Liquid Inlet Velocity Research Articles

Intensification of a microbial electrolysis cell for biohydrogen production

Hydrogen can be the fuel of the future, and there are multiple approaches for its production and storage. Most hydrogen production comes from non-renewable sources, primarily natural gas reforming, which is efficient but unsustainable. Microbial electrolysis cells (MEC) are alternative developing technologies that exploit conductor-like properties of electrogenic bacteria to both oxidize organic contaminants and get protons reduced in a cathode, thus producing hydrogen. Here, the aim is to design a model-based optimization framework to intensify the MEC efficiency. The constructed process model is proposed by considering transport phenomena, microbial kinetics, and a secondary current distribution model to estimate steady-state reactor performance and electrical efficiency. The results show a value of 25 % for electrical efficiency as hydrogen recovered. Global sensitivity analysis was performed and determined a strong dependency on inlet liquid velocity, and a built-in, gradient-free optimization algorithm was implemented to the model to maximize electrical efficiency under a defined range of inlet liquid velocity, inlet substrate concentration, and applied voltage. The proposed model predicts a maximum increase of efficiency of about 267 % by increasing inlet velocity and substrate concentration. Intensification of the cell's performance can be greatly achieved when halving hydraulic retention time and by having a more concentrated feed.

Accurate Liquid Level Measurement with Minimal Error: A Chaotic Observer Approach

This paper delves into precisely measuring liquid levels using a specific methodology with diverse real-world applications such as process optimization, quality control, fault detection and diagnosis, etc. It demonstrates the process of liquid level measurement by employing a chaotic observer, which senses multiple variables within a system. A three-dimensional computational fluid dynamics (CFD) model is meticulously created using ANSYS to explore the laminar flow characteristics of liquids comprehensively. The methodology integrates the system identification technique to formulate a third-order state–space model that characterizes the system. Based on this mathematical model, we develop estimators inspired by Lorenz and Rossler’s principles to gauge the liquid level under specified liquid temperature, density, inlet velocity, and sensor placement conditions. The estimated results are compared with those of an artificial neural network (ANN) model. These ANN models learn and adapt to the patterns and features in data and catch non-linear relationships between input and output variables. The accuracy and error minimization of the developed model are confirmed through a thorough validation process. Experimental setups are employed to ensure the reliability and precision of the estimation results, thereby underscoring the robustness of our liquid-level measurement methodology. In summary, this study helps to estimate unmeasured states using the available measurements, which is essential for understanding and controlling the behavior of a system. It helps improve the performance and robustness of control systems, enhance fault detection capabilities, and contribute to dynamic systems’ overall efficiency and reliability.

Based on Fluent, the numerical simulation of the flow field on the filter disk surface of the rotary filter device

The rotary screen filter is the most typical basic structural element in rotating mechanical devices. It is being widely applied in various fields of industrial production. Using a spinning disc as the research subject, this study utilizes Computational Fluid Dynamics (CFD) techniques to establish a physical model of the filter disc. Various parameters and their corresponding boundary conditions are set, followed by a comprehensive and detailed three-dimensional numerical simulation of the high-speed rotating disc using the Fluent software platform. The objective is to investigate the effects of disc rotation speed and liquid inlet velocity on the surface flow field, as well as the influence of rotational speed on the attachment of particle impurities to the surface. Finally, the computational results will be visualized and thoroughly analyzed.

Density-induced segregation property of solid phase in a three-dimensional liquid-solid fluidized bed

This study employs the multiphase particle-in-cell method to explore fluid dynamics and solid segregation processes in a liquid-solid fluidized bed. The model reliability is established through rigorous experimental verification. Subsequently, this study scrutinizes the segregation behaviors of solid phase under various operational parameters. The findings indicate that turbulent viscosity predominantly localizes in regions where liquid and solid phases interact. Increasing the liquid inlet velocity amplifies both radial and axial mass fluxes of liquid and solid phases. Conversely, enlarging the diameter ratio between small and large solid particles, as well as adjusting the density of small solids, exerts negligible influence on radial and axial mass fluxes of liquid phase. As the liquid inlet velocity increases, a gradual reduction in solid concentration occurs, accompanied by an expansion in the solid movement zone. The diameter and density of solid particles exhibit little impact on the axial distribution of solid volume fraction. Notably, disparities in the particle Reynolds number become more apparent beyond an axial height of 0.05 m. Increasing the inlet velocity of liquid phase diminishes segregation intensity. Conversely, altering the solid diameter ratio and the density of smaller solid particles enhances solid segregation. However, solid segregation becomes constrained when the density of smaller solid particles exceeds 1700 kg/m3.

Modeling of water film generation in up-inclined low liquid loading natural gas pipeline elbows and its implication on internal corrosion occurrence

Condensed water often accompanies natural gas in the transmission process. The water forms thin film when parameters such as temperature and pressure change. This accelerates pipeline corrosion and makes the pipeline wall become thinner. Severe corrosion can lead to pipeline rupture, endangering the pipeline safety and leading to economic losses. The distribution of a water film plays a significant role in the corrosion process, So the work of predicting the distribution of a water film and flow characteristics becomes a key priority when analyzing corrosion in a pipe elbow. In this study, Eulerian, RNG (re-normalization group) k-ε and Eulerian wall film models are employed to establish a pipe elbow model that predicts the locations of water phase accumulation. Combining with a limiting diffusion current density, this model can be used to predict the potential corrosion locations and extent. The proposed model is validated by using velocity and water film distributions and it shows substantial agreement with previous models and results in the literature. From the simulation outcomes, a water film is mainly distributed at bottom while the thickness of the water film increases significantly at the pipe elbow. At the elbow bottom the inlet gas velocity increases, this shifts the high corrosion rate zone from elbow rear to front. Corrosion at the elbow front is more serious regardless of the changes in the inlet liquid velocity, elbow angle or water holdup. Meanwhile, when the gas velocity or elbow angle is large, the water film gradually spreads from the elbow bottom to the side and top parts which are in a high corrosion rate zone and more dangerous. Therefore, weak positions where pipeline elbow corrosion failures may occur can be quickly and conveniently computed and determined by the proposed model.

Computational investigation on the flow and mass transfer properties inside ejector of loop reactor based on CFD-PBM simulation

Conventional stirred kettle reactors suffer from inadequate gas-liquid mixing in many production processes, and their reaction rates are greatly limited. The loop reactor can achieve high mass transfer rates with low energy consumption. It is well suited for multiphase reactions with limited mass transfer and has the advantage of being excellent sealing and low cost. In this paper, ejector as the core of the loop reactor was investigated. Combining the Computational Fluid Dynamics (CFD) and Population Balance Model (PBM), the industrial-scale ejector model was constructed. The detailed motion behavior of bubbles and bubble size distribution were predicted. Due to the entrainment of the liquid phase, the gas enters the suction chamber and throat of the ejector, where the gas is mainly sheared and broken, providing a large specific surface area of the gas-liquid interface. Moreover, the flow and transfer properties were closely related to parameters such as nozzle-throat diameter ratio and liquid inlet velocity. Based on the results of the simulation, the gas-liquid mass ratio and the volumetric mass transfer coefficient were correlated with the structure and process parameters, and the correlation model was obtained, which provides guidance for the design of the loop reactor.

Effect of inlet gas and liquid velocity profiles on one-group interfacial area transport equation in a vertical large rectangular channel

Bubbly flows appear in many heat and mass transfer equipment. The interfacial area concentration is a critical parameter in determining the performance of the heat and mass transfer systems. The one-dimensional one-group interfacial area transport equation (IATE) was developed based on area-averaged bubbly flow data collected under uniform inlet flow boundary conditions. The applicability of the IATE to the flow systems with non-uniform inlet flow boundary conditions was not comprehensively examined. This study investigated the effect of inlet liquid and gas velocity profiles on measured interfacial area concentration changes along the flow direction. The data used in this study were collected for vertical upward air-water two-phase flow in a rectangular channel with a gap length of 10 mm and width of 200 mm. The test conditions were the superficial gas velocity ranging from 0.0870 to 0.288 m/s and the superficial liquid velocity ranging from 0.515 to 2.53 m/s. The interfacial area concentrations with uniform and non-uniform inlet flow boundary conditions measured in a large vertical rectangular channel were compared under the same area-averaged flow rate conditions. Then, the predictive capability of the IATE to the bubbly flow test data with uniform and non-uniform inlet flow boundary conditions was assessed. Some non-uniform inlet flow boundary conditions, including channel-center peaking of liquid flow (CPF), channel-center peaking of gas flow (CPG), single-side-wall peaking of liquid flow (SPF), and single-side-wall peaking of gas flow (SPG), significantly affected the interfacial area concentration changes along the axial location at relatively high superficial gas or liquid velocity conditions. The IATE's predictive capability deteriorated for several non-uniform inlet flow boundary conditions, including double-side-wall peaking of gas flow (DPG) and single-side-wall peaking of liquid flow (SPF), specifically at relatively high superficial liquid velocity conditions. The maximum percentage error of the interfacial area concentration prediction by the IATE for these non-uniform inlet flow boundary conditions reached 75%.

Gas holdup, bubble size distribution, and mass transfer in an airlift reactor with ceramic membrane and perforated plate distributor

AbstractThe airlift reactor is one of the most commonly used gas–liquid two‐phase reactors in chemical and biological processes. The objective of this study is to generate different‐sized bubbles in an internal loop airlift reactor and characterize the behaviours of the bubbly flows. The bubble size, gas holdup, liquid circulation velocity, and the volumetric mass transfer coefficient of gas–liquid two‐phase co‐current flow in an internal loop airlift reactor equipped with a ceramic membrane module (CMM) and a perforated‐plate distributor (PPD) are measured. Experimental results show that CMM can generate small bubbles with Sauter mean diameter d32 less than 2.5 mm. As the liquid inlet velocity increases, the bubble size decreases and the gas holdup increases. In contrast, PPD can generate large bubbles with 4 mm < d32 < 10 mm. The bubble size and liquid circulation velocity increase as the superficial gas velocity increases. Multiscale bubbles with 0.5 mm < d32 < 10 mm can be generated by the CMM and PPD together. The volumetric mass transfer coefficient kLa of the multiscale bubbles is 0.033–0.062 s−1, while that of small bubbles is 0.011–0.057 s−1. Under the same flow rate of oxygen, the kLa of the multiscale bubbles increases by up to 160% in comparison to that of the small bubbles. Finally, empirical correlations for kLa are obtained.

Experimental investigation and performance improvement of a new combined T-junctions gas-liquid separator

The objective of this paper is to study the gas-liquid separation performance and its improvement of a new combined T-junctions separator by experiments. This separator is constructed of large-diameter T-junctions (50 mm and 60 mm), symmetrically arranged in annulus. The test conditions include complete separation and incomplete separation. The gas-liquid flow characteristics of the combined T-junctions were visually observed and analysed during the separation process. The separation characteristic was quantified (F) and the effects of liquid level, inlet superficial velocities (JG1 and JL1) and outlet valve opening degree on the separation efficiency (F) were confirmed. The results show the connections between the parameters and separation efficiency. Based on the above, a self-regulating level controller is designed, which can significantly extend the range of inlet gas velocity (JG1) to 4.5 times and inlet liquid velocity (JL1) to two times for complete separation, but the level controller fails when the inlet gas-liquid velocities are too high (JG1 > 10.27 m/s, JL1 > 0.52 m/s). [Received: December 14, 2021; Accepted: August 7, 2022]

Thermal management of solid oxide fuel cells with liquid metal

Effective thermal management of SOFCs is necessary for their long life and highly efficient operation, while the conventional method through excess air cooling is limited due to the inherently low thermal conductivity and capacity of air. In this study, a novel temperature control strategy is proposed by using liquid metal as a new kind of coolant that can work in both the stable operation stage and start-stop stage of an SOFC stack. A three-dimensional model is developed considering chemical/electrochemical reactions, mass, momentum and heat transfer processes to assess the effect of liquid metal cooling. The simulation results show that liquid metal has an excellent ability to improve the temperature uniformity and electric performance of the cell unit. The temperature difference of the cell unit cooled by air cooling is 60 K, which can be decreased to 15 K with liquid tin cooling. Furthermore, inlet air has little effect on the performance of the cell unit when liquid metal is chosen as coolant. The pumping powers of the air and liquid metal are compared at different excess air ratios and inlet velocities of liquid metal. The total pumping power consumption could be dramatically decreased when liquid metal is utilized as the coolant. Furthermore, the variations in the conductivity, heat capacity and convective resistance at different liquid metal inlet velocities are discussed.

Flow characteristics and thickness distribution of liquid film in trickle bed reactor

In trickle bed reactor (TBR), the gas-liquid mass transfer is closely related to the thickness of liquid film and the wetting of catalyst particles. Therefore, knowledge on the flow and distribution of liquid film on particle surface is critical for evaluating the performance of TBR. In this work, high-speed camera was used to study the flow behavior of liquid film by using continuous droplets impacting on the top of particles with several layers. It was found that liquid tends to accumulating toward the contact point between adjacent particles due to capillary force. When the liquid inlet flow rate doubles, the wetting ratio of the particle surface increases by about 30%, while the liquid film thickness doubles. With the particle surface wettability increasing, the wetting ratio of particle surface can be improved while the liquid film thickness remains almost unchanged. • Liquid film flow behavior of continuous droplets impacting particles was studied. • Spatial and temporal distributions of liquid film on particle surface were analyzed. • The liquid film thickness and its distribution on particle surface were obtained. • Effects of liquid inlet velocity and wettability of particle surface were discussed.

Research on the Influence of Liquid on Heat Dissipation and Heating Characteristics of Lithium-Ion Battery Thermal Management System

A battery thermal management system (BTMS) with functions of heat dissipation and heating by using only one liquid and one structure was studied, and a design for a new type of thermal management device structure was proposed. To find the influence factors of the BTMS on heat dissipation and heating characteristics, we selected and simulated three parameters: inlet size, liquid flow rate, and temperature. The convective heat transfer coefficient h and the Nusselt number Nu were used to analyze the influence of inlet size and liquid velocity on heat transfer intensity. The results show that: (1) In the temperature environment of 298 K with different discharge rates, a pipe diameter of 10 mm is the best size of the BTMS; (2) The increase in flow rate can increase the convective heat transfer coefficient h and the Nusselt number Nu. When the flow rate is 0.02 m/s, the growth rate of h and Nu is the largest; (3) The higher the fluid temperature, the faster the temperature of the battery pack increases in cold environments, but the uneven surface temperature of the battery is also more obvious.

Modeling of vapor-liquid interactions in condensing ejectors

Ejectors are compact mechanical devices that utilize the expansion of a high-pressure primary fluid to entrain and compress a low-pressure secondary fluid by means of momentum transfer between the two streams of fluid. Condensing ejectors feature both momentum and heat transfer through the interaction between the vapor and liquid streams. The goal of this paper is to develop and validate a one-dimensional slug flow model to simulate the vapor–liquid interactions in two types of condensing ejectors – one with primary liquid and secondary vapor flows (Type I), and the other with primary vapor and secondary liquid flows (Type II). Control volume analysis of the mass, momentum, and energy balance in each phase and across the interface was conducted for the ejectors. The slug flow models for both types of ejectors are validated with published results in the literature. The friction coefficient on the inner wall of the ejectors and the interfacial heat transfer coefficient are identified as controlling parameters for the ejector performance in terms of pressure and temperature distributions along the axis. The detailed parametric study shows that the liquid inlet velocity and mixing tube diameter have a significant impact on the performance of the Type I ejectors, and the performance of the Type II ejectors is mainly controlled by the secondary liquid flow inlet temperature.

Computational fluid dynamic modeling of methane hydrate formation in a subsea jumper

Gas hydrate in subsea pipelines is a serious flow assurance issue that may impose operational challenges to offshore petroleum production and transportation. The effects of fluid properties on hydrate formation in complex geometries such as jumpers are not fully understood. This study aims to assess hydrate formation in the jumper for the water-methane system using the Eulerian multiphase flow model through employing computational fluid dynamic (CFD) software (STAR CCM+). The numerical model is developed through consideration of transport phenomena equations, including conservation of mass, momentum, and energy in which mass transfer, hydrate reaction kinetics model, and heat of hydrate formation are incorporated in the multiphase flow equations in the form of source terms in the CFD software. In this study, first, the hydrate mass fraction for the fluid velocity of 5 m/s with an inlet temperature of 7 °C and a gas volume fraction of 0.2 is calculated. The sensitivity analysis is then performed considering the influences of changes in the inlet fluid velocity, gas volume fraction, inlet temperature, and subcooling on the hydrate formation. The results reveal that the developed CFD model is capable of predicting hydrate formation behaviors in the jumper with acceptable precision. An increase in the liquid inlet velocity and gas inlet temperature lowers the amount of hydrate formed in the jumper. In contrast, an increase in the subcooling and gas volume fraction leads to more hydrate formation. The proposed CFD model can be successfully used to simulate hydrate formation in pipelines under various process and thermodynamic conditions so that it can help to find reliable/effective methods for hydrate management.

CFD simulation of flow distribution in the randomly packed bed Dixon ring

ABSTRACT The maldistribution in randomly packed beds with a high diameter ratio is a result of wall-flow formation and channeling. In this study, the thin randomly packed bed (dp/D = 1/8) filled with Dixon ring is simulated with a porous media model. The motivation of our study is to understand the effect of surface tension and liquid inlet velocity on the height of the wall-flow formation. Furthermore, the flow structure in this packed bed was described by numerical simulation. The results show that increasing the liquid inlet velocity and surface tension causes a faster distribution of liquid flow that led to faster formation of wall flow. Increasing the surface tension from 0.05 to 0.07 N/m causes the lower wall-flow formation from 0.19 m to 0.15 m in liquid velocity of 0.015 m/s and 0.09 to 0.06 in liquid velocity of 0.08 m/s. According to the findings, the 30% increasing the surface tension (from 0.07 N/m to 0.085 N/m) led to 30% decreases in height of wall-flow formation in the case of lower liquid velocity (0.015 m/s) and 50% decreases in the height of wall-flow formation in case of higher liquid velocity (0.08 m/s).

Study on water treatment effect of dispersion discharge plasma based on flowing water film electrode

To improve the utilization rate of plasma active species, in this study, a closed non-uniform air gap is formed by a flowing water film electrode and a sawtooth insulating dielectric layer to realize the diffuse glow discharge in the atmosphere. Firstly, the electric field distribution characteristics of non-uniform air gap in the sawtooth dielectric layer are studied, and the influence of aspect ratio on the characteristics of diffuse discharge plasma is discussed. Subsequently, the effects of wire mesh, the inclination angle of the dielectric plate, and liquid inlet velocity on the flow characteristics of the water film electrode are analyzed. The results show that the non-uniform electric field distribution formed in the sawtooth groove can effectively inhibit the filamentous discharge, and the 1 mm flowing water film is directly used as the electrode, and high-active plasma is formed directly on the lower surface of the water film. In addition, a plasma flowing water treatment device is built to treat the methyl orange solution and observe its decolorization effect. The experimental results show that after 50 min of treatment, the decolorization rate of the methyl orange solution reaches 96%, which provides a new idea for industrial applications of wastewater treatment.

Hydrodynamic mechanism study of the diameter-varying spray tower with atomization impinging spray

Our group proposed a diameter-varying spray tower and a new spray mode of dual-nozzle opposed impinging spray method to achieve the low-energy-consumption and environmentally-friendly CO2 capture process and some meaningful results have been obtained by experiments. However, the detailed information about the hydrodynamics (like liquid and gas phase distribution, gas-liquid contacting area and gas-liquid contacting time causing by impinging spray) inside the proposed tower is hard to be obtained by experimental work. In this work, to specifically explain the hydrodynamic mechanism with impinging spray inside the proposed spray tower, ANSYS Fluent18.0 and Euler-Lagrange approach were used to simulate the complex gas-liquid two-phase flow based on experimental results. The effects of nozzle location, nozzle number, spray angle, liquid injection velocity and gas intake mode were investigated, and the optimal design scheme of the spray tower was proposed. Simulation results indicated that the dual-nozzle opposed impinging spray method (DOSM) showed better absorption performance compared with the single-nozzle side spray method (SSSM) and single-nozzle middle spray method (SMSM). Spray angle of 60 degrees had efficient gas-liquid distribution. The liquid inlet velocity of 8 m·s−1 was suggested under the experimental conditions. The double-sided gas intake mode intensified gas-liquid absorption performance. The simulation results were well verified by experiments. The relationship between flow field optimization and CO2 absorption performance enhancing was also discussed comprehensively. Finally, it was concluded that both the numerical simulation and experimental results proved that the diameter-varying spray tower with the impinging spray method is a promising reactor for the CO2 capture system.

Numerical analysis of liquid fall type gas entrainment in pool-type fast reactor

Argon covering the free surface of the pool-type sodium-cooled fast reactor may be mixed into the coolant in form of entrainment bubbles due to the fluctuation of liquid surface, which introduces positive reactivity to the core, reduces the heat exchange capacity of the core and intermediate heat exchangers (IHXs), and possibly leads to the cavitation of the primary sodium pump (PSP), threatening the safe operation of the reactor. In this study, the computational fluid dynamics (CFD) simulation of liquid sodium fall entrained argon was carried out based on the Volume of Fluid (VOF) interface tracking method to describe the entrainment process in detail, and the influences of geometry size, initial liquid level height and inlet velocity on entrainment were analyzed successively. It was found that the re-submergence velocity, having a linear relation with the re-submergence angle, is the key factor of the liquid fall type gas entrainment. It can be used to judge whether the liquid fall type entrainment occurs conservatively. In addition, the parameters affecting the re-submergence velocity are specifically analyzed from the supplementary cases, according to the results of which, the empirical relation of the re-submergence velocity is obtained. Therefore, the situation of liquid fall type gas entrainment under various working conditions can be predicted numerically.

Numerical Simulation and Experimental Analysis of the Influence of Asymmetric Pressure Conditions on the Splitting of a Gas-Liquid Two-Phase Flow at a T-Junction

Dedicated experiments and numerical simulations have been conducted to investigate the splitting characteristics of a gas-liquid two phase flow at a T junction. The experiments were carried out for different gas-liquid velocities. The flow rates in the two branches were measured accurately to determine how the two considered phases distribute in the two outlets. The experimental results have shown that when the two outlet pressures are asymmetric, the two-phase flow always tends to flow into the outlet which has a lower pressure. As the inlet liquid velocity increases, however, the two-phase flow gradually tends to split evenly. Compared with the experiment results, the pressure difference between the two outlets can be determined more accurately by means of numerical simulation. The trends of experimental results and simulations are in very good agreement.

Flow and temperature distributions in a disc type winding-part I: Forced and directed cooling modes

The thermal design of a power transformer determines its lifetime and loading capability, so correct modelling of liquid flow and temperature distributions in the winding is of vital importance. Existing standards and widely used simple calculation models can seriously under/overestimate winding hotspot temperatures under certain circumstances. In this paper, liquid flow and temperature distributions in a physical model representing a disc-type winding in a liquid forced and directed cooling mode are investigated experimentally using Particle Image Velocimetry (PIV) and a temperature measurement system and numerically using Computational Fluid Dynamics (CFD). Dimensional analysis is used to generalise the results into a form useful for design review. The operating conditions investigated include different liquid inlet velocities, inlet temperatures, power losses in individual disc segments, and the effect of alternative liquids. It is shown that hotspot temperature and position within the winding are a non-linear function of liquid inlet velocity, with stagnation and reverse flow demonstrated in both experiments and CFD models. Comparisons of liquid flow and temperature distributions between measurements and CFD simulation results show that 2D CFD results are representative when there are no reverse flows and 3D CFD simulations are needed when reverse flows occur. The results are presented first in dimensional forms to show the effect of each parameter, and then in non-dimensional forms to provide a generalised insight into transformer thermal design.