Description Of Flow Research Articles

Study of the hydraulic parameters of the flow of solid particles in the process of hydrotransport

The article presents the characteristics of transferring solids together with water in the process of hydrotransport at pumping stations, that is, the influence on the distribution of kinematic and dynamic parameters of the flow of hydraulic transport, the description of the pressure dispersed flows in the process of hydrotransport with high volume concentrations and a wide range of particle sizes and densities of solid particles that form mixtures.

Benefits of controlled inclination for contactless transport by squeeze-film levitation

Developed in this paper is a theoretical description of the fluid flow involved in contactless transport systems that operate using squeeze-film levitation. Regular perturbation methods are employed to solve the appropriate Reynolds equation that governs the viscous, compressible flow of air in the slender film separating the oscillator and the levitated object. The resulting reduced formulation allows efficient computation of the time-averaged levitation force and moment induced by fluid pressure, as well as the accompanying quasistatic thrust force that accounts additionally for shear stresses. Investigated, in particular, is the possibility of combining two distinct methods of thrust generation that have been experimentally demonstrated in previous studies – (i) inclination of the levitated body and (ii) generation of asymmetrical flexural deformations, such as travelling waves, on the oscillator surface – the latter of which is shown to allow a transition from the typically repulsive levitation force to one that is attractive. Computations reveal that systematic control of the inclination angle can provide significant performance benefits for squeeze-film transport systems. In the case of attractive levitation, the amount of improvement that can be obtained appears to correlate closely with the degree of lateral asymmetry exhibited by the flexural oscillations.

Algorithm for Locating Multiple Leaks in a Pipeline with an Invariance Condition

This paper addresses the problem of multiple leaks’ location in a pipeline by considering available measurements of pressure and flow rate at the ends of the pipeline. New conditions are derived that allow the establishment of a well-posed identification problem for two leaks. These conditions are deduced from the existence of the redundant description of the intermediate flow in the line, the invariance of the conduit's physical parameters with respect to the flow's operating points, and the relationship that links the hydraulic gradients of the respective scenarios of one and two leaks. These joint conditions, which have not been established before, eliminate the assumption of sequential leaks reported in the literature and are the paper's main contribution. Moreover, a minimization algorithm considering these conditions is introduced here. Synthetic data demonstrate the proposed algorithm's effectiveness for five situations.

A note about convected time derivatives for flows of complex fluids.

We present a direct derivation of the typical time derivatives used in a continuum description of complex fluid flows, harnessing the principles of the kinematics of line elements. The evolution of the microstructural conformation tensor in a flow and the physical interpretation of different derivatives then follow naturally.

Information system for data analysis of electronic operational documentation to support the development of economic processes

The article presents an information system for data analysis of electronic operational documentation, the main purpose of which is the storage, collection and analysis of information, as well as the formation of an expert decision and forecasting to improve the quality of user work and the speed of processing large amounts of information. The functional structure of maintaining operational documentation was considered, a description of data flows and business processes was carried out, and the interaction of decision support systems with the subject area was studied.

Model of vehicle interactions with autonomous cars and its properties

<p style='text-indent:20px;'>We study a hierarchy of models based on kinetic equations for the descriptions of traffic flow in presence of autonomous and human–driven vehicles. The autonomous cars considered in this paper are thought of as vehicles endowed with some degree of autonomous driving which decreases the stochasticity of the drivers' behavior. Compared to the existing literature, we do not model autonomous cars as externally controlled vehicles. We investigate whether this feature is enough to provide a stabilization of traffic instabilities such as stop and go waves. We propose two indicators to quantify traffic instability and we find, with analytical and numerical tools, that traffic instabilities are damped as the penetration rate of the autonomous vehicles increases.</p>

How to accurately predict nanoscale flow: Theory of single-phase or two-phase?

Accurate evaluation and recognition of nanoscale flow is the premise of the extension of classical theories of fluid mechanics to nanoscales. Despite the widely reported nonuniform characteristics of nanoconfined fluids, nanoscale flow is still considered as a single-phase flow in general, resulting in large deviations in theoretical predictions of velocity profile and flow rate. Considering the significant characteristics of a two-phase flow in nanoscales and the similarity between nanoscale flow and gas–liquid two-phase annular flow, we put forward a novel viewpoint that nanoscale flows should be described based on the theory of a two-phase flow. To support this idea, nanoscale flows under different fluid types, densities, temperatures, fluid–solid interactions, and driving pressures are extensively tested using molecular dynamics simulations. The results demonstrate that nanoscale flows can be divided into an adsorption phase and a bulk phase, and the characteristics of a two-phase flow are especially obvious under low fluid density, strong fluid–solid interaction, and low fluid temperature. The reasonability is further demonstrated by systematically analyzing the interphase density difference, interphase velocity difference, interphase mass exchange, and interfacial fluctuation, which are typical characteristics of a two-phase flow at macroscales. Finally, we present a series of theoretical descriptions of nanoscale flow from the perspective of a two-phase flow. By adopting different viscosity and density in the adsorption phase and bulk phase, the new model can better capture the physical details of nanoscale flow, such as velocity distribution and flow rate.

Aerosols and human health – A multiscale problem

Chemical engineering is a scientific discipline that uses physicochemically based quantitative analysis of the momentum, energy, and mass transfer to design and optimize industrial processes. Technical issues are considered on different scales, starting from the molecular interactions, through the nano- and micrometric levels up to the design and control of the full-scale equipment and industrial installations. Such a multi-scale approach is needed to identify the critical factors of any process. In a similar way, chemical engineering can solve problems of physiology and medicine. This paper is focused on pulmonary drug delivery, which needs using a combination of the knowledge of lung physiology with the quantitative description of aerosol generation, multi-phase flow and interfacial phenomena in the respiratory system. The scientific evidence of the effectiveness of this approach has been referred to the extensive studies of the author's research team working in the field of chemical and process engineering.

Modelling a Turbulent Non-Premixed Combustion in a Full-Scale Rotary Cement Kiln Using reactingFoam

No alternatives are currently available to operate industrial furnaces, except for hydrocarbon fuels. Plant managers, therefore, face at least two challenges. First, environmental legislation demands emission reduction. Second, changes in the origin of the fuel might cause unforeseen changes in the heat release. This paper develops the hypothesis for the detailed control of the combustion process using computational fluid dynamic models. A full-scale mock-up of a rotary cement kiln is selected as a case study. The kiln is fired by the non-premixed combustion of Dutch natural gas. The gas is injected at Mach 0.6 via a multi-nozzle burner located at the outlet of an axially mounted fuel pipe. The preheated combustion air is fed in (co-flow) through a rectangular inlet situated above the attachment of the fuel pipe. The multi-jet nozzle burner enhances the entrainment of the air in the fuel jet. A diffusion flame is formed by thin reaction zones where the fuel and oxidizer meet. The heat formed is transported through the freeboard, mainly via radiation in a participating medium. This turbulent combustion process is modeled using unsteady Favre-averaged compressible Navier–Stokes equations. The standard k-ϵ equations and standard wall functions close the turbulent flow description. The eddy dissipation concept model is used to describe the combustion process. Here, only the presence of methane in the composition of the fuel is accounted for. Furthermore, the single-step reaction mechanism is chosen. The heat released radiates throughout the freeboard space. This process is described using a P1-radiation model with a constant thermal absorption coefficient. The flow, combustion, and radiative heat transfer are solved numerically using the OpenFoam simulation software. The equations for flow, combustion, and radiant heat transfer are discretized on a mesh locally refined near the burner outlet and solved numerically using the OpenFoam simulation software. The main results are as follows. The meticulously crafted mesh combined with the outlet condition that avoids pressure reflections cause the solver to converge in a stable manner. Predictions for velocity, pressure, temperature, and species distribution are now closer to manufacturing conditions. Computed temperate and species values are key to deducing the flame length and shape. The radiative heat flux to the wall peaks at the tip of the flame. This should allow us to measure the flame length indirectly from exterior wall temperature values. The amount of thermal nitric oxide formed in the flame is quantified. The main implication of this study is that the numerical model developed in this paper reveals valuable information on the combustion process in the kiln that otherwise would not be available. This information can be used to increase fuel efficiency, reduce spurious peak temperatures, and reduce pollutant emissions. The impact of the unsteady nature of the flow on the chemical species concentration and temperature distribution is illustrated in an accompanying video.

Modeling and Analysis of Mass Transport Losses of Proton Exchange Membrane Water Electrolyzer

Proton exchange membrane water electrolyzers (PEMWEs) coupled with renewable energy resources are considered to be a key technology for producing green hydrogen. However, the high current density PEMWE operation features remarkable voltage losses. A significant part of these losses is due to the mass transport resistance in the PEMWE. Even though the importance of mass transport resistance is widely recognized, it is still poorly understood. Currently, the two-phase transport through the anode porous transport layer (PTL) and catalyst layer is considered to be the main cause of the mass transport losses. In this work, a dynamic macroscopic mathematical model, coupling electrochemical reaction with mass transport through the PTL and flow channels, has been developed to study the two-phase flow in the PTL and mass transport losses of a PEMWE. The influence of the current density, inlet water flow rate, PTL structural parameters, and capillary pressure curve was evaluated. The existence of the critical current density was observed, as well as its dependence on the operating parameters and PTL structure. Even though the results show that the PTL structure has a significant influence on the PEMWE performance, they indicate that a better mathematical description of the two-phase flow in the PTL is necessary.

Numerical study of multiphase hyperbolic models

Baer–Nunziato (BN) type models introduce fundamental and widely used class of multi-fluid and multi-velocity models to describe evolution of multi-phase flows. The original BN model is supposed to describe multi-phase flows at spatial scales substantially larger than the characteristic scale of elements of the dispersed phase. Recently a number of attempts have been performed to apply it to the description of multi-phase flows with resolved, at the large spatial scale, inter-phase boundaries. A number of still not well understood issues arise in this situation, related to the complex interplay of the topics related to (i) justification of the hierarchy of BN-type models for diffuse interface type description of multi-phase flows with resolved inter-phase boundaries; (ii) the questions of “correct” definition of generalized solutions of first order quasi-linear hyperbolic systems and (iii) development of “really” path-conservative and asymptotic preserving schemes for quasilinear hyperbolic systems with stiff relaxation terms. The goal of the paper is to study numerically such interplay when BN7 model is applied to describe 1D two-phase flows. Our main target is the diffuse interface type formulations. The obtained numerical solutions are compared to analytical solutions of the “more equilibrated” BN5 equations and heterogeneous formulations for the standard Euler equation. The goal is to provide factual information for the performed tests. We also try to summarize the obtained results in a systematic way from a practical point of view. To avoid ambiguity in interpretation of the numerical results, we provide detailed description of the algorithms and perform a number of auxiliary numerical tests.

Scaling Description of Creep Flow in Amorphous Solids.

Amorphous solids such as coffee foam, toothpaste, or mayonnaise display a transient creep flow when a stress Σ is suddenly imposed. The associated strain rate is commonly found to decay in time as γ[over ˙]∼t^{-ν}, followed either by arrest or by a sudden fluidization. Various empirical laws have been suggested for the creep exponent ν and fluidization time τ_{f} in experimental and numerical studies. Here, we postulate that plastic flow is governed by the difference between Σ and the transient yield stress Σ_{t}(γ) that characterizes the stability of configurations visited by the system at strain γ. Assuming the analyticity of Σ_{t}(γ) allows us to predict ν and asymptotic behaviors of τ_{f} in terms of properties of stationary flows. We test successfully our predictions using elastoplastic models and published experimental results.

Investigating the Effect of Rotor Design Changes on Mechanical Losses Due to Rotor-Fluid Interaction

Abstract The overall efficiency of high-speed rotating machines depends largely on their mechanical efficiency. Mechanical efficiency is not just a matter of bearing losses, but includes all interactions of the rotor with the environment. Analytical and empirical descriptions of turbulent or laminar flow around rotating surfaces have been used to estimate the mechanical losses of a turbocharger rotor based on geometric parameters and operating conditions. Based on the knowledge of the effect of each parameter, design changes to the rotor were proposed. The positive effect of simple design modifications on mechanical losses was experimentally verified by measurements on a test turbocharger.

An experimental and numerical study of turbulent heat transfer enhancement for graphene nanofluids produced by pulsed discharge

• Time and cost-effective production of graphene nanofluids by pulsed discharge is tried and tested. • A new two-step method for producing graphene nanofluids has been developed. • Graphene nanofluids generated by pulsed discharge and ultrasound, like other graphene nanofluids, have high turbulent heat transfer performance (35% higher than water). • The numerical results show considerable increase in turbulent kinetic energy (8%) and velocity gradients near the wall due to physical interaction between continuous phase(water) and dispersed phase (graphene nano-particles). • The exchange of momentum and energy due to the movement of particles is considered as a cause-and-effect relationship between the aggregation of particles and the change in physical quantities in the continuous phase. Developing production methods for graphene nanofluids that can produce them in large quantities at once in a short time and at a low cost will contribute to the development of a wide range of industries that use nanofluids, and understanding their properties through mathematical modeling and experiments will lead to the development of new nanofluids. In this study, the new production method of graphene nanofluids is proposed and experimental and numerical investigations of the turbulent heat transfer performance of graphene nanofluids in a horizontal circular tube subjected to constant heat flux are conducted. The experimental investigation is conducted to evaluate the turbulent heat transfer performance of graphene nanofluids which are made by a new method using pulsed discharge and to compare them with numerical results. In the numerical investigation, the finite volume method with a Realizable k-ε model and Two-layer model is employed to solve the continuity, momentum, and energy conservation in two-dimensional domains. The Lagrangian two-phase model is applied to consider the physical interaction between the dispersed phase and continuous phase. In this model, the particles are tracked in a Lagrangian manner and coupled with the Eulerian flow description. Since the computational burden would be tremendous if individual nanoparticles were tracked in a Lagrangian manner, we defined a cluster of particles, called a parcel and treated it statistically. This concept of parcels allowed the average behavior of nanoparticles to be established as an analytical parameter. As a result, graphene nanofluids are not produced by pulsed discharge alone but are successfully produced by applying ultrasonic. Experimental investigations show a 33% increase in the Nu number of graphene nanofluid produced by pulsed discharge compared to water as the flow velocity increased. Numerical investigations confirm changes in the properties (Turbulent kinetic energy, Velocity distribution, Temperature distribution) of the continuous phase due to physical interactions between the dispersed and continuous phases. It is also shown that these changes contribute to the improved turbulent heat transfer performance of the nanofluid and that the aggregation of particles into the center of the tube is responsible for these changes.

A Hierarchy of Probability, Fluid and Generalized Densities for the Eulerian Velocivolumetric Description of Fluid Flow, for New Families of Conservation Laws

The Reynolds transport theorem occupies a central place in continuum mechanics, providing a generalized integral conservation equation for the transport of any conserved quantity within a fluid or material volume, which can be connected to its corresponding differential equation. Recently, a more generalized framework was presented for this theorem, enabling parametric transformations between positions on a manifold or in any generalized coordinate space, exploiting the underlying continuous multivariate (Lie) symmetries of a vector or tensor field associated with a conserved quantity. We explore the implications of this framework for fluid flow systems, based on an Eulerian velocivolumetric (position-velocity) description of fluid flow. The analysis invokes a hierarchy of five probability density functions, which by convolution are used to define five fluid densities and generalized densities relevant to this description. We derive 11 formulations of the generalized Reynolds transport theorem for different choices of the coordinate space, parameter space and density, only the first of which is commonly known. These are used to generate a table of integral and differential conservation laws applicable to each formulation, for eight important conserved quantities (fluid mass, species mass, linear momentum, angular momentum, energy, charge, entropy and probability). The findings substantially expand the set of conservation laws for the analysis of fluid flow and dynamical systems.

Simplified Numerical Model for Transient Flow of Slurries at Low Concentration

Rapid transients are particularly dangerous in industrial hydro-transport systems, where solid-liquid mixtures are transported via long pressure pipelines. A mathematical description of such flow is difficult due to the complexity of phenomena and difficulties in determining parameters. The main aim of the study was to examine the influence of the simplified mixture density and wave celerity description on satisfactory reproduction of pressure characteristics during the transient flow of slurry at low concentrations. The paper reports and discusses the selected aspects of experimental and numerical analyses of transient slurry flow in a polyethylene pipe. The experiments were conducted by using the physical model of a slurry’s transportation pressure. The aim of the experiments was to determine the wave celerity during a transient flow in slurries. A low concertation of slurries, which was used during experiments, is typical for one of the biggest slurry networks in Poland. A comparison of the effects of different wave celerity descriptions was performed. The research reported that the theoretical formulas for slurry wave celerity and mixture density were not sufficiently accurate to obtain satisfactory compliance between calculations and observations. To improve the model, the experimental values of wave celerity and the concept of equivalent mixture density have been applied to indirectly consider the influence of variable mixture parameters. With such modifications, the calculated pressure characteristics in all analyzed episodes demonstrated satisfactory compliance with observations. The simplified approach proved to be effective in properly reproducing the intensity and frequency of rapid pressure changes.

Changing Flows Balance Nutrient Absorption and Bacterial Growth along the Gut.

Small intestine motility and its ensuing flow of luminal content impact both nutrient absorption and bacterial growth. To explore this interdependence we introduce a biophysical description of intestinal flow and absorption. Rooted in observations of mice we identify the average flow velocity as the key control of absorption efficiency and bacterial growth, independent of the exact contraction pattern. We uncover self-regulation of contraction and flow in response to nutrients and bacterial levels to promote efficient absorption while restraining detrimental bacterial overgrowth.

Computational and Experimental Assessment of a MW-Scale Supercritical CO2 Compressor Operating in Multiple Near-Critical Conditions

Abstract This work illustrates the results of a wide experimental campaign in the frame of the EU-funded project sCO2-Flex, which focused on the investigation of a MW-scale sCO2 compressor operating in plant-representative conditions. The experimental tests were carried out for four temperature levels between 304.15 K and 309.15 K at a fixed pressure of 79.79 bar, hence covering an extended thermodynamic region close to the critical point. The experimental results are thoroughly discussed with the support of steady computational fluid-dynamics simulations, assuming homogeneous flows and thermodynamic equilibrium for the two-phase flow description. Changing the upstream total state, two peculiar variabilities in the compressor pressure ratio and choking flow rate are experimentally and computationally observed. While the former is mainly related to the single-phase flow thermodynamics, the latter originates from the onset of two-phase flows. As the simulations predict the experimental choking with a maximum error of 3%, the corresponding two-phase speed of sound is analyzed to infer the underlying equilibria between phases. It is found that, for the tested conditions, two-phase flows quickly achieve thermodynamic equilibrium, and non-equilibrium or metastable effects arguably play a marginal role in the process.

Flexibility of fluorinated graphene based memristor structures: current flow model in a multi-barrier system under tensile strain

The flexibility of two types of memristor structures with fluorinated graphene (FG) based active layers (FG with graphene islands on polyvinyl alcohol, FG/PVA, and films from nanoparticles of V2O5 capsulated with FG, FG/V2O5) under the tensile strain in bending conditions was investigated and compared in the present study. Both types of memristors show a similar mechanism of resistance switchings (current paths on traps without filaments). Multi-barrier model of current flow was used to estimate the barrier parameters connected to FG from experiments on resistive switching of memristor structures in the bending condition. The first type of structures (Ag/FG/PVA/Ag) demonstrates the record high values of flexibility: ON/OFF current relation is not changed up to 7% tensile strain created by bending. The second type of structures (Gr/FG/V2O5/Gr with graphene contacts) show a decrease in ON current already for tensile strain more than 2%. The similar mechanism of current flow allows us to use the similar theory for description of the current flow versus the tensile strain. In spite of different structures and morphology of memristors, the typical values of the barrier height extracted from the theoretical description were similar: ∼1.5 eV with an effective barrier thickness of ∼16.5 nm and ∼1.3–1.6 eV with thickness 13.5–15.0 nm for FG/PVA and FG/V2O5 structures, respectively. Increase in the barrier thickness over 19 nm in both cases leads to the strong decrease in ON current of memristors.

A scalable collocated finite volume scheme for simulation of induced fault slip

We present a scalable collocated Finite Volume Method (FVM) to simulate induced seismicity as a result of pore pressure changes. A discrete system is obtained based on a fully-implicit fully-coupled description of flow, elastic deformation, and contact mechanics at fault surfaces on a flexible unstructured mesh. The cell-centered collocated scheme leads to a convenient integration of the different physical equations, as the unknowns share the same discrete locations on the mesh. Additionally, a generic multi-point flux approximation is formulated to treat heterogeneity, anisotropy, and cross-derivative terms for both flow and mechanics equations. The resulting system, though flexible and accurate, can lead to excessive computational costs for field-relevant applications. To resolve this limitation, a scalable processing algorithm is developed and presented. Several proof-of-concept numerical tests, including benchmark studies with analytical solutions, are investigated. It is found that the presented method is indeed accurate and efficient; and provides a promising framework for accurate and efficient simulation of induced seismicity in various geoscientific applications.