bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated Fate and Toxicity Assessment for Site Contaminants
Authors: McDonell Margaret , Peterson John , Finster Molly , Hildebrand R. Douglas
Published: June 2009

Understanding the fate and toxicity of environmental contaminants is essential to framing practical management decisions. Forms and bioavailable concentrations often change over time due to natural physical, chemical, and biological processes. For some sites, hundreds of contaminants may be of initial interest, and even small projects can involve a substantial number of contaminants. With multiple assessments common, attention to effectiveness and efficiency is important, and integrating fate and toxicity information provides a valuable way to focus the analyses. Fate assessments help identify what forms may be present where and when, while toxicity information indicates what health effects could result if people were exposed. The integration process is illustrated by an application for the Hanford site, to support long-term management decisions for the cesium and strontium capsules. Fate data, health-based benchmarks, and related toxicity information were effectively combined to indicate performance targets for chemicals and radionuclides identified for capsule leachate that could migrate to groundwater. More than 50 relevant benchmarks and toxicity context were identified for 15 of the 17 study contaminants; values for chronic drinking water exposure provided the common basis for selected indicators. For two chemicals, toxicity information was identified from the scientific literature to guide the performance targets.
International Radioactive Material Recycling Challenges
Authors: Greeves John T. , Lieberman James
Published: June 2009

The paper explores current examples of successful International radioactive recycling programs and also explores operational regulatory and political challenges that need to be considered for expanding international recycling world-wide. Most countries regulations are fully consistent with the International Atomic Agency (IAEA) Code of Practice on the International Transboundary Movement of Radioactive Material and the IAEA Code of Conduct on the Safety and Security of Radioactive Sources. IAEA member States reported on the status of their efforts to control transboundary movement of radioactive material recently during the Joint Convention on the Safety of Spent Fuel management and on the Safety of Radioactive Waste Management meeting in May 2006.
Chemical Decontamination of the Residual Heat Removal System (RHRS) of Flamanville 1
Authors: Steinkuhler Claude , Coomans Reginald , Lenie Koen
Published: June 2009

The purpose of the decontamination of the RHRS at Flamanville 1 was the reduction of the general dosimetry and the elimination of hot spots. This was done to allow the maintenance on the RHRS equipment. The main challenge of this project was the execution of a complicated operation on the critical path of a shutdown. The redox attack of the oxides at the surface of the circuit in Flamanville, was performed by an EDF qualified process of the EMMAC family. The functions required by the decontamination system were very diverse and therefore an existing decontamination loop, which was previously developed for the decontamination of small system volumes, was re-developed and adapted for bigger circuits. Due to different reasons, an important delay on the planning happened. Therefore, only one cycle EMMAg was performed, totalling 2 hours of decontamination. Despite this, a DRRF (dose rate reduction factor) of 3,7 average was reached. The re-designed equipment and a shortened process were validated during this project. An acceptable DRRF was reached with no delay on the critical path. The capability of maintenance on the RHRS equipment is recovered with a gain of factor 5 on dosimetry.
Lessons Learnt From Ignalina NPP Decommissioning Project
Authors: Naisse Jean-Claude
Published: June 2009

The Ignalina Nuclear Power Plant (INPP) is located in Lithuania, 130 km north of Vilnius, and consists of two 1500 MWe RBMK type units, commissioned respectively in December 1983 and August 1987. On the 1st of May 2004, the Republic of Lithuania became a member of the European Union. With the protocol on the Ignalina Nuclear Power in Lithuania which is annexed to the Accession Treaty, the Contracting Parties have agreed: - On Lithuanian side, to commit closure of unit 1 of INPP before 2005 and of Unit 2 by 31 December 2009; - On European Union side, to provide adequate additional Community assistance to the efforts of Lithuania to decommission INPP. The paper is divided in two parts. The first part describes how, starting from this agreement, the project was launched and organized, what is its present status and which activities are planned to reach the final ambitious objective of a green field. To give a global picture, the content of the different projects that were defined and the licensing process will also be presented. In the second part, the paper will focus on the lessons learnt. It will explain the difficulties encountered to define the decommissioning strategy, considering both immediate or differed dismantling options and why the first option was finally selected. The paper will mention other challenges and problems that the different actors of the project faced and how they were managed and solved. The paper will be written by representatives of the Ignalina NPP and of the Project Management Unit.
The Next Generation: How Are We Equipping Our Young Generation for the Future
Authors: Horsfall Corhyn
Published: June 2009

The nuclear industry until a few years ago was perceived to be a dying breed in the UK. As the lifetime of our operating station comes to a close younger engineers and scientists favoured other industries such as IT, manufacturing or banking. As we enter a nuclear renaissance in the UK it is becoming increasingly more important to attract and retain the best scientists and engineers to secure our energy requirements for the future as well as decommission the current liabilities. This paper discusses 3 groups focusing on graduate recruitment and retention, Companies, YGN and NDA. All three need to work together to not only promote the nuclear industry and encourage graduates but also to develop them for the future. Companies are continuously refocusing their schemes to the changing requirements of the industry, the YGN are a link between these companies assisting with career developing of new recruits and the NDA have launched a programme to encourage a national graduate programme. All three elements are discussed and required to evolve together to ensure the successful development of the industry on a national level.
Spent Fuel Management—A User’s Perspective: Summary of Panel Discussions and Findings From WM’07 in Tucson, Arizona
Authors: Berry Dennis L. , Callan Bart R.
Published: June 2009

A global partnership between nuclear energy supplier nations and user nations could enable the safe and secure expansion of nuclear power throughout the world. Although it is likely that supplier nations and their industries would be anxious to sell reactors and fuel services as part of this partnership, their commitment to close the fuel cycle (i.e., permanently take back fuel and high-level waste) remains unclear. At the 2007 Waste Management Symposia in Tucson, Arizona, USA, a distinguished international panel explored fuel take back and waste disposal from the perspective of current and prospective user nations. This paper reports on the findings of that panel and presents a path for policy makers to move forward with the partnership vision.
Decontamination and Decommissioning of the Uranium Mill and Processing Plant at Seelingstaedt, Germany
Authors: Barnekov Ulf , Bauroth Matthias , Paul Michael
Published: June 2009

In Eastern Germany uranium mining lasted from 1946 till 1990 including a production of in total 220,000 t of uranium. The Seelingsta¨dt Uranium Mill and Processing Plant, located in Thuringia, Germany, was one of two large uranium mills owned by Wismut. The mill was erected by 1960 and covered an area of 93 ha. From 1961 till 1991 a total of about 110 million t of different types of uranium ores were milled and processed at the Seelingsta¨dt mill. The mill produced ca. 110,000 t of uranium (in yellow cake). Demolition of the buildings and industrial facilities of the Seelingsta¨dt mill and processing plant site are nearly completed. The site is being decommissioned with respect to after-use aiming at afforestation and grasslands allowing for a stable plant succession. Decommissioning includes excavation and relocation of contaminated materials, reshaping of the site and construction of ditches for granting a stable surface runoff as well construction of access and maintenance roads. About 85% of the demolition and relocation works have been completed till to date. Last decommissioning works shall be completed by 2015. The present paper presents experiences made and progress achieved till to date.
Mechanism for Formation of Highly Monodisperse Droplet in a Microfluidic T-Junction Device
Authors: Liu Zhipeng , Xu Jinliang
Published: June 2009

Droplet formation in a microfluidic T-junction device which is high aspect ratio rectangular channel connected by a perpendicular channel were investigated experimentally. This geometry is quite similar to the classic T-junction device, however the perpendicular channel is a slightly narrower with respect to the dispersed phase inlet, leading to remarkably different result. The perfectly controllable droplets were found to be monodispersed with a less than 2% variation in micron size. Experimental results, including the relation between diameter and flow rates, the change of the velocity and pressure at drop break-up process, had been analyzed in detail. The single breakup process and the quasistatic character were described by evolution of the width and length of the liquid-liquid interface. Finally, in contrast to the capillary instability in an unbounded fluid, the breakup process was explained in term of absolute instabilities.
Effects of Interfacial Phenomena and Conduction on an Evaporating Meniscus
Authors: Wayner Peter C.
Published: June 2009

An overview of some of the theoretical models describing the effects of chemical potential, excess free energy, free energy gradient, film thickness profile, temperature profile, superheat, thermal conduction, concentration gradient, velocity profile, slip velocity, apparent contact angle, and kinetic theory on the phase change heat transfer processes in an evaporating meniscus are presented. The relative importance of the parameters is demonstrated. Experimental techniques and confirming experimental data are also presented. In essence, the microscopic thickness profile of the evaporating meniscus is measured optically to obtain the details of the liquid pressure field and modeled to give the fluid flow rate and the evaporative heat flux. The macroscopic temperature field of the substrate is measured and numerically modeled to give the microscopic temperature field and a complementary calculation of the evaporative heat flux. For closure, the values of the slip velocity and concentration change on evaporation need to be correctly assumed. The interfacial transport processes are very sensitive to small interfacial temperature and concentration changes, which are difficult, if not impossible, to measure directly. However, the liquid pressure gradients can be directly measured. The effects of the interacting phenomena on the phase change processes are demonstrated using these complementary experimental-modeling procedures. The processes are found to be very complex and simple modeling/experiments can only confirm the general phenomena and give insight.
A Review of Models for Water Droplet Detachment From the Gas Diffusion Layer-Gas Flow Channel Interface in PEMFCs
Authors: Schillberg Charles H. , Kandlikar Satish G.
Published: June 2009

Understanding the fundamental mechanisms of water transport in proton exchange membrane fuel cells (PEMFCs) is necessary for effective management of product water. Among the transport mechanisms affecting the performance of PEMFCs are droplet formation, growth, and detachment at the gas diffusion layer (GDL)-gas flow channel interface. The presence of water droplets on the GDL blocks the access of gases to the reaction sites, increases channel pressure drop, and creates inconsistencies in the gas velocity fields down the channel length, all resulting in performance deterioration. In order to gain an insight into controlling droplets, an in-depth review of PEMFC water droplet detachment models published in the literature is presented here. Summaries of supporting data, modeling techniques, and conclusions are also presented.
A New Active Micro Mixing Strategy
Authors: Tardu Sedat , Nacereddine Rabia
Published: June 2009

An active micro-mixing strategy through forcing the flow by synthetic wall jets is proposed. It is based on the interaction of induced streamwise vortices in a specific way. There is a spanwise shift between two quasi-streamwise vortices in such a way that one of them compresses the wall normal vorticity layer created by the other, leading to the generation of new wall normal vortical structures. The latter are subsequently tilted by the shear to give birth to new small-scale longitudinal active structures that are efficient in mixing. The feasibility of this strategy is shown through direct numerical simulations of high spatial and temporal resolution.
Effects of Low Uniform Relative Roughness on Single-Phase Friction Factors in Microchannels and Minichannels
Authors: Brackbill Timothy P. , Kandlikar Satish G.
Published: June 2009

Nikuradse’s [1] work on friction factors focused on the turbulent flow regime in addition to being performed in large diameter pipes. Laminar data was collected by Nikuradse, however only low relative roughness values were examined. A recent review by Kandlikar [2] showed that the uncertainties in the laminar region of Nikuradse’s experiments were very high, and his conclusion regarding no roughness effects in the laminar region is open to question. In order to conclusively resolve this discrepancy, we have experimentally determined the effects of relative roughness ranging from 0–5.18% in micro and minichannels on friction factor and critical Reynolds numbers. Reynolds numbers were varied from 30 to 7000 and hydraulic diameters ranged from 198μm to 1084μm. There is indeed a roughness effect seen in the laminar region, contrary to what is reported by Nikuradse. The resulting friction factors are well predicted using a set of constricted flow parameters. In addition to higher friction factors, transition to turbulence was observed at decreasing Reynolds numbers as relative roughness increased.
Flow Boiling in a 1.1 mm Tube With R134A: Experimental Results and Comparison With Model
Authors: Shiferaw D. , Karayiannis T. G. , Kenning D. B. R.
Published: June 2009

A detailed comparison of the three-zone evaporation model, proposed by Thome et al. (2004), with experimental heat transfer results of two stainless steel tubes of internal diameter 4.26 mm and 2.01 mm using R134a fluid was presented by Shiferaw et al. (2006). In the current paper the comparison is extended to flow boiling in a 1.1 mm tube using R134a as the working fluid. Other parameters were varied in the range: mass flux 100–600 kg/m2.s; heat flux 16–150 kW/m2 and pressure 6–12 bar. The experimental results demonstrate that the heat transfer coefficient increases with heat flux and system pressure, but does not change with vapour quality when the quality is less than about 50% for low heat and mass flux values. The effect of mass flux is observed to be insignificant. For vapour quality values greater than 50% and at high heat flux values, the heat transfer coefficient does not depend on heat flux and decreases with vapour quality. This could be caused by partial dryout. The three-zone evaporation model predicts the experimental results fairly well, especially at relatively low pressure. However, the partial dryout region is highly over-predicted by the model. The sensitivity of the performance of the model to the three optimized parameters (confined bubble frequency, initial film thickness and end film thickness) and some preliminary investigation relating the critical film thickness for dryout to measured tube roughness are also discussed.
Unsteady Laminar Flow Regimes and Mixing in T-Shaped Micromixers
Authors: Kockmann Norbert , Dreher Simon , Woias Peter
Published: June 2009

Convective micromixers create vortices in curved channel elements and allow characteristic mixing times below 1 millisecond for gaseous and liquid media. The flow regimes in the T-shaped junction of rectangular microchannels determine the mixing characteristics of the device. This contribution gives an overview about the flow regimes of symmetrical 1:1 mixing in T-shaped micromixers for Reynolds numbers from 0.01 to 1000 in the mixing channel. CFD simulations with the CFD-ACE+ code of ESI group give a detailed picture of the flow and mixing regimes in the investigated range of Reynolds numbers Re. First symmetrical vortices are formed at the entrance of the mixing channel for Re > 10. Due the symmetrical flow and the undisturbed interface between the components, the mixing quality at a distinct mixing channel length decreases with increasing Re number. At a certain Re number of about 140, the flow symmetry is disturbed, fluid from one side swaps to the opposite side and creates a double vortex within the mixing channel. For Re > 240 the flow becomes unsteady. The vortex formation at the mixing channel entrance is disturbed and a kind of wake flow establishes within the mixing channel. From 240 < Re < 500 the wake flow is periodic with a dimensionless frequency, the Strouhal number Sr of about 0.2. The Sr number is found to be the same in scaled mixer geometries. The mixing quality shows also a periodic behavior and reaches its maximum at this point. With further increasing Re number, the flow starts to become chaotic and the two components are often flowing parallel in the mixing channel leading to a decreasing mixing quality. Besides detailed CFD simulations, the periodic flow is observed in experimental studies with colored flow and stroboscopic imaging and has the same frequency. The decreasing mixing quality is also reflected in a lower selectivity of parallel, chemical test reactions for Re numbers larger than 500. With the knowledge of the flow regimes in microchannels, design criteria can be formulated for efficient mixing devices.
Effects of Freezing and Thawing on the Structures of Porous Gas Diffusion Media
Authors: Pelaez Joaquin A. , Kandlikar Satish G.
Published: June 2009

Fuel cells are a very promising technology for transportation applications in the future. Many companies are performing research in order to make the implementation of fuel cell-powered vehicles more feasible. One issue that needs to be addressed is the fact that fuel cell vehicles will be used in sub-freezing climates. Vehicles undergo frequent shut down and startup events, and as such, freezing and thawing effects on fuel cell components become important when the vehicle is stored overnight in cold climates. When shut off, fuel cells will maintain water in the membrane electrode assembly (MEA) and gas diffusion media unless certain purging protocols are adhered to. When the cell is subjected to sub-freezing temperatures, the water remaining in these media will freeze. This freezing could have a detrimental impact on the pore structure, fiber integrity, and binder effectiveness in the GDL, thereby decreasing the electrochemical active surface area of the electrolytes and hurting the overall performance of the cell. This paper details the prior research in the area of freezing and thawing effects in these media and also details current research on the degradation of the GDL specifically.
Band Broadening During High-Throughput Mutation Detection in Microchannels
Authors: Dorfman Kevin D. , Laachi Nabil
Published: June 2009

Cycling temperature gradient electrophoresis represents a promising method for performing high-throughput DNA mutation detection in a microfluidic platform. Sweeping the temperature between an “all denatured” and “all annealed” state eliminates difficulties introduced by the low thermal mass of the system, while still preserving a mobility difference between the wild type and mutant alleles. We describe a theoretical analysis of this method of mutation detection, based on a multiple-time scales analysis that is valid when the DNA experience many temperature cycles before reaching the detector [1]. We focus on the band-broadening incurred by the interplay between the relaxation time of the chemical system and the thermal oscillations. New results are presented for the case where the denaturing and annealing reactions proceed at identical rates. Our analysis indicates that this separation would be best operated at low electric fields.
Assessing Uncertainties in Friction Factor Measurement as a Tool in Devising Experimental Set-Ups
Authors: Lorenzini Marco , Morini Gian Luca , Henning Torsten , Brandner Juergen J.
Published: June 2009

The promising performance of microchannels has given rise to intensive research on pressure drop and heat transfer characteristics of flows at the small- validate new ones, experiments need to be conducted, which are particularly difficult given the characteristic dimensions involved and the magnitude of the fluxes to be measured. Although more care has been devoted lately to the design of experiments in terms of control of geometry and boundary conditions, the uncertainties which inevitably affect each measurement do not seem to have been given the proper consideration. Correctly calculating uncertainties not only allow to a correct assessment of the experimental data obtained, but can also be used to decide which measurements need to have the highest precision to achieve a certain accuracy, thus saving money on the others. In this paper, a quantitative criterion is given to assess the accuracy achievable in the determination of the friction factor in the laminar regime for the flow of a fluid in a circular microtube. The influence of the six quantities (pressure drop, outlet pressure, temperature, length, pressure and volume flow rate) measured to determine f in the laminar regime are studied separately and when combined. It is found that at low Reynolds numbers flow rate and pressure drop measurements are determinant for the final value of the uncertainty, while at larger Reynolds numbers the influence of the accuracy in measuring the hydraulic diameter prevails and also limits the minimum value that the total uncertainty can take.
Lattice Boltzmann Method for Steady Gas Flows in Microchannels With Imposed Slip Wall Boundary Condition
Authors: Gokaltun Seckin , Dulikravich George S.
Published: June 2009

In this paper, we use a lattice Boltzmann method (LBM) for simulation of rarefied gas flows in microchannels at the slip flow regime. LBM uses D2Q9 lattice structure and BGK collision operator with single relaxation time. The solid wall boundary conditions used in this paper are based on the idea of bounceback of the non-equilibrium part of particle distribution in the normal direction to the boundary. The same idea is implemented at inlet and exit boundaries as well as at the wall surfaces. The distribution functions at the solid nodes are modified according to imposed density and slip velocity values at the wall boundaries. Simulation results are presented for microscale Couette and Poiseuille flows. The results are validated against analytical and/or experimental data for the slip velocity, nonlinear pressure drop and mass flow rate at various flow conditions. It was observed that the current application of LBM can accurately recover the physics of microscale flow phenomena in microchannels. The type of boundary treatment used in this study enables the implementation of coupled simulations where the flow properties at the regions near the wall can be obtained by other numerical methods such as the Direct Simulation Monte Carlo method (DSMC).
Near-Wall Scaling of the Navier-Stokes Constitutive Relations for Accurate Micro Gas Flow Simulations
Authors: Lockerby D. A. , Reese J. M.
Published: June 2009

A new model is described for micro gas flows that combines a second-order slip boundary condition with a near-wall scaling of the Navier-Stokes constitutive relations. This scheme, which is easily implemented within a conventional CFD framework, is shown to be far more accurate than the conventional second-order slip model at predicting high Knudsen number micro Couette and Poiseuille flows. It is also of equivalent computational cost, and as such, represents a more attractive alternative to the conventional slip approach. It is also shown that the current model is capable of accurately predicting combined Couette/Poiseulle flows at a much higher Knudsen number than second-order slip conditions, which bodes well for the applicability of the scheme to more general configurations.
Experimental Study on Flow and Heat Transfer Characteristics in a Microscale Heat Exchanger
Authors: Wang Tao , Hu Xuegong , Tang Dawei
Published: June 2009

To solve the questions of the middle heat exchanger of space-based laser cooling system such as large heat transfer area and operating mode instability, a MC-MG (Microchannel-Microgroove) microscale heat exchanger is proposed and experimental study is carried out. The experimental results indicate that as the Reynolds number increases, the Nusselt number originally increases and then keeps constant. While adding the volumetric flow rate of distilled water in the microchannels, the total thermal resistance is first reduced and then becomes steady. With increasing the volumetric flow rate of distilled water, the total quantity of heat transfer increases first, then decreases and finally tends to be constant. The average heat transfer coefficient of the heat exchanger reaches to 1.6 × 104W/ (m2-K) and total thermal resistance is less than 0.21K/W. Therefore the solution to cooling laser with the heat exchanger is preferable.
Different Type Tube Bundle Heat Transfer to Vertical Foam Flow
Authors: Gylys Jonas , Sinkunas Stasys , Zdankus Tadas , Giedraitis Vidmantas
Published: June 2009

Gas-liquid foam due to especially large inter-phase contact surface can be used as a coolant. An experimental investigation of the staggered and in-line tube bundles’ heat transfer to the vertically upward and downward laminar foam flow was performed. The experimental setup consisted of the foam generator, vertical experimental channel, tube bundles, measurement instrumentation and auxiliary equipment. It was determined dependency of heat transfer intensity on flow parameters: flow velocity, direction of flow, volumetric void fraction of foam and liquid drainage from foam. Apart of this, influence of tube position in the bundle to heat transfer was investigated. Foam flow structure, distribution of the foam’s local void fraction and flow velocity in cross-section of the channel were the main factors which influenced on heat transfer intensity of the different tubes. Experimental investigation showed that the heat transfer intensity of the frontal and further tubes of the bundles to vertical foam flow is different in comparison with one-phase fluid flow. The results of the experimental investigation are presented in this paper.
Detailed Experimental Investigation on the Observed Scattering in Heat Transfer Characteristics for Flow Boiling in a Small Diameter Tube
Authors: Ohta Haruhiko , Inoue Koichi , Ando Makiko , Watanabe Kei , Ito Yuta
Published: June 2009

Effects of flow fluctuation at the test section inlet on flow boiling heat transfer were investigated for FC72 by the use of a horizontal circular tube with a diameter of 0.51mm. Flow fluctuation was minimized by employing a high-powered syringe pump in one experiment, while it was intensified in another experiment by the connection of an auxiliary tank exposed to atmosphere allowing the reverse flow. In the experiments of strict inlet flow rate regulation, heat transfer characteristics were similar to those observed in normal size tubes. But if the flow rate was fluctuated up to ± 20% of the total under the weak inlet flow rate regulation, the trend that the heat transfer coefficient was increased with increasing vapor quality in moderate vapor quality region was disappeared and heat transfer deterioration due to partial dryout started at lower vapor quality. Boiling heat transfer characteristics in minichannels could be changed considerably by the existence of flow fluctuation caused by the rapid axial growth of elongated bubbles at low vapor quality. The regulation of inlet flow rate seems to be one of key parameters to reduce the scattering in heat transfer data encountered in flow boiling of minichannels. Experimental data obtained by using a pump of weak power or data using a liquid reservoir can never be inherently consistent with those obtained for the constant inlet flow rate conditions. Although such weak restriction of inlet conditions are actually encountered in application systems, the difference in heat transfer characteristics between the normal and mini tubes should be clarified, as the first objective of the research, under the same inlet conditions without flow fluctuation.
Numerical and Experimental Research on Fluid Flow and Heat Transfer in Miniscale Channels
Authors: Geng Wenguang , Chen Baoming
Published: June 2009

The high rates of heat transfer obtained by using micro or mini channels makes them an attractive alternative to conventional methods of heat dissipation, especially in microelectronics cooling system. In this paper, three dimensional fluid flow and heat transfer phenomena for different coolant in rectangular, elliptic and triangular miniscale channels is investigated. In all computational regions this paper improved the Boussinesq and the thermal physical properties of the coolant are temperature dependent. The heat transfer Nusselt numbers and flow resistance coefficients of different channels are obtained, and the pressure drop and the temperature increasing of the coolant in three mini channels are studied. The numerical simulation shows that the mini rectangular channels’ heat transfer and flow resistance characteristics are optimal.
Measurement of Liquid Film Thickness by a Fringe Method
Authors: Kariyasaki Akira , Ousaka Akiharu , Yamasaki Yoshikazu , Kagawa Masazumi , Nagashima Tohru , Morooka Sigeharu
Published: June 2009

A technique to measure the local thickness of a droplet or a liquid film by an interference fringe pattern that was formed by reflecting laser lights was developed and tested. Monochromatic epi-illumination through an objective lens of a microscope was provided by a 5mw-300mw laser and a filter to remove the noise caused by laser speckle. The incremental height difference of the liquid layer between neighboring maxima or minima of fringes was evaluated from the wavelength of the laser light and the refractive index of the liquid. Estimation error of a local inclination angle was discussed using ray tracing under parallel illumination approximation (Ku¨hner et al., 1996). Droplet profiles evaluated from the interferogram that were obtained by the present fringe method agreed well with those by Laser Focus Displacement Meter (LFD) (Fukamachi et al., 2003). Measurement was tried to make sure the usefulness of the present technique. It was made clear that a) contact angle of a liquid droplet could be obtained precisely and swiftly even in small size or small contact angle, and b) instantaneous three dimensional profile of a liquid film on a bubble moving in a micro-channel could be measured. The fringe method had sufficient potential to obtain more detailed information about three dimensional characteristics of liquid film in flow phenomena such as the generation, break down and growth of waves and the liquid film of a bubble at the beginning of movement.
Temperature Dependence of Thermal Conductivity of Amorphous and Crystal Thin Film by Molecular Dynamics Simulation
Authors: Huang Zhengxing , Tang Zhenan , Bai Suyuan , Yu Jun
Published: June 2009

For crystal materials, thermal conductivity (TC) is proportional to T3 at low temperatures and to T−1 at high temperatures. TCs of most amorphous materials decrease with the decreasing temperatures. If a material is thin film, boundary will influence the TC and then influence the temperature dependence. In this paper, we calculate the TC of crystal and amorphous SiO2 thin films, which is a commonly used material in micro devices and Integrated Circuits, by NEMD simulations. The calculation temperatures are from 100K to 700K and the thicknesses are from 2nm to 8nm. TCs of crystal thin films reach their peak values at different temperatures for different thicknesses. The smaller thickness the larger peak values obtained. But for amorphous thin films, the results show that the temperature dependence of thin films is the same as bulk materials and not relative to their thicknesses. The obtained temperature dependence of the thin films is consistent with some previous measurements and the theory predictions.
Mixing Performance of Different Serpentine Microchannels
Authors: Nonino C. , Savino S. , Del Giudice S.
Published: June 2009

The results of a comparative numerical study aimed at assessing the mixing performance of planar zig-zag, curvilinear and square-wave microchannels of square cross-section is presented in the paper. To evaluate the mixing enhancement characteristics of each geometry, suitable mixing indices are computed at different axial locations of a single repetitive module of each microchannel when this is fed with two equal streams of fluid having the same thermophysical properties, but different solute concentrations. To separate the effects of the geometry from those of molecular diffusion, entrance flow and channel length, the mixing by pure diffusion in straight microchannels of the same length is also evaluated for comparison. Reynolds numbers in the range from 5 to 150 are considered, while the Pe´clet number is held constant and equal to 2500. All the numerical simulations are carried out using an in-house finite element code for the solution of all model equations.
On the Characterisation of Finned and Finless Heat Sinks for Portable Electronics
Authors: Egan V. , Walsh P. , Walsh E. , Grimes R.
Published: June 2009

Reliable and efficient cooling solutions for portable electronic devices are now at the forefront of research due to consumer demand for manufacturers to downscale their existing technologies. The power required for these technologies now has to be dissipated over smaller areas resulting in elevated heat fluxes. The most popular choice among engineers in terms of cooling solutions is to integrate a fan with a heat sink and for portable electronic devices this involves the use of a low profile solution. In this paper an experimental investigation on the thermal performance of a finned and finless heat sink integrated with an axial fan, for the purpose of cooling a microchip, is presented. The objective is to characterise the performance of each heat sink in terms of thermal resistance and to develop an understanding of the flow structures in such systems. One of the smallest commercially available fans is used in conjunction with each heat sink giving a total footprint area of 465m2 and profile height of 5mm. Thermal resistances are measured over a range of fan speeds and detailed velocity measurements were taken of the flow within the heat sinks using Particle Image Velocimetry (PIV). The thermal analysis results indicate that the thermal resistance of the system is of order 30 deg C/W for both heat sinks. However, the finless heat sink resulted in slightly lower values over a range of intermediate fan speeds. Hence, indicating that the maximum heat transfer density, for a range of fan speeds, can be achieved with a finless heat sink. The results also define the limiting heat fluxes that can be dissipated in low profile miniature applications.
Liquid Bridges: A Novel Approach for Dispensing Biofluids, Characterisation and Correlations
Authors: Forget Magali , Davies Mark
Published: June 2009

Control of fluids at the microscale represents an important point of interest in the widely studied field of Microfluidics. In fact, most of the biological and medical research undergone would benefit from Microfluidic solutions. One of the engineering challenges brought about by this technologic evolution involves the dispensing of fluids at these scales. The study presented in this paper concerns the development of a novel dispenser of biofluids, which would find its first application in the measurement of multi-gene expression levels as part of cancer diagnosis. The studied geometry is termed “two-way liquid bridge” and consists of injecting a continuous fluid to be segmented via an inlet PFE tubing in a microgravity environment until an isothermal mass of liquid is held by surface tension between the inlet and outlet tubings, parallel and opposite. Due to constant pressurisation of the microgravity environment, this mass eventually ruptures delivering a segmented volume of biofluids on which an analysis such as PCR can be performed. Experimental investigations were conducted in a backlighted transparent PMMA device in which fluids were injected using Harvard Apparatus syringe pumps. A CMOS colour camera recorded the images which were automatically analysed using a Canny edge detection algorithm. A dimensional analysis was conducted highlighting the main dimensionless groups for a complete understanding of the occurring phenomena. Experimental observations showed good repeatability and consistency in the dispensing process. It was also shown that fluids flowrates, tubings sizes and length of separation between inlet and outlet tubings have a direct impact on the size and frequency of the produced droplets. The present paper addresses the complete characterisation of the geometry as well as the establishment of correlations in order to provide a useful engineering design tool.
PDMS Surface Modification for Application on Thermally-Responsive Hydrogel Microvalves
Authors: Mohammed Mohammed , Major Jaycoda , Zhang Zongqin , Faghri Mohammad , Meyer Donna , Fadl Ahmed
Published: June 2009

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.
Passive Heat Transfer Enhancement in Microchannels Using Wall Features
Authors: Arora Ravi , Tonkovich Anna Lee , Lamont Mike J. , Yuschak Thomas , Silva Laura
Published: June 2009

The two important considerations in the design of a heat exchanger are — the total heat transfer rate and the allowable pressure drop. The allowable pressure drop defines the maximum flow rate through a single microchannel and economics drives the design towards this flow rate. Typically the flow rate in the microchannel is in laminar flow regime (Re < 2000) due to smaller hydraulic diameter. The laminar flow heat transfer in a smooth microchannel is limited by the boundary layer thickness. Commonly the heat transfer rate is enhanced by passively disrupting the laminar boundary layer using protrusions or depressions in the channel walls. More often these methods are best applicable at small range of Reynolds number where the heat transfer rate enhancement is more than the pressure drop increase and break down as the flow rate is changed outside the range. The benefit of a flow disruption method can be reaped only if it provides higher heat transfer enhancement than the increase in the pressure drop at the working flow rates in the microchannel. A heat transfer efficient microchannel design has been developed using wall features that create stable disrupted flow and break the laminar boundary layer in a microchannel over a wide range of flow rates. The paper experimentally investigates the developed design for the heat transfer enhancement and pressure drop increase compared to a smooth wall microchannel. A simple microchannel device was designed and fabricated with and without wall features. The experiments with single gas phase fluid showed promising results with the developed wall feature design as the heat transfer rate increase was 20% to 80% more than the pressure drop increase in the laminar regime. The wall feature design was an important variable to affect the magnitude of performance enhancement in different flow regime. A general criterion was developed to judge the efficacy of wall feature design that can be used during a microchannel heat exchanger design.
Optimal Shape Design of Pressure-Driven Microchannels Using Adjoint Variable Method
Authors: Tonomura Osamu , Takase Tatsuya , Kano Manabu , Hasebe Shinji
Published: June 2009

The shape of microchannels is an important design variable to achieve the desired performance. Since most microchannels are, at present, designed by trial and error, a systematic optimal shape design method needs to be established. Computational fluid dynamics (CFD) is often used to rigorously examine the influence of the shape of microchannels on heat and mass transport phenomena in the flow field. However, the rash combination of CFD and the optimization technique based on evaluating gradients of the cost function requires enormous computation time when the number of design variables is large. Recently, the adjoint variable method has attracted the attention as an efficient sensitivity analysis method, particularly for aeronautical shape design, since it allows one to successfully obtain the shape gradient functions independently of the number of design variables. In this research, an automatic shape optimization system based on the adjoint variable method is developed using C language on a Windows platform. To validate the effectiveness of the developed system, pressure drop minimization problems of a 180° curved microchannel and a branched microchannel in incompressible flows under constant volume conditions are solved. These design examples illustrate that the pressure drop of the optimally designed microchannels is decreased by about 20% ∼ 40% as compared with that of the initial shape.
Numerical Simulation on Micromixer Based on Syntehtic Jet
Authors: Liu M. H. , Zhang X. F. , Cai X. D. , Chen Y. L.
Published: June 2009

This paper studied a concept of micromixer with a synthetic jet placed at the bottom of a rectangular channel. Due to periodic ejections from and suctions into the channel, the fluids are mixed effectively. To study the effects of the inlet velocity, the jet intensity and frequency, and the jet location on the mixing efficiency, 3-D numerical simulations of the micromixer have been carried out. It has been found that when the jet intensity and the frequency are fixed, the mixing efficiency increases when Re<50, and decreases when Re>50 with the best mixing efficiency achieved at Re=50. When the ratio of the jet velocity magnitude to the inlet velocity is taken as 10 and the jet frequency is 100Hz, the mixing index reaches the highest value. It has also been found that to get better mixing efficiency, the orifice of the synthetic jet should be asymmetrically located away from the channel’s centerline.
Effect of Longitudinal Mini-Grooves on Flow Stability and Wave Characteristics of Falling Liquid Films
Authors: Helbig Klaus , Nasarek Ralph , Gambaryan-Roisman Tatiana , Stephan Peter
Published: June 2009

Falling liquid films are used in many industrial apparatuses. In many cases the film flow along a wall with topography is considered advantageous for intensification of the transport processes. We use the shadow method and the chromatic white light sensor (CHR) method to study the wavy structure of falling films on flat walls and on walls with longitudinal grooves. We show that the wavy pattern substantially changes on walls with topography. The wave frequency, the wave propagation velocity and the area of the liquid-gas interface decrease on grooved walls. The linear stability of the film has been analyzed using the long-wave theory, which relies on the assumption that the average film thickness is much smaller than the scale of the film thickness variation. The linear stability analysis predicts that the disturbance growth rate, the frequency of the fastest growing disturbance mode and the wave propagation speed decrease on a tube with longitudinal mini-grooves in comparison with a smooth tube. These results agree well with the experimental findings.
Fully-Coupled Modelling of Electrokinetic Flow and Migration of Electrolytes in Microfluidic Devices
Authors: Barz Dominik P. J. , Ehrhard Peter
Published: June 2009

We investigate the electrokinetic flow and mass transport in a microchannel junction, serving as an injector of a microelectrophoresis device. In order to consider all essential features of this complex system, the electrical situation, the fluid dynamics, and the (physical) chemistry is taken into account. The electrical situation is modeled by a combination of an electrostatic and an electrodynamic approach. The fluid dynamics can be described by the Navier-Stokes equations, extended by an additional force term. The chemistry of the system is represented by source terms in the mass transport equations. Moreover, the interaction between the buffer concentration and the physicochemical properties of the channel wall is taken into consideration by an empirical approach. All equations are encoded in a dimensionless form so that dimensionless groups control the problem. Approximative analytical solutions for the phenomena within the electrical double layer can be found and, thus, we can reduce the numerical costs due to an asymptotic matching procedure. The models are implemented in a Finite Element Method (FEM) code and time-dependent, two-dimensional simulations are performed. The results of the simulations show the strong coupling between the involved physicochemical processes.