Steady-state Flow Conditions Research Articles

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.

Horizontal well hydraulics in leaky confined aquifer near a stream: analytical solutions for induced drawdown and water budget components.

Horizontal wells have gained popularity as a technology for exploring water resources and remediating aquifers over the last decades, due to costs and numerous technical benefits compared to traditional vertical wells. This study presents a set of analytical solutions for drawdown distribution and various components of water budget contributing to flow toward a horizontal well in an aquifer-aquitard system interacting with a fully penetrating stream. It is assumed that the water level in the upper unconfined aquifer remains fixed at a specific elevation during the course of the pumping in the lower leaky aquifer. The water budget components account for inflows from aquifer storage, stream depletion, and leakage across the aquifer-aquitard interface. Analytical solutions to this three-dimensional, transient, non-axisymmetric Darcian flow model are given for both transient and steady-state flow conditions, relying on a four-fold integral transform technique that includes a Robin-type boundary condition at the aquifer-aquitard interface. It is shown how various components of water budget collectively counterbalance the effect of pumping discharge, confirming that the mass is conserved under both continuous and non-continuous pumping scenarios. Response maps are prepared to assess how different components of water budget react to changes in the well position. Furthermore, it is found that the components of water budget are most sensitive to the well-to-stream distance and anisotropy ratio of the leaky aquifer.

Non-invasive measurement of wall shear stress in microfluidic chip for osteoblast cell culture using improved depth estimation of defocus particle tracking method.

The development of a non-invasive method for measuring the internal fluid behavior and dynamics of microchannels in microfluidics poses critical challenges to biological research, such as understanding the impact of wall shear stress (WSS) in the growth of a bone-forming osteoblast. This study used the General Defocus Particle Tracking (GDPT) technique to develop a non-invasive method for quantifying the fluid velocity profile and calculated the WSS within a microfluidic chip. The GDPT estimates particle motion in a three-dimensional space by analyzing two-dimensional images and video captured using a single camera. However, without a lens to introduce aberration, GDPT is prone to error in estimating the displacement direction for out-of-focus particles, and without knowing the exact refractive indices, the scaling from estimated values to physical units is inaccurate. The proposed approach addresses both challenges by using theoretical knowledge on laminar flow and integrating results obtained from multiple analyses. The proposed approach was validated using computational fluid dynamics (CFD) simulations and experimental video of a microfluidic chip that can generate different WSS levels under steady-state flow conditions. By comparing the CFD and GDPT velocity profiles, it was found that the Mean Pearson Correlation Coefficient is 0.77 (max = 0.90) and the Mean Intraclass Correlation Coefficient is 0.66 (max = 0.82). The densitometry analysis of osteoblast cells cultured on the designed microfluidic chip for four days revealed that the cell proliferation rate correlates positively with the measured WSS values. The proposed analysis can be applied to quantify the laminar flow in microfluidic chip experiments without specialized equipment.

Links between soil pore structure, water flow and solute transport in the topsoil of an arable field: Does soil organic carbon matter?

An improved understanding of preferential solute transport in soil macropores would enable more reliable predictions of the fate of agrochemicals and the protection of water quality in agricultural landscapes. The objective of this study was to investigate how soil organic carbon (SOC) and soil texture shape soil pore structure and thereby determine the susceptibility to preferential transport under steady-state near-saturated flow conditions. To do so, we took intact topsoil samples from an arable field that has large variations in SOC content (1.1–2.7%) and clay content (8–42%). Soil pore structure was quantified by X-ray tomography and soil water retention measurements. Non-reactive solute transport experiments under steady-state near-saturated conditions were carried out at irrigation rates of 2 and 5 mm h−1 to quantify the degree of preferential transport. Near-saturated hydraulic conductivities at pressure heads of −1.3 and −6 cm were also measured using a tension disc infiltrometer. The results showed that larger abundances of small macropores (240–720 µm diameter) and mesopores (5–100 µm diameter) resulted in weaker preferential transport, due to larger hydraulic conductivities in the soil matrix that prevented the activation of water flow and solute transport in large macropores. In particular, the degree of preferential transport was most strongly and negatively correlated with the mesoporosity in the 30–100 µm diameter class. In contrast, the degree of preferential transport was not correlated with connectivity measures (e.g. the percolating fraction and critical pore diameter for the macropore network), probably because i.) the pore space of almost all samples was highly connected, being dominated by one percolating cluster, and ii.) only a part of this percolating macroporosity was active under the near-saturated conditions of the experiment. We also found that the degree of preferential transport was strongly and negatively correlated with clay content, whilst the effects of SOC were not significant. Nevertheless, macroporosity in the 240–720 µm diameter class and mesoporosity were positively correlated with SOC content in our soils and in some previous studies. Therefore, SOC sequestration in arable soils may potentially reduce the risk of preferential transport under near-saturated flow conditions through better developed networks of small macropores and mesopores.

Release of contaminants from polymer surfaces under condition of organized fluid flows

The use of polymers for water storage or distribution is closely monitored, especially with regard to the possible contamination with substances coming from the material's surfaces. Different standards are practiced across countries according to type of applied materials and such test methods are prevalently based on constant temperature conditions. However, these polymers systems could be located in diverse environment which does not necessarily provide constant conditions. Experimental findings show that exposure of liquid inside polymeric materials to specific temperature gradients, and consequently to emerging organized flows, can result in an accelerated leaching of undesirable substances from the solid surface. In presented work model steady-state and organized flow conditions are used to compare release of contaminates from polyethylene by measuring of surface tension, UV–Vis spectroscopy, FTIR, scanning electron microscopy and elemental analysis of polymer surfaces and water leachates. The pilot study shows that convective flow generated via temperature gradient significantly affects contaminant release in comparison to a steady state and mixing flow conditions.

Isolation of the contribution of viscous flow to initiation of pentaerythritol tetranitrate during sub-shock impact

The drop weight impact experiment is used routinely to provide an initial screening of the handling sensitivity of new explosives. Despite the ubiquity and simplicity of the drop weight impact test, the physical mechanisms responsible for generating temperatures sufficiently high for the initiation of explosive reactions are not well understood. Preliminary work has shown that temperatures sufficient for ignition are in theory achievable in steady-state Poiseuille flow at the flow velocities observed experimentally with temperature-dependent shear viscosities. However, it is far from certain that such steady-state flow conditions can be achieved in the drop weight impact test because of its short duration. Therefore, here we study heat generation both experimentally and numerically to quantify the temperature distributions in molten pentaerythritol tetranitrate (PETN). Drop weight experiments have been performed starting with PETN that has been melted on a transparent anvil. The experimental results are consistent with our finite element calculations that indicate that the temperature does not approach the level needed for ignition on the time scales of the experiment. Interestingly, ignition regularly occurs in solid samples under the same conditions, so we discuss the phenomenology of ignition of both solid and molten PETN in the drop weight test and provide constraints to numerical simulations.

Localization estimation of two leaks in pipelines through Monte Carlo simulations and hydraulic-spatial constraints

The problem of localizing two leaks using only flow rate and pressure measurements at the boundaries of a pipeline, and under steady-state flow conditions, is ill-posed due to the undetermined nature of the inverse problem, which involves two coupled equations with four unknowns associated with the presence of the leaks: two emitter coefficients and two locations. Therefore, attempting to solve this problem using any method without imposing additional constraints leads to an unbounded solution space, which contains solutions that may be physically meaningless. In this article, we propose a four-algorithm method that incorporates both spatial and hydraulic constraints to filter out physically infeasible solutions. The proposed method is based on Monte Carlo simulations, which use input data from hydraulic instruments installed at the boundaries of the pipeline, as well as random values with predefined probabilities that are bounded by the hydraulic-spatial constraints. The outputs of the method are probability distributions for the four unknowns. To demonstrate the feasibility of the method, results obtained through simulations and experimental testing on a test bed are presented.

Measurement of effective thermal conductivity of composite powders of 2D materials and metals for additive manufacturing

Laser Powder Bed Fusion (LPBF), a promising additive manufacturing technique for composites of 2D materials and metals, requires knowledge of thermophysical properties, such as the thermal conductivity of powder, for process optimization. In this study, we measured the effective thermal conductivity of the most representative Cu-graphene composite powder in the field of heat transfer applications. To measure thermal conductivity, we propose a differential scanning calorimetry (DSC) method to measure the thermal resistances of a powder bed under steady-state heat flow conditions. We observe that the thermal conductivity of a composite powder is 1,000 times lower than that of the bulk metal without 2D material addition; e.g., exhibiting ~ 0.30 W/mK in Cu-1wt.% graphene powder. Furthermore, we discuss powder size and morphology impact on thermal conductivity influencing the number of contact points and thermal contact resistance. Our findings contribute to understanding the thermal conductivity of composite powders in a powder bed and aid in optimizing LPBF processes.

Roadmap for Recommended Guidelines of Leak Detection of Subsea Pipelines

The leak of hydrocarbon-carrying pipelines represents a serious incident, and if it is in a gas line, the economic exposure would be significant due to the high cost of lost or deferred hydrocarbon production. In addition, the leakage of hydrocarbon could pose risks to human life, have an impact on the environment, and could cause an image loss for the operating company. Pipelines are designed to operate at full capacity under steady-state flow conditions. Normal operations may involve day-to-day transients such as the operations of pumps, valves, and changes in production/delivery rates. The basic leak detection problem is to distinguish between the normal operational transients and the occurrence of non-typical process conditions that would indicate a leak. To date, the industry has concentrated on a single-phase flow, primarily of oil, gas, and ethylene. The application of a leak-monitoring system to a particular pipeline system depends on environmental issues, regulatory imperatives, loss prevention of the operating company, and safety policy rather than pipe size and configuration. This paper provides a review of the recommended guidance for leak detection of subsea pipelines in the context of pipeline integrity management. The paper also presents a review of the capability and application of various leak detection techniques that can be used to offer a roadmap to potential users of the leak detection systems.

Water hammer mitigation by internal rubber hose

The aim of this research was to experimentally analyse the possibility of using a rubber hose placed inside a pipeline to mitigate the water hammer phenomenon. The experiments were conducted using a steel pipeline with an inner diameter of 53 mm and an EPDM rubber hose with a diameter of 6 mm. Hydraulic transients were induced by a rapid closure of the valve located at the downstream end of the pipeline system. In order to analyse the influence of steady-state flow conditions on the maximum pressure increase, measurements were carried out for different values of initial pressure and discharge. The experimental results indicate that placing a rubber hose inside a pipeline can substantially attenuate valve-induced pressure oscillations. It was observed that the initial pressure has a significant influence on the capacity of the rubber hose to dampen the water hammer phenomenon. Comparative numerical calculations were performed using the Brunone–Vitkovský instant acceleration-based model of unsteady friction. It was demonstrated that this approach does not allow satisfactory reproduction of the observed pressure oscillations due to the viscoelastic properties of the EPDM hose used in the tests.

Computational investigation on the energy efficiency of heat exchangers using Al2O3 nanofluids

In this research, we perform a numerical investigation to examine the dynamic and thermal properties of a rectangular counterflow heat exchanger under forced convection. Our specific focus is on a novel category of heat transfer fluids referred to as nanofluids, and we investigate their performance in conditions of steady-state laminar flow. The analysis is conducted through the application of the finite volume method within the Ansys-Fluent software. The findings obtained reveal that the heat exchanger attains its peak efficiency of 35% when operated with reduced flow rates ( m ̇ c = 0.08 kg s and m ̇ h = 0.03 kg / s ) and a significant nanoparticle volume fraction of 3%. Furthermore, it has been detected that the use of steel as a material enhances the overall efficiency of the thermal transfer device. These results highlight the enhanced efficiency of nanoparticle-infused fluids in improving the heat exchanger’s performance.

The Method of Images Revisited: Approximate Solutions in Wedge‐Shaped Aquifers of Arbitrary Angle

AbstractThis paper focuses on deriving new approximate analytical solutions in wedge‐shaped aquifers. The proposed methodology is applicable to any type of aquifer namely, leaky, confined and unconfined, under both steady state and transient flow conditions. By applying the method of images and separating the flow field into sections using physical arguments, approximate analytical expressions are obtained for the drawdown function, which in contrast to the conventional theory, are applicable to any arbitrary wedge angle. Moreover, the solutions fully observe the boundary conditions, while they preserve the continuity of the drawdown, which can be calculated directly at any point of the flow field. Nevertheless, comparison of the results of the new approximate analytical solutions to numerical ones, has been considered necessary to check their validity. MODFLOW, a well‐known numerical tool is used to calculate the numerical results. The discrepancies between the numerical results and those of the approximate analytical solution are negligible. The main advantages of the proposed methodology are the following: (a) The model needs only finite number of terms compared to conventional analytical and numerical solutions that involve infinite series, (b) The computational load is low, so it can be easily used in conjunction with meta‐heuristic algorithms to solve groundwater resources optimization problems, (c) Stream depletion rate can be calculated rather accurately and (d) The method is applicable to related flow problems.

Integrated particle image velocimetry and fluid–structure interaction analysis for patient-specific abdominal aortic aneurysm studies

BackgroundUnderstanding the hemodynamics of an abdominal aortic aneurysm (AAA) is crucial for risk assessment and treatment planning. This study introduces a low-cost, patient-specific in vitro AAA model to investigate hemodynamics using particle image velocimetry (PIV) and flow-simulating circuit, validated through fluid–structure interaction (FSI) simulations.MethodsIn this study, 3D printing was employed to manufacture a flexible patient-specific AAA phantom using a lost-core casting technique. A pulsatile flow circuit was constructed using off-the-shelf components. A particle image velocimetry (PIV) setup was built using an affordable laser source and global shutter camera, and finally, the flow field inside the AAA was analyzed using open-source software. Fluid–structure interaction (FSI) simulations were performed to enhance our understanding of the flow field, and the results were validated by PIV analysis. Both steady-state and transient flow conditions were investigated.ResultsOur experimental setup replicated physiological conditions, analyzing arterial wall deformations and flow characteristics within the aneurysm. Under constant flow, peak wall deformations and flow velocities showed deviations within − 12% to + 27% and − 7% to + 5%, respectively, compared to FSI simulations. Pulsatile flow conditions further demonstrated a strong correlation (Pearson coefficient 0.85) in flow velocities and vectors throughout the cardiac cycle. Transient phenomena, particularly the formation and progression of vortex structures during systole, were consistently depicted between experimental and numerical models.ConclusionsBy bridging high-fidelity experimental observations with comprehensive computational analyses, this study underscores the potential of integrated methodologies in enhancing our understanding of AAA pathophysiology. The convergence of realistic AAA phantoms, precise PIV measurements at affordable cost point, and validated FSI models heralds a new paradigm in vascular research, with significant implications for personalized medicine and bioengineering innovations.

Visualization and Analysis of Temporal and Steady-State Gas Concentration in Process Chamber Using 70-dB SNR 1000 fps Absorption Imaging System

We are developing a 70-dB SNR 1,000 frame-per-second absorption imaging system, and it enables us to visualize gas concentration distribution in a vacuum chamber for semiconductor manufacturing. This article presents the measurement and analysis of temporal and steady-state NO2 gas concentration distribution using this system. In the steady-state gas flow condition which supplied from a shower plate, the spectrometry of NO2 gas shows a good linear relationship between the absorbance and the partial pressure with the system. The system enables the visualization of steady-state of NO2 gas concentration distribution which supplied from one hole of shower plate, and the results are compared with simulation to discuss the reasonability of the measurement. The system also enables to visualize the temporal NO2 gas concentration distribution supplied from a single nozzle, and the advantages of the system’s features of 70-dB and 1,000 fps are discussed.

Performance of a SWRO membrane under variable flow conditions arising from wave powered desalination

A wave-powered desalination unit couples a wave energy converter and reverse osmosis (RO) membrane to produce fresh water from pressurized seawater. Although renewable energy technologies have been increasingly used for desalination, the concept of direct wave-powered desalination system is still at an early stage of development. One of the challenges with direct wave-powered desalination is that while reverse osmosis (RO) membranes are typically designed to operate at a constant feed flow and pressure, wave energy converter outputs in the form of hydraulic pressures and flows are typically highly variable. In this work, a RO membrane is investigated under variable feed flow conditions to determine the potential impact of such operation on membrane performance. The feed flow and pressure are varied using both a traditional sinusoidal profile and a rectified sinusoidal profile - a case more representative for wave-powered desalination. The permeate recovery and permeate salinity for both cases are compared with the equivalent time-averaged steady-state conditions. For purely sinusoidal flow, the performance of the RO membrane was similar to the equivalent steady-state flow conditions. For rectified sinusoidal flow, there is a marginal increase in permeate recovery, while a significant increase in permeate salinity is observed. In addition, a membrane integrity test was carried out after both sets of varying flow conditions. A significant change in membrane performance was detected after the test with the rectified sinusoidal flow.

Analysis of the choking condition of one-dimensional diabatic flows with wall friction

The choking condition of a one-dimensional steady-state diabatic flow, with wall friction, of a perfect gas through a constant cross-section pipe has been analysed by applying a recent analytical solution. Such a choking condition can be achieved for an initially subsonic flow and a supersonic one, even when the heat flux goes from the fluid to the wall. Entropy–enthalpy diagrams have been analysed, and a universal choking condition for compressible diabatic flows with wall friction has been determined. The analytical solution of a supersonic flow, in which a normal shock occurs, has been obtained for a diabatic flow with wall friction and compared with the results of a numerical model.

Application of PIV for Virtual Mass Coefficient Measurement

The particle image velocimetry (PIV) technique is employed for the measurement of the virtual mass of a submerged object, an important parameter in the two-fluid model, particularly so for reactor thermal-hydraulic and safety analyses. Instead of carrying out the measurement through traditional transient processes that mix steady-state drag, virtual mass force, and Basset force, a new PIV approach is developed for steady-state flows through the integration of the fluid kinetic energy around the object. The Basset force, an inseparable transient force in viscous flows, is eliminated in the new approach, making virtual mass quantification possible. This new method has been applied to the virtual mass measurement of a solid cylinder, and although the measurement uncertainty from the flow’s random fluctuations is substantial, the results are very encouraging. The results suggest that the existence of drag force in viscous flow affects the virtual mass, as the flow field is different from the ideal potential flow. When the measurement method was applied to the quantification of air bubbles, no reliable data were obtained due to complications from bubble lateral motions and deformation. Further study is needed for the PIV method to be employed for bubble virtual mass force measurements under steady-state flow conditions.

Empirical model to assess leaching of pesticides in soil under a steady-state flow and tropical conditions

An empirical model of leaching of pesticides was developed to simulate the concentration of fungicides throughout unsaturated soil. The model was based on chemical reactions and the travel time of a conservative tracer to represent the travel time required for water to flow between soil layers. The model’s performance was then tested using experimental data from dimethomorph and pyrimethanil applied to the soil under field and laboratory conditions. The empirical model simulated fungicide concentration on soil solids and in soil solution at different depths over time (mean square error between 2.9 mg2 kg−2 and 61mg2 kg−2) using sorption percentages and degradation rates under laboratory conditions. The sorption process was affected by the organic carbon, clay, and the effective cation exchange capacity of the soil. The degradation rate values of dimethomorph (0.039 d−1–0.009 d−1) and pyrimethanil (0.053 d−1–0.004 d−1) decreased from 0 to 40 cm and then remained constant in deeper soil layers (60–80 cm). Fungicide degradation was a critical input in the model at subsurface layers. The model was determined to be a reliable mathematical tool to estimate the leachability of pesticides in tropical soil under a steady-state flow. It may be extended to other substances and soils for environmental risk assessment projects.Graphical abstract

Maldistribution of a Thermal Fluid along the U-Tube with a Different Bending Radius—CFD and PIV Investigation

This paper investigates the effect of changing the bending radius of pipes on the maldistribution of velocity and turbulence of thermal fluid when flowing through a u-shaped tube bundle used in compact heat exchangers, among other applications. The study included three bending radii corresponding to successive rows of the actual tube bundle of a compact heat exchanger. Both liquid flow velocities recommended for compact heat exchangers and velocities elevated from the recommended ones were adopted. The results of the study were obtained by Computational Fluid Dynamics (CFD) and the performed experiment using the Particle Image Velocimetry (PIV) method. The limits of maldistribution were indicated by parameterizing this phenomenon with related geometric and flow values (turbulent flow intensity factor, flow velocity, pipe diameter, and bending radius). An increase in flow velocity above the recommended values did not result in a significant increase in turbulent flow intensity factor for u-tubes with large d/rg values. The shortest distance at which the return to steady-state flow conditions in a straight section of pipe downstream of an elbow took place was determined. This distance was 17d for geometry rg = 0.009 m, with velocity vp = 1.44 m/s. The localization of the areas of highest and lowest fluid velocity in the elbow element of the u-tube for extreme values of rg was opposite. This fact has an exploitable significance (non-uniform erosive effect of thermal fluid on pipes in different rows).

Effective rheology of immiscible two-phase flow in porous media consisting of random mixtures of grains having two types of wetting properties

We consider the effective rheology of immiscible two-phase flow in porous media consisting of random mixtures of two types of grains having different wetting properties using a dynamic pore network model under steady-state flow conditions. Two immiscible fluids, denoted by “A” and “B”, flow through the pores between these two types of grains denoted by “+” and “−”. Fluid “A” is fully wetting, and “B” is fully non-wetting with respect to “+” grains, whereas it is the opposite with “−” grains. The direction of the capillary forces in the links between two “+” grains is, therefore, opposite compared to the direction in the links between two “−” grains, whereas the capillary forces in the links between two opposite types of grains average to zero. For a window of grain occupation probability values, a percolating regime appears where there is a high probability of having connected paths with zero capillary forces. Due to these paths, no minimum threshold pressure is required to start a flow in this regime. When varying the pressure drop across the porous medium from low to high in this regime, the relation between the volumetric flow rate in the steady state and the pressure drop goes from being linear to a power law with exponent 2.56, and then to linear again. Outside the percolation regime, there is a threshold pressure necessary to start the flow and no linear regime is observed for low pressure drops. When the pressure drop is high enough for there to be a flow, we find that the flow rate depends on the excess pressure drop to a power law with exponents around 2.2–2.3. At even higher excess pressure drops, the relation becomes linear. We see no change in the exponent for the intermediate regime at the percolation critical points where the zero-capillary force paths disappear. We measure the mobility at the percolation threshold at low pressure drops so that the flow rate versus pressure drop is linear. Assuming a power law, the mobility is proportional to the difference between the occupation probability and the critical occupation probability to a power of around 5.7.