Ersin Sayar

Multifield analysis of a piezoelectric valveless micropump: effects of actuation frequency and electric potential

Coupled multifield analysis of a piezoelectrically actuated valveless micropump device is carried out for liquid (water) transport applications. The valveless micropump consists of two diffuser/nozzle elements; the pump chamber, a thin structural layer (silicon), and a piezoelectric layer, PZT-5A as the actuator. We consider two-way coupling of forces between solid and liquid domains in the systems where actuator deflection causes fluid flow and vice versa. Flow contraction and expansion (through the nozzle and the diffuser respectively) generate net fluid flow. Both structural and flow field analysis of the microfluidic device are considered. The effect of the driving power (voltage) and actuation frequency on silicon-PZT-5A bi-layer membrane deflection and flow rate is investigated. For the compressible flow formulation, an isothermal equation of state for the working fluid is employed. The governing equations for the flow fields and the silicon-PZT-5A bi-layer membrane motions are solved numerically. At frequencies below 5000 Hz, the predicted flow rate increases with actuation frequency. The fluid–solid system shows a resonance at 5000 Hz due to the combined effect of mechanical and fluidic capacitances, inductances, and damping. Time-averaged flow rate starts to drop with increase of actuation frequency above (5000 Hz). The velocity profile in the pump chamber becomes relatively flat or plug-like, if the frequency of pulsations is sufficiently large (high Womersley number). The pressure, velocity, and flow rate prediction models developed in the present study can be utilized to optimize the design of MEMS based micropumps.

Dynamic Analysis of Bulk Acoustic Wave Piezoelectric Micropumps: Effects of Inlet-Outlet Port Angles and Overall Pump Size

Dynamic structural and fluid flow analysis of bulk acoustic wave piezoelectric valveless micropumps are carried out for the transport of water. The micropumps consist of trapezoidal prism inlet/outlet elements; the pump chamber, a thin structural layer and a piezoelectric element (PZT-5A), as the actuator. Governing equations for the flow fields and the structural-piezoelectric bi-layer membrane motions are considered. For the compressible flow formulation, an isothermal equation of state for the working fluid is employed. Two-way dynamic coupling of forces and displacements between the solid and the liquid domains in the systems are considered where actuator deflection and motion causes fluid flow and vice-versa. The effects of inlet-outlet port angles and overall pump size on the flow rate are investigated. The flow rate is found to increase with decreasing outlet convergence angle and increasing inlet divergence angle. In the second part of the present work, the size of the entire micropump is scaled to 50%, 100%, and 200% respectively while electrical parameters are kept constant.Copyright

Electroosmotic Augmentation in Flexural Plate Wave Micropumps

We investigate the effectiveness and applicability of electroosmotic augmentation in flexural plate wave (FPW) micropumps for enhanced capabilities. Flow rates generated in FPW micro-scale flow systems are restricted particularly when the channel height is greater than the acoustic wave length. The proposed concept can be exploited to integrate micropumps into complex microfluidic chips improving the portability of micro-total-analysis systems along with the capabilities of actively controlling acoustics and electrokinetics for micro-mixer applications. A computational study of electroosmotic augmentation in FPW micropumps is presented where FPWs are considered by a moving wall model. A transient analysis of compressible flows of water is performed for microchannels. An isothermal equation of state for water is employed. The nonlinear Poisson-Boltzmann and Laplace equations are used to model the induced electric double layer (EDL) potential and the applied electric potential. Coupled electroosmotic and acoustics cases are investigated for two channel heights while the electric field intensity of the electrokinetic body forces and actuation frequency of acoustic excitations are varied. For deeper microchannels, increasing the actuation frequency of the wall motion does not improve the generated flow rate significantly. Inclusion of electroosmotic effects is more efficient than increasing the intensity of acoustic perturbations whenever high flow rates are required in micro-mixer applications.

Multifield Analysis of a Piezoelectric Valveless Micropump

Coupled multifield analysis of piezoelectrically actuated valveless-micropump MEMS devices are carried out for liquid transport applications. We consider the three-way coupling between electrical, mechanical and fluidic fields in such systems where actuator deflection causes fluid flow through a micropump. Flow contraction and expansion (through a nozzle and a diffuser respectively) generates net fluid flow as the bilayer structural-piezoelectric membrane of the actuator deflects. The analysis involves structural and fluid field couplings in a sequential structural-fluid analysis of the microfluidic device. The effect of the driving voltage on silicon-PZT-5A membrane deflection and flow rate through the inlet/outlet is investigated via time averaging the predicted instantaneous velocity fields. At low actuation frequencies (below 10 kHz), the excitation voltage is a dominant factor on the flow rate of the micropump. The pressure, velocity and flow rate prediction models developed in the present study can be utilized to optimize the design of MEMS based micropumps.Copyright

On the Hydrodynamic Analysis and Heat Transfer Investigation of Forced Oscillated Vertical Annular Fluid Column

Heat transfer from a forced oscillated water column is investigated experimentally and theoretically. Further details of the water flow can be given as mini-scale, vertical, annular, internal, reciprocating and single phase. The inner wall of the stationary concentric element is heated and water is oscillated through the annuli. The data is acquired from the measurements both in the initial transient period and in the pseudo-steady (cyclic) period from the experimental set-up. The effect of the oscillations is observed on the measured temperature field and heat transfer. There is minor radial temperature variation in the water column. Experimental study proved that the frequency, wall heat flux and related wall temperatures are important parameters affecting heat transfer. It is understood that, the effective heat transfer mechanism is enhanced in oscillating flows. Cycle and space-averaged heat convection coefficients are calculated for the present oscillating flows. The physical and mathematical behavior of the resulting heat convection coefficients are analyzed using the data acquired from the experiments. The predicted cycle-space averaged heat convection coefficients using the experimental data are shown to have a logical trend with the experimental observations. The analysis is carried out for different oscillation frequencies at various applied wall heat fluxes while the displacement amplitude remains constant. A novel control volume formulation is introduced in order to investigate pressure distribution and energy balance of water over a cycle for the present reciprocating flow and the formulations are reorganized in order to capture the cycle-averaged energy balance of the control volume. The present study is novel because it appears to be the first paper on the analytical hydrodynamic analysis of forced oscillated vertical annular fluid flow. The present investigation has possible applications in moderate sized wicked heat pipes, solid matrix compact heat exchangers compromising of metallic foams (in some other types of heat exchengers as well), possibly in boilers, filtration equipment, and steam generators.Copyright

Effects of the Structural Layer Material and its Thickness on Positive Displacement Piezoelectric Micropump Performance

Structural dynamic and fluid flow analysis of positive displacement piezoelectric micropumps are carried out for microfluidic water transport applications. The micropump consists of trapezoidal prism inlet/outlet elements; the pump chamber; a thin structural layer and a piezoelectric transducer element. Governing equations for the flow fields; the structural-piezoelectric bi-layer membrane motions and electrical variables are considered. Two-way dynamic coupling of forces and displacements between the solid and the liquid domains in the systems are considered. The effects of the structural layer material selection and the thickness of thin structural layer on the structural deformation and fluid flow are investigated. The variation the structural layer material and its thickness enable the selection of the best micropump design among the investigated micropumps made of silicon and Pyrex glass while other parameters are kept unchanged. The change of the structural layer material is considered here through the variation of density, Young’s modulus and Poisson’s ratio. Optimum membrane thickness is also investigated aiming to generate higher rates of time-averaged flow for the selected micropump structural layer material. The present study is useful in the implementation of the micropumps into lab-on-a-chip microfluidic systems.Copyright

Dynamic Analysis of Piezoelectric Valveless Micropumps: Effects of Piezoelectric Transducer Material

Dynamic structural and fluid flow analysis of bulk acoustic wave piezoelectric valveless micropumps are carried out for the transport of water. The micropumps consist of trapezoidal prism inlet/outlet elements; the pump chamber, a thin structural layer (Pyrex glass) and a piezoelectric transducer element (PZT-5A, PZT-4, or BaTiO3), as the actuator. Flow contraction and expansion, through the trapezoidal prism inlet and outlet respectively, generates net fluid flow. Governing equations for the flow fields and the structural-piezoelectric bi-layer membrane motions are considered. For the compressible flow formulation, an isothermal equation of state for the working fluid is employed. Two-way dynamic coupling of forces and displacements between the solid and the liquid domains in the systems are considered where actuator deflection and motion causes fluid flow and vice-versa. The effects of the piezoelectric transducer material on the flow rate are investigated for several commonly used actuators: PZT-5A, PZT-4, and BaTiO3. The net flow rate developed by the pump varies with the piezoelectric material. PZT-5A actuator generates the largest pump net flow, and the BaTiO3 actuator results in the lowest pump flow.© 2013 ASME

Three Dimensional Dynamic Analysis of a Piezoelectric Valveless Micropump: Effects of Working Fluid

Coupled structural and fluid flow analysis of a piezoelectric valveless micropump is carried out for liquid transport applications. The valveless micropump consists of trapezoidal prism inlet/outlet elements; the pump chamber, a thin structural layer (Pyrex glass) and a piezoelectric element (PZT-5A), as the actuator. Two-way coupling of forces and displacements between the solid and the liquid domains in the systems are considered where actuator deflection and motion causes fluid flow and vice-versa. Flow contraction and expansion (through the trapezoidal prism inlet and outlet respectively) generates net fluid flow. The pressure, velocity, flow rate and pump membrane deflections of the micropump are investigated for six different working fluids (acetone, methanol, ethanol, water, and two hypothetical fluids). For the compressible flow formulation, an isothermal equation of state for the working fluid is employed. Three-dimensional governing equations for the flow fields and the structural-piezoelectric bi-layer membrane motions are considered. Comparison of the pumping characteristics of the micropumps operating with different working fluids can be utilized to optimize the design of MEMS based micropumps in drug delivery and biomedical applications.Copyright

Modeling of Acoustically Augmented Electroosmotic Flows in Microchannels

Effective mixing is restricted in electrosmotically driven flows in microchannels. We investigate the effectiveness and applicability of acoustic augmentation in such flow geometries for enhanced mixing. The proposed device geometry can be exploited to integrate micropumps into complex microfluidic chips improving the portability of micro-total-analysis systems along with the capabilities of actively controlling acoustics and electrokinetics. A computational study of acoustically augmented electroosmotic flow is carried out where flexural plate waves (FPW) are considered. A transient analysis is performed for microchannels with a flexural plate wave with an applied electric field parallel to the channel walls. The nonlinear Poisson-Boltzmann and Laplace equations are used to model the induced electrical double layer (EDL) potential and the applied electric potential. The model predictions are compared with results available in the literature for electroosmotic flow, and for the flows generated by acoustic waves.Copyright