Numerical Simulation of Intermittent-Controlled Multiple Jets

2019 ◽  
Author(s):  
Koichi Tsujimoto ◽  
Kango Kitahara ◽  
Toshihiko Shakouchi ◽  
Toshitake Ando
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Near Field ◽  
Vortex Structures ◽  
Mixing Efficiency ◽  
Intermittent Control ◽  
Mixing Performance ◽  
Multiple Jets ◽  
Inflow Condition ◽  
And Diffusion

Abstract Multiple jets are used in industrial processes such as combustion, ventilation and so on, and their improvement of mixing and diffusion is demanded. Unlike single jet, since the jets issuing from nozzles will coalescence, merge or combine with each other, it is necessary to reduce mixing performance such as entrainment from surroundings and spreading into surroundings. It is well known that the characteristics such as mixing and diffusion of the jet are strongly dependent on the large-scale vortex structures being formed near the nozzles. Therefore, an appropriate inflow condition at a nozzle is capable of controlling the large vortex structures near field around the nozzle and improves the mixing performance. In this study, we examine an intermittent control of jets varying the control frequency and the jet spacing so as to reduce the interaction between each jet. We conduct the DNS (direct numerical simulation) of intermittently-controlled two round jets. In order to quantify the mixing efficiency of the intermittent control, statistical entropy and entrainment are examined. Compared to the uncontrolled jet, it is confirmed that the mixing efficiency is markedly improved, suggesting that the intermittent control can be expected to be useful for the improvement of mixing performance of multiple jets.

A NOVEL 3D MICROMIXER WITH QUARTIC KOCH CURVE FRACTAL

2021 ◽  
pp. 2150049
Author(s):  
SIYUE XIONG ◽  
XUEYE CHEN
Keyword(s):  
Numerical Simulation ◽  
Deflection Angle ◽  
Reynolds Numbers ◽  
Mixing Efficiency ◽  
Flow State ◽  
Koch Curve ◽  
Mixing Performance ◽  
Chaotic Convection ◽  
The Deflection Angle ◽  
High Application

In this paper, we mainly study the mixing performance of the micromixer with quartic Koch curve fractal (MQKCF) by numerical simulation. Changing the structure of the microchannel based on the fractal principle can significantly improve the fluid flow state in the microchannel and improve the mixing efficiency of the micromixer. This paper discussed the effects of different fractal deflection angles, microchannel heights and different fractal times on the mixing efficiency under four different Reynolds numbers (Re). It is found that changing the deflection angle of the fractal can bring extremely high benefits, which makes the fluid deflect and fold in the microchannel, enhancing the chaotic convection in the microchannel, and improve the mixing efficiency of the fluid. Under the reasonable arrangement of the quartic Koch curve fractal principle, it can give the micro-mixture more than 99% mixing efficiency. Based on the excellent mixing performance of MQKCF, it also has extremely high application value in the biochemical neighborhood.

Numerical simulation of three-dimensional passive micromixer based on the principle of Koch fractal

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Siyue Xiong ◽  
Xueye Chen
Keyword(s):  
Numerical Simulation ◽  
Fluid Flow ◽  
Cross Section ◽  
Three Dimensional ◽  
Mixing Efficiency ◽  
Mixing Performance ◽  
Chaotic Convection ◽  
Passive Micromixer ◽  
Koch Fractal ◽  
Koch Fractal Principle

Abstract In this paper, We arrange the obstacles based on the Koch fractal principle (OKF) in the micromixer. By changing the fluid flow and folding the fluid, a better mixing performance is achieved. We improve the mixing efficiency by placing OKF and changing the position of OKF, then we studied the influence of the number of OKF and the height of the micromixer on the mixing performance. The results show that when eight OKF are staggered in the microchannel and the height is 0.2 mm, the mixing efficiency of the OKF micromixer can reach 97.1%. Finally, we compared the velocity cross section and velocity streamline of the fluid, and analyzed the influence of OKF on the concentration trend. Through analysis, it is concluded that OKF can generate chaotic convection in the fluid, and enhance the mixing of fluids by generating vortices and folding the fluid. It can effectively improve the mixing efficiency of the micromixer.

Numerical Mixing Analysis of a Vaned Circular Micromixer

2006 ◽  
Author(s):  
Richard Bergman ◽  
Alexander Efremov ◽  
Pierre Woehl
Keyword(s):  
Numerical Analysis ◽  
Turbulent Mixing ◽  
Parametric Study ◽  
Large Scale ◽  
Acceptable Level ◽  
Mixing Efficiency ◽  
Mixing Process ◽  
Mixing Performance ◽  
Numerical Mixing ◽  
Cutting And Stacking

Mixing of fluids is a common and often critical step in microfluidic systems. In typical large scale processes turbulence greatly speeds the mixing process. At the mini and micro-scales, however, the flow is laminar and the benefits of turbulent mixing are not present. Mixing at the mini- and micro-scales tends to become a more highly engineered process of bringing fluids together in predictable ways to achieve a predetermined and acceptable level of mixing. This paper summarizes a numerical analysis of the mixing performance of a vaned circular micromixer. A newly developed mixing metric suitable for reacting fluids is developed for this study. Applying the basic steps of stretching, cutting, and stacking to effect mixing, a useful micromixer is analyzed numerically for its mixing efficiency. A parametric study of flow and viscosity indicate that a flow Re of 12 or higher is sufficient to achieve effective and rapid mixing in this device.

Numerical Simulation of Micromixing with Isolate Bubbles in Microfluidic Flow-Focusing Devices

2013 ◽  
Vol 781-784 ◽  
pp. 2876-2880
Author(s):  
Liang Yao Su ◽  
Yue Yang ◽  
Zhong Bin Xu
Keyword(s):  
Numerical Simulation ◽  
Phase Difference ◽  
Microfluidic Devices ◽  
Mixing Efficiency ◽  
Flow Focusing ◽  
Velocity Amplitude ◽  
Mixing Performance ◽  
Microfluidic Flow ◽  
Best Value ◽  
Two Parameter

Microbubbles play an important role in the micromixing of micro-fluidic systems. However, there are few results in the literature about the mixing of the liquids caused by bubbles flow. The paper presents the numerical simulation of bubbles flow in microfluidic, which agrees well with the experimental results. The influence of velocity amplitude, frequency and phase difference on the mixing performance was investigated. The results show that the isolate bubbles as obstruction can improve mixing efficiency in the true straight microchannel, the bigger the velocity amplitude, and the higher the frequency, the better the mixing efficiency is, but the mixing efficiency has nothing to do with the number of bubbles and just benefit from the certain phase difference. With the other two parameter remains unchanged, the mixing performance achieves the best value when the velocity amplitude is 0.25m/s, the frequency is 25HZ, the phase difference is 0.25, respectively. The study referring to bubbles flow induced mixing performance is very important for many microfluidic devices.

ON IMPACT OF LARGE-SCALE VORTEX STRUCTURES ON FLAME SHAPE IN A SWIRLING JET FLOW

2018 ◽  
Vol 11 (2) ◽  
pp. 31-39
Author(s):  
L. М. Chikishev ◽  
◽  
V. М. Dulin ◽  
A. S. Lobasov ◽  
D. М. Markovich ◽  
...  
Keyword(s):  
Large Scale ◽  
Jet Flow ◽  
Vortex Structures ◽  
Swirling Jet ◽  
Large Scale Vortex ◽  
Flame Shape

Accidental Sustainability

2017 ◽  
Author(s):  
Geoffrey Jones
Keyword(s):  
Large Scale ◽  
Negative Impact ◽  
Positive Impact ◽  
Organic Food ◽  
The United States ◽  
Air Travel ◽  
Business Leaders ◽  
Natural Beauty ◽  
And Diffusion ◽  
Whole Foods

This chapter examines the scaling and diffusion of green entrepreneurship between 1980 and the present. It explores how entrepreneurs and business leaders promoted the idea that business and sustainability were compatible. It then examines the rapid growth of organic foods, natural beauty, ecological architecture, and eco-tourism. Green firms sometimes grew to a large scale, such as the retailer Whole Foods Market in the United States. The chapter explores how greater mainstreaming of these businesses resulted in a new set of challenges arising from scaling. Organic food was now transported across large distances causing a negative impact on carbon emissions. More eco-tourism resulted in more air travel and bigger airports. In other industries scaling had a more positive impact. Towns were major polluters, so more ecological buildings had a positive impact.

A proposed wavy shield for suppression of supersonic jet noise utilizing reflections

2021 ◽  
Vol 20 (1-2) ◽  
pp. 4-34
Author(s):  
Reda R Mankbadi ◽  
Saman Salehian
Keyword(s):  
Large Scale ◽  
Flat Surface ◽  
Near Field ◽  
Supersonic Jet ◽  
Jet Noise ◽  
Dominant Frequency ◽  
Wavy Surface ◽  
Initial Region ◽  
Reflected Waves ◽  
Free Jet

In this work we propose replacing the conventional flat-surface airframe that shields the engine by a wavy surface. The basic principle is to design a wavy pattern to reflect the incoming near-field flow and acoustic perturbations into waves of a particular dominant frequency. The reflected waves will then excite the corresponding frequency of the large-scale structure in the initial region of the jet’s shear layer. By designing the frequency of the reflected waves to be the harmonic of the fundamental frequency that corresponds to the radiated peak noise, the two frequency-modes interact nonlinearly. With the appropriate phase difference, the harmonic dampens the fundamental as it extracts energy from it to amplify. The outcome is a reduction in the peak noise. To evaluate this concept, we conducted Detached Eddy Simulations for a rectangular supersonic jet with and without the wavy shield and verified our numerical results with experimental data for a free jet, as well as, for a jet with an adjacent flat surface. Results show that the proposed wavy surface reduces the jet noise as compared to that of the corresponding flat surface by as much as 4 dB.

scholarly journals Numerical Simulation of EPB Shield Tunnelling with TBM Operational Condition Control Using Coupled DEM–FDM

2021 ◽  
Vol 11 (6) ◽  
pp. 2551
Author(s):  
Hyobum Lee ◽  
Hangseok Choi ◽  
Soon-Wook Choi ◽  
Soo-Ho Chang ◽  
Tae-Ho Kang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Tunnel Boring Machine ◽  
Chamber Pressure ◽  
Screw Conveyor ◽  
Shield Tunnel ◽  
Pressure Balance ◽  
Operational Conditions ◽  
Shield Tunnelling ◽  
Epb Shield

This study demonstrates a three-dimensional numerical simulation of earth pressure balance (EPB) shield tunnelling using a coupled discrete element method (DEM) and a finite difference method (FDM). The analysis adopted the actual size of a spoke-type EPB shield tunnel boring machine (TBM) consisting of a cutter head with cutting tools, working chamber, screw conveyor, and shield. For the coupled model to reproduce the in situ ground condition, the ground formation was generated partially using the DEM (for the limited domain influenced by excavation), with the rest of the domain being composed of FDM grids. In the DEM domain, contact parameters of particles were calibrated via a series of large-scale triaxial test analyses. The model simulated tunnelling as the TBM operational conditions were controlled. The penetration rate and the rotational speed of the screw conveyor were automatically adjusted as the TBM advanced to prevent the generation of excessive or insufficient torque, thrust force, or chamber pressure. Accordingly, these parameters were maintained consistently around their set operational ranges during excavation. The simulation results show that the proposed numerical model based on DEM–FDM coupling could reasonably simulate EPB driving while considering the TBM operational conditions.

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