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

Design & evaluation of a Passive Micromixer with curved shape obstacles & 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: o Flows are laminar (non turbulent) and thus controllable o Thermal gradients are reduced o Minute quantities can be handled o 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 100 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 m m, d = 400 m m, h = 100 m m (d = 420 m m in design OM-2, shown in next slide)

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), OM-1 [0.25, 75] has been tested 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 Fluids: Water and Ethanol, flow is defined D ew = 1.2 x 10E-09 m 2 /s. • Tools in Star-CCM+: • Re is calculated in the mixing channel o Geometry and mesh generation 3D-CAD Model, Volume Mesh • A hybrid mesh is used and arranged to o CFD provide sufficient resolution. A preliminary mesh size sensitivity study is carried out to • Boundary conditions: obtain the suitable size for convergence. o Inlet sections: Velocity: Mass inflow • Mesh models used: Prism Layer Mesher, Inlet A: Mass fraction = 0 Surface Remesher, Trimmer Inlet B: Mass fraction = 1 o Walls: Non-slip o Outlet section: Gauge pressure = 0

Methodology Volume mesh

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

Results and Analysis Analysis in designs without grooves Mixing level vs Re Pressure drop (Pa) vs Re 1 32500 30000 OM1 0.9 OM1 27500 0.8 25000 0.7 22500 OM1op OM1op 20000 0.6 17500 0.5 15000 0.4 12500 OM2 OM2 10000 0.3 7500 0.2 5000 T-mixer 0.1 T-mixer 2500 0 0 0.25 1 5 10 20 35 50 75 0.25 1 5 10 20 35 50 75

Results and Analysis Analysis in designs without grooves OM-1 Re = 35 OM-1op OM-2

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 of 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 m m, and depth, d = 33 m m, 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 m m x d = 33 m m, Re = 35 OM-1 OM-1op OM-2 Outlet section

Results and Analysis Designs with grooves, w = 50 m m x d = 33 m m, Re = 35 Mixing level vs. distance in the channel Pressure drop in the mixing channel 0.80 6500 0.75 6000 0.70 5500 0.65 OM-1 OM-1 5000 0.60 Pressure drop (Pa) 0.55 4500 OM- Mixing index 0.50 4000 OM- 1op 0.45 1op 3500 0.40 3000 OM-2 0.35 OM-2 2500 0.30 0.25 2000 OM- OM- 0.20 1500 2_ng 2_ng 0.15 1000 0.10 500 0.05 0.00 0 0 0.3 0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.8 0 0.3 0.7 1.1 1.5 1.9 2.3 2.7 3.1 3.5 3.8 Distance along mixing channel (mm) Distance along mixing channel (mm)

Results and Analysis Velocities in designs w/o grooves and with grooves w50 x d33 m m with grooves w50 x d33 m m w/o grooves OM-1 Re = 35 OM-1op OM-2

Results and Analysis Definition of design points in geometry parametric study • The grooves have shown an important Orthogonal Array L9 effect on flow characteristics with Re = 35, Parameters which in turn enhances mixing remarkably. Experiment Number A B C D 1 1 1 1 1 • With grooves, the level of mixing increases 2 1 2 2 2 more than 100% in the three designs, while 3 1 3 3 3 pressure drop increases less than 3% 4 2 1 2 3 5 2 2 3 1 • The Taguchi’s Orthogonal Array L9 has 6 2 3 1 2 been used to define 9 designs based on 7 3 1 3 2 original design OM-1. Groove width and 8 3 2 1 3 groove depth are used as geometric 9 3 3 2 1 parameters. Parameter A = Groove Width, level 1 = 50 m m, level 2 = 62.5 m m, level 3 = 75 m m • Parameter B = Groove Depth, level 1 = 33 m m, level 2 = 50 m m, level 3 = 67 m m

Results and Analysis L9 designs based on design OM-1 d = 33 d = 50 d = 67 W = 50 DOE1 DOE2 DOE3 Re = 35 W = 62.5 DOE6 DOE4 DOE5 W = 75 DOE7 DOE8 DOE9

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 m m resulted in a remarkable increase of the • mixing level of more than 100% while the pressure drop does not increase significantly (less than 3%).