Buoyancy-driven algebraic (localised) boundary-layer disturbances

We show that a new class of steady linear eigenmodes exist in the Falkner–Skan boundary layer, associated with an algebraically developing, thermally coupled three-dimensional perturbation that remains localised in the spanwise direction. The dominant mode has a weak temperature difference that decays (algebraically) downstream, but remains sufficient (for favourable pressure gradients that are below a critical level) to drive an algebraically growing disturbance in the velocity field. We determine the critical Prandtl number and pressure gradient parameter required for downstream algebraic growth. We also march the nonlinear boundary-region equations downstream, to demonstrate that growth of these modes eventually gives rise to streak-like structures of order-one aspect ratio in the cross-sectional plane. Furthermore, this downstream flow can ultimately become unstable to a two-dimensional Rayleigh instability at finite amplitudes.

Flush Flow Behaviour Affected by the Morphology of Intravascular Endoscope: A Numerical Simulation and Experimental Study

Background: Whilst intravascular endoscopy can be used to identify lesions and assess the deployment of endovascular devices, it requires temporary blockage of the local blood flow during observation, posing a serious risk of ischaemia.Objective: To aid the design of a novel flow-blockage-free intravascular endoscope, we explored changes in the haemodynamic behaviour of the flush flow with respect to the flow injection speed and the system design.Methods: We first constructed the computational models for three candidate endoscope designs (i.e., Model A, B, and C). Using each of the three endoscopes, flow patterns in the target vessels (straight, bent, and twisted) under three different sets of boundary conditions (i.e., injection speed of the flush flow and the background blood flowrate) were then resolved through use of computational fluid dynamics and in vitro flow experiments. The design of endoscope and its optimal operating condition were evaluated in terms of the volume fraction within the vascular segment of interest, as well as the percentage of high-volume-fraction area (PHVFA) corresponding to three cross-sectional planes distal to the microcatheter tip.Results: With a mild narrowing at the endoscope neck, Model B exhibited the highest PHVFA, irrespective of location of the cross-sectional plane, compared with Models A and C which, respectively, had no narrowing and a moderate narrowing. The greatest difference in the PHVFA between the three models was observed on the cross-sectional plane 2 mm distal to the tip of the microcatheter (Model B: 33% vs. Model A: 18%). The background blood flowrate was found to have a strong impact on the resulting volume fraction of the flush flow close to the vascular wall, with the greatest difference being 44% (Model A).Conclusion: We found that the haemodynamic performance of endoscope Model B outperformed that of Models A and C, as it generated a flush flow that occupied the largest volume within the vascular segment of interest, suggesting that the endoscope design with a diameter narrowing of 30% at the endoscope neck might yield images of a better quality.

Rational design of the inlet configuration of flow systems for enhanced mixing

High mass transfer rate is a key advantage of microreactors however, under their characteristic laminar flow, it is dominated by slow diffusion rather than fast convection. In this paper, we demonstrate how the configuration of the inlet, i.e. mixers, can promote different flow patterns to greatly enhance mixing efficiency downstream. A systematic evaluation and comparison of different widely adopted mixers as well as advanced designs is presented using a combination of computational fluid dynamics (CFD) and backward particle tracking to accurately calculate diffusion, in the absence of numerical diffusion (false diffusion). In the method, the convection contributed concentration profile is obtained by tracking sampling points from a cross-sectional plane to the inlet point, and diffusion is estimated subsequently. In conventional T- and Y-mixers, the shape of channel, circular or square, is key with only the latter promoting engulfment flow. In cyclone mixers, the resulting average inlet velocity, independent of Reynolds number or geometry, is the dominating design parameter to predict mixing efficiency. This work will serve as a guideline for the design of efficient flow systems with predicted mixing as a way of maximising selectivity and product quality.

Image segmentation and analysis for densification mapping of nanoporous gold after nanoindentation

Segmentation of scanning electron microscopy (SEM) images of focused ion beam (FIB) cross-sections through indented regions in nanoporous gold (np-Au) is carried out. A key challenge for image analysis of open porous materials is the appropriate binarization of the pore and gold ligament regions while excluding material lying below the cross-sectional plane. Here, a manual approach to thresholding is compared to global and local approaches. The global thresholding resulted in excessive deviations from the nominal solid fraction, due to a strong gray-scale gradient caused by the tilt angle during imaging and material shadowing. In contrast, the local thresholding approach delivered local solid fractions that were free of global gradients, and delivered a quality comparable to the manual segmentation. The extracted densification profiles vertically below the indenter as well as parallel to the surface showed an exponential-type decay from the indenter tip towards the nominal value of 1 far from the indenter. Graphic abstract

Accuracy Analysis of a Next-Generation Tissue Microarray on Various Soft Tissue Samples of Wistar Rats

This study aimed to investigate accuracy in different sectional planes of the TMA Grand Master (3DHISTECH) Workstation in various soft tissue samples collected from Wistar rats. A total of 108 animals were sacrificed and 963 tissue specimens collected from 12 soft-tissue types. A total of 3307 tissue cores were punched and transferred into 40 recipient TMA blocks. Digital image analysis was performed. Core loss showed a significant correlation with tissue type and was highest in skin tissue (p < 0.001), renal medulla and femoral artery, nerve, and vein bundle (p < 0.01). Overall, 231 of 3307 tissue cores (7.0%) were lost. Hit rate analysis was performed in 1852 punches. The target was hit completely, partially and missed totally by 89.4%, 7.2% and 2.2%. A total of 54.5% of punches had good accuracy with less than 200 µm deviation from the centre of the targeted region and 92.6% less than 500 µm. Accuracy decreases with greater sectional depth. In the deepest sectional plane of roughly 0.5 mm median depth, almost 90% of cores had a deviation below 500 µm. Recommendations for automated TMA creation are given in this article. The ngTMA®-method has proven accurate and reliable in different soft tissues, even in deeper sectional layers.

Modeling of fuel transport in pressure-fed systems with flow passage opening devices

This study presents a numerical model of a pressure-fed system with flow passage opening devices (FPODs) designed for an air vehicle with a high degree of maneuverability. The FPOD is a mechanical device that connects two separate fuel reservoirs and functions as a valve allowing liquid fuel to flow while minimizing the movement of pressurizing gas from upstream fuel tanks into downstream fuel tanks. A reduced-order model for the fuel motion in an annular fuel tank was developed to configure the depth and inclination angle of the free fuel surface on the cross-sectional plane of an annular fuel tank under accelerating conditions during flight. Furthermore, a newly proposed model that reflects the dynamic characteristics of the FPOD is used to determine the fluid type that is transported through the device. A simulation example shows that the full numerical model captures changes of the fuel transport condition over time in a complete pressure-fed system of annular fuel tanks with FPODs subject to acceleration.

Use of a pin-penetration wood density meter to determine the density of 25 Indonesian species

The pin-penetration device is a minimally destructive instrument that is widely used to estimate the physical properties of wood, e.g., density, with advantages such as reduced testing times, low costs, and fewer defects induced in the wood being tested. In this study, such a device was used on 25 Indonesian hardwood species with a strength class (SC) distribution from SC II to IV (according to the Indonesian classification of wood SCs). Tests were conducted on three different orthogonal planes, i.e., cross-sectional, radial, and tangential planes. The wood density ranged from 0.28 to 0.88 g/cm3, and the specific gravity was 0.25 to 0.76. The cross-sectional plane penetration depth of the wood was significantly greater than that of either the radial or tangential plane, whereas the pin penetration values of the radial and tangential planes were not significantly different. A prediction model for predicting the density and specific gravity of wood via pin penetration showed a significant regression. Thus, the use of a pin-penetration device was found to be suitable for estimating wood density and specific gravity in a range of SCs of tropical wood species regardless of species.

Simulation tests of selected gas flow parameters through combustion engine valves

The article presents the numerical analysis of a single-cylinder gasoline engine with indirect injection and spark ignition. The goal is to recognize and analyze gas flow through inlet and outlet valves and channels. These data were obtained from the simulation of a four-cycle engine cycle without combustion of the fuel-air mixture. The simulation was carried out in ANSYS, using a dedicated IC Engine module. After the simulation, the result was analyzed on the cross-sectional plane of both the valves and the combustion chamber. This method provided the necessary and concise representation of the flow characteristics. Five separate stages are presented - two describing the different displacement of the valve for each inlet and exhaust stroke and one representing the phenomenon of overlapping. The type of flow, its speed and tendency to create turbulence are described