scholarly journals Long Bubble Penetration through Viscoelastic Fluids in a Suddenly Contracting and Expanding Tube

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Ching-Chuan Chang ◽  
Huang-Chih Lin ◽  
Ming-Yuan Lin ◽  
Te-Hui Tsai
Keyword(s):  
Reynolds Number ◽  
Shear Viscosity ◽  
Gas Flow ◽  
Bubble Diameter ◽  
Viscoelastic Fluids ◽  
Weissenberg Number ◽  
Bubble Velocity ◽  
Sudden Expansion ◽  
Expansion Tube ◽  
Front Shape

This study investigated the properties of long bubbles penetrating viscoelastic fluids in a suddenly contracting and expanding tube. Injection gas flow is controlled by a mass flow controller (MFC). Some of dimensionless parameters, such as the capillary number (Ca), the Reynolds number (Re), the fractional ratio (m), and the Weissenberg number (Wi), are discussed herein. The experimental results showed that bubble velocity, Ca, and Wi increase as shear viscosity increases under a constant gas flow by MFC. However, as shear viscosity increases, bubble diameter decreases, andmincreases. When gas flow is 200 mL/min and shear viscosity increases, the bubble front is sharper in the contraction tube, and the bubble front shape is blunter in the sudden expansion tube. When gas flow is 600 mL/min and shear viscosity increases, the bubble front is blunter in the contraction tube and exhibits a torch shape in the sudden expansion tube.

scholarly journals The Long Bubbles Penetration through Viscoelastic Fluids with Shear-Thinning Viscosity in a Curved Tube

2017 ◽  
Vol 2017 ◽  
pp. 1-11
Author(s):  
Ching-Chuan Chang
Keyword(s):  
Flow Rate ◽  
Gas Flow ◽  
Viscoelastic Fluids ◽  
Weissenberg Number ◽  
Fluid Viscosity ◽  
Gas Flow Rate ◽  
Difference Variable ◽  
Curved Tube ◽  
Number Increase ◽  
The Difference

The purpose of this research is to investigate the behavior of a long bubbles penetrating through viscoelastic fluids in a curved tube. The injection gas flow is controlled by a mass flow controller (MFC). The results of the experiments show that the bubbles width approaches constant value at the location six-diameter upstream from the bubbles front. A difference variable is introduced at the six-diameter location to show the shifting deviation of the bubbles in the curved tube. It is shown that, with the same fluid viscosity and the curved angle, the difference is higher when the gas flow rate is higher. Also, the difference increases proportionally when the capillary number and the Weissenberg number increase.

A Survey of Heat Transfer in Separated and Reattached Flows

2000 ◽  
Vol 53 (8) ◽  
pp. 219-235 ◽  
Author(s):  
Terukazu Ota
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Exchangers ◽  
Plane Channel ◽  
Review Article ◽  
Sudden Expansion ◽  
Expansion Tube ◽  
Geometric Configurations ◽  
Laminar And Turbulent Flow ◽  
Flow Configurations

Heat and mass transfer in the separated, reattached, and redeveloping regions of incompressible or compressible flow is very important in relation to many types of heat exchangers. There have been numerous works published describing these flows for a wide variety of geometric configurations, In the present article, a survey is made of published studies of heat transfer in the separated, reattached, and redeveloping regions of incompressible flow around or in a wide variety of flow configurations. Flow configurations cited in the article are the downward facing step, the sudden expansion plane channel, the abrupt expansion tube, the blunt flat plate, the longitudinal blunt circular cylinder, and the surface mounted obstacle. The laminar and turbulent flow cases using both experimental and numerical methodologies are reviewed. This review article includes 268 references.

scholarly journals Simulation of Gas Flow Over a Micro Cylinder

2009 ◽  
Author(s):  
Yuan Hu ◽  
Quanhua Sun ◽  
Jing Fan
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Drag Coefficient ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Low Reynolds Number ◽  
Pressure Drag ◽  
Low Reynolds ◽  
Rarefied Gas Effect ◽  
Gas Effect

Gas flow over a micro cylinder is simulated using both a compressible Navier-Stokes solver and a hybrid continuum/particle approach. The micro cylinder flow has low Reynolds number because of the small length scale and the low speed, which also indicates that the rarefied gas effect exists in the flow. A cylinder having a diameter of 20 microns is simulated under several flow conditions where the Reynolds number ranges from 2 to 50 and the Mach number varies from 0.1 to 0.8. It is found that the low Reynolds number flow can be compressible even when the Mach number is less than 0.3, and the drag coefficient of the cylinder increases when the Reynolds number decreases. The compressible effect will increase the pressure drag coefficient although the friction coefficient remains nearly unchanged. The rarefied gas effect will reduce both the friction and pressure drag coefficients, and the vortex in the flow may be shrunk or even disappear.

Mass Transfer Coefficients during Steel Decarburization in a RH Degasser

2008 ◽  
Vol 273-276 ◽  
pp. 679-684
Author(s):  
Roberto Parreiras Tavares ◽  
André Afonso Nascimento ◽  
Henrique Loures Vale Pujatti
Keyword(s):  
Mass Transfer ◽  
Reynolds Number ◽  
Transfer Coefficient ◽  
Mass Transfer Coefficient ◽  
Gas Flow ◽  
Vacuum Chamber ◽  
Volumetric Mass Transfer Coefficient ◽  
Gas Flow Rate ◽  
Rh Process ◽  
Kinetics Of

The RH process is a secondary refining process that can simultaneously attain significant levels of removal of interstitial elements, such as carbon, nitrogen and hydrogen, from liquid steel. In the RH process, the decarburization rate plays a very important role in determining the productivity of the equipment. The kinetics of this reaction is controlled by mass transfer in the liquid phase. In the present work, a physical model of a RH degasser has been built and used in the study of the kinetics of decarburization. The effects of the gas flow rate and of the configurations of the nozzles used in the injection of the gas have been analyzed. The decarburization reaction of liquid steel was simulated using a reaction involving CO2 and caustic solutions. The concentration of CO2 in the solution was evaluated using pH measurements. Based on the experimental results, it was possible to estimate the reaction rate constant. A volumetric mass transfer coefficient was then calculated based on these rate constants and on the circulation rate of the liquid. The logarithm of the mass transfer coefficient showed a linear relationship with the logarithm of the gas flow rate. The slope of the line was found to vary according to the relevance of the reaction at the free surface in the vacuum chamber. A linear relationship between the volumetric mass transfer coefficient and the nozzle Reynolds number was also observed. The slopes of the lines changed according to the relative importance of the two reaction sites, gas-liquid interface in the upleg snorkel and in the vacuum. At higher Reynolds number, the reaction in the vacuum chamber tends to be more significant.

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.

Numerical Simulation on Heat Transfer Characteristics of Turbulent Gas Flow in Micro-Tubes

2011 ◽  
Author(s):  
Kyohei Isobe ◽  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Ichiro Ueno
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Wall Temperature ◽  
Gas Flow ◽  
Tube Diameter ◽  
Turbulence Energy ◽  
Stagnation Temperature ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Turbulent Gas Flow

Numerical simulations were performed to obtain for heat transfer characteristics of turbulent gas flow in micro-tubes with constant wall temperature. The numerical methodology was based on Arbitrary-Lagrangian-Eulerinan (ALE) method to solve compressible momentum and energy equations. The Lam-Bremhorst Low-Reynolds number turbulence model was employed to evaluate eddy viscosity coefficient and turbulence energy. The tube diameter ranges from 100 μm to 400 μm and the aspect ratio of the tube diameter and the length is fixed at 200. The stagnation temperature is fixed at 300 K and the computations were done for wall temperature, which ranges from 305 K to 350 K. The stagnation pressure was chosen in such a way that the flow is in turbulent flow regime. The obtained Reynolds number ranges widely up to 10081 and the Mach number at the outlet ranges from 0.1 to 0.9. The heat transfer rates obtained by the present study are higher than those of the incompressible flow. This is due to the additional heat transfer near the micro-tube outlet caused by the energy conversion into kinetic energy.

Stability of Viscoelastic Channel Flow

2007 ◽  
Author(s):  
Nariman Ashrafi
Keyword(s):  
Reynolds Number ◽  
Viscosity Ratio ◽  
Weissenberg Number ◽  
Base Flow ◽  
Galerkin Projection ◽  
Large Reynolds Number ◽  
One Dimensional ◽  
Stress Effects ◽  
The Stability ◽  
The One

The nonlinear stability and bifurcation of the one-dimensional channel (Poiseuille) flow is examined for a Johnson-Segalman fluid. The velocity and stress are represented by orthonormal functions in the transverse direction to the flow. The flow field is obtained from the conservation and constitutive equations using the Galerkin projection method. Both inertia and normal stress effects are included. The stability picture is dramatically influenced by the viscosity ratio. The range of shear rate or Weissenberg number for which the base flow is unstable increases from zero as the fluid deviates from the Newtonian limit as decreases. Typically, two turning points are observed near the critical Weissenberg numbers. The transient response is heavily influenced by the level of inertia. It is found that the flow responds oscillatorily. When the Reynolds number is small, and monotonically at large Reynolds number when elastic effects are dominated by inertia.

Study on Effective Radial Thermal Conductivity of Gas Flow through a Methanol Reactor

2015 ◽  
Vol 13 (1) ◽  
pp. 103-112 ◽  
Author(s):  
Kun Lei ◽  
Hongfang Ma ◽  
Haitao Zhang ◽  
Weiyong Ying ◽  
Dingye Fang
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Reynolds Number ◽  
Temperature Distribution ◽  
Large Scale ◽  
Gas Flow ◽  
Fixed Bed ◽  
Heat Transfer Model ◽  
Transfer Model ◽  
Particle Reynolds Number

Abstract The heat conduction performance of the methanol synthesis reactor is significant for the development of large-scale methanol production. The present work has measured the temperature distribution in the fixed bed at air volumetric flow rate 2.4–7 m3 · h−1, inlet air temperature 160–200°C and heating tube temperature 210–270°C. The effective radial thermal conductivity and effective wall heat transfer coefficient were derived based on the steady-state measurements and the two-dimensional heat transfer model. A correlation was proposed based on the experimental data, which related well the Nusselt number and the effective radial thermal conductivity to the particle Reynolds number ranging from 59.2 to 175.8. The heat transfer model combined with the correlation was used to calculate the temperature profiles. A comparison with the predicated temperature and the measurements was illustrated and the results showed that the predication agreed very well with the experimental results. All the absolute values of the relative errors were less than 10%, and the model was verified by experiments. Comparing the correlations of both this work with previously published showed that there are considerable discrepancies among them due to different experimental conditions. The influence of the particle Reynolds number on the temperature distribution inside the bed was also discussed and it was shown that improving particle Reynolds number contributed to enhance heat transfer in the fixed bed.

scholarly journals Peristaltic transport of Johnson–Segalman fluid in a curved channel with compliant walls

2012 ◽  
Vol 17 (3) ◽  
pp. 297-311 ◽  
Author(s):  
Sadia Hina ◽  
Tasawar Hayat ◽  
Saleem Asghar
Keyword(s):  
Reynolds Number ◽  
Mathematical Analysis ◽  
Channel Wall ◽  
Peristaltic Flow ◽  
Weissenberg Number ◽  
Peristaltic Transport ◽  
Curved Channel ◽  
Long Wavelength ◽  
Channel Effects ◽  
Compliant Walls

The present investigation deals with the peristaltic flow of an incompressible Johnson–Segalman fluid in a curved channel. Effects of the channel wall properties are taken into account. The associated equations for peristaltic flow in a curved channel are modeled. Mathematical analysis is simplified under long wavelength and low Reynolds number assumptions. The solution expressions are established for small Weissenberg number. Effects of several embedded parameters on the flow quantities are discussed.

Efficient mixing of viscoelastic fluids in a microchannel at low Reynolds number

2006 ◽  
Vol 3 (1) ◽  
pp. 101-108 ◽  
Author(s):  
Hiong Yap Gan ◽  
Yee Cheong Lam ◽  
Nam Trung Nguyen ◽  
Kam Chiu Tam ◽  
Chun Yang
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Viscoelastic Fluids ◽  
Low Reynolds
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