Zongqin Zhang

Metered-dose inhaler efficiency enhancement: A case study and novel design

The efficiency of the metered-dose inhaler (MDI) is a critical issue in aerosol medicine because it deals with delivering a life-saving medication to patients with various lung diseases. Mouthpiece diameter, air flow rate, and entrance angle are among many parameters that influence the MDI penetration efficiency. It is well known that inertial impaction accounts for the massive aerosol deposition in the oral airway. In this study, the authors present a novel simple modification of the inhaler mouthpiece using a wire-based jet depressor to reduce the inertial impaction of aerosols. A 0.5 mm diameter wire is placed inside the MDI mouthpiece at a distance of 2 mm in front of the MDI nozzle. Two mouthpieces were modified and employed in the experiments (16 and 20 mm). The penetration efficiencies are measured and the results of the modified mouthpiece are compared with the conventional mouthpiece. The experiments are conducted at three different air flow rates (30, 60, and 90 L/min) and five entrance/spray angles (0°, 10°, 20°, 30°, and 40°). The results show that the new modified mouthpiece has higher aerosol penetration efficiency than the ones with the conventional mouthpiece. A second type of experiment is conducted to evaluate the relative strength of the aerosol impaction.

A Streaming Flow Based Lab-on-Chip Platform Technology

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 costeffective 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.

Experiments on Contact Melting Under Vibration Within Rectangular Enclosures

Nomenclature A = amplitude of vibration AR = aspect ratio, H/W a = maximum acceleration of vibration, (27r/)A Cp = specific heat Fo = Fourier number, at/HW Fr = Froude number, alg f = frequency of vibration Gr = Grashof number, gfi(Tw Tf)H/v g = gravitational acceleration H = height of test cell k = thermal conductivity Ste = Stefan number, CP(TV Tf)/&hf T = temperature t = time W = width of test cell a = thermal diffusivity j8 = thermal expansion coefficient A/I/ = latent heat of phase change material

Experimental Investigation on Geometric Effect on Micro Fluidic Diodicity

The Micro pump is an essential component in a Micro Total Analysis System (μTAS). A feasible and reliable design of the micro pump is a key for the development of the μTAS. The Valve-less Rectification Micro Pump (VRMP) has many advantages, such as: non-moving parts, independent of fluids and channels properties, reliable, and easy to fabricate. Fluid diodicity is an essential parameter of the VRMP design. In this study, we investigate the fluid diodicity (the ratio of forward to reverse flow’s pressure drop) of micro rectifying geometries for more effective design of VRMPs. An experimental apparatus is designed and constructed. In our preliminary experiments, we measured diodicities of four different rectifying geometries, including bifurcation, heart shape, semi-circle and triangle. Experimental results demonstrate that rectifying geometries can take different designs that differ from the conventional diffuser-nozzle and Tesla’s designs; therefore, there is an opportunity to enhance the performances of VRMP by choosing the application-specific rectifying geometries.Copyright

A Valve-Less Rectification Minipump Based on Dynamic Rectifying Geometries

The advantages of valve-less rectification micro pumps include having no moving parts, low cost, reliable, having the ability to pump particles-laden fluids and live cells, being compatible with a wide range of micro channel materials and working fluids. Most valve-less rectification micro pumps are based on passive rectifying geometries such as a nozzle/diffuser, Tesla (Valvular Conduit), and Bifurcation geometries. In this study, we present a new valve-less rectification minipump based on a dynamic rectifying geometry. The present work includes design, fabrication, and testing of the pump. The experimental results are presented in terms of flow rates and maximum back pressures.Copyright

The Effect of Different Monolithically Integrated Check Valve Designs on the Efficiency of Disposable PZT-PDMS-Micropumps

In the presented study, check valve micropumps with three different valve designs have been developed, fabricated, and successfully tested. These check valves — in the form of differently shaped flaps — were integrated monolithically within the microchannel inlet and outlet of the pump chamber which allows for rapid and inexpensive fabrication of the device. The pump is made of Polydimethylsiloxane (PDMS) with a fully integrated circular piezo-electric transducer (PZT) as a micropump actuator. The performance of the micropumps was characterized under different actuator frequencies, depending on the excitation signal (square, sinusoidal or saw tooth), the implemented PZT diameter (10 mm or 15 mm), as well as the applied offset voltage (positive or negative). Ethanol was used as the working fluid in all experiments. The fabrication technology of the monolithically designed micropump is described, and the results are presented in terms of flow rates. The presented work suggests that the check valve design has an apparent effect on the micropump performance under different operational conditions. All in all, the first results show promising characteristics for easy and inexpensive integration of the proposed micropump in disposable lab-on-a-chip systems.© 2010 ASME

The Effect of Material Properties on the Efficiency of Valve-Less Rectification Micropumps

High efficiency valve-less rectification micropumps are essential in developing effective microfluidic systems. Many parameters have been reported in the literature to have an effect on the efficiency of valve-less rectification micropumps. These parameters are related to the dynamics of fluid flow (such as Reynolds number), rectifying geometries, or actuators (such as actuator frequency). In this work, we studied the effect of the material properties on the efficiency of valve-less rectification micropumps. Two valve-less rectification micropumps based on the same rectifying geometry, bifurcation, are fabricated using two different materials, Polydimethylsiloxane (PDMS) and SU-8 photoresist. The pumps are tested and results are compared. Experimental results suggest that the material properties have an apparent effect on the pumping performance of valve less rectification micropumps. The results are presented in terms of flow rates and maximum back pressures.Copyright

A Multifunctional Microfluidic Device Based on Bifurcation Geometry

Developing multifunctional devices are essential to realize more efficient Microsystems. With miniaturization processes taking place in many different applications, the rooms for single function microfluidic devices are limited. In this study, we introduce a multifunctional micro fluidic device based on bifurcation geometry which is capable of performing pumping and mixing at the same time. Optical lithography is used to fabricate the designed microfluidic device. The microfluidic device is tested at low actuator frequencies, and ethanol is employed as a working fluid. The operational principles are based on rectifying the oscillatory flows by using bifurcation structures for flow rectification. The results prove the feasibility of the novel design, and results are presented in terms of flow rates and maximum back pressures.Copyright

A Concept of Pumpless Convective Micro/Micro Channel Cooling Technology

The sustained drive for faster and smaller micro electronic devices has led to a considerable increase in power density. The ability to effectively pump and enhance heat transfer in micro/mini channels is of immense technological importance. The micro channel heat exchanger has great advantages for high heat flux applications due to their high surface-to-volume ratio. Unfortunately, the small dimension of the micro channel leads to a large pressure drop and low Reynolds flow, which is usually associated with the low heat transfer coefficient. Therefore, forced convection micro heat exchangers require advanced micro pumping and heat transfer enhancement technologies. Using oscillatory flow to enhance the convective heat transfer coefficients in micro/mini channels is one of many new concepts and methodologies that have been proposed. In this paper, we propose a novel and simple streaming-based micro/mini channel cooling technology. The phenomenon of the flow streaming are found in zero-mean velocity oscillating flows in a wide range of channel geometries. Although there is no mass flow (zero-mean velocity) passing through the channel, the 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 to achieve the convective cooling. The advantages of the streaming based convective cooling technique includes enhanced heat transfer coefficient, pumpless, and cost-effective. Preliminary results of scaling analysis and computer simulations are presented to demonstrate the potential of the stream based technology for micro cooling applications.Copyright

PDMS Surface Modification for Application on Thermally-Responsive Hydrogel Microvalves

Recent developments in (MEMS) fabrication techniques have exploited the properties of polymers. Traditional lithographic techniques have been used to create a template in a thick layer of photoresist that can be filled with a heat -0r-UV curable polymer and used to cast numerous replicas of Tesla channels in an elastomeric material-poly (dimethylsioloxane) (PDMS). The surface of this replica, and that of a flat slab of PDMS, is oxidized in oxygen plasma and brought into conformal contact to seal tightly. N-isopropylacrylamide polymers have attracted much interest in the area of scientific research and microfluidic technologies due to their unique thermal response in aqueous medium. To design microactuators of these gels with a high aspect ratio and a strong adhesion to the microchannel, substrates have to be developed. To achieve this, a modification of the simple (NIPA) polymer is needed; therefore, this calls for chemical modification of the (NIPA) material itself and the PDMS. The integration of autonomous microvalves into complex microfluidic Tesla channel networks is presented. Hydrogel directly grown onto vinyl modified PDMS and is in contact with process medium. Thermoelectric element capable of changing the temperature of the system is used to actuate the valve. A distortable diaphragm at the center coupled to a piezoelectric that is connected to the ports of two channels. The other ends are connected to two small water tanks. Valve operation results in an oscillating or a positive net flow depending on valve status.Copyright