The Distortion of a Jet by Coil Inserts

2002 ◽  
Vol 124 (2) ◽  
pp. 500-504 ◽  
Author(s):  
Huy T. Hoang ◽  
Hamid R. Rahai
Keyword(s):  
Wire Diameter ◽  
Turbulent Jet ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Streamwise Vortices ◽  
Inside Diameter ◽  
Constant Pitch

Results of experimental investigations of the effects of distortion caused by coil inserts on a turbulent jet are presented. The coils have different wire diameters with constant pitch spacing. The ratios of the coil wire diameter to the tube inside diameter, d/D, are 0.06, 0.08, 0.11, 0.13, and 0.16 and the ratio of the pitch spacing to the tube inside diameter, p/D, is 1.2. Results show that the coil inserts enhance the mixing process. At the jet-outlet, mixing enhancement is increased when d/D<0.1. However, further downstream, the highest mixing is achieved for the coil with the largest d/D ratio. Results suggest that the streamwise vortices generated by the coil inserts are the mechanism behind the high entrainments and the mixing process.

Numerical and Experimental Investigations of a Turbulent Jet From a Round Ribbed Tube

2002 ◽  
Author(s):  
Huy Trong Hoang ◽  
Hamid R. Rahai
Keyword(s):  
Numerical Method ◽  
Control Volume ◽  
Flow Characteristics ◽  
Turbulent Jet ◽  
Experimental Investigations ◽  
Control Volume Method ◽  
Mixing Process ◽  
Inside Diameter ◽  
Approximate Distance ◽  
Volume Method

Results of numerical and experimental investigations of turbulent jet from a round ribbed tube are presented. The round ribbed tube is a coil-inserted tube. The ratio of the coil wire diameter to the tube inside diameter, d/D, is 0.1 and the ratio of the coil pitch spacing to the tube inside diameter, p/D, is 1.2. The coil is placed inside the tube such that it terminates at the tube outlet. The standard k-e turbulence model along with the control volume method is used in the numerical calculations. The numerical results provided more insights into the flow characteristics in the radial planes. Results show that the coil inserts generates a weak swirl at the tube outlet that dissipates at an approximate distance of X/D = 1 where at this location the generated free vortices off the coil become the main mechanism behind the entrainment and mixing process. Comparisons of the numerical and experimental results show over estimation of the results by the numerical method.

Enhancement of Mixing Effectiveness in Skewed Streams

2004 ◽  
Author(s):  
B. Deinert ◽  
J. Hourmouziadis
Keyword(s):  
Wake Flow ◽  
Test Facility ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Plane Shear ◽  
Jet Mixing ◽  
Mixing Noise ◽  
Rotational Direction

Forced mixers are used to improve the performance (thrust and SFC) and to reduce jet-mixing noise of turbofan engines. Therefore every effort has been made to enhance the mixing from forced exhaust mixers. A lobed type of forced mixer induces rapid mixing by enhancing the streamwise vorticity and increasing the interfacial area. Lobed mixer effectiveness can be further enhanced through the introduction of smaller scale mixing devices. For the design of these mixing devices it is important to keep in mind, that the devices have to produce smaller scale vorticity, but with an acceptable pressure loss. Several investigations have been reported on mixing enhancement in a plane shear layer and in wake flows using tabs. One important result was that each tab produces a dominant pair of counter-rotating streamwise vortices with a rotational direction opposite to that of the vortices generated by the induced upstream stagnation field (horseshoe vortex). Due to the high relevance for many engineering applications such as for the mixing processes behind lobed exhaust mixers in turbojet engines, the present investigation also considers skewed streams with delta tabs. In an attempt to explain the basic flow behaviour downstream of a mixing device in a constant skewed stream, qualitative and quantitative measurements have been carried out. The experiments are carried out in a low-speed test facility, which generates a two-stream skewed flow at different angles. This investigation considers the evolution of coherent structures and the characteristic flow field of parallel and skewed streams generated by mixing devices in the form of delta tabs (triangular-shaped tabs with their apex leaning downstream). Later on the results of this study are to be applied to the design of mixing devices introduced on a lobed mixer. One significant result of these experimental investigations in skewed streams is that each tab generates a pair of counter-rotating streamwise vortices with the same rotational direction as in the unskewed stream, but both vortices are not equally strong. This is caused by the fact that the pressure field ceases to be symmetric upstream of the tab. Farther downstream, the wake flow appears to be wrapped around the stronger vortex.

Mixing Enhancement of Two Gases in a Microchannel Using DSMC

2013 ◽  
Vol 307 ◽  
pp. 166-169 ◽  
Author(s):  
Masoud Darbandi ◽  
Elyas Lakzian
Keyword(s):  
Gas Flow ◽  
Flow Analysis ◽  
Direct Simulation Monte Carlo ◽  
Equilibrium Composition ◽  
Mass Composition ◽  
Mixing Enhancement ◽  
Mixing Process ◽  
Result Section ◽  
Flow Through ◽  
Simulation Monte Carlo

Microgas flow analysis may not be performed accurately using the classical CFD methods because of encountering high Knudsen number regimes. Alternatively, the gas flow through micro-geometries can be investigated reliably using the direct simulation Monte Carlo (DSMC) method. Our concern in this paper is to use DSMC to study the mixing of two gases in a microchannel. The mixing process is assumed to be complete when the mass composition of each species deviates by no more than ±1% from its equilibrium composition. To enhance the mixing process, we focus on the effects of inlet-outlet pressure difference and the pressure ratios of the incoming CO and N2 streams on the mixing enhancement. The outcome of this study is suitably discussed in the result section.

scholarly journals Prechamber optimal selection for a two stage turbulent jet ignition type combustion system in CNG-fuelled engine

2019 ◽  
Vol 176 (1) ◽  
pp. 16-26 ◽  
Author(s):  
Ireneusz PIELECHA ◽  
Wojciech BUESCHKE ◽  
Maciej SKOWRON ◽  
Łukasz FIEDKIEWICZ ◽  
Filip SZWAJCA ◽  
...  
Keyword(s):  
High Speed ◽  
Internal Combustion Engines ◽  
Combustion Process ◽  
Optimization Methods ◽  
Turbulent Jet ◽  
Experimental Investigations ◽  
Combustion System ◽  
Two Stage ◽  
Lean Burn ◽  
High Speed Engine

Searching for further reduction of fuel consumption simultaneously with the reduction of toxic compounds emission new systems for lean-mixture combustion for SI engines are being discussed by many manufacturers. Within the European GasOn-Project (Gas Only Internal Combustion Engines) the two-stage combustion and Turbulent Jet Ignition concept for CNG-fuelled high speed engine has been proposed and thoroughly investigated where the reduction of gas consumption and increasing of engine efficiency together with the reduction of emission, especially CO2 was expected. In the investigated cases the lean-burn combustion process was conducted with selection of the most effective pre-combustion chamber. The experimental investigations have been performed on single-cylinder AVL5804 research engine, which has been modified to SI and CNG fuelling. For the analysis of the thermodynamic, operational and emission indexes very advanced equipment has been applied. Based on the measuring results achieved for different pre-chamber config-urations the extended methodology of polioptimization by pre-chamber selection and the shape of main chamber in the piston crown for proposed combustion system has been described and discussed. The results of the three versions of the optimization methods have been comparatively summarized in conclusions.

Flow structures of a lobed mixer and effects of streamwise vortices on mixing enhancement

2019 ◽  
Vol 31 (6) ◽  
pp. 066102 ◽  
Author(s):  
Xin-xin Fang ◽  
Chi-bing Shen ◽  
Ming-bo Sun ◽  
Richard D. Sandberg ◽  
Peng Wang
Keyword(s):  
Flow Structures ◽  
Mixing Enhancement ◽  
Streamwise Vortices

Influence of Micro-Lobed Burner on the Non-Premixed Combustion of Methane and Oxygen

2019 ◽  
Vol 12 (1) ◽  
Author(s):  
Yi Xie ◽  
Chuan-li Yi
Keyword(s):  
Mass Fraction ◽  
Equivalence Ratio ◽  
Premixed Combustion ◽  
Maximum Temperature ◽  
Mixing Enhancement ◽  
Combustion System ◽  
Streamwise Vortices ◽  
Maximum Temperature Difference ◽  
Burner Exit ◽  
Combustion Enhancement

Abstract Non-premixed combustion was implemented in a micro-lobed combustion system, and its influence on combustion was studied using both experiments and simulations. The results show that a micro-lobed burner produces streamwise vortices with intensities that increase with the equivalence ratio of methane to oxygen (Φ). Due to the streamwise vortices and the increment of the contact area between methane and oxygen, the gasses mix well in the micro-lobed burner, giving it a larger OH mass fraction and higher temperatures than the micro-splitter burner. Moreover, the equivalence ratio greatly influences the combustion enhancement from the micro-lobed burner, especially near the burner exit. The maximum temperature difference between the two micro-burners at the Z/D = 0.01 cross section is 171 K, when Φ is 0.6. However, when the mixing enhancement caused by the streamwise vortices disappears, Φ has little influence on the combustion temperature of the micro-lobed burner, especially when Φ ≥ 1. In this case, the maximum temperature variation between the micro-lobed burner and micro-splitter burner remains nearly constant.

scholarly journals Current Advances in Ejector Modeling, Experimentation and Applications for Refrigeration and Heat Pumps. Part 2: Two-Phase Ejectors

Inventions ◽  
2019 ◽  
Vol 4 (1) ◽  
pp. 16 ◽  
Author(s):  
Zine Aidoun ◽  
Khaled Ameur ◽  
Mehdi Falsafioon ◽  
Messaoud Badache
Keyword(s):  
Heat Pumps ◽  
Operating Conditions ◽  
Industrial Processes ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Data Generation ◽  
Two Phase ◽  
Wide Range ◽  
Potential Applications ◽  
And Performance

Two-phase ejectors play a major role as refrigerant expansion devices in vapor compression systems and can find potential applications in many other industrial processes. As a result, they have become a focus of attention for the last few decades from the scientific community, not only for the expansion work recovery in a wide range of refrigeration and heat pump cycles but also in industrial processes as entrainment and mixing enhancement agents. This review provides relevant findings and trends, characterizing the design, operation and performance of the two-phase ejector as a component. Effects of geometry, operating conditions and the main developments in terms of theoretical and experimental approaches, rating methods and applications are discussed in detail. Ejector expansion refrigeration cycles (EERC) as well as the related theoretical and experimental research are reported. New and other relevant cycle combinations proposed in the recent literature are organized under theoretical and experimental headings by refrigerant types and/or by chronology whenever appropriate and systematically commented. This review brings out the fact that theoretical ejector and cycle studies outnumber experimental investigations and data generation. More emerging numerical studies of two-phase ejectors are a positive step, which has to be further supported by more validation work.

The flow characteristics of a confined square jet with mixing tabs

1998 ◽  
Vol 212 (2) ◽  
pp. 63-76 ◽  
Author(s):  
S C M Yu ◽  
Y X Hou ◽  
S C Low
Keyword(s):  
Flow Characteristics ◽  
Side Wall ◽  
Laser Doppler Anemometer ◽  
Mixing Enhancement ◽  
Streamwise Vortices ◽  
Streamwise Vorticity ◽  
Mean Velocity ◽  
Downstream Distance ◽  
Two Component ◽  
Breadth Ratio

The flow characteristics of a confined square jet with mixing tabs have been determined by measurements obtained using a two-component laser Doppler anemometer at a Reynolds number of 1.026 × 105 (based on the exit hydraulic diameter, DH = 60 mm, and bulk mean velocity, Ur, of the stream at 1.71 m/s). Both tabs of rectangular and triangular shapes are considered with the same height-breadth ratio ( h/b = 1.35) and with their apex leaning downstream. Altogether four tabs have been used, with one tab each located at the centre of each side wall at the exit plane. Each tab is found to produce a dominant pair of counter-rotating streamwise vortices. The combined effects of the four tabs bifurcate the jet into four ‘fingers’, resulting in a significant increase in entrainment at the downstream locations. The strength of the streamwise vorticity generated by the rectangular tabs is some 30 per cent higher than the triangular ones and decays faster with downstream distance. This appears due to a larger tab surface area which creates a larger pressure differential across the rectangular tab than the triangular tab. The region of high turbulent kinetic energy is found firstly at the locations where the streamwise vortices stretch the normal vortices and subsequently at locations where the streamwise vortices break down, resulting in significant mixing enhancement. Finally, the effects of the so-called secondary tabs have also been examined and are found to enhance the mixing further. The orientation of the secondary tabs is, however, crucial for the mixing enhancement to occur.

Mixing Enhancement in Spiral Microchannels

2016 ◽  
Author(s):  
Lakshmi Balasubramaniam ◽  
Rerngchai Arayanarakool ◽  
Samuel D. Marshall ◽  
Bing Li ◽  
Poh Seng Lee ◽  
...  
Keyword(s):  
Industrial Applications ◽  
Secondary Flows ◽  
Experimental Investigations ◽  
Mixing Enhancement ◽  
Curved Channel ◽  
Cross Sectional ◽  
Mixing Performance ◽  
Dean Vortices ◽  
Potential Applications ◽  
Sectional Shape

Advancements in the field of microfluidics has led to an increasing interest to study laminar flow in microchannel and its potential applications. Understanding mixing at a microscale can be useful in various biological, heating and industrial applications due to the space and time reduction that micro mixing permits. This work aims to study mixing enhancement due to curved microchannel and the influence of varying microchannel cross sectional shape through numerical and experimental investigations. Unlike prior studies which use channel dimensions in the lower microscale range, this work has been conducted on channels with dimensions in the higher end of micrometer range. Using a cross sectional hydraulic diameter of 600 μm enables introduction of flow into the curved channel at a Reynolds Number ranging from 0.15 to 75, the findings of which show considerable improvement in the mixing performance as compared to that of equivalent straight channels, due to the development of secondary flows known as Dean Vortices.

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