On the Thermal Characteristics of Two-Phase, Liquid-Liquid, Non-Boiling Droplet Flow in Minichannels

2011 ◽  
Author(s):  
Marc Mac Giolla Eain ◽  
Vanessa Egan ◽  
Jeff Punch
Keyword(s):  
Reynolds Number ◽  
Capillary Number ◽  
Thermal Characteristics ◽  
Flow Regimes ◽  
Two Phase ◽  
Flux Boundary Condition ◽  
Number Range ◽  
Droplet Flow ◽  
Micro Fluidics ◽  
Phase Liquid

Two-phase flow regimes offer numerous advantages over traditional single phase flows, resulting in a wide variety of uses in diverse applications such as electronics cooling, heat exchange systems, pharmacology and biological micro-fluidics. This paper experimentally investigates the enhanced heat transfer rates attainable with two-phase liquid-liquid non-boiling droplet flow. A custom experimental facility was constructed, allowing the flow to be analysed in a minichannel geometry subjected to a constant heat flux boundary condition. Parameters of Reynolds number, Capillary number, droplet length and droplet spacing were varied during the course of the experimentation. The experiments were conducted over the Reynolds number range of 46 ≤ Re ≤ 71.8 and a Capillary number range of 0.00849 ≤ Ca ≤ 0.0102. The flow passed through a capillary of 1.5mm internal diameter and 0.25mm wall thickness. Local Nusselt numbers were obtained at the entrance region through the use of infrared thermography. Enhancements of 144% over fully developed Poiseuille flow were encountered. The findings of this paper highlight the thermal characteristics of two-phase liquid-liquid flow regimes and are of practical relevance to applications in both the thermal management and biological micro-fluidics industries.

Simulations of Droplet Collisions in Shear Flow

2012 ◽  
Author(s):  
Orest Shardt ◽  
J. J. Derksen ◽  
Sushanta K. Mitra
Keyword(s):  
Reynolds Number ◽  
Shear Flow ◽  
Capillary Number ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Simple Shear Flow ◽  
Number Range ◽  
Droplet Collisions ◽  
Critical Capillary Number ◽  
Boltzmann Method

When droplets collide in a shear flow, they may coalesce or remain separate after the collision. At low Reynolds numbers, droplets coalesce when the capillary number does not exceed a critical value. We present three-dimensional simulations of droplet coalescence in a simple shear flow. We use a free-energy lattice Boltzmann method (LBM) and study the collision outcome as a function of the Reynolds and capillary numbers. We study the Reynolds number range from 0.2 to 1.4 and capillary numbers between 0.1 and 0.5. We determine the critical capillary number for the simulations (0.19) and find that it is does not depend on the Reynolds number. The simulations are compared with experiments on collisions between confined droplets in shear flow. The critical capillary number in the simulations is about a factor of 25 higher than the experimental value.

Shear-Layer Flow Regimes and Wave Instabilities and Reattachment Lengths Downstream of an Abrupt Circular Channel Expansion

1972 ◽  
Vol 39 (3) ◽  
pp. 677-681 ◽  
Author(s):  
L. H. Back ◽  
E. J. Roschke
Keyword(s):  
Reynolds Number ◽  
Shear Layer ◽  
Reverse Flow ◽  
Flow Region ◽  
Flow Regimes ◽  
Circular Channel ◽  
Number Range ◽  
Channel Expansion ◽  
Wave Instabilities ◽  
Layer Flow

An experimental investigation of water flow through an abrupt circular-channel expansion is described over a Reynolds number range between 20 and 4200. The shear layer between the central jet and the reverse flow region along the wall downstream behaved differently in the various flow regimes that were observed. With increasing Reynolds number these regimes changed progressively from a laminar flow to an unstable vortex sheetlike flow and then to a more random fluctuating flow. The distance between the step and the reattachment location downstream correspondingly increased, reached a maximum, and then decreased. Of particular significance are the shear layer wave instabilities observed in the shear flow and their relationship to rettachment which apparently has not received much attention previously. Visual observations aided in understanding the results.

Interface Dynamics During Two Phase Flow in Stratified Porous Medium

2018 ◽  
Author(s):  
Aniket S. Ambekar ◽  
Vivek V. Buwa ◽  
Jyoti Phirani
Keyword(s):  
Porous Medium ◽  
Flow Regimes ◽  
Low Velocity ◽  
Two Phase ◽  
Flow Paths ◽  
Capillary Suction ◽  
Permeable Layer ◽  
Micro Fluidics ◽  
Relative Placement ◽  
Wetting Fluid

Immiscible displacement of a non-wetting fluid by a wetting fluid is important for many fields for example, biomedical devices, paper micro-fluidics, oil reservoirs and water aquifers. In a multi-layered porous medium the displacement velocity and relative position of the layers with respect to each other is significant in determining the flow paths of the fluids. Earlier studies on two-layered porous medium indicate presence of different flow regimes in every layer depending upon the velocity. However, the effect of relative positioning of these layers in different flow regimes is still unknown. In the present work we experimentally show that at low velocity, a capillary regime is developed i.e. the wetting fluid front leads in the least permeable layer, while at high velocity the wetting fluid front leads in the highest permeability layer. At all flow rates, the least permeable layer is found to draw fluid from the high permeability layer due to capillary suction. We also show the effect of relative placement of the layers on the interphase dynamics.

Study of the Effect of Wetting on Viscous Fingering Before and After Breakthrough by Lattice Boltzmann Simulations

2021 ◽  
Author(s):  
Peter Mora ◽  
Gabriele Morra ◽  
Dave Yuen ◽  
Ruben Juanes
Keyword(s):  
Reynolds Number ◽  
Oil Recovery ◽  
Lattice Boltzmann ◽  
Capillary Number ◽  
Viscosity Ratio ◽  
Viscous Fingering ◽  
Wetting Angle ◽  
Recovery Factor ◽  
Transition To Turbulence ◽  
Two Phase

Abstract We present a suite of numerical simulations of two-phase flow through a 2D model of a porous medium using the Rothman-Keller Lattice Boltzmann Method to study the effect of viscous fingering on the recovery factor as a function of viscosity ratio and wetting angle. This suite involves simulations spanning wetting angles from non-wetting to perfectly wetting and viscosity ratios spanning from 0.01 through 100. Each simulation is initialized with a porous model that is fully saturated with a "blue" fluid, and a "red" fluid is then injected from the left. The simulation parameters are set such that the capillary number is 10, well above the threshold for viscous fingering, and with a Reynolds number of 0.2 which is well below the transition to turbulence and small enough such that inertial effects are negligible. Each simulation involves the "red" fluid being injected from the left at a constant rate such in accord with the specified capillary number and Reynolds number until the red fluid breaks through the right side of the model. As expected, the dominant effect is the viscosity ratio, with narrow tendrils (viscous fingering) occurring for small viscosity ratios with M ≪ 1, and an almost linear front occurring for viscosity ratios above unity. The wetting angle is found to have a more subtle and complicated role. For low wetting angles (highly wetting injected fluids), the finger morphology is more rounded whereas for high wetting angles, the fingers become narrow. The effect of wettability on saturation (recovery factor) is more complex than the expected increase in recovery factor as the wetting angle is decreased, with specific wetting angles at certain viscosity ratios that optimize yield. This complex phase space landscape with hills, valleys and ridges suggests the dynamics of flow has a complex relationship with the geometry of the medium and hydrodynamical parameters, and hence recovery factors. This kind of behavior potentially has immense significance to Enhanced Oil Recovery (EOR). For the case of low viscosity ratio, the flow after breakthrough is localized mainly through narrow fingers but these evolve and broaden and the saturation continues to increase albeit at a reduced rate. For this reason, the recovery factor continues to increase after breakthrough and approaches over 90% after 10 times the breakthrough time.

Two-Phase Heat Transfer for Flow in Tubes and Over Rod Bundles With Blockages

1984 ◽  
Vol 106 (4) ◽  
pp. 856-864 ◽  
Author(s):  
M. I. Drucker ◽  
V. K. Dhir ◽  
R. B. Duffey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Rod Bundles ◽  
Two Phase ◽  
Number Range ◽  
Transfer Data ◽  
Void Fractions ◽  
Two Phase Heat Transfer ◽  
The Heat Transfer Coefficient

A study of single- and two-component, two-phase heat transfer mechanisms for vertical flow inside of tubes and over rod bundles with blockages has been made. Existing heat transfer data for air–water flow in tubes with a liquid Reynolds number range of 2000 to 150,000 and void fractions up to 0.40 have been correlated as a function of αGr/Re2. The correlation has also been found to compare well with limited high Prandtl number data obtained with liquids other than water and for flow over rod bundles when an empirical constant is modified. Correlations have also been developed for the heat transfer coefficient in the vicinity of flow blockages in rod bundles. The heat transfer data have been obtained on a four rod bundle with sleeve-type blockages for a Reynolds number range of 230 to 6900 and void fractions up to 0.15. Significant enhancement of the heat transfer coefficient has been observed downstream of the blockages.

Oil-Water Flow Visualization and Flow Regimes in a 3.7 mm Mini-Channel

2016 ◽  
Author(s):  
Kevin K. Bultongez ◽  
Melanie M. Derby
Keyword(s):  
Pressure Drop ◽  
Water Flow ◽  
Glass Tube ◽  
Flow Regimes ◽  
Two Phase ◽  
Pressure Drops ◽  
Flow Apparatus ◽  
Phase Liquid ◽  
Oil Water ◽  
Minor Losses

This study investigates adiabatic oil and water flow patterns in a 3.7-mm-inner-diameter borosilicate glass tube. A closed-loop flow apparatus was constructed and pressure drop was verified using single-phase liquid water. Minor losses were shown to be negligible, and 98% of the pressure drop occurred in the glass tube. Oil-water tests were conducted over a range of oil superficial velocities (0.27 < jo < 3.3 m/s) and water superficial velocities (0.07 < jw < 4.96 m/s). Annular, intermittent, and dispersed flow regimes were observed and shown. For nearly all cases, an annular water ring formed along the perimeter of the glass tube. Two-phase pressure drops are reported.

Experimental visualization of two-phase flow patterns and transition from stratified to slug flow

2010 ◽  
Vol 225 (2) ◽  
pp. 382-389 ◽  
Author(s):  
M J Vaze ◽  
J Banerjee
Keyword(s):  
Reynolds Number ◽  
Slug Flow ◽  
Two Phase Flow ◽  
Dominant Role ◽  
Thermal Characteristics ◽  
Air Entrainment ◽  
Flow Patterns ◽  
Phase Flow ◽  
Two Phase ◽  
Regime Map

The transition from stratified to slug flow generates oscillations in pressure and flowrates. Large liquid surges associated with slug flow are detrimental to the operation of process equipments involving two-phase flow. The characterization of two-phase flow regimes and their transition is thus an important area of research. In the present work, flow patterns for various regimes of air—water two-phase flow are captured experimentally. A flow pattern map is established based on the visualized images. The developed flow regime map is compared with that obtained by Ghajar and Tang. Slug frequency is recorded for a variety of superficial Reynolds number to show the instances of impact pressure. The development of slug and transition to slug flow from stratified flow are analysed using these captured images. It is observed that slug becomes highly chaotic with dispersion of air bubbles, when gas superficial Reynolds number is increased for a fixed value of liquid superficial Reynolds number. For lower gas superficial Reynolds number, the slug is observed to be very clear (without air entrainment). This is true for higher value of liquid superficial Reynolds number as well. The air entrainment increases with increasing gas superficial Reynolds number. This air entrainment might play a dominant role in deciding the flow and thermal characteristics of such two-phase flows.

scholarly journals Effect of flow separation of TiO2 nanofluid on heat transfer in the annular space of two concentric cylinders

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 1007-1018 ◽  
Author(s):  
Tuqa Abdulrazzaq ◽  
Hussein Togun ◽  
Safaei Reza ◽  
Salim Kazi ◽  
Mohd Ariffin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Separation Flow ◽  
Annular Space ◽  
Flux Boundary Condition ◽  
Number Range ◽  
Concentric Cylinders ◽  
Contraction Ratio

In the wake of energy crises, the researchers are encouraged to explore new ways of enhancement in the thermal performance of heat exchanging equipment. In the current research, the SST k-? model and finite volume method were employed to augment heat transfer into the separation flow of TiO2 nanofluid in the annular space of two concentric cylinders. In the present investigation TiO2 nanoparticles of volume fractions, 0.5%-2% at Reynolds number range of 10000-40000, and contraction ratios from 1 to 2 were considered at constant heat flux boundary condition. Simulation results reveal that the highest enhancement in the heat transfer coefficient is corresponding to the annular pipe with a contraction ratio of 2 due to the generated re-circulation flow zone that begins after the separation point on the wall. Further, the surface heat transfer coefficient enhances with the increase of nanoparticles volume fraction and Reynolds number. The velocity distribution profile before and after the steps reveals that increasing the height of the step and Reynolds number, re-circulation regions also increases. Numerical results indicate that the highest pressure drop occurs at the Re = 40000 and contraction ratio of 2.

Experimental Investigation and Empirical Correlations of Heat Transfer in Different Regimes of Air–Water Two-Phase Flow in a Horizontal Tube

2016 ◽  
Vol 9 (2) ◽  
Author(s):  
S. A. Nada
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Flow Rate ◽  
Two Phase Flow ◽  
Horizontal Tube ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase

This article reports on the experimental investigation of heat transfer to cocurrent air–water two-phase flow in a horizontal tube. The idea is to enhance heat transfer to the coolant liquid by air injection. Experiments were conducted for different air water ratios in constant temperature heated tube. Visual identification of flow regimes was supplemented. The effects of the liquid and gas superficial velocities and the flow regimes on the heat transfer coefficients were investigated. The results showed that the heat transfer coefficient generally increases with the increase of the injected air flow rate, and the enhancement is more significant at low water flow rates. A maximum value of the two-phase heat transfer coefficient was observed at the transition to wavy-annular flow as the air superficial Reynolds number increases for a fixed water flow rate. It was noticed that the Nusselt number increased about three times due to the injection of air at low water Reynolds number. Correlations for heat transfer by air–water two-phase flow were deduced in dimensionless form for different flow regimes.

Steady shear rheology of a viscous emulsion in the presence of finite inertia at moderate volume fractions: sign reversal of normal stress differences

2016 ◽  
Vol 805 ◽  
pp. 494-522 ◽  
Author(s):  
Priyesh Srivastava ◽  
Abhilash Reddy Malipeddi ◽  
Kausik Sarkar
Keyword(s):  
Reynolds Number ◽  
Normal Stress ◽  
Capillary Number ◽  
Volume Fraction ◽  
Small Range ◽  
Sign Reversal ◽  
Interfacial Stresses ◽  
Number Range ◽  
Shear Rheology ◽  
Normal Stress Differences

The shear rheology of an emulsion of viscous drops in the presence of finite inertia is investigated using direct numerical simulation. In the absence of inertia, emulsions display a non-Newtonian rheology with positive first and negative second normal stress differences. However, recently it was discovered that a small amount of drop-level inertia alters their signs – the first normal stress difference becomes negative and the second one becomes positive, each in a small range of capillary numbers (Li & Sarkar,J. Rheol., vol. 49, 2005, pp. 1377–1394). Sign reversal was shown numerically and analytically, but only in the limit of a dilute emulsion where drop–drop interactions were neglected. Here, we compute the rheology of a density- and viscosity-matched emulsion, accounting for the interactions in the volume fraction range of 5 %–27 % and Reynolds number range of 0.1–10. The computed rheological properties (effective shear viscosity and first and second normal stress differences) in the Stokes limit match well with previous theoretical (Choi–Schowalter in the dilute limit) and simulated results (for concentrated systems) using the boundary element method. The two distinct components of the rheology arising from the interfacial stresses at the drop surface and the perturbative Reynolds stresses are investigated as functions of the drop Reynolds number, capillary number and volume fraction. The sign change is caused by the increasing drop inclination in the presence of inertia, which in turn directly affects the interfacial stresses. Increase of the volume fraction or capillary number increases the critical Reynolds number for sign reversals due to enhanced alignment of the drops with the flow directions. The effect of increasing the volume fraction on the rheology is explained by relating it to interactions and specifically to the contact pair-distribution function computed from the simulation. The excess stresses are seen to show an approximately linear behaviour with the Reynolds number in the range of 0.1–5, while with the capillary number and volume fraction, the variation is weakly quadratic.

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