Parallel Sidewalls Research Articles

Volumetric Lagrangian temperature and velocity measurements with thermochromic liquid crystals

We propose a Lagrangian method for simultaneous, volumetric temperature and velocity measurements. As tracer particles for both quantities, we employ encapsulated thermochromic liquid crystals (TLCs). We discuss the challenges arising from color imaging of small particles and present measurements in an equilateral hexagonal-shaped convection cell of height h = 60 mm and distance between the parallel side walls w = 104 mm, which corresponds to an aspect ratio Γ=1.73 . As fluid, we use a water-glycerol mixture to match the density of the TLC particles. We propose a densely-connected neural network, trained on calibration data, to predict the temperature for individual particles based on their particle image and position in the color camera images, which achieves uncertainties below 0.2 K over a temperature range of 3 K. We use Shake-the-Box to determine the 3D position and velocity of the particles and couple it with our temperature measurement approach. We validate our approach by adjusting a stable temperature stratification and comparing our measured temperatures with the theoretical results. Finally, we apply our approach to thermal convection at Rayleigh number Ra = 3.4×107 and Prandtl number Pr = 10.6. We can visualize detaching plumes in individual temperature and convective heat transfer snapshots. Furthermore, we demonstrate that our approach allows us to compute statistics of the convective heat transfer and briefly validate our results against the literature.

Unsteady Flow of Casson Fluid between Two Side Walls over an Infinite Plate

In the present study, the velocity field corresponding to the unsteady flow of Casson fluid between two parallel side walls perpendicular to an infinite plate that exerts an oscillating shear stress to the fluid is determined with the help of Fourier sine and cosine transforms. Exact solutions are obtained and given in simple form as a combination of transient and steady-state solutions, which satisfy the governing equation and all imposed initial and boundary conditions. These solutions are reduced to the similar solutions corresponding to the motion over an infinite plate, when and Newtonian fluid by making Casson parameter Furthermore, effect of side walls on the motion of fluid, the time which is required to attain the steady state and the distance between the side walls for which their presence can be ignored are graphically determined.

Unsteady MHD flow of a fractional second grade fluid in a channel passing through a porous medium subject to a time-dependent motion of the bottom plate

The velocity of an unsteady flow of a viscous fluid of the second-grade MHD-type enclosed between two parallel side walls perpendicular to a plate was obtained by applying the integral transformation. The fluid is required to move by the plate, which over time [Formula: see text] subjected the fluid to shear stress. The solutions satisfy the given equation as well as the boundary and initial conditions, and they were separated into two types: steady state and transient state. Furthermore, through [Formula: see text], we are able to recover the results found in the literature for motion across an infinite plate. Graphs depict the effect of the side walls and the time it takes to reach the steady state. The solutions are shown in graphs and discussed physically to examine the impact of different flow parameters. It is found that the fluid velocity decreases with an increasing fractional parameter [Formula: see text] and second-grade parameter [Formula: see text]. Also, it is noticed that the fluid velocity decreases with increasing values of Reynolds number and effective permeability. Numerous industrial products, including honey, paints, varnishes, coffee, chocolate and jelly, use this type of fluid flow concept.

Flow-field characteristics of a synthetic jet impinging on a circular cylinder in a free and constrained environment

The flow field of a synthetic jet (SJ) impinging on a circular cylinder has been investigated while varying jet-cylinder separation distances in a free and constrained environment. For the free environment case, the cylinder was placed in the SJ flow field in a quiescent environment, and its separation distance downstream from the slot exit was varied. Whereas for the constrained environment case, two parallel sidewalls were mounted along the shorter side of the slot, and the cylinder was placed between these sidewalls. The slot width (w = 6.4 mm) and aspect ratio (25) were kept constant for both cases. The experimental results for the SJ impinging on a circular cylinder showed that the flow-field behavior differs significantly from that of a cylinder in uniform flow and is largely affected by the jet-cylinder separation distance and the operating environment, i.e., free or constrained. The plots of the pressure distribution and normalized standard deviation of the fluctuating pressure around the cylinder surface revealed higher flow fluctuations associated with SJ impingement. The flow visualization and the hot wire measurements further unveiled that no obvious vortex shedding occurs in the cylinder wake. However, evidence for vortex dipoles rising from the cylinder surface was found, on either side of the cylinder (perpendicular to the flow direction).

A Simple Micromilled Microfluidic Impedance Cytometer with Vertical Parallel Electrodes for Cell Viability Analysis.

Microfluidic impedance cytometry has been demonstrated as an effective platform for single cell analysis, taking advantage of microfabricated features and dielectric cell sensing methods. In this study, we present a simple microfluidic device to improve the sensitivity, accuracy, and throughput of single suspension cell viability analysis using vertical sidewall electrodes fabricated by a widely accessible negative manufacturing method. A microchannel milled through a 75 µm platinum wire, which was embedded into poly-methyl-methacrylate (PMMA), created a pair of parallel vertical sidewall platinum electrodes. Jurkat cells were interrogated in a custom low-conductivity buffer (1.2 ± 0.04 mS/cm) to reduce current leakage and increase device sensitivity. Confirmed by live/dead staining and electron microscopy, a single optimum excitation frequency of 2 MHz was identified at which live and dead cells were discriminated based on the disruption in the cell membrane associated with cell death. At this frequency, live cells were found to exhibit changes in the impedance phase with no appreciable change in magnitude, while dead cells displayed the opposite behavior. Correlated with video microscopy, a computational algorithm was created that could identify cell detection events and determine cell viability status by application of a mathematical correlation method.

Towards merged-element transmons using silicon fins: The FinMET

A merged-element transmon (MET) device based on silicon (Si) fins is proposed, and the first steps to form such a “FinMET” are demonstrated. This new application of fin technology capitalizes on the anisotropic etch of Si(111) relative to Si(110) to define atomically flat, high aspect ratio Si tunnel barriers with epitaxial superconductor contacts on parallel sidewall surfaces. This process circumvents the challenges associated with the growth of low-loss insulating barriers on lattice matched superconductors. By implementing low-loss, intrinsic float-zone Si as the barrier material rather than commonly used, potentially lossy AlOx, the FinMET is expected to overcome problems with standard transmons by (1) reducing dielectric losses; (2) minimizing the formation of two-level system spectral features; (3) exhibiting greater control over barrier thickness and qubit frequency spread, especially when combined with commercial fin fabrication and atomic-layer or digital etching; (4) potentially reducing the footprint by several orders of magnitude; and (5) allowing scalable fabrication. Here, as a first step to making such a device, the fabrication of Si fin capacitors on Si(110) substrates with shadow-deposited Al electrodes is demonstrated. These fin capacitors are then fabricated into lumped element resonator circuits and probed using low-temperature microwave measurements. Further thinning of silicon junctions toward the tunneling regime will enable the scalable fabrication of FinMET devices based on existing silicon technology while simultaneously avoiding lossy amorphous dielectrics for the tunnel barriers.

Unsteady MHD Flow for Fractional Casson Channel Fluid in a Porous Medium: An Application of the Caputo-Fabrizio Time-Fractional Derivative

Theoretically, this work describes the exact solutions of fractional Casson fluid through a channel under the effect of MHD and porous medium. The unsteady fluid motion of the bottom plate, which is confined by parallel but perpendicular sidewalls, supports the flow. By introducing the dimensionless parameters and variables, the momentum equation, as well as the initial and boundary conditions, has been transformed to a dimensionless form. A mix of Laplace and Fourier transformations is used to get the exact solution for the momentum equation. The constitutive equations for Caputo-Fabrizio’s time-fractional derivative are also incorporated for recovering the exact solutions of the flow problem under consideration. After recovering the exact solutions for flow characteristics, three different cases at the surface of the bottom plate are discussed, by addressing the limiting cases under the influence of the side walls. Moreover, these solutions are captured graphically, and the effects of the Reynolds number Re , fractional parameter α , effective permeability K eff , and dimensionless parameter for Casson fluid β on the fluid’s motion are observed.

Late Middle Pleistocene Harbin cranium represents a new Homo species

Late Middle Pleistocene Harbin cranium represents a new Homo species

Aerodynamic Free-Flight Conditions in Wind Tunnel Modelling through Reduced-Order Wall Inserts

Parallel sidewalls are the standard bounding walls in wind tunnels when making a wind tunnel model for free-flight condition. The consequence of confinement in wind tunnel tests, known as wall-interference, is one of the main sources of uncertainty in experimental aerodynamics, limiting the realizability of free-flight conditions. Although this has been an issue when designing transonic wind tunnels and/or in cases with large blockage ratios, even subsonic wind tunnels at low-blockage-ratios might require wall corrections if a good representation of free-flight conditions is intended. In order to avoid the cumbersome streamlining methods especially for subsonic wind tunnels, a sensitivity analysis is conducted in order to investigate the effect of inclined sidewalls as a reduced-order wall insert in the airfoil plane. This problem is investigated via Reynolds-averaged Navier–Stokes (RANS) simulations, and a NACA4412 wing at the angles of attack between 0 and 11 degrees at a moderate Reynolds number (400 k) is considered. The simulations are validated with well-resolved large-eddy simulation (LES) results and experimental wind tunnel data. Firstly, the wall-interference contribution in aerodynamic forces, as well as the local pressure coefficients, are assessed. Furthermore, the isolated effect of confinement is analyzed independent of the boundary-layer growth. Secondly, wall-alignment is modified as a calibration parameter in order to reduce wall-interference based on the aforementioned assessment. In the outlined method, we propose the use of linear inserts to account for the effect of wind tunnel walls, which are experimentally simple to realize. The use of these inserts in subsonic wind tunnels with moderate blockage ratio leads to very good agreement between free-flight and wind tunnel data, while this approach benefits from simple manufacturing and experimental realization.

Non-Uniform Narrow Groove Plasmonic Nano-Gratings for SPR Sensing and Imaging

A surface plasmon resonance sensing and imaging platform based on plasmonic non-uniform nano-gratings with narrow groove (sub-10 nm) is presented. In these nanogratings, normally incident optical radiation is directly coupled to surface plasmons without the requirements of any other conventional surface plasmon coupling mechanisms such as prism-based or grating-based coupling. Theoretical analysis of practically realizable plasmonic non-uniform nano-gratings with rounded tops and slanted sidewalls is carried out to numerically to determine reflectance and differential reflectance signals when the localized refractive index of the medium around the gold layer present in these nano-gratings is changed. This change in the localized refractive index can occur due to the binding of biomolecules to the gold layer. Two kinds of plasmonic non-uniform nano-gratings are studied using finite difference time domain (FDTD) modelling: gold nano-gratings (GNGs) and gold-coated silicon nano-gratings (GSNGs). The plasmonic non-uniform nano-gratings being proposed, more specifically the GSNGs, can be easily fabricated with the presently existing nanofabrication and thin film deposition methods as opposed to uniform nano-gratings (with parallel sidewalls) that are very difficult to fabricate. The plasmonic non-uniform nano-gratings with narrow grooves eliminate the strict requirements on the angle of incidence for coupling of light into surface plasmons, which are needed in conventional prism-based coupling mechanisms. By employing FDTD calculations, we demonstrate that these plasmonic non-uniform nano-gratings provide very high differential reflectance amplitude values, which are indicative of high sensitivities of the SPR or SPRi sensors when the localized refractive index around the sensors is varied. Moreover, the sensors being proposed in this article provide a maximum sensitivity of localized refractive index sensing (i.e. surface sensitivity or $\text{S}_{\mathrm {S}}$ ) of 70 nm/nm with a figure of merit of the localized sensor (FOMS) of 1.5 nm $^{-1}$ . This sensitivity of localized refractive index sensing is the highest reported thus far in comparison with previously reported plasmonic sensors. Moreover, these plasmonic non-uniform nano-grating based sensors exhibit significantly better performance when compared with conventional SPR or SPRi sensors based on the Kretschmann configuration.

Independent and grouped 3D cell rotation in a microfluidic device for bioimaging applications

Cell rotation reveals important information which facilitates identification and characterization of different cells. Markedly, achieving three dimensional (3D) rolling rotation of single cells within a larger group of cells is rare among existing cell rotation techniques. In this work we present a simple biochip which can be used to trap and rotate a single cell, or to rotate multiple cells relative to each other within a group of individual red blood cells (RBCs), which is crucial for imaging cells in 3D. To achieve single RBC trapping, we employ two parallel sidewall 3D electrodes to produce a dielectrophoretic force which traps cells inside the capturing chambers of the microfluidic device, where the hydrodynamic force then induces precise rotation of the cell inside the chamber. We have also demonstrated the possibility of using the developed biochip to preconcentrate and rotate RBC clusters in 3D. As our proposed cell trapping and rotation device reduces the intricacy of cell rotation, the developed technique may have important implications for high resolution 3D cell imaging in the investigation of complex cell dynamics and interactions in moving media.

An experimental investigation on oscillating length scale of gas pipeline leakage flame restricted by parallel sidewalls

This work focuses on studying the oscillating length scale of gas pipeline leakage flame restricted by parallel sidewalls with various separation distances. A series of experiments are conducted with 3, 6 and 10 mm nozzles and propane is used as fuel. Results show that reduction of the sidewall separation distance hinders the air entrainment, and provokes significant enlargement of the oscillation amplitude. Besides, the oscillating length scale of propane jet fire is also found to increase with the fuel flow rate. Finally, a new physical model, based on the scaling analysis of the fuel flow field and previous work, is proposed to characterize the variation of oscillating length for the restricted propane jet fire. The results obtained in this work and in previous studies, correlate with a better agreement using the present model than a previous suggested model. This work is not only a significant supplement to the flame oscillation instability physics from previous results for the flame restricted by parallel sidewalls, but also can provide some scientific basis to the design and management on the gas fuel energy storage and transportation systems in the cities to reduce the possible fire thread to the surrounding buildings.

Comparison of the flow-field characteristics of a slot synthetic jet with and without sidewalls

In this paper, experimental investigation of the flow-field of a slot synthetic jet (SJ) with and without sidewalls, issuing into a quiescent environment is systematically reported. Two parallel sidewalls were mounted along the shorter side of the slot extending in the streamwise direction to constrain the flow along the slot span. Hot-wire anemometry was used to explore the flow-field characteristics of both configurations at a Reynolds number of 4000 based on the slot-width and slot average exit velocity during the ejection phase. The present work is a first step towards the investigation of the SJ flow-field characteristics in a bounded region. In a number of generic situations, this work is of high importance as the SJ is deployed in constrained environments (e.g., in cooling applications) where sidewalls may be present. The relative difference in the magnitude of the distinct peaks in the near-field spanwise velocity profiles for both configurations reveals that the vortex does not get curled up towards the centerline in the case of the synthetic jet with sidewalls due to the presence of the no-slip walls. Spectral analysis in the near-wall region further confirms the absence of the phenomenon of axis-switching in the case of the synthetic jet with sidewalls. This behavior is also demonstrated with the help of the relative spreading rate in both configurations, where the unbounded synthetic jet spreads rapidly compared to the bounded one, due to greater entrainment of the surrounding fluid. The statistically two-dimensional region for a synthetic jet with sidewalls is found to extend over a longer axial distance in the downstream. The other jet properties such as turbulence intensity, skewness, and flatness factors further reveal the differences in the flow-field of the two configurations. The results show that the presence of the sidewalls strongly influences the SJ flow-field and hence, it would significantly impact the heat transfer capacity of the SJ.

Investigating the Effects of the Block Geometries and Sidewall Divergences on the Local Scour Downstream of Baffled Chute Spillways

Due to the lack of any specific study about the sidewalls and other blocks’ changes in the case of hydraulic and scour downstream, the present study was conducted to investigate this issue. For this purpose, drainage projects and spillway chutes, as well as many baffle block chutes, were designed and constructed with the parallel sidewalls and trapezoidal shape using the U.S. Bureau of Reclamation (USBR) instructions. Three divergence ratios of ((b1/b2) = 1.45, 1.75, and 2.45), a parallel sidewall of (b1/b2 = 1), and also three geometry blocks including trapezoidal USBR, trihedral, and semicircle blocks were applied and tested in the hydraulic laboratory using a baffle chute with the slope of (2 : 1), (H : V). The material used in this study was sediment sand with a uniform grain size of d50 = 1.2 mm, 15 cm of thickness, and 2 m of length. The experiment was conducted with seven different discharges in lasting condition, and the flow characteristic and scour hole dimensions were measured. The results revealed that in comparison with the USBR blocks, changes in the baffle sidewall and block shape made an approximate 50% reduction in the maximum depth of the scour hole. Thus, increasing the divergence ratio from 1 to 2.45 had a significant effect on reducing the maximum depth and the topographic shape of the scour hole. According to the range mentioned in the literature for the Weber number, the scale effect was negligible for the chute with baffle blocks. Generally, it can be concluded that the sidewall changes also can make a reduction in the number of overbaffle blocks, causing a reduction in the construction cost.

Experimental study on the vertical temperature distribution of window ejected fire from an enclosure with adjacent side walls

SummaryThis paper measured and analyzed the vertical temperature profile of window ejected fire from a cubic enclosure with the effect of adjacent parallel sidewalls. A cubic enclosure size is 0.4 m (height) × 0.4 m (width) × 0.4 m (length). And two side walls were fixed on the both side of the compartment openings, its distance can be changed. K‐Type thermocouples (T1‐T4) were installed in the inside compartment (inner and outer corner), the vertical position along the façade wall and the center of side wall, respectively. It is found that the side wall distance was independent of the temperature distribution inside the enclosure when the opening size changed from 0.2 m to infinity, and the vertical temperature profile along the side wall significantly increased with the decrease of the separation distances of two sidewalls. A dimensionless correlation was proposed to describe the vertical temperature along the facade wall for various side wall separation dimensions. The new findings and the proposed dimensionless correlation provide basic knowledge for describing vertical temperature along the facade wall.

Molecular recognition using tetralactam macrocycles with parallel aromatic sidewalls.

This review summarizes the supramolecular properties of tetralactam macrocycles that have parallel aromatic sidewalls and four NH residues directed into the macrocyclic cavity. These macrocycles are versatile hosts for a large number of different guest structures in water and organic solvents, and they are well-suited for a range of supramolecular applications. The macrocyclic cavity contains a mixture of polar functional groups and non-polar surfaces which is reminiscent of the amphiphilic binding pockets within many proteins. In water, the aromatic surfaces in the tetralactam cavity drive high affinity due the hydrophobic effect and the NH groups provide secondary interactions that induce binding selectivity. In organic solvents, the supramolecular factors are reversed; the polar NH groups drive high affinity and the aromatic surfaces provide the secondary interactions. In addition to an amphiphilic cavity, macrocyclic tetralactams exhibit conformational flexibility, and the combination of properties enables them to be effective hosts for a wide range of guest molecules including organic biscarbonyl derivatives, near-infrared dyes, acenes, precious metal halide complexes, trimethylammonium ion-pairs, and saccharides.

Numerical and Theoretical Evaluations of a Full-Scale Compartment Fire with an Externally Venting Flame

Understanding of the physics and mechanisms of externally venting flames from enclosure fires with parallel sidewalls at the opening is fundamental to investigating fire spread of U-shape building facade. This work aims to identify the impact of separation distance of sidewalls on facade flame height, heat flux and sustained internal combustion. A series of numerical simulations is conducted in a full-scale compartment with 3.6 m in length/width and 3.1 m in height. An external facade wall is measured 6 m in height and 3.6 m in width. A pyrolysis surface with an area of 3.2 × 3.2 m2 is placed in the middle of the enclosure with a theoretical heat lease rate varying from 1 to 8 MW. The semi-empirical correlations, derived from a reduced cubic enclosure, are evaluated for a full scale facade fire for identifying the flame height dependence on the separation distance of sidewalls. It is found that an enhanced buoyancy-induced flow between sidewalls leads to an increase of the flame height by a factor of 50% and a rise of the peak of radiation heat flux by a factor of 20% as compared to a flat facade fire. The height of externally venting flame is sensitively reduced by a factor of 40% to 50% with an increase of the normalized sidewalls distance by opening width up to 3. The predicted flame height is more pronounced with an increase of flame height by a factor of 40% for a full scale facade than for a small scale one due to turbulence development. The predicted internal HRR is in quantitative agreement with the one from the correlation for a global equivalence ratio below 3. The predicted temperatures are in good agreement with the experimental data except in the intermittent-like regions where an over-prediction of the temperature by a factor of 50% is found due to a reduction in accuracy of LES combustion model.

Thermohydraulic performance of microchannel heat sinks with triangular ribs on sidewalls – Part 1: Local fluid flow and heat transfer characteristics

Triangular ribs are mounted on the parallel sidewalls of microchannels in order to reinitialize the thermal boundary layer and improve the mixing of cold and hot fluids. This paper presents a detailed numerical study on local laminar fluid flow and heat transfer characteristics in microchannel heat sinks with tandem triangular ribs for Reynolds number of 443. Three-dimensional conjugate heat transfer models considering entrance effect, viscous heating, as well as temperature-dependent thermophysical properties are employed. Water and silicon are respectively used as fluid and solid for the computational domain. Triangular ribs are attached in microchannels with either aligned or offset arrangement. Four non-dimensional geometry parameters relative to the width, height, converging-diverging ratio and spacing of triangular ribs are proposed to investigate the influence on local fluid flow and heat transfer characteristics. Velocity contour, pressure and temperature distributions are examined to demonstrate the basic fluid flow and heat transfer mechanism. Local pressure and temperature profiles are studied to show the influence of the triangular ribs on fluid flow and heat transfer process. Local friction factor and Nusselt number for different non-dimensional geometry variables are further investigated to comprehensively indicate the impact of triangular ribs. Results shows that the triangular ribs can significantly reduce the temperature rise of the heat sink base and efficiently prevent the drop of local heat transfer coefficient along the flow direction, but also result in higher local friction factor than the straight microchannel. For the studied operation conditions and geometry parameters of flow passage, the heat sink base temperature varies in the range of from 301.90 to 324.31 K, the computed pressure drop and heat transfer coefficient fluctuate from one triangular rib to the next and their amplitude and wavelength significantly depend on the geometry and arrangement of triangular ribs. Compared to the reference straight microchannel heat sink, a superior configuration considered in this paper can yield an improvement of up to 2.15 times higher of average Nusselt number.

Unsteady MHD flow of a Brinkman type fluid between two side walls perpendicular to an infinite plate

Abstract In this paper, we calculated the velocity of the unsteady flow of a Brinkman MHD type viscous fluid which is enclosed between two parallel side walls perpendicular to a plate by applying the Fourier transformation. The movement of the fluid is caused by the plate which at time t = 0 + , exerts shear stress to the fluid. We presented the solutions into two categories i.e. steady state and transient state, which satisfy the given equation as well as boundary and initial conditions. Furthermore, by making h → ∞ , we recover the solutions obtained in the literature corresponding to the motion over an infinite plate. The effect of the side walls and the time required to reach the steady state are discussed through graphs. Also we checked the effect of different parameters by graphical representations. When K eff and Reynolds number become zero and one respectively, the general solution obtained in this manuscript reduce to special cases in the literature.

Experimental Investigation on the Effect of a Reduced Pressure on the Combustion Characteristics and Flame Height of Gaseous Fuel Jets in Parallel Sidewalls

The increasing energy demand stimulates the increase of natural gas transmitting pipeline all around China and provoke serious fire risks due to accidental pipeline breaks and gas leakage, especially in cities at different altitudes. This work concerns the pressure effect on the flame height of buoyant jet diffusion flames restricted by parallel sidewalls in reduced pressure, which does exist in natural gas leakage fire accident in high plateau areas. Experiments were conducted in Lhasa, Tibet (Altitude: 3650m, Pressure: 0.64 atm), and the corresponding comparison results conducted in normal pressure are referred from our previous work obtained in Hefei, Anhui (Altitude: 50m, Pressure: 1.0 atm). The evolution of the flame heights of a buoyant jet diffusion flame restricted by parallel sidewalls in a reduced pressure are examined, and the major new findings are that the evolution of a parabolic uprising buoyant vortex at the flame boundary and the flame height vary much like that in normal pressure as the ...