A valve-less micro-pump was realized with just one diffuser/nozzle element. The pressure-loss in a nozzle is lower than that in a diffuser, and therefore one-way flow may be realized in the nozzle direction. The frequency characteristics and the pump characteristics are measured. Dimensionless numbers are introduced to rearrange the measured data and to understand the physical mechanisms of the micro-pump. Simplified analysis was done for unsteady operation of the pump by considering the channel geometries and pressure-loss coefficients based on Bernoulli’s theorem. The calculated pump characteristics agreed with the measured ones. Numerical calculations were made using the commercial CFD (computational fluid dynamics) code CFX. The calculated flow patterns showed differences between the diffuser and nozzle directions.

This paper reports the fabrication of planar nanochannels in silicon and thermoplastic. Conventional technologies such as reactive ion etching (RIE) and anodic bonding were used for fabricating the silicon-based nanochannels, while hot embossing and thermal bonding were used for polymer-based nanochannels. Due to the limit of photolithography, the lateral dimension of the channels are kept on the order of micrometers. The depth can be controlled precisely by etch rate or deposition rate. While fabrication technologies for nanochannels in silicon and glass are established and straightforward to implement, fabrication of planar nanochannels in a plastic is challenging because of the more severe collapsing of the structure during bonding. Besides the silicon technology, we demonstrate a simple and low-cost fabrication technology of planar nanochannels by hot-embossing in a thermoplastic and bonding below the glass transition temperature.

Mini and microchannel applications have become an important and attractive research area during the past decades. For micro systems design purposes, numerical and experimental studies have been conducted on flow and heat transfer characteristics of mini and microchannels and various friction factor and Nusselt number correlations have been proposed. Some researchers have tried to apply conventional tube correlations to mini and micro channels, rather than deriving new correlations. In this study, using commercial CFD software, flow and heat transfer characteristics in laminar and turbulent flow through circular channels are analyzed numerically. The applicability of conventional correlations in calculating the friction factor and Nusselt number is investigated. It is concluded that, in laminar regime conventional correlations can be used to calculate the friction factor for the channel sizes considered. In turbulent regime, however, numerical results for friction factor yielded greater values than those calculated by the conventional correlations. Numerical Nusselt numbers are found to be closer to the conventional values in laminar and turbulent regimes. In turbulent regime, on the other hand, Nusselt number values calculated with the microchannel correlations are determined to be greater than the numerical results and the values calculated with the conventional correlations.

A novel technique for the fabrication of electromagnetic micro actuators was proposed and a prototype was designed and fabricated in this study. The constituent parts of the designed actuator are comprised of the diaphragm, the micro coils, and the magnet. When an electrical current was applied to the micro coils, the magnetic force between the magnet and the coil is produced, causes the diaphragm to deflect and becomes the source of actuation. The fabrication process of the actuator combines Optical Lithography, Electron Beam Evaporation, and Electroplating. The structure of the actuating device uses PDMS as the vibrating diaphragm and electroplated copper as the coils. The diaphragm deflection can be regulated by varying the electrical current passed through the micro coil and hence the actuating effects can be controlled. The experimental results show that the maximum diaphragm deflection within elastic limits is 150 μm at an electrical current of 0.6 A for a micro coil of 100 μm line width. The micro electromagnetic actuator proposed in this study is easily fabricated and is readily integrated with Lab-on-a-Chip systems due to its planar structure.

Many biological studies, drug screening methods, and cellular therapies require culture and manipulation of living cells outside of their natural environment in the body. The gap between the cellular microenvironment in vivo and in vitro, however, poses challenges for obtaining physiologically relevant responses from cells used in basic biological studies or drug screens and for drawing out the maximum functional potential from cells used therapeutically. One of the reasons for this gap is because the fluidic environment of mammalian cells in vivo is microscale and dynamic whereas typical in vitro cultures are macroscopic and static. This presentation will give an overview of efforts in our laboratory to develop programmable microfluidic systems that enable spatio-temporal control of both the chemical and fluid mechanical environment of cells. The technologies and methods close the physiology gap to provide biological information otherwise unobtainable and to enhance cellular performance in therapeutic applications. Specific biomedical topics that will be discussed include subcellular signalling in normal and cancer cells, in vitro fertilization on a chip, studies of the effect of physiological and pathological fluid mechanical stresses on endothelial and epithelial cells, and microfluidic stem cell engineering. In the nanoscale regime, tunable nanochannels that can manipulate single DNA molecules will be discussed.

The fluidic oscillator is one solution to the problems of water management of the Polymer Electrolyte Membrane Fuel Cell (PEMFC). In low temperature fuel cells such as the PEMFC, liquid water is produced as a byproduct. At low gas flow rates, the water produced has a tendency to plug the reactant supply channels. When the channels are plugged, reactant supply to the catalyst sites is prohibited and results in fuel cell failure. One proposed method of removing a water drop is to oscillate the drop near its natural frequency in order to free it from the substrate. A variety of methods for oscillating the drop are available including mechanical vibrations, acoustic vibrations and flow pulsations. It is the latter method, i.e., use of the fluidic oscillator that is investigated in this study. The purpose of this paper is to use the experimental and numerical techniques to study and simulate a fluidic oscillator so that detail of flow physics inside the oscillator can be realized. Method on how to use the flow field solution to determine the oscillator response frequency is also described. Numerically results of oscillator frequency will be compared with the available experimental data.

This study presents a diffuser micropump and characterizes its output flow rates, like the parabola shape on the frequency domain and the effecting factors. First, equivalent circuit using fluid-electric analogy was built up; then, the flow rate analysis results were compared to experiment results to verify the applicability of the circuit simulation. The operation frequency was 800 Hz for both cases and the maximum flow rates were 0.078 and 0.075 μl/s for simulation and experiment result, respectively. The maximum flow rate difference was 3.7%. The circuit then was used to analyze the inertial effects of transferred fluid as well as system components to the output flow rates. This work also explains why the flow rate spectrum has the shape of parabola. The analysis results showed that without inertial effects, the micropump flow rates are linearly proportional to the operation frequency; otherwise it has parabola shape. The natural frequency of the actuator-membrane structure was recognized using finite element method to verify if this parameter affects the characteristics of the flow rates. The experiment and simulation results demonstrated 800 Hz and 91.4 kHz for the frequency of the maximum pumping flow rate and the first mode natural frequency of actuator-membrane structure, respectively. It indicates that the structure natural frequencies of the actuator-membrane structure do not play any role to operate the micropumps.

The objective of the present study is to investigate the effects of the microchannel geometry on the dynamic behaviour of liquid water emerging from a pore into a microchannel of a cross gas flow. The flow characteristics are resolved using the volume-of-fluid (VOF) method in conjunction with an interface tracking technique. A microchannel with dimensions of a typical proton exchange membrane fuel cell (PEMFC) gas channel (a square cross section of 250 μm in width) and a pore of 50 μm in diameter on the bottom wall is adopted as the baseline case. Simulations for microchannels of different cross sections, including trapezoid, upside-down trapezoid, triangle, rectangle, and rectangle with a arch bottom wall, are performed and the results are compared with the baseline case. The evolution of liquid water includes stages identified as emergence, growth, deformation, detachment, and remove. The simulations show that the cross section of the microchannel has significant impacts on the dynamics of the water droplet. The detachment time and diameter and the remove time of the water droplet are found to be in this order: triangle < trapezoid < rectangle with arch bottom wall < rectangle < upside-down trapezoid. The present study will advance our understanding in the transport of liquid water in a PEMFC where water is produced in the catalyst layer and flows through the pores of the porous electrode to the gas channel.

Fundamental studies in nanofluidics have attracted significant attention in the past decade since the success of nanofluidic devices depends on a thorough understanding of the fluidic, ionic, and molecular behaviors in highly confined nano-environments. In this work, molecular dynamics simulations of the effect of surface charge densities on the ion and water distribution in the near wall region has been performed for both (100) and (111) silicon surfaces. We demonstrate that surface charges not only interact with mobile ions in the electrolyte, but also interact with water molecules due to their polarizability and hence influence the orientation of water molecules close to the charged surface. It is shown that as the surface charge density increases, water molecules within ∼ 5 Å from the (100) silicon surface can evolve from one layer into two layers and meanwhile, the orientation of water molecules is more aligned instead of randomly distributed. However, no extra water layer is observed near a (111) silicon surface even under a surface charge density of as high as −0.2034 C/m 2 . The above phenomenon may be related to the different surface atom densities of (100) and (111) silicon surfaces.

This paper reports flow visualization experiments of fluid mixing in a microchamber on a rotating disk. The two centrifuge-driven sample fluids were brought in contact at the Y-junction microchannel and then flowed to a circular mixing chamber where the main course of mixing took place. The flow images were acquired using a micro-image-capturing unit in synchronization with the rotational motion to allow only one shot of the targeted object on the rotating disk per revolution. Both the visualization and quantification of flow images show that the mixing efficiency of the two fluids depends not only on the rotational speed but also on the depth of the channels. It is found that the mixing efficiency generally decrease with increasing rotational speed in the lower speed range (≤ 420 rpm). Beyond this lower speed range, the mixer with a larger channel depth h = 300 μm shows an increase of mixing efficiency with increasing rotational speed to reach as much as 83% at 1200 rpm. For the mixer with a smaller channel depth h = 200 μm, however, the mixing efficiency continues deceasing or becomes flat with increasing rotational speed. It is also found that the counter-clockwise rotation produces a better mixing efficiency than the clockwise rotation in the high speed range.

Nanofluidic sensors have been developed over the past decade and demonstrated the capability of sensing single DNA molecules. One class of nanofluidic devices is based on the resistive pulse sensing technique and a modulation of the baseline ionic current can be observed when molecules are translocated through the sensing nanopore or nanochannel. In this scheme, the ionic current modulation is approximately the same as the channel resistance modulation, requiring the channel size be comparable to the molecules to be detected. In this paper, we present a new sensing scheme to detect the translocation of particles through a fluidic channel, which amplifies the resistance modulation by 40–80 times. The device connects the gate of a MOSFET with a fluidic circuit and monitors the drain current modulation of the MOSFET to detect particles, instead of directly monitoring the ionic current through the fluidic channel. The minimum volume ratio detected is 0.006%, about ten times smaller than the lowest detectable volume ratio reported in the literature by using the resistive pulse sensing technique. Although at current stage the device is only fabricated at microscale level, we envision that the same scheme can be applied in nanofluidic devices for single molecule detection.

This study demonstrated electroosmotic pumping with high flow rate per unit area at a rather low applied voltage through an alumina nano-porous membrane driven by Platinum mesh electrodes. The electrode was placed perpendicular to, and had direct contact with nano-channel inlet to reduce the electric voltage drop in the reservoir. The complete set of the Poisson-Nernst-Planck equations for electrical potential and ionic concentration, coupled with the Navier-Stokes equation were solved for the purpose of a full understanding of the ionic transport and flow characteristics of EOF in nano-fluidics capillaries. The measured flowrate versus electrolyte (KCl) concentration reveals that the flowrate is usually high in low concentration (10 −5 M∼10 −7 M) regime in which a maximum value also occurs. In addition, a remarkable surge of flow rate is observed when the concentration surpasses below 10 −4 M. The maximum flowrate achieved from this study is 0.09 mL min −2 V −1 cm −2 and the energy transfer efficiency is 0.43% at an operation voltage of 20V. The flowrates investigated in this study are comparable to other existing results whereas the corresponding operation voltage used this study is about one to two order lower than most existing results. Numerical results exhibit correct trends for nano flows involving strong overlap of electrical double layers. Comparisons of numerical and experimental results were made and discussed.

The current study presents a new integrated microfluidic chip for rapid ribonucleic acid (RNA) purification, extraction and reverse transcription (RT) in an automatic fashion. The miniature system consists of two individual functional devices including a two-way microfluidic control module and a magnetic field/temperature control module. The functional microfluidic control module can perform pumping, mixing, purification and concentration of the RNA samples by incorporating with the magnetic bio-separator consisting of 2-dimension twisted microcoils. Notably, the magnetic bio-separators are developed either to perform the separation of magnetic beads or to control the temperature field for the subsequent RT process. Experimental results showed that the total RNA was successfully purified and extracted by the magnetic beads, and the subsequent RT process of RNA was completed automatically. As a whole, the developed system may provide a powerful platform for biomedical application and biological analysis.

Optical devices which incorporate liquids as a fundamental part of the structure can be traced at least as far back as the 18th century where rotating pools of mercury were proposed as a simple technique to create smooth mirrors for use in reflecting telescopes. Modern microfluidic and nanofluidics has enabled the development of a present day equivalent of such devices centered on the marriage of fluidics and optics which we refer to as “Optofluidics.” In this review paper we will present an overview of our approach to the development of three different optofluidic devices. In the first of these we will demonstrate how the fusion of novel nanophotonic structures with micro- and nanofluidic networks can be used to perform ultrasensitive, label free biomolecular analysis. This will be done in the context of our newly developed devices for screening of Dengue and Influenza virus RNA. For the second class of device I will discuss and demonstrate how optical forces (scattering, adsorption and polarization) in solid and liquid core nanophotonic structures can be used to drive novel microfluidic processes. Some of the advanced analytical, numerical and experimental techniques used to investigate and design these systems will be discussed as well as issues relating to integration and their fabrication.

The governing equations of electroosmotic flow, including the Navier-Stokes (N-S) equations, Laplace equation and Poisson-Boltzmann equation, are set up in a straight microchannel. The meshless method is employed as a discrete scheme for the solution domain. The semi-implicit multistep (SIMS) method is used to solve the Navier-Stokes equations. The simulation results demonstrated that different patterns of the zeta potential over the channel surface could induce different flow profiles for the vortex. The rotational direction of the vortex is determined by the electroosmotic driving force.

A novel method for in-situ temperature measurements of microfluidic devices using thin-film poly(dimethylsiloxane) (PDMS) saturated with Rhodamine B dye is reported. Rhodamine B, a dye with temperature dependent fluorescent intensity, is frequently injected into the working fluid for on-chip temperature field visualization of glass and silicon based microfluidic devices. However, such a visualization method results in unreliable temperature measurements due to high absorption and adsorption for polymeric devices such as PDMS. Thus, an inexpensive temperature measurement technique is developed in which a thin PDMS layer (∼30 μm) is fabricated and submersed for several days into a Rhodamine B solution. To prevent backward diffusion of the dye into the working fluid during operation, a glass barrier (∼150 μm) is bonded between the thin film and the PDMS mold containing the microchannel design of interest. Temperature measurements are made by utilizing standard method of measuring changes in the normalized fluorescent intensity. For verification purposes, a new calibration curve is developed and the thin film is tested with a microchannel subjected to joule heating. The resulting temperature field along the axial direction of the channel for different applied powers compares well with numerical simulations. Analysis of dye intensities before and after experiments provides temperature deviation estimates due to photobleaching. Errors in temperature measurement due to the film thickness are discussed.

Carbon dioxide bubble removal in anode diffusion layer is a critical technique in micro direct methanol fuel cells (μDMFCs) [1, 2]. By deriving a thermal lattice-Boltzmann model, we investigate the hydrophilic, thermal and geometric effects on the two-phase flow (CO 2 bubbles in methanol-water solution) in a microchannel of a μDMFC. The dimension of the example microchannel is similar to the diffusion layer. The length is 15.9 μm while the width (or height) is 1.5 μm, which are equivalent to the averaged pore size of the porous diffusion layer. A two-dimensional, nine-velocity (D2Q9) thermal lattice-Boltzmann model (TLBM) was derived in this paper.

Small triangle channels are frequently encountered in microelectromechanical systems (MEMS). In this paper, the electro-osmotic flows with a constant wall temperature in triangle microchannels are studied. We numerically solved the Poisson equation for electric potential, the Navier-Stokes equation, and the energy equation for the mixed electroosmotic/pressure driven flows with varying physical properties in triangle microchannels using the Galerkin method. The effects of the pressure gradient, the length ratio, κD h , and Joule heating on mass flux of electro-osmotic flow are discussed, respectively. The numerical results show the mass-flux increases with the increase of imposed positive pressure gradient. A larger Joule number leads to a larger mass flux of electrolytic solution under positive pressure gradient. It is also found that the mass flux increases with increasing the length ratio, κD h , at a given pressure gradient. The increase in Ju number induces a larger increase in the mass flux at a larger κD h .

Centrifugal force has been found to be an excellent method to control fluidic flow in biochips. Most micro-fluidics researchers already use the computer to simulate micro-fluidics flow behavior to save time and reduce mistakes. In this study, the overflow design accurately fixes the liquid volume with less than 5% error. Centrifugal force driven micro-fluidics system is designed with both simulation and experiment. The 3D simulations to utilize computational fluid dynamic software (CFD) to simulate the fluid flow and calculate burst frequency at different capillary switching and several dimension of micro-channels (300, 400, 500μm wide and each 200μm deep). For mercurochrome, the simulation results (384, 360, 348 rpm) shows burst frequency matches experimental results (468, 426, 402rpm) and accurately predicts measured trends followed the effect of channel width. This study also demonstrates the centrifugal application of an advanced computational fluidic dynamics model for the design and analysis of a centrifugal force driven micro-fluidics system.

Numerous studies on microfluidics diagnostic devices have been published in the last decade. Although the first generation of Lab-on-chip (LOC) devices was functional in 1999, some of the promises of microfluidics (integration of all functions on a chip and the commercialization of truly handheld microfluidic instruments) have yet to be fulfilled. The major challenges of LOC technology include cost–effective pumping, function integration, multiple detection, and system miniaturization. In this paper, we propose a novel and simple streaming-based LOC technology that may have potential to directly address these challenges. The phenomenon of the flow streaming is found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no net flow (zero-mean velocity) across the channel, a discrepancy in velocity profiles between the forward flow and backward flow causes fluid particles near the walls to drift toward one end, while fluid particles near the centerline drift to the other end. We hypothesize that the unique characteristics of flow streaming could be used: 1) to transport, mix and separate particles/molecules/bacterium/cells entrained in flows; 2) to perform multi-channel/generation micro-array sample distributions; and 3) to achieve function integrations and biomarker detections. Mechanisms of using flow streaming to achieve the various LOC functions are described. Preliminary results are presented to demonstrate the potential of this technology for LOC applications.