11th International Conference on Mechanical Engineering (ICME2015) Paper ID: 502 Effects of Flow Properties on the Performance of a Diffuser-Nozzle Element of a Valveless Micropump Authors: Partha Kumar Das A.B.M. Toufique Hasan Department of Mechanical Engineering Bangladesh University of Engineering & Technology (BUET)

Objective To study the flow behaviour through a diffuser-nozzle element of a valveless micropump To process the performance parameters(rectification capability, energy loss, etc) of diffuser-nozzle element To simulate the performance of diffuser-nozzle element for different boundary conditions To compare the performance of diffuser-nozzle element for different conditions and its compatibility for different applications

Micropump specialized microfluidic device a length scale in micrometer range both small scale flow (usually less than 30 μL/min) high pressure fluid transport .

Micropump Classification Mechanical Displacement Micropump Piezoelectric Thermopneumatic Electrostatic Bimetallic Electromagnetic Acoustic Standing Wave Micropump (ASWMP) Dynamic Micropump Magnetohydrodynamic (MHD Electrohydrodynamic (EHD) Electroosmotic Application of Micropumps Micropump has found a wide range applications in different fields like- Biofluidic and Microfluidic Field Chemical and Biological Sample Analysis Electronic Cooling in Micro Integrated Circuits (µ-IC)

Acoustic Standing Wave Micropump: The youngest micropump in literature

Valves vs. Diffuser-nozzle Element Dynamic Effect of Flow in a diffuser-nozzle element: causes a greater flow resistance in nozzle direction than in diffuser direction for the same pressure difference As a result a net flow is achieved through outlet port.

Geometry of the Present Work A planar, 2-D diffuser-nozzle element has been used Inlet length: 0.2 mm in x-direction Inlet height from symmetry line: 0.06 mm in y-direction Diffuser-nozzle section: 1.2 mm in x-direction Outlet length: 0.2 mm in x-direction Outlet height from symmetry line:1.26 mm in y-direction

2-D Meshing A hybrid meshing has been used with structured mesh in inlet and outlet region and unstructured mesh in main diffuser-nozzle section. Total no. of cells varies from 30000 to 40000.

3-D Meshing Span in z direction: 1mm Total No. of cells: 427910 12226 Cells in 2D 35 Cells along 1 mm Span

Numerical Procedures ANSYS Fluent pressure based solver (based on Finite Volume Method) has been used for the simulation process with the following conditions- Planer 2D space, Laminar, Transient flow Working Fluid: Water (Density=998.2 kg/m3, viscosity=0.001003 kg/ m.s) Boundary Conditions: Operating condition=101325 Pa Pressure-Inlet: sinusoidal pressure inlet, P(t) = P sin(ωt) Pressure-Outlet: zero pressure outlet Symmetry Boundary Condition in planer boundary Number of Time Step per Cycle: 200 The post-processing is done on TECPLOT software

Governing Equations Conservation of Mass Conservation of Momentum (Navier-Stokes Equation)

Diffuser Efficiency (η) Diffuser efficiency is one of the most important performance parameter indicating the net flow rate through diffuser-nozzle element. where, εn and εd are the flow resistance or pressure loss coefficients of the nozzle and diffuser direction respectively. Rectification Capability The capability of a diffuser-nozzle element to direct the flow in a definite direction. Higher the rectification capability higher amount of flow towards diffuser direction lower backflow towards nozzle direction Rectification Capability , ξ= ∅ + − ∅ − ∅ + + ∅ − Ø+ total volume flow in the diffuser direction ∅ + Ø- total volume flow in the nozzle direction ∅ −

Validation with Reference Paper Frequency: 10 kHz, Peak Pressure: 10 kPa Reference: Nabavi, M. and L. Mongeau (2009). "Numerical analysis of high frequency pulsating flows through a diffuser-nozzle element in valveless acoustic micropumps." Microfluidics and Nanofluidics 7(5): 669-681.

Justification of 2-D assumption with 3-D model

Stream Function Contour for 2-D Model Peak Pressure: 10 kPa, Frequency: 10 kHz, Inlet length / Outlet length: 0.2 mm / 0.2 mm α =9°° α =0°° (b) (a) α =45°° (c) α : Phase angle α =68.4°° (a) α =72°° (b)

Stream Function Contour for 2-D Model (b) α =85°° α =80°° (a) (d) α =255°° α =171.5°°

Stream Function Contour for 2-D Model (b) α =260°° α =262°° (c) α =265°°

Stream Function Contour for 2-D Model (b) α =269°° α =266°° (c) α =270°°

Stream Function Contour for 2-D Model (b) α =273°° α =271°° (c) α =275°°

Stream Function Contour for 2-D Model (b) α =281°° α =279°° (c) (d) α =288°° α =295°°

Stream Function Contour for 2-D Model (b) α =325°° α =300°° (c) α =358°°

Driving Frequency (kHz) Comparison of Performance Parameters Peak Pressure = 10 kPa Driving Frequency (kHz) 5 10 20 30 50 Net Velocity (mm/min) 8922 3156 1336 423 252 Net Volume Flow Rate (mL/min) 1.07065 0.3786 0.1603 0.05076 0.03024 Rectification Capability , ξ= 32.01% 22.34% 19.33% 10.02% 9.2% Diffuser Efficiency, η= 2.149 1.726 1.62 1.2731 1.279

Conclusion The asymmetry of velocity wave represents a net flow in diffuser direction Flow circulation occurs at the peak positive and negative pressure region. With increase in frequency, diffuser-nozzle element becomes ineffective in flow rectification.

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Appendix Calculation procedures of performance parameters of diffuser-nozzle element for 50 kHz

Fig.A5 Total pressure difference between inlet2 and outlet2