Milli-Scale Junction Flow Experiments

2010 ◽  
Author(s):  
Evan C. Lemley ◽  
Willy L. Duffle ◽  
Jesse K. Haubrich ◽  
Andrew W. Henderson
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Small Scale ◽  
Energy Losses ◽  
Turbulent Regime ◽  
Pressure Losses ◽  
Inlet Tube ◽  
Flow Experiments

Laminar flow is increasingly important area of study as it dominates microscale and milliscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been focused on turbulent flow conditions that exist in larger scale piping systems. There is a need for laminar flow studies of energy losses in junctions so that engineers can better predict, design, and analyze flow in microscale and other small scale systems. Unlike in the turbulent regime, Reynolds number plays a dominant role in energy losses for laminar flow, so new studies should document the effects of Reynolds number. This paper documents laminar flow experiments in a milliscale junction. This work builds on previous experience of the authors in computational fluids dynamics simulations of junctions. The planar junction under study consists of a circular tubes with two outlets and one inlet. A general technique has been developed to produce computer and physical models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. The junction test sections for experiments are milled from cast acrylic in two pieces to match three-dimensional computer models. The test sections are placed in a system that provides steady-state flow of water to test sections and has been designed to measure pressure losses and flow rates through the test section.

Flow Experiments in Microjunction Networks

2012 ◽  
Author(s):  
Andrew W. Henderson ◽  
Ozlem Yasar ◽  
Ane Joan Muvadgah ◽  
Evan C. Lemley
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Dominant Role ◽  
Experimental Studies ◽  
Physical Models ◽  
Energy Losses ◽  
Turbulent Regime ◽  
Pressure Losses ◽  
Inlet Tube ◽  
Flow Experiments

Laminar flow dominates microscale applications in devices such as microvalves, pumps, and turbines and in biomedical applications such as stents and biological flows. Studies of pressure losses in junctions have mostly been focused on turbulent flow conditions that exist in larger scale piping systems. There is a need for laminar flow studies of energy losses in junctions and networks of junctions so that engineers can better predict, design, and analyze flow in microscale systems. Unlike in the turbulent regime, Reynolds number plays a dominant role in energy losses for laminar flow. Studies focused on Reynolds number dependence are needed. This paper documents laminar flow experiments in networks constructed from microscale junctions (microjunctions). This work builds on previous experience of the authors in computational fluids dynamics simulations of junctions and networks of junctions. The planar junctions studied consist of circular tubes with two outlets and one inlet. A general technique has been developed to produce computer and physical models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. There have been several techniques used to create the experimental microjunction networks: a “lost wax” method that creates the network in Polydimethylsiloxane (PDMS), stereolithography-based junctions connected by tubing, and photopolymer cured by ultraviolet radiation. Results are presented for pressure losses in various microjunction networks as a function of Reynolds number.

Entropy Generation in Laminar Flow Junctions

2012 ◽  
Author(s):  
Mauricio Sanchez ◽  
Andrew W. Henderson ◽  
Dimitrios V. Papavassiliou ◽  
Evan C. Lemley
Keyword(s):  
Laminar Flow ◽  
Entropy Generation ◽  
Dominant Role ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Energy Losses ◽  
General Technique ◽  
Circular Pipes ◽  
Inlet Tube ◽  
Three Dimensional Models

Laminar flow dominates microscale and milliscale applications. This work is focused on laminar energy losses in junctions (bifurcations). Reynolds number plays a dominant role in energy losses for laminar flow. The physical cause of these energy losses is entropy generation. This paper analyzes the energy losses in junctions by considering the entropy generation. This paper documents results from computational fluid dynamics (CFD) simulations of laminar flow in planar junctions. The junctions studied consisted of circular pipes with two outlets and one inlet tube with Reynolds numbers ranging from one to 1000. A general technique has been developed to produce computer models of junctions in which the inlet tube size is set, but the outlets are allowed to vary in size and angle relative to the inlet tube. A generalized algorithm has been implemented to create three-dimensional models of the junctions for both computational and experimental studies. The entropy generation has been determined in junctions from simulation results for the velocity field. Results for entropy generation as a function of geometry and Reynolds are presented. Energy loss coefficients are derived from the simulations and compared to experimental measurements of energy losses in microscale junctions.

Reynolds Number Dependence of Laminar Loss Coefficients for a Rectangular-Cross Section Square-Cornered Tee Junction

2014 ◽  
Author(s):  
Brock P. Ring ◽  
Yunhao Lin ◽  
Andrew W. Henderson ◽  
Mohammad Hossan ◽  
Evan C. Lemley
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Loss Coefficient ◽  
Small Scale ◽  
Energy Losses ◽  
Water Mixture ◽  
Macro Scale ◽  
Tee Junction ◽  
Loss Coefficients

Energy losses in junctions are often found by using an assumed loss coefficient for the particular geometry. While this coefficient remains nearly constant under turbulent conditions, this is not true for laminar flow. The loss coefficient through a dividing junction tends to decrease as a function of Reynolds number converging to some value once fully turbulent flow occurs. Research has been done to catalog losses for various geometries under turbulent flow; yet, there has not been the same detailed research for the laminar conditions. This is mostly due to many applications at the macro scale where turbulent flow is prevalent. Flow in microchannels and nanochannels is mostly laminar. Applications at this small scale have created a demand for the study of these loss coefficients under the laminar flow conditions. This paper focuses on simulations done of flow through a square-cornered tee-junction with a rectangular cross sectional area of 6 by 7 millimeters. The fluid consisted of a glycerin and water mixture that was 30 percent water and 70 percent glycerin by volume. Measurements were made of an actual mixture’s density and viscosity and these parameters were used in the simulations. The mixture was chosen to give sufficient pressure drop to measure in validation experiments. Using these simulations, a detailed account of the energy losses in the junction was observed as a function of Reynolds number. The Reynolds number range in this study was 1–100. Higher Reynolds numbers were simulated where signs of a transition to turbulence were observed. The stagnation loss coefficient, which includes kinetic energy and pressure changes through the junction, was found to be inversely proportional to Reynolds number. Initial experimental verification has been performed, in which the experimental stagnation loss coefficient followed the same trend as the simulations. Additional experimental validation is underway.

Bifurcation Characteristics of Flows in Rectangular Sudden Expansion Channels

2005 ◽  
Author(s):  
Francine Battaglia ◽  
George Papadopoulos
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Critical Reynolds Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Expansion Ratio ◽  
Sudden Expansion ◽  
Two Dimensional ◽  
Effective Expansion ◽  
Three Dimensional Simulations

The effect of three-dimensionality on low Reynolds number flows past a symmetric sudden expansion in a channel was investigated. The geometric expansion ratio of in the current study was 2:1 and the aspect ratio was 6:1. Both experimental velocity measurements and two- and three-dimensional simulations for the flow along the centerplane of the rectangular duct are presented for Reynolds numbers in the range of 150 to 600. Comparison of the two-dimensional simulations with the experiments revealed that the simulations fail to capture completely the total expansion effect on the flow, which couples both geometric and hydrodynamic effects. To properly do so requires the definition of an effective expansion ratio, which is the ratio of the downstream and upstream hydraulic diameters and is therefore a function of both the expansion and aspect ratios. When the two-dimensional geometry was consistent with the effective expansion ratio, the new results agreed well with the three-dimensional simulations and the experiments. Furthermore, in the range of Reynolds numbers investigated, the laminar flow through the expansion underwent a symmetry-breaking bifurcation. The critical Reynolds number evaluated from the experiments and the simulations was compared to other values reported in the literature. Overall, side-wall proximity was found to enhance flow stability, helping to sustain laminar flow symmetry to higher Reynolds numbers in comparison to nominally two-dimensional double-expansion geometries. Lastly, and most importantly, when the logarithm of the critical Reynolds number from all these studies was plotted against the reciprocal of the effective expansion ratio, a linear trend emerged that uniquely captured the bifurcation dynamics of all symmetric double-sided planar expansions.

scholarly journals Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution

Micromachines ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 323 ◽  
Author(s):  
Jojomon Joseph ◽  
Danish Rehman ◽  
Michel Delanaye ◽  
Gian Luca Morini ◽  
Rabia Nacereddine ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
Experimental Studies ◽  
Wire Mesh ◽  
Pressure Losses ◽  
Macro Scale ◽  
Flow Maldistribution

Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%).

LOW REYNOLDS NUMBER FLOW OVER A SQUARE RIB

1997 ◽  
Vol 21 (4) ◽  
pp. 371-387
Author(s):  
D.A Billenness ◽  
N. Djilali ◽  
E. Zeidan
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Separation Bubble ◽  
Three Dimensional ◽  
Recirculation Region ◽  
Number Range ◽  
Reynolds Number Flow ◽  
First Results ◽  
Region Length ◽  
Number Flow

Laminar flow over a square rib placed in a fully developed channel flow is investigated over the Reynolds number range 80-350. The effect of Reynolds number on the flow and the variation of the primary reattachment length with Reynolds number are investigated using flow visualization and laser-Doppler velocimetry. The primary recirculation region length is found to increase in a slightly non-linear fashion with Reynolds number up to Reh = 250, at which point shear layer instabilities first appear downstream of the rib. Increasing the Reynolds number further, first results in continuing growth of the separation bubble, and then for Reh ≳ 300, in the appearance of three dimensional vortices and gradual shortening of the bubble. The measurements are complemented by two- and three-dimensional numerical simulations using a finite volume method with a high-order descretization scheme. These simulations yield excellent agreement with the measured reattachment lengths and velocity profiles over the steady laminar flow régime.

Experimental Investigation of a Generic Compressor Bleed System

2006 ◽  
Author(s):  
Reinaldo A. Gomes ◽  
Carsten Schwarz ◽  
Michael Pfitzner
Keyword(s):  
Flow Field ◽  
Annular Flow ◽  
Experimental Studies ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Complex Flow ◽  
Pressure Losses ◽  
Aero Engines

Extensive experimental studies on axial compressor bleed-flow systems have been carried out on a three dimensional model of a generic bleed-flow configuration typical for aero engines. The compressor flow is modeled as a clean annular flow. One row of stator vanes is used to impart a constant swirl upstream of the bleed system. The rig is designed modularly in order to allow for inexpensive changes in all of its components and therefore to enlarge the variability of the model. The research is focused onto the generation of an experimental data base, which can be used to derive correlations for the calculation of effective areas and pressure losses. Those data are gained using steady pneumatic measurement technique. In addition, the highly complex flow field in the manifold, which has an important effect onto the bleed-flow, is analyzed using Doppler-Global-Velocimetry (DGV). These measurements were conducted in collaboration with DLR Cologne, who have developed the DGV technique. In this paper the flow field in the manifold is analyzed in detail for two different configurations featuring two and four bleed ducts, respectively. Furthermore the use of a flush design of the slot is compared with a lip design. These data are compared to results from the literature achieved using 2-dimensional configurations.

Effects of wavelength and amplitude of a wavy cylinder in cross-flow at low Reynolds numbers

2009 ◽  
Vol 620 ◽  
pp. 195-220 ◽  
Author(s):  
K. LAM ◽  
Y. F. LIN
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Circular Cylinder ◽  
Drag Coefficient ◽  
Shear Layer ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Spanwise Direction ◽  
Free Shear Layer ◽  
The Mean

Three-dimensional numerical simulations of laminar flow around a circular cylinder with sinusoidal variation of cross-section along the spanwise direction, named ‘wavy cylinder’, are performed. A series of wavy cylinders with different combinations of dimensionless wavelength (λ/Dm) and wave amplitude (a/Dm) are studied in detail at a Reynolds number of Re = U∞Dm/ν = 100, where U∞ is the free-stream velocity and Dm is the mean diameter of a wavy cylinder. The results of variation of mean drag coefficient and root mean square (r.m.s.) lift coefficient with dimensionless wavelength show that significant reduction of mean and fluctuating force coefficients occurs at optimal dimensionless wavelengths λ/Dm of around 2.5 and 6 respectively for the different amplitudes studied. Based on the variation of flow structures and force characteristics, the dimensionless wavelength from λ/Dm = 1 to λ/Dm = 10 is classified into three wavelength regimes corresponding to three types of wake structures. The wake structures at the near wake of different wavy cylinders are captured. For all wavy cylinders, the flow separation line varies along the spanwise direction. This leads to the development of a three-dimensional free shear layer with periodic repetition along the spanwise direction. The three-dimensional free shear layer of the wavy cylinder is larger and more stable than that of the circular cylinder, and in some cases the free shear layer even does not roll up into a mature vortex street behind the cylinder. As a result, the mean drag coefficients of some of the typical wavy cylinders are less than that of a corresponding circular cylinder with a maximum drag coefficient reduction up to 18%. The r.m.s. lift coefficients are greatly reduced to practically zero at optimal wavelengths. In the laminar flow regime (60 ≤ Re ≤ 150), the values of optimal wavelength are Reynolds number dependent.

scholarly journals An experimental investigation on Lagrangian correlations of small-scale turbulence at low Reynolds number

2007 ◽  
Vol 574 ◽  
pp. 405-427 ◽  
Author(s):  
MICHELE GUALA ◽  
ALEXANDER LIBERZON ◽  
ARKADY TSINOBER ◽  
WOLFGANG KINZELBACH
Keyword(s):  
Reynolds Number ◽  
Time Scales ◽  
Correlation Functions ◽  
Time Scale ◽  
Cross Correlation ◽  
Strain Tensor ◽  
Three Dimensional ◽  
Small Scale ◽  
Production Term ◽  
Long Time

Lagrangian auto- and cross-correlation functions of the rate of strain s2, enstrophy ω2, their respective production terms −sijsjkski and ωiωjsij, and material derivatives, Ds2/Dt and Dω2/Dt are estimated using experimental results obtained through three-dimensional particle tracking velocimetry (three-dimensional-PTV) in homogeneous turbulence at Reλ=50. The autocorrelation functions are used to estimate the Lagrangian time scales of different quantities, while the cross-correlation functions are used to clarify some aspects of the interaction mechanisms between vorticity ω and the rate of strain tensor sij, that are responsible for the statistically stationary, in the Eulerian sense, levels of enstrophy and rate of strain in homogeneous turbulent flow. Results show that at the Reynolds number of the experiment these quantities exhibit different time scales, varying from the relatively long time scale of ω2 to the relatively shorter time scales of s2, ωiωjsij and −sijsjkski. Cross-correlation functions suggest that the dynamics of enstrophy and strain, in this flow, is driven by a set of different-time-scale processes that depend on the local magnitudes of s2 and ω2. In particular, there are indications that, in a statistical sense, (i) strain production anticipates enstrophy production in low-strain–low-enstrophy regions (ii) strain production and enstrophy production display high correlation in high-strain–high-enstrophy regions, (iii) vorticity dampening in high-enstrophy regions is associated with weak correlations between −sijsjkski and s2 and between −sijsjkski and Ds2/Dt, in addition to a marked anti-correlation between ωiωjsij and Ds2/Dt. Vorticity dampening in high-enstrophy regions is thus related to the decay of s2 and its production term, −sijsjkski.

Experimental Investigation of the Laminar Flow Heat Transfer Enhancement in a Small-Scale Square Duct With Aqueous Carbopol Solutions

1996 ◽  
Vol 118 (3) ◽  
pp. 555-561 ◽  
Author(s):  
Cheng-Xian Lin ◽  
Shao-Yen Ko ◽  
F. K. Tsou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Polymer Concentration ◽  
Small Scale ◽  
Transfer Enhancement ◽  
Enhance Heat Transfer ◽  
Square Duct ◽  
Number Range

This paper presents results of an experimental study on the heat transfer enhancement in laminar flow of non-Newtonian fluids, aqueous Carbopol-934 solutions through a small-scale square duct. The square duct is a top-wall heated configuration with a hydraulic diameter of 0.4 cm. The aqueous Carbopol solutions examined are those neutralized, and have a polymer concentration range of 1000–2000 wppm. It is shown that the enhanced heat transfer behavior of the Carbopol solutions within low Reynolds number range is different from that within relatively high Reynolds number range. There exists a limiting polymer concentration, Cmax, at which the non-Newtonian fluid possesses the maximum ability to enhance heat transfer. If the polymer concentration becomes too high, the minimum Reynolds number required to enhance heat transfer increases with the increasing polymer concentration.

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