Mass Transfer Characteristics Research Articles

The Phase Distribution Characteristics and Interphase Mass Transfer Behaviors of the CO2-Water/Saline System under Gathering and Transportation Conditions: Insights on Molecular Dynamics.

In order to investigate the interphase mass transfer and component distribution characteristics of the CO2-water system under micro-scale and nano-scale transport conditions, a micro-scale kinetic model representing interphase mass transfer in the CO2-water/saline system is developed in this paper. The molecular dynamics method is employed to delineate the diffusion and mass transfer processes of the system's components, revealing the extent of the effects of variations in temperature, pressure, and salt ion concentration on interphase mass transfer and component distribution characteristics. The interphase mass transfer process in the CO2-water system under transport conditions can be categorized into three stages: approach, adsorption, and entrance. As the system temperature rises and pressure decreases, the peak density of CO2 molecules at the gas-liquid interface markedly drops, with their aggregation reducing and their diffusion capability enhancing. The specific hydration structures between salt ions and water molecules hinder the entry of CO2 into the aqueous phase. Additionally, as the salt concentration in water increases, the density peak of CO2 molecules at the gas-liquid interface slightly increases, while the density value in the water phase region significantly decreases.

Effect of Hydrogen Pressure on The Mass Transfer Characteristics of Hydrogen-Bromine Flow Battery Electrodes

The mass transfer characteristics of porous carbon electrodes in the liquid side of a hydrogen bromine redox flow battery (H2-Br2 RFB) were investigated under compressive deformation caused by operation at elevated hydrogen pressure. Here, flow cell measurements of permeability and micro-particle image velocimetry (μPIV), alongside electrochemical measurements of capacitance and battery discharge were used to characterize changes in the liquid side electrode compression, in-plane liquid flow, accessible surface area, polarization, and mass transfer scaling brought by hydrogen pressure. We studied two electrode types with different structures, carbon paper and carbon cloth, in untreated well as heat-treated forms in the pressure range 0–8 bar H2. It was found that pressure-induced compression of the liquid side electrode increases the accessible area of untreated electrodes, with little effect on heat-treated electrodes, but decreases the electrochemical performance of the battery in all cases by increasing the ohmic resistance of the cell and decreasing the mass transfer coefficient of the porous electrode. Overall, heat treatment is shown to affect the rigidity, saturation behavior, and generalized mass transfer of paper electrodes but not of cloth electrodes. Our findings will guide the selection of electrode materials and operation parameters for the H2-Br2 RFB.

Experimental study on the mass transfer and microscopic distribution characteristics of remaining oil and CO2 during water-miscible CO2 flooding

Accurate understanding and quantitative characterization of the microscopic distribution and mobilization mechanisms of remaining oil are crucial for further enhancing oil recovery during CO2 flooding. In this study, miscible CO2 flooding experiments after water flooding were performed to investigate the mass transfer and microscopic distribution characteristics of remaining oil and CO2 using micro-computed tomography technique. Additionally, the distribution characteristics of multiphase fluids (oil, water and CO2) in the pores were comprehensively investigated. Furthermore, the mass transfer effects during the miscible CO2 flooding process, as well as the CO2 sequestration ratio (SR) and sequestration factor (SF) were systematically examined. The experimental results show that the ultimate oil recovery factor after miscible CO2 flooding were 80.9 %, 70.7 %, and 64.7 %, respectively. During the water flooding stage, the produced oil mainly consisted of light hydrocarbons (C5–C16), followed by medium hydrocarbons (C17–C27). The remaining oil was mainly in cluster and network pattern, followed by multiple and oil film pattern. After miscible CO2 flooding, the produced gas mainly consisted of CO2 and CH4, with a significant increase in the mass fraction of light hydrocarbons (C5–C16) in the produced oil. The remaining oil was mainly in multiple and singlet pattern, followed by network and film pattern, with a small portion in cluster pattern. The higher the displacement rate, the smaller the SR, but most of the injected CO2 (SR > 70 %) was retained in the porous media, demonstrating the feasibility of CO2 geological sequestration during the miscible flooding process.

Numerical investigation of heat and mass transfer characteristics of steam condensation containing non-condensable gas in vertical corrugated tube

A numerical simulation of steam condensation containing non-condensable gas is conducted in this paper to analyze the heat and mass transfer characteristics in vertical corrugated tube. The species transport model, Euler liquid film model and diffusion-balance model with Dehbi factor to correct the diffusion effect are applied to simulate the mass and energy transfer processes. The effects of different corrugated tube structural parameters and inlet steam parameters on steam condensation rate, liquid film distribution and heat transfer are simulated. The results show that vortex and accumulated non-condensable gas in the corrugated region significantly influence condensation heat transfer, which are closely related to corrugation height (H=0–5 mm) and corrugation length (L=13, 16, 19, 22, and 25 mm) of the corrugations, as well as inlet velocity (Vin = 5, 7, 9, 11, 13, and 15 m·s−1) and inlet steam content (Ws = 0.6, 0.7, 0.8, 0.9, 0.99, and 1). The total heat transfer coefficient varies linearly with inlet velocity when inlet velocity increase from 5 m·s−1 to 15 m·s−1, which increase 89.6–108.1 %; total heat transfer coefficient increases almost exponentially when inlet steam content increase from 0.6 to 1, which increase 389–460 %; and the best corrugated tubes are those with corrugation height of 0.075 times diameter of tube and corrugation length of 0.325 times diameter of tube.

Computation of soret effect in sisko nanofluid flow over a stretching sheet encompassing chemical reaction and viscous dissipation

This article examines the characteristics of mass and heat transfer in Sisko fluid flow. The consideration is given to continuous, two-dimensional movement of Sisko fluid exhibiting incompressible and viscous characteristics. The fluid flows over a stretching sheet encompassing chemical reaction and subjected to the soret effect and viscous dissipation. The arising set of interconnected PDEs is converted to nonlinear ODEs using similarity transformations. This study reveals that an increase in the Soret number induces an upward shift in the concentration profile across the flow region. Also, an increase in the Sisko fluid parameter gives rise in the skin-friction coefficient. Following the calculations, the results for the heat, mass transfer rate and skin-friction coefficient, are compiled and presented in a tabulated form. A systematic discussion of similarity solutions in comparison with established findings not only validates the accuracy of the numerical results but also underlines the reliability and robustness of the methodology applied in this study.

An investigation on hydrodynamic behavior of horizontal gas–liquid intermittent flow by S-PLIF and parallel-wire conductance sensors

Horizontal gas–liquid two-phase flows widely exist in a variety of industrial fields such as the environment, chemical industry and energy. Intermittent flow, characterized by the quasi-periodic alternation motion of liquid slugs and large-scale Taylor bubbles, is the most prevalent flow pattern in horizontal gas–liquid two-phase flows. Comprehensive research on the hydrodynamic behavior of gas–liquid intermittent flow is essential for revealing the mass and heat transfer characteristics between phases, thereby establishing physical models of flow parameters. In this study, a structured planar laser-induced fluorescence (S-PLIF) system and paired parallel-wire conductance sensors (PWCSs) are designed to detect the gas–liquid interface structures and the hydrodynamic parameters. The S-PLIF system consists of a laser, a visualization box, a Ronchi ruling-plate and a pair of high-speed cameras. An optical linear prism forms a laser sheet in the transverse direction and the middle of the test section, and the cameras are positioned at 70° and 90° respectively to the plane of the laser sheet, referred to as S-PLIF70 and S-PLIF90. Under the laser excitation, bright and dark stripes generated by the Ronchi ruling-plate are deflected at the gas–liquid interface. The influence of total reflection can be effectively avoided by identifying the deflection position of the stripes, allowing for accurate detection of the gas–liquid interfacial structures. The effects of the interface fluctuations and detached bubbles on the S-PLIF70&90 results are investigated. Fluctuation and evolution characteristics of the gas–liquid interface are analyzed by probability density function (PDF) and power spectral density (PSD). Meanwhile, hydrodynamic parameters, i.e., Taylor bubble nose and tail velocity, Taylor bubble and slug length, and slug frequency, are detected by the PWCSs, and compared with previous correlations. The evolution characteristics of the interfacial structures and hydrodynamic parameters are uncovered as the flow condition changes.

Comparative numerical study featuring magnetized nanofluids configured by elongating sheet with thermophoresis and Brownian motion

This study investigates the heat and mass transfer characteristics of MHD rotating Fe₃O₄-Al₂O₃/H₂O hybrid nanofluid flow over a three-dimensional stretching surface. Comparative analysis was conducted among the base fluid H₂O, Al₂O₃-H₂O nanofluid, and Fe₃O₄-Al₂O₃/H₂O hybrid nanofluid, focusing on velocity, temperature, and concentration distributions influenced by thermophoresis, Brownian motion, Hall current, temperature ratio, magnetic parameter, rotation, and thermal radiation. The governing nonlinear partial differential equations were transformed into ordinary differential equations using similarity adaptations and solved numerically with the BVP-5C method in MATLAB. Results indicate that increasing the thermophoresis and Brownian motion parameters elevates the temperature profile while affecting the concentration distribution differently. The hybrid nanofluid exhibited a higher temperature distribution compared to the nanofluid and base fluid, whereas the base fluid showed a greater concentration gradient.

Study on the mass transfer characteristics of hydrogen in heavy oil by a modified dynamic pressure step method

The dissolved hydrogen, rather than gaseous hydrogen, plays a crucial role in the hydrogenation process. A thorough understanding of hydrogen dissolution is essential for optimizing the hydrogenation process. In this paper, the dynamic pressure step method was modified to reduce the temperature difference between the hydrogen and solution, from which the hydrogen solubility and volumetric liquid-side mass transfer coefficient (kLa) of the vacuum residue were obtained. It was discovered that temperature was the most critical factor in hydrogen dissolution, simultaneously enhancing both the hydrogen solubility and kLa. Pressure played a significant role in promoting hydrogen solubility, but had a relatively small impact on kLa. Stirring speed, although it enhanced kLa, did not affect hydrogen solubility. By normalizing the dissolution parameter, the results showed that the gas-liquid mass transfer rate decreased continuously during hydrogen dissolution and that the SD-tD curves after normalization were almost the same in all experimental conditions.

A numerical study of heat and mass transfer characteristic of three-dimensional thermally radiated bi-directional slip flow over a permeable stretching surface

Within fluid mechanics, the flow of hybrid nanofluids over a stretching surface has been extensively researched due to their influence on the flow and heat transfer properties. Expanding on this concept by introducing porous media, the current study explore the flow and heat and mass transport characteristics of hybrid nanofluid. This investigation includes the effect of magnetohydrodynamic (MHD) with chemical reaction, thermal radiation, and slip effects. The nanoparticles, copper, and alumina are combined with water for the formation of a hybrid nanofluid. Using the self-similar method for the reduction of Partial differential equations (PDEs) to the system of Ordinary differential equations (ODEs). These nonlinear equation systems are solved numerically using the bvp4c (boundary value solver) technique. The effect of the different physical non-dimensional flow parameters on different flow profiles such as velocity, temperature, concentration, skin friction, Nusselt and mass transfer rate are depicted through graphs and tables. The velocity profiles diminish with the effect of magnetic and slip parameters. The temperature and concentration slip parameters reduce the temperature and concentration profile respectively. The higher values of magnetic factor lessened the skin friction coefficient for both slip and no-slip conditions. An elevation in the thermal slip parameter reduced the boundary layer thickness and the heat transfer from the surface to the fluid. The Nusselt number amplified with the climbing values of the radiation parameter. The mass transfer rate depressed with the solutal slip parameter. Comparison is made with the published work in the literature and there is excellent agreement between them.

Boundary layer analysis on magnetohydrodynamic dissipative Williamson nanofluid past over an exponentially stretched porous sheet by engaging OHAM

PurposeThis investigation delves into the rationale behind the preferential applicability of the non-Newtonian nanofluid model over alternative frameworks, particularly those incorporating porous medium considerations. The study focuses on analyzing the mass and heat transfer characteristics inherent in the Williamson nanofluid’s non-Newtonian flow over a stretched sheet, accounting for influences such as chemical reactions, viscous dissipation, magnetic field and slip velocity. Emphasis is placed on scenarios where the properties of the Williamson nanofluid, including thermal conductivity and viscosity, exhibit temperature-dependent variations.Design/methodology/approachFollowing the use of the OHAM approach, an analytical resolution to the proposed issue is provided. The findings are elucidated through the construction of graphical representations, illustrating the impact of diverse physical parameters on temperature, velocity and concentration profiles.FindingsRemarkably, it is discerned that the magnetic field, viscous dissipation phenomena and slip velocity assumption significantly influence the heat and mass transmission processes. Numerical and theoretical outcomes exhibit a noteworthy level of qualitative concurrence, underscoring the robustness and reliability of the non-Newtonian nanofluid model in capturing the intricacies of the studied phenomena.Originality/valueAvailable studies show that no work on the Williamson model is conducted by considering viscous dissipation and the MHD effect past over an exponentially stretched porous sheet. This contribution fills this gap.

Quantitative analysis of heat and mass transfer in MoS2-Al2O3/EG hybrid flow between parallel surfaces with suction/injection by numerical modeling of HPM method

This description focuses on how the magnetic field affects mass and heat transfer in a hybrid nanofluid (Hnf) between two parallel, rotating plates. By dispersing aluminum oxide (Al2O3) and molybdenum disulfide (MoS2) nanoparticles (NPs) in ethylene glycol (EG), a hybrid nanofluid (Hnf) is created. This research aims to analyze the heat and mass transfer characteristics in the flow of a hybrid nanofluid (MoS2-Al2O3/EG) between two rotating parallel plates under the influence of a magnetic field. Furthermore, the statistical technique of response surface methodology (RSM) has been employed to optimize the parameters of velocity, temperature, and concentration of the nanofluid within the flow region bounded by the rotating plates. Dimensionless differential equations have been calculated and checked using the Homotopy perturbation method. This study introduces a novel approach by utilizing the RSM method to identify optimal points for velocity and temperature parameters of nanofluids between two stretching plates for the first time. Additionally, the article innovatively applies the exact HPM method to validate dimensionless linear and non-linear coupling equations. As the Reynolds number and the suction/injection coefficient of nanofluids flowing between two plates under tension increase, the results indicate a decrease in the velocity field. This decrease in velocity field can be attributed to the reduction in fluid diffusion as viscous forces diminish with varying Reynolds numbers. The ideal temperature distribution for nanofluids flowing between two parallel plates occurs when they are uniformly dispersed at the midpoint between them. As the distance from the initial point of nanofluid entry to the end of the plates increases, along with the vertical distance from the bottom plate, the temperature gradient diminishes, reducing the thickness of the thermal boundary layer. The velocity gradient and the rate of heat flux transfer between the nanofluid and plate rise by 34 % when the volume percentage is raised from 1 % to 5 %.

Characterization of turbulent multiphase particle mass transfer in gas-liquid flows

Turbulent mass transfer is crucial in the design and operation of industrial multiphase gas-liquid flow reactors. Despite its ubiquity, due to the complexity of multiphase turbulent flows, there is a lack of computational models and experimental data on mass transfer fluxes at the local scale for non-ideal bubbles. We develop a new measuring technique to visualize a well-known multiphase transfer problem: the local retention of water-soluble aerosols in large rising cap bubbles. The hydrodynamics of the bubble and the liquid phase electrolyte concentration of the water-soluble aerosols are resolved with high spatial and temporal resolution via conductivity measurements using a high-resolution Wire-mesh sensor of 1mm pitch with an acquisition frequency of 3200Hz. We obtain a representation of prototypical cap bubbles of 8.25mm equivalent spherical volume bubble diameter, and the associated wakes containing the dissolved aerosol material based on reconstruction from the available large ensemble of bubbles. These high-fidelity grade data can be directly used to develop and validate particle mass transfer models for heterogeneous multiphase flows. At the multiphase flow regime in this work, the particle mass transfer is governed by inertial effects in the gas phase and by turbulent diffusivity and interface-related oscillations in the liquid phase. We formulate a physical model of the phenomenon that considers turbulence's stochastic nature via the Reynolds decomposition of the investigated variables. Our model supports the interpretation of the measured data. It also enables the calculation of the particle mass transfer flux directly from the concentration field in the mass transfer wake. The predictions and assumptions of our model are validated against the experimental measurements. This work will be extended to resolve the transient behavior of the aerosol retention, and to calculate the associated particle mass transfer coefficients.

Numerical investigation of corrosive gases absorption process by water injection in hydrogenation reaction effluent system

Abstract Water injection for absorbing corrosive gases NH3, HCl and H2S is a widely employed method to mitigate the risk of ammonium salt corrosion in the hydrogenation units. To ensure the efficient prevention of ammonium salt corrosion, a numerical model integrating the hydrodynamics of gas–liquid and the reaction of interphase mass transfer was built based on Euler–Lagrange method in this work. The flow and mass transfer characteristics of complex multi-component system in water injection pipeline were investigated, and the correlation between process operating conditions and gas removal performance was analyzed. The results reveal that the removal efficiencies of corrosive gases in pipeline are influenced by the characteristics of gas–liquid flow and mass transfer, with HCl showing higher removal efficiency compared to NH3 and H2S. Furthermore, the increasing flow rate of water injection, the reducing corrosive medium content and the decreasing droplet diameter have a positive impact on the removal efficiencies of corrosive gases, while the impact of gas-flow velocity on the removal efficiencies of corrosive gases primarily depends on the residence time of droplets. These results have important theoretical value and engineering guiding significance for intensifying the process of water injection in hydrogenation units.

Gas–liquid mass-transfer characteristics during dissolution and evolution in quasi-static and dynamic processes

This study aims to understand the comprehensive behavior of the gas–liquid flow and dissolution–evolution mass transfer. A quasi-static closed-tank experiment was designed to measure the static mass-transfer coefficients of the dissolution and evolution processes using the diffusion equation. After a detailed uncertainty analysis, a dynamic ventilated-pipe experiment with different-sized orifice plates was designed to illustrate the relationship between the hydrodynamic parameters, physical structure, and gas–liquid mass-transfer characteristics. The results showed that, as the static pressure and liquid-level height increase, both the dissolution and evolution coefficients exhibit increasing trends. However, when the physical condition reaches the initial state after pressurization and depressurization, the gas absorbed by the solution cannot completely evolve from the solution; that is, the dissolution rate is always greater than or equal to the evolution rate. For the equal-diameter pipe, as the gas flow rate increases, the concentration increment decreases slightly after reaching the peak, owing to the reduction in mass-transfer time caused by the increase in liquid flow rate. In particular, the maximal dissolved concentration, an increment of 210.9 %, occurred in the double large-orifice plate with the ventilated condition, far exceeding the maximum value in the quasi-static process. Moreover, the concentration under the layout of two small-orifice plates decreases slightly, and the larger gas content enables the solution to have more gas nuclei, making it easier to induce the gas evolution. The current study provides guidance for the gas–liquid-mixture transportation and improvement of the dissolved efficiency.

Simulation study on heat and mass transfer characteristics within tubular moving bed heat exchangers

In the field of waste heat recovery, tubular moving bed heat exchangers (MBHEs) hold great promise as equipment capable of effectively handling large-sized granular materials with high temperature. To further clarify the heat and mass transfer characteristics within tubular MBHEs, this study firstly conducted detailed investigations on the contributions of different heat transfer mechanisms. The result shows that heat radiation (∼45 %) and gas film heat conduction (∼42 %) control the heat transfer processes involving tube walls, with an inlet particle temperature of 600 °C, tube wall temperature of 50 °C, and particle descent velocity of 2 mm/s. These contributions can be influenced by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. Additionally, for a specific particle, its heat transfer state is highly depended on where it is located. Subsequently, the time-varying and space-varying characteristics of the heat transfer processes involving tube walls are studied. The results suggest that the time-varying and space-varying characteristics are inherent in tubular MBHEs due to the difficulty to achieve complete stability. Meanwhile, temporal fluctuations intensify with an increase in the inlet particle temperature, a decrease in wall temperature, or an increase in particle descent velocity. The result of power spectral density (PSD) indicates that the heat transfer processes exhibit a degree of chaotic behavior due to the nonlinear property of sub-models, as well as the randomness in particle feeding and contacts. The space-varying characteristic is mainly determined by the inlet particle temperature and the tube wall temperature, rather than the particle descent velocity. This characteristic can be observed in both the axial and circumferential directions, with the circumferential variation being more pronounced than the axial variation. Furthermore, a double-tube MBHE, a topic that has received scant attention in previous research, is investigated in comparison to a single-tube MBHE to explore the differences in heat and mass transfer between the two configurations. It indicates that under the same boundary conditions, there are differences in heat transfer results, which are attributed to the interactions between two vertically arranged tubes. These interactions are reflected in the reconstruction of particle flow patterns and the effect altering the temperature distribution for the particles or fluid surrounding the tubes. The obtained results provide valuable insights into the mass and heat transfer behaviors of particles and fluids within tubular MBHEs, laying a foundation for advancing the development of efficient tubular MBHEs.

Study of electric field-enhanced mass transfer and Li/Mg separation of N, N-bis (1-methylheptyl) acetamide/TBP-NaFeCl4 composite membrane

Using N,N-bis(1-methylheptyl)acetamide (N503) synergized with TBP-NaFeCl4 (TFe), a ternary composite extraction membrane known as TFeN-PIM was created. Under optimum membrane phase conditions, the mass transfer properties of TFeN-PIM-Li(Ⅰ) and its Li/Mg selective separation performance by electric field augmentation were examined, and confirmed the mechanism of TFeN-PIM-Li(Ⅰ) electric field enhanced mass transfer. The findings demonstrate a homogeneous distribution of [FeCl4-] in the TFeN-PIM membrane phase and a decrease in the water contact angle as the TFe content increases. In the TFeN-PIM membrane, the cation binding order of the composite carrier was H+>Li+>Na+>Mg2+, and the mass transfer was carried out at the interface of the two phases of the membrane through the mechanism of "cation exchange-neutralization", in which Li(Ⅰ) was bonded with the carrier in the form of 2N503-LiFeCl4-2TBP, and showed a fixed-site "hopping" mass transfer characteristics under the reinforcement of electric field. The mass transfer process of the TFeN-PIM- Li(Ⅰ) system under electric field enhancement conforms to the first-order kinetic rate equation, and the voltage (5–45 V) is positively correlated with the permeability coefficient PLi(Ⅰ) but decreases the Li/Mg selectivity of TFeN-PIM. The SLi(Ⅰ)/Mg(Ⅱ) of TFeN-PIM was 9.18 at 3 V. After three cycles of 72 h cycling at 40 V, the decrease rate of PLi(Ⅰ) was <7.42 %, which showed good stability.

Experimental and modeling study of CO2 capture by phase change blend of triethylenetetramine-ethanol solvent

Post combustion Carbon capture based on chemical absorption is the best-known technology to reduce CO2. Recently, attention has been paid to biphasic solvents due to their excellent potential in reducing energy consumption. This study investigated carbon dioxide absorption by biphasic non-aqueous triethylenetetramine (TETA)-ethanol solvent in a T-shaped microchannel. Effect of four parameters including: concentration of TETA (4–8 wt%), liquid flow (2–5 ml/min), inlet CO2 concentration (5–20 vol%) and gas flow (100–175 ml/min) have been examined. Mass transfer characteristics has been assessed by investigation of absorption percentage, molar flux and overall mass transfer coefficient. The results show that increasing the concentration of amine diminishes all three responses by increasing the solution viscosity. As a result, it decreases the penetration of CO2 in the solution and the rate of absorption.Furthermore, the TETA-ethanol phase change solvent has been compared with aqueous monoethanolamine (MEA). The results of this comparison indicated that the efficiency of CO2 absorption and mass transfer coefficient, for TETA-ethanol biphasic solvent are higher than MEA solvent, respectively. Finally, the dimensionless Damköhler number (Da) was utilized in the new correlation to predict KLa for CO2 absorption into TETA-Ethanol solution with acceptable accuracy.

Influence of flight acceleration on heat transfer and carbon deposits of aviation kerosene under supercritical conditions

During the acceleration or escape of the hypersonic vehicle, the flight acceleration will have an important impact on heat and mass transfer characteristics of pyrolytic hydrocarbon fuel in the regenerative cooling channel of scramjet. Based on the detailed pyrolytic mechanism and coking kinetics model, numerical model was established to study the flight acceleration effect on flow field, fuel pyrolysis, heat transfer and carbon deposit of supercritical hydrocarbon fuel in the horizontal cooling channel. Results indicate that the secondary flow is induced in the cross-section of horizontal cooling channels because of the flight acceleration and density gradient. Due to the secondary flow, thermal and fuel conversion stratifications in the radial distribution increase. The bottom wall heat transfer coefficient is higher, while the wall temperature and carbon deposits are lower than that of the top wall. Meanwhile, with the increase of the flight acceleration, the thermal and fuel conversion stratifications become larger. The differences of heat transfer coefficient, wall temperature and carbon deposits between the top and bottom walls rise. The operating pressure enhances the flight acceleration effect on the heat transfer and carbon deposits. In addition, Petukhov’s criterion is proved to be applicable to evaluate the flight acceleration effect quantitatively.

Development of Pseudo-Homogeneous Three-Dimensional Reaction Anode Structure for Proton Exchange Membrane Water Electrolysis

Solid Polymer Electrolyte (SPE) diaphragm such as Nafion🄬 has been applied to proton exchange membrane water electrolysis (PEMWE) due to the high efficiency and response. The structure of PEMWE consists of a catalyst layer, diffusion layer, current collector, flow-field, etc. In addition to the membrane, these elements and structural parameters were adapted from the proton exchange membrane fuel cell (PEMFC) technology due to the time series factors in the development process and are still strongly influenced by that technology today. Although PEMFC technology is applied to these elements in PEMWE, the material composition, structure, and various parameters are not fully optimized, and the basic structure and technology are diverted from various PEMFC conditions, although the main object of fluid has greatly changed from the gas phase to the liquid phase. As the above background, PEMWE technology needs to go back to the basic level of structural design, mainly from the viewpoint of mass transfer, and reconstruct the component structure.In this study, we focused on the mass transfer characteristics that most affect the performance of PEMWE and investigated a new structure for gas-liquid two-phase fluids for the electrode structure, which is the most important element of PEMWE.Figure 1 shows the two and three-dimensional reaction electrode structures in PEMWE. Figure 1(a) is the electrode structure of a conventional general PEMWE, which is the catalyst reaction in the catalyst layer on the rate-limiting electrode side proceeds in a heterogeneous two-dimensional reaction area. In this current method, sufficient diffusion cannot be maintained from the viewpoint of mass transfer, which leads to performance decrease due to the inability to remove obstacles such as bubbles to mass transport to the catalyst layer. Figure 1 (b) shows the pseudo-homogeneous three-dimensional reaction electrode structure developed in this study. The catalyst is supported on the porous current collector itself. This structure dramatically increases the reaction area from two-dimensional to three-dimensional, and it is expected to greatly improve electrolytic performance by optimizing various parameter conditions.The experimental was performed as following. The anode catalyst IrOx was synthesized from H2IrCl6-nH2O and NaNO3 by the Adams method1). Catalyst Ink, which mixed with the synthesized catalyst and Nafion🄬 dispersion solution, was dropped onto a Ti-web current collector and dried. The anode catalyst loading current collector was evaluated in a 1 cm2 component evaluation electrolyzer2).In this development, the essential issue is the establishment of the conditions to support the catalyst in the three-dimensional reaction area and to maintain the supply path of the proton from the SPE membrane efficiently.References T. Saida, S. Hirano, E. Niwa, F. Sato, and M. Maruyama, ECS Trans., 85, 865 (2018). K. Nagasawa, T. Ishida, H. Kashiwagi, Y. Sano, S. Mitsushima, Int. J. Hydrog. Energy, 46, 36619 (2021). Figure 1

Energy Efficiency of Steady DC and Half Sine Pulsed DC in the High Voltage Pre-Plasma and Plasma Alkaline Water Electrolysis

The research addresses the contrasting views on the energy efficiency of alkaline water electrolysis using the regular DC vs the pulsed DC. We compare the high voltage steady DC electrolysis with the high voltage half-wave rectified (HWR) AC (or the half Sine pulsed DC, an unexplored form of the pulsed DC) across a wide range of voltage regimes, with a particular focus on the less explored Plasma electrolysis (PE) regime. In addition, the current-voltage characteristics are mapped across the voltage regimes (NE to PE) using a novel high-voltage 3-electrode circuit, which allows better control over the working electrode potential. The experimental design considers critical parameters such as energy efficiency, Faradaic efficiency, and current density, providing a comprehensive evaluation of the regular DC Vs. the half-wave rectified AC electrolysis.Pulsed electrolysis can facilitate bubble removal and ensure timely replenishment of reactant during the low-bias phase and this is expected to diminish over potential losses due to mass transfer resistance. However, the preliminary energy efficiency assessment suggests that the regular DC is ~13% higher at 33 V bias and ~24% higher at 26.5 V bias than the half sine pulsed DC(50 Hz) electrolysis. This suggests that for these particular reaction conditions, the fluctuations in the current leading to reactive losses in the circuit and other internal losses overwhelm any enhancement in the mass transfer characteristic of pulsed electrolysis. The study also points to regimes where significant thermal decomposition results in a significant increase in the apparent Faradaic efficiency.