bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and application of the emergency response mobile phone‐based information system for infectious disease reporting in the Wenchuan earthquake zone
Authors: Ma Jiaqi , Zhou Maigeng , Li Yanfei , Guo Yan , Su Xuemei , Qi Xiaopeng , Ge Hui
Published: May 2009

Objective To describe the design and application of an emergency response mobile phone‐based information system for infectious disease reporting.

Methods Software engineering and business modeling were used to design and develop the emergency response mobile phone‐based information system for infectious disease reporting.

Results Seven days after the initiation of the reporting system, the reporting rate in the earthquake zone reached the level of the same period in 2007, using the mobile phone‐based information system. Surveillance of the weekly report on morbidity in the earthquake zone after the initiation of the mobile phone reporting system showed the same trend as the previous three years.

Conclusion The emergency response mobile phone‐based information system for infectious disease reporting was an effective solution to transmit urgently needed reports and manage communicable disease surveillance information. This assured the consistency of disease surveillance and facilitated sensitive, accurate, and timely disease surveillance. It is an important backup for the internet‐based direct reporting system for communicable disease.
Searching for health information online: characteristics of online health seekers
Authors: Gallagher S , Doherty DT
Published: May 2009

Objective To investigate the use of, and willingness to use, the internet for health information purposes in Ireland, with a particular focus on the demographic and mental health of users and non‐users.

Methods Data from the Health Research Board National Psychological Wellbeing and Distress Survey were analyzed. This telephone survey included 2711 adults aged 18 years and over living in private households in Ireland. Internet use was measured using three items: past use, use specifically for health information, and willingness to use the internet in the future. Current psychological wellbeing was measured using the 12‐item General Health Questionnaire. In addition, mental health problems in the previous year were measured. Sociodemographic variables examined included age, gender, employment status, and education.

Results Online health‐seeking differed significantly by gender, age, employment status, and educational level. A substantial proportion of internet users with poor mental health were found to have searched for health information online. A high willingness to use the internet for health information in the future by non‐users was reported.

Conclusion This study has shown that those with mental health problems use the internet to search for health information more often than those who have not experienced such problems. It has also shown that there is still a digital divide in terms of online health seeking, which is influenced by age, gender, education, and employment status. These findings highlight the need to address access, technological, psychological, and perceptual issues that may present barriers to the use of online health seeking.
Detection of High Levels of European Bat Lyssavirus Type‐1 Viral RNA in the Thyroid Gland of Experimentally‐Infected Eptesicus fuscus Bats
Authors: Fooks A. R. , Johnson N. , Müller T. , Vos A. , Mansfield K. , Hicks D. , Nunez A. , Freuling C. , Neubert L. , Kaipf I. , Denzinger A. , Franka R. , Rupprecht C. E.
Published: May 2009

Two common bat lyssavirus species have been identified in many European countries: European bat lyssavirus type‐1 and ‐2 (EBLV‐1 and EBLV‐2). Only limited knowledge on the susceptibility of the natural EBLV‐hosts, insectivorous bats, to lyssavirus infection is available. Our study was undertaken to evaluate the susceptibility and pathology associated with an EBLV‐1 infection in Eptesicus fuscus following different routes of virus inoculation including intracranial (n = 6), intramuscular (n = 14), oral (n = 7) and intranasal (n = 7). Blood and saliva samples were collected from all bats on a monthly basis. Four bats inoculated intracranially developed rabies with a mean of 11 days to death, whilst seven bats inoculated intramuscularly developed rabies, with an extended incubation period prior to death. We did not observe any mortality in the oral (p.o.) or intranasal (i.n.) groups and both groups had detectable levels of virus neutralizing antibodies (data not shown). Virus shedding was demonstrated in the saliva by virus isolation and the detection of viral RNA in ill bats, particularly immediately prior to the development of disease. In addition, the presence of virus and viral RNA was detected in the thyroid gland in bats challenged experimentally with EBLV‐1, which exceeded that detected in all other extra‐neural tissue. The significance of detecting EBLV‐1 in the thyroid gland of rabid bats is not well understood. We speculate that the infection of the thyroid gland may cause subacute thyroiditis, a transient form of thyroiditis causing hyperthyroidism, resulting in changes in adrenocortical activity that could lead to hormonal dysfunction, thereby distinguishing the clinical presentation of rabies in the rabid host.
Experimental Study of DRA for Vertical Two-Phase Annular Flow
Authors: Fernandes R. L. J. , Fleck B. A. , Heidrick T. R. , Torres L. , Rodriguez M. G.
Published: May 2009

Experimental investigation of drag reduction in vertical two-phase annular flow is presented. The work is a feasibility test for applying drag reducing additives (DRAs) in high production-rate gas-condensate wells where friction in the production tubing limits the production rate. The DRAs are intended to reduce the overall pressure gradient and thereby increase the production rate. Since such wells typically operate in the annular-entrained flow regime, the gas and liquid velocities were chosen such that the experiments were in a vertical two-phase annular flow. The drag reducers had two main effects on the flow. As expected, they reduced the frictional component of the pressure gradient by up to 74%. However, they also resulted in a significant increase in the liquid holdup by up to 27%. This phenomenon is identified as “DRA-induced flooding.” Since the flow was vertical, the increase in the liquid holdup increased the hydrostatic component of the pressure gradient by up to 25%, offsetting some of reduction in the frictional component of the pressure gradient. The DRA-induced flooding was most pronounced at the lowest gas velocities. However, the results show that in the annular flow the net effect will generally be a reduction in the overall pressure gradient by up to 82%. The findings here help to establish an envelope of operations for the application of multiphase drag reduction in vertical flows and indicate the conditions where a significant net reduction of the pressure gradient may be expected.
Exergy Analysis of an Industrial Waste Heat Recovery Based Cogeneration Cycle for Combined Production of Power and Refrigeration
Authors: Khaliq A. , Kumar R. , Dincer I.
Published: May 2009

In this paper, a novel industrial waste heat recovery based cogeneration is proposed for the combined production of power and refrigeration. The system is an integration of Rankine power cycle and absorption refrigeration cycle. A thermodynamic analysis through energy and exergy is employed, and a comprehensive parametric study is performed to investigate the effects of exhaust gas inlet temperature, pinch-point, and gas composition on energy efficiency, power-to-cold ratio, and exergy efficiency of the cogeneration cycle and exergy destruction in each component. The variation in specific heat with exhaust gas composition and temperature is accounted in the analysis for further discussion. The first-law efficiency decreases while power-to-cold ratio and exergy efficiency increase with increasing exhaust gas inlet temperature. The parameters, such as power-to-cold ratio and second-law efficiency, decrease while first-law efficiency increases with increasing pinch-point. Exergy efficiency significantly varies with gas composition and oxygen content of the exhaust gas. Approximating the exhaust gas as air, and the air standard analysis leads to either underestimation or overestimation of cogeneration cycle performance on exergy point of view. Exergy analysis indicates that maximum exergy is destroyed during the steam generation process; which represents around 40% of the total exergy destruction in the overall system. The exergy destruction in each component of the system varies significantly with exhaust gas inlet temperature and pinch-point. The present analysis contributes further information on the role of composition, exhaust gas temperature, and pinch-point influence on the performance of a waste heat recovery based cogeneration system from an exergy point of view.
Utilization of Heat, Power, and Recovered Waste Heat for Industrial Processes in the U.S. Chemical Industry
Authors: Ozalp Nesrin
Published: May 2009

This paper presents energy end-use model of the U.S. Chemical Industry. The model allocates combustible fuel and renewable energy inputs among generic end-uses including intermediate conversions through on-site power and steam generation. The results of this model provide the basis to scale energy process-step models. The main federal database to construct energy end-use models is Manufacturing Energy Consumption Survey of the U.S. Energy Information Administration. This database provides information on how much energy is used for each end-use on a national scale in each industry. The secondary federal database to construct the energy end-use models is the Energy Information Administration’s “EIA-860B: Annual Electric Generator Report.” This database provides information about fuel consumed, gross generation, and recovered waste heat at the prime mover level of detail. The results of the model show that the majority of the fuel input is used directly for the end-uses. Although the rest of the fuel is used to generate steam and power, most of this energy contributes to the end-uses as steam. Therefore, the purpose of fuel consumption at nonutility plants is to run their end-uses. During the course of this study, the most recent U.S. federal energy database available was for the year 1998. Currently, the most recent available U.S. federal energy database is given for the year 2002 based on the data collected from 15,500 establishments.
High Performance Single-Phase Liquid Coolers for Power Electronics
Authors: Cheong Brian C. Y. , Ireland Peter T. , Siebert Annegret W.
Published: May 2009

This paper presents three generically similar impingement liquid coolers that have been engineered for cooling power electronics on future aero gas turbines. The thermal and hydraulic performances of the coolers have been compared with that of a commercial, state-of-the-art pin fin liquid cooler. It is demonstrated that the impingement liquid coolers outperform thermally the baseline pin fin cooler, and with significantly lower pressure drops. The impingement liquid coolers could also be easily modified to trade reduced pressure drop against higher flowrate or reduced thermal performance. A scaling model has also been developed to predict the thermal performances of the coolers for other types of coolants and flow conditions. The model has been applied for predicting the convective thermal performances of the coolers assuming hot aircraft fuel as the coolant. Future work would include an investigation of alternative convective applications in which the cooling system could be systematically explored.
Complete Micro-PIV Characterisation of Microfluidic Devices
Authors: Bown Mark R. , MacInnes Jordan M. , Allen Ray W. K.
Published: May 2009

Microfluidic devices can take advantage of novel physics only available at the micro-scale. As a result, new physical models for the flow behaviour within these devices are required. In recent years micron resolution particle image velocimetry (Micro-PIV) has established itself as a reliable verification tool for these models. Micro-PIV measures the velocity profile across a single 2D plane within a microfluidic device. Here, Micro-PIV data is obtained from several planes within a device to create a complete mapping of the flow field. Combination of the data from all the planes allows the flow profile on the plane perpendicular to the original images to be studied and the volumetric flowrate through the device to be measured. By fitting the measured velocities to known flow profiles, the width and depth of the device can also be measured with sub micron precision. The technique is applied to an isotropically etched microchannel, where the results are compared to an independent computational fluid dynamics solution. Good agreement is found between the two data sets. The technique is then demonstrated in a more complex flow in a mixing channel device. In order to image an entire device a large field of view may be required. This dictates the use of low magnification lenses, which in turn have a large depth of field. A theoretical model for the measured Micro-PIV velocity demonstrates that, if care is taken when measuring near to curved walls, the use of these low magnification lenses does not significantly reduce the quality of the data obtained.
Numerical Simulations of Macromolecular Syntheses in Micro-Mixers: Towards a Better Control of the Polymerization
Authors: Serra Christophe , Sary Nicolas , Schlatter Guy
Published: May 2009

This paper investigates the modeling of styrene free radical polymerization in two different types of micro-mixer for which the wall temperature is kept constant. The simulations are performed with the help of the finite elements method which allows solving simultaneously partial differential equations resulting from the hydrodynamics, thermal and mass transfer (convection, diffusion and chemical reaction). The different micro-mixers modeled are on one hand an interdigital multilamination micro-mixer with a large focusing section and on the other hand a simple T-junction with three different radii followed by a tube reactor having the same radius. The results are expressed in terms of reactor temperature, polydispersity index, number-average degree of polymerization and monomer conversion for different values of the chemical species diffusion coefficient. Despite of the heat released by the polymerization reaction, it was found that the thermal transfer in such microfluidic devices is high enough to ensure isothermal conditions. Concerning the polydispersity index, the range of diffusion coefficients over which the polydispersity index can be maintained close to the theoretical value for ideal conditions increases as the tube reactor radius decreases. The interdigital multilamination micro-mixer was found to act as a T-junction and tube reactor of 0,72 mm ID but gives up to 15% higher monomer conversion. This underlines that the use of microfluidic devices can lead to a better control of the polymerization.
Quantitative Evaluation of Mixing Efficiency of Split-and-Recombine Mixing Method
Authors: Hamanaka Osamu , Kato Hiroharu
Published: May 2009

In this paper, we present the acceleration of mixing and chemical reaction by a split-and-recombine (SAR) mixing method quantitatively, which was performed by numerical computation using the heat fluid analysis software, Star-CD. The authors have newly defined the mixing efficiency, which is a quantitative measure of the mixing of two fluids. The calculated result of the mixing efficiency in SAR device with two different channel configurations, angled and curved channels, showed that the secondary flow is important in increasing mixing efficiency. The angled channel is more effective than the curved channel, because the secondary flow is much stronger in the angled channel. The abrupt increase in sectional area also increases mixing efficiency. The split angle at the split point in the SAR device also affects mixing efficiency, because the secondary flow becomes stronger with the split angle. The mixing efficiency was greater (about 1.3 times) with a split angle of 45 degrees than that with a split angle of 15 degrees. According to the above-mentioned results, the authors designed a three-successive-SAR device, whose mixing efficiency was approximately 7.5 times greater than that of straight channel. The present findings are different from the existing mixing increase concept of the SAR device, which produces many thin layers from two fluids.
Microfluidic Device Fabrication Method Using Direct Thick Film Writing
Authors: Grande William J. , Fino Gary A.
Published: May 2009

A novel technique based on direct thick film writing has been developed for the rapid prototyping of microfluidic devices. The direct writing process is based on pressure driven dispensing of precursor materials through a micro-capillary tip. The process exhibits wide latitude in both the materials that can be patterned and the substrate formats and shapes that can be accommodated. A fabrication process flow sequence with general applicability to microfluidic devices was developed and its efficacy was demonstrated by the construction of two-input mixer devices. Integration of fluidic components with electrical circuitry was also demonstrated.
Design of a Test Facility and Micro-Channel Heat Exchanger Prototype for High Power Electronic Components
Authors: McGlen Ryan J. , Lee Jon , Buffone Cosimo
Published: May 2009

Increased processing speed, miniaturisation and higher packing densities of electronic processing chips has lead to the development of high power, high heat flux electronics cards used by the telecom and server industries to process digital signals. The drive towards higher system performance has put a large demand on forced air convection cooling techniques and is heading towards the thermal limit of the technology. Thermal management is becoming the limiting factor in the development of higher power electronic devices. To meet future heat transfer demands, innovative methods of thermally managing electronic devices are required. This paper looks at the creation of a test facility and single phase, prototype microchannel heat exchanger design to cool high power silicon and optical chips.
3-D Numerical Analysis for Fluid Flow and Heat Transfer in a Micro Chip by Using an Electro-Hydrodynamic Micro-Pump
Authors: Lin Chia-Wen , Jang Jiin-Yuh
Published: May 2009

A computational investigation of the heat transfer for a high performance integrated chip by using an electrohydrodynamic (EHD) pump was studied. This paper presents a fully computational system bundle with electro field, fluid flow and heat transfer for a cooling device. The micro pump provides the required pumping power by using the dipole moment generated from polarizing molecules and induces the flow to cool down the heat source. The computational domain of the micro channel for length and depth are kept in 1500μm and 500μm with parallel electrodes pitch (20μm, 40μm, 80μm). The effects of different applied voltage VE ranging from 100V to 500V, using oil as the working fluid and the heat flux of the heat source fixed at 2.5W/cm2 is investigated in detail. It is found that the EHD micro pump is more effective for lower channel pitch and higher applied voltage. For VE = 500V and electrodes pitch = 20μm, this study identifies a maximum performance of 49.36kPa in the pressure head and 9.55W/cm2 in the heat transfer. In addition, the performance of flow rate, liquid velocity and averaging Nusselt number for the specific condition are 0.94 L/min-mm2, 0.12 m/s, and 106.10. However, it also identifies the performance of the heat transfer for electrodes pitch = 40μm is about 146.0% of that for pitch = 80μm. But for pitch = 20μm, it is only 10.5% higher than that for pitch = 40μm.
A Computational Model for Heat Transfer in Multichannel Microreactors
Authors: Hardt S. , Baier To
Published: May 2009

A reduced-order model is developed allowing for a fast computation of the temperature field in multichannel microreactors. The model regards the fluid and the solid phase as interpenetrating continua and incorporates heat exchange between the two phases via a heat-transfer coefficient characteristic for the channel geometry under study. The geometry of the channel walls determines the components of the thermal conductivity tensor which govern conductive heat transfer to the envelope of the reactor. The mean-field model is solved numerically for a test case inspired from practical applications. Parallel to that, a detailed model is set up with the purpose to benchmark the results of the mean-field model. This full model incorporates the geometric details of the multichannel reactor and contains consider-ably more degrees of freedom than the mean-field model, resulting in a much larger computational effort. It is found that the temperature fields computed with the two models agree reasonably well. Thus, the mean-field model appears as an efficient tool to evaluate the thermal performance of multichannel microreactors, especially in the context of parameter studies or system optimization.
Study of the Temperature Field in Microchannels of a PDMS Chip With Embedded Local Heater Using Temperature-Dependent Fluorescent Dye
Authors: Fu Rachel , Xu Bo , Li Dongqing
Published: May 2009

This paper presents a simple microheater design for microfluidic devices by embedding resistance wire into a PDMS chip, and the results of an experimental study of the thermal response of liquid samples in the PDMS chip with the embedded local heater. Temperature-dependent fluorescent dye was used to measure the temperature distribution within a microchannel heated by the local heater. Two heater configurations were built, tested, and compared with numerical simulation. Through comparing the performance of these two configurations, heating and cooling rates and uniformity of the temperature field were evaluated. Additionally, thermal cycling at two different temperature levels was achieved by controlling the power of the local heater.
Comparison of Microchannel Array Water Evaporator Designs by High-Speed Videography
Authors: Henning Torsten , Brandner Juergen J. , Schubert Klaus
Published: May 2009

Arrays of 68 microchannels, each one 200 μm wide, 100 μm deep and 40 mm long, were fabricated by mechanical micro-machining of brass foils, and used to evaporate water in the mass flux range between 61 kg m−2s−1 and 123kg m−2s−1 in an electrically powered device. Three different microchannel designs were tested: straight channels with and without impactor structures at the microchannel exits, and curved channels following a sinusoidal path. Variations of the average steam quality inside the microchannel arrays (pulsation) were observed by high-speed videography. Even when the device as a whole produced overheated steam, pulsation inside the channel array near the outlet, spatial maldistribution of the two phase flow, and liquid water reaching the outlet plenum were observed in many cases. From these observations and their analysis, conclusions are drawn for the further empirical optimization of microchannel array evaporators.
Review and Fabrication of Nanochannels for Single Phase Liquid Flow
Authors: Perry Jeffrey L. , Kandlikar Satish G.
Published: May 2009

The topic of single phase liquid flow in submicron or nanochannels is a nascent field. There have only been a couple papers that have dealt with this area directly. The most probable reason for this is that currently most research in fluid mechanics or heat transfer is being focused on micron size channels. To help facilitate researchers to focus on this undeveloped area, this paper serves as a review for some of the micro-fabrication processes that will make it possible for engineers and scientists to study this field in greater detail.
Experimental Investigation of Flow Boiling in a Vertical Narrow Channel
Authors: Sobierska Ewelina , Chmiel Klaudia , Kulenovic Rudi , Mertz Rainer
Published: May 2009

Experimental investigations on thermofluid-dynamic phenomena in a vertical narrow rectangular microchannel with the hydraulic diameter dh = 0.27 mm were carried out. The experiments are performed under fluid-inlet subcooling conditions with de-ionised and degassed water for different mass fluxes (50–2000 kg/m2s) and heat fluxes (2–150 kW/m2). Moreover, flow visualisation of the two-phase flow patterns along the channel is performed using a digital high-speed video camera. Investigations on pressure drop during single- and two-phase flow have been carried out. The present work is concentrated on two-phase heat transfer. The mean heat transfer coefficient and the local heat transfer coefficient at saturated conditions were calculated and the latter ones was compared with available correlations.
A Wire Loop Design for Convection-Enhanced Dielectrophoretic Bioparticle Trapping
Authors: Gagnon Zachary , Chang Hsueh-Chia
Published: May 2009

Tailor-designed AC electro-osmotic (AC-EO) stagnation flows are used to convect bioparticles globally from a bulk solution to localized dielectrophoretic (DEP) traps that are aligned at flow stagnation points. The multi-scale trap, with a typical trapping time of seconds for a one cc sample, is several orders of magnitude faster than conventional DEP traps and earlier AC-EO traps with disjoint electrodes. A novel serpentine wire resistor loop capable of sustaining a high field, up to 20,000 V/cm, is fabricated to produce strong AC electro-osmotic flow with two separated stagnation lines, one aligned with the field minimum and one with the field maximum. The continuous loop design allows a large applied voltage without inducing Faradaic electrode reactions. Particles are trapped within seconds at one of the traps depending on whether they suffer negative or positive DEP (n-DEP, p-DEP). The particles can also be rapidly released from their respective traps (and recaptured in the opposite traps) by varying the frequency of the applied AC field below particle-distinct cross-over frequencies. Zwitter ion addition to the buffer allows further geometric and frequency alignments of the AC-EO and DEP motions. The same device hence allows fast trapping, detection sorting and characterization of a sample with realistic conductivity, volume and bacteria count.
Experimental Error Analysis and Heat Polynomial Method Improvement for Boiling Heat Transfer Numerical Calculations in Minichannels
Authors: Piasecka Magdalena , Poniewski Mieczyslaw E. , Hozejowska Sylwia
Published: May 2009

The paper continues the discussion of experimental and numerical investigations of forced convection boiling heat transfer in vertical minichannels covered by two former editions of this conference and our previous papers. Liquid crystal thermography technique was used for measuring the two-dimensional heating surface temperature distribution and boiling front detection. Influence of selected parameters on boiling heat transfer and nucleation hysteresis was observed and discussed. The two-dimensional heat transfer model and the analytic-numerical heat polynomial method were applied to solve the inverse boundary value problem and determine the temperature distributions in the heating foil and protecting glass and the boiling heat transfer coefficient as well. This paper shows how to modify and improve the heat polynomial method if we know the measurement errors and implement them into the numerical procedure. The accuracy of temperature measurements on the heating surface with liquid crystal method was estimated and the analysis of experimental results was given. The functions sought in numerical calculations describe temperature distribution in the protecting glass and the heating foil of the minichannel. They are presented in the form of linear combination of heat polynomials. The adopted boundary conditions and temperature measurements are used to construct error functionals. The latter express the root-mean-square errors, with which computed solutions satisfy relevant boundary conditions. On the basis of functional minimalisation unknown coefficients of linear combinations are determined. The solutions obtained satisfy the differential equations in the exact manner whereas the adopted boundary conditions are met in the approximate fashion. The unknown boiling heat transfer coefficient is the function computed from the boundary condition of the third kind. In the modified method, measurement errors are weights for individual temperature measurements. The more accurate is the measurement, i.e. has a smaller error, the greater is the weight put to it in further calculations. Therefore, it is possible to heighten the accuracy with which glass and foil temperature distributions, determined experimentally, fulfil the assumed equality conditions on the contact surface. Temperature distributions in the glass and the foil, computed on the basis of the modified method, are closer to real values than those obtained with the basic one. Local heat transfer coefficients obtained for two-dimensional boiling heat transfer model with both the basic and the modified heat polynomial methods are also compared.
Boiling Enhancement in a Mini-Channel of a Three-Phase Circulating Fluidised Bed
Authors: Arumemi-Ikhide Michael , Sefiane Khellil
Published: May 2009

In fouling, the accumulation of poorly conducting materials on the surface of process equipment, results in an increased resistance to heat transfer and hence reduces heat exchanger effectiveness. Under most conditions fouling is more severe during boiling heat transfer, due to the mechanisms of bubble formation and detachment. Thus, in order to enhance heat transfer and mitigate fouling in boiling processes, a new type of vapour-liquid-solid (three-phase) circulating fluidised bed boiling system has been designed, combining circulating fluidised bed technology with boiling heat transfer. Experiments are conducted in a glass mini-channel of square cross sectional area 21.5 mm × 11mm, height 1000mm, and fitted with an electrically heated cartridge heater rod of 8mm diameter × 730mm length. The set-up uses stainless steel balls to investigate the effect of particle properties (specifically particle size) on three-phase boiling heat transfer enhancement. Experimental results show that overall, compared with two-phase flow boiling, the presence of solid particles in the three-phase boiling system augments the heat transfer coefficient. Results are presented and discussed.
Pressure Drop Over MEMS-Based Micro Scale Pin Fin Heat Sinks
Authors: Peles Yoav , Kos¸ar Ali , Mishra Chandan , Kuo Chih-Jung , Schneider Brandon
Published: May 2009

Pressure drops and friction factors related to forced flow of de-ionized water over staggered/ in-line micro pin fin bundles (100-μm long, with hydraulic diameter of 50-μm and 100-μm, and with horizontal and vertical pitch ratios 1.5 and 5) possessing different cross-sections (circular/ diamond) have been experimentally investigated over Reynolds numbers ranging between 5–128. The applicability of conventional scale correlations to evaluate micro flow tests results has been assessed. It has been shown that available large-scale correlations do not adequately predict the pressure drop obtained at the micro scale.
Droplet Movements and Continuous Flows in Rough and Hydrophobic Microchannels
Authors: Zhang Junfeng , Mohammadi Reza , Kwok Daniel Y.
Published: May 2009

In this paper, we have studied the droplet movements and continuous flows confined between two rough and hydrophobic surfaces. A recently proposed mean-field free-energy lattice Boltzmann model was employed. The movement of contact point over a well-patterned rough surface displays a periodic sticking-jumping-slipping behavior; while the dynamic contact angle changes accordingly from maximum to minimum values. These complex varying behaviors are totally different from those on flat surfaces and implies more carefulness is necessary in interpreting measured contact angles on rough surfaces. Two regimes were found of the droplet velocity changing with the surface roughness: first decreasing and then increasing; and qualitative analysis was given. We have also studied the continuous flow rates and two cases, with and without vapor trapped, were compared. Simulation results show the vapor trapped can indeed reduce the resistance to fluid motion from the channel surfaces, and such information could be useful for microfluidic applications.
Electrokinetic Generation Efficiency With Finite External Loads
Authors: Lu Fuzhi , Mansouri Ali , How Tuck Y. , Kostiuk Larry W. , Kwok Daniel Y.
Published: May 2009

Electrokinetic (EK) pumping efficiency has recently been a hot topic due largely to its applications in microfluidics for liquid transport. As the Onsager reciprocity relation suggests that the exact opposite of EK pumping is EK generation, experimental study on the efficiency of the latter is seldom reported. This paper examines electrokinetic generation efficiency in the presence of finite external loads through the use of different ceramic filters. The electrical output power was measured experimentally as a function of different external loadings. When the experiments were performed continuously on subsequent days, the EK generation efficiency for all the tested filters can be made to increase and approach a maximum limit. The experimental data also indicated that, when pore size of the filter decreases, the curve for potential versus current becomes more non-linear and the maximum efficiency does not occur when the current is half the zero-potential current.
Effect of Solid-Fluid Energy Parameters on Streaming Potential and Flow Rate in Pressure-Driven Flow in Microchannels
Authors: Tian Fuzhi , Zhang Junfeng , Kwok Daniel Y.
Published: May 2009

Electrokinetic phenomena play an important role in microfluidic transport behavior. Review of literature suggests that surface energetic can also be an important factor, but rarely explored. Typically, surface energetic is taken into account by consideration as an arbitrarily selected slip boundary condition in the modified Navier-Stokes equation. In this paper, instead of selecting this arbitrary slip condition, we examine how solid-liquid energy parameters influence the transport of microfluidics in terms of streaming potential. The simultaneous effects of surface energetics and electrokinetics will be conducted by means of a mean-field free energy lattice boltzmann approach recently proposed. Rather than using the conventional Navier-Stokes equation with a slip condition, the description solid-liquid energetic is manifested by the more physical energy parameters in the mean-field description of the method. As a result, the magnitude of liquid slip can be related directly to the solid-liquid interfacial slip. These results will be employed in conjunction with the description of electrokinetic transport phenomena for streaming potential. The variation of streaming potential as a function of the energy parameters (solid-liquid interaction) is clearly demonstrated. In pressure-driven liquid microfluidics, the flow rate may be decreased due to the counter-effect between the electrokinetic and slip.
Flow Characteristics of Micro Diffuser/Nozzles for a Valveless Micropump
Authors: Jeong Siyoung , Kim Donghwan , Kim Hyun Keun , Hur Nahmkeon
Published: May 2009

In this study, the flow characteristics have been experimentally investigated for various shapes of the diffuser/nozzles, and the results are compared with the numerical simulation. Three chambers (inlet, exit, and middle) and two identical diffuser/nozzles are fabricated on a silicon wafer. The inlet and middle chamber is connected by one diffuser/nozzle; and the middle and exit chamber is connected by another diffuser/nozzle. The experiments are performed in a pump mode in which pressure is applied to the middle chamber and a supply mode in which pressure is supplied to the inlet and exit chamber. The net flow rate is determined by the flow difference between the pump and supply mode. The important parameters considered in this study are the throat width (30–12μm) and the taper angle (3.15–25.2°). For the taper angle and the throat width, it is found that there exists an optimum at which the net flow rate is the greatest. The optimal taper angle is in the range of 10–20° for all the pressure differences; and the throat width indicates an optimal value near 90μm for the case of 35kPa pressure difference. This tendency has been verified by the numerical simulation. From the numerical simulation, it is also found that the net flow rate is influenced by the size of the middle chamber. With decreasing chamber size, the net flow rate is reduced because of the interference between two streams flowing into the middle chamber.
Experimental Evaluation of Pressure Drop Elements and Fabricated Nucleation Sites for Stabilizing Flow Boiling in Minichannels and Microchannels
Authors: Kandlikar Satish G. , Willistein Daniel A. , Borrelli John
Published: May 2009

The flow boiling process suffers from severe instabilities induced due to nucleation of vapor bubbles in a minichannel or a microchannel in a superheated liquid environment. In an effort to improve the flow boiling stability, several modifications are introduced and experiments are performed on 1054 × 197 μm microchannels with water as the working fluid. The cavity sizes and local liquid and wall conditions required at the onset of nucleation are analyzed. The effects of an inlet pressure restrictor and fabricated nucleation sites are evaluated as a means of stabilizing the flow boiling process and avoiding the backflow phenomena. The results are compared with the unrestricted flow configurations in smooth channels.
Aerosol Particle Deposition in a T-Shaped Micro Mixer
Authors: Wengeler Robert , Heim Michael , Wild Markus , Nirschl Herrmann , Kasper Gerhard , Kockmann Norbert , Engler Michael , Woias Peter
Published: May 2009

Micro technology supported aerosol processes provide a basis for integrated control of complex processes and therefore a promising research subject. A key aspect in aerosol technology is to control particle deposition, either to avoid clogging or to achieve a well defined coating of surfaces. As a first step we conducted an experimental and theoretical study of the particle deposition in a simple static T-shaped micro mixer. For the experiments monodisperse sodium chloride particles in the particle size range between 10 nm and 700 nm were used. The aerosol was introduced into one branch of the micro reactor and mixed with a particle-free air stream. The predominant particle deposition effect within the mixer is due to impaction, which is induced by the high curvature of stream lines at the inlet and in the mixing zone. Additional CFD calculations confirm the experimental results and show ways of optimizing the inlet geometry of the mixer, which should result in a significant reduction in impaction losses.
Optofluidic Microscopy
Authors: Heng Xin , Erickson David , Psaltis Demetri , Yang Changhuei
Published: May 2009

Recent advances in the development of lab-on-a-chip devices have been rapid and broad ranging. In general however these devices, while containing micro- or even nano-scale components, rely heavily on macroscale infrastructure (e.g. microscopes, chip readers and power sources) to perform much of the actual product detection and subsequent analysis. As such to enable the next generation of portable lab-on-chip devices, techniques for simply and cheaply integrating on-chip analysis functionalities will be required. In this work we present our work directed towards the development of a new concept in rapid on-chip imaging which we refer to as “optofluidic microscopy (OFM)”. Here we present an overview of the imaging theory, fabrication procedure and operational details of the initial prototype. Preliminary experimental results of this on-chip optical imager are also reported. A significant advantage of the technique is that through proper spatial scaling, sub-wavelength resolution can be achieved without bulk optics.
Pull-In Extension of MEMS Electrostatic Microactuators Using an Active Control Method
Authors: Sun Y. , Piyabongkarn D. , Rajamani R. , Nelson B. J.
Published: May 2009

Parallel-plate and transverse comb-drive types of electrostatic microactuators are commonly used MEMS-based devices. Although they have the advantages of favorable scaling, fast response, and low power consumption, these electrostatic microactuators have had a fundamental limitation in that the allowable travel range is limited to 1/3 of the total gap between comb capacitor plates. Travel beyond this allowable range results in “pull-in” instability, independent of mechanical design parameters such as stiffness and mass. This paper presents the extension of stable travel ranges through the development of an active control system that stabilizes electrostatic microactuators and allows travel almost over the entire available gap between comb capacitor plates, providing a practical approach to extending travel range of electrostatic microactuators for applications that require high fill factors. The addressed challenges include the nonlinear dynamics of microactuators and system parameters that vary among fabricated devices. A nonlinear model inversion technique was proposed to address the nonlinear dynamics, which allows the use of traditional linear controller design methodologies for obtaining a desired linear system response. An adaptive controller was developed to provide improved position tracking in the presence of device parameter variations caused by fabrication imperfections. For experimental verification, the control system was implemented on a transverse comb-drive electrostatic microactuator fabricated using deep reactive ion etching on silicon-on-insulator wafers. Experimental results demonstrate that the resulting system is capable of traveling 4.0μm over a 4.5μm full range without “pull in.” Satisfactory tracking performance was obtained over a wide frequency band.
Performance Characteristics of a Membrane Driven Variable Flow Rate Micro-Pump
Authors: Jeong Su-Young , Thorud Jonathan D. , Pence Deborah V. , Liburdy James A.
Published: May 2009

A micropump was developed for a fluidic system that requires fluid transport in the 100+ μL/min flow range. The constraints on the design included the ability to control the flow rate over a reasonable range of flow rates, operate at fairly high pressure loads, and non-contact of the working fluid with the pump actuation system. The design was based on a displacement style pump, actuated by a piezoelectric element, with one-way polymer membrane check valves. The valves provided essentially zero backflow based on the elastic character of the material. Results are presented for three membrane thicknesses, three valve opening diameters, over a range of operating frequencies. The flow rate versus frequency curves show a characteristic trend with three regions of operation, the first a linear region at low frequencies, the second a region of decreasing slope resulting in a maximum flow rate regime and the third a region of reduced flow rate with increasing frequency. Results also show that a suction lift could be overcome with the micropump whose value depends on the valve size. The performance is compared to an ideal case indicating that larger diameter valves with thinner membranes obtain the best performance.
Molecular Dynamics Simulation of Injection Flow in a Nano-Meter Syringe by Consideration of Extra Pairwise Interactions for Positive and Negative Ions
Authors: Huang Cunkui , Nandakumar Kumar , Kwok Daniel Y.
Published: May 2009

The average concentration of ions in a liquid depends on the size of a channel if the charges on solid surface do not change. The relation between them is that the concentration of ions is inversely proportional to the channel size. When a channel decreases from a micro to a nano size, the concentration of ions will increase 1000 times. In this case, the ion’s distribution in liquid may not be considered as dilute if the charges on solid surface is large, and interactions among ions have to take into account. In this paper, molecular dynamics is applied to study the effect of extra-pairs of positive/negative ions on liquid transport properties in a nano syringe under a constant injection flow rate boundary condition. In simulations, the Coulomb’s law and 12-6 Lennard-Jones potential are used to govern the interaction between ion-ion, ion-liquid, ion-solid, liquid-liquid and liquid-solid molecules. Four different cases (no ions, counter-ions, and counter-ions combining with small and large extra-pairs of positive/negative ions in liquid) are carried out. The non-equilibrium molecular dynamics (NEMD) simulation results show that the concentration of extra-pairs of positive/negative ions has significant influence on liquid velocity profile and ion distributions. For liquid flow without ions, a quasi-parabolic velocity distribution was obtained. When the counter-ions and extra-pairs of positive/negative ions are considered, the flow approaches a plug flow as the number of extra-pair of ions increases. We also found that charges in liquid do not follow the Poisson-Boltzmann distribution, especially for the net charges which have a valley located at about 1.5 molecular sizes away from the solid surface.
Heat Transfer Characteristics of a Mini Channel Compact Heat Exchanger Using Copper Wire Spring Fins
Authors: Im Yong-Bin , Lee Ki-Taek , Kim Jon Jong-Soo , Choi Yoon-Hwan
Published: May 2009

The heat transfer and pressure drop characteristics of compact heat exchangers having mini channels and copper wire spring fins are investigated experimentally. A copper capillary tube is used as heat transfer tube (length: 250 mm, inside diameter: 1.4 mm and wall thickness: 0.2 mm). The copper wire spring fin (CSF) is made of thin copper wire whose thickness is 0.5 mm and length is 8.4 m, respectively. The heat transfer area density of heat exchanger is 1,880 m2/m3. Water is employed inside the circular tube to transfer heat with air for convenience. The air flow entering into the test section is a fully developed duct flow and velocity is varied from 0.5 to 2.0 m/s with 0.5 m/s intervals. Based on the experimental data, heat transfer rate, pressure drop, f–factor and j–factor are investigated.
Three-Dimensional Microfluidic Focusing With Surface Charge Patterning
Authors: Coleman Jeffrey T. , Sinton David
Published: May 2009

Electrokinetically-driven flow circulations resulting from heterogeneous surface patches have previously been employed to improve mixing in microchannels. Here, numerical simulations demonstrate local in-channel hydrodynamic focusing through the use of strategically-patterned surface charge. Presented first is the case of a single straight channel with an axially-localized cross-sectional surface patch (ring). The surface patch exhibits a zeta potential equal in magnitude to the native microchannel surface but opposite in sign. The unsteady species transport in the presence of the electrokinetically-induced circulations is modelled, and a mean residence time is quantified. In general, residence times indicate the potential application of these circulations to microfluidic-based memory storage. Next, an improved focusing process for pinched-injection is demonstrated that exploits non-uniform surface patches. Lastly, surface patches are applied to enhance stream focusing in the microfluidic cross geometry. It is demonstrated that with this technique three-dimensional hydrodynamic focusing can be achieved in a single planar microfluidic structure. In one case, the microfluidic fluid stream was constrained to the centre of the channel and focused to 12% of its original cross-sectional area. Extensions of this work are discussed, as are the microfabrication and surface modification processes required for lab-on-chip implementation of these numerically simulated processes.