Flow characterization of valveless micropump using driving equivalent moment: theory and experiments

In recent research, there has been a growing interest in the analysis of flow through microdiffusers and micropumps in order to characterize and optimize the performance of these devices. In this review, the recent advances in the numerical and experimental analysis of the steady and pulsating flows through microdiffusers and valveless micropumps are surveyed. The differences between the performance of microdiffusers and micropumps in steady and unsteady flow regimes are described. Qualitative and quantitative discussions of the effects of different design parameters on the performance of microdiffusers and valveless micropumps in both steady and unsteady flow regimes along with the contradictory results reported in the literature in this regard are provided. In addition, a summary of the latest micropump technologies along with the advantages and disadvantages of each mechanism with the emphasis on the innovative and lessreviewed micropumps are presented. Two important types of fixed microvalves, as part of valveless micropumps are described in details. Experimental flow visualization of steady and pulsating flows through microdiffusers and micropumps as a useful tool for better understanding the underlying micro-fluid dynamics is discussed. The present review reveals that there are many possible areas of research in the field of steady and unsteady flows through microdiffusers and micropumps in order to understand the effects of all important design parameters on the performance of these devices. List of symbols uVelocity in x direction (m/s) v Velocity in y direction (m/s) u max Maximum velocity in x direction (m/s) Q Volumetric flow rate (m 3 /s) Q net Net flow rate (m 3 /s) q Density (kg/m 3 ) p Pressure (Pa) p 0 Static pressure (Pa) t Time (s) x Axial position (m) y Transverse position (m) T Excitation period (s) l Shear viscosity (kg/m s) m Kinematic viscosity (m 2 /s) Re = u max D h /m Reynolds number St = x D h /u max Strouhal number Ro = x D h 2 /m = Re.St Roshko number Wo = D h /d Womersley number V Volume-average velocity (m/s) P Maximum pressure (Pa) Dp Frictional pressure drop (Pa) g Diffuser efficiency g max Maximum diffuser efficiency n d Total pressure loss coefficient in the diffuser direction n n Total pressure loss coefficient in the nozzle direction

Section: Microscale Fluid Rectification: Microvalvesmentioning

confidence: 98%

“…Flow rate increased with increasing the frequency. Hwang et al (2008) developed a numerical model using ANSYS to evaluate the flow rate of a reciprocating valveless micropumps. They compared their calculated results with the experimental data with respect to the peakto-peak voltage (V pp ) and the driving frequency (f).…”

Section: Flow Separationmentioning

confidence: 99%

Steady and unsteady flow analysis in microdiffusers and micropumps: a critical review

Nabavi

2009

“…Pan et al (2001) suggested an optimal frequency range for reciprocating valveless micropumps based on an analytical model. Hwang et al (2008) developed a numerical model using ANSYS to evaluate the flow rate of a reciprocating valveless micropumps. Tsui and Lu (2008) analyzed the flow in a reciprocating valveless micropump using both numerical and lumpedelement methods.…”

Section: Introductionmentioning

confidence: 99%

Numerical analysis of high frequency pulsating flows through a diffuser-nozzle element in valveless acoustic micropumps

Nabavi

Mongeau

2009

The concept of a valveless acoustic micropump was investigated. Two-dimensional, time-varying, axisymmetric, incompressible viscous flows through a planar diffuser-nozzle element were analyzed for applications in valveless acoustic micropumps. The diffuser divergence half-angles (h), and the maximum pressure amplitudes (P) were independently varied. The inflow was periodic and the excitation frequency (f) was varied over the range 10 kHz B f B 30 kHz. The net time-averaged volume flux and the rectification capability of the diffuser were found as functions of h, f, and P. The phase difference between pressure and velocity waveforms, the life time and the size of large scale flow recirculation regions inside the microdiffuser, and energy losses were found to be strongly frequency dependent. Keywords Acoustic micropumps Á Acoustic standing waves Á Microdiffuser Á Numerical analysis List of symbols DP Pressure drop (Pa) d Stokes layer thickness (m) g Rectification capability k Acoustic wavelength (m) l Shear viscosity (kg/m s) m Kinematic viscosity (m 2 /s) x Angular frequency (rad/s) q Density (kg/m 3 ) h Diffuser divergence half-angle (°) n d Pressure loss coefficient in the diffuser direction n n Pressure loss coefficient in the nozzle direction D h Hydraulic diameter of the microdiffuser at the inlet (m) f Excitation frequency (Hz) I Flow inductance (kg/m 4 ) I d Flow inductance in the diffuser direction (kg/m 4 ) I n Flow inductance in the nozzle direction (kg/m 4 ) N Cell numbers P Maximum pressure (Pa) p Pressure (Pa) p 0 Static pressure (Pa) Q Volumetric flow rate (m 3 /s) Q net Net flow rate (m 3 /s) R Flow resistance (kg/m 4 s) R d Flow resistance in the diffuser direction (kg/m 4 s) R n Flow resistance in the nozzle direction (kg/m 4 s) Re Reynolds number T Excitation period (s) t Time (s) U Maximum velocity (m/s) u Velocity in x direction (m/s) v Velocity in y direction (m/s) V net Sectional net velocities (m/s) Wo Womersley number x Axial position (m) x max Maximum fluid displacement during one oscillation cycle (m) y Transverse position (m) Z Flow impedance (kg/m 4 s) Z d Flow impedance in the diffuser direction (kg/m 4 s) Z n Flow impedance in the nozzle direction (kg/m 4 s)

“…The valveless type rectifiers generate a net flow based on a direction-dependent resistance. Some examples, such as the nozzle/diffuser element Olsson et al 2000;Hwang et al 2008), the Tesla structure (Gamboa et al 2006), and a combination form of nozzle/diffuser and Tesla structure (Izzo et al 2007), show that the flow can be pumped out using these simple-patterned designs.…”

Section: Introductionmentioning

confidence: 97%

A microfluidic flow-converter based on a double-chamber planar micropump

Hsu

Sheen

2008

A microfluidic flow-converter that transforms an oscillatory flow into a steady-like flow in a reciprocating-type pumping device is successfully developed in this study. The flow quality at the outlet is found to be significantly improved. The present micro-device is composed of two single-chamber PZT micropumps in parallel arrangement and can be fabricated using simple micro-electromechanical-system (MEMS) techniques. Based on the concept of the electronic bridge converter, the flow rectification is supported by four passive planar valves. Two operation modes, in-phase and anti-phase, were used to test the performance of the present device. In addition, the flow characteristics at the outlet were examined by an externally triggered micro-PIV system. The results reveal that the current flow-converter provided both high volume and smoothly continuous flow rates at the outlet when it was in anti-phase mode. Moreover, the volume flow rate was linearly proportional to the excitation frequency within a specific frequency regime. This indicates that the flowconverter was easily operated and controlled. The present microfluidic flow-converter has great potential for integration into future portable micro-or bio-fluidic systems.