Rotation Of Cylinder Research Articles

Microparticle sorting in microfluidic Taylor–Couette flows

In this experimental study, we demonstrate that settling polymethyl methacrylate (PMMA) microparticles with diameters ranging from 6 to 60 µm segregate into distinct bands according to their size when subjected to a rotating laminar annular gap flow with a diverging gap width in the axial direction. Different gap widths ranging from 130 to 1200 µm have been investigated in the fully laminar flow regime. Distinct, spatially separated particle bands of different particle sizes have been observed for nine different geometric configurations, including non-conical, conical, double conical, and variously inclined conical inner cylinder shapes. The study considers different rotation rates, geometric combinations, particle volume fractions, and particle size combinations. Particle size separation was achieved at volume fractions ranging from 2.2% to 11% for rotating inner cylinders. In contrast, no separation occurs during the experimental run when both the outer and inner cylinders are perfectly cylindrical, with no significant variation in the annular gap height. Our experiments also show that rotation of the inner cylinder results in more pronounced particle separation than rotation of the outer cylinder. Microscopic particle image velocimetry (µPIV) measurements show that the presence of particles induces an axial velocity component, which acts as a key transport mechanism. In addition, a significant variation in shear rate is observed across particle bands, which may explain size segregation by shear-induced migration. Furthermore, single particle simulations show that particle trajectories and velocities vary significantly with particle size.

Forced flow reversal in ferrofluidic Couette flow via alternating magnetic field

Time-dependent boundary conditions are very common in natural and industrial flows and by far no exception. An example of this is the movement of a magnetic fluid forced due to temporal modulations. In this study, we used numerical methods to examine the dynamics of ferrofluidic wavy vortex flows (WVF2, with dominant azimuthal wavenumber m=2) in the counter-rotating Taylor–Couette system, which was subjected to time-periodic modulation/forcing in a spatially homogeneous magnetic field. In the absence of a magnetic field, all WVF2 states move in the opposite direction to the rotation of the inner cylinder, they are retrograde. However, when strength or frequency of the alternating magnetic field increases, the motion direction of the flow pattern changes. Thus, the alternating field provides a precise and controllable key parameter for triggering the system response and controlling the flow. Aside, we also observed intermittent behavior when one solution became unstable, leading to random transitions in both, the transition time and toward the different final solutions. Our findings suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which may have applications in the development of modern fluid devices in laboratory experiments. These findings provide a framework to study other types of magnetic flows driven by time-dependent forcing.

Numerical study on the flow and noise control mechanisms of a forced rotating cylinder

This numerical study proposes an active control method aiming to suppress aerodynamic noise from bluff bodies by employing a forced rotating cylinder and investigates its noise reduction effects and mechanisms. A three-dimensional large eddy simulation combined with the Ffowcs William–Hawkings equation was adopted to study the influence of different rotation ratios on the aerodynamic and aeroacoustic characteristics of a cylinder at a Reynolds number of 4.7×104, and to elucidate the primary mechanisms by which cylinder rotation reduces aerodynamic noise. The numerical method is validated through a comparison with previous numerical and experimental results of both flow field and far-field noise. The present numerical results indicate that cylinder rotation can not only effectively reduce aerodynamic drag but also significantly suppress aerodynamic noise across the entire frequency range, including vortex-shedding tonal noise and broadband noise. Two primary mechanisms of flow and noise control by the rotating cylinder are revealed within different ranges of rotation ratio. One mechanism stabilizes the shear layer, thereby suppressing vortex shedding. The other mechanism attenuates the Kelvin–Helmholtz instability on the upper side of the cylinder, leading to a transition into laminar flow which inhibits the formation of large-scale coherent turbulent structures.

Effects of CaF2 and La2O3 on the phase structure of rare earth in CaO–SiO2–La2O3–CaF2 slags

The rare earth in the rare earth slag can be separated and enriched by heating and melting the rare earth slag and then slowly cooling crystallisation. In this process, it is of great significance to study the effect of chemical composition on the crystallisation of rare earth phase in slag and the effect of slag viscosity on crystal growth. The rare earth slag melt samples were prepared according to the main chemical composition of rare earth slag by using an analytical pure reagent. The effects of CaF2 and La2O3 contents on the phase structure and morphology of rare earth phase in CaO–SiO2–La2O3–CaF2 slags were studied by SEM-EDS and XRD. The relationship between the viscosity of the slag and the crystal growth behaviour was studied by measuring the melt viscosity with the cylinder rotation method. The results show that the rare earth in CaO–SiO2–La2O3–CaF2 slags exists in the form of CaLa4(SiO4)3O. The change of CaF2 and La2O3 content has no effect on the structure of rare earth phase, but the size of rare earth crystal phase changes obviously. With the increase of CaF2 and La2O3 content, the size of rare earth crystal phase increases gradually. CaF2 and La2O3 can reduce the viscosity transition temperature of slag melt and increase the crystallisation temperature range of rare earth phase to promote crystal growth.

Predicting MHD mixed convection in a semicircular cavity with hybrid nanofluids using AI

This study presents a numerical analysis of magnetohydrodynamic (MHD) mixed convection in a semicircular enclosure containing a rotating inner cylinder and filled with nanofluids and hybrid nanofluids. The investigation explores the effects of Al2O3-TiO2-SWCNT-water hybrid nanofluids with varying nanoparticle compositions, as well as Al2O3-water, TiO2-water, and SWCNT-water nanofluids. The analysis includes the development of an artificial neural network (ANN) model to predict outcomes, achieving 97.34 % accuracy in training and 97.41 % in testing for the average Nusselt number. The study examines the impact of Reynolds number (Re), Richardson number (Ri), Hartmann number (Ha), cylinder rotation speed (Ω), cylinder size, and nanoparticle volume fraction (φ) on heat transfer and fluid flow. Key findings include a 6.98 % increase in heat transfer for SWCNT-water nanofluid from Ri = 1 to Ri = 10, a reduction in heat transfer with higher Hartmann numbers, and a significant 21.12 % enhancement when cylinder speed increases to Ω = 10 compared to a stationary cylinder. Larger cylinder sizes also improve convective heat transfer, with a 66.14 % increase for SWCNT-water nanofluid. Additionally, higher concentrations of SWCNT and Al2O3 in hybrid nanofluids enhance heat transfer performance.

Modulation of human induced neural stem cell-derived dopaminergic neurons by DREADD reveals therapeutic effects on a mouse model of Parkinson’s disease

BackgroundStem cell-based therapy is a promising strategy for treating Parkinson’s disease (PD) characterized by the loss of dopaminergic neurons. Recently, induced neural stem cell-derived dopaminergic precursor cells (iNSC-DAPs) have been emerged as a promising candidate for PD cell therapy because of a lower tumor-formation ability. Designer receptors exclusively activated by designer drugs (DREADDs) are useful tools for examining functional synaptic connections with host neurons.MethodsDREADD knock-in human iNSCs to express excitatory hM3Dq and inhibitory hM4Di receptors were engineered by CRISPR. The knock-in iNSCs were differentiated into midbrain dopaminergic precursor cells (DAPs) and transplanted into PD mice. The various behavior test such as the Apomorphine-induced rotation test, Cylinder test, Rotarod test, and Open field test were assessed at 4, 8, or 12 weeks post-transplantation with or without the administration of CNO. Electrophysiology were performed to assess the integrated condition and modulatory function to host neurons.ResultsDREADD expressing iNSCs were constructed with normal neural stem cells characteristics, proliferation ability, and differentiation potential into dopaminergic neuorns. DAPs derived from DREADD expressing iNSC showed matched function upon administration of clozapine N-oxide (CNO) in vitro. The results of electrophysiology and behavioral tests of transplanted PD mouse models revealed that the grafts established synaptic connections with downstream host neurons and exhibited excitatory or inhibitory modulation in response to CNO in vivo.ConclusioniNSC-DAPs are a promising candidate for cell replacement therapy for Parkinson’s disease. Remote DREADD-dependent activation of iNSC-DAP neurons significantly enhanced the beneficial effects on transplanted mice with Parkinson’s disease.

Simulation of an operation of nested Halbach cylinder arrays in regenerative magnetic cooling cycles: The way to maximum thermal span

In this study, a numerical model of the Active Magnetic Regenerator (AMR) cycle, implemented in the reciprocal demonstrator, was developed using COMSOL Multiphysics. A nested Halbach cylinder (NHC) array served as the magnetic field source. Additional simulation of an operation of the NHC array was carried out. To eliminate the discrepancies between the heat exchange duration of the heat transfer medium (HTM) and the hot and cold ends of the regenerator, an adequate time dependence of the inner cylinder rotation angle was calculated. The latter provides the symmetrical sinusoidal form of time dependence of the magnetic flux density in the gap of NHC array, which is important for enhancing the performance of a magnetic refrigerator. It was established that in order to achieve a maximal temperature span, it is necessary to shift the phases of the magnetic field insertion/removal and heat transfer fluid pumping processes by nearly half of the operating cycle period. The latter brings the simulated cycle closer to the ideal AMR cycle.

Micro-mixing enhancement in a Taylor-Couette reactor using the inner rotors with various surface configurations

This study investigates the effects of various inner cylinder configurations on micromixing and fluid dynamics within a Taylor-Couette (TC) reactor using the inner cylinders with different surface designs, including the traditional smooth-surfaced rotor cylinder. The four innovative inner cylinders were specifically designed with axial corrugations (N40 and N80) and three-dimensional rough surfaces (NZ40 and NZ80). Micromixing efficiency was assessed experimentally using the iodide-iodate reaction as a probe. To further understand the impact of the rotors' surface structures on micromixing, computational fluid dynamics (CFD) modelling was utilized to analyse the fluid dynamics within the TC reactor. An incorporation model was employed to calculate the micromixing time. The experimental findings reveal that the segregation index decreases with increasing rotation speed for all inner cylinders. Besides, NZ80′s micro-mixing efficiency surpasses that of its counterparts, NZ40, N40, and N80. The CFD modelling results underscore the significant influence of the inner cylinder's surface configuration on the turbulence dissipation rate and volume probability distribution, which are likely to contribute positively to the micromixing efficiency within the TC reactor. Furthermore, the empirical correlations obtained have been established to understand the micro-mixing time within TC reactors using different rotating cylinders.

Computational study of Newtonian laminar annular horizontal displacement flows with rotating inner cylinder

We computationally study the effects of inner cylinder rotation on the laminar displacement flow of two Newtonian fluids along a horizontal eccentric annulus. This flow arises in primary cementing operations in the oil and gas industry, used to seal wells and prevent leakage. We investigate how the rotational motion of the inner cylinder influences the displacement, affecting the interplay of viscosity and density differences, as well as eccentricity. We first simulate a series of experiments recently performed, in order to validate the computational approach. We then study the effects of the rotating inner cylinder in more detail. The rotation shears the fluid in the narrow annular gap and also drags fluid around the annulus, typically resulting in helical streamlines and a spiral pattern of the concentration. Over short timescales, the rotation tends to increase dispersion, but the redistribution of the fluids around the annulus can then improve the overall displacement, i.e., reducing slumping effects due to buoyancy. We also observe a new patterning instability at the inner cylinder, which was not visible in the previous experiments. This instability arises from destabilization of the wall film of displaced fluid, which forms naturally on the walls of the annular gap. We have studied the dimensional parameter space where this instability occurs. Strong buoyancy can suppress the instability, and a threshold value of dimensionless rotation velocity is required for onset of the instability.

Dynamics of two cylinders in a cavity filled with liquid under modulated rotation

Abstract The dynamics of cylindrical bodies in a rotating horizontal cylinder filled with a high-viscosity fluid is experimentally studied. The cylinder rotation rate is modulated. When the cylinder rotates uniformly, the bodies are located near the cylindrical wall and rotate together with the cylinder. The dynamics of bodies depending on the amplitude and frequency of modulation of the cylinder rotation rate is studied in detail. It is found that the cylindrical bodies undergo azimuthal and rotational oscillations. When the critical amplitude of modulation is reached, the bodies repel from the wall and obtain a steady state position at some distance from the wall.

Numerical investigation of cylinder rotors with various endplates

For a finite-length cylinder rotor, rotation induces unique pattern tip vortices at the free end, significantly altering the aerodynamic characteristics of the rotor. Endplates are often applied to finite-length cylinders as a means of restraining end effects. The endplates change the aerodynamic characteristics of the rotor by affecting the end axial flow. In the present study, cylinder rotors with static and rotating endplates of various diameters are investigated by means of large eddy simulation. By analyzing the aerodynamic force, wind pressure, and flow field characteristics of the rotors, the varying patterns and reasons for the aerodynamic characteristics of rotors with static and rotating endplates are clarified. The results show that the endplate induces disk vortices and changes the vortex patterns at the free end of the rotor, and the static endplates show little effect on the development of tip vortices, so the wake vortices show the triple vortex pattern, whereas the rotating endplates enhance the intensity of the plate vortices and inhibit the tip vortices development, leading to the double vortex pattern, which in turn produces a different pattern of aerodynamic characteristics compared to the rotor with the static endplates. The mechanism of the variation in the aerodynamic characteristics and vortex patterns is partially explained by analyzing and discussing the flow field results.

Coupled response of flow-induced vibration and flow-induced rotation of a circular cylinder with a triangular fairing

In this paper, a numerical simulation investigation is carried out on the coupled response of the flow-induced vibration (FIV) and flow-induced rotation (FIR) of a circular cylinder attached with a triangular fairing at a low Reynolds number of Re = 100. The primary focus is on the impact of FIR on FIV. The vibration response, hydrodynamic coefficient, vortex shedding mode, and flow field characteristics are examined for the fairings within the vibrational reduced velocity Ur range of 3–16 with shape angle of α = 45°, 60°, and 90°. The results reveal that at low Ur, all the three considered fairings have a good suppression effect on the FIV. Nevertheless, the galloping response emerges as Ur increases when α = 45° and 60°. In contrast, the vibration response of 90° fairing presents a wider lock-in region. The rotatable 2-degree of freedom (2-DoF) fairing has a better performance in the reduction of response amplitude and hydrodynamic coefficients. The 2S (two single vortices) vortex shedding mode mainly occurs in the vortex-induced vibration (VIV) region, while 2S–8S (from two to eight vortices), 2P (two pairs of vortices), 2T (two triplets of vortices), and P + T (a pair of vortices and a triple of vortices) modes emerge in the galloping branch. Moreover, four modes of wake structures are identified according to the variation of recirculation region and the migration of boundary layer separation point. Finally, the reduced regions of drag, lift, and amplitude are highlighted compared to the bare cylinder.

Advancements in mathematical modeling and numerical simulation: Immersed boundary method for Navier-Stokes equations applied to stationary and rotating isothermal cylinders

This study investigates the growing scientific and industrial interest in the dynamics of fluids around bodies, with a particular focus on thermal fluctuations. These phenomena are prevalent in various scenarios, such as oil extraction platforms, power transmission lines, and fluid-structure interactions, necessitating a comprehensive understanding of vortex generation, heat transfer, and fluid dynamic forces. We employ the Immersed Boundary Method (IBM) to simulate two-dimensional, incompressible flows around stationary and rotating heated (isothermal) cylinders. Using a computational framework developed in C/C++, we analyze the effects of variations in cylinder rotation rates on flow dynamics and thermal distributions. This study involves multiple simulations to evaluate the stability of the method and extract relevant parameters, including drag, lift coefficients and Nusselt numbers, along with velocity, pressure, vorticity, and temperature fields. Through systematic comparison with existing literature, we aim to validate our findings and contribute to the continuous improvement of numerical accuracy in this domain. By elucidating these complex phenomena, our research aims to provide valuable insights for practical applications in industrial and engineering contexts. The objective of this work is to analyze the combination of heat transfer phenomena with rotation in isothermal cylinders and their thermofluid-structure interaction. To achieve this, a low computational cost C/C++ code (in terms of memory and computational resources) was developed. Furthermore, numerical simulations indicated that with an increase in the Reynolds number, there is an increase in the drag coefficient, highlighting the significant influence of the pressure distribution downstream of the cylinder. This pressure distribution is strongly affected by vortex formation and detachment, thereby validating the methodology.

Aerodynamic Performance of a Hovering Cycloidal Rotor: A CFD Study with Experimental Validation

A three‐dimensional (3D) unsteady Reynolds averaged Navier‐Stokes (URANS) computational fluid dynamics (CFD) toolkit for cycloidal rotors was developed and used to perform a parametric study. It included blade aspect ratio, side disks, pitch mechanism, blade camber, and shaft size. The influence of the pitch rod length showed the importance of the lift distribution between the upstream and downstream parts of the rotor cylinder. The application of blade camber significantly affected thrust and power, while having a limited effect on efficiency. A similar effect was obtained by varying the pitch rod lengths. The presence of a central axis in the rotor had a negligible effect on efficiency. The most significant impact on efficiency came from the side disks, which behaved similarly to winglets on fixed‐wing aircraft. However, changing the aspect ratio of the blades showed a similar response to that of aircraft wings, but with a smaller effect, making it conceivable to fly a square-bladed cyclorotor without side disks. To verify the CFD model, a cycloidal rotor was also built using 3D printed parts and carbon fiber tubing. It was then operated on a test rig where thrust and power were measured for speeds ranging from 408 to 2528 RPM. On the test bench, the blades were pitched with a uniform asymmetric mechanism. The maximum nose‐up pitch angle in upstream of the rotor axis was 34.8°. Due to its rotation around the rotor and its pitching in the opposite direction, the maximum nose‐up pitch angle of the downstream blade was 38.6°. The obtained rotor thrust and power curves and the flow visualization around the rotor confirmed the validity of the CFD toolkit.

Numerical study of particle dispersion in the wake of a static and rotating cylinder at Re = 140 000

In this study, the particle-laden flow in the wake of a static and a rotating cylinder at Reynolds number of 140 000 was investigated using the Reynolds Averaged Navier–Stokes numerical approach. Three turbulence models such as k–ω shear stress transport, Reynolds stress model, and local-correlation transition model (LCTM) were selected to predict the flow topology. Lagrangian approach with one-way coupling was used to track solid spherical particles of different sizes (0.01, 0.1, 2.5, 10, and 50 μm). The study reveals that LCTM is the most accurate to predict the flow topology in both cases. Cylinder's rotation generates different effects on flow structure. It breaks the wake's symmetry and reduces its width, and increases the frequency of vortex shedding and the size of the recirculation zone. Particle transport analysis has revealed that particles' response to the flow depends on their Stokes number and wake flow topology. Particles of 0.01, 0.1, and 2.5 μm distribute in and around vortex cores, while particles of 10 and 50 μm do not penetrate vortex cores. Instead, 10 μm particles accumulate mainly around the periphery of vortices, while 50 μm particles skip the vortex street to the thin shear flow region between vortices to be transported by the mainstream flow. Finally, cylinder rotation reduces the particle spread in the vertical direction and shifts all particle distributions in the cylinder's rotation direction. Analysis of particle dispersion functions showed that cylinder's rotation reduces differences in dispersion extent depending on particle size.

RETRACTED: Research on the kinetics characteristics and in-cylinder combustion of opposed rotary piston engine for different power output modes

As a new type of internal combustion engine, opposed rotary piston (ORP) engine has the advantages of simple structure and high working frequency, and can achieve high power density. Consequently, it stands as an ideal power source for hybrid power systems and unmanned aerial vehicles. The ORP engine has different power output modes, corresponding to different piston rotation and volume evolutions of combustion chamber. However, the effect of power output modes on kinetics characteristics and in-cylinder combustion of ORP engines are still uncovered. In this paper, the kinematic model of an ORP engine is established for scenarios involving power output by different shafts (Shaft 1 and Shaft 3). Meanwhile, the piston rotation patterns and cylinder volume variations are investigated correspondingly. Further, three-dimensional numerical model of the ORP engine is established, enabling analysis of in-cylinder combustion characteristics, engine performance, as well as nitrogen oxides (NOx) emissions. The results indicate that the volume variations of all cylinders follow a consistent pattern under the power output by Shaft 3. A pair of opposed cylinders features longer durations of intake and expansion strokes, and shorter durations of compression and exhaust strokes, the other pair of combustion chambers is the opposite under the power output by Shaft 1. The engine demonstrates a charging efficiency of 95.36 %, with corresponding indicated thermal efficiency and indicated power output of 38.08 % and 40.9 kW, respectively. The two adjacent cylinders present significantly different operation processes in the case of the power output by Shaft 1, achieving charging efficiencies of 94.29 % and 89.11 %, respectively, with the indicated thermal efficiency of 34.49 % and 31.60 %. The corresponding minimum indicated specific fuel consumption under the two power output modes are 211.7 g/kW∙h and 243.7 g/kW∙h, respectively, accompanied by NOx emission factors of 25.3 g/kW∙h and 17.6 g/kW∙h. With the given range of ignition timing, a trade-off relationship exists between the engine performance and NOx emissions. The power density of the case of power output by Shaft 3 is superior to that of Shaft 1.

Vortex-induced rotation of a square cylinder under the influence of Reynolds number and density ratio

Numerical simulations are carried out on the vortex-induced rotations of a freely rotatable rigid square cylinder in a two-dimensional uniform cross-flow. A range of Reynolds numbers between 40 and 150 and density ratios between 0.1 and 10 are considered. Results show eight different characteristic regimes, expanding the classification of Ryu & Iaccarino (J. Fluid Mech., vol. 813, 2017, pp. 482–507). New regimes include the transition and wavy rotation regimes; in the ${\rm \pi}$ -limited oscillation regime we observe multipeak subregimes. Moment-generating mechanisms of these regimes and subregimes are further elucidated. A phenomenon related to the influence of density ratio is the tooth-like shape of the ${\rm \pi} /2$ -limit oscillation regime observed in the regime map, which is explained as a result of the imbalance relation between the main frequencies of rotation response and the vortex shedding frequency. In addition, existence of multiple regimes and multistable states are discussed, indicating multiple stable attractive structures in phase space.

MHD mixed convection of nanofluid flow Ag- Mgo/water in a channel contain a rotational cylinder

This investigation explores the mixed convection phenomenon of a hybrid nanofluid flowing within a Channel oriented horizontally featuring a triangular cavity attached to the lower channel wall. The cavity houses a rotating circular cylinder with a radius of R = 0.12. The fluid within the enclosure is a water-based nanofluid containing Ag-MgO nanoparticles. Two scenarios of combined natural and forced convection are examined: in Case 1, all channel walls, the left wall of the cavity, and the surface of the rotating cylinder are adiabatic, while the inclined wall of the cavity is isothermal. In Case 2, all channel walls, the ready wall of the cavity, and the surface of the rotating cylinder are adiabatic, except for the left wall of the cavity, which is isothermal. The dimensionless governing equations are solved under steady flow conditions for various physical parameters using a higher-order and stable Galerkin-based finite element method implemented through the software package FlexPDE. Key governing parameters such as Re number (falling within the amplitude of 10 to 100), Ri number (ranging from Ri = 0.1 to 30), and the location of cylinder rotation (Xo = 0.65 to 0.9) are simulated. The study presents results in terms of average Nusselt numbers and contour maps of streamlines and isotherms. It is observed that the average Nusselt number increases with higher Reynolds number, angular rotation speed, cylinder location, and Richardson number. Specifically, heating the inclined surface suggests that the optimal location for the rotating cylinder is Xo = 0.9, whereas if the left wall of the cavity is heated, the preferred location for the cylinder is Xo = 0.75. These findings are corroborated by comparing them with previous research, demonstrating significant agreement.

Nanofluid cooling of a hot rotating circular cylinder employing cross-flow channel cooling on the upper part and multi-jet impingement cooling on the lower part

This study explores the convective cooling features of a hot rotating cylinder by using the combined utilization of cross-flow on the upper part and multi-jet impingement on the bottom part. The analysis is performed for a range of jet Reynolds number (Re) values (between 100 and 500), cross-flow Re values (between 100 and 1000), rotational Re values (between −1000 and 1000), cylinder size (between 0.25wj and 3wj in radius), and center placement in the y direction (between −1.5wj and 1.5wj). When the cylinder is not rotating, the average Nu increment becomes 102% at the highest jet Re, while it becomes 140.82% at the highest cross-flow Re. When rations become active, the impacts of cross-flow and jet impingement cooling become slight. As compared to a motionless cylinder, at the highest speed of the rotating cylinder, the average Nu rises by about 357% to 391%. For clockwise rotation of the cylinder, a lager cylinder results an increase in the average Nu by about 86.3%. At the lowest and highest cross-flow impinging jet Re value combinations, cooling performance improvement becomes a factor of 8.1 and 2, respectively. When the size of the cylinder changes, entropy generation becomes significant, while the vertical location of the cylinder has a slight impact on entropy generation.

EXPERIMENTAL STUDY OF NON-EQUILIBRIUM RHEOLOGICAL EFFECTS DURING THE FLOW OF PARAFFINIC OILS OF TIMAN-PECHORA BASIN. THIXOTROPY, SUPER ANOMALOUS VISCOSITY, OSCILLATIONS OF SHEAR STRESS

Laboratory experiments were carried out to study the non-stationary and non-equilibrium flow regimes of some paraffinic and high paraffinic crude oils of the Timan-Pechora Basin in a rotational viscometer. The presence of thixotropic properties (shear thinnig and hy steresis loops on the flow curves) is shown. The threshold character of the dependence of the area of the hysteresis loop on the oil tempera ture is demonstrated. Experiments have shown that under certain conditions on the flow curves of the studied oils, there are areas of a decrease in shear stress with an increase in shear rate, similar to areas of a «super anomalous» viscosity (SAV) in plastic lubricants. The shape and size of these areas, i.e. the intensity of the «superanomality» manifestation strongly depends on the experiment conditions and are poorly reproducible from experiment to experiment. In experiments, the SAV phenomenon at temperatures below the gelation temperature was always observed when the sample of paraffinic oil was at rest for a sufficiently long time before deformation. If, however, it was in the gap between the viscometer cylinders after the end of the next measurement cycle for a short time (no more than a few minutes), then at the next cycle of recording the flow curve, the SAV phenomenon can be practically imperceptible, although the hysteresis remains. Experiments show that if a sample of high paraffinic oil is deformed at a constant low shear rate, i.e. constant angular velocity of rotation of the device cylinder, and a temperature below the temperature of gelation, then on the falling curve of the dependence of shear stress on time («shear thinning»), oscillations in shear stress with a period equal to the period of rotation of the viscometer cylinder can be observed.