Flow Rate Conditions Research Articles

Numerical and Experimental Approach to Evaluate Microplastic Transport in Saturated Porous Media

Under varying flow rate conditions, the transport and retention of polydisperse microplastics (MPls), with an average particle size of 16 ± 6 µm, were investigated in saturated porous media. First-order reversible and irreversible kinetic sorption models were used to describe the sorption kinetics. Sensitivity analyses provided insight into the effects of each sorption parameter. Both numerical modeling and experimental measurements were utilized to evaluate the retention rates of sand filters. The influence of flow rate on sorption was reflected in variations in the distribution coefficient (Kd), the mass transfer coefficient (β), and the irreversible sorption rate (K1). Lower flow rates were associated with higher Kd and β values, indicating increased sorption and reduced mass transfer rates. An increase in Kd resulted in a more gradual sorption process, with a decrease in peak concentration, whereas changes in β had a comparatively smaller impact on sorption rate and peak concentration. Lower K1 values were linked to higher peak concentrations and decreased retention efficiency. Numerical modeling revealed retention rates of 28 ± 1% at a flow rate of 31 mL min−1 and 17 ± 1% at 65 mL min−1. The introduction of MPls into saturated sand environments modifies the transport dynamics within the medium. Consequently, these alterations affect the hydrological characteristics of porous media, impacting groundwater quality and agricultural output. The mean absolute error (MAE) of 6% between the modeled and observed retention rates indicated a high level of accuracy. This study underscores the importance of examining retention efficiency and the accuracy of numerical models in understanding MPl transport in porous media.

Performance Evaluation of Different Rotating Detonation Combustor Designs Using Simulations and Experiments

Abstract Rotating Detonation Engines (RDEs) present a potential avenue for enhancing the efficiency of gas turbine combustors through the utilization of a detonation-driven process. However, integrating an RDE with a downstream turbine poses a significant challenge due to the shock-laden and highly unsteady nature of the RDE exit flow, coupled with a high degree of flow periodicity. In contrast, gas turbines are designed to operate with relatively small velocity and temperature fluctuations at the turbine inlet. The objective of the present study is to develop an understanding of how geometric profiling can improve RDE performance and mitigate exhaust flow field unsteadiness. Three RDE designs are analyzed: an annular combustor with a constant cross-sectional area, an annular combustor with a converging nozzle near the exit, and an annular combustor with a rapid to gradual (RTG) area convergence. Three-dimensional unsteady reacting simulations are conducted for each configuration using the same fuel-oxidizer composition and mass flow rate condition. All simulations are validated against experimental measurements, and RDE performance is assessed based on total pressure gain/loss, unsteadiness at the exit of the RDE, and detonation effectiveness. Results show significant performance improvement for both the convergent nozzle and the RTG profile compared to the constant cross-sectional area configuration, and the RTG design performed better than the convergent nozzle design. Therefore, strategically constricting the flow in an RDE can be used to optimize the performance of an RDE and should be considered in future designs.

Numerical modeling and validation of dike-induced water flow dynamics using OpenFOAM

ABSTRACT The basic purpose of the present research is to numerically elucidate the flow around a single dike in four different geometric configurations (CN: no cylinders, C5: 5 cylinders, C10: 10 cylinders, C15: 15 cylinders), under conditions of a constant flow rate and subcritical flow. This involved substituting the impermeable dike with varying numbers of piles to validate the observed experimental flow patterns, particularly the conditions leading to reverse flow formation. OpenFOAM, an open-source algorithm, was utilized for the simulation, incorporating the volume of fluid (VOF) method. Accurately depicting the reverse flow formation with minimal numerical diffusion, a strategy involving multizone meshing and the application of mesh refinement zones was utilized. These refinements were particularly focused on the section between 1.8 m and 2.2 m within the numerical domain. The water surface profile in front section of the dike and the averaged velocity at five different locations, which were then compared with the numerical results. The numerically predicted streamwise velocity showed a percentage error ranging between 0.5% and 4.5%. The numerical results from this study are pivotal in dike design, aiming to mitigate accelerated wear during flood events and to protect both the dike head and the adjacent bank from high energy flow failures.

Design of a partial discharge shrouded impeller for the centrifugal compressor of supercritical carbon dioxide power cycles

In this paper, the concept of partial discharge shrouded impeller is proposed to enhance the performance of supercritical carbon dioxide (S-CO2) centrifugal compressor under low flow rates, thereby increasing the overall efficiency of the S-CO2 Brayton cycle. The influence mechanism of the partial discharge shrouded impeller on the flow behavior inside the impeller domain has been revealed by computational fluid dynamics (CFD) simulation. The results indicate a notable enhancement in the pressure ratio and isentropic efficiency of the S-CO2 centrifugal compressor utilizing the best partial discharge shrouded impeller, showcasing improvements of 0.9% and 10.2% respectively under designed flow rate condition, while the stability parameter (SP) surpasses 0 at lower flow rates when compared to conventional impeller. With the partial discharge shrouded impeller, the flow separation on the blade pressure surface tends to occur nearer the impeller outlet, restricting the wake secondary flow shedding off to the diffuser, thus the flow loss being weakened. Meanwhile, with the optimized compressor by employing the best partial discharge shrouded impeller, the efficiency of S-CO2 Brayton cycle has been increased by 5% relative to that with full discharge shrouded impeller.

Optimized flow rate and efficient shaft water cooling method for EV's PMSM temperature-dependent energy system output power increase

One possible way to enhance the power density of electric vehicle (EV) powertrains is by utilizing temperature-sensitive permanent magnet synchronous motors (PMSMs) managed through liquid cooling. The management of benefits and costs from EV PMSM liquid cooling versus power are carried out for energy system output power (ESOP) increase. This study examines the effects of optimizing flow rate into housing water jackets (HWJ) and implementing compound shaft water (SWJ) cooling as management strategies using numerical multiphysics simulations and experiments. The PMSM with higher temperature at higher speed shows larger profit space brought by enhanced cooling. The optimized HWJ flow rate is a highly-efficient strategy to increase ESOP when overall pumping efficiency e1 for HWJ is less than 5 %, increasing more than 5.6 %, 2.1 % and 2.4 % ESOP at 1500, 3500, and 7000 rpm continuous working point. ESOP is insensitive to the condition of HWJ flow rate below 6 L/min or e1 over 30 %. The SWJ cooling is proved to be a low-cost and high-yield energy management strategy roughly independent of SWJ flow rate and EV's cooling system arrangement. ESOP is further increased by up to 3.9 %, 6.2 % and 4.4 % with SWJ cooling at 1500, 3500, and 7000 rpm.

Investigation of Operational Parameters for Nanoelectrokinetic Purification and Preconcentration.

This work reports on experimental investigations into the operational parameters of nanoelectrokinetic purification and preconcentration, especially utilizing on ion concentration polarization (ICP). ICP as a nanoscale electrokinetic phenomenon has demonstrated promising advances in various fields utilizing an ion depletion zone (IDZ) with a steep electric field gradient inside the ICP layer. However, the inevitable electrokinetic instability occurring within the IDZ has posed a challenge in operating the ICP system stably. To address the need for a stable and efficient ICP operation in various devices and applications, we propose an operational strategy along with conducted research to determine optimal operating ranges. In order to investigate the operational parameters, a unit voltage (VTH) is introduced as the threshold for initiating ICP. We examined the applicability of VTH across various operating ranges to ensure its effectiveness and versatility. In ICP purification, we categorize three modes (steady, burst, and unsteady) based on IDZ expansion and stability under varying VTH and flow rate conditions, presenting optimal operational conditions that minimize the voltage margin. In ICP preconcentration, a systematic investigation is conducted to observe the influence of background electrolyte concentration and voltage conditions on preconcentration efficiency, offering insights into the correlation between preconcentration factor, electrical conditions, and preconcentration time. Therefore, this research would contribute to the practical understanding of nanoelectrokinetics, providing insight into experimental designs. These findings are expected to offer valuable guidance to researchers aiming to utilize ICP's potential across a spectrum of applications, from purification to preconcentration, in the realm of micro/nanofluidic systems.

Influence of structural properties and connectivity of initial fracture network on incipient karst genesis

A karst system is generally difficult to characterize especially regarding its conduits pattern and morphology. Even though speleology allows to map the geometry of cave systems, a large part of karst conduit networks remains unreachable underground. In this study, we use a reactive transport model that simulates dissolution processes in fracture networks to investigate the effect of discrete fracture network (DFN) properties (i.e., anisotropy, connectivity, fracture intersection types) on incipient karst conduit geometry under different boundary conditions (constant hydraulic head versus constant flow rate conditions, directional versus concentrated recharge conditions). We focused on single fracture (with/without cementation) and ladder like fracture networks which are common on limestone. Results show that fracture network properties, play a major role in the final geometry and topology of the incipient karst conduit patterns. Also, the presence of cement on a single fracture favors tortuous and curvilinear wormholes, while the anisotropy of the fracture network favors the formation of anisotropic incipient karst geometries. Finally, the type of hydraulic BC remains a major factor that governs dissolution processes and thus incipient karst conduit geometry.

Flow field analysis and performance evaluation of a mini-hydrocyclone for ultra-low inlet flow rate

It is difficult for hydrocyclone to separate oil-water under the condition of ultra-low inlet flow rate, which commonly exist in the field of energy engineering. Mini-hydrocyclone is an effective technology to solve this problem. The flow field characteristics and oil droplet migration trajectory in the mini-hydrocyclone are the key to guide its efficient work. An innovative mini-hydrocyclone are studied via computational fluid dynamics (CFD) and experiment method. The good separation performance of mini-hydrocyclone for ultra-low inlet flow rate and tiny particle size of oil droplets is verified and analyzed. Furthermore, The distribution of velocity, oil volume fraction and oil migration trajectories in the mini-hydrocyclone are analyzed systematically. The effects of oil droplet size, inlet flow rate and split ratio on the separation performance of mini-hydrocyclone are investigated. The results show that the maximum separation efficiency of the mini-hydrocyclone for 1.0 L/min ultra-low inlet flow rate is 99.98 %, when the split ratio is 30 %, the oil phase volume fraction is 2 %. Moreover, the morphological and distribution of oil core in mini-hydrocyclone are basically consistent between simulation and experiment results, under the conditions of different operating parameters. The minimum error of numerical simulation and experiment results is less than 2.23 %, the accuracy of the numerical simulation method is verified.

Effect of airflow rate on droplet deposition of an impinging-jet inhaler in the human respiratory tract

This paper presents a numerical investigation to understand the transport and deposition of sprays emitted by an impinging-jet inhaler in the human respiratory tract under different inhalation flow rates. An injection model is used for the numerical simulations considering the spreading angles of the spray in the two directions, which are measured from experiments. The model parameter is adjusted to match the mean droplet size measured in the previous experiment. A time-varying sinusoidal inhalation flow rate is utilized as airflow conditions, which is closer to the actual situation when using an inhaler. The results demonstrate that the inhalation airflow rate significantly affects the spray’s transport behavior and deposition results in the respiratory tract. Both excessively high and low inhalation flow rates lead to an increase in deposition in the mouth-throat. A moderate inhalation flow rate reduces throat deposition while maximizing lung deposition. Higher inhalation flow rates enable faster delivery of the droplets to the lungs, whereas lower inhalation flow rates achieve a more uniform deposition over time in the lungs. The amount of deposition in different parts of the lung lobes follows a fixed order. This study provides valuable insights for optimizing the inhalation flow rate conditions of the impinging-jet inhaler for clinical applications.

Flow characteristics of a low-head and high-discharge hydraulic turbine under various operating conditions

A low-head and high-discharge hydraulic turbine holds significant potential for energy recovery across various engineering applications, owing to its capacity to manage substantial flows. However, the intricate mechanisms of energy loss within this turbine, particularly concerning its impeller and discharge tube, have received limited investigation. In this study, we present a comprehensive examination of the energy dissipation mechanisms, flow characteristics, and streamwise vorticity of the low-head and high-discharge hydraulic turbine. Utilizing the enstrophy dissipation theory, we conducted analyses under diverse operational conditions. Our findings reveal that energy dissipation predominantly occurs within the impeller and discharge tube. Volume enstrophy dissipation power contributes to over 80% of the total hydraulic loss under three flow rate conditions. Flow separation and intricate turbulence patterns emerge as primary factors contributing to energy loss within the impeller, while backflow and turbulence are that in the discharge tube. The regions with high energy loss in impeller is near the leading and trailing edges and in the discharge tube that is around the entrance.

Novel superhard BC10N synthesized by microwave plasma CVD

Microwave Plasma Chemical Vapor Deposition (MPCVD) was used to synthesize novel superhard BC10N on silicon substrates. Feedgas mixtures of H2, CH4, N2, and B2H6 were used for a range of systematically varied microwave power, chamber pressure, and flow rate conditions. Optical Emission Spectroscopy (OES) was used to guide the synthesis of BC10N. Plasma optical emission from the C2 peak increases with pressure up to 80 Torr and saturates in the 80–100 Torr range. The C2 emission also follows the same trend, growing non-linearly with increasing microwave power (for fixed chamber pressure of 30 Torr). The presence of abundant C2 in the plasma is advantageous under specific growth conditions to produce superhard carbon-rich BC10N, a material that has been theoretically predicted but not yet synthesized. Findings obtained from X-ray Photoelectron Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) elucidate the existence of BC, CN, BN, and B-N-C bonding in the synthesized coating. Nanoindentation hardness measurements are within the superhard regime, showing an average hardness of 63 GPa.

Multiobjective hydraulic optimization of the diffuser vane in an axial flow pump

Separation flows tend to induce a chaotic flow field that eventually leads to energy losses and reduced efficiency. The present study performed a multiobjective optimization to improve the hydraulic performance of an axial flow pump at the best efficiency point (BEP) and critical stall point based on the diffuser vane (DV) geometry. Computational fluid dynamics were applied to predict the hydraulic performance of a series of DV models with design points generated through design of experiment. Six different surrogate models were evaluated based on the R-squared criteria. The nondominated sorting genetic algorithm II was also employed to search for optimum solutions for design variables. Hydraulic performance balance between low and high flow rate conditions was analyzed based on the velocity triangle. After optimization, the efficiency and total head at the BEP of the optimum model were increased by 2.341% and 2.779%, respectively, compared to the reference model. Despite the minimal changes to the hydraulic performance at the critical stall point, the optimal operating range was notably expanded in the high flow rate region. Thorough evaluation of losses attributed to horseshoe, corner, and trailing-edge vortices was conducted in meridional planes, multiple spans, and various cross sections in the DV domain. Additionally, the formation and development of turbulent flow were analyzed in detail by transient simulation. Vibration and noise caused by instabilities in the flow characteristics of the reference model were substantially reduced by 36.76% and 67.342% at the first higher-harmonic frequencies at the BEP and the critical stall point, respectively.

Thermal-hydraulic analysis of a full-scale lead-bismuth cooled fast reactor core considering inter-wrapper flow

The Lead-bismuth cooled Fast Reactors (LFR) utilizes wrapped hexagonal fuel assemblies arranged in a honeycomb pattern. The inter-wrapper flow (IWF) between adjacent assemblies has a significant influence on the core thermal-hydraulics. In this paper, the LFR core assembly analysis model, inter-wrapper flow and heat transfer model, and multi-scale coupling analysis model were developed and were implemented into the previously self-developed subchannel-level three-dimensional thermal hydraulic analysis code CorTAF-LBE for whole core of LFR, which is based on the OpenFOAM computational fluid dynamics simulation platform. The inter-wrapper flow and heat transfer model was validated against the KALLA-IWF experiment. Whole core steady state operating condition and low flow rate condition simulations were performed with reference to the 19-rod bundle geometry from KALLA laboratory and typical LFR core assembly arrangement. The whole core steady state distribution laws of key thermal-hydraulic parameters were obtained, and the influence of low flow rate operation on safety parameters such as cladding and pellet temperatures was analyzed. Under low flow rate operating conditions, the IWF heat transfer was accounted for 4.87% of the core thermal power, which was 315.6 kW higher than that under normal operating conditions, playing an important role in core heat removal and safe operation. This work provides important insights into LFR core design and the assessment of the role of IWF under low flow rate conditions.

Physicochemical properties and CO2 absorption performance of poly(ethylene glycol) 300 + hydroxyethyl ethylenediamine mixed solution

Density (ρ) and viscosity (η) data of the polyethylene glycol 300 (PEG300) and hydroxyethyl ethylenediamine (AEEA) mixed solution were measured at P = 1005 hPa and T = (298.15–318.15) K. Following these data, Jouyban-Acree model exhibited superior correlation to density in the mixed system compared to nonlinear least square method, while the McAllister four-body equation yielded a better fitting for kinematic viscosity than other models. Utilizing ρ and η data, the Redlich-Kister equation was employed for the systematic computation and analysis of excess molar volume (VmE), excess activation Gibbs free energy (ΔG*E), partial molar volumes (V1¯ and V2¯), and viscosity deviation (Δη) in the PEG300 (1) + AEEA (2) mixed solution. These excess properties indicated the advantageous nature of intermolecular binding in the PEG300 (1) + AEEA (2) mixed solution, further substantiated on the basis of various spectroscopic characterizations. Finally, under conditions of CO2 flow rate at 150 mL/min, absorption experiments were conducted for 4 h in the PEG300 (1) + AEEA (2) mixed solution, pure AEEA, and pure PEG300, which indicated that the mixed solution exhibited the highest CO2 absorption capacity of 0.95 mol CO2/mol AEEA, demonstrating superior absorption performance compared to the two pure substances.

A micro-capillary jetting technology for liquid-liquid microdispersion with narrow size distribution

Liquid-liquid microdispersion is one of the key foundations for chemical process intensification. However, liquid-liquid microdispersion at the conditions of high phase ratio and high volume flow rate remains a problem and new microdispersion technology is highly required. Based on the microscale effect of the liquid jet, we developed the micro-capillary jetting technology. It can produce microdroplets (250–500 μm) with narrow size distribution (CV ≈ 10–20 %) in a wide range of physical properties with large capacity and little cost without the restriction of phase ratio. This paper reports the laws of the micro-capillary jetting technology. The liquid-liquid flow patterns and mechanism are studied, and a precise quantitative model to distinguish different jetting patterns is provided for the first time based on the energy analysis in the microscale. Then important factors including physical properties, dispersion mode and structural parameters are investigated. Accordingly, a mathematical model for the prediction of the average droplet size is established and the energy utilization in the jetting dispersion process is calculated.

Pore‐Scale Modeling of Carbon Dioxide and Hydrogen Transport During Geologic Gas Storage

AbstractGeologic storage of CO2 and H2 are climate‐positive techniques for meeting the energy transition. While similar formations could be considered for both gases, the flow dynamics could differ due to differences in their thermophysical properties. We conduct a rigorous pore‐scale study of water/CO2 and water/H2 systems at relevant reservoir conditions in a Bentheimer rock sample using the lattice Boltzmann method to quantify the effects of capillary, viscous, inertial, and wetting forces during gas invasion. At similar conditions, H2 invasion is weaker compared to CO2 due to unfavorable viscosity ratios. Increasing flow rate, however, increases the breakthrough saturation for both gas systems in the range of capillary numbers studied. At isolated conditions of flow rate, viscosity ratio, and wettability, local inertial effects are found to be critical and show consistent increase in the invaded gas saturation. The effect of inertial forces persits for both gases across all field conditions tested.

Microencapsulation improves the effects of octacosanol to ameliorate alcoholic liver injury

AbstractOctacosanol is a plant natural product with the potential to ameliorate alcoholic liver injury. However, its poor solubility limits its application in the food industry. This study first verified that octacosanol has a favorable effect on acute and subchronic alcoholic liver injury in mice by protecting the gastric mucosa and ameliorating disease levels. Additionally, octacosanol microcapsules were prepared under the optimal drying conditions of the feed flow rate of 400 mL/h and drying temperature of 180°C to improve the ameliorative effects of octacosanol, with moisture content, water activity, dispersibility, and solubility of 1.53%, 0.16%, 89.84%, and 95.30%, respectively. The microcapsules had a spherical structure, and the droplet sizes after redissolution ranged from 0.061 to 4.63 µm. Instrumental measurements and simulated digestion experiments have shown that microencapsulation enhanced the solubility and thermal stability of octacosanol, with 90.88% of the octacosanol being continuously released. As expected, microencapsulation significantly enhanced the effect of octacosanol in ameliorating alcoholic liver injury by determining the disease index in the mice model. This study demonstrated the beneficial effects of octacosanol on alcoholic liver injury and explored a viable method to improve its solubility and bioaccessibility, thereby enhancing its therapeutic efficacy for the treatment of alcoholic liver injury.

Pump System Model Parameter Identification Based on Experimental and Simulation Data

In this paper, the entire downhole fluid-sucker rod-pump system is replaced with a viscoelastic vibration model, namely a third-order differential equation with an inhomogeneous forcing term. Both Kelvin’s and Maxwell’s viscoelastic models can be implemented along with the dynamic behaviors of a mass point attached to the viscoelastic model. By employing the time-dependent polished rod force measured with a dynamometer as the input to the viscoelastic dynamic model, we have obtained the displacement responses, which match closely with the experimental measurements in actual operations, through an iterative process. The key discovery of this work is the feasibility of the so-called inverse optimization procedure, which can be utilized to identify the equivalent scaling factor and viscoelastic system parameters. The proposed Newton–Raphson iterative method, with some terms in the Jacobian matrix expressed with averaged rates of changes based on perturbations of up to two independent parameters, provides a feasible tool for optimization issues related to complex engineering problems with mere information of input and output data from either experiments or comprehensive simulations. The same inverse optimization procedure is also implemented to model the entire fluid delivery system of a very viscous non-Newtonian polymer modeled as a first-order ordinary differential equation (ODE) system similar to the transient entrance developing flow. The convergent parameter reproduces transient solutions that match very well with those from fully fledged computational fluid dynamics models with the required inlet volume flow rate and outlet pressure conditions.

The Influence of Different Working Fluid Temperatures on the Hydraulic Performance of Magnetic Vortex Pumps

Magnetic vortex pumps are characterized by their high performance and zero leakage, and in recent years, they have been applied for the transportation of antifreeze coolant in varying-temperature environments. This paper combines Computational Fluid Dynamics (CFD) with experimental verification to study the external and internal flow characteristics of magnetic vortex pumps when transporting working fluid at different temperatures, considering radial clearance flow. The results indicate that as the temperature of the medium increases, both the pump head and efficiency improve. Specifically, under the design flow rate condition, the pump head increases by 16.7% when transporting a medium at 90 °C compared to ambient-temperature conditions. Conversely, the pump head is only 16.8% of that observed under ambient-temperature conditions when transporting a medium at −30 °C. Analysis of the internal flow field reveals that the changes in pump hydraulic performance at different working fluid temperatures are primarily due to variations in the vorticity of the internal flow field.

Investigation of flow-induced sound source generation in a centrifugal pump

Abstract This study investigates the mechanism of sound source generation in a centrifugal pump under different flow conditions. The calculated results are in good agreement with experimental data by employing the delayed detached eddy simulation and flow-acoustic coupling method to compute the flow-induced noise. Based on the vortex sound theory and vorticity binary decomposition, the sound source (STA) is divided into a shear-induced source (STS) and a rigid rotation-induced source (STR). The results show that the sound source induced by shear is the main factor. The fluctuation amplitude of STS can be nine times larger than STR at monitor point near the tongue under the design flow rate condition. There is a mutual cancellation effect between the STS and STR. The fluctuation amplitude of STA at the blade passing frequency is 86% of STS at monitor point near the tongue under high flow rate conditions, indicating that sometimes rigid rotation can suppress noise generation.