Multiphase Medium Research Articles

Numerical Study of the Influence of Boundary Conditions on Calculations of the Dynamics of Polydisperse Gas Suspension

The work numerically simulates the flow of a polydisperse gas suspension in a channel. The carrier medium was described as a viscous, compressible, heat-conducting gas. The mathematical model implemented a continuum technique for the dynamics of multiphase media, taking into account the interaction of the carrier medium and the dispersed phase. For each component of the mixture, a complete hydrodynamic system of equations of motion for the carrier phase and dispersed phase fractions was solved. The dispersed phase consisted of particles with different sizes of dispersed inclusions. For the carrier medium, homogeneous Dirichlet boundary conditions were specified on the side surfaces of the channel. For fractions of the dispersed phase, boundary conditions for slippage. The influence of the boundary conditions of the flow of the carrier medium on the dynamics of gas suspension fractions has been revealed.

It’s a Breeze: The Circumgalactic Medium of a Dwarf Galaxy Is Easy to Strip

The circumgalactic medium (CGM) of star-forming dwarf galaxies plays a key role in regulating the galactic baryonic cycle. We investigate how susceptible the CGM of dwarf satellite galaxies is to ram pressure stripping in Milky Way–like environments. In a suite of hydrodynamical wind tunnel simulations, we model an intermediate-mass dwarf satellite galaxy (M * = 107.2 M ⊙) with a multiphase interstellar medium (ISM; M ISM = 107.9 M ⊙) and CGM (M CGM,vir = 108.5 M ⊙) along two first-infall orbits to more than 500 Myr past pericenter of a Milky Way–like host. The spatial resolution is ∼79 pc in the star-forming ISM and 316−632 pc in the CGM. Our simulations show that the dwarf satellite CGM removal is fast and effective: more than 95% of the CGM mass is ram pressure stripped within a few hundred megayears, even under a weak ram pressure orbit where the ISM stripping is negligible. The conditions for CGM survival are consistent with the analytical halo gas stripping predictions in McCarthy et al. We also find that including the satellite CGM does not effectively shield its galaxy, and therefore the ISM stripping rate is unaffected. Our results imply that a dwarf galaxy CGM is unlikely to be detected in satellite galaxies; and that the star formation of gaseous dwarf satellites is likely devoid of replenishment from a CGM.

The generation of a multiphase medium in ‘Splash’ bridge systems: towards an understanding of star formation suppression in turbulent galaxy systems

ABSTRACT Cloud–cloud collisions in splash bridges produced in gas-rich disc galaxy collisions offer a brief but interesting environment to study the effects of shocks and turbulence on star formation rates in the diffuse intergalactic medium, far from the significant feedback effects of massive star formation and active galactic nucleus. Expanding on our earlier work, we describe simulated collisions between counter-rotating disc galaxies of relatively similar mass, focusing on the thermal and kinematic effects of relative inclination and disc offset at the closest approach. This includes essential heating and cooling signatures, which go some way towards explaining the luminous power in H$_2$ and [C ii] emission in the Taffy bridge, as well as providing a partial explanation of the turbulent nature of the recently observed compact CO-emitting clouds observed in Taffy by the Atacama Large Millimeter Array (ALMA). The models show counter-rotating disc collisions result in swirling, shearing kinematics for the gas in much of the post-collision bridge. Gas with little specific angular momentum due to collisions between counter-rotating streams accumulates near the centre of mass. The disturbances and mixing in the bridge drive continuing cloud collisions, differential shock heating, and cooling throughout. A wide range of relative gas phases and line-of-sight velocity distributions are found in the bridges, depending sensitively on initial disc orientations, and the resulting variety of cloud collision histories. Most cloud collisions can occur promptly or persist for quite a long duration. Cold and hot phases can largely overlap throughout the bridge or can be separated into different parts of the bridge.

Signatures of gas flows – II. Connecting the kinematics of the multiphase circumgalactic medium to galaxy rotation

ABSTRACT The multiphase circumgalactic medium (CGM) hosts critical processes that affect galaxy evolution such as accretion and outflows. We searched for evidence of these phenomena by using the EW co-rotation fraction ($f_{\rm EWcorot}$) to study the kinematic connection between the multiphase CGM and host galaxy rotation. We examined CGM absorption from Hubble Space Telescope /Cosmic Origins Spectrograph (including, but not limited to, Si ii, C ii, Si iii, C iii, and O vi) within $21\le D\le ~276$ kpc of 27 galaxies. We find the median $f_{\rm EWcorot}$ for all ions is consistent within errors and the $f_{\rm EWcorot}$ increases with increasing N$({{{\rm H} \rm{\small I}}})$. The $f_{\rm EWcorot}$ of lower ionization gas decreases with increasing $D/R_{\rm vir}$, while O vi and H i are consistent with being flat. The $f_{\rm EWcorot}$ varies minimally as a function of azimuthal angle and is similar for all ions at a fixed azimuthal angle. The larger number of O vi detections enabled us to investigate where the majority of co-rotating gas is found. Highly co-rotating O vi primarily resides along the galaxies’ major axis. Looking at the $f_{\rm EWcorot}$ as a function of ionization potential (${{\rm d}{({f_{\rm EWcorot}})}}/{{\rm d}{(\rm eV)}}$), we find a stronger co-rotation signature for lower ionization gas. There are suggestions of a connection between the CGM metallicity and major axis co-rotation where low-ionization gas with higher $f_{\rm EWcorot}$ exhibits lower metallicity and may trace large-scale filamentary inflows. Higher ionization gas with higher $f_{\rm EWcorot}$ exhibits higher metallicity and may instead trace co-planar recycled gas accretion. Our results stress the importance of comparing absorption originating from a range of ionization phases to differentiate between various gas flow scenarios.

CloudFlex: A Flexible Parametric Model for the Small-scale Structure of the Circumgalactic Medium

We present CloudFlex, an open-source tool for predicting absorption-line signatures of cool gas in galaxy halos with small-scale structure. Motivated by analyses of ∼104 K material in hydrodynamical simulations of turbulent, multiphase media, we model cool gas structures as complexes of cloudlets sampled from a power-law distribution of mass ∝mcl−α with velocities drawn from a turbulent velocity field. The user may specify α, the lower limit of the cloudlet mass distribution ( mcl,min ), and several other parameters that set the mass, size, and velocity distribution of the complex. This permits investigation of the relation between these parameters and absorption-line observables. As a proof-of-concept, we calculate the Mg ii λ2796 absorption induced by the cloudlets in background quasi-stellar object (QSO) spectra. We demonstrate that, at fixed metallicity, the covering fraction of sight lines with equivalent widths W 2796 < 0.3 Å increases significantly with decreasing mcl,min , cloudlet number density (n cl), and complex size. We then use this framework to predict the halo-scale W 2796 distribution around ∼L * galaxies. We show that the observed incidences of W 2796 > 0.3 Å sight lines with impact parameters 10 kpc < R ⊥ < 50 kpc in projected QSO–galaxy studies are consistent with our model over much of parameter space. However, they are underpredicted by models with mcl,min≥100M⊙ and n cl ≥ 0.03 cm−3, in keeping with a picture in which the inner cool circumgalactic medium (CGM) is dominated by numerous low-mass cloudlets (m cl ≲ 100M ⊙) with a volume filling factor ≲1%. When used to model absorption-line data sets built from multi-sight line and/or spatially extended background probes, CloudFlex enables detailed constraints on the size and velocity distributions of structures comprising the photoionized CGM.

Objects May Be Closer than They Appear: Significant Host Galaxy Dispersion Measures of Fast Radio Bursts in Zoom-in Simulations

We investigate the contribution of host galaxies to the overall dispersion measures (DMs) for fast radio bursts (FRBs) using the Feedback in Realistic Environments (FIRE-2) cosmological zoom-in simulation suite. We calculate DMs from every star particle in the simulated L* galaxies by ray-tracing through their multiphase interstellar medium, summing the line-of-sight free thermal electron column for all gas elements within ±20 kpc of the galactic midplane. At z = 0, we find average (median) host-galaxy DMs of 74 (43) and 210 (94) pc cm−3 for older (≳10 Myr) and younger (≲10 Myr) stellar populations, respectively. Inclination raises the median DM measured for older populations (≳10 Myr) in the simulations by a factor of ∼2 but generally does not affect the younger stars deeply embedded in H ii regions except in extreme edge-on cases (inclination ≳85°). In kinematically disturbed snapshots (z = 1 in FIRE), the average (median) host-galaxy DMs are higher: 80 (107) and 266 (795) pc cm−3 for older (≳10 Myr) and younger (≲10 Myr) stellar populations, respectively. FIRE galaxies tend to have higher DM values than cosmological simulations such as IllustrisTNG, with larger tails in their distributions to high DMs. As a result, FRB host galaxies may be closer (lower redshift) than previously inferred. Furthermore, constraining host-galaxy DM distributions may help significantly constrain FRB progenitor models.

Numerical analysis on crystallization inside porous sandstone induced by salt phase change

The behavior of water and salt inside porous sandstone is crucial for determining the durability of stone heritage. This involves multiphase coupled processes, yet previous analyses have paid insufficient attention to the spatial and temporal characterization of solution-crystal phase change. Based on the salt crystallization experiments, theoretical models and numerical computational frameworks are synthesized to simulate multiphase processes. Subsequently, equations are established for coupled water-salt-heat-mechanical interactions in the multiphase media. Then, the critical state of solution-crystal phase change is analyzed through the evolution of saturation, crystallization pressure, and porosity. The findings indicate rapid solution saturation growth at positions with minimal wetting front fluctuations, leading to initial crystallization. Further tracing reveals that crystallization evolves through discrete crystallization, annular crystallization, and crystallization expansion stages. By investigating the crystallization pressure and the crystal morphology, it is possible to quantify the dynamics of crystal pressure on constraint surfaces and solution pressure. In addition, the change in porosity can be observed by simulation of dry and wet cycles to obtain crystallization initiation. The numerical calculations agree well with the experimental results, providing valuable insights into the deterioration mechanism induced by salt crystallization in the porous sandstone of Dazu Rock Carvings.

Inversion of gas hydrate saturation and solid frame permeability in a gas hydrate-bearing sediment by Stoneley wave attenuation

Natural gas hydrate is a potential novel energy resource that is widely distributed globally. Acoustic logging can effectively provide information on the surrounding reservoir and plays an important guiding role in gas hydrate exploration and development. Natural gas hydrate-bearing sediments are composed of a solid frame with natural gas hydrates and water-filled pores. The borehole mode wave characteristics of two-phase porous media cannot be used to evaluate the parameters of such a multiphase porous medium. We explore factors that influence the monopole Stoneley wave in a borehole embedded in a multiphase porous medium containing two solids and one fluid and analyze the influence of each factor on monopole Stoneley wave attenuation systematically. The sensitivity analysis results indicate that the Stoneley wave attenuation is highly sensitive to solid frame permeability and gas hydrate saturation. Building upon this foundation, a method to invert for gas hydrate saturation and solid frame permeability is first developed using Stoneley wave attenuation. Synthetic logging data are used to demonstrate the feasibility of this method for inverting for gas hydrate-bearing sediment properties. Even in the presence of considerable noise added to the receiver signal arrays, the inversion method is stable, and reliably evaluates gas hydrate saturation and solid frame permeability.

Antiscaling Pickering Emulsions Enabled by Amphiphilic Hairy Cellulose Nanocrystals.

Nucleation and growth of sparingly soluble salts, referred to as scaling, has posed substantial challenges in industrial processes that deal with multiphase flows, including enhanced oil recovery (EOR). During crude oil extraction/recovery, seawater is injected into oil reservoirs and yields water-in-oil (W/O) emulsions that may undergo calcium carbonate (CaCO3) scaling. Common antiscaling macromolecules and nanoparticles have adverse environmental impacts and/or are limited to functioning only in single-phase aqueous media. Here, we develop a novel antiscaling cellulose-based nanoparticle that enables scale-resistant Pickering emulsions. Cellulose fibrils are rationally nanoengineered to yield amphiphilic hairy cellulose nanocrystals (AmHCNC), bearing hydrophilic dicarboxylate groups and hydrophobic alkyl chains on disordered cellulose chains (hairs) protruding from nanocrystal ends. The unique chemical and structural properties of AmHCNC render them the first dual functional antiscaling and emulsion stabilizing nanoparticle. AmHCNC stabilize W/O Pickering emulsions at a concentration of 1.00 wt % for 1 week while inhibiting CaCO3 scale formation up to 70% by mass at a supersaturation degree of ∼101 compared with the synthetic surfactant Span 80. To the best of our knowledge, this study presents the first biopolymer-based solution for the long-lasting scaling challenge in multiphase media, which may set the stage for developing sustainable scale-resistant multiphase flows in a broad spectrum of industrial sectors.

Simulation of melting characteristics of thermal washing of the wax layer in the pipeline based on lattice Boltzmann method

ABSTRACT The escalation of transportation costs and the obstruction of pipelines due to wax deposition significantly impact the secure and efficient production of oil fields. The thermal washing method, characterized by its simplicity and cost-effectiveness, is widely employed for dewaxing crude oil gathering pipelines. The investigation of the melting mechanism of the wax layer during thermal washing is extremely important. In this paper, the two-zone composite model of multiphase flow-porous medium in the mushy zone is introduced into the solid-liquid phase change lattice Boltzmann model based on the enthalpy method, and the problem of circumferential inhomogeneity in the melting of the wax layer and the important influence of flow and heat transfer in the mushy zone on the thermal washing are systematically investigated. The demarcation point (γ tr) between the high and low liquid fraction zones is measured to be 0.81 by microscopic experiment. The impacts of varying γ tr and Ste numbers on wax melting at different circumferential locations are analyzed in detail. The results show that the melting efficiency of wax exhibits a nonlinear enhancement from − 90° to 90°. The melting efficiency of wax decreases with increasing γ tr for wax layers between 90° and − 45°. The melting efficiency of wax increases with higher Ste numbers at all angles. The Ste number increases from 0.42 to 5.0, and the melting efficiency of the wax layer at angles ranging from 90° to − 90° increases by factors of 2.16, 2.16, 2.20, 2.61, and 3.33 respectively. The growth of the Ste number improves the warming rate and shortens the generation time of convection at the center point of the wax layer. The research findings serve as a fundamental reference for formulating a rational and efficient thermal washing scheme.

Research Progress of Advanced Design Method, Numerical Simulation, and Experimental Technology of Pumps in Deep-Sea Resource Exploitation

Amid the escalating global demand for raw materials, the gradual exhaustion of terrestrial mineral resources, and the rise in extraction costs and energy consumption, the development of deep-sea mineral resources has become a focal point of international interest. The pipeline lifting mining system, distinguished by its superior mining efficiency and minimized environmental impact, now accounts for over 50% of the total energy consumption in mining operations. Serving as the “heart” of this system, the deep-sea lifting pump’s comprehensive performance (high pressure tolerance, non-clogging features, elevated lift capacity, wear resistance, corrosion resistance, and high reliability, etc.), is critical to transport efficiency, operational stability, and lifespan of the mining system. As a mixed transport pump for solid and liquid media under extreme conditions, its internal flow structure is exceedingly complex, incorporating gas–liquid–solid multiphase flow. A precise understanding of its internal flow mechanisms is essential for breaking through the design limitations of deep-sea lifting pumps and enhancing their operational stability and reliability under various working conditions and multiphase media, thereby providing technical support for advancing global marine resource development and offshore equipment upgrades. This paper comprehensively reviews the design theory, optimization methods, numerical simulations, and experimental studies of deep-sea lifting pumps. It discusses the application of various design optimization techniques in hydraulic lifting pumps, details the multiphase flow numerical algorithms commonly used in deep-sea lifting pumps along with their modified models, and summarizes some experimental methodologies in this field. Lastly, it outlines the forthcoming challenges in deep-sea lifting pump research and proposes potential directions to promote the commercial development of deep-sea mining, thereby offering theoretical and engineering support for the development of deep-sea mining slurry pumps.

The ALMA-QUARKS Survey. II. The ACA 1.3 mm Continuum Source Catalog and the Assembly of Dense Gas in Massive Star-Forming Clumps

Leveraging the high resolution, sensitivity, and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array (ALMA), the QUARKS survey, standing for “Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures”, is observing 139 massive star-forming clumps at ALMA Band 6 (λ ∼ 1.3 mm). This paper introduces the Atacama Compact Array (ACA) 7 m data of the QUARKS survey, describing the ACA observations and data reduction. Combining multi-wavelength data, we provide the first edition of QUARKS atlas, offering insights into the multiscale and multiphase interstellar medium in high-mass star formation. The ACA 1.3 mm catalog includes 207 continuum sources that are called ACA sources. Their gas kinetic temperatures are estimated using three formaldehyde transitions with a non-LTE radiation transfer model, and the mass and density are derived from a dust emission model. The ACA sources are massive (16–84 percentile values of 6–160 M ⊙), gravity-dominated (M ∝ R 1.1) fragments within massive clumps, with supersonic turbulence ( M>1 ) and embedded star-forming protoclusters. We find a linear correlation between the masses of the fragments and the massive clumps, with a ratio of 6% between the two. When considering fragments as representative of dense gas, the ratio indicates a dense gas fraction (DGF) of 6%, although with a wide scatter ranging from 1% to 10%. If we consider the QUARKS massive clumps to be what is observed at various scales, then the size-independent DGF indicates a self-similar fragmentation or collapsing mode in protocluster formation. With the ACA data over four orders of magnitude of luminosity-to-mass ratio (L/M), we find that the DGF increases significantly with L/M, which indicates clump evolutionary stage. We observed a limited fragmentation at the subclump scale, which can be explained by a dynamic global collapse process.

Assessment of different agricultural soil compaction levels using shallow seismic geophysical methods

A well-developed soil structure is crucial for a fertile soil and rules its influence on the ecosystem. Slight variations in the way soil components are organized and connected can greatly impact the soil mechanical and hydraulic characteristics. However, these features are challenging to measure at a scale that is relevant for agricultural management. In this study, we assess the capability of two seismic geophysical methods, i.e. Seismic Refraction Tomography and Multichannel Analysis of Surface Waves, to monitor the effects of compaction on agricultural bare soil. The purpose is to highlight the different mechanical response caused both by soil plastic deformation and soil water distribution due to increasing compaction. Results demonstrate that both geophysical techniques provide sufficient information to capture the effects of soil compaction and distinguish its significance, while traditional direct measurements, being punctual, lack sufficient spatial coverage. P-wave velocities carry a strong imprint of soil compaction, provided by seismic refraction, incorporating the information given by the multiphase medium in its entirety. On the other hand, S-wave velocity derived from Surface Waves discriminates the effect of solid matrix structure. This work, moreover, aims to pave the way for seismic methods to spatially characterize compaction at field scale, illustrating its potential and suggesting possible developments.

Fatigue Behavior of Medium Entropy Alloys AlCrFe&lt;sub&gt;2&lt;/sub&gt;Ni&lt;sub&gt;2&lt;/sub&gt; and AlCrFe&lt;sub&gt;2&lt;/sub&gt;Ni&lt;sub&gt;2&lt;/sub&gt;Mo&lt;sub&gt;0.1 &lt;/sub&gt;- A Comparison with Super Duplex Steel 1.4517

In the present study the notched fatigue behavior of two multi-phase medium entropy alloys (MEAs) AlCrFe2Ni2 and AlCrFe2Ni2Mo0.1 was characterized by three-point-bending (3-PB), along with a super-duplex steel 1.4517 as a reference material. An analytical approach for characterizing the fatigue notch factor (kf), based on grain size analysis in combination with finite element modelling (FEM) was used, relating the theory of critical distances (TCD) to the grain size of the material. To validate the approach, for the reference steel, the fatigue notch factor was also determined experimentally by comparing the fatigue behavior of notched and smooth specimens, resulting in an experimentally determined fatigue notch factor (kf) ~ 1.07. The numerically and analytically estimated notch effects increase with decreasing average grain size and vary between ~ 1.07 for the coarse-grained reference material – in very good agreement with the experimental results – and ~ 1.35 for the much more fine-grained AlCrFe2Ni2Mo0.1 medium entropy alloy. Note that these values are significantly lower than the stress concentration factor (kt) ~ 1.58, associated with the notch geometry. Fatigue endurance limits were measured at a fatigue stress ratio R ~ 0.1 (unidirectional stress), but were converted to fatigue amplitudes at R = -1 (σa, R-1, fully reversed stress), to be able to make due comparisons with available literature data, by using the elliptical relationship. The resulting fatigue endurance limit amplitudes for specimens surviving at least 2E+06 cycles for a minimum of three tested samples and including notch effects are σa, R-1 ~ 508 MPa for the AlCrFe2Ni2 alloy, σa, R-1 ~ 540 MPa for the AlCrFe2Ni2Mo0.1 alloy modification and σa, R-1 ~ 400 MPa for the reference super-duplex steel, putting the analyzed MEAs into a very competitive position compared to Cobalt containing multi-phase high or medium entropy alloys as well as commercially available steels.

Wave propagation across fluid-solid interfaces with LBM-LSM coupling schemes

Seismic wave propagation in fluid-solid coupled media is currently a popular topic. However, traditional wave equation-based simulation methods have to consider complex boundary conditions at the fluid-solid interface. To address this challenge, we propose a novel numerical scheme that integrates the lattice Boltzmann method (LBM) and lattice spring model (LSM). In this scheme, LBM simulates viscoacoustic wave propagation in the fluid area and LSM simulates elastic wave propagation in the solid area. We also introduce three different LBM-LSM coupling strategies, a standard bounce back scheme, a specular reflection scheme, and a hybrid scheme, to describe wave propagation across fluid-solid boundaries. To demonstrate the accuracy of these LBM-LSM coupling schemes, we simulate wave propagation in a two-layer model containing a fluid-solid interface. We place excitation sources in the fluid layer and the solid layer respectively, to observe the wave phenomena when seismic waves propagate to interface from different sides. The simulated results by LBM-LSM are compared with the reference wavefields obtained by the finite difference method (FDM) and the analytical solution (ANA). Our LBM-LSM coupling scheme was verified effective, as the relative errors between the LBM-LSM solutions and reference solutions were within an acceptable range, sometimes around 1.00%. The coupled LBM-LSM scheme is further used to model seismic wavefields across a more realistic rugged seabed, which reveals the potential applications of the coupled LBM-LSM scheme in marine seismic imaging techniques, such as reverse-time migration and full-waveform inversion. The method also has potential applications in simulating wave propagation in complex two- and multi-phase media.

Overview of the Current State of Physical-Mathematical Modelling of Solid Fuel Combustion Processes

This study provides a comprehensive introduction to the combustion of solid propellants. We conduct a thorough review of existing physical-mathematical models related to solid fuel combustion processes. Additionally, we explore the heat propagation within the solid phase, examine the physical chemical processes in the k–phase, and investigate the fundamental solution of the heat conduction equation in a multiphase (k–phase) medium. The heat conduction equation plays a crucial role in governing the temperature distribution within a given material, and a profound understanding of its fundamental solution is essential for various engineering and scientific applications. In this research, we expand our analysis to a multiphase scenario, considering different phases with distinct thermal properties coexisting.

Understanding the drying mechanism of straw substrate culture block: Physicochemical properties, pore structure, and drying optimization

As a new type of agricultural waste block substrate utilization, the initial wet base state of the substrate culture block needs to be dried. Therefore, studying the drying mechanism of substrate culture block is critical. In this study, the substrate culture block in a dry state was taken as the research object. Based on physical and chemical properties, the internal section of the substrate culture block was characterized by scanning electron microscopy and the pore condition of the particles was quantified. The results showed that the internal pore structure was uniform and favorable for plant root growth. Based on the pore structure, pore channel modeling was constructed to investigate the distribution of the internal multiphase medium and to distinguish between channels and pore-blind channels. The applicability of the modeling was verified and discussed. By measuring the drying rate of the substrate culture block and classifying its drying stages as fast speed, constant speed, and slow speed, it is clarified that the forms of moisture existence are bound-state water and free-state water, and the moisture migration is prioritized as surface adsorption water, interparticle water, particle attached water, and capillary water. Innovate a method to quantify the change of pore space in the drying process by pore coefficient ratio to evaluate the drying quality. The results show that when the pore coefficient ratio is about 40 %, its moisture content is 20 %∼30 %, and the drying effect is best at this time. The physical drying test further confirmed the correctness of the conclusion of the drying stage division and water loss law. This study can provide a theoretical reference for the modeling study of the pore structure of the block matrix and the exploration of its drying mechanism.

Selected aspects of blood flow simulations in arteries

This article discusses selected aspects of modelling blood flow in the arteries. The method of reproducing the variable-in-time geometry of coronary arteries is given based on a sequence of medical images of different resolutions. Within the defined shapes of the arteries, a technique of generation of numerical meshes of the same topology is described. The boundary conditions and non-Newtonian rheological models used in blood flow are discussed, as well as the description of blood as a multiphase medium. The work also includes a discussion of tests on the phantom of the carotid artery for the accuracy of measurements made using ultrasonography.

Unsteady flow of bubble liquid in hydraulic systems of aircraft and helicopters

The subject of this work is the phenomenon of a water hammer in a liquid that contains a small volume of gas bubbles. Historically, this phenomenon began to be studied as the dynamics of gas bubbles (Rayleigh-Pleset equation). Today, thanks to progress in computer technology, this phenomenon is studied at the level of bubble deformation during hydraulic shock. Another approach is to consider the dynamics of a multiphase (two-phase) medium in the form of a bubbly liquid. After several assumptions, the main one being a relatively small gas content in the liquid, the model consists of two differential equations with respect to the shock wave propagation speed and the resulting pressure perturbations. The specified system of equations differs from the corresponding classical water hammer equations: they consider the convection of the velocity field. In addition, the friction of the liquid against the wall according to the Weisbach-Darcy model is considered. Because of the small content of gas bubbles, the Weissbach-Darcy friction is approximated in the same way as in a homogeneous liquid, i.e., in a certain sense, greater than the real friction. Maybe that is why more or less physical results are obtained only for small values of the dimensionless parameter responsible for the friction of the liquid against the wall. It concerns the non-contradiction of the assumptions and the results obtained on their basis. Thus, in the front region of the shock pulse, where the pressure increases, the radial velocity of the bubbles is negative; however, for relatively large values of the friction parameter, the maximum pressure disturbance moves from the center of the shock pulse. This contradicts the assumption about compression: after passing the maximum pressure, gas bubbles expand due to a decrease in pressure. The graphical dependence obtained in this study are compared with the results related to a homogeneous liquid. They agree, but the shock pulse in a bubbly liquid is not as concentrated in space as that in a homogeneous liquid. Its length is 10-12 times greater than the corresponding value in a homogeneous liquid. Research methods are purely theoretical. The well-known bubble liquid model is used as a single-speed model continuum. Differential equations are solved analytically, approximately (series expansion), and numerically. In addition, the original approach of obtaining an analytical solution of an autonomous system is used-finding the function of pressure disturbances from the velocity of propagation of the shock pulse (and vice versa). Conclusions. A simple one-dimensional hydraulic model of shock wave (impulse) propagation in a bubbly liquid is proposed. In contrast to classical ideas (solutions) about a water hammer, which consists of two waves of opposite directions of propagation, a shock pulse is a region of pressure disturbances in which the speed of motion of fluid particles is also variable – from the maximum value to almost zero.

Cartography of liquid-liquid flow in corrugated millichannels

If the interest of heat exchanger/reactors have been demonstrated for homogeneous liquid phase applications, many chemical syntheses take place in multiphase media (gas-liquid, liquid-liquid, gas-liquid-solid…). Thus, in order to evaluate the versatility of a plate-type heat exchanger/reactor with a 2D-meandering millichannel, this work is focused on the characterization of hydrodynamics of liquid-liquid flow in the reaction channel. Therefore, several prototypes are built with millichannels of increasing dimensions to address the scale-up issue. Flow visualizations are performed with a high-speed camera; four flow regimes with octanol/water fluid system are observed: annular/plug, annular, annular/dispersed, and dispersed. The study shows that interfacial tension and dispersed phase inertia are the main forces driving the interface. A dimensionless map based on the dispersed phase Weber number as a function of the continuous phase internal Dean number is built up. This map turns out to be valid in the range (2–4 mm) of the tested corrugated millichannel size.