Alireza Azarbadegan

Analytical Model of Valveless Micropumps

The flow driven by a valveless micropump with a single cylindrical pump chamber and two diffuser/nozzle elements is studied theoretically using a 1-D model. The pump cavity is driven at an angular frequency omega so that its volume oscillates with an amplitude <i>V</i> _m. The presence of diffuser/nozzle elements with pressure-drop coefficients zeta₊, zeta_- (> zeta +) and throat cross-sectional area <i>A</i> ₁ creates a rectified mean flow. In the absence of frictional forces the maximum mean volume flux (with zero pressure head) is <i>Q</i> ₀ where <i>Q</i> ₀/<i>V</i> _momega = (zeta_- - zeta₊)pi/16(zeta_-+ zeta₊), while the maximum pressure that can be overcome is Delta<i>P</i> _max where Delta<i>P</i> _max <i>A</i> ₁ ²/<i>V</i> _m ² omega² = (zeta_- - zeta₊)/16. These analytical results agree with numerical calculations for the coupled system of equations and compare well with the experimental results of Stemme and Stemme.

Investigation of Double-Chamber Series Valveless Micropump: An Analytical Approach

We describe an analytical study of the characteristics of a double-chamber series valveless micropump using a one-dimensional non-linear model. We derive a closed-form expression for relationship between the mean volume flux, pressure difference and measurable characteristics of the pump. To first order, the results show the linear decrease of the volume flux with the pressure difference, which is consistent with other types of valveless pump configurations.

Combination Rules for Multichamber Valveless Micropumps

The general design rules indicate that when identical macroscale pumps (each with a maximum flowrate Qm, and maximum pressure drop ΔPmax) are combined in series, the maximum flowrate is Qm, but the maximum pressure drop becomes 2ΔPmax, while combined in parallel the maximum flowrate becomes 2Qm, and the maximum pressure is ΔPmax. In this paper, we test whether these design rules apply to microscale valveless micropumps using highly resolved CFD calculations. The variation of flow with pump pressure drop is studied by varying the resistance of an external circuit. The analysis confirmed that the macroscale design rules for macroscale pumps are applicable to microscale pumps. The study also enabled the influence of different forcing strategies on the pump performance to be analyzed.

Fluid–structure coupling in valveless micropumps

Valveless micropumps work on the principle that the reciprocal forcing of fluid by an actuator through diffuser/nozzle elements generates a rectified mean flow. The pump characteristics depend on the coupling between the fluid and structure. We analyze the characteristics of valveless micropumps by developing a coupled model for the area-averaged membrane displacement and the rectified flow through the diffuser/nozzle elements. Analytical expressions are derived for the pump flow rate Q and pressure drop ΔP characteristics as functions of the forcing frequency. The predicted natural angular frequency is compared against published results and the agreement is reasonable. The model shows that the maximum flow rate Qmax satisfies Qmax ~ ω for ω/ωN 1, which is supported by published experimental data. The maximum pressure ΔPmax satisfies ΔPmax ~ ω2 for ω/ωN 1. The available experimental data are sparse (in comparison to Qmax). The general model is applicable to all valveless micropumps which incorporate diffuser/nozzle elements.

CHARACTERIZATION AND OPTIMIZATION OF A THREE DIMENSIONAL T-TYPE MICROMIXER FOR CONVECTIVE MIXING ENHANCEMENT WITH REDUCED PRESSURE LOSS

Numerical simulations and experiments are used to evaluate the flow and mixing characteristics of a proposed convective 3-D T-type micromixer. The study presents a parametric study and performance optimization of this micromixer based on the variation of its geometry. To investigate the effect of design and operation parameters on the device performance, a systematic design and optimization methodology is applied; it combines Computational Fluid Dynamics (CFD) with an optimization strategy that integrates Design of Experiments (DOE), Surrogate modeling (SM) and Multi-Objective Genetic Algorithm (MOGA) techniques. The degree of mixing and the pressure loss in the mixing channel are the performance criteria to identify optimum designs at different Reynolds numbers (Re). The convective flow generated in the 3-D T-type micromixer drastically enhances mixing at Re > 100 by making the two fluids to roll up along the mixing channel. The resulting optimum designs are fabricated on polymethylmethacrylate (PMMA) by CNC micromachining. Experiments are carried out to visualize the streams of de-ionized water and aqueous fluorescein solution, by which the extent of mixing is determined, based on the standard deviation of fluorescein intensities on cross-section images. This study applies a systematic procedure for evaluation and optimization of a proposed 3-D T-mixer which has a configuration of channels that promote convective mixing since the two fluids come into contact. The methodology applied can also be used to efficiently modify and customize current micromixers.Copyright

Analysis and optimization of a passive micromixer with curved-shaped baffles for efficient mixing with low pressure loss in continuous flow

Numerical simulations and an optimization method are used to study the design of a planar T-micromixer with curved-shaped baffles in the mixing channel. The mixing efficiency and the pressure loss in the mixing channel have been evaluated for Reynolds number (Re) in the mixing channel in the range 1 to 250. A Mixing index (Mi) has been defined to quantify the mixing efficiency. Three geometric dimensions: radius of baffle, baffles pitch and height of the channel, are taken as design parameters, whereas the mixing index at the outlet section and the pressure loss in the mixing channel are the performance parameters used to optimize the micromixer geometry. To investigate the effect of design and operation parameters on the device performance, a systematic design and optimization methodology is applied, which combines Computational Fluid Dynamics (CFD) with an optimization strategy that integrates Design of Experiments (DOE), Surrogate modeling (SM) and Multi-Objective Genetic Algorithm (MOGA) techniques. The Pareto front of designs with the optimum trade-offs of mixing index and pressure loss is obtained for different values of Re. The micromixer can enhance mixing using the mechanisms of diffusion (lower Re) and convection (higher Re) to achieve values over 90%, in particular for Re in the order of 100 that has been found the cost-effective level for volume flow. This study applies a systematic procedure for evaluation and optimization of a planar T-mixer with baffles in the channel that promote transversal 3-D flow as well as recirculation secondary flows that enhance mixing.Copyright

Optimization of diffuser/nozzle elements for rectification valveless micropumps

There has been a growing interest in understanding the flow behaviour inside diffuser/nozzle elements in order to identify performance characteristics of these elements for micropump applications. Flat-walled diffuser/nozzle element is the most commonly used type for valveless micropump applications due to its ease of fabrication and compact design. In this paper, we study generic flat-walled diffuser/nozzle elements and apply optimization techniques to explore how the pumping efficiency can be improved by changing geometry to provide higher rectification efficiency and lower pressure drop in rectification valveless micropumps. The primary motivation for this study is to evaluate the performance of flat-walled diffuser/nozzle elements based on geometry variations under several Reynolds numbers (Re). In this study we employ a design methodology for diffuser/nozzle elements that incorporates computational fluid dynamics (CFD) within an optimization methodology. To start the process a series of geometric parameters are selected including element neck width, depth, divergence angle, and entrance fillet radius. Then, the pressure drop and rectification property of an element are calculated as performance parameters, i.e., by varying the geometry it is desirable to maximise pressure rise and the rectification property of the element. Design of experiments (DOE) is employed to generate the experimental table which corresponds to different geometries representing the design space. These limited numbers of geometries generated by DOE are evaluated by using CFD to obtain corresponding performance parameters. By preparing all the design and performance parameters, Surrogate model (SM) technique is applied to obtain the relationship (approximation function) between design and performance parameters. Eventually, based on the developed approximation functions or response surfaces, a multi-objective genetic algorithm (MOGA) is employed to maximise pressure rise and rectification property of diffuser/nozzle element. This design methodology is a very powerful tool to design and optimise flat-walled diffuser/nozzle elements for micropump applications and can speed up the micropump design process significantly.

Computational study of peristaltic micropumps

A computational study of peristaltic micropumps is presented. The peristaltic micropump considered in this study consists of two to five chambers in series which rectify the flow by means of both peristaltic movement of actuators and diffuser/nozzle elements. We consider a closed loop configuration in order to reduce the error introduced by presence of inlet/outlet boundary conditions. The characteristics of these pumps such as maximum volume flux and pressure drop were investigated. In addition, the viability of such pumps to work with cells was examined by calculating the maximum shear stress and strain rate.