Velocity Distribution Research Articles

Effect of horizontal magnetic field position on oxygen distribution in CZ silicon crystal growth

The horizontal magnetic field-assisted Czochralski(CZ) method is gaining significant popularity in the semiconductor industry for producing 200 mm semiconductor-grade silicon wafers. In this study, the impact of the horizontal magnetic field position on the oxygen content and radial uniformity of semiconductor-grade silicon crystals produced by the CZ method was investigated. Three-dimensional simulations were conducted using finite element software to calculate the melt convection and oxygen content before and after adjustment of the magnetic field position, respectively. The simulations results predicted a decrease in the oxygen content of the crystals following the adjustment of the magnetic field position from 0 to 75 mm below the free surface, and this was experimentally verified. The velocity distribution of the free melt surface exhibits better uniformity when lowering the magnetic field position. The influence of the magnetic field position on the temperature distribution and Marangoni flow in the melt was investigated, and the result of oxygen concentration difference identified the adjustment of the magnetic field position promoted the greater Marangoni flow below the free melt surface, which promoted the volatilization of SiO gas and thus reduced the oxygen concentration in the silicon ingot. Therefore, adjusting the position of the magnetic field is an effective way to increase the Marangoni flow and to obtain semiconductor-grade silicon crystal with lower oxygen content and better oxygen radial homogeneity.

Hydraulic performance assessment on dynamic fluidic and complete fluidic sprinklers under indoor and outdoor conditions

Since Complete Fluidic Sprinklers (CFS) cannot function well in low-pressure environments, Dynamic Fluidic Sprinkler (DFS) were developed to address this issue. In 2021, research in the field and laboratory were conducted to examine how well DFS and CFS performed hydraulically in both indoor and outdoor conditions. In this investigation, a Thiess Clima laser precipitation monitor was used to evaluate the droplet size and velocity distribution of two different types of sprinklers indoors. From the findings, DFS velocities ranged from 0.1 to 4 m/s whereas CFS ranged from 0.1 to 5.3 m/s. The maximum frequency value was obtained at velocities of 1 m/s for each combination. The DFS had a slightly greater discharge coefficient and spray pattern than the CFS. The DFS's maximum spray range was 12.2 m, while the CFS's maximum spray range was 10.8 m, with standard deviations of 1.07 and 1.66, respectively. Under high wind speed conditions, the maximum combined Coefficient of Uniformity (CU) of DFS and CFS were 81.1% and 78%, respectively. For a given pressure and sprinkler spacing, DFS delivered higher CU values than CFS, especially while running at low pressure, demonstrating that DFS offered a more favoured water distribution pattern at low pressure. At different distances from the sprinkler, the highest application rates for DFS and CFS were 6.7 mm h−1 at 7 m and 6.5 mm h−1 at 7 m, respectively. A comparison of DFS and CFS under hydraulic performance indicated that DFS had a better performance than CFS. The study can serve as a guide for how to conserve water in sprinkler-irrigated fields.

Probing the dark matter velocity distribution via daily modulation

We consider dark matter velocity distributions with an anisotropic component, and analyze how the velocity structure can be probed in a solid-state ionization detector with no directional detection capability using a daily modulation effect due to the anisotropic response function of the target. We show that with an energy resolution of <10 eV it is possible to identify the presence of an anisotropic component consistent with observations for sub-GeV dark matter, and that introduction of daily modulation information substantially improves the sensitivity in a narrow mass range. Published by the American Physical Society 2024

Analytical solution to boundary layer flow and convective heat transfer for low Prandtl number fluids under the magnetic field effect over a flat plate

AbstractThe present study aims to quantify the flow field, flow velocity, and heat transfer features over a horizontal flat plate under the influence of an applied magnetic field, with a particular emphasis on low Prandtl number fluids. Nonlinear partial differential expressions can be incorporated into the ordinary differential framework with the use of appropriate transformations. This research utilizes the variational iteration method (VIM) to approximate solutions for the system of nonlinear differential equations that define the problem. The objective is to demonstrate superior flexibility and broader application of the VIM in addressing heat transfer issues, compared to alternative approaches. The results obtained from the VIM are compared with numerical solutions, revealing a significant level of accuracy in the approximation. The numerical findings strongly suggest that the VIM is effective in providing precise numerical solutions for nonlinear differential equations. The analysis includes an examination of the flow field, velocity, and temperature distribution across various parameters. The study found that improving temperature patterns, velocity distribution, and flow dynamics were all positively impacted by increasing the Prandtl numbers. As a result, this leads to the thickness of the boundary layer to decrease and improves heat transfer at the moving surface. Thus, the convection process becomes more efficient. When the strength of the magnetic field is increased, the velocity of the fluid decreases. This observation aligns with expectations since the magnetic field hampers the natural flow of convection. Notably, the convection process can be precisely controlled by carefully applying magnetic force.

Methods for obtaining the actual radial distribution of the fragment velocity through X-ray photography

Short charges are typically used in the measurement of radial fragment velocity distributions by pulsed X-ray photography, due to the arrangement constraint of X-ray tubes. However, the radial velocity distribution of the one-line asymmetrical initiation was found to be significantly influenced by the end rarefaction waves. This means that the fragment velocity distribution measured using short charges cannot reflect the real influence of the initiation styles or warhead designs. This study proposes new methods for measuring the radial velocity distribution using X-ray photography while eliminating the effect of end-rarefaction waves. It can provide important references for related X-ray test methods and the development of high-lethality warheads.

Embedded large eddy simulation of boundary layer transition behind a micro-ramp

Boundary layer transition induced by surface roughness elements plays an important role in aerodynamic and aero-thermodynamic design of subsonic/supersonic/hypersonic vehicles. However, the effect of three-dimensional isolated roughness element in the process of promoting/suppressing boundary layer transition is far from being fully understood, particularly in the incompressible laminar flow. In the present study, the laminar-to-turbulent transition induced by a three-dimensional isolated micro-ramp element immersed in an incompressible laminar boundary layer is investigated numerically. The embedded large eddy simulation (ELES) combining the intermittency transition model and the wall-modeled large eddy simulation (WMLES) S − Ω model is employed for the first time. Numerical results on the time-averaged/instantaneous flow field and the statistical flow fluctuations are analysed and validated thoroughly by the existing experimental measurements. It is found that the interaction of the secondary and the tertiary streamwise vortices causes a high level of wall shear and an inflectional velocity distribution in the near-wall region. An additional eddy system that develops nonlinearly from the unstable inflectional flow may trigger the boundary layer transition. The present study validates that the ELES combined with the WMLES S − Ω model is an efficient simulation tool for industrial wall-bounded flows allowing effective compromise between flexibility, cost, and accuracy.

Peristaltic transport of diethylene glycol-based magnesium aluminate nanofluid under the effects of viscous dissipation and Hall current

ABSTRACT The fundamental importance of peristaltic phenomena in numerous biological systems, including dialysis, heart-lung machines, urine transportation, invertebrate locomotion, and the passage of gallbladder bile into the intestines, persuaded scientists to investigate the different aspects of it over the past few years. In addition, peristaltic pumping is an important consideration in industrial processes including, roller pumps used for the transport of sanitary materials, finger pumps, cell separation, and endoscopes. Keeping such inspirational applications in mind, the present investigation is dedicated to exploring the peristaltic transport of a Cross-magneto nanofluid through a curved geometry in the presence of heat transfer. The inspection of the heat transfer is conducted by utilizing variable viscosity and ohmic heating aspects. This study also retains the characteristics of viscous dissipation, heat generation/absorption, and thermal conductivity of nanofluids. Modeling of the 2D, incompressible Cross nanofluid with peristaltic movement is carried out using a curvilinear coordinate system. The basic equations of the problem are mPodeled in the light of physical laws and then simplified by adopting the lubrication theory. The solutions of the resulting nonlinear system are computed numerically. The outcomes of the related flow parameters on the nanofluid’s temperature, pressure gradient, velocity distribution, heat transfer, streamlines pattern, and stresses at the wall are discussed through graphs. The graphical results depict that the rates of heat transfer are augmented by increasing the curvature parameter, Hartmann number, and nanoparticles’ volume fraction while decreasing the Hall parameter and temperature-dependent viscosity parameter. Moreover, the nanofluid’s temperature increases by improving the values of the heat generation parameter, whereas it decreases for the Hall parameter. Furthermore, a reduction in the axial velocity occurs near the center of the channel, when Hartmann number attains higher values.

Comparative Evaluation of Dissolution Performance in a USP 2 Setup and Alternative Stirrers and Vessel Designs: A Systematic Computational Investigation.

The dissolution testing method described in the United States Pharmacopeia (USP) Chapter ⟨711⟩ is widely used for assessing the release of active pharmaceutical ingredients from solid dosage forms. However, extensive use over the years has revealed certain issues, including high experimental intervariability observed in specific formulations and the settling of particles in the dead zone of the vessel. To address these concerns and gain a comprehensive understanding of the hydrodynamic conditions within the USP 2 apparatus, computational fluid dynamic simulations have been employed in this study. The base design employed in this study is the 900 mL USP 2 vessel along with a paddle stirrer at a 50 rpm rotational speed. Additionally, alternative stirrer designs, including the hydrofoil, pitched blade, and Rushton impeller, are investigated. A comparison is also made between a flat-bottom tank and the USP round-bottom vessel of the same volume and diameter. Furthermore, this work examines the impact of various parameters, such as clearance distance (distance between the bottom of the impeller and bottom of the vessel), number of impeller blades, impeller diameter, and impeller attachment angle. The volume-average shear rate (Stv), fluid velocity (Utv), and energy dissipation rates (ϵtv) represent the key properties evaluated in this study. Comparing the USP2 design and systems with the same stirrer but flat-bottom vessel reveals more homogeneous mixing compared to the USP2 design. Analyzing fluid flow streamlines in different designs demonstrates that hydrofoil stirrers generate more suspension or upward movement of fluid compared to paddle stirrers. Therefore, when impellers are of a similar size, hydrofoil designs generate higher fluid velocities in the coning area. Furthermore, the angle of blade attachment to the hub influences the fluid velocity in the coning area in a way that the 60° angle design generates more suspension than the 45° angle design. The findings indicate that the paddle stirrer design leads to a heterogeneous shear rate and velocity distributions within the vessel compared with the other designs, suggesting suboptimal performance. These insights provide valuable guidance for the development of improved in vitro dissolution testing devices, emphasizing the importance of optimized design considerations to minimize hydrodynamic variability, enhance dissolution characterization, and reduce variability in dissolution test results. Ultimately, such advancements hold potential for improving in vitro-in vivo correlations in drug development.

A Simulation Study of Hybrid Solar Drying Chamber for Agriculture Product

Hybrid solar drying chamber is an application that is widely used today for agriculture products because it can promise the hygiene of the product. However, drying chambers nowadays still lack uniformity in drying products within a drying chamber, leading to food wastage and compromised product quality. This study aims to design an innovative hybrid solar drying chamber system and investigate the uniformity of temperature and velocity within the chamber using Computational Fluid Dynamics (CFD). The methodology involves validating the simulation results by comparing them with existing journal data, with a validation error of less than 5%. A new design is proposed after the validation process, considering factors such as tray arrangement and air inlet size. The results show that a tray arrangement with 0.20 m spacing between each tray provides better uniformity in temperature and air velocity distribution compared to other arrangements. Additionally, an inlet size of 0.05 m2 demonstrates the most suitable temperature distribution for drying purposes, falling within the ideal range of 318 K to 343 K. The study showed that the performance of the drying chamber under different operating conditions has consistent temperature distribution and is suitable for uniform drying. Overall, the proposed hybrid solar drying chamber system offers improved temperature control and uniformity for effective drying process.

Study on Flow Characteristics of Integrated Natural Circulation Reactor Under Inclined Conditions

In order to study the flow characteristics of an integrated natural circulation reactor under inclined conditions, a typical three-dimensional analysis model of natural circulation was established. The natural circulation under inclined conditions was numerically simulated using the computational fluid dynamics method, and the velocity and temperature distribution characteristics of heat exchangers and mixed-flow channels with different inclined angles were analyzed. The results show that as the inclination angle of the heat exchanger flow rate increases, there is a spatial migration phenomenon corresponding to the direction of the average flow rate. A large inclination angle will lead to a serious deterioration of the natural circulation capacity in the lower channel. Under inclined conditions, there is a phenomenon of temperature stratification in the mixed-flow channel.

Analytical Solution for MHD Casson Nanofluid Flow and Heat Transfer due to Stretching Sheet in Porous Medium

The feature of having a surface that can stretch has garnered attention in numerous industrial and engineering fields because of its advantages. Nevertheless, most fluid mechanics simulations for stretchable surfaces have predominantly relied on numerical solutions, with a notable lack of theoretical investigations into this matter. Consequently, the current research aims to contribute a theoretical exploration of heat transfer and boundary layer flow for Casson nanofluid on a linearly stretching sheet, considering the existence of porosity and magnetic field effects. Two distinct types of water-based nanofluids containing aluminium oxide and silicon dioxide are examined. By employing similarity transformations, the governing momentum and energy equations undergo transformation and subsequent analytical resolution using Laplace transformations. The resulting solutions are graphically presented to examine the influence of key parameters on temperature and velocity distribution. The analysis indicates that heat transfer is improved by the inclusion of nanoparticles, porosity, and a magnetic field. However, the velocity distribution slows down as a result of higher nanoparticle volume fraction, porosity, and magnetic field imposition.

Unsteady MHD dusty fluid flow over a cone in the vicinity of porous medium: a numerical study

This research presents an unsteady free convection magnetohydrodynamics (MHD) dusty fluid flow over a vertical cone enclosed inside a porous medium. The Crank–Nicolson approach is used to get the numerical solutions for these non-linear partial differential equations (PDEs). The velocity and temperature distributions are graphed numerically for a wide range of physical parameters to highlight important characteristics of the solutions. The results showed that increasing the porosity parameter leads to a rise in the velocity profile for the fluid and dust phases, while doing the reverse with the rise of the magnetic parameter, fluid-particle interaction parameter, and mass concentration of the particle phase parameter. Additionally, it is shown that the temperature profile rises as the magnetic parameter and the mass concentration of particle phase parameter grow, whereas the fluid-particle interaction parameter and porosity parameter show the opposite tendency.

Nonlinear heat radiation and mass transfer characteristics on MHD Walters’ B fluid flow through a porous medium over a stretching sheet

To handle the continuous thermal power supply is very important in thermal systems and industries, so magnetized heat transport with non-Newtonian fluid is an appropriate platform for thermal power energy. In view of this usefulness, this paper provides a numerical assessment of electrically conducting Walter's B fluid flow through nonlinear permeable stretching sheet subject to mixed convective, porous medium, and Newtonian heating phenomena. Thermophoresis and Brownian motion effects have been included in energy and species diffusion equations to account for the impacts of nonlinear thermal radiation, joule heating, heat source and chemical reaction. The system of governing equations has been reduced to dimensionless nonlinear coupled equations using similarity transformations. The bvp4c technique has been used to obtain the solution for velocity, temperature, and concentration distributions. We consider both regions of assisting and opposing flow and provide various tables and graphs to examine the impact of varying values of emerging factors. Heat source and thermal radiation characteristics are found to enhance the thermal boundary layer thickness, which may be used to dissipate heat. The magnetic parameter augmented the fluid temperature and decelerated the velocity field. The chemical reaction parameter accelerated the concentration distribution. Further, the Sherwood number, Nusselt number, and skin friction coefficient have been determined and compared well to prior research that has been published.

Velocity (μPIV) and temperature/concentration (μLIF) measurements in a dual serpentine microchannel of a micro DMFC stack

Herein, we present an experimental study of the flow, as well as the thermal and concentration characteristics of two serpentine microchannels, via micro particle image velocity/micro laser induced fluorescence optical visualization techniques, which simulate the flow channels at the anode of a typical micro direct methanol fuel cell stack (two cells: Cell A/B). The flow channel consists of two serpentine microchannels. Each channel has one channel and six paths. Channels A and B were connected by a connecting tube to create an entire flow loop with methanol as the working fluid. The velocity, temperature and concentration distribution along the channel downstream for 5.7 ≤ Re ≤ 594 were visualized and measured. At a particular operation condition of methanol flow rate of 1 ml/min and concentration of 1 M at stack temperature of 25 °C, both in series and parallel arrangements were examined with a peak power density of 61.4 mW/cm2 (current density 120 mA/cm2 and voltage 1.0 V) and of 75 mW/cm2 (current density 120 mA/cm2 and voltage 1.2 V), respectively. CO2 ellipse-like bubbles were found at the up/down stream corners with a definite major/minor axis length. Furthermore, relevant (f, Nu, and Sh) correlations regarding the relationship of the methanol solution pumping power, heat transfer and utilization with Reynolds number in form of power law were developed with 95 % accuracy of experimental data. With these related results, it might be beneficial to the configuration design of the μDMFC stack.

Tightly Trapped Atom Interferometer inside a Hollow-Core Fiber

We demonstrate a fiber-guided atom interferometer in a far-off-resonant trap (FORT) of 100 μK. The differential light shift (DLS) introduced by the FORT leads to the inhomogeneous dephasing of the tightly trapped atoms inside a hollow-core fiber. The DLS-induced dephasing is greatly suppressed in π/2-π-π/2 Doppler-insensitive interferometry. The spin coherence time is extended to 13.4 ms by optimizing the coupling of the trapping laser beam into a quasi-single-mode hollow-core anti-resonant fiber. The Doppler-sensitive interferometry shows a much shorter coherence time, indicating that the main limits to our fiber-guided atom interferometer are the wide axial velocity distribution and the irregular modes of the Raman laser beams inside the fiber. This work paves the way for portable and miniaturized quantum devices, which have advantages for inertial sensing at arbitrary orientations and in dynamic environments.

Heat transfer performance and electrohydrodynamic characteristics optimization of a dividing-wall-type ionic wind heat exchanger

Heat exchangers play a major role in reducing emissions and conserving energy. There is a plethora of theoretical research on the enhancement of heat transfer caused by ionic wind, but there is still a lack of studies on the practical application of ionic wind in heat exchangers to increase heat exchange capacity. This work developed an original ionic wind heat exchanger with a dividing wall. It may be applied to difficult circumstances when conventional heat exchangers fail for air-to-air heat exchange. The study conducted experiments to investigate the impact of many factors, including intake air velocity, discharge spacing, and electrode distribution scheme, on the ionic wind intensity and the heat exchanger's increased heat transfer coefficient. A two-dimensional model was used to analyze the internal flow and thermal properties of the heat exchangers with wire emitters. By combining active and passive heat exchange technologies, an ionic wind heat exchanger with serrated grounded electrodes was presented. The outcomes demonstrated that a suitable intake air velocity enhances the heat exchanger's capacity for heat exchange. The improved heat exchange effect of ionic wind is more important when the inlet wind speed is less than 1 m/s. When the intake air velocity approaches 1.3 m/s, the ionic wind has less of an impact on the heat exchanger's capacity for heat exchange. The benefits of improved heat transfer are promoted by placing the emitter closer to the channel entry. Increasing the operating voltage further enhances the heat transfer enhancement ratio (HTER). The number and arrangement of wire electrodes should be chosen with consideration for the 'barrier effect' between neighboring emitters and the distance from the entrance when utilizing multiple wire electrodes. In comparison to the three-wire and five-wire electrodes, the four-wire electrode heat exchanger's HTER values were increased by 5.9 % and 14.3 %, respectively. The ionic wind heat exchanger's capacity for heat transfer is further increased using a zigzag grounding electrode. The zigzag uses a decreased aspect ratio, and the emitter is positioned slightly above the tip, improving the system's heat transfer capabilities. When compared to a heat exchanger with a flat plate grounded electrode, the four-wire electrode heat exchanger produced a 158 % increase in HTER value.

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode.

Controlling the ion velocity in an ion sheath by applying an alternating current (AC) voltage to an electrode and/or a substrate is critical in plasma material processes. To externally control the velocity distribution of incident ions on a substrate, the application of tailored-waveform AC voltages instead of sinusoidal voltages has garnered interest in recent years. In this study, to investigate temporal changes in ion-velocity distributions, we developed a time-resolved laser-induced fluorescence spectroscopy (LIF) system using a continuous-wave diode laser as an excitation-laser source. A time-resolved LIF system entails the capture of temporally continuous and spectrally discrete LIF spectra during an AC voltage cycle. By measuring temporal changes in the LIF signal intensity at various excitation-laser wavelengths, the argon-ion velocity distribution near the electrode following the AC voltage can be characterized. The results of applying sinusoidal, triangular, and rectangular bias waveforms indicate that the LIF measurement scheme proposed herein can be used to investigate the dynamic behavior of ion-velocity distributions controlled by tailored-waveform AC voltages.

Numerical study of bubble rise in plunging breaking waves

During the occurrence of plunging wave breaking, a substantial number of multi-scale bubbles are generated. These submerged bubbles persist for extended periods and contribute to the distinct acoustic and optical characteristics of the wake. In this study, we utilize high-fidelity simulations, combined with the adaptive refinement strategy to accurately track bubbles of multi-scales during the entire rising stage. Unlike previous studies, our emphasis is specifically on investigating the process of bubble rising during plunging wave breaking. Comprehensive statistical analyses are performed and characteristics of bubbles across various scales are also provided. Our findings reveal that most bubbles are concentrated in small scales, while larger bubbles rapidly ascend to the surface or undergo fragmentation into smaller bubbles through breaking cascades eventually. A distinct stratification of bubble size distribution along the depth direction is observed. Bubble velocity distributions are also important characteristics that are frequently neglected in studies of plunging wave breaking. Bubbles primarily spread along the spanwise direction, with a uniform distribution of velocity in this dimension. The velocity distribution of bubbles displays asymmetric tails that extend to higher velocities, and within this high-velocity regime, a power law behavior is observed, similar to the size distributions. Ultimately, the flow field is left with only a few small bubbles, moving at an exceedingly low speed. Furthermore, dynamical evolution of bubble rise in plunging wave breaking is described in detail and we analyze the intricate interactions between bubbles and turbulent flows. We observe that vortices are predominantly generated in close proximity to the bubbles, and bubble motion plays a crucial role in initiating turbulent flows. Simultaneously, these vortices contribute to the fragmentation of large-scale bubbles, transforming them into smaller counterparts due to turbulent fluctuations.

Research on bionic foldable spray aircraft wings

In this paper, the hind wing of Coccinella septempunctata is selected as the research object to design the bionic foldable spray aircraft wing. The structure of the bionic wing, the related flapping mechanism, the folding mechanism and other aircraft components are designed, and the two key parts of the bionic wing and arm are statically analyzed and optimized. To reduce the vibration in flight, modal analysis of the bionic wing and arm is carried out, and the natural frequencies and modes of the two parts are explored. The results show that the lower natural frequency has the greatest influence on the dynamic characteristics of the components. The influence of the material properties on the modal characteristics is studied by changing the material characteristics of the components. The flow around the bionic wing is simulated by FLUENT software. The velocity distribution and pressure distribution of the flow field around the bionic wing are obtained. The influence of aerodynamics with attack angle α is analyzed to clarify the flight principle of the bionic wing.

Flow dynamics through cellular material based on a structure with triply periodic minimal surface

Triply Periodic Minimal Surface (TPMS)-based cellular structures are widely adopted due to their high surface-to-volume area, superior mechanical characteristics, and adaptive properties. This paper is dedicated to deriving a new semi-empirical equation for pressure drop in TPMS-based structures (specifically Schwarz-P, Schoen I-WP, Neovius). Both numerical and experimental tests were conducted to analyze the impact of TPMS parameters on pressure drop and velocity distribution. It was determined that flow through the Schwarz-P structure exhibits a tubular flow pattern, flow through the Neovius structure demonstrates active flow mixing, and flow through the Schoen I-WP structure does not have stagnant (dead) zones. A novel semi-empirical equation was formulated to calculate pressure drop as a function of flow parameters and TPMS-based structure parameters. This equation incorporates both viscous resistance (Δp=f(v)) and kinetic energy loss (Δp=f(v2)), enabling its application for predicting pressure drop across a wide range of practically interesting operational parameters.