Velocity Flow Research Articles

Wicking dynamics into two-rail open channel with periodical branches

Wicking into open channels with branches is frequently adopted in multiple assays for medical testing. The penetration velocity plays a key role in improving efficiency. However, it is significantly reduced in the bifurcation microfluidic systems. As a result, understanding and enhancing wicking dynamics in bifurcation capillary flow is imperative. Capillary imbibition into a two-rail channel with periodical branches is investigated by many-body dissipative particle dynamics. The influences of the branch width and surface wettability on the penetration velocity and imbibition flow rate are examined. Four different types of spontaneous capillary flows are observed, including no invasion into branches, reduction in the penetration velocity, stick-slip motion, and inter-branch gap covered by liquid. Four regimes are identified accordingly, the phase diagram relates the flow behavior to the branch width, and surface wettability is established. As the branch width is significantly large (small gap), the penetration velocity is found to be greater than that without branches. It is attributed to the partial covering behavior, which leads to the effective width more than the main channel width.

Oblique stagnation point flow of micropolar nanofluid impinge along a vertical surface via modified Chebyshev collocation method

This article contains a study of mixed convection in micropolar nanofluid near an oblique stagnation point in the presence of a magnetic field. Similarity transformations are used to convert governing partial differential equations to non-linear ordinary differential equations. Modified Chebyshev collocation method in computational software Maple is used for the solution of governing nonlinear differential equations. A comparison of numerical results obtained by modified Chebyshev collocation method and finite difference method is made to show the accuracy of the method. Graphical results for velocity components, microrotation, temperature, and flow patterns are part of this study. Numerical values for free parameter (A), skin friction, and Nusselt numbers for different parameters are also calculated. It is found that microrotation profiles are enhanced by increasing the effect of stretching while decline with enhancing angle of strike γ. Also, the temperature of micropolar nanofluid is increased by increasing the value of the magnetic parameter and micropolar coefficient. The temperature gradient of nanofluid shows a decline when values of stretching parameter and the angle of the strike are increased.

Manyetik Alan Altinda Nanoakişkanlarin Akiş Karakteristiklerinin İncelenmesi

The existence/application of an externally induced magnetic field, like in satellite cooling applications, causes a decrement in heat transfer when used with nanofluids. This study investigates the flow characteristics and velocity profile of distilled water, alumina nanofluid, and cobalt ferrite ferrofluid in a horizontal cylindrical heat pipe flowing in a laminar regime and being exposed to an external magnetic field. All of the simulations were performed with ANSYS Fluent MHD module, for a concentration of 2%, Reynolds number of 10, and Hartmann numbers of 25, 50, and 150. The velocity profiles, pressure drops, and flow characteristics are examined by varying the magnetic field intensity while keeping all other parameters constant. It is concluded that an external magnetic field causes a deterioration in the velocity profiles of the nanofluid, especially in cobalt ferrite, while it does not have a significant effect on water. When the magnitude of the magnetic field is increased by 2 times, it is seen that the velocity of the fluid decreases by 6% and increasing the magnetic field from 0 to 50 Tesla causes a deceleration rate of 9%, which leads to the conclusion that application of a magnetic field for the first time has a more significant slowing effect when comparing it to increasing the magnetic field. In addition, when a magnetic field of 50 Tesla is considered, the maximum velocity of alumina is lower than that of water by 5.10%, and the maximum velocity of cobalt ferrite is lower by 28.57%.

Theoretical and experimental research on valve-less piezoelectric pump with arc-shaped tubes

In order to apply a valve-less piezoelectric pump in navigation equipment, this work first revealed a valve-less piezoelectric pump with arc-shaped tubes and then researched the relationship between the main structural parameters of arc-shaped tubes and the output flow rate. According to the velocity difference between clockwise and counterclockwise directions of liquid in circular arc-shaped tubes, the flow characteristics of liquid in circular arc-shaped tubes are analyzed in this paper, and the velocity difference model and flow equation of a piezoelectric pump are established. By using three-dimensional printing technology, five types of prototypes with different parameters were made, and the experimental research was carried out. The results show that at the optimal frequency, the pump output flow is the largest. The output flow is proportional to the driving voltage, the base circle radius, and the cross section area of the pipe. The low-cost and miniaturized navigation equipment made by using the piezoelectric pump has potential application value in unmanned aerial vehicle and intelligent vehicle navigation.

Physical Properties of the Crust Influence Aftershock Locations

AbstractAftershocks do not uniformly surround a mainshock, and instead occur in spatial clusters. Spatially variable physical properties of the crust may influence the spatial distribution of aftershocks. I study four aftershock sequences in Southern California (1992 Landers, 1999 Hector Mine, 2010 El Mayor—Cucapah, and 2019 Ridgecrest) to investigate which physical properties are spatially correlated with aftershock occurrence. I find that aftershocks correlate with several properties, including measures of stress and stress change from the mainshock, fault structure, kinematics, seismic velocity, and heat flow. Aftershock spatial density exhibits an order of magnitude or more variation as a function of these properties. I determine simple empirical relations between each of the properties and the aftershock spatial density, and use these relations to construct new spatial models that describe aftershock locations. The new spatial models are a significant improvement over a simple base model, but do not fully capture the dense spatial clustering of aftershocks. Numerous spatially varying physical properties exhibit no (or poor) correlation with aftershock spatial density, including temperature, rock composition, and rheological properties that might be expected to control aftershock occurrence. These results suggest that while spatially variable physical properties appear to influence aftershock locations, more work is necessary in order to establish the connections between aftershock occurrence and the causative physical properties.

Macropore Regulation of Hydroxyapatite Osteoinduction via Microfluidic Pathway.

Macroporous characteristics have been shown to play a key role in the osteoinductivity of hydroxyapatite ceramics, but the physics underlying the new bone formation and distribution in such scaffolds still remain elusive. The work here has emphasized the osteoinductive capacity of porous hydroxyapatite scaffolds containing different macroporous sizes (200–400 μm, 1200–1500 μm) and geometries (star shape, spherical shape). The assumption is that both the size and shape of a macropore structure may affect the microfluidic pathways in the scaffolds, which results in the different bone formations and distribution. Herein, a mathematical model and an animal experiment were proposed to support this hypothesis. The results showed that the porous scaffolds with the spherical macropores and large pore sizes (1200–1500 μm) had higher new bone production and more uniform new bone distribution than others. A finite element analysis suggested that the macropore shape affected the distribution of the medium–high velocity flow field, while the macropore size effected microfluid speed and the value of the shear stress in the scaffolds. Additionally, the result of scaffolds implanted into the dorsal muscle having a higher new bone mass than the abdominal cavity suggested that the mechanical load of the host tissue could play a key role in the microfluidic pathway mechanism. All these findings suggested that the osteoinduction of these scaffolds depends on both the microfluid velocity and shear stress generated by the macropore size and shape. This study, therefore, provides new insights into the inherent osteoinductive mechanisms of bioceramics, and may offer clues toward a rational design of bioceramic scaffolds with improved osteoinductivity.

Determining flame temperature by broadband two color pyrometry in a flame spreading over a thin solid in microgravity

Fire spread inside a spacecraft is a constant concern in space travel. Understanding how the fire grows and spreads, and how it can potentially be extinguished is critical for planning future missions. The conditions inside a spacecraft can greatly vary from those encountered on earth, including microgravity, low velocity flows, reduced ambient pressure and high oxygen, and thus affecting the combustion processes. In microgravity, the contributions of thermal radiation from gaseous species and soot can play a critical role in the spread of a flame and the problem has not been fully understood yet. The overall objective of this work is to address this by studying the soot temperature of microgravity flames spreading over a thin solid in microgravity. The experiments presented here were performed as part of the NASA project Saffire IV, conducted in orbit on board the Cygnus resupply vehicle before it re-entered the Earth’s atmosphere. The fuel considered is a thin fabric made of cotton and fiberglass (Sibal) exposed to a forced flow of 20 cm/s in a concurrent flow configuration. Reconstruction of the flame temperature fields is extracted from two color broadband emission pyrometry (B2CP) as the flame propagates over the solid fuel. A methodology, relevant assumptions and its applicability to other microgravity experiments are discussed here. The data obtained shows that the technique provides an acceptable average temperature around ∼1300 K, which remains relatively constant during the spread with an error value smaller than 117 K. The data presented in this work provides a methodology that could be applied to other microgravity experiments to be performed by NASA. It is expected that the results will provide insight for what is to be expected in different conditions relevant for fire safety in future space facilities.

Microvascular Flow Imaging: A State-of-the-Art Review of Clinical Use and Promise.

Vascular imaging with color and power Doppler is a useful tool in the assessment of various disease processes. Assessment of blood flow, from infarction and ischemia to hyperemia, in organs, neoplasms, and vessels, is used in nearly every US investigation. Recent developments in this area are sensitive to small-vessel low velocity flow without use of intravenous contrast agents, known as microvascular flow imaging (MVFI). MVFI is more sensitive in detection of small vessels than color, power, and spectral Doppler, reducing the need for follow-up contrast-enhanced US (CEUS), CT, and MRI, except when arterial and venous wash-in and washout characteristics would be helpful in diagnosis. Varying clinical applications of MVFI are reviewed in adult and pediatric populations, including its technical underpinnings. MVFI shows promise in assessment of several conditions including benign and malignant lesions in the liver and kidney, acute pathologic abnormalities in the gallbladder and testes, and superficial lymph nodes. Future potential of MVFI in different conditions (eg, endovascular repair) is discussed. Finally, clinical cases in which MVFI correlated and potentially obviated additional CEUS, CT, or MRI are shown.

A novel double-image-sequence correlation method for time-resolved particle image velocimetry

This work reports a novel method with a goal of improving the accuracy and robustness of time-resolved particle image velocimetry (TR-PIV) measurements. This method, named double-image-sequence correlation (DISC), accomplishes this goal by utilizing the temporal information stored in TR-PIV measurements. The key to such utilization is that the DISC method constructs two separate image sequences with well-selected sequence length and separation time. As a result, multiple cross-correlation maps from consecutive image pairs can be averaged to reduce the random measurement noises (e.g., due to laser shot-to-shot variation and out-of-plane flow motion), and also each individual cross-correlation map can be obtained using the image pair separated with optimal time to further reduce the uncertainties due to other factors such as non-optimal in-plane velocity gradients and flow accelerations. The DISC method was validated both numerically and experimentally. The results illustrated that this method was able to enhance the accuracy of velocity measurements by 20.4–47.2% in terms of velocity error and by 7.8–22.9% in terms of non-physical Eulerian acceleration, compared to past multi-frame PIV methods.

Review and Analysis of Electro-Magnetohydrodynamic Flow and Heat Transport in Microchannels

This paper aims to develop a review of the electrokinetic flow in microchannels. Thermal characteristics of electrokinetic phenomena in microchannels based on the Poisson–Boltzmann equation are presented rigorously by considering the Debye–Hückel approximation at a low zeta potential. Several researchers developed new mathematical models for high electrical potential with the electrical double layer (EDL). A literature survey was conducted to determine the velocity, temperature, Nusselt number, and volumetric flow rate by several analytical, numerical, and combinations along with different parameters. The momentum and energy equations govern these parameters with the influences of electric, magnetic, or both fields at various preconditions. The primary focus of this study is to summarize the literature rigorously on outcomes of electrokinetically driven flow in microchannels from the beginning to the present. The possible future scope of work highlights developing new mathematical analyses. This study also discusses the heat transport behavior of the electroosmotically driven flow in microchannels in view of no-slip, first-order slip, and second-order slip at the boundaries for the velocity distribution and no-jump, first-order thermal-slip, and second-order thermal-slip for the thermal response under maintaining a uniform wall-heat flux. Appropriate conditions are conferred elaborately to determine the velocity, temperature, and heat transport in the microchannel flow with the imposition of the pressure, electric, and magnetic forces. The effects of heat transfer on viscous dissipation, Joule heating, and thermal radiation envisage an advanced study for the fluid flow in microchannels. Finally, analytical steps highlighting different design aspects would help better understand the microchannel flow’s essential fundamentals in a single document. They enhance the knowledge of forthcoming developmental issues to promote the needed study area.

Time‐dependent natural convection fluid flow of stably stratified fluid in an asymmetrically heated vertical channel filled with an anisotropic porous material

AbstractThis paper presents a theoretical analysis of the combined effects of anisotropic porous material and thermal stratification on the transient natural convection fluid flow in an asymmetrically heated vertical parallel channel. The solutions of the governing equations for the temperature and velocity fields are obtained using Laplace transform technique, Riemann sum approximation, and the D'Alembert method. The choice of the D'Alembert method is to provide a simple decoupling procedure for the coupled governing equations while still retaining their original orders. The research established that owing to the layering effect induced by the thermal stratification , the temperature and the velocity distributions of the fluid are found to be attenuated with an increase in thermal stratification. It is also observed that the inclusion of anisotropic parameters in the transport equations aids in regulating the fluid velocity, temperature, Nusselt number, skin friction, and mass flow rate. In addition, by neglecting the anisotropic parameter and taking into account the adiabatic stratification of the fluid, the numerical values for the mass flow rate of the present research favorably compared with the numerical results obtained by Singh et al.

Analysis of Fractional Thin Film Flow of Third Grade Fluid in Lifting and Drainage via Homotopy Perturbation Procedure

Analysis of thin film flows is an important topic in fluid dynamics due to the large number of industrial applications such as food processing, chip manufacturing, irrigation, oil refining process, painting finishing, etc. Analysis involves studying the effects of various parameters in absolute conditions. These parameters may be film thickness, volumetric flux, liquid velocity profile, viscosity, shear stress, gravity, density, and different boundary formations. We have expanded the formulations of non-Newtonian third grade fluid for lifting and draining in fractional space. Fractional calculus along with Homotopy Perturbation Method is used for the solution and analysis purposes. The suitability and consistency of the solutions is determined by detecting residuals in each case. Velocity profile, average velocity, and volume flow for lifting and drainage cases are calculated. To the best of authors knowledge, thin film flow of fractional third grade fluid is not attempted before in lifting and drainage. Investigation shows increase in value of fractional parameter that decreases the velocity profile in lifting while increases the velocity in drainage scenario. Also, the frictional parameter and the gravitational parameter have opposite, while material constant has direct relationship with the velocity profile in lifting case. All the parameters showed inverse effect on the velocity in drainage case.

Risk-averse design of tall buildings for uncertain wind conditions

Reducing the intensity of wind excitation via aerodynamic shape modification is a major strategy to mitigate the reaction forces on supertall buildings, reduce construction and maintenance costs, and improve the comfort of future occupants. To this end, computational fluid dynamics (CFD) combined with state-of-the-art stochastic optimization algorithms is more promising than the trial and error approach adopted by the industry. The present study proposes and investigates a novel approach to risk-averse shape optimization of tall building structures that incorporates site-specific uncertainties in the wind velocity, terrain conditions, and wind flow direction. A body-fitted finite element approximation is used for the CFD with different wind directions incorporated by re-meshing the fluid domain. The bending moment at the base of the building is minimized, resulting in a building with reduced cost, material, and hence, a reduced carbon footprint. Both risk-neutral (mean value) and risk-averse optimization of the twist and tapering of a representative building are presented under uncertain inflow wind conditions that have been calibrated to fit freely-available site-specific data from Basel, Switzerland. The risk-averse strategy uses the conditional value-at-risk to optimize for the low-probability high-consequence events appearing in the worst 10% of loading conditions. Adaptive sampling is used to accelerate the gradient-based stochastic optimization pipeline. The adaptive method is easy to implement and particularly helpful for compute-intensive simulations because the number of gradient samples grows only as the optimal design algorithm converges. The performance of the final risk-averse building geometry is exceptionally favorable when compared to the risk-neutral optimized geometry, thus, demonstrating the effectiveness of the risk-averse design approach in computational wind engineering.

Simultaneous desulfurization and denitrification of flue gas enabled by hydrojet cyclone

Boiler flue gas in the chemical industry contains SO2 and nitrogen oxides (NOx). These flue gases not only pollute the environment, but also seriously endanger human health. In this work, we studied the process of jet atomization and swirl enhancement. Then we constructed a miniaturized hydrojet cyclone. After that, we proposed a new type of flue gas purification technology to achieve integrated and efficient desulfurization and denitrification. All studies were based on combining the liquid jet field with the three-dimensional swirl field to increase the mass transfer area of the gas and liquid phases. The industrial sideline test results showed that the gas purification efficiency increased with the increase of inlet velocity and absorption liquid flow rate, Efficiency is always above 80%. Increasing the concentration of activator could significantly improve the desulfurization efficiency by 27%. Increasing the concentration of oxidant was beneficial to denitrification, and the maximum denitrification efficiency of methyldiethanolamine (MDEA) was 98.2%. Overall, this technology can not only help enterprises save maintenance and treatment costs, but also protect the environment by avoiding the harm caused by flue gas pollution.

CFD analysis of base drag reduction using indent modification in suddenly expanded nozzle

The total drag is the combination of skin friction, wave and base region drags. With all moving projectiles, rockets, missiles, and launch vehicles, the base pressure at the base or back face is a common concern. Base drag increase in unexpectedly bigger flows due to a sudden expansion of duct size at exhaust. At the duct’s outflow, the base pressure is vacuum or sub-atmospheric. To lower the base drag, the vacuum must be increased to near atmospheric pressure to reduce total drag. Base drag is undesirable since it accounts for a large portion of the total drag. The reduction in base drag benefits the space and defense programmers greatly. This is highly responsible to major losses of energy as a result of drag. Out of the different types of drag, base drag, commonly known as wake drag is responsible for increased drag in case of high velocity flow through the nozzles. Henceforth it is imperative to have drag reduction techniques. There are active or passive methods used to reduce base drag. The proper recovery of base pressure can be done by optimum indent geometry and position optimization. In this numerical analysis, different geometric shape and position indents are used on the exhaust duct so at to reduce base drag. It was found from the analysis that the outlet velocity radically alters from the inlet to outlet. Furthermore, the magnitude of velocity was high for the nozzle with a circular indent when compared with other indent geometries in the analysis.

Liver and heart failure: an ultrasound relationship.

Liver and heart are anatomically and patho-physiologically related. In heart failure (HF) the increased right atrial pressure and volume overload cause histological changes in hepatocytes, leading to a condition known as "congestive hepatopathy" (CH), with consequent variations in liver functioning and ultrasound (US) findings. CH has specifical US findings especially regarding venous vessels aspect, easily detecting by gray-scale study, but many others can be distinguished by Doppler analysis. Usually, hepatic veins look enlarged and hypocollassing, together with signs of portal hypertension (hepatomegaly, ascites, splenomegaly, porto-systemic collaterals). Typically, in CH Doppler findings regard alterations in venous vessel flow and arterial resistance (venous system hyperpulsatility, reduced velocity flow, high resistance index in hepatic arterial Doppler spectrum). Sometimes CH and other primary hepatopathy can coexist, and therefore some of the expected variations may not manifest: it allows suspecting an unknown underlying liver disease. At last, US technologies of more recent applications, even if not routinely used, allow investigating additional aspects such as elastography that detects changes in liver elasticity or contrastographic US, able to show differences in hepatic venous opacification. However, most of these US signs are not pathognomonic, and therefore a multidisciplinary clinical reasoning must not be lacking. The aim of the present review is to easily provide US signs of liver alterations in HF, in particular right heart failure with volume overload, suggesting including liver US in instrumental diagnosis and therapeutic monitoring of HF.

Effects of nitrogen dilution on flame characteristics and stability of lifted propane fire whirl

Nitrogen dilution effects on flame characteristics and stabilization mechanism were experimentally investigated in lifted propane fire whirls. A small rotating screen facility with finely controlled imposed circulation (Γ) and propane heat release rate (Q˙=2.0–4.0 kW) was used for experiments. The nitrogen volume fractions (φ) in the diluted propane flow ranged from 0 to 90%. The stereoscopic particle image velocimetry (SPIV) technique, as well as the synchronized color imaging technique, was utilized to obtain 3-D instantaneous velocity distributions of fire whirl. It was found that the initially anchored fire whirl (φ=0) could be lifted after attaining a critical value of φ in the propane flow. Three regimes, including the attached flame, the lifted flame, and extinction, were identified in φ-Г coordinates. The fire whirl could exhibit flame liftoff and flame attachment under the same φ and Г, depending on the initial flame state in the φ-Г plot. The flame liftoff height and the flame diameter increased, and the flame length decreased with increasing φ. SPIV measurement results showed that the axial velocity followed an S-shaped distribution in the vertical direction. The mean axial velocity conditioned at the instantaneous lifted flame base decreased with φ and increased with Γ. The stable equilibrium was achieved at the locations where the flame propagation velocity and the axial velocity were roughly balanced, and the axial velocity curve had a negative slope with height. The variations of φ and Γ could change the flame liftoff height by breaking the local balance between flame propagation velocity and gas flow velocity. In addition, the peak value in the axial velocity curve, which was related to Γ, strongly affected the transitions among the different regimes.

Experimental investigation of the effects of shrub filter strips on debris flow trapping and interception

Ecological engineering plays an increasingly significant role in mountain hazard control, but the effect of species selection and arrangement (e.g., row spacing and stem spacing) on debris flow suppression is still unclear. To further understand the interception efficiency of shrub arrangement parameters on debris flow and explore the difference with slow hydraulic erosion, sixteen sets of small-scale flume experiments with different stem and row spacings were done to study the effects of shrubs on debris flow severity, flow rate, velocity, and particle size. The results suggest that, for a dilute debris flow, sediment interception effectiveness (27.4%–60.9%) decreases gradually as stem spacing increases. Moreover, as row spacing increases, flow velocity reduction (34.4%–44.9%) and flow reduction (18.5%–47.4%) gradually decrease; and the bulk density reduction (0.5%–5.3%) and sediment interception increase initially and then decrease. In contrast, for a viscous debris flow, the flow reduction, flow velocity reduction, and sedimentation interception decrease gradually as the stem spacing increases. As row spacing increases, the flow velocity reduction, flow reduction, and sediment interception all increase initially and then decrease. A formula for the flow velocity of dilute debris flow after the filter strip was derived based on the energy conservation law and Bernoulli's equation, confirming that debris flow movement is closely related to the degree of vegetation cover. This research strengthens the current understanding of the effectiveness of vegetation in debris flow disaster prevention and control and can guide practical applications.

Coupled VOF and Level-Set methods for simulating nozzle geometry effect on axisymmetric water jet breakup

In this work, a numerical investigation of nozzle geometry effect on axisymmetric water jet breakup by coupling the Volume-Of-Fluid (VOF) method with Level-Set (LS) was carried out. Through this coupling, the benefit from the advantages of both approaches in order to get better results is realized. The impact of two nozzle geometries (cone-up and cone-down configurations) on the characteristics of water jets flow downstream of the nozzle has been discussed for pressures below 172 bars. Flow was assumed to be two dimensional, viscous, incompressible, and unsteady. Velocity distributions, turbulence sensitivity, and flow discharge coefficient Cd was examined as a function of Reynolds number and injection pressure. CFD simulations have been validated with the published experimental data of Vahedi et al. and Ghassemieh et al. After simulation, it can be found that the calculated solutions are in good agreement with experiment data. The agreement between the calculations and the experimental data indicates that the model provides a good prediction of the discharge coefficient. The pressure injection and turbulence have a great influence on the velocity profile and the intact length.

Study on the Recommended Placement and Air Distribution of Split Floor-Standing Room Air Conditioners

In recent years, split floor-standing room air conditioners have been widely used in civil and office buildings because of their high cooling capacity and easy installation, and the air draft sensation has attracted more and more attention. In this study, a target air supply evaluation index for regional thermal comfort evaluation in the work area, the air velocity target value, is proposed. A computational fluid dynamics model for common office is established, and a total of 204 working conditions are numerically simulated for each combination of different positions, different rotation angles, and different air supply velocities (1 m/s, 2 m/s and 3 m/s) of air conditioners in the room. The influence of the rotation angle of the air conditioner on the indoor air distribution was studied, and the distribution of the indoor velocity flow field at different positions was analyzed. The air-conditioning rotation angle that makes the velocity target value of the five preset planes in the room smaller under different conditions is summarized as the recommended rotation angle. The numerical simulation results were verified by experimental means and found to be consistent with the measured results. This study can provide theoretical guidance and reference for the placement of indoor air conditioning units for users in real life.