Bi-objective topology optimization of asymmetrical fixed-geometry microvalve for non-Newtonian flow

Fixed-geometry microvalves such as Tesla microvalves rely on the inertial forces of the fluid to allow flow in the desired direction while inhibiting flow in undesired direction. In the traditional topology optimization design methods of fixed-geometry microvalves, single objective function is used to minimize the energy dissipation of forward flow. And several previous studies have widely used diodicity to indicate the performance of fixed-geometry microvalves, which is defined as the ratio of the pressure drop of reverse flow to that of the forward flow. However, higher diodicity does not reflect the degree of forward energy dissipation, leading to a significant pumping power is required to drive flow. Therefore, treating the forward flow pressure drop and its performance independently by a bi-objective formulation is preferable to design fixed-geometry microvalve. This paper proposes a bi-objective topology optimization design method and uses the regularization constraint to design asymmetrical fixed-geometry microvalve for non-Newtonian flow. Several numerical examples with different bifurcation angles, Darcy number and weight coefficients of the bi-objective functions are studied and the validity of the topology optimization method presented in this paper is demonstrated.

     

The effect of the microfluidic diodicity on the efficiency of valve-less rectification micropumps using Lattice Boltzmann Method

The efficiency of the valve-less rectification micropump depends primarily on the microfluidic diodicity (the ratio of the backward pressure drop to the forward pressure drop). In this study, different rectifying structures, including the conventional structures (nozzle/diffuser and Tesla structures), were investigated at very low Reynolds numbers (between 0.2 and 60). The rectifying structures were characterized with respect to their design, and a numerical approach was illustrated to calculate the diodicity for the rectifying structures. In this study, the microfluidic diodicity was evaluated numerically for different rectifying structures including half circle, semicircle, heart, triangle, bifurcation, nozzle/diffuser, and Tesla structures. The Lattice Boltzmann Method (LBM) was utilized as a numerical method to simulate the fluid flow in the microscale. The results suggest that at very low Reynolds number flow, rectification and multifunction micropumping may be achievable by using a number of the presented structures. The results for the conventional structures agree with the reported results.     

Modeling and experimental validation of a piezoelectric micropump with novel no-moving-part valves

No-moving-part (NMP) valves are microconduits able to partially rectify an oscillating fluid moving through them. The modeling of such valves is not at all trivial. Even greater difficulties arise when the behavior of the whole micropump equipped with those NMP valves is investigated, because of the complex fluid-dynamic phenomena interacting with deformable structures. This paper proposes a generalization of the efficiency modeling, nowadays used for single valves, to whole micropump equipped with them. Such modeling has been applied to design a novel, high efficiency NMP valve to be used in a piezoelectric micropump. The main feature of the new valve is the presence of some properly shaped vortex area along its fluid-dynamic pattern, allowing to improve micropump performance. For comparison purposes, the same modeling has been applied to a standard nozzle-diffuser NMP valve to be used with the same piezoelectric actuator. The experimental comparison of micropump performance (maximum flow rate and pressure head) shows that the proposed modeling technique is able to discriminate between better and worse performer. The effects of unsteady dynamic effects have been evaluated a posteriori, confirming their important weight on the actual performance of the micropumps equipped with NMP valves.     

Single-step replicable microfluidic check valve for rectifying and sensing low Reynolds number flow

This paper presents a new microfluidic check valve well suited for low Reynolds number flow rate sensing, micropump flow rectification, and flow control in lab-on-a-chip devices. The valve uses coupling between fluid movement in a channel and an elastomeric column (flap) suspended in the fluid path to generate a strong anisotropic flow resistance. Soft lithography-based molding techniques were used to fabricate the valve, allowing for a low-cost, single-step fabrication process. Three valves—having heights of 25, 50, and 75 μm, respectively—were fabricated and experimentally evaluated; the best of them demonstrated a maximum fluidic diodicity of 4.6 at a Reynolds number of 12.6 and a significant diodicity of 1.6 at the low Reynolds number of 0.7. The valve’s notable low Reynolds number response was realized by adopting a design methodology that balances the stiffness of the elastomer flap and adhesion forces between the flap and its seat. A pair of elastomer check valves integrated with a miniature membrane actuator demonstrated a flow rectification efficiency of 29.8%. The valve’s other notable features include a wide bandwidth response, the ability to admit particles without becoming jammed, and flow rate sensing capability based on optical flap displacement measurements.     

Analysis of fluid flow and deflection for pressure-balanced MEMS diaphragm valves

Based on the linear plate theory for an elastic thin plate and the Bernoulli equation for a steady incompressible and inviscid fluid flow, the effect of fluid flow on the deformation of microelectromechanical systems (MEMS) diaphragm valve is investigated both analytically and numerically. For a given configuration of diaphragm valve, a relationship between the applied pressure and resulting contact area between diaphragm and valve seat is derived. Possible instability of such a system under the pressure-balanced mechanism is demonstrated with both analytical and numerical solutions for the deflection. Deflection as a function of flow speed, radius of outlet orifice, inlet gap, and bending stiffness of diaphragm are presented. In addition, the effect of diaphragm making contact with the valve seat due to pressure differential and fluid flow is analyzed and a relation between the contact zone and the external pressure is obtained. The results of the analysis suggest important parameters in the design of MEMS diaphragm valves and can be used as a basis in the design of such valves.     

A ferrofluidic magnetic micropump

A microfluidic pump is described that uses magnetic actuation to push fluid through a microchannel. Operation relies on the use of magnetically-actuated plugs of ferrofluid, a suspension of nanosize ferromagnetic particles. The ferrofluid contacts but is immiscible with the pumped fluid. The prototype circular design demonstrates continuous pumping by regenerating a translating ferrofluidic plug at the conclusion of each pumping cycle. The flow rate can be controlled by adjusting device dimensions or the velocity of an external permanent magnet that directs the motion of the ferrofluid. The ferrofluidic plugs also serve as valves; if the magnetic actuator is stopped, pressure can be maintained with no power consumption. Flow can also be reversed by switching the direction of actuation. The maximum flow rate achieved with minimal backpressure was 45.8 μl/min. The maximum pressure head achieved was 135 mm water (1.2 kPa)     

Liquid and gas flows in microchannels of varying cross section: a comparative analysis of the flow dynamics and design perspectives

This paper presents a comparative study of the flow of liquid and gases in microchannels of converging and diverging cross sections. Towards this, the static pressure across the microchannels is measured for different flow rates of the two fluids. The study includes both experimental and numerical investigations, thus providing several useful insights into the local information of flow parameters as well. Three different microchannels of varying angles of convergence/divergence (4°, 8° and 12°) are studied to understand the effect of the angle on flow properties such as pressure drop, Poiseuille number and diodicity. A comparison of the forces involved in liquid and gas flows shows their relative significance and effect on the flow structure. A diodic effect corresponds to a difference in the flow resistance in a microchannel of varying cross section, when the flow is subjected alternatively to converging and diverging orientations. In the present experiments, the diodic effect is observed for both liquid and gas as working fluids. The effect of governing parameters—Reynolds number and Knudsen number, on the diodicity is analysed. Based on these results, a comparison of design perspectives that may be useful in the design of converging/diverging microchannels for liquid and gas flows is provided.     

Subdynamic asymptotic behavior of microfluidic valves

Decreasing the Reynolds number of microfluidic no-moving-part flow control valves considerably below the usual operating range leads to a distinct "subdynamic" regime of viscosity-dominated flow, usually entered through a clearly defined transition. In this regime, the dynamic effects on which the operation of large-scale no-moving-part fluidic valves is based, cease to be useful, but fluid may be driven through the valve (and any connected load) by an applied pressure difference, maintained by an external pressure regulator. Reynolds number ceases to characterize the valve operation, but the driving pressure effect is usefully characterized by a newly introduced dimensionless number and it is this parameter which determines the valve behavior. This summary paper presents information about the subdynamic regime using data (otherwise difficult to access) obtained for several recently developed flow control valves. The purely subdynamic regime is an extreme. Most present-day microfluidic valves are operated at higher Re, but the paper shows that the laws governing subdynamic flows provide relations useful as an asymptotic reference.     

基于STAR-CCM+的高速动车组驱动齿轮箱内部流场分析

为研究齿轮箱初始注油量、齿轮旋转方向等因素对齿轮箱内部润滑油瞬态分布、压力瞬态分布和各轴承进/回油孔润滑油质量流量的影响,基于齿轮箱内部不可压缩的气液两相流,采用STAR-CCM+软件的重叠网格技术对高速动车组驱动齿轮箱内部流场进行仿真.结果 表明:当大齿轮正转时,受螺旋方向的影响,车轮侧各轴承进油量大于电机侧轴承进油量;当大齿轮反转时,各轴承进油量受螺旋方向的影响较小;随着初始注油量增加,各轴承进油孔的质量流量也增加;齿轮箱内部流场达到稳态时,内部压力总体上较为平均,仅啮合区存在局部高压区与负压区.研究结果对齿轮箱润滑流道结构设计具有指导意义.     

Polymer microvalve with pre-stressed membranes for tunable flow�Cpressure characteristics

A novel, inexpensive, polymer-based valve approach is presented that offers the combination of a check valve’s rectifying properties with the possibility to actively control the flow rate in the forward (open) direction. An elastic membrane with an incision is clamped between two rigid polymer plates and expands when pressure is applied in the forward direction allowing fluid to pass. In the backward direction, expansion of the membrane is not possible and flow is prevented. Varying the clamping force influences the expansion capability of the membrane due to its elasticity and thus enables control of the flow rate.     

Optimization of design and characterization of a novel micro-pumping system with peristaltic motion

In this work, we present a novel design of peristalsis based micro pump with optimized fluid chambers possessing improved discharge efficiency per unit volume of the pumping architecture and reduced reverse flow. Such designs are very often important from the standpoint of blood cell sorting assays where a full delivery of fluid containment within the pumping chamber is critical. The paper uses FLUENT and COMSOL simulations to look at the fluid flow within the pumping chamber due to the deflecting actuator membrane during pumping cycle. The resulting effect of fluid-membrane interaction has been evaluated on different chamber designs for observing the lateral velocity distribution profile of fluid in the connecting channels. It has been observed through particle image velocimetry (PIV) that the optimized design has minimized chamber retainability with maximum deflection of the actuator membrane and minimum reverse flow component. Optimized geometrical profile formulated above was seen to allow the maximum contact area between actuating membrane and fluid containment thus reducing the problem of fluid retainability. Other experimental studies show that the new design has much lower percentage retainability of biological and other fluids contained within the chambers which makes it a comparatively high efficiency micropumping system with respect to the conventional design with circular membrane and chambers. The experimental evaluation of the new micro pump design has shown its least count to be 0.1 μl/min which is very well comparing with some of the other micropumping mechanisms like electro-osmotic, magneto-hydrodynamic mechanisms (Laser and Santiago in J Micromech Microeng 14:35, 2004; Iverson et al. 2008) and additionally provides better discharge efficiency per unit volume of the pumping architecture, lower retainability, minimized reverse flow and precise pumping of fluids.     

Development of micro-vibrating flow pumps using MEMS technologies

In the present paper, we propose a micro-vibrating flow pump (micro-VFP), which is a novel micropump. The micro-VFP is constructed using an actively vibrating valve that has a cantilever-like structure fixed on a wall of a microchannel and a slit orifice downstream. The slit orifice is designed to make the flow asymmetric around the vibrating valve and to effectively generate a net flow in one direction. At the same time, the valve works as an actuator to induce liquid flow in the microchannel. Since the valve is made of a flexible material including magnetic particles, it is manipulated by changing the magnetic field from outside the micro-VFP. This design allows external operation of the micro-VFP without any electrical or mechanical connections. In addition, the micro-VFP, which realizes pumping with a chamber free design, is advantageous for implementation in a small space. In order to demonstrate its basic pumping performance, a prototype micro-VFP was fabricated in a microchannel with a cross section of 240?μm?×?500?μm using microelectromechanical systems technologies. The vibration characteristics of the valve were investigated using a high-speed camera. The pump performance at various actuation frequencies in the range of 5 to 25?Hz was evaluated by measuring the hydrostatic head and the flow rate. The proposed micro-VFP design exhibited an increase in performance with the driving frequency and had a maximum shut-off pressure of 3.8?±?0.4?Pa and a maximum flow rate of 0.38?±?0.02?μl/min at 25?Hz. Furthermore, in order to clarify the detailed pumping process, the flow characteristics around the vibrating valve were investigated by analyzing the velocity field based on micron-resolution particle image velocimetry (micro-PIV). The validity of the hydrostatic measurement was confirmed by comparing the volume flow rate with that estimated from micro-PIV data. The present study revealed the basic performance of the developed micro-VFP.     

Proportional directional valve based automatic steering system for tractors

Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3- position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative (PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods.     

Passive MEMS Valves With Preset Operating Pressures for Microgas Analyzer

In this paper, we present integrated disk-in-cage poppet valves with tuned spring stiffness for gas flow control of a microgas analyzer. The valves require zero power and close at preset offset pressures (0–35 psig) to switch from gas sample loading onto a preconcentrator to concentrated constituent sample injection into a microgas chromatograph. Air flow rates of 4.5 mL/min at pressures of $-$ 2.5–$-$5 psig (vacuum sample loading) were measured. Hydrogen leak rates of 0.1 $muhbox{L}/hbox{s}$ (0.006 mL/min) were measured with valves closed at 15 psig. Analytical and numerical modeling was used to guide design of valve spring constants (ranging from 10 to 1500 N/m) that control the valve open position, flow rate, and closing pressure. The parameter design space is limited to a range of seat overlap, valve size, and spring stiffness that will allow adequate flow rate, sealing, and closing at predictable pressures. A linear curve defining closing pressure as a function of spring constant, valve gap, valve size, and seat overlap fit measured closing pressure data and can be used to predict closing pressure for future designs. $hfill$ [2008-0002]      

Optimization of a butterfly valve disc using 3D topology and genetic algorithms

Butterfly valves are a mechanical component used to regulate flow and pressure on a variety of tanks and pipeline systems. The design of this flow-control device needs to consider its structural performance as well as the flow of the fluid. In this sense, simulation and optimization tools play an important role in a butterfly valve successful development. This paper presents a global optimization of the disc of a butterfly valve by the combination of topology and shape optimization techniques. Topology optimization is employed during concept design stage to evaluate the best material distribution from a structural performance point of view. Then, based on the topology optimization results, a shape optimization, managed by Genetic Algorithms (GAs), is conducted considering structural and fluid dynamics at the same time. The results demonstrate the suitability of the proposed approach to obtain a light butterfly valve disc which satisfies the structural safety and the flow requirements.

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A polymer-based bidirectional micropump driven by a PZT bimorph

This paper presents a polymer-based micropump for liquid control or drug delivery. The dimension of the pump was 20 × 24 × 3 mm³. A pair of O-ring SU-8 passive valves was fabricated by lift-off technique to control the fluid movement. Micropumps with dimple, bridge, and cantilever valves were studied. The PZT bimorph acted on the polymer membrane to periodically drive fluid. The maximum flow rate was 16.4 ml/min, and the back pressure was 1,525 mmH₂O at 150 V (Vp-p). In frequency sweeping experiments, two flow rate peaks and back pressure peaks were analyzed. Bidirectional flow rate was achieved by changing the valve seat from a one-size hole to a step hole. The maximum backward flow rate was 5.1 ml/min, and the driving frequency was about 355 Hz higher than the forward flow rate driving frequency.     

Hydrodynamic trap-and-release of single particles using dual-function elastomeric valves: design, fabrication, and characterization

This paper introduces a simple method for trapping and releasing single particles, such as microbeads and living cells, using dual-function elastomeric valves. Our key technique is the utilization of the elastomeric valve as a dual-function removable trap instead of a fixed trap and a separate component for releasing trapped particles, thereby enabling a simple yet effective trap-and-release of particles. We designed, fabricated, and characterized a microfluidic-based device for trapping and releasing single beads by controlling elastomeric valves driven by pneumatic pressure and a fluid flow action. The fluid flow is controlled to ensure that beads flowing in a main stream enter into a branch channel. A bead is trapped by deflected elastomeric valves positioned at the entrance of a branch channel. The trapped bead is easily released by removing the applied pressure. The trapping and releasing of single beads of 21?μm in diameter were successfully performed under an optimized pressure and flow rate ratio. Moreover, we confirmed that continuous trapping and releasing of single beads by repeatedly switching elastomeric valves enables the collection of a controllable number of beads. Our simple method can be integrated into microfluidic systems that require single or multiple particle arrays for quantitative and high-throughput assays in applications within the fields of biology and chemistry.     

预应力压电泵的结构设计与实验研究

提出了一种由压电晶片驱动的新结构微泵,采用精密机械加工工艺制作而成。设计了预应力阀膜,组装压电微泵,对预应力阀的可靠性和压电微泵的液体输送特性做了研究。通过系统的实验研究证明：预应力压电泵具有很好的防倒吸能力,稳定性高,具有很好的工作性能,在250V,200Hz方波信号下,流速可达5．5027mL／min,且适于微型化,可为该类型泵的实际应用提供有意义的借鉴。     

Topology optimization applied to the design of 2D swirl flow devices

The design of fluid devices, such as flow machines, mixers, separators, and valves, with the aim to improve performance is of high interest. One way to achieve it is by designing them through the topology optimization method. However, there is a specific large class of fluid flow problems called 2D swirl flow problems which presents an axisymmetric flow with (or without) flow rotation around the axisymmetric axis. Some devices which allow such simplification are hydrocyclones, some pumps and turbines, fluid separators, etc. Once solving a topology optimization problem for this class of problems using a 3D domain results in a quite high computational cost, the development and use of 2D swirl models is of high interest. Thus, the main objective of this work is to propose a topology optimization formulation for 2D swirl flow fluid problem to design these kinds of fluid devices. The objective is to minimize the relative energy dissipation considering the viscous and porous effects. The 2D swirl laminar fluid flow modelling is solved by using the finite element method. A traditional material model is adopted by considering nodal design variables. An interior point optimization (IPOPT) algorithm is applied to solve the optimization problem. Numerical examples are presented to illustrate the application of this model for various 2D swirl flow cases.