilizes algorithm of pseudopotential-based contact angle scheme. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the algorithm becomes stable. The subcooling condition also decreases the simulated contact angle magnitude compared with that under an isothermal condition. The fluid density variation near a microcavity wall simulated by pseudopotential-based contact angle scheme plays the role of the condensation nucleus and triggers “condensation nucleation”. However, with a ghost fluid layer constructed on the substrate or using geometric formulation scheme, the simulated fluid density distribution near the wall is uniform so that no condensation nucleus appears in the microcavity. Thus, “condensation nucleation” cannot occur spontaneously in the microcavity unless a thin liquid film is initialized as a nucleus in the microcavity. The heat flux at the microcavity wall is unphysical during the “condensation nucleation” process, but it becomes reasonable with a liquid film formed in the microcavity. As a whole, it is recommended to use pseudopotential-based contact angle scheme with a ghost fluid layer constructed on the substrate or use the geometric formulation scheme to simulate condensation under subcooling conditions. This study provides guidelines for choosing the desirable numerical schemes of contact angle in condensation simulation by pseudopotential lattice Boltzmann model so that more efficient strategies for condensation heat transfer enhancement can be obtained from numerical simulations.

Based on the dynamic microlayer and macrolayer evaporation models, the mechanisms of single bubble micro and macrolayer evaporation were studied. The nucleate boiling heat transfer and the dynamic characteristics of a single bubble in micro and macrolayers are closely related to the wall temperature. The present work investigates the effects of time and distance on the formation of micro and macrolayer during the growth of a single bubble on a heated horizontal wall. A new complex microlayer and macrolayer model is established. The initial microlayer thickness, dry spot radius, and macrolayer thickness are calculated. The model is compared with experimental data on the evaporation of water and ethanol in the presence of nucleating bubbles. It is found that the previous experimental data are within the range of ±25% of the proposed model, and the predicted data of the model are in good agreement with the experimental data.

Hydrate crystals' microscopic characteristics and agglomerating morphologies play an important role in the hydrate reaction equipment's flow assurance and heat transfer. In order to study the formation process of hydrate, experimental quartz tubes with small diameters were selected, and a fully visualized flow loop system was established. The study investigated the effects of supercooling, solution concentration, tube diameter, and flow rate on hydrate blockage time and agglomeration morphology. The results show that under the same supercooling conditions, the density of single crystal hydrate formed in 10 wt%-20 wt% TBAB (Tetra-n-butylammonium bromide) hydrate solution is low, and the crystal front appears needle-like or sword-like, which is conducive to mass and heat transfer. High concentration TBAB solution(30 wt%-40 wt%) can form dense hydrate crystals, and the tip effect was significantly weakened. For low concentration TBAB solution, the increased flow rate can accelerate the formation of new nuclei and inhibit the growth of large crystals. Grout solutions with different particle sizes can be obtained by adjusting the flow rate. It was found that the initial morphology of TBAB hydrate crystals included spherical and cylindrical shapes, and the morphological evolution process of a single hydrate crystal was similar. Finally, a microscopic physical model of the TBAB hydrate growth and aggregation process was established.

It is well established that the microlayer beneath the bubble plays a pivotal effect in the heat trans-fer in nucleation boiling. However, experimental studies of microlayers in small channel flow boiling are scarce due to measurement difficulty. In this study, laser interferometry and high-speed camera tech-niques were used simultaneously to investigate the microlayer dynamic characteristics beneath boiling bubbles in a small channel. It is found that the microlayer's interference fringe is still not a complete "Newtonian ring" in small horizontal channels. The downstream of the bubble, the microlayer still shows a "wedge" structure, and the initial microlayer thickness distribution is similar to that of the pool boiling. The microlayer is not entirely evaporated, and the rewetting phenomenon occurs simultaneously with the evaporation of the microlayer. The newly dry spot area and the rewetting area show the characteristics of first increasing to a maximum and then decreasing. (c) 2022 Elsevier Ltd. All rights reserved.

In this paper, simulation results of droplet impact motion on hydrophilic (theta=80 degrees) and hydrophobic (theta=160 degrees) orifice surfaces are obtained by a single component multiphase lattice Boltzmann model (LBM). And a piecewise relaxation time is used to improve the numerical stability under high liquid/vapor density and low droplet viscosity. The effects of Weber (We) number, Ohnesorge (Oh) number, orifice thickness, and the diameter ratio of the orifice and droplet on the deformation process of the droplet impact on hydrophilic and hydrophobic orifice plates were studied, including the phenomena of liquid slug and breakage. As a result, at a low We number, the droplet is not easy to pass through the orifice, and the liquid plug phenomenon will be formed in the hydrophilic orifice, which is because of the hydrophilic effect on the orifice surface forms capillary action. At a high We number, the droplet will break when it impacts the orifice plate. In addition, the critical We number of droplets passing through the surface of a hydrophilic orifice has a linear relationship with the thickness of the orifice, while there is a critical We number of droplets passing through the surface of a hydrophobic orifice, which corresponds to two different forms of passage: peristaltic form and rapid through the form. The state diagram of the droplet with different We number, orifice diameter and droplet diameter ratio is obtained, which can be used to predict the different states of the droplet after impacting the orifice. According to the We number and Oh number, a graph for predicting droplet rupture is obtained. The critical We number increases with the increase of The Oh number, which means that the more viscous droplet requires a larger We number to rupture.

Based on lattice Boltzmann method, the numerical simulation of droplet impinging on orifice plates with different wettability was carried out. The influence of weber number (We) number, wettability of orifice surface and orifice size on different states of droplet passing through orifice plate during droplet impact was studied. The numerical simulation results show that different phenomena will occur in the process of droplet impacting the orifice plate: when the orifice plate is hydrophilic, the droplet will not detach from the surface of the orifice plate, but adhere to the lower surface of the orifice plate at a lower We number, and the droplet will rise a certain distance in the orifice channel under the action of capillarity, forming liquid plugging phenomenon. At higher We numbers, droplets will pass through the orifice plate and rupture will occur. When the orifice plate is hydrophobic, the droplets can not pass through the orifice plate and can not migrate to the lower surface at a lower We number, and finally stabilize on the orifice channel. At higher We numbers, droplets can pass through the orifice plate, and when they pass through, they will break, leaving droplets remaining on the surface of the orifice plate. When the orifice size was changed, it was found that the droplet was not easy to pass through when the orifice size was smaller or the orifice thickness was thicker.

The microlayer present at the bottom of the bubble plays a very important role in heat transfer during nucleation boiling. In this paper, the dynamic characteristics of microlayer at the bottom of boiling bubble in a small channel were studied by laser interferometry method and high speed camera, and the results were compared with pool boiling experiments. The results show that the bubbles have an obvious tendency to slip in the flow boiling. The microlayer interference fringe is deformed and no longer a complete Newtonian ring. By analyzing the thickness distribution of microlayer in different directions in flow boiling and the change of micro-contact angle in the flow direction, it was found that the micro-contact angle in the flow direction became larger with the growth of bubbles.

The rapid formation rate and high storage capacity of clathrate hydrates are crucial for natural gas storage and transportation. In this study, a series of wet tobacco samples prepared by soaking different masses of tobacco shred/granules in water were used to store methane in the hydrate. Gas consumption experiments were conducted in an unstirred reactor to investigate the hydrate formation kinetics in the tobacco/water mixtures and their filtrates at 274.15 K and 8.0 MPa. The results demonstrated that the tobacco solutions with surfactivity played a promoting role in the hydrate formation. The wet loose biomass materials provided abundant nucleation sites for gas to solid hydrates. Compared to pure water, the tobacco-water mixtures significantly shorten the induction time of nucleation and accelerate hy-drate growth. The amount of methane stored in tobacco granule systems ranged from 112.3 to 160.3 cm(3) cm(-3), and the storage rates reached 2.06-5.58 cm(3) cm(-3)center dot min(-1). The wet tobacco shreds exhibited higher gas uptakes (132.6-171.6 cm(3) cm(-3)) than the tobacco granule systems and tobacco shreds filtrates at the same liquid-solid ratio. The use of green wet tobacco samples to enhance of hydration should be helpful for the extension of hydrate-based technology. (c) 2021 Elsevier Ltd. All rights reserved.

TBAB (tetrabutylammonium bromide) can generate semi-cage hydrate at atmospheric pressure, which has high energy storage density and can be applied to cold storage technology. Small channel has the characteristics of high heat exchange efficiency and can generate hydrate more efficiently. In this paper, 2 mm and 3 mm quartz tubes with inner diameter were used as experimental tubes. The hydrate crystal morphology and agglomeration morphology generated by the flow in the tube were captured by industrial microscope. The effects of undercooling degree and diameter of solution concentration and flow rate on the blockage time and agglomeration process of hydrate morphology were studied. It was found that the density of single crystal hydrate formed by TBAB (10 wt