Design & evaluation of a Passive Micromixer with curved shape - - PowerPoint PPT Presentation

Design & evaluation of a Passive Micromixer with curved shape

• bstacles & grooves in the Mixing Channel

Cesar A. Cortes-Quiroz School of Engineering and Technology

STAR Global Conference, 17-19 March 2014, Vienna, Austria

Outline

• Introduction
• Micromixer designs
• Methodology
• Results and Analysis
• Conclusions

Outline

• Introduction
• Micromixer designs
• Methodology
• Results and Analysis
• Conclusions

Introduction Microfluidics

• Microfluidics is the technology of manipulating fluids in a chip of a few millimetres.
• It refers to fluid flow in microchannels as well as to microdevices (pumps, valves, mixers,

etc.) and systems where microlitre-scale volumes are involved. One of the dimensions of the flow device is measured in μm: e.g. channel.

• Microfluidics is essentially interdisciplinary: Micro-Fabrication, Chemistry, Biology,

Mechanics, Control Systems, Micro-Scale Physics and Thermal/Fluidic Transport, Numerical Modelling, Material Science, System Integration and Packaging, Validation & Experimentation, Reliability Engineering, etc.

Introduction Microfluidics

• In microfluidic systems:
• Flows are laminar (non turbulent) and thus controllable
• Thermal gradients are reduced
• Minute quantities can be handled
• Highly parallel systems can be devised
• This has been exploited to build separation systems, analyse DNA conformations,

implement lab-on-a-chips, etc.

Lab-on-a-chip DNA analyzers Separator

Introduction Micromixers

• Micromixers are the components of lab-on-a-chip, bio-MEMS and chemical microreaction

systems designed to achieve suitable mixing for the required process.

• Passive micromixers are preferred to active micromixers in several applications, due to

their simple design, easiness of fabrication and integration into systems.

• Planar designs are easier to fabricate and to integrate in microfluidic systems.

Nevertheless, to achieve high mixing performance, they have to operate with Re > 100 resulting in a very high pressure loss (200 KPa), or they need long channels of over 10 mm with Re < 1.

• A passive micromixer design is presented. A series of baffles are located alternated and

periodically in the mixing channel to increase fluids interface and generate transverse flows. Additionally, grooves strategically located on bottom surface promote swapping of fluids position in the channel. Mixing is enhanced by the fluid structures that are formed in the channel.

Outline

• Introduction
• Micromixer designs
• Methodology
• Results and Analysis
• Conclusions

Micromixer designs Curved shape protrusions

• Designs with curved shape obstacles

have been proposed for the numerical investigation

• These lateral obstacles change the flow

direction without forming large dead zones

• The constriction zones in the channel

have no axial length to reduce blogging of the device

• General dimensions in the designs:

R = 100 mm, d = 400 mm, h = 100 mm (d = 420 mm in design OM-2, shown in next slide)

100

Micromixer designs Analysis in original designs without grooves

• Three designs have been investigated

with their original geometry, i.e., channel with baffles, without grooves

• A wide range of Reynolds number (Re),

[0.25, 75] has been tested

OM-1 OM-1op OM-2

Outline

• Introduction
• Micromixer designs
• Methodology
• Results and Analysis
• Conclusions

Methodology CFD – Numerical simulations with Star-CCM+

• A viscous, steady, laminar, incompressible

flow is defined

• Tools in Star-CCM+:
• Geometry and mesh generation

3D-CAD Model, Volume Mesh

• CFD
• Boundary conditions:
• Inlet sections:

Velocity: Mass inflow Inlet A: Mass fraction = 0 Inlet B: Mass fraction = 1

• Walls: Non-slip
• Outlet section: Gauge pressure = 0
• Fluids: Water and Ethanol,

Dew = 1.2 x 10E-09 m2/s.

• Re is calculated in the mixing channel
• A hybrid mesh is used and arranged to

provide sufficient resolution. A preliminary mesh size sensitivity study is carried out to

• btain the suitable size for convergence.
• Mesh models used: Prism Layer Mesher,

Surface Remesher, Trimmer

Methodology Volume mesh

Outline

• Introduction
• Micromixer designs
• Methodology
• Results and Analysis
• Conclusions

Results and Analysis Analysis in designs without grooves

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0.25 1 5 10 20 35 50 75

Mixing level vs Re

OM1 OM1op OM2 T-mixer 2500 5000 7500 10000 12500 15000 17500 20000 22500 25000 27500 30000 32500 0.25 1 5 10 20 35 50 75

Pressure drop (Pa) vs Re

OM1 OM1op OM2 T-mixer

Results and Analysis Analysis in designs without grooves

OM-1 OM-1op OM-2

Re = 35

Results and Analysis Purpose of including grooves in the original designs

• Grooves form a path for fluid streams to flow in transverse direction to the main flow
• The groove volume reduces the nozzle effect at the tip
• f the baffles in the constricted zones
• Flow in the grooves increase the contact surface of the fluids to enhance mixing and

chemical reaction

• Higher/faster mixing  Shorter channel length  Lower pressure loss with same flow rate
• Small grooves of width, w = 50 mm, and depth, d = 33 mm, have been included in the three

designs, for analysis with Re = 35 (considering results obtained in designs without grooves)

Results and Analysis Designs with grooves, w = 50 mm x d = 33 mm, Re = 35

OM-1 OM-2 OM-1op

Outlet section

Results and Analysis Designs with grooves, w = 50 mm x d = 33 mm, Re = 35

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.3 0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.8

OM-1 OM- 1op OM-2 OM- 2_ng

Mixing index Distance along mixing channel (mm)

Mixing level vs. distance in the channel

500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 0.3 0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.8

OM-1 OM- 1op OM-2 OM- 2_ng

Pressure drop (Pa) Distance along mixing channel (mm)

Pressure drop in the mixing channel

Results and Analysis Velocities in designs w/o grooves and with grooves w50 x d33 mm

OM-1 OM-2

w/o grooves

Re = 35

with grooves w50 x d33 mm

OM-1op

Results and Analysis Definition of design points in geometry parametric study

• The grooves have shown an important

effect on flow characteristics with Re = 35, which in turn enhances mixing remarkably.

• With grooves, the level of mixing increases

more than 100% in the three designs, while pressure drop increases less than 3%

• The Taguchi’s Orthogonal Array L9 has

been used to define 9 designs based on

• riginal design OM-1. Groove width and

groove depth are used as geometric parameters.

Orthogonal Array L9

Experiment Number Parameters A B C D 1 1 1 1 1 2 1 2 2 2 3 1 3 3 3 4 2 1 2 3 5 2 2 3 1 6 2 3 1 2 7 3 1 3 2 8 3 2 1 3 9 3 3 2 1

• Parameter A = Groove Width, level 1 = 50 mm, level 2 = 62.5 mm, level 3 = 75 mm

Parameter B = Groove Depth, level 1 = 33 mm, level 2 = 50 mm, level 3 = 67 mm

Results and Analysis L9 designs based on design OM-1

DOE1 DOE2 DOE3 DOE4 DOE5 DOE6 DOE7 DOE8 DOE9 W = 50 W = 62.5 W = 75 d = 33 d = 50 d = 67

Re = 35

Results and Analysis Design DOE8, best performance with Re = 35

Results and Analysis Design DOE8 with Re = 1, 10 and 50

Re = 1

Results and Analysis Design DOE8 with Re = 1, 10 and 50

Re = 10

Results and Analysis Design DOE8 with Re = 1, 10 and 50

Re = 50

Results and Analysis Design DOE8 with Re = 1, 10 and 50

Re = 1 Re = 10 Re = 50 T-mixer Re = 10

Outline

• Introduction
• Micromixer designs
• Methodology
• Results and Analysis
• Conclusions

Conclusions Micromixers with baffles and grooves

• Passive micromixers (3) with curved-shaped baffles and grooves on the bottom wall of the

mixing channel have been studied through numerical simulations in Star-CCM+. The study identifies the effect on flow patterns and mixing level of conveniently located and dimensioned grooves in addition to the baffles structures.

• From the outcomes in designs with obstacles working with Re between 0.25 and 75, an

inflexion zone in the ‘Mixing level - Re’ curves was identified, in which the mixing is poor. Therefore, Re = 35 has been taken as the starting value of a cost-effective range of Re in these designs.

• First inclusion of grooves of w = 50 and d = 33 mm resulted in a remarkable increase of the

mixing level of more than 100% while the pressure drop does not increase significantly (less than 3%).

Conclusions Micromixers with baffles and grooves

• Design of Experiments through Taguchi’s Orthogonal Array was used with the width and

depth of the grooves as design parameters in design OM-1. It has been found that wider and deeper grooves help to enhance the mixing, although it seems that there is an upper limit in effectiveness of groove depth between 50 and 67 mm.

• The effect of grooves in generating transverse flow to enhance mixing has been confirmed

for Re = 1, 10 and 50. At this last value, a mixing level higher than 90% is achieved in the design OM-1 with pressure drop around 11 KPa.

• Further work:
• To evaluate the efficiency of the grooves for different Re values in the range 0.25 to 50
• To identify the threshold of groove dimensions (width and depth) in increasing mixing

performance

• To include the aspect ratio of the mixing channel as design parameter
• Multi-objective OPTIMIZATION, Study of PARTICLES mixing

Acknowledgments

Special thanks to:

• University of Hertfordshire
• Science and Technology Research Institute
• Microfluidics & Microengineering Research Group
• Cd-adapco

THANK YOU FOR YOUR ATTENTION

Questions