Liquid Distribution Research Articles

A comprehensive investigation on a modified interdigitated-jet hole flow field for under-rib mass transfer

The flow field is a crucial component of proton exchange membrane electrolyzer cell (PEMEC), significantly impacting cell performance and distribution uniformity. This study introduces a modified flow field structure, named the Modified Interdigitated-jet hole Flow Field (MIJFF), based on the interdigitated-jet hole flow field with added under-rib holes. The goal is to increase water supply to the porous electrode and facilitate gas discharge from the diffusion layer, thereby improving under-rib mass transfer and enhancing the uniformity of current density. Three control groups are compared: a single-path serpentine flow field, an interdigitated flow field, and an interdigitated-jet hole flow field. A two-phase, muti-dimensional model is developed to simulate different flow field structures, which are then validated through the experimental approaches. Results indicate that the MIJFF, with added under-rib holes, can better improve under-rib mass transfer, provide water supply and allow timely gas expulsion, avoiding unevenness and performance degradation due to local gas accumulation. Furthermore, the introduction of under-rib holes further increases vertical flow velocity. Compared to the control groups, applying MIJFF to the anode improves liquid saturation, current density and temperature distribution uniformity by 19.65 %, 36.24 % and 37.64 %, respectively, while increasing vertical flow velocity in the channel by 60.6 %.

A means of destroying sites of perennial root shoot weeds with pests and diseases in them

BACKGROUND: The subject of the study is the technological process of protective spraying of agricultural crops using a combined method against perennial weeds in sites in the field using two pneumohydraulic devices with slot atomizers as part of an improved small-sized boom sprayer. AIM: Development of a technical mean for exterminating sites of perennial root shoot weeds with pests and diseases in them. METHODS: The developed pneumohydraulic devices were used for an improved mounted boom sprayer of plants to treat sites of perennial weeds in the field. Chemical spraying with combined use of the traditional method and the developed pneumohydraulic devices with axial fans and 12 V electric motors, ensuring the distribution of droplet liquid on the treatment surface with two sprayers over 4 meters, is able to reduce the amount of the applied chemicals compared to the conventional technology and to reduce the pesticide load on crop plants by local destruction of sites of weeds, pests and diseases. Based on the developed methods, the results of spraying the surface with a drop liquid with a known dispersion using slot sprayers and controlled liquid pressures with a dial gauge during experiments were obtained. SCIENTIFIC NOVELTY: For the first time, a combined method and technical mean of achieving the research aim have been proposed for the destruction of sites of perennial weeds in the field and the diseases and pests of agricultural crops spread in them. RESULTS: When using a mounted sprayer with two containers for working fluids of combined herbicide solutions or for an insecticide solution in one of the containers and installation of the improved pneumohydraulic devices on the edges of the boom with a conventional arrangement of slot atomizers, it is possible to meet agrotechnical requirements for the use of herbicides, insecticides and fungicides. The simultaneous impact of large drops of herbicides on weeds and the penetration of small drops into plants will destroy sites of rhizome and root weeds with pests and diseases to ensure favorable conditions for the production of agricultural crops. CONCLUSION: A combined method and the technical mean of chemical treatment of perennial weeds with pests and diseases to create favorable conditions for the production of cultivated plants has been experimentally substantiated. Compliance with the conditions is ensured by equipping the mounted sprayer with two containers, pumps for supplying liquid through hoses to slot atomizers, and installing pneumohydraulic liquid nozzles at the edges of the boom. Working liquid sprayers ensure spraying width of more than 4 m, taking into account the size of a site, as well as spraying inaccessible areas using conventional technical means. The efficiency of the developed combined protective spraying of agricultural crops against perennial weeds and pests by the technical mean of its implementation lies in the savings of expensive herbicides and insecticides up to 70% in the later stages of their growing season (as they grow over the field area) compared to the forced continuous application of the herbicide over the entire field area.

Synthesis and characterization of p-CuO/n-ZnO heterostructured composite thin films for the detection of formaldehyde gas.

We report the synthesis and characterization of pure CuO and CuO-ZnO nanostructured composite thin films sprayed on particle-free glass substrates using chemical spray pyrolysis method. The films were systematically analyzed through microstructural, morphological, chemical, and gas-sensing studies. X-ray diffraction (XRD) studies confirmed the polycrystalline nature of the films, with a predominant monoclinic phase along the (002) direction. Key structural parameters, such as crystallite size, dislocation density, strain, and the number of crystallites per unit area, were reported from XRD analysis. Field emission scanning electron microscopy (FESEM) revealed a bundled-like morphology with uniform particle distribution, enhancing the surface area for effective gas interaction. X-ray photoelectron spectroscopy (XPS) results indicated that Cu and Zn ions existed predominantly in the 2+ oxidation state, contributing to the films' reactivity. Significantly, the gas sensing studies were investigated with static liquid distribution method, highlighting the remarkable performance of the 30 wt.% CuO-ZnO composite thin film. This composite exhibited a substantial response to 5 ppm formaldehyde at ambient conditions, showing a recovery time of 22 seconds and a response time of 15 seconds. These findings underscore the potential of CuO-ZnO composites for efficient formaldehyde gas sensing applications, marking a notable advancement in the field of environmental monitoring.

Bounded support: Success and limitations of liquidity support during times of crisis

AbstractOur paper sheds light on the complexity of liquidity injection programs by showing unintended consequences that arise when firm heterogeneity is overlooked. Utilizing firm‐level data from the Paycheck Protection Program, we find government lending effectively reduced closures, particularly if received during the first two weeks. However, we find significant heterogeneity in the effectiveness of funds, resulting from broad‐brush eligibility guidelines and differences in how firms process information. The implementation relied on the banking system, which exacerbated the distributional effects by favoring firms with stronger customer capital. Our findings highlight the importance of thoughtful liquidity distribution design to maximize its benefits.

Eulerian multi-fluid simulations of local liquid distribution in a bed packed with cylindrical particles

Packed bed reactors (PBRs) are extensively used in chemical process industries to perform solid-catalyzed gas–liquid reactions. Their performance is significantly influenced by liquid distribution which is a strong function of particle shape and size. In the present work, we simulated the steady-state local liquid distribution, pressure drop (ΔP/L), and overall liquid holdup (〈εL〉) for the beds packed with spherical and cylindrical particles using a three-dimensional (3D) Eulerian multifluid model and validated the predictions using corresponding high-speed imaging measurements performed in pseudo-2D packed beds. We showed that the Eulerian model with existing closures significantly underpredicts the liquid distribution for the bed randomly packed with cylindrical particles. To address this, we proposed a modification in existing mechanical dispersion force (F→D) model as a function of average particle orientation angle (θ). The modification significantly improved agreement between the predictions and the corresponding measurements. Using the modified model, we showed that the increased magnitude of F→D in the lateral direction leads to higher lateral liquid spreading for cylindrical particles as compared to that for the spherical particles. Importantly, the modified model also predicted the local liquid distribution and ΔP/L for beds packed manually with cylindrical particles oriented at different θ in a satisfactory agreement with the corresponding measurements. On increasing θ, the F→D in lateral direction (i.e., perpendicular to flow) as well as liquid–solid interaction force (F→LS) in axial direction (i.e., parallel to flow) found to increase significantly. As a result, the lateral liquid spreading as well as ΔP/L decrease substantially on increasing θ.

Characterization of liquid-thickness distribution in micropores on elastic surface under sliding and pressurizing conditions.

To improve the performance of studless tires on ice surfaces, the mechanism of liquid film removal must be elucidated. In this study, an experimental system is developed to simulate the running conditions of a studless tire, and the microscopic liquid film flow generated between the rubber surface and glass is observed to evaluate the liquid thickness distribution. Liquid film removal by micropores on foamed rubber samples is investigated by visualizing the liquid thickness in the micropores. The proposed system enables variations in the pressure and sliding velocity between the rubber and glass. The liquid thickness in the micropores is measured using laser-induced fluorescence, and the effects of pressure and sliding velocity on the thickness are examined. Water penetrates the micropores on the rubber sample surface, and different liquid thicknesses are obtained for each pore. The amount of liquid penetrating the pores is affected to a greater extent by the sliding velocity than by the pressure. Therefore, liquid penetration is more strongly influenced by the hydrodynamic effect of the increasing inertia of the liquid under high sliding velocities than by the elastic deformation of the pore.

Performance enhancement of latent heat thermal energy storage systems via dynamic melting process of PCM under different control strategies

Latent heat thermal energy storage (LHTES) systems merging high energy densities with near isotherm operations have made a reliable solution to ease the intermittence difficulties of renewable energy and manage periodic energy demands to ensure supply–demand balances on electricity grids. This study experimentally and numerically explores the liquefaction characteristics of phase change material (PCM) in the LHTES tank with the dynamic melting technique, involving the liquid PCM recirculation in the liquefying process to enhance the melting outcomes. Experimental measurements are conducted to investigate the dynamic melting progression for revealing the system effectiveness in terms of the complete melt time and mean power with different control strategies modifying the formations and inlet velocities of recirculating PCM flows. The computational fluid dynamics (CFD) simulations are also conducted to resolve the liquid fraction, vorticity and temperature distributions for offering the insights of the transfiguration of heat transfer and liquefaction behaviors. The photos of ice-water interfaces and measured temperature data in the LHTES tank are thus acquired to verify the computational model generating the CFD predictions. The performance assessments signpost the optimization of dynamic melting arrangements adopting the top to bottom layout with a PCM inlet velocity of 0.22 m/s, achieving the reduction of full melting time by 48.1 % and the enhancement of estimated mean power by 132.6 %, respectively.

Physics-informed neural networks approach for pollutant dispersion flow caused by magnetic dipole

Abstract Research on the liquid flow and distribution of waste discharge concentration over cylindrical surfaces might lead to the growth of efficient waste management and pollution controlling strategies. In view of this, the pollutant concentration and magnetic dipole impact on the liquid flow through the cylinder with a porous medium are explored in the present analysis. Moreover, Fourier’s and Fick’s laws are considered to explore heat transport features. The governing partial differential equations (PDEs) of the present study are converted into non-dimensional ordinary differential equations (ODEs) utilizing similarity variables. Also, the current study proposes a novel implementation of neural networks based on physics knowledge for the liquid flow past a cylinder. The self-updating weights and bias facilitate the network to satisfy the minimization objective function and provide accurate results. Additionally, the solution obtained by Runge Kutta Fehlberg's fourth-fifth order (RKF-45) method is utilized to validate the physics-informed neural network (PINN) results, presenting mean squared errors from 10-9 to 10-11. Furthermore, it is found that the increase in temperature relaxation time parameter decreases the Nusselt number gradually at the rate of 1 to 5%. An upsurge in the values of the pollutant external source parameter and the pollutant external source variation parameter decreases the concentration profile.

Modeling phosphorus transport in soil columns amended with polyaluminum chloride and anionic polyacrylamide water treatment residuals: implications for stormwater bioretention systems

ABSTRACT Understanding phosphorus transport in soil columns amended with polyaluminum chloride and anionic polyacrylamide water treatment residuals (PAC-APAM WTRs) is crucial for the effective recycling of PAC-APAM WTRs into traditional soil-based stormwater bioretention systems. Phosphorus transport in columns containing three distinct soil types amended with PAC-APAM WTRs under saturated steady-state flow conditions was effectively modeled using three different models: the convection-dispersion equation (CDE) model with linear isotherm, the CDE model with Langmuir isotherm, and the chemical non-equilibrium two-site model (TSM). In Soils 1 and 2, amended with PAC-APAM WTRs, the primary mechanism governing phosphorus transport transitioned from instantaneous adsorption to two-site adsorption as flow rate increased. In contrast, Soil 3 amended with PAC-APAM WTRs was predominantly governed by two-site adsorption throughout the experiments. An increase in flow rate reduced the solid–liquid distribution coefficient and the fraction of equilibrium adsorption sites, resulting in decreased phosphorus adsorption and increased phosphorus mobility. This study strongly recommends the selection of soil amended with PAC-APAM WTRs that exhibits higher instantaneous phosphorus adsorption. Additionally, this study emphasizes the importance of appropriately designing the depth of the ponding layer, utilizing the TSM model, and refining modeling techniques to optimize phosphorus retention and mitigate pollution risks in stormwater management.

Liquid Water Transport and Distribution in the Gas Diffusion Layer of a Proton Exchange Membrane Fuel Cell Considering Interfacial Cracks

The proton exchange membrane fuel cell (PEMFC), with a high energy conversion efficiency, has become an important means of hydrogen energy utilization. However, water condensation is unavoidable in the PEMFC because of low operating temperatures. The impact of liquid water on PEMFC performance and stability is significant. The gas diffusion layer (GDL) provides a critical transport path for liquid water in the PEMFC. Liquid water saturation and distribution in the GDL determine water flooding and mass transfer efficiency in the PEMFC. In this study, focusing on the effects of the water introduction method, osmotic pressure, and contact angle, the liquid water transport in the GDL was numerically investigated based on a pore-scale model using the volume of fluid (VOF) method. The results showed that compared with the conventional water introduction method without cracks, the saturation and spatial distribution of water inside the GDL obtained in the simulation were more consistent with the experimental results when the water was introduced through the microporous layer (MPL) crack. It was found that increasing the osmotic pressure resulted in a faster rate of water penetration, faster approaching the steady-state performance, and higher saturation. The ultra-high osmotic pressure contributed to the secondary breakthrough with a significant increase in saturation. Increasing the contact angle caused higher capillary resistance, especially in the region with small pore sizes. At a constant osmotic pressure, as the contact angle increased, the liquid water gradually failed to penetrate into the small pores around the transport path, causing saturation reduction and an ultimate failure to break through the GDL. Increasing the contact angle contributed to a higher breakthrough pressure and secondary breakthrough pressure.

Correlating Catalyst Growth with Liquid Water Distribution in Polymer Electrolyte Fuel Cells.

This study investigates the impact of liquid water distribution in a polymer electrolyte fuel cell (PEFC) on the spatially heterogeneous platinum (Pt) catalyst degradation. The membrane electrode assemblies (MEAs) are aged using accelerated stress tests (ASTs) in varied cathode gas environments (N2 and air) to instigate Pt catalyst degradation. The study employs high-resolution neutron imaging and synchrotron micro-X-ray diffraction (micro-XRD) to map liquid water distribution and Pt particle size, respectively. Neutron radiographs reveal liquid water accumulation primarily within the diffusion media, especially under flow field lands, due to thermal resistance differences between channels and lands. Aged MEAs exhibit increased water retention, likely due to increased hydrophilicity of the diffusion media with aging. Synchrotron micro-XRD maps unveil significant heterogeneity in Pt particle size distribution in the aged MEAs, correlated with preferential liquid water accumulation under flow field lands. This study highlights the critical role of flow field design and water distribution in catalyst degradation, underscoring the need for innovative strategies to enhance fuel cell durability and performance.

Characterization and Evaluation of an Electrostatic Knapsack Sprayer Prototype for Agricultural Crops

Pesticide application development has grown exponentially in recent decades thanks to the implementation of new technologies and improved quality of spray input application. Electrostatic technology for increasing deposition has proven to be a suitable tool under specific study conditions, such as when working with very small droplet sizes, with air assistance, or typically in greenhouse environments. However, its effectiveness in hydraulic spraying, as well as its application from a commercial point of view in agriculture, is still challenging. The aim of this study was to evaluate the performance of this technology by implementing a modified lance on a small commercial knapsack sprayer, equipped with a hydraulic nozzle providing a range of droplet size values (Dv50) from 136 μm to 386 μm in the pressure range between 2 and 6 bar. This setup allowed operation under normal conditions (disconnected electrostatic system: NES) or with the connected electrostatic system (ES), with both configurations being tested in this study. Liquid distribution profiling as well as qualitative and quantitative evaluation of deposition were carried out both under laboratory conditions and in tomato crops under greenhouse conditions. The results showed no differences between the ES and NES in terms of flow rate (L min−1) characterization or in the total accumulated volume collected with the vertical bench. The impact of the electrostatic system connection was clearly observed in laboratory trials, with total deposition increases of up to 66%. In field trials, this effect decreased in unexposed areas and in denser sections of the crop. However, the overall increase in deposition, mainly associated with the exposed side, continued to be significant.

Performance of the multi-U-style structure based flow field for polymer electrolyte membrane fuel cell

The design of the reactant gas flow field structure in bipolar plates significantly influences the performance of proton exchange membrane fuel cells (PEMFCs). In this study, we introduced four innovative U-shaped flow field designs, namely: In-Out Multi-U, Out-In Multi-U, Distro In-Out Multi-U, and Distro Out-In Multi-U. To investigate the impact of these various flow fields on PEMFC performance, we conducted computational fluid dynamics (CFD) numerical simulations, validated through model experiments. Our results indicate that the Distro Out-In Multi-U flow field offers notable advantages compared to the conventional parallel flow field (CPFF) and conventional serpentine flow field (CSFF). These benefits include reduced inlet and outlet pressures, lower liquid water content, more uniform liquid water distribution, and a more even current density distribution. Furthermore, the Distro Out-In Multi-U design demonstrates improved efficiency, consuming less H2 (91.9%) than the CSFF while achieving a higher net power density output (10.1%). As a result, for the same power output, the Distro Out-In Multi-U utilizes only 83.5% of the H2 consumed by the CSFF. In summary, the U-shaped structured flow field exhibits superior output performance, enhanced energy efficiency, and improved resistance to flooding. These findings suggest that the U-shaped flow field design holds significant potential as a reactive flow field for PEMFCs.

Horizontal Distribution of Liquid in an Over-Row Sprayer with a Secondary Air Blower

The aim of this study was to determine the influence of boom height above a crop stand and the spacing between nozzles and diffusers in an over-row sprayer on the uniformity of the horizontal spray distribution and the uniformity of the air velocity distribution. The experimental setup involved a prototype over-row sprayer equipped with a boom with a working width of 8 m and ten air diffusers with spray nozzles. Air diffusers were connected to one or two nozzles each, and they were installed on the boom at intervals of 60, 80, and 90 cm. Terminal airflow velocity at a canopy is determined by the height of a sprayer boom and the diffuser spacing, ranging from around 2 m s–1 to around 27 m s–1. The sprayer boom should be positioned at a height of 50 cm above a crop stand due to the difference between the minimum and maximum airflow velocities. The horizontal spray distribution was more uniform when the sprayer was equipped with hollow-cone nozzles instead of flat-fan nozzles; hollow-cone nozzles should be applied if the distance between nozzles needs to be adjusted to the row width and row spacing. The analyzed coefficients did not exceed 10% when the boom was positioned 50 cm above the crop stand and when the nozzles were spaced 80 cm apart, which suggests that, in this configuration, sprayers equipped with hollow-cone nozzles can also be applied to close-grown crops.

Investigation of cavitation with air injection using Eulerian-Lagrangian method

Abstract Air injection can be used to reduce the cavitation erosion in fluid machinery. However the inverse result that the injected air indeed increases the size of cavitation may be obtained. To find out the interaction between air injection and cavitation, the present work proposes a Eulerian-Lagrangian method to investigate the effect of air injection on the characteristics of cavitating flow. The Eulerian method is used to describe the liquid and vapor distribution, and the morphology of large cavities are tracked by the Volume of Fluid (VOF) method in the Eulerian frame. On the other side, the Lagrangian method is used to track both air and vapor bubbles in small scale. With the Eulerian-Lagrangian coupling, discrete micro bubbles in sub-grid scale as well as the large cavities can be well captured and simulated. This work takes two cavitation situations in different cavitation numbers of σ = 0.81 and 0.70 into account. The cavitation features in σ = 0.81 are mainly characterized by the intermittent shedding of small-scale cavities under re-entrant flow mechanism. For σ =0.70, the injected air flow plays an important part which enhances the scale of cavity. For both cases, simulated results of the cavity shapes and distribution of discrete bubbles anastomoses well with experimental results, which verifies the accuracy of the algorithm. The interaction between injected air and vapor is also analysed.

Research on the Balance Axial Force of the Back Blade of Centrifugal Pump Impeller based on CFD

Abstract One popular way to decrease the pump’s axial force is by utilizing the back blade. In this paper, by changing the number and width of back blades and using CFD 3D simulation technology, the influence law of back blades on pump performance, pump chamber liquid pressure characteristics and axial force characteristics is obtained. By changing the number of the back blade and width of the back blade, this paper adopt CFD 3D simulation technology to study, get pump performance, pump cavity liquid pressure characteristic and the influence law of axial force characteristics. The results show that the pump head and power increase with the increase of the width and number of back blades. However, the efficiency of the pump gradually decreases with the increase of the width and number of back blades. The impeller mounted back blade can change the pressure distribution of liquid of the pump chamber, and affect the axial force of the pump. The size and direction of the axial force change with the number and width of the back blades.

Comparative experiments on the flow morphology of liquid nitrogen and water in perforated structured packing

Cryogenic distillation is the primary method for air separation, with corrugated plate packing as the main packing for heat and mass transfer between nitrogen and oxygen. The perforated structure on the corrugated plate packing can directly change the liquid distribution characteristics, thereby affecting the packing’s flow and mass transfer performance. Currently, the effect of perforated structure is mainly revealed by room temperature fluids such as water and air, while on the practical cryogenic fluids such as liquid nitrogen, it is seldom studied. In this study, the effects of perforation size ranging from 2 to 8 mm on the flow of water and liquid nitrogen on the perforated plates were investigated and compared by a high-speed camera. It was observed that water could hardly flow through the perforations, it completely covers the perforations, forming a continuous liquid film on the surface of the perforations. The expected role of perforations in redistributing water on the back side of the corrugated plate is relatively minor. While for liquid nitrogen, the presence of the perforated structure helps fluid redistribution on the back side of the plate, as it can easily flow through the perforations with diameters between 2 mm and 8 mm. It is found that when the perforation diameter exceeds 6 mm, liquid nitrogen will form suspended liquid droplets within the holes, which could be a risk of premature flooding. Under similar conditions, the wetting rate of liquid nitrogen reaches 86.90 % −99.48 %, higher than that of water which is about 10.26 % −78.82 %. The results show that perforations have quite different effects on the flow characters of water and liquid nitrogen due to their disparate physic properties.

Water Permeability and Oxygen Transport Resistance of Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layer

Enhancing water management to mitigate the performance impact of humidity fluctuations is crucial in PEFC applications. A novel microporous layer (MPL) incorporated with both hydrophilic and hydrophobic properties, applied to the gas diffusion layer (GDL), has been developed and demonstrated to enhance robustness under varying humidity levels. This study utilized water permeability test results to analyze the composite MPL, distinguishing between hydrophobic and hydrophilic absolute permeability ratios. By elucidating these ratios, insights into their roles in liquid water distribution and oxygen transport resistance were gained, distinguishing the composite MPL from conventional hydrophobic and hydrophilic MPLs. Ultimately, the performance of the composite MPL under high and low humidity conditions highlighted its robustness across diverse humidity environments.

Water Permeability and Oxygen Transport Resistance of Hydrophilic and Hydrophobic Composite Microporous Layer Coated Gas Diffusion Layer

Enhancing water management to mitigate the performance impact of humidity fluctuations is crucial in PEFC applications. A novel microporous layer (MPL) incorporated with both hydrophilic and hydrophobic properties, applied to the gas diffusion layer (GDL), has been developed and demonstrated to enhance robustness under varying humidity levels. This study utilized water permeability test results to analyze the composite MPL, distinguishing between hydrophobic and hydrophilic absolute permeability ratios. By elucidating these ratios, insights into their roles in liquid water distribution and oxygen transport resistance were gained, distinguishing the composite MPL from conventional hydrophobic and hydrophilic MPLs. Ultimately, the performance of the composite MPL under high and low humidity conditions highlighted its robustness across diverse humidity environments.

CFD-DEM modeling for optimized liquid distribution in fluidized bed spray granulation

In this work, CFD-DEM simulations of two different fluidized bed granulator geometries were performed, aiming to provide an insight into how the injected liquid behaves within the particle bed and thus an overall better understanding of the granulation process itself. Simulation results were evaluated regarding the fate of sprayed droplets, e.g. deposition on a particle, elutriation from fluidized bed, or collision with apparatus walls. For the deposited droplets, the particle–droplet collisions were tracked in order to obtain a locally resolved deposition rate. Spray parameters as well as geometric specifications of the nozzle setup were varied, investigating a broad range of different process conditions. By optimizing apparatus design, especially the air inlet, an even distribution of the liquid droplets within the fluidized bed and overall higher deposition rate can be achieved and a stable steady state with a well-defined spray zone is reached within a broad range of varied spray parameters.