1. 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)

2. 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

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

4. 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)

5. Acoustic Standing Wave Micropump: The youngest micropump in literature

6. 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.

7. 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

8. 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 to

9. 3-D Meshing Span in z direction: 1mm Total No. of cells: 427910
12226 Cells in 2D
35 Cells along 1 mm Span

10. 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= kg/ m.s)
Boundary Conditions: Operating condition= 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

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

12. 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
∅ −

13. 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):

14. Justification of 2-D assumption with 3-D model

15. 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)

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

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

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

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

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

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

22. 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)
0.3786
0.1603
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

23. 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.

24. THANK YOU ?

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

28. Fig.A5 Total pressure difference between inlet2 and outlet2