Fluid Stirring Research Articles

Numerical simulation of rotating flow of CNT nanofluids with thermal radiation, ohmic heating, and autocatalytic chemical reactions

The dispersion of carbon nanotubes in conventional fluids provides a variety of applications, using their unique features to develop efficiency, performance, and functionality in many industrial and scientific processes. Some of the applications are energy conversion, fluid stirring, aligned nanocomposites, heat exchangers, electronics cooling, etc. Considering the aforementioned applications, this communication presents a comparative examination of the rotating flow of CNTs past a stretchable sheet with suction and velocity slip. This study is unique because it looks at the non-linear radiative, Darcy–Forchheimer, and rotational flow of CNTs past a stretchable sheet with considering ohmic heating and homogeneous/heterogeneous reactions. These type of issues have not been previously discussed. Suitable conversions are adopted to alter the governing nonlinear PDEs into nonlinear ODEs. The reduced ODEs are numerically reckoned by adopting the bvp4c scheme in MATLAB. The repercussions of flow factors on velocity, temperature, nanoparticle concentration, skin friction coefficients, and local Nusselt number are provided via tables and graphs. It is revealed that the primary velocity profile dwindles when augmenting the values of suction/injection, porosity, rotational, and magnetic field parameters. The temperature ratio and radiation parameters contribute to the thermal profile’s development. The magnetic field parameter and the Forchheimer number play a dual role in both directional skin friction coefficients. The larger values of radiation and temperature ratio parameters improve the heat transfer rate.

Improved slip mechanism and convective heat impact for ternary nanofluidic flowing past a riga surface

This study of electro-magneto-hydrodynamics has great significance due to its numerous applications like chromatography, fluid pumping, micro coolers and fluid stirring thermal reactors and flow regulation in fluidics systems. Subject to upper functions on electrical magnetic field, the consequences of electromagnetic initiation into ternary nanofluids flow through the Riga plate were noticed. Furthermore, this ternary hybrid nanofluid flow was based on the effect on slip condition, uniform heat source, convective energy and thermal radiation. The ternary hybrid nanofluid was built from the scattering of silver, copper and copper oxide nanoparticles by this base fluid blood. This phenomenon had been formed by the model of the system in partial differential equations; it was made easy in the dimensionless nonlinear structure of ordinary differential equations by employing comparison substitutions. This result on the acquired set of the differential equations was simulated over the bvp4c method. It has been discovered that the ternary hybrid nanofluid velocity is essentially lower along the differing numbers of permeable media, although it amplifies along the upshot on the Hartmann number. Moreover, an enhanced heat transport rate of up to 14% was marked for the triple nanoparticle nanofluid by relating it to another nanofluid and establishing an excellent behavior on triple nanoparticle nanofluids.

Inclusion of Hall and Ion slip consequences on inclined magnetized cross hybrid nanofluid over a heated porous cone: Spectral relaxation scheme

The cone geometry has a great significant for heat transmission in many industrial processes due to its ability to induce turbulence, enable directional flow, promote uniform temperature distribution, and offer versatility in applications. The current study aims to investigate the heat transport process of an inclined magnetized cross hybrid nanofluid over a heated porous cone under the influence of Hall and Ion slip consequences. Additionally, porous medium the flow is past under the effect of inclined uniform magnetic field and porosity of the medium is used to enhance heat transfer. The framed set of governing equations took the form of dimension free structure through appropriate transformations and then finally solved by an effective spectral relaxation method. Thermal impacts and heat transport mechanism associated with the hybrid flow is seen through different values of emerging parameters. Heat transport is seen higher with higher radiation parameters, as radiation and rising temperature are similar. Augmented values of Fr causes pressure drop in fluids which reduces the fluid motion and brings depreciation in velocity field. Eckert number also boosts the temperature of the fluid stirring via a porous rotating cone.

Acoustic driven circulation around cylindrical obstructions in microchannels

We introduce an approach to generate direction-controlled circulation around cylindrical obstructions in channels using a piezoelectric transducer embedded porous-channel device fabricated by photolithography. To transmit acoustic signals into the channel, a single piezoelectric transducer was attached, operating at voltage levels of 5, 10, 15, and 20 V. Microscopic particle image velocimetry was employed to analyze the flow patterns in the channels. The analysis revealed two opposing circulation tendencies around the pillars located at two opposite sides of the channel in the longitudinal direction. The strength of circulation was found to be minimal in the middle of the channel and increased gradually toward the two ends of the channels. Furthermore, we observed that the circulation strength was maximum near the axial centerline and minimum at the boundaries along the width of the channels. Comparing the voltage levels, the higher voltage signals produced a higher strength of circulation than the lower voltage signals in all cases. Additionally, we found that the strength of circulation increased almost linearly and then decayed exponentially in the radial direction from the surfaces of the pillars. The observed velocity fields around individual cylinders matched well with the Görtler vortex model. The reported circulation phenomenon around pillars can be applied in non-contact fluid stirring and mixing in bio-chemical systems and lab-on-a-chip systems and may also provide additional degrees of freedom in object tweezing, trapping, and levitation.

Intensified convective energy tapping in modified tubes using Azadirachta indica brewed zinc oxide as potential thermo-fluids

Reusing certain types of decomposed tree leaves is beneficial for biosynthesizing nanoparticles for nanofluids to meet energy sustainability and conservation. Encapsulating and reductant agents in Azadirachta indica (neem) help with fluid stability besides providing higher thermal transport properties. Sol-gel technique was adopted to prepare zinc oxide (ZnO) nanoparticles with neem solution to obtain neem-doped zinc oxide (ZnOneem) particles. According to the Debye-Scherrer relation, the size of ZnOneem was 36 nm. Optimal fluid stirring and sonication parameters were identified to synthesize and stabilize 0.05, 0.2, and 0.6% concentrated nanofluids with aqua-antifreeze (50:50) without surfactant. While the optimal stirring speed and time of 0.05, 0.2, and 0.6% nanofluids were 322 rpm and 36 min, 329 rpm and 33 min, and 334 rpm and 29 min, respectively, the optimal sonication time were 39 min, 34 min, and 32 min, respectively. However, sodium dodecyl sulphate (SDS) at a dispersion fraction of 0.6 ensured 35 months of good suspension. Pumping these turbulent fluids (Re = 5000–10000) through a microfin tube snug-fit with twisted tape inserts (twist pitch, y = 63, 84, and 105 mm) ensured the best outcomes with all the fluid samples. The Nusselt number ratio of 2.114 is the best at a penalty of 2.228 friction factor ratio with 0.6% concentrated nanofluid at Re = 10,000 circulating within the tube fit with Y = 6 tape. For this case, the Bejan number was 0.72, with the maximum Performance Evaluation Factor (PEF) and the Entropy Performance Evaluation Factor (EPEF) being 1.619 and 154.02, respectively.

Dynamos in the Inner Solar System

Dynamo magnetic fields are primarily generated by thermochemical convection of electrically conductive liquid metal within planetary cores. Convection can be sustained by secular cooling and may be bolstered by compositional buoyancy associated with core solidification. Additionally, mechanical stirring of core fluids and external perturbations by large impact events, tidal effects, and orbital precession can also contribute to sustaining dynamo fields. Convective dynamos cease when the core-mantle heat flux becomes subadiabatic or if specific crystallization regimes inhibit core fluid flows. Therefore, exploring the histories of magnetic fields across the Solar System provides a window into the thermal and chemical evolution of planetary interiors. Here we review how recent spacecraft-based studies of remanent crustal magnetism, paleomagnetic studies of rock samples, and planetary interior models have revealed the magnetic and evolutionary histories of Mercury, Earth, Mars, the Moon, and several planetesimals, as well as discuss avenues for future exploration and discovery. ▪ Paleomagnetism and remanent crustal magnetism studies elucidate the magnetic histories of rocky planetary bodies. ▪ Records of ancient dynamo fields have been obtained from 3 out of 4 terrestrial planets, the Moon, and several planetesimals. ▪ The geometries, intensities, and longevities of dynamo fields can provide information on core processes and planetary thermal evolution.

A Cut-and-Fold Self-Sustained Compliant Oscillator for Autonomous Actuation of Origami-Inspired Robots.

Origami-inspired robots are of particular interest due to their potential for rapid and accessible design and fabrication of elegant designs and complex functionalities through cutting and folding of flexible two-dimensional sheets or even strings, that is, printable manufacturing. Yet, origami robots still require bulky rigid components or electronics for actuation and control to accomplish tasks with reliability, programmability, ability to output substantial force, and durability, restricting their full potential. In this study, we present a printable self-sustained compliant oscillator that generates periodic actuation using only constant electrical power, without discrete components or electronic control hardware. This oscillator is robust (9 out of 10 prototypes worked successfully on the first try), configurable (with tunable periods from 3 to 12 s), powerful (can overcome hydrodynamic resistance to consistently propel a swimmer at ∼1.6 body lengths/min or 3.66 mm/s), and long lasting (∼103 cycles); it enables driving macroscale devices with prescribed autonomous behaviors, for example, locomotion and sequencing. This oscillator is also fully functional underwater and in high magnetic fields. Our analytical model characterizes essential parameters of the oscillation period, enabling programmable design of the oscillator. The printable oscillator can be integrated into origami-inspired systems seamlessly and monolithically, allowing rapid design and prototyping; the resulting integrated devices are lightweight, low cost, compliant, electronic free, and nonmagnetic, enabling practical applications in extreme areas. We demonstrate the functionalities of the oscillator with: (1) autonomous gliding of a printable swimmer, (2) LED flashing, and (3) fluid stirring. This work paves the way for realizing fully printable autonomous robots with high integration of actuation and control.

Dynamics of water conveying SWCNT nanoparticles and swimming microorganisms over a Riga plate subject to heat source/sink

Electromagnetohydrodynamic (EMHD) is very important because of its numerous advantages such as flow control in fluidics networks, fluid pumping, thermal reactors, mixing, fluid stirring, liquid chromatography, and micro coolers. Based on the above applications in this article discussed the electromagnetic forces on the SWCNT/water flow with microorganisms over a Riga plate subject to slip effects. In addition, the uniform heat source/sink effect is used in the energy equation, as well as the thermophoretic effect in the concentration equation. The governing nonlinear system of partial differential equations (PDEs) was reduced to ordinary differential equations (ODEs) by applying the appropriate similarity variables. Hence, Runge-Kutta-Fehlberg (RKF-45) method was applied to numerically solve the extremely nonlinear system. Based on the analysis of the results, it is worth concluding that raising the role of slip effects lowers the velocity, temperature, and concentration curves, while increasing the solid volume fraction increases the temperature, concentration, and motile microorganism density.

Slippery and magnetically responsive micropillared surfaces for manipulation of droplets and beads

Stimuli-responsive surfaces are of practical importance for applications ranging from enhanced mixing of reagents in lab-on-a-chip systems until probing cellular traction forces. Non-destructive reversible bending of cilia-inspired magnetic pillars can be used for controlled transportation of non-magnetic objects and bio-inspired sensing. Magnetic actuation of micropillars suspended in liquids allows controlled mixing, propelling, and stirring of fluids as well as droplet manipulation, which are important for various applications including generation of cell spheroids and droplet coalescence in microfluidic systems. In order to expand their practical applications, fabrication processes capable of rapid prototyping have to be developed. Inspired by biological cilia and their functionalities, actuating hairy surfaces are herein fabricated and implemented to manipulate both microbeads and droplets. The artificial cilia are based on microscale magnetic pillar arrays made of flexible polydimethylsiloxane functionalized with magnetic microparticles. The arrays are fabricated by a new method using patterned molds that relies on cryogenic separation to produce transparent cilia-inspired arrays without requiring manual interference to clean the templates during the process. Magnetic actuation of the pillar arrays is demonstrated in isopropanol and silicone oil. Filling with oil yields magnetically responsive slippery lubricated surfaces allowing directional motion of droplets by repetitive bending and recovery of the flexible magnetic pillars. The achieved structures allow manipulation of microbeads and droplets which is uncommon even at the sub-mm scale; directional motion is demonstrated for 250 μm–550 μm sized droplets. Droplet transportation is facilitated by extremely low hysteresis and a high degree of omnidirectional bending of the pillar array.

Polarization-dependent non-uniform rotation rates of rhombohedral calcite

We demonstrate the polarization-dependent torque on rhombohedral calcite in an optical trap. Our precipitate technique produces regular crystals approximately 10μm on all edges. The regularity of the crystal shape makes it possible to visually identify the optical axis as well as the orientation of the polarization axes. When a rhombohedral crystal is trapped in an elliptically polarized beam, it orients itself with its optic axis approximately parallel to the beam axis. While in this orientation, the total torque increases and decreases relative to three extraordinary and ordinary axes of the crystal. We measure this axis-dependent calcite rotation through video analysis and model the dependence of the torque on the crystal orientation. The ability to predict the motion of calcite gives an analytical tool for applications such as fluid stirring or "lab on a chip" systems.

Lyapunov Exponents for the Random Product of Two Shears

We give lower and upper bounds on both the Lyapunov exponent and generalised Lyapunov exponents for the random product of positive and negative shear matrices. These types of random products arise in applications such as fluid stirring devices. The bounds, obtained by considering invariant cones in tangent space, give excellent accuracy compared to standard and general bounds, and are increasingly accurate with increasing shear. Bounds on generalised exponents are useful for testing numerical methods, since these exponents are difficult to compute in practice.

Proposal of fluid stirring by multi-layered trenches for liquid metal divertor

This study proposes ″multi-layered trenches″ as a new liquid metal flow stirring structure for the flowing-type liquid metal divertor to prevent the temperature stratification and the evaporation of liquid metal.Then it investigates the characteristics of the liquid metal flow induced by this structure experimentally and numerically. The proof-of-principal experiment using a torus channel simulating the trenches successfully demonstrated the liquid metal wavy flow where the ratio of meandering component to the main stream was 27% under the magnetic field up to 5 T. The experiment and three-dimensional magnetohydrodynamics flow simulation also proved that magnitudes of the wavy flow and the vorticity increased with a rise in the magnetic field. Moreover, two-dimensional heat transfer model simulation showed the heat transfer enhancement by the wavy flow. Maximum temperature was 26.6 K lower than that in the case without the wavy flow.

Induced-charge electrokinetics, bipolar current, and concentration polarization in a microchannel-Nafion-membrane system.

The presence of a floating electrode array located within the depletion layer formed due to concentration polarization across a microchannel-membrane interface device may produce not only induced-charge electro-osmosis (ICEO) but also bipolar current resulting from the induced Faradaic reaction. It has been shown that there exists an optimal thickness of a thin dielectric coating that is sufficient to suppress bipolar currents but still enables ICEO vortices that stir the depletion layer, thereby affecting the system's current-voltage response. In addition, the use of alternating-current electro-osmosis by activating electrodes results in further enhancement of the fluid stirring and opens new routes for on-demand spatiotemporal control of the depletion layer length.

流体摩擦と流体撹拌を併用した風力発熱システムにおける撹拌フィンの影響

流体摩擦と流体撹拌を併用した風力発熱システムにおける撹拌フィンの影響

Fluid dwell impact induces peritoneal fibrosis in the peritoneal cavity reconstructed in vitro.

Peritoneal fluid dwell impacts the peritoneum by creating an abnormal physiological microenvironment. Little is known about the precise effects of fluid dwell on the peritoneum, and no adequate in vitro models to analyze the impact of fluid dwell have been established. In this study, we developed a peritoneal fluid dwell model combined with an artificial peritoneal cavity and fluid stirring generation system to clarify the effects of different dwelling solutions on the peritoneum over time. To replicate the peritoneal cavity, we devised a reconstructed peritoneal cavity utilizing a mesothelial layer, endothelial layer, and collagen membrane chamber. The reconstructed peritoneal cavity was infused with Dulbecco's modified Eagle's medium, saline, lactated Ringer's solution or peritoneal dialysis solution with repeated 4-h dwells for 10 or 20 consecutive days. The above-described solutions induced epithelial-mesenchymal transition (EMT) and hyperplasia of mesothelial cells. All solution types modulated nitric oxide synthase activities in mesothelial and endothelial cells and nitric oxide concentrations in dwelling solutions. Inhibition of nitric oxide synthase activity acted synergistically on mesothelial EMT and hyperplasia. The present findings suggest that solutions infused into the peritoneal cavity are likely to affect nitric oxide production in the peritoneum and promote peritoneal fibrosis. Our newly devised peritoneal cavity model should be a promising tool for understanding peritoneal cellular kinetics and homeostasis.

Bistability in inhomogeneity—Effects of flow coherent structures on the fate of a bistable reaction

We present a numerical study on the mixing process between two stable states of a chemical reaction model. The two stable states of the reactions are found in practice not to coexist, and a single stable state of homogeneous scalar concentration is achieved over long time. With all other parameters fixed, we find the dependence of the final state on the rate of reaction. Interestingly, with the existence of coherent structures, at a range of intermediate rate of reaction, we find that the final state also depends on the initial locations of the scalar impurity. The exact dependence on initial condition is explored in detail. These results lead to the fundamental understanding on the variability of biogeochemical tracers in the environment induced by nonlinear fluid stirring.

Flagellar phenotypic plasticity in volvocalean algae correlates with Péclet number

Flagella-generated fluid stirring has been suggested to enhance nutrient uptake for sufficiently large micro-organisms, and to have played a role in evolutionary transitions to multicellularity. A corollary to this predicted size-dependent benefit is a propensity for phenotypic plasticity in the flow-generating mechanism to appear in large species under nutrient deprivation. We examined four species of volvocalean algae whose radii and flow speeds differ greatly, with Péclet numbers (Pe) separated by several orders of magnitude. Populations of unicellular Chlamydomonas reinhardtii and one- to eight-celled Gonium pectorale (Pe ∼ 0.1-1) and multicellular Volvox carteri and Volvox barberi (Pe ∼ 100) were grown in diluted and undiluted media. For C. reinhardtii and G. pectorale, decreasing the nutrient concentration resulted in smaller cells, but had no effect on flagellar length and propulsion force. In contrast, these conditions induced Volvox colonies to grow larger and increase their flagellar length, separating the somatic cells further. Detailed studies on V. carteri found that the opposing effects of increasing beating force and flagellar spacing balance, so the fluid speed across the colony surface remains unchanged between nutrient conditions. These results lend further support to the hypothesized link between the Péclet number, nutrient uptake and the evolution of biological complexity in the Volvocales.

Six Degrees-of-Freedom Haptic Interaction with Fluids

We often interact with fluids in our daily life, either through tools such as when holding a glass of water or directly with our body when we swim or we wash our hands. Multimodal interactions with virtual fluids would greatly improve the simulations realism, particularly through haptic interaction. However, achieving realistic, stable, and real-time force feedback from fluids is particularly challenging. In this work, we propose a novel approach that allows real-time six Degrees of Freedom (DoF) haptic interaction with fluids of variable viscosity. Our haptic rendering technique, based on a Smoothed-Particle Hydrodynamics physical model, provides a realistic haptic feedback through physically based forces. 6DoF haptic interaction with fluids is made possible thanks to a new coupling scheme and a unified particle model, allowing the use of arbitrary-shaped rigid bodies. Particularly, fluid containers can be created to hold fluid and hence transmit to the user force feedback coming from fluid stirring, pouring, shaking, and scooping, to name a few. Moreover, we adapted an existing visual rendering algorithm to meet the frame rate requirements of the haptic algorithms. We evaluate and illustrate the main features of our approach through different scenarios, highlighting the 6DoF haptic feedback and the use of containers.

Chaotic Advection in an Archipelago*

Abstract Techniques from dynamical systems theory have been applied to study horizontal stirring of fluid in the Philippine Archipelago. The authors’ analysis is based on velocity fields produced by two high-resolution (3 and 6 km) numerical models. Particular attention is paid to identifying robust surface flow patterns and associating them with dominant Lagrangian coherent structures (LCSs). A recurrent wind-driven dipole in the lee of the coastline is considered in detail. The associated LCSs form a template for stirring, exchange, and biological transport in and around the dipole. Chaotic advection is argued to provide a relevant framework for interpreting mesoscale horizontal stirring processes in an archipelago as a whole. Implications for the formation of filaments, the production of tracer variance, and the scale at which stirring leads to mixing are discussed in connection with an observed temperature record.

On internal waves generated by large-amplitude circular and rectilinear oscillations of a circular cylinder in a uniformly stratified fluid

This paper presents an experimental study of internal waves generated by circular and rectilinear oscillations of a circular cylinder in a uniformly stratified fluid. The synthetic schlieren technique is used for quantitative analysis of the internal-wave parameters. It is shown that at small oscillation amplitudes, the wave pattern observed for circular oscillations is in good agreement with linear theory: internal waves are radiated in the wave beams passing through the first and third quadrants of a Cartesian coordinate system for the clockwise direction of the cylinder motion, and the intensity of these waves is twice the intensity measured for ‘St Andrew's cross’ waves generated by purely horizontal or vertical oscillations of the same frequency and amplitude. As the amplitude of circular oscillations increases, significant nonlinear effects are observed: (i) a strong density-gradient ‘zero-frequency’ disturbance is generated, and (ii) a region of intense fluid stirring is formed around the cylinder serving as an additional dissipative mechanism that changes the shape of wave envelopes and decreases the intensity of wave motions. In the same range of oscillation amplitudes, the wave generation by rectilinear (horizontal and vertical) oscillations is shown to be by and large a linear process, with moderate manifestations of nonlinearity such as weak ‘zero-frequency’ disturbance and weak variation of the shape of wave envelopes with the oscillation amplitude. Analysis of spatiotemporal images reveals different scenarios of transient effects in the cases of circular and rectilinear oscillations. In general, circular oscillations tend to generate disturbances evolving at longer time scales.