scholarly journals Numerical and Experimental Study of Cross-Sectional Effects on the Mixing Performance of the Spiral Microfluidics

Micromachines ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1470
Author(s):  
Omid Rouhi ◽  
Sajad Razavi Bazaz ◽  
Hamid Niazmand ◽  
Fateme Mirakhorli ◽  
Sima Mas-hafi ◽  
...  
Keyword(s):  
Cross Sections ◽  
Numerical Study ◽  
Large Angle ◽  
Element Model ◽  
Channel Length ◽  
Cross Sectional ◽  
Flow Rates ◽  
Lab On Chip ◽  
Mixing Performance ◽  
Dean Flow

Mixing at the microscale is of great importance for various applications ranging from biological and chemical synthesis to drug delivery. Among the numerous types of micromixers that have been developed, planar passive spiral micromixers have gained considerable interest due to their ease of fabrication and integration into complex miniaturized systems. However, less attention has been paid to non-planar spiral micromixers with various cross-sections and the effects of these cross-sections on the total performance of the micromixer. Here, mixing performance in a spiral micromixer with different channel cross-sections is evaluated experimentally and numerically in the Re range of 0.001 to 50. The accuracy of the 3D-finite element model was first verified at different flow rates by tracking the mixing index across the loops, which were directly proportional to the spiral radius and were hence also proportional to the Dean flow. It is shown that higher flow rates induce stronger vortices compared to lower flow rates; thus, fewer loops are required for efficient mixing. The numerical study revealed that a large-angle outward trapezoidal cross-section provides the highest mixing performance, reaching efficiencies of up to 95%. Moreover, the velocity/vorticity along the channel length was analyzed and discussed to evaluate channel mixing performance. A relatively low pressure drop (<130 kPa) makes these passive spiral micromixers ideal candidates for various lab-on-chip applications.

Effect of Deterministic Asperity Geometry on Hydrodynamic Lubrication

2004 ◽  
Vol 126 (3) ◽  
pp. 527-534 ◽  
Author(s):  
Ravinder B. Siripuram ◽  
Lyndon S. Stephens
Keyword(s):  
Friction Coefficient ◽  
Cross Sections ◽  
Numerical Study ◽  
Hydrodynamic Lubrication ◽  
Leakage Rate ◽  
Area Fraction ◽  
Cross Sectional ◽  
Constant Height ◽  
Sectional Shape ◽  
The Impact

This paper presents a numerical study of the effects of different shapes of deterministic microasperities in sliding surface lubrication when hydrodynamic films are found. Positive (protruding) and negative (recessed) asperities of constant height (depth) are considered with circular, square, diamond, hexagonal and triangular cross-sections. Of particular interest is the impact of asperity/cavity cross-sectional geometry on friction and leakage, which has importance in sealing applications. The results indicate that the friction coefficient is insensitive to asperity/cavity shape, but quite sensitive to the size of the cross-section. By contrast, leakage rates are found to be quite sensitive to both cross-sectional shape and size, with triangular asperities giving the smallest leakage rate and square asperities giving a largest leakage rate. The minimum coefficient of friction for all shapes is found to occur at an asperity area fraction of 0.2 for positive asperities and 0.7 for negative asperities. Finally, the results indicate the existence of a critical asperity area fraction where the performance curves for positive and negative asperities cross over. These cross-over points are identified for friction coefficient and leakage rate.

Buckling of High-Strength Steel Cylinders Under Cyclic Bending in the Inelastic Range1

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
George E. Varelis ◽  
Spyros A. Karamanos
Keyword(s):  
Finite Element ◽  
High Strength Steel ◽  
Numerical Study ◽  
Local Buckling ◽  
High Strength ◽  
Element Model ◽  
Cyclic Plasticity ◽  
Repeated Loading ◽  
Cross Sectional ◽  
Cyclic Bending

The present paper examines the structural behavior of elongated steel hollow cylinders, referred to as tubes or pipes, subjected to large cyclic bending, through a rigorous finite element simulation. The bent cylinders exhibit cross-sectional distortion, in the form of ovalization, combined with excessive plastic deformations. Those deformations grow under repeated loading and may lead to structural instability in the form of local buckling (wrinkling) and, eventually, failure of the loaded member. The study focuses on relatively thick-walled seamless cylindrical members made of high-strength steel, which exhibit local buckling in the plastic range of the steel material. The analysis is conducted using advanced nonlinear finite element models capable of describing both geometrical and material nonlinearities. A cyclic plasticity model that adopts the “bounding surface” concept is employed. The material model is calibrated through special-purpose material testing, and implemented within ABAQUS, using a user-subroutine. The finite element model is validated by comparison with two experiments on high-strength steel tubular members. Special emphasis is given on the increase of ovalization and the gradual development of small-amplitude initial wrinkles with repeated loading cycles. A parametric numerical study is conducted, aimed at determining the effects of initial wrinkles on plastic buckling performance.

Numerical Modeling and Parametric Optimization of Micromixer for Low Diffusivity Fluids

2017 ◽  
Vol 16 (3) ◽  
Author(s):  
K. Karthikeyan ◽  
L. Sujatha ◽  
N. M Sudharsan
Keyword(s):  
Pressure Loss ◽  
Parametric Optimization ◽  
Channel Length ◽  
Mixing Length ◽  
Cross Sectional ◽  
Lab On Chip ◽  
Viscous Forces ◽  
Optimum Configuration ◽  
On Chip ◽  
Micro Mixer

AbstractThis paper deals with the design, analysis and optimization of micro-mixer for fluids having very low diffusivity (in the order of 10−12m2/s) to be used in Lab on Chip (LOC) for medical diagnosis. As flow is laminar and the cross-sectional area is in microscale, the viscous forces are strong causing the fluids to be transported in streamline with minimum diffusion. The main objective in designing a micro mixer is to achieve complete mixing with minimum channel length and pressure drop. In this work a passive micro mixer with two inlets and one outlet (Y shaped passive micro mixer) with obstacles in various shapes and sizes is modelled, to study the effect of mixing. After a CFD analysis, Analysis of variance (ANOVA) of 3Kdesign with 3 parameters as well as a 2Kdesign with 4 parameters was performed to study the effect of parameters on mixing index (mixing length) and pressure loss. There is a negative correlation between the response obtained for mixing length and pressure loss while varying the parameters. This makes it difficult to predict the optimum configuration. Taguchi method is used to obtain an optimum configuration to overcome this negative correlatiozn.

scholarly journals Evaluation of the Crack Model of V Type Longitudinal Ribs on Orthotropic Deck Using Finite Element Analysis

2021 ◽  
pp. 72-89
Author(s):  
فاتح علم دار
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Cross Sections ◽  
Fatigue Cracks ◽  
Element Model ◽  
Crack Model ◽  
Element Analysis ◽  
Cross Sectional ◽  
Longitudinal Ribs ◽  
Long Span

The long span orthotropic bridge decks applied around the world are used with open or closed cross-sectional longitudinal ribs placed below the steel deck to increase the strength of the deck. Fatigue cracks are developed in the longitudinal ribs due to traffic loadings. In this study, v type of longitudinal rib cross-sections are modelled and the stresses for the rib are evaluated under tire load loading using finite element analysis. Longitudinal ribs are used for long span steel bridges. The aim of this study is to compare the fatigue crack path of the longitudinal rib on a real bridge with the stress pattern in the finite element model.

Numerical Study of External Flow over Ducts with Various Cross-Sections

2016 ◽  
Vol 366 ◽  
pp. 10-16 ◽  
Author(s):  
Erfan Maleki ◽  
Hani Sadrhosseini
Keyword(s):  
Cross Sections ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
External Flow ◽  
Two Dimensions ◽  
Wake Region ◽  
Reattachment Point ◽  
Cross Sectional ◽  
Low Reynolds Numbers ◽  
Stagnation Points

In this article a comprehensive numerical study is performed to compare the effect of fluid flow across a duct with various cross sectional shapes and with different velocities of the flow. Circular, elliptical and rectangular cross sections have been chosen for the ducts and air flows across them with four values of low Reynolds numbers in the range of Re = 1 to Re = 1000. Continuity and momentum equations with proper boundary conditions are solved in two dimensions. Streamlines, pressure distribution and Velocity profiles are obtained and creation of vortices, boundary layers, separation region, wake region, reattachment point and stagnation points are studied in detail and the results are compared for various cases. The value of the Reynolds number which the flow transits from steady to unsteady has been compared for the different cross sectional shapes.

scholarly journals Research on Optimization of Cross-sectional shape for Aircraft Door Rubber Seal

2021 ◽  
Vol 2133 (1) ◽  
pp. 012005
Author(s):  
Xiuqi Yuan
Keyword(s):  
Cross Sections ◽  
Element Model ◽  
Sound Insulation ◽  
Structural Form ◽  
Concentrated Force ◽  
Cross Sectional ◽  
Sealing Performance ◽  
Calculation Results ◽  
Sectional Shape ◽  
Heat Preservation

Abstract Rubber seals are widely used in aircraft door structures, which play important roles on sealing, sound insulation and heat preservation. Aircraft door rubber seals are critical to the normal flight of the aircraft and the safety of the passengers. In this paper, a finite element model of rubber seals for aircraft door with different cross-sections is established. The deformation and stress distribution of the seals under the action of concentrated force and compressive displacement are analyzed, and the calculation results of seals with different cross-sections are compared. The optimal structural form of the cross-sectional shape of the seal is obtained. The research results are of great significance to improve the safety and durability of seals and enhance the sealing performance.

scholarly journals Numerical Modelling and Design of Aluminium Alloy Angles under Uniform Compression

CivilEng ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 632-651
Author(s):  
Evangelia Georgantzia ◽  
Michaela Gkantou ◽  
George S. Kamaris
Keyword(s):  
Aluminium Alloy ◽  
Cross Sections ◽  
Numerical Study ◽  
Local Buckling ◽  
Design Standards ◽  
Uniform Compression ◽  
Cross Sectional ◽  
Modified Method ◽  
Aspect Ratios ◽  
Modelling Assumptions

Research studies have been reported on aluminium alloy tubular and doubly symmetric open cross-sections, whilst studies on angle cross-sections remain limited. This paper presents a comprehensive numerical study on the response of aluminium alloy angle stub columns. Finite element models are developed following a series of modelling assumptions. Geometrically and materially nonlinear analyses with imperfections included are executed, and the obtained results are validated against experimental data available in the literature. Subsequently, a parametric study is carried out to investigate the local buckling behaviour of aluminium alloy angles. For this purpose, a broad range of cross-sectional aspect ratios, slenderness and two types of structural aluminium alloys are considered. Their effect on the cross-sectional behaviour and strength is discussed. Moreover, the numerically obtained ultimate strengths together with literature test data are utilised to assess the applicability of the European design standards, the American Aluminium Design Manual and the Continuous Strength Method to aluminium alloy angles. The suitability of the Direct Strength Method is also evaluated and a modified method is proposed to improve the accuracy of the strength predictions.

Wall proximity effects on flow over cylinders with different cross sections

2014 ◽  
Vol 92 (10) ◽  
pp. 1141-1148 ◽  
Author(s):  
Seyfettin Bayraktar ◽  
Sedat Yayla ◽  
Alparslan Oztekin ◽  
Haolin Ma
Keyword(s):  
Cross Sections ◽  
Stokes Equations ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Proximity Effects ◽  
Navier Stokes ◽  
Cross Sectional ◽  
Navier Stokes Equations ◽  
Finite Volume Discretization ◽  
Wall Proximity

This paper presents the results of a numerical study on flow characteristics over circular, square, and diamond cross-sectional cylinders. Investigations are performed in a two-dimensional domain using the finite volume discretization method solver for Reynolds number, Re = 20 000. Unsteady Reynolds averaged Navier–Stokes equations with Spalart–Allmaras turbulence model have been used as a turbulence closure. After the validation of the simulations with the available experimental data from the open literature, global characteristics of the flow field around different shaped cylinders near the wall have been presented. Effects of wall proximity on cylinders are investigated for four different gap width (G) to cylinder width (D) ratios.

Mixing Performance of Different Serpentine Microchannels

2007 ◽  
Author(s):  
C. Nonino ◽  
S. Savino ◽  
S. Del Giudice
Keyword(s):  
Cross Section ◽  
Molecular Diffusion ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Channel Length ◽  
Mixing Enhancement ◽  
Finite Element Code ◽  
Mixing Performance ◽  
Pure Diffusion ◽  
Model Equations

The results of a comparative numerical study aimed at assessing the mixing performance of planar zig-zag, curvilinear and square-wave microchannels of square cross-section is presented in the paper. To evaluate the mixing enhancement characteristics of each geometry, suitable mixing indices are computed at different axial locations of a single repetitive module of each microchannel when this is fed with two equal streams of fluid having the same thermophysical properties, but different solute concentrations. To separate the effects of the geometry from those of molecular diffusion, entrance flow and channel length, the mixing by pure diffusion in straight microchannels of the same length is also evaluated for comparison. Reynolds numbers in the range from 5 to 150 are considered, while the Pe´clet number is held constant and equal to 2500. All the numerical simulations are carried out using an in-house finite element code for the solution of all model equations.

scholarly journals A Numerical Study of Initiation and Migration of Trapped Oil in Capillaries with Noncircular Cross Sections

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Long Long ◽  
Yajun Li ◽  
Houjian Gong ◽  
Mingzhe Dong
Keyword(s):  
Cross Sections ◽  
Numerical Study ◽  
Darcy Flow ◽  
Viscous Force ◽  
Cross Sectional ◽  
Deformation Law ◽  
Discontinuous Phase ◽  
Computational Fluid Dynamics Cfd ◽  
And Migration ◽  
Sectional Shape

To clarify the initiation and migration mechanisms of a discontinuous oil phase in pores, a numerical study was performed to interpret the starting phenomenon and flowing rules of oil trapped in capillaries that have noncircular cross sections. In this study, capillaries with three different cross sections were used to investigate the deformation law of oil and the pressure drop across these microchannels at different displacement velocities by computational fluid dynamics (CFD). The geometrical structure of the microchannels was precisely controlled, and the migration process of the oil, which is too small to be observed by direct experimentation, was assessed and quantitatively analyzed. By analyzing the shape of the trapped oil after reaching a steady state at different velocities, the nonstart and start conditions could be distinguished and the accuracy of the numerical method was verified by a comparison with an analytical method (the MS-P method). Two aspects of oil migration in noncircular microchannels were observed in combination with previous studies: there is a driving force on the cross section of the oil drop and a viscous force at the oil-water interface in the corners, and the more irregular the pore section is, the more easily the trapped oil will migrate. Additionally, the influence of the microchannel cross-sectional shape on the non-Darcy flow of a discontinuous oil phase was clarified. It can be concluded that the presence of the non-Darcy flow in pores arises because trapped oil, as a discontinuous phase, cannot be separated from the capillary wall without reaching critical velocity.

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