Homogeneous Fluid Research Articles

Surface-Modified Nanoparticle Gelled-Acid System Stimulates Without Formation Damage

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 22443, “Surface-Modified Nanoparticle-Based Novel Gelled-Acid System: A Unique Formation-Damage-Free Well-Stimulation Technology,” by Rajendra Kalgaonkar, SPE, and Nour Baqader, SPE, Saudi Aramco. The paper has not been peer reviewed. Copyright 2022 International Petroleum Technology Conference. Reproduced by permission. Gelled-acid systems based on the gelation of hydrochloric acid (HCl) are used extensively in both matrix and fracture acidizing to prevent acidizing-fluid leakoff. However, these systems can lead to formation damage. To mitigate this risk, the authors have developed a self-breaking, formation-damage-free, novel nanoparticle-based gelled-acid system to replace polymer-based gelled-acid systems. Nanoparticle-Based Gelled-Acid System The complete paper showcases a method for gelling up an acid formulation for stimulating a carbonate reservoir. The technique is based on surface-modified nanoparticles. The new gelled-acid system does not contain any polymer-based gelling agents. It consists of inorganic nanoparticles with a gelation-activator material to activate viscosification. The increase in viscosity will lead to a slowdown of the reaction rate of the acid with the carbonate formation. Suitable functionalities are used to surface-modify the nanoparticles to stabilize them in acidic media. The treatment fluid can be pumped downhole as a single homogeneous fluid system in the same pumping stage. The nanoparticles are easily miscible with the acid formulation without any need for the batch-mixing processes that may be required for a polymer-based gelled-acid system to account for polymer hydration. Thus, this formulation can be mixed easily while pumping the acidic fluid downhole. This ensures that the new gelled-acid system can increase operational efficiency by reducing operational time substantially. Nanoparticle gelation takes place in situ in the acid fluid and does not require a separate pumping stage to introduce the activator. The gelation of nanoparticles is predominantly a pH-based phenomenon. The gelation rate can be influenced also by temperature. As the fluid’s temperature increases, the treatment fluid viscosifies, thus diverting the tail-end acid to less-permeable zones in the reservoir. As the acid spends after reacting with the carbonate formation and the pH of the system increases beyond a pH of 4, the nanoparticles lose their ability to further viscosify the acid, thus reducing the viscosity of the fluid system. This enables easy flowback of the fluid post-treatment. Because the viscosifying material used in the present invention is a nanoparticulate, it will be potentially nondamaging to the formation because of effective flowback and no residual deposition inside the formation.

Carbon Allotropes-Based Paints and Their Composite Coatings for Electromagnetic Shielding Applications.

The present manuscript reports on optimized formulations of alcohol-based conductive paints for electromagnetic interference shielding (EMI), which can ensure compatibility and reduce the visibility of electronic equipment, as a continuation of our previous work in this field, which examined water-based formulations for other applications. Graphite, carbon black, graphene, Fe3O4, Fe ore, and PEDOT:PSS in various ratios and combinations were employed in an alcohol base for developing homogeneous paint-like fluid mixtures that could be easily applied to surfaces with a paintbrush, leading to homogeneous, uniform, opaque layers, drying fast in the air at room temperature; these layers had a reasonably good electrical conductivity and, subsequently, an efficient EMI-shielding performance. Uniform, homogeneous and conductive layers with a thickness of over 1 mm without exfoliations and cracking were prepared with the developed paints, offering an attenuation of up to 50 dB of incoming GHz electromagnetic radiation. The structural and morphological characteristics of the paints, which were studied in detail, indicated that these are not simple physical mixtures of the ingredients but new composite materials. Finally, mechano-climatic and environmental tests on the coatings demonstrated their quality, since temperature, humidity and vibration stressors did not affect them; this result proves that these coatings are suitable for commercial products.

Global characterization of oscillating grid turbulence in homogeneous and two-layer fluids, and its implication for mixing at high Peclet number

For oscillating grid turbulence (OGT) in homogeneous fluids, the turbulence intensity decreases with the distance to the vibrating grid used to generate the forcing, and it is usually described in terms of depth profiles of turbulent quantities (kinematic energy, integral length scale, and eddy viscosity) . Here we propose revised parametric laws for these quantities in homogeneous fluid, and present new results for a two-layer fluid for which the turbulent quantities are strongly altered by the fluid interface. In the case of a two-layer fluid, we also investigate the mixing and discuss the role of turbulent flow properties at the interface as well as weak mean flow features.

Abiotic passive nitrogen and methane enrichment during exhumation of subducted rocks: Primary multiphase fluid inclusions in high‐pressure rocks from the Cabo Ortegal Complex, NW Spain

AbstractPrimary multiphase fluid inclusions (MFI) were studied in one eclogite and two granulites from the Cabo Ortegal Complex (COC, NW Spain) by means of Raman imaging, Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM‐EDS) and Focused Ion Beam ‐ Scanning Electron Microscopy (FIB)‐SEM. Complementary, secondary MFI in pyroxenites from COC were also investigated. MFI hosted in eclogite and granulites occur along growth zones or in 3D clusters in garnet porphyroblasts suggesting a primary origin at high‐pressure (HP) metamorphic conditions. The mineral assemblage of MFI is mainly composed of Fe‐Mg‐Ca‐carbonates and phyllosilicates ± graphite ± quartz ± corundum ± pyrite ± apatite ± rutile and a fluid phase composed of nitrogen ± methane ± carbon‐dioxide. The mineral proportions vary among the lithologies. Dominant carbonates and hydrous silicates are interpreted as step‐daughter minerals (crystals formed in the MFI after entrapment as a result of fluid–host interaction), whereas apatite, quartz and rutile are considered in part as accidentally trapped minerals since they also occur as crystal inclusions together with MFI in each rock type. Quartz and corundum occur together in MFI in ultramafic granulite and are regarded as step‐daughter minerals in this lithology. These observations suggest that the MFI are products of post‐entrapment reactions of a homogeneous COHN fluid system with the host mineral. Thermodynamic calculations in the CaFMAS‐COHN system confirmed that bulk composition of the MFI in eclogite is similar to the host garnet+COHN composition except for a potential lost of H2O. Carbonation and hydration reaction between the host (i.e. garnet or pyroxene) and the fluid inclusion results in the consumption of all CO2 and part of the H2O from the fluid phase producing Ca‐Fe‐Mg‐carbonates and hydrous step‐daughter minerals, mostly pyrophyllite and chlorite. Nitrogen content of the originally trapped COHN fluid in eclogite was estimated to have a maximum value of 10 mol% at peak HP conditions and 30–40 mol% at retrograde conditions that is within the range of the observed MFI in the residual fluid (13–68 mol%). Pseudosection modelling confirmed the stability of the phase assemblage in the MFI in a specific low‐pressure, low‐temperature stability field (between 300°C and 400°C at pressures < 1 GPa), caused by H2O‐ and CO2‐consuming reactions possibly in a single step. Our findings indicate that such processes in the exhuming HP units may play a role in global nitrogen and carbon cycling as well as potentially contributing to nitrogen and methane supply to subsurface–surface environments during devolatilization in the forearc regions of convergent plate margins.

Modelling of low-speed magnetic gear with viscose ferrofluid

PurposeIn this paper, a computational model of a coaxial magnetic gear (MG) design with viscose ferrofluid between rotors is proposed. Viscose ferrofluid is used to decrease the magnetic reluctance and therefore creates higher magnetic torque. However, viscose friction of ferrofluid is undesirable and must be minimised in this particular application. MG is supposed to operate under low rotational speeds, where the dynamic viscose friction is very low, and the effects of the viscose ferrofluid over the MG’s efficiency must be estimated. The paper aims to analyze the performance of MG with viscose ferrofluid and to estimate the MG efficiency by computational model using finite element method (FEM).Design/methodology/approachAn MG design with viscose ferrofluid between the outer low-speed rotor and modulating steel segments was modelled as a coupled transient magnetic field problem and a kinematic model with viscous friction coefficients derived from a previously computed fluid dynamics model.FindingsThe proposed computational implementation is suitable for homogeneous magnetic fluid modelling in electromagnetic actuators and rotational machines. The results regarding power and torque transmission of MG were obtained by coupled finite element modelling. The efficiency of MG significantly decreased due to ferrofluid friction.Originality/valueThe described MG design with viscose ferrofluid is a novel device with new operational characteristics, and new results for the effects of viscose ferrofluid friction in the outer magnetic field over the MG efficiency are estimated.

Исследования процессов выделения газов из жидких сред в судовых сепарационных установках и аппаратах

Object and purpose of research. This paper discusses plants and units for splitting homogeneous (multi-phase) fluids into homogenous phases for shipbuilding and other industrial applications. The purpose of this work is to determine efficiency of hardware and solutions of various versions through simulation of separation processes for aerated 3D flows by means of configurable dummies at the experimental rig. Materials and methods. Official scientific and technical publications about analytical and experimental studies on the processes taking place in separation plants and units. Methodology of fluid and gas mechanics, dimension theory methods, experimental methods. Main results. This paper discusses the state of the art in development and operation of de-aeration plants and units in shipbuilding and related industries, with classification of main physical principles of fluid degassing. Experimental studies were performed at hydraulic test rig with unified versions of reconfigurable dummy for a variety of typical solutions currently applied at marine and industrial separation plants and units for controllable splitting of multi-phase flows into separate phases. Experimental assessment has found structural imperfections demonstrating the low technical level of investigated objects. It also highlighted behavioral patterns of highly saturated multi-phase flows with physical parameters established as per the practice of operating the equipment as part of systems, i.e. in different conditions and different configurations of closed-loop circuits. The study yielded new knowledge about the interaction of multi-phase flows with structural parts of a number of separation units. Finally, the study highlighted current obstacles for the optimization of separation processes, as well as suggested promising ways to high-end designs of separation plants and units. Conclusion. The findings of this work enable an objective decision-making about the application of given separation unit type in given service conditions as part of various marine or industrial systems. Technical solutions suggested in it will be helpful insights for development of more advanced and competitive separation units that would replace the imported products. The test data obtained in this work could also be helpful for further development of design requirements to marine ballast systems with high-capacity pumps.

Roughness Volumes: An Improved RoughMob Concept for Predicting the Increase of Molecular Mobility upon Coarse-Graining.

The reduced number of degrees of freedom in a coarse-grained molecular model compared to its parent atomistic model not only makes it possible to simulate larger systems for longer time scales but also results in an artificial mobility increase. The RoughMob method [Meinel, M. K. and Müller-Plathe, F. J. Chem. Theory Comput. 2020, 16, 1411.] linked the acceleration factor of the dynamics to the loss of geometric information upon coarse-graining. Our hypothesis is that coarse-graining a multiatom molecule or group into a single spherical bead smooths the molecular surface and, thus, leads to reduced intermolecular friction. A key parameter is the molecular roughness difference, which is calculated via a numerical comparison of the molecular surfaces of both the atomistic and coarse-grained models. Augmenting the RoughMob method, we add the concept of the region where the roughness acts. This information is contained in four so-called roughness volumes. For 17 systems of homogeneous hydrocarbon fluids, simple one-bead coarse-grained models are derived by the structure-based iterative Boltzmann inversion. They include 13 different homogeneous aliphatic and aromatic molecules and two different mapping schemes. We present a simple way to correlate the roughness volumes to the acceleration factor. The resulting relation is able to a priori predict the acceleration factors for an extended size and shape range of hydrocarbon molecules, with different mapping schemes and different densities.

An incidental finding behind adrenal incidentaloma.

SummaryA 61-year-old man went to the Emergency Department with left upper abdominal quadrant pain and low-grade fever, as well as a loss of weight (3 kg in 6 weeks). A solid-cystic lesion in the left adrenal lodge was discovered by abdominal ultrasonography. A slight increase in the serum amylase with normal lipase was observed, but there were no signs or symptoms of pancreatitis. A contrast-enhanced CT revealed a tumor that was suspected of adrenocortical cancer. Therefore, he was referred to the endocrine unit. The hormonal evaluation revealed no signs of excessive or inadequate adrenal secretion. To characterize the mass, an MRI was performed; the lesion showed an inhomogeneous fluid collection with peripheral wall contrast-enhancement, as well as a minor 18-fluorodeoxyglucose uptake at PET/CT images. The risk of primary adrenal cancer was minimal after the multidisciplinary discussion. An acute necrotic collection after focal pancreatitis was suspected, according to the characteristics of imaging. Both CT-guided drainage of the necrotic accumulation and laboratory analysis of the aspirated fluid confirmed the diagnosis.Learning pointsDifferent types of expansive processes can mimic adrenal incidentalomas.Necrotic collection after acute focal pancreatitis could be misdiagnosed as an adrenal mass, since its CT characteristics could be equivocal.MRI has stronger capacities than CT in differentiating complex lesions of the adrenal lodge.A multidisciplinary approach is fundamental in the management of patients with a newly discovered adrenal incidentaloma and equivocal/suspicious imaging features (low lipid content and size >4 cm).

Heat transfer and flow patterns in a minichannel with various acoustic standing wave configurations and thermal boundary conditions

In this work, we investigate the effects of acoustic standing wave configurations and thermal boundary conditions on heat transfer and flow patterns in the minichannel cavity subjected to acoustic standing wave fields. Upon differential heating, the fluid properties such as density, speed of sound, and acoustic impedance become inhomogeneous. When this heated inhomogeneous fluid is subjected to acoustic fields, the resulting acoustic body force which is proportional to impedance gradient induces fluid convection and determines the heat transfer. We observed that the heat transfer and fluid motion vary significantly with respect to thermal boundary conditions, wavenumber (quarter, half, and full-wave), and direction of the standing wave; this can be attributed to the fact that the acoustic body force is strongly dependent on the position of inhomogeneity. We have studied 18 different combinations of wave configurations and thermal boundary conditions to understand their effects on heat transfer and flow patterns. It is observed that certain combinations favor heat transfer, whereas few others don't. The results of all the cases are explained clearly and compared with natural convection to understand the effectiveness of the heat transfer process due to the acoustic field. For both ethanol and water, maximum heat transfer is achieved when the acoustic standing full wave is applied perpendicular to the hot bottom plate and cold top plate, we obtained the maximum heat transfer increase of 3.18 times in ethanol and 2.49 times in water when compared to the natural convection. For ethanol, heat transfer is reduced to 0.21 times of natural convection, when the quarter-wave is applied parallel to the hot bottom plate and top cold plate such that node is at top plate and antinode is at the bottom plate. For water, heat transfer is reduced to 0.51 times of natural convection, when half-wave is applied parallel to the hot bottom plate and cold top plate.

Magnetohydrodynamic blood flow study in stenotic coronary artery using lattice Boltzmann method

Background and objective: Cardiovascular diseases such as atherosclerosis are the first engender of death in the world. The malfunctioning of cardiovascular system is attributed mainly to hemodynamics. However, blood magnetic properties are of major haemodynamic interest, with significant clinical applications. The aim of this work is to study numerically the effect of high magnetic field on blood flow in stenotic artery.Methods: In this paper, a double population D2Q9 lattice Boltzmann model is proposed. Velocity and magnetic field are both solved using Lattice Boltzmann method with single relaxation time. Blood is considered homogeneous and Newtonian bio-magnetic fluid. The results of the proposed model are compared and validated by recent numerical and experimental studies in the literature and show good agreement. In this study, simulations are carried out for both hydrodynamics and magneto-hydrodynamics. For the magneto-hydrodynamic case, five values of Hartmann number of 10, 30, 50, 75 and 100 at Reynolds number of 400, 600 and 800 are investigatedResults: The results show that velocity and recirculation zone increase with the increase of the degree of stenosis and Reynolds number. In addition, a considerable decrease in velocity, recirculation zones and pressure drop across the stenotic artery is noticed with the increase of Hartmann number.Conclusion: The suggested model is found to be effective and accurate in the treatment of magneto-hydrodynamic blood flow in stenotic artery. The found results can be used by clinicians in the treatment of certain cardiovascular disorders and in regulating blood flow movement, especially during surgical procedures.

Modified Poisson–Boltzmann equations and macroscopic forces in inhomogeneous ionic fluids

We propose a field-theoretical approach based on the thermodynamic perturbation theory and within it derive a grand thermodynamic potential of the inhomogeneous ionic fluid as a functional of electrostatic potential for an arbitrary reference fluid system. We obtain a modified Poisson–Boltzmann (PB) equation as the Euler–Lagrange equation for the obtained functional. Applying Noether’s theorem to this functional, we derive a general mean-field expression for the stress tensor consistent with the respective modified PB equation. We derive a general expression for the macroscopic force acting on the dielectric or conductive body immersed in an ionic fluid. In particular, we derive a general mean-field expression for the disjoining pressure of an ionic fluid in a slit pore. We apply the developed formalism to describe three ionic fluid models of practical importance: nonpolarizable models (including the well-known PB and Poisson–Fermi equations), polarizable models (ions carry nonzero permanent dipole or static polarizability), and models of ion-dipole mixtures (including the well-known PB–Langevin equation). For these models, we obtain modified PB equations and respective stress tensors, which could be valuable for different applications, where it is necessary to estimate the macroscopic forces acting on the dielectric or conductive bodies (electrodes, colloids, membranes, etc) together with the local electrostatic potential (field) and ionic concentrations.

Theory of nonlinear acoustic forces acting on inhomogeneous fluids

Recently, the phenomena of streaming suppression and relocation of inhomogeneous miscible fluids under acoustic fields were explained using the hypothesis on mean Eulerian pressure. In this work, we derive the expression for the acoustic body force without relying on any prior assumptions regarding the second-order Eulerian pressure. We present a theory of nonlinear acoustics for inhomogeneous fluids from first principles, which explains streaming suppression and acoustic relocation in both miscible and immiscible inhomogeneous fluids inside a microchannel. This theory predicts the relocation of higher impedance fluids to pressure nodes of the standing wave, which agrees with recent experiments.

Separation of monodisperse poly(3-hydroxybutyrate) particles by fractionation: Theory and practice

A new method is proposed in this article which is based on fractionation and results poly(3-hydroxybutyrate) particles of nearly monodisperse size distribution. This kind of separation is achieved by taking advantage of the phenomenon that the movement of particles triggered by a constant force in a homogeneous fluid have a velocity depending on the diameter of the particle. The procedure consists of two steps. First, a set of particles with a wide distribution of diameters is produced by using the emulsion-suspension method followed by their separation into fractions on hydrogel columns in the second step. The novel concept of statistical filters has been introduced in order to describe this phenomenon quantitatively. Additionally, mathematical models have been developed that allow the simulation and prediction of the outcome of particle separation. Our method was verified by model calculations and measurements; the results of the two approaches correlated closely. The proposed method is very advantageous for the preparation of drug carrier matrices, because it allows the close control and modeling of the kinetics of drug release.

Visible-light-driven TiO2@N-Au nanorobot penetrating the vitreous

For ophthalmology, there remain many uncertainties and challenges for traditional passive diffusion-based drug intervention. One of the major hurdles is the limited penetration caused by the complex vitreous bodies and biological macromolecules within. Here, we demonstrate for the first time that a novel TiO2@N-Au nanowire (NW) motor/locomotive robot actuated by wireless natural visible light can autonomously and efficiently penetrate into the vitreous body via photoelectrophoresis mechanism. With the efficient propulsion, and the nanoscale size of the NW motor matching the voids of the vitreous network, noninvasive advancing deep into the vitreous body and overcoming the inhomogeneous non-Newtonian fluid (shear thinning and viscoelastic) barriers are allowed. We envision the active visible-light-powered TiO2@N-Au NW motor holds immense application prospects for deep eye diseases and wireless bioelectronics.

Zun-Kholba Orogenic Gold Deposit, Eastern Sayan, Russia: Geology and Genesis

In this paper, we present a new point of view on the deposit geology and genesis of the largest gold deposit in Eastern Sayan, Zun-Kholba. Quartz–sulfide replacement ores and shallow quartz veins are of great economic importance. At the deposit, quartz–pyrite ore bodies are dominant, whereas paragenetically late base metal-bearing quartz veins occur only at shallow levels. The study of the fluid inclusions, stable isotopes (C–O–S), and mineral geothermometry allowed us to determine the P–T conditions of ore deposition. It is established that the temperature of ore formation changed from 380 to 433 °C at the deepest levels of the deposit to 316 °C at the shallowest levels. The pressure estimates for gold deposition at 570–950 bar were calculated for the 1490-m level in the center of the deposit. The determined P–T conditions can help estimate the average depth of deposit formation at about 3.6 km. Ore mineral assemblages were formed from homogeneous fluids of low to moderate salinity (2.4–7.9 wt.% eq. NaCl). The sulfur isotope composition of sulfide minerals (δ34S = 0–4.6‰), as well as pyrite geochemistry, corresponds to that of older volcanogenic massive sulfide (VMS) occurrences, which are widespread within the Eastern Sayan ophiolitic belts. Lens-like fragments of metamorphosed VMS-type sulfide ores are also present in the Zun-Kholba deposit. The oxygen isotope data indicate a metamorphic origin for the ore-forming fluids. Migrating metamorphic fluids may have become enriched in gold, sulfur, and other metals during the flow through the complex ore-hosting lithologies, including ophiolitic bodies with sulfide-rich VMS fragments that are characterized by a relatively high content of gold and related ore elements. The obtained data allow us to suggest a metamorphic devolatilization model for the genesis of the Zun-Kholba gold deposit.

Numerical Simulation of Tailings Flow from Dam Failure over Complex Terrain.

A tailings dam failure can lead to disastrous impacts on people’s livelihood and the surrounding ecological environment. Due to interactions among water, tailings and ground, the mechanism of a tailings flow is more complicated than that of a flood flow. In this paper, the tailings flow is regarded as a homogeneous and incompressible non-Newtonian fluid. Its rheological properties were studied through rheological tests conforming to the Bingham model. The rheological parameters were further used in a Computational Fluid Dynamics (CFD) simulation over complex terrain to explore the tailings flow characteristics. The method was validated with experimental results of a non-Newtonian dam-break flow from literature. The flow characteristics, including flow velocity, runout distance, inundation area and depth, were analyzed in the case of the Dagangding tailings dam. The results showed that the downstream railway and village would not be affected in a conservative scenario. Finally, the effects of two measures for preventing tailings flow hazards were discussed. Setting the check dam and planting grasses and trees can effectively mitigate the damage of tailings flow.

Retrieval of the piecewise‐constant mass density in the Bergman wave equation

This investigation is concerned with the 2D acoustic scattering problem of a plane wave propagating in a non‐lossy, isotropic, homogeneous fluid host and soliciting a linear, isotropic, macroscopically homogeneous, generally lossy, flat‐plane layer in which the mass density and wavespeed are different from those of the host. The focus is on the inverse problem of the retrieval of the layer mass density. The data are the transmitted pressure field, obtained by simulation (resolution of the forward problem) in exact, explicit form via the domain integral form of the Bergman wave equation. This solution is exact and more explicit in terms of the mass‐density contrast (between the host and layer) than the classical solution obtained by separation of variables. A perturbation technique enables the solution (in its form obtained by the domain integral method) to be cast as a series of powers of the mass density contrast, the first three terms of which are employed as the trial models in the treatment of the inverse problem. The aptitude of these models to retrieve the mass density contrast is demonstrated both theoretically and numerically.

Analytical and experimental investigation of flexural waves in horizontal pipes conveying two-phase periodic intermittent flow

Two-phase flow in pipes can generate different geometric distribution of phases depending on the flow conditions, called flow patterns. The identification of such flow patterns is fundamental for designing operational conditions of complex oil and gas industrial plants for production and transport of such fluids by pipes. Amongst them, the intermittent flow is the most relevant for industrial applications as it can lead to increased vibration levels with catastrophic failures, and also to several flow assurance problems. In this flow condition, an elongated gas bubble travels along the pipe followed by a liquid slug with or without dispersed bubbles. The two-phase flow induced vibration research have been mostly focused on the modal approaches, which can be very sensitive to boundary and operational conditions thus limiting its practical applicability in field conditions. On the other hand, wave-based approaches can overcome this limitation since they are based on local properties. In this paper, bending wave propagation in horizontal ducts conveying intermittent flow is investigated. A periodic unit cell model is assumed to describe the intermittent flow and the mass density along the duct is thus given by a Fourier series, representing space and time fluctuations. Subsequently, the wave dispersion characteristics can be analytically calculated for a duct in bending conveying intermittent flow, assuming small mixture velocity when compared to the bending waves. The periodic flow creates a periodic dispersion diagram which is distorted by the flow velocity. This effect accounts for the asymmetry in the wave propagating along and against the flow direction. The wave dispersion curves are experimentally estimated for typical intermittent flow conditions and it is shown that they can be approximated by equivalent homogeneous fluid. In addition, this curve is sensitive to the gas fraction of the two-phase fluid. The presented approach introduces a new perspective on two-phase flow induced vibrations of pipes and opens the way for better understanding the effect of the periodic two-phase flow in the dynamic behaviour of pipes.

Two-dimensional stability analysis of finite-amplitude interfacial gravity waves in a two-layer fluid

We explore basic mechanisms for the instability of finite-amplitude interfacial gravity waves through a two-dimensional linear stability analysis of the periodic and irrotational plane motion of the interface between two unbounded homogeneous fluids of different density in the absence of background currents. The flow domains are conformally mapped into two half-planes, where the time-varying interface is always mapped onto the real axis. This unsteady conformal mapping technique with a suitable representation of the interface reduces the linear stability problem to a generalized eigenvalue problem, and allows us to accurately compute the growth rates of unstable disturbances superimposed on steady waves for a wide range of parameters. Numerical results show that the wave-induced Kelvin–Helmholtz (KH) instability due to the tangential velocity jump across the interface produced by the steady waves is the major instability mechanism. Any disturbances whose dominant wavenumbers are greater than a critical value grow exponentially. This critical wavenumber that depends on the steady wave steepness and the density ratio can be approximated by a local KH stability analysis, where the spatial variation of the wave-induced currents is neglected. It is shown, however, that the growth rates need to be found numerically with care and the successive collisions of eigenvalues result in the wave-induced KH instability. In addition, the present study extends the previous results for the small-wavenumber instability, such as modulational instability, of relatively small-amplitude steady waves to finite-amplitude ones.

A scientific report of singular kernel on the rate-type fluid subject to the mixed convection flow

The response of inhomogeneous fluids whose material properties are strongly interconnected with mean normal stress and shear rate; such phenomenon undergo to rate constitutive-type theories within thermodynamical aspects. In this context, the thermodynamic approach for modeling a class of viscoelastic fluids so-called Oldroyd-B fluid is investigated through a singular kernel. This is because role of the singular kernel has become imperative due to the wide applications of rate-type fluid subject to the mixed convection flow. To have the systematical and molecular dynamics of Oldroyd-B fluid, the temperature distribution, velocity profile, and Nusselt numbers have been explored by invoking the Laplace transform on the governing equations. Owing to the strengthening of physical parameters, the enhancement of convective heat transfer is emphasized based on relaxation as well as retardation phenomenon. Additionally, the evaluation of thermal and flow characteristics of Oldroyd-B fluid has resulted in discovering more evolutionary mechanisms of the considered problem of rate-type fluid subject to the mixed convection flow.