Differential Flow Velocity Research Articles

Steppingstone-inspired construction of high vertical thermal conductivity material with low carbon fiber content

Thermal interface materials (TIMs) with good thermal conductivity are paramount in mitigating the heat concentration challenges encountered during the operation of highly integrated components in sophisticated electronic devices. To optimize the comprehensive performance of TIMs, a balance must be struck: minimizing the filler concentration to attenuate materials hardness while maximizing filler content to bolster the thermal conduction pathway. Drawing inspiration from the orientation of tree branches passing through steppingstones in river, a method was proposed in this study. This method exploits the shear effect of carbon fiber (CF), owing to viscosity variances during diameter extrusion, and the differential flow velocity between CF and alumina to induce a significant degree of orientation. Combined with subsequent flipping and bonding, a TIM with vertically oriented CF was prepared. The TIM was obtained with a mere 12.1 wt% CF incorporation, the composite exhibits a through-plane thermal conductivity of 21.29 W/(m·K), representing an enhancement of two orders of magnitude relative to pristine silicone rubber, while retaining its flexibility and deformability. The orientation degree and high efficiency orientation effect of CF have been characterized via scanning electron microscopy (SEM), thermal conductivity test and light-emitting diode (LED) temperature rise test.

Differential flow velocities control method for push-bending of the thin-walled tube with a 0.9D bending radius by differential lubrication

The smaller the relative bending radius of the bent tube, the more difficult the tube blank is to be bent. In this paper, the push-bending process for the aluminum tube with a relative bending radius of 0.9D was analyzed through simulation. There was tangential tensile stress concentration occurring at the front endpoint of tube intrados, which increased the risk of cracking. That is because the bending tube’s extrados moves less angular distance than its intrados by the uniform lubrication method, causing excessive deformation of the cross-section. Therefore, a differential lubrication method using the lubricant with a larger friction coefficient at intrados and the lubricant with a smaller friction coefficient at extrados was proposed to increase the angular velocity of the tube’s extrados. It was found that the differential lubrication method helped avoid excessive thinning at the front endpoint of tube intrados through simulations. Furthermore, push-bending experiments of 5A02 aluminum alloy with a relative bending radius of 0.9D were carried out to investigate this effect. The experimental results showed that the differential lubrication method effectively avoided cracking, which agreed with the simulation results.

Численное моделирование аэродинамических процессов движения воздушных масс в тоннелях метрополитена с учетом «поршневого» воздействия подвижного состава

Purpose: To consider the issue on verification of numerical model of air exchange during the movement of a train in a subway tunnel, taking into account the process of interaction of regular ventilation with the piston effect of the displaced air by the body of the moving train. Methods: Data scanning and processing. The equipment used was a pressure cylindrical Pitot tube PFM 2 for measuring differential pressure and air flow velocity, volumetric flow and temperature. Results: The dynamic structure of disturbed fluid media at the time of rolling stock arrival and departure has been established. Practical importance: Factors of design solutions of tunnel portal part affecting the process of air exchange at the combined work of ventilation and piston effect of moving trains have been determined.

Time-series analysis of differential pressure and flow velocity signals by means of weighted statistics

Turbulence intensity levels are assigned different values according to set a probability distribution. Many researchers do not consider probability distributions when determining turbulence intensity levels. This is one cause of the disagreement between numerical simulations of turbulence modeling and experimental data. This study focuses on the use of weighted statistics to evaluate turbulence intensity levels through three types of examples. The first is a hands-on example with a Pitot-static tube. The second utilizes numerical data and the Monte Carlo method. The third relies on a dataset by constant temperature anemometry and laser Doppler anemometry, available from the literature. This study finds that turbulence intensity evaluations differ depending on the selection of the probability distribution. The turbulence intensity according to a Gaussian distribution is reduced by more than 30% in comparison with that set with a rectangular distribution. The notion of the true and engineering turbulence intensity is introduced.

Solar cycle-related variation in solar differential rotation and meridional flow in solar cycle 24

We studied temporal variation of the differential rotation and poleward meridional circulation during solar cycle 24 using the magnetic element feature tracking technique. We used line-of-sight magnetograms obtained using the helioseismic and magnetic imager aboard the Solar Dynamics Observatory from May 01, 2010 to March 26, 2020 (for almost the entire period of solar cycle 24, Carrington rotation from 2096 to 2229) and tracked the magnetic element features every 1 h. We also estimated the differential rotation and poleward meridional flow velocity profiles. The observed profiles are consistent with those of previous studies on different cycles. Typical properties resulting from torsional oscillations can also be observed from solar cycle 24. The amplitude of the variation was approximately ±10 m s^{-1}. Interestingly, we found that the average meridional flow observed in solar cycle 24 is faster than that observed in solar cycle 23. In particular, during the declining phase of the cycle, the meridional flow of the middle latitude is accelerated from 10 to 17 m s^{-1}, which is almost half of the meridional flow itself. The faster meridional flow in solar cycle 24 might be the result of the weakest cycle during the last 100 years.

Mechanism of “Differential Flow Velocity Cell Corrosion” of Cast Iron in Seawater

Mechanism of “Differential Flow Velocity Cell Corrosion” of Cast Iron in Seawater

Effects of alpha-proton drift velocity on alpha particle firehose instability

In situ measurements have shown that the less-abundant alpha particles are characterized by temperature anisotropy which could drive the anisotropy-driven kinetic instabilities in the solar wind. In the collisionless plasma, the differential alpha-proton flow velocity Vd=Vα−Vp usually has a non-zero value of the order of the local Alfvén velocity. The presence of such differential flow may affect the properties of dispersion relations for anisotropy-driven instabilities. Based upon linear Vlasov dispersion theory in a homogeneous plasma, the present study investigates the effects of the alpha-proton drift velocity on the parallel and oblique firehose instabilities driven by an excessive parallel temperature anisotropy of alpha particles, where the parallel and oblique represent directions of fluctuation propagation relative to the background magnetic field. It is found that for oblique firehose mode as well as parallel mode, the dispersion properties are affected by the presence of the alpha-proton drift velocity, which in turn results in the increase of the maximum growth rates as Vd increases and consequently leads to the modification of the marginal stability conditions in the parameter space (β∥α,T⊥α/T∥α). We discuss the relevance of our results to the measured temperature anisotropy of alpha particles in the solar wind context.

Hydrodynamically controlled cell rotation in an electroporation microchip to circumferentially deliver molecules into single cells

We present a hydrodynamically controlled, single-cell-rotation method to demonstrate electroporation-mediated molecular delivery in a microfluidic channel. Using a two-inlet geometry to control the carrier-flow profile, cell flow path and angular velocities can be controlled. When the flow-rate ratio between the fluid sheath and cell streams is balanced, fluidic shear occurs near the walls of the channel due to differential flow velocities between the streamlines. Single-cell angular velocities can then be explicitly controlled by using higher flow-rate ratios between the streams. Using sheathing streams with sufficiently high flow-rate ratios between the sheath and sample streams, cells are pinched against the sidewalls of the channel, which results in large degrees of cell rotation. We applied this technique to single-cell electroporation to increase the delivery of small molecules into the cell. Cell orientation was controlled along the length of the microchannel to continuously expose new cell membrane surface area to an applied electric field. Thus, the cell membrane becomes circumferentially permeabilized, resulting in a more efficient and uniform transport of micro- and macromolecules into rotating cells compared to the non-rotating one. Hydrodynamic control of cell rotation offers a new means to enhance intracellular delivery efficiency in single-cell electroporation.

Terahertz acoustics in hot dense laser plasmas.

We present a hitherto unobserved facet of hydrodynamics, namely the generation of an ultrahigh frequency acoustic disturbance in the terahertz frequency range, whose origins are purely hydrodynamic in nature. The disturbance is caused by differential flow velocities down a density gradient in a plasma created by a 30 fs, 800 nm high-intensity laser (∼5×10(16) W/cm(2)). The picosecond scale observations enable us to capture these high frequency oscillations (1.9±0.6 THz) which are generated as a consequence of the rapid heating of the medium by the laser. Adoption of two complementary techniques, namely pump-probe reflectometry and pump-probe Doppler spectrometry provides unambiguous identification of this terahertz acoustic disturbance. Hydrodynamic simulations well reproduce the observations, offering insight into this process.

LIMITS ON ALPHA PARTICLE TEMPERATURE ANISOTROPY AND DIFFERENTIAL FLOW FROM KINETIC INSTABILITIES: SOLAR WIND OBSERVATIONS

Previous studies have shown that the observed temperature anisotropies of protons and alpha particles in the solar wind are constrained by theoretical thresholds for pressure-anisotropy-driven instabilities such as the Alfv\'en/ion-cyclotron (A/IC) and fast-magnetosonic/whistler (FM/W) instabilities. In this letter, we use a long period of in-situ measurements provided by the {\em Wind} spacecraft's Faraday cups to investigate the combined constraint on the alpha-proton differential flow velocity and the alpha-particle temperature anisotropy due to A/IC and FM/W instabilities. We show that the majority of the data are constrained to lie within the region of parameter space in which A/IC and FM/W waves are either stable or have extremely low growth rates. In the minority of observed cases in which the growth rate of the A/IC (FM/W) instability is comparatively large, we find relatively higher values of $T_{\perp\alpha}/T_{\perp p}$ ($T_{\parallel\alpha}/T_{\parallel p}$) when alpha-proton differential flow velocity is small, where $T_{\perp\alpha}$ and $T_{\perp p}$ ($T_{\parallel\alpha}$ and $T_{\parallel p}$) are the perpendicular (parallel) temperatures of alpha particles and protons. We conjecture that this observed feature might arise from preferential alpha-particle heating which can drive the alpha particles beyond the instability thresholds.

Influence of Flowfield on CO<sub>2</sub> Hydrate Film Thickness

In order to realize of CO2 ocean sequestration, it is important to reveal the knowledge of CO2 hydrate film thickness which forms on the interface between CO2 and water. However, knowledge of CO2 hydrate film thickness under various parameter conditions such as temperature, flow velocity on CO2 hydrate film, and elapsed time from hydrate formation is little. The objective of the present study is to investigate the influence of temperature and flow velocity on CO2 hydrate film thickness. CO2 hydrate film thickness is measured under differential temperature and flow velocity conditions. In this study, CO2 hydrate film thickness is measured with laser interference method. And, CO2 hydrate film thickness is estimated based on duality of CO2 saturated solubility under CO2 hydrate formation condition. As the result, the measured CO2 hydrate film thickness decrease with increase in temperature and flow velocity. And, the estimated CO2 hydrate film thickness denotes the same tendency of measured CO2 hydrate film thickness.

EFFECT OF DIFFERENTIAL FLOW OF ALPHA PARTICLES ON PROTON PRESSURE ANISOTROPY INSTABILITIES IN THE SOLAR WIND

In the solar wind, when the effects of proton-proton Coulomb collisions are negligible, alpha particles usually flow faster than the protons in such a way that the differential alpha-proton flow velocity V{sub d} = V{sub {alpha}} - V{sub p} is on the order of the Alfven speed, is directed away from the Sun, and is nearly aligned with the local mean magnetic field. When this differential flow is taken into account, solutions of the hot plasma dispersion relation show that for the parallel propagating electromagnetic ion cyclotron (EMIC) instability driven by the proton temperature anisotropy T{sub perpendicularp} > T{sub ||p}, the maximum growth rate occurs in the + V{sub d} direction and for the parallel firehose instability driven by the opposite proton temperature anisotropy T{sub ||p} > T{sub perpendicularp}, the maximum growth rate occurs in the - V{sub d} direction. Thus, the EMIC instability preferentially generates left circularly polarized Alfven-ion-cyclotron waves propagating away from the Sun and the parallel firehose instability preferentially generates right circularly polarized magnetosonic-whistler waves propagating toward the Sun with the maximum growth rates occurring for frequencies on the order of the proton cyclotron frequency and wavenumbers on the order of the proton inertial length. Because ofmore » the Doppler shift caused by the motion of the solar wind, both types of waves are left circularly polarized in the spacecraft frame for observations taken when the local mean magnetic field is collinear with the solar wind flow velocity. Theoretical investigation of these instabilities also shows that regions of parameter space exist where the unstable waves are generated propagating unidirectionally such as, for the EMIC instability for example, when the temperature anisotropy is small |(T{sub perpendicular{sub p}}/T{sub ||{sub p}}) - 1| < 1. Taken together, the above properties can explain the origin of parallel propagating electromagnetic waves recently observed near the proton inertial length in high-speed solar wind. The observed waves are most likely produced in situ by these instabilities. A remarkable property of the proposed mechanism that may be of practical importance is that the magnetic helicity of the unstable waves has the same sign no matter whether the proton temperature anisotropy (T{sub p{sub perpendicular}}/T{sub p{sub ||}}) - 1 is positive or negative.« less

H111 CO_2ハイドレート膜厚に及ぼす流れ場の影響(OS11 温暖化対策とCO_2削減技術)

The objective of the present study is to investigate the influence of temperature and flow velocity on CO_2 hydrate film thickness. CO_2 hydrate film thickness is measured under differential temperature and flow velocity conditions. In this study, CO_2 hydrate film thickness is measured with laser interference method. And, CO_2 hydrate film thickness is estimated based on duality of CO_2 saturated solubility under CO_2 hydrate formation condition. As the result, the measured CO_2 hydrate film thickness decrease with increase in temperature and flow velocity. And, the estimated CO_2 hydrate film thickness denotes the same tendency of measured CO_2 hydrate film thickness.

A case study of a pipe line burst in the Mihama Nuclear Power Plant

AbstractOn August ninth, 2004, at the Mihama nuclear power plant in Japan, a carbon steel pipe line carrying hot water under high pressure burst, killing five workers employed in maintenance job nearby. The major cause for the burst was presumed to be the pipe wall thinning due to so‐called erosion‐corrosion which had been revealed to be the cause of similar accident in 1986 at the Surry nuclear power plant in USA. However, the opinion of this author is that the wall thinning must have been caused through differential flow velocity corrosion accompanied with passivation, the origin of which was irregularities in the fluid flow velocity as well as in the pipe wall temperature. A rationale is presented that is consistent with this hypothesis. A countermeasure to this type of corrosion is also proposed.

The Feasibility of Differential Flow Velocity Dividing Working Areas in a Cleanroom

The possibility of dividing working areas by airflow velocity differences in a cleanroom with fan-filter unit (FFU) systems was investigated. Without physical partitions, the cleanroom area was divided into working and non-working areas defined by the FFU exit flow velocities, which were maintained at constant value in the working areas and reduced in the non-working areas. As uniform micro-sized particles were released from a particle generator in the non-working area, the concentrations of particles in the working area were monitored by a particle counter. The results showed that high downward flow velocity in the working area can effectively prevent particles from spreading. The results also suggested an optimum velocity ratio of 20% between adjacent flow regions, in terms of the balance between energy savings and the effective partition insulation.

Dual wetting-film multi-syringe flow injection analysis extraction: Application to the simultaneous determination of nitrophenols

A dual wetting-film extraction/back-extraction system based on a multi-syringe flow injection analysis (MSFIA) set-up coupled to additional burettes and solenoid valves is proposed. The system performs on-line analyte extraction from an aqueous medium to an organic solvent based on the differential flow velocities of the aqueous and organic phases into PTFE tubing, which is due to the formation of a thin and pseudo-stationary organic film adhered to the inner walls of the extraction coil. The pre-concentrated analytes are eluted into a small eluting solution segment and conducted to a diode-array spectrophotometer for analysis. The peak maximum spectrum is used for the simultaneous determination of different analytes by using multi-component analysis with multi-linear regression (MLR). This dual system is applied to the multi-component determination of 2-, 3- and 4-nitrophenol. By using 8 ml of sample and 88 μl of 1-chlorobutane in 1-octanol (66/34, v/v) as organic phase, a sample throughput of 11 analyses per hour can be obtained. The detection limits for 2-, 3- and 4-nitrophenol are 0.11, 0.46 and 0.07 μM, respectively, and the relative standard deviations are less than 4%.

Picrite from the Katse area, Lesotho: evidence for flow differentiation

A basalt flow in the Katse area of Lesotho displays composite features with tholeiitic characteristics along its margins and a picritic composition in the centre. Geochemical modelling of the magma and the composition of microscopic melt inclusions indicate that the primary magma was olivine-rich. The chemical variation of the flow is evidence for fractionation of olivine from the magma, causing a trend towards tholeiitic compositions. The derived lava flow was modified by flow differentiation so that olivine concentrated progressively towards the centre, owing to differential flow velocity. Evidence from geochemical modelling corroborates these conclusions.

Sequential-injection extraction for sample preparation

This report introduces a flow-based extraction method where an aqueous sample and organic solvent are injected sequentially into an extraction coil, then mixed and separated due to the differential flow velocities of the aqueous and organic phases. A 500 μl aqueous sample is propelled through a 50 μl segment of organic solvent whose flow is impeded due to hydrophobic interactions with the walls of a Teflon extraction coil. This wall drag allows the faster moving aqueous sample to penetrate through and ultimately separate from the slower organic solvent. These steps are repeated with a back extraction into a second aqueous segment (100 μl) that is collected and analyzed with high-pressure liquid chromatography (HPLC). The configuration of this novel sequential-injection extraction (SIE) system allows ease of changing reagents and uses minimum organic solvent volumes, as it avoids continuous pumping of reagents. Barbiturates (phenobarbital, amobarbital, pentobarbital and secobarbital) and serotonin re-uptake inhibitors (SRIs) — venlafaxine, paroxetine, sertraline and norsertraline — were extracted as model acidic and basic compounds from urine into a 1 : 4 (v : v) mixture of 1-octanol and butyl chloride and back extracted into 0.45 M NaOH and 0.18 M H 3PO 4, respectively. Absolute recoveries of the analytes were: venlafaxine 29%; paroxetine 30%; norsertraline 25%; sertraline 20%; phenobarbital 11%; amobarbital 24%; pentobarbital 23%; and secobarbital 27%. The sample throughput, including extraction and back extraction, was 20 samples h −1.

Flow Injection Preconcentration Using Differential Flow Velocities in Two-Phase Segmented Flow

In this work, a pseudostationary phase of organic solvent replaces the microcolumn in flow injection preconcentration. This pseudostationary phase results from the wetting of hydrophobic tubing by the organic solvent within the concurrent flow of two immiscible phases through narrow tubing. If this wetting film is sufficient thick, a differential velocity between the aqueous and organic phases develops within the two-phase segmented flow. The effect of experimental parameters such as sample volume, flow rate, phase ratio, and tubing diameter on the preconcentration factor are characterized. Using these procedures, preconcentration factors in excess of 50-fold are obtained with a throughput of 30 samples/h.

Solvent Extraction-Flow Injection without Phase Separation through the Use of the Differential Flow Velocities within the Segmented Flow

A simple and robust flow injection extraction system has been developed. The system exploits the wetting film of the organic phase which forms on the walls of the hydrophobic Teflon tubing. This wetting film is stationary and thus reduces the average linear velocity of the organic flow. Any component extracted into the organic phase requires more time to pass through the extraction coil than the unextracted components. Using organic solvents such as hexanol, which have a high viscosity and low interfacial tension, the differential flow velocities can yield a separation in time between unextracted and extracted components