bluuebunny/crossref_metadata_2025 huggingface dataset:
The Use of a Waste Conversion Index as a Long Term Performance Indicator for Civil Nuclear Laibilities
Authors: Fawcett Pauline , Spencer David , Jarvis Richard , Linekar George
Published: March 2009

In November 2001 the UK Government issued a statement on the future management of public sector nuclear liabilities and in its white paper “Managing the nuclear legacy” proposed the establishment of a Liabilities Management Authority, or the Nuclear Decommissioning Authority (NDA) as it is now called. With the advent of the NDA, whose aim will be to safely and cost effectively reduce nuclear liabilities, and existing Government Policy which requires systematic and progressive reduction in hazard, there is a need for some form of index to demonstrate progress. Although there are many indices in use, mainly within the chemical industry, none of these are considered suitable for this purpose. A Waste Conversion Index is currently being developed to satisfy these needs. The Waste Conversion Index will reflect an emphasis on passive safety rather than the more traditional safety analysis which focuses on risk. It is intended to be applicable across all UK civil nuclear sites and may act as one of a number of long-term performance indicators. This paper describes how the index is formulated, and the various factors used in the calculation together with its main uses including its use as a predictive tool to demonstrate progressive hazard reduction as nuclear liabilities are reduced. In addition the paper warns against the misuse of the index as a sole means of decision making in developing hazard reduction strategies, prioritising projects and allocating funding. Finally, some examples are given of its application to existing facilities.
Independent Quality Checking of UK Low Level Radioactive Waste for Plutonium Using the SCK•CEN Hexagon 2000 Passive Neutron Coincidence Counter
Authors: May R. , Strange R. , Bruggeman M. , De Boeck W.
Published: March 2009

Checking low level wastes requires the detection of sub-milligram levels of plutonium. This is an extreme challenge for passive neutron coincidence counting as the levels of true signal are close to the background signal caused by cosmic ray interactions. The origin of cosmic-induced background is discussed. We describe the Hexagon 2000 passive neutron coincidence counter that has been designed and built for waste quality checking of low-level radioactive waste in the UK for the Environment Agency. The instrument uses computed neutron coincidence counting and improved filtering of high multiplicity cosmic-induced events. The instrument also correlates background signal with atmospheric pressure to further increase sensitivity. Preliminary measurements of background data and of test drums containing small amounts of plutonium are described.
Decommissioning AECL Whiteshell Laboratories
Authors: Koroll G. W. , Ryz M. A. , Harding J. W. , Ridgway W. R. , Rhodes M. J. , McCamis R. H.
Published: March 2009

AECL operates two nuclear R&D laboratories in Canada, Chalk River Laboratories (CRL) near Ottawa, Ontario, and Whiteshell Laboratories (WL), near Winnipeg, Manitoba. Whiteshell Laboratories have been in operation since about 1965. R&D programs carried out at WL included the WR-1 research reactor, which operated from 1965 to 1985, reactor safety research, small reactor development, materials science, post irradiation examination, chemistry, biophysics and radiation applications. The Canadian Nuclear Fuel Waste Management Program was conducted and continues to operate at WL and also at the nearby Underground Research Laboratory. In the late-1990s, AECL began to consolidate research and development activities at CRL and initiated preparations for decommissioning WL. Preparations for decommissioning included a formal environmental assessment under Canadian environmental assessment legislation, a prerequisite to AECL’s application for a decommissioning licence. In 2002 December, the Canadian Nuclear Safety Commission issued a decommissioning licence for WL, valid until December 31, 2008. The licence authorizes the first planned phase of site decommissioning as well as the continuation of selected research programs. The six-year licence for Whiteshell Laboratories is the first overall decommissioning license issued for a Canadian Nuclear Research and Test Establishment and is the longest licence term ever granted for a nuclear installation of this complexity in Canada. The first phase of decommissioning is now underway and focuses on decontamination and modifications to nuclear facilities, such as the shielded facilities, the main R&D laboratories and the associated service systems, to achieve a safe state of storage-with-surveillance. Later phases have planned waste management improvements for selected wastes already in storage, eventually followed by final decommissioning of facilities and infrastructure and removal of most wastes from the site. This paper provides an overview of the planning, environmental assessment, licensing, and organizational processes for decommissioning and selected descriptions of decommissioning activities currently underway at AECL Whiteshell Laboratories.
Disposal of Spent Sealed Sources
Authors: Stefanova Ira G.
Published: March 2009

Novi Han Repository is the only existing repository in Bulgaria for the disposal of radioactive waste from nuclear applications in industry, medicine and research. The disposal vault for spent sealed sources is not designed for disposal of powerful 137Cs and 60Co sources. Long-lived waste from nuclear applications are also not allowed for disposal at Novi Han Repository. As an operator of Novi Han Repository the Institute for Nuclear Research and Nuclear Energy initiated a program, for assessment of the possible utilization of deep shaft Gabra for disposal of such waste. The results of the preliminary study are discussed.
Towards a Holistic Risk Management Strategy or Long-Term Interim Storage
Authors: Wickham S. M. , Galson D. A. , Hicks T. W. , Kemp R. V. , White M. J.
Published: March 2009

Long-term surface storage of intermediate-level radioactive waste (ILW) has become an important issue for regulators and site operators in the UK following deferral of the Nirex deep repository for the disposal of ILW, and the resulting hiatus in Government policy. This paper identifies some key life-cycle issues associated with interim safe storage (ISS) of ILW, and also some of the key features of existing stores. Important risk management issues include store design and environmental controls, conditioning and packaging, package handling and cranes, operation, monitoring of waste packages, package retrieval, external environmental factors, stakeholder issues and costs. All of these issues will need to be addressed during the design, construction and operation of an ILW store. Given the wide and diverse range of issues requiring consideration, it may be difficult to choose between alternative design concepts or risk management strategies. We demonstrate a multi-criteria decision analysis approach to ILW storage in which the various attributes of alternative store designs and management strategies are scored and collectively compared using the program OnBalance. By varying the weighting of the different attributes, the sensitivity of the overall score of the various designs to their attributes may be evaluated. Ultimately, the technical issues related to store design, construction and operation will have to be balanced against the non-technical factors that may influence the development of a store, particularly those related to stakeholder interactions and public concerns. Developing a long-term interim storage strategy requires a holistic approach that embraces all of these factors.
Workplace Safety and Health Is a Leadership Issue
Authors: Seabrook Kathy A.
Published: March 2009

Organizations where executive leadership identifies and manages worker safety and health as a business risk, rather than strictly as a compliance issue, are better positioned to reap both financial and reputational benefits from stakeholders such as customers, shareholders, employees and regulators. The advantages, both short and long term, of leadership engagement in the strategic management of safety and health can lead to enhanced brand reputation, greater sales and less contentious employee and regulatory relationships.
Adsorption Site of Cs+ in Bentonite: Determination by EXAFS
Authors: Nakano M. , Kawamura K. , Hara K. , Amemiya K.
Published: March 2009

This study elucidated the location where Cs atoms resided at the solid–water interface in smectite hydrates that composed bentonite using EXAFS spectroscopy. Samples were prepared by adding 4ml of a 0.1M CsCl solution to 2g dry weight of suspended KunipiaF bentonite at pH 3.9, 7.1, and 9.8. The Cs K-edge absorption was measured in transmission mode at a synchrotron, Spring-8, Japan, using a Si(311) monochromator at room temperature for the wet paste and air-dried compacted samples. Data were analyzed with the program TECHXAS. The structural parameters were determined by a two-oxygen-shell fit using the ab initio program FEFF6 and ATOMS code. EXAFS analyses have suggested that for air-dried samples the first shell consisted of about 5O at a distance of 3.19–3.20 Å, and the second shell consisted of about 7O at a distance of 3.59–3.60 Å. For the wet paste, the first shell was observed at a distance of 3.15–3.16 Å with the coordination number of about 7O. The second shell consisted of about 6O at a distance of 3.59–3.60 Å. Debye-waller factors of the first oxygen shells were 0.021 and 0.04 Å2 for the air-dried and wet paste samples, respectively. For the second oxygen shells they were 0.039 and 0.052 Å2, respectively. Based on coordination numbers and Debye-waller factors, it concluded that the adsorption sites of Cs+ on smectite hydrates were positioned near the edge of the oxygen hexagonal cavity of the siloxane sheets on basal surface, and appeared between two aluminol sheets at fractured sections, assuming that the first shells were formed by oxygen of inter-layer water, and that the second shells consisted of oxygen forming clay minerals. Furthermore, in the wet paste Cs ions were considered to form incomplete inner-sphere-like complexes and to roam freely in inter-layer water in smectite.
Improved Technologies for Decontamination and Reuse of Plutonium Contaminated Gloveboxes
Authors: McFee John , Barbour Kevin
Published: March 2009

The Los Alamos Large Scale Demonstration and Deployment Project (LSDDP), in support of the US Department of Energy (DOE) Deactivation and Decommissioning Focus Area (DDFA), has been identifying and demonstrating technologies to reduce the cost and risk of management of transuranic element contaminated large metal objects, i.e. gloveboxes. DOE must dispose of hundreds of gloveboxes from Rocky Flats Environmental Technology Site (RFETS), Los Alamos National Laboratory (LANL), and other DOE sites. This paper reports on the results of four technology demonstrations on decontamination of plutonium-contaminated gloveboxes with each technology compared to a common baseline technology, wipedown with nitric acid. The general objective of the demonstrations was decontamination to an alpha-emitting nuclide disintegration rate of less than 50,000 disintegrations per minute per 100 square centimeters (dpm/100 cm2), the surface activity level desired for re-application of these particular gloveboxes to a new mission. The technologies demonstrated include: • A LANL-developed electrochemical decontamination system (EDS) technique utilizing a recycled electrolyte solution to contact the glovebox surface via a small electrode fixture, which is moved from location to location until the entire metal surface is decontaminated. • A commercial three-step decontamination technology marketed by Environmental Alternatives Inc. (EAI) was demonstrated to quantify its performance relative to the baseline technology. • Cerium (IV) nitrate decontamination, previously utilized at other DOE sites and developed for application to gloveboxes at RFETS, was demonstrated to quantify its performance in this application. • A Russian-developed electrochemical decontamination (ECD) technology was monitored by the Los Alamos LSDDP for potential application in DOE. Although this decontamination activity was not an LSDDP “demonstration,” it was planned, monitored, and reported using LSDDP methodologies. Generally, the experience from these demonstrations shows that all innovative technologies perform better than the baseline, nitric acid wipedown. The goal of meeting 50,000 dpm/100 cm2 was not achieved by the baseline technology or cerium nitrate decontamination at all measured locations with the number of decontamination technologies used in the demonstration. Additional decontamination cycles were estimated for achievement of the targeted activity for cost estimating purposes. However, the actual decontamination achieved may be acceptable for LLW status at some facilities. Both electrochemical techniques are capable of decontaminating surfaces to the targeted contamination level and, if desired, can decontaminate to very low levels. The EAI technology is the best performing of the wipedown techniques, but is more costly. Table I summarizes the number of cycles the various technologies required to achieve the desired decontamination level and the associated decontamination factor.
Melt Treatment for Conditioning of Drums Produced During Soil Reclamation of Low Activity Trenches
Authors: Lippolis G. , Petagna E. , Ragazzo G. , Tortorelli P.
Published: March 2009

In the past years, many studies had been carried out in the ITREC Plant, located in ENEA – Trisaia Research Centre, in the field of nuclear fuel reprocessing and with re-fabrication techniques to the Th-233U cycle as an alternative to the U-Pu cycle. During these activities low level solid wastes were produced, containerised, stored into trenches and progressively covered with earth. In the 1980’s the trenches were reclaimed obtaining 3000 drums (200 liter volume) of solid LLW and about 6000 drums of low contaminated soil. In this presentation are described the action of reclamation of the trenches, sealing the low contaminated soil, and the melting campaign of contaminated drums.
Technique for Radiological Characterisation and Task Dose Evaluation Based on Gamma Scanning, Work Simulation and 3D Dose Modelling of a Work Site
Authors: Vermeersch F.
Published: March 2009

The need exists in the nuclear world to reduce the doses to the workers in radioactive environments be it in routine maintenance or in decommissioning activities. A key factor in satisfying this need is the availability of a fast and adequate characterization and modeling of the work area. In this paper we propose a method to combine gamma and geometrical scanning measurements with the modeling and source fitting capabilities of the VISIPLAN 3D ALARA planning tool to model a nuclear site. The presentation also includes the application of human modeling tools to assess the dose to the worker for a given task. The characterization method is demonstrated based on an application in an industrial site.
Optimalisation by the Conditioning of Liquid and Solid Low- and Intermediate Radioactive Waste for Final Disposal in Slovakia
Authors: Remia´sˇ Vladimir , Kra´sny Dusan
Published: March 2009

The radioactive waste treatment and conditioning are the most important step in radioactive waste management. In Slovak Republic the waste treatment and conditioning are including in the “Strategy of Radioactive waste management”. According to this “Strategy..” all sorts of low- and intermediate radioactive waste have to be conditioned to the fiber reinforced concrete container, i.e. “waste package”, only acceptable form for disposal in surface repository in Mochovce. In spite of good design of “Strategy..., in whole process should be occur some difficulty or difference. In the Radioactive Waste Treatment and Conditioning Center in Jaslovske Bohunice, built in 1999, the German treatment and conditioning technology together with French design of waste container was engaged. Presented paper summarized the practices during about 3 years operational period of conditioning radwaste in Jaslovske Bohunice. Till the presented results was achieved the harmonization of conditioning technology, particularly the cementation, has been necessary to accomplish with selected waste package. This aim had been reached after 1 years testing and analyzing with main fixed-target to find suitable formulation for radioactive grouting. The specific experiences had been received after 3 years operational period, which could be use for improving of whole process. In next time, the effects of conditioning process should be done especially in connection to the final disposal namely in term of economical efficiency. Based on present practice the great allowance indicated in area of concentration limits exploitation.
Setting-to-Work a State-of-the-Art Solid Waste Characterisation Facility at JRC Ispra
Authors: Huhtiniemi Ilpo , Anselmi Massimo , Vassallo Gary , Bruno Flaviano , Panini Giulio
Published: March 2009

This paper reviews the experience gained when setting-to-work a state-of-the-art waste characterisation facility that will be a fundamental element in the JRC’s strategy to characterise radioactive wastes originating from four decades of nuclear research activities conducted at the Ispra Site. In a previous paper at ICEM ’01, the authors described the specifications for the principal components of a Waste Characterisation System (WCS) and the ensuing contractor selection process via a public tendering procedure. The present paper has a broader perspective by addressing the whole waste characterisation facility of which the WCS forms a part. In the opening section, the main constituents of the facility are reviewed, and their optimised integration to respect emerging Italian standards, conventional safety principles, ALARA and operational efficiency, are discussed. The second part of the paper examines the analyses required for the licensing of the waste characterisation facility. Finally, the paper concludes with a summary of the lessons learned from the setting-to-work phase of the facility. Since the facility combines a state-of-the-art NDA solution with comprehensive process automation in an industrial environment, the experience is expected to be of significant interest to the radioactive waste management community.
Decommissioning of a Caesium-137 Sealed Source Production Facility
Authors: Murray A.
Published: March 2009

This paper describes the techniques and approaches used in the decommissioning of a Caesium-137 sealed source production facility belonging to Amersham plc. The facility become redundant in 1991. The facility comprised of nine interconnected containment boxes operated from behind a seven-inch lead wall using tongs. Viewing was through lead glass windows. After operations had ceased the facility had deteriorated due to radiation damage. The plastic ventilation system and transfer tunnels between the boxes had collapsed. Some of the viewing windows had also become crazed preventing direct viewing into the boxes. Man entry into the facility was not possible due to the high doserates. The facility contained in the order of 150TBq (4000Ci) of activity with initial ambient doserates in the facility circa 5S v/h γ. There was no acceptable route for transfer of waste out of the facility. The facility was expected to continue to deteriorate further. The project started with an options study in 1993 and was followed on with detailed planning, design and build of bespoke equipment and installing it, followed by the decommissioning operations beginning in 1997. The facility was adjacent to other fully operational facilities less than 1/2 metre away. The equipment designed and built included: • Telerobotic System; • Remote Waste Posting Facility; • New Primary Ventilation System; • Secondary Containment, with its own ventilation system; • Maintenance Facility for repairs to the Telerobotic System. The equipment was successfully deployed and used to size reduce the total contents of the facility and the fibreglass containment boxes themselves. 2300kg of ILW was packed remotely into 14litre waste cans and then remotely posted out for safe storage. The doserates on the waste cans was up to 30S v/h γ. The remaining structure was then decontaminated remotely. When this work was completed in 2001, approximately 150TBq of activity was removed, which was 99.9% of the total activity in the facility. The ambient doserate in the facility was then reduced to 1–3mSv/h allowing man entry into the facility to complete the decommissioning. This is a significant achievement for robotic decommissioning. After a year of manual decommissioning and dismantling the ambient doserate in the facility was reduced to less than 10μSv/h and loose activity levels to less than 0.1Bq/cm2. The dose received by the team during remote decommissioning was 30man mSv over a four year period. This included 12man mSv for maintenance of the Telerobotic System. The team received a similar figure of 30man mSv during manual decommissioning operations but over a one year period.
Minichannel Heat Transfer: An Overview on Activities in Europe
Authors: Groll Manfred , Mertz Rainer
Published: March 2009

An overview will be given about investigations on heat and mass transfer in narrow channels and narrow cavities, from work carried out in the last years up to the current status of research of some relevant scientific groups in Europe. The major topics of this report are evaporation heat transfer and the flow boiling pressure drop in narrow channels; microscale heat and mass transfer phenomena in pool boiling from enhanced evaporator tubes with sub-surface channels are also addressed. In the last years a challenging topic has been the enhancement of the efficiency of heat exchangers by employing micro-structured heat transfer surfaces. The need for smaller heat exchangers with higher heat transfer rates and/or smaller thermal approaches is caused by the ongoing miniaturisation of mechanical and electronic components, leading to higher heat fluxes which can damage or even destroy the components. On the other hand, enhanced heat transfer in big equipment, e.g. heat exchangers for the petrochemical and chemical industries, can lead to significant materials and energy savings and thus reduce environmental pollution. Therefore the European Union, European industries and national organisations have supported various projects to develop and to investigate a new generation of heat transfer surfaces, to better understand the related heat transfer phenomena and to model the heat transfer from these micro heat exchanger elements. There is a very extensive research in this scientific field, comprising both flow boiling and pool boiling. The present paper deals with heat transfer in narrow channels and/or cavities and with the flow boiling pressure drop occurring during heat and mass transfer in narrow channels. Investigations of major European institutions, carried out in the past and at the moment will be presented as a contribution to the overview on the current state-of-the-art in Europe, without claim of completeness. Some recent results on microscale pool boiling and flow boiling obtained in our institute will also be presented (Shuai et al., 2002; Kulenovic et al., 2002; Chen et al., 2002a, b).
Micro Thermal Systems in France: From Knowledge to Technological Development
Authors: Thonon B. , Marty Ph.
Published: March 2009

This paper presents an overview of the research activities performed in France, and presents more precisely the work carried out by the “microthermique” group in Grenoble (“Micro thermal exchanges”), which is composed of 5 teams. Examples of fundamentals and applied research projects on micro-channel heat exchangers and systems are presented.
Some Flow and Thermal Phenomena at Microscale
Authors: Li Zhi-Xin , Guo Zeng-Yuan
Published: March 2009

The physical mechanisms for the size effects on the flow and heat transfer have been divided into two classifications: (a) variations of the predominant factors influence the relative importance of various phenomena in the flow and heat transfer as the characteristic length decrease, even if the continuum assumption is still valid; (b) the continuum assumption breaks down as the characteristic length of the flow becomes comparable to the mean free path of the molecules. The departure of most flow and thermal phenomena in the MEMS from conventional ones is due to the variation of predominant factors in the flow and heat transfer problems, rather than that Navier-Stokes equation and Fourier heat conduction equation etc are no longer valid. Due to the larger surface to volume ratio for microchannels and microdevices, factors related to surface effects have more impact to microscale flow and heat transfer. For example, surface friction induced flow compressibility makes the fluid velocity profiles flatter and leads to higher friction factors and Nusselt numbers; surface roughness is likely responsible for the increased friction factor, the early transition from laminar to turbulent flow and Nusselt number; and other effects, such as the axial heat conduction in the channel wall, the channel surface geometry, surface electrostatic charges, and measurement errors, could lead to different flow and heat transfer behaviors from that at conventional scales. The condensation/evaporation across the liquid-vapor interface and the liquid-vapor nucleation are processes at nanometer scale. In these cases the macroscopic approach is hard to reveal the details at nanometer scales, while the molecular dynamic simulation is a powerful tool to describe such microscopic processes, and has been applied to investigate the density and temperature profiles across the liquid-vapor interface. The condensation coefficient on the liquid-vapor interface under thermodynamic equilibrium condition has been well predicted based on the characteristic time method, which can distinguish the condensed particles from the reflected particles. Molecular dynamics simulations show that liquid-vapor nucleation undergoes three stages, namely, cavity growth, cavity coalescence and bubble formation.
Single-Phase Laminar-Flow Heat Transfer and Two-Phase Oscillating-Flow Heat Transport in Microchannels
Authors: Nishio Shigefumi
Published: March 2009

The present review article focuses on the research field of heat transfer of single-phase laminar-flow and two-phase self-exciting oscillating-flow in microchannels. First, to make prominent the special features of Micro Thermal Systems (MTSs), the definition of the term “Nano Thermal Systems” (NTSs) is discussed from the viewpoint of local equilibrium. Next, to show the special features of flow and heat transfer in microchannels, some thermal functions appearing in microchannels are introduced. Further, focusing on flow and heat transfer characteristics of single-phase laminar liquid-flow in microchannels, researches in the literature and recent results at IIS (Institute of Industrial Science, the University of Tokyo) are introduced, and it is shown that the results obtained for tubes larger than 0.1mm in inner diameter are in good agreement with the conventional analyses. Finally, Japanese researches and recent results at IIS on micro SEMOS heat pipes (mSEMOSs) are introduced and it is shown that a mSEMOS of 0.5mm in inner diameter can transport a significant amount of heat.
Recent Work on Transport Phenomena in Microsystems at HKUST
Authors: Cheng Ping
Published: March 2009

Recent work on transport phenomena in microsystems, carried out at the Hong Kong University of Science and Technology (HKUST) during the past few years, is summarized in this paper. This includes convective and boiling heat transfer in silicon microchannels with application to electronic cooling; periodic generation of micro bubbles as a thermal actuator for enhanced mixing in biosensors; and fractal tree-like microchannel nets for electronic cooling and for the fuel distribution in the current collector of a micro fuel cell.
Condensation of Refrigerant in a Multi-Port Channel
Authors: Koyama Shigeru , Kuwahara Ken , Nakashita Koichi
Published: March 2009

In the present paper, the local characteristics of pressure drop and heat transfer are investigated experimentally for the condensation of pure refrigerant R134a in four kinds of multi-port extruded aluminum tubes of about 1 mm in hydraulic diameter. Two tubes are composed of plane rectangular channels, while remaining two tubes are composed of rectangular channels with straight micro-fins. The experimental data of frictional pressure drop (FPD) and heat transfer coefficient (HTC) in plane tubes are compared with previous correlations, most of which are proposed for the condensation of pure refrigerant in a relatively large diameter tube. It is confirmed that parameters such as tube diameter, surface tension, free convection in FPD and HTC correlations should be taken into account more precisely. Considering the effects of surface tension and kinematic viscosity, new correlation of FPD is developed based on the Mishima-Hibiki correlation. New correlation of HTC is also developed modifying the effect of diameter in the correlation of Haraguchi et al. Both new correlations are compared with experimental data for tubes with micro-fins. Satisfactory agreement between experimental and predicted results is obtained. This means that the micro-fin effect is taken into account by using hydraulic diameter and the heat transfer enhancement effect of micro-fins is mainly due to the enlargement of heat transfer area.
Developing Adiabatic Two Phase Flow in Headers
Authors: Hrnjak Pega
Published: March 2009

Heat exchangers with microchannels (hydraulic diameter less than 1mm) are attracting significant attention lately. Performance of these heat exchangers, evaporators mostly, are greatly affected by imperfect distribution of a two-phase fluid to each channel. This paper presents overview of the issue, shows basic option to evenly distribute single and two-phase fluid, and methods to determine maldistribution. Special attention is given to describing two-phase regimes in an adiabatic horizontal header with R134a as a fluid, describing a two-phase map with area of good distribution.
The Effect of Viscous Heat Dissipation on Convective Heat Transfer in Small-Scale Slipping Gaseous Flows
Authors: Hadjiconstantinou Nicolas G.
Published: March 2009

The presence of slip in small-scale gaseous flows leads to shear work and dissipation at the boundary. This effect has been neglected in recent studies investigating the effect of viscous dissipation on convective heat transfer in small scale channels. In this paper we illustrate the effect of shear work at solid boundaries in small-scale gaseous flows through the solution of the constant-wall-heat-flux problem in the slip-flow regime. We show that dissipation at the boundary scales with the Brinkman number similarly to viscous heat dissipation inside the channel, and increases with increasing Knudsen number. As a result, it is incorrect to neglect this effect when viscous heat generation needs to be considered. An analytical expression for the fully developed slip-flow Nusselt number under constant-wall-heat-flux conditions in the presence of viscous heat dissipation is presented. This expression is verified by direct Monte Carlo solutions of the Boltzmann equation. An expression for the skin friction coefficient under fully developed flow conditions for arbitrary Knudsen numbers is presented. Simple approximate expressions for the skin friction coefficient in the ranges 0 ≤ Kn ⪝ 0 4 . and 0.4 ⪝ Kn ⪝ 3 are also presented. These expressions are in agreement with direct Monte Carlo solutions of the Boltzmann equation.
Analytical Results for Sound Wave Propagation in Small-Scale Two-Dimensional Channels
Authors: Hadjiconstantinou Nicolas G.
Published: March 2009

When the characteristic scale of a channel decreases, wave propagation is increasingly dominated by viscous effects. This was first realized by Lamb who predicted that when the channel size is small compared to the diffusion length based on the oscillation frequency, the gas inertia becomes negligible (the fluid motion is effectively quasi-steady) and the flow is isothermal. This parameter regime is referred to as the narrow channel regime. We take advantage of this observation to derive analytical results for wave propagation in small scale channels for arbitrary Knudsen numbers, since due to their small transverse dimensions micro and nanochannels satisfy the narrow channel requirement except at very high frequencies. In the slip-flow regime in particular where the equations of motion can be integrated analytically, we show that thermal effects are always negligible and that the long wavelength approximation is always satisfied for narrow channels. We also discuss how this theory can be extended beyond the narrow channel approximation, that is, to include the effects of inertia and heat conduction to first order. Our results are verified by direct Monte Carlo simulations of the Boltzmann equation.
Gaseous Slip Flow in a Micro-Channel
Authors: Hsieh Shou-Shing , Tsai Huang-Hsiu , Lin Chih-Yi , Huang Ching-Fang , Chien Cheng-Ming
Published: March 2009

An experimental and theoretical study of low Reynolds number compressible gas flow in a micro channel is presented. Nitrogen gas was used. The channel was microfabricated on silicon wafers and were 50 μm deep, 200 μm wide and 24000 μm long. The Knudsen number ranged from 0.001 to 0.02. Pressure drop were measured at different mass flow rates in terms of Re and found in good agreement with those predicted by analytical solutions in which a 2-D continuous flow model with first slip boundary conditions are employed and solved by perturbation methods.
Heat Transfer Characteristics of Gaseous Flows in Micro-Channels
Authors: Asako Yutaka , Toriyama Harumi
Published: March 2009

Two-dimensional compressible momentum and energy equations are solved to obtain the heat transfer characteristics of gaseous flows in parallel-plate micro-channels. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The computations were performed for channels with adiabatic walls to obtain the adiabatic wall temperature. The channel height ranges from 10 to 100 μm and the channel length is fixed at 30 mm. The stagnation pressure varies from 1.1×105 to 4×106 Pa. The outlet pressure is fixed at the atmosphere. The computations were also performed for channels with isothermal walls. The aspect ratio of the channel height and length is 100 or 200. The bulk temperature is compared with that of the incompressible flow in the conventional sized parallel plate channel.
Effects of Axial Heat Conduction in the Wall on Convection in Microtubes
Authors: Li Zhi-Xin , Wang Wei , Guo Zeng-Yuan
Published: March 2009

Single-phase convective heat transfer in microtubes was numerically studied with consideration on the heat conduction in the tube wall. It indicates that the Nusselt numbers of the fully developed laminar convective heat transfer in microtubes with convective boundary condition outside the tube vary from 3.66 to 4.36, which represent the conventional results for isothermal and constant heat flux boundaries respectively. The Nusselt number depends on the parameters of thermal conductivity ratio (k*), diameter ratio (D*), and Biot number. One-dimensional thermal resistance model could underestimate the Nusselt number if the axial heat conduction in the wall can not be ignored. Discrepancies between the experimental results for the Nusselt number based on 1-D model and the standard values might be misunderstood as being caused by novel phenomena at microscales.
Simulation of Flow and Mass Transport in a Meander Microchannel Subject to Electroosmotic Pumping
Authors: Barz Dominik P. J. , Ehrhard Peter
Published: March 2009

We have investigated the flow and mass transport within an electroosmotically-pumped incompressible liquid through a meander microchannel system. We employ two-dimensional, time-dependent Finite Element simulations in conjunction with a matched asymptotic treatment of the electrical double layers. The electroosmotic pumping is realized for two idealized and two realistic electrical fields, while a pressure-driven flow is used for comparison. We focus on the aspects of the electroosmotic transport. We find for most of the electroosmotically-driven cases rather complex flow fields, involving recirculation regions. These recirculation regions in all cases increase dispersion. (i) The least dispersion is associated with a plug-type velocity profile, which is obtained for an idealized purely wall-tangential orientation of the electrical field. (ii, iii) We find that both, the idealized horizontal electrical field and the real electrical field between two vertical plates give considerably higher dispersion than the pressure-driven flow. Vertical plate electrodes, therefore, do not allow for a electrical field, which minimizes dispersion. (iv) The arrangement of two point electrodes at the in and out sections likewise proves to be no optimal means to reduce dispersion beyond the pressure-driven flow. Thus, meander geometries of channels, in general, cause severe problems if electroosmotic pumping needs to be achieved in combination with minimized dispersion.
The Electric Double Layer Effect on the Microchannel Flow Stability
Authors: Tardu Sedat
Published: March 2009

The effect of the electric double layer (EDL) on the linear stability of Poiseuille planar channel flow is reported. It is shown that the EDL destabilises the linear modes, and that the critical Reynolds number decreases significantly when the thickness of the double layer becomes comparable with the height of the channel. The planar macro scale Poiseuille flow is metastable, and the inflexional EDL instability may further decrease the macro-transitional Reynolds number. There is a good correspondence between the estimated transitional Reynolds numbers and some experiments, showing that early transition is plausible in microchannels under some conditions.
A Micro-Channel Flow and Heat Transfer Study by Lattice Boltzmann Method
Authors: Yang Ru , Wang Chin-Sheng
Published: March 2009

A Lattice Boltzmann method is employed to investigate the flow characteristics and the heat transfer phenomenon between two parallel plates separated by a micro-gap. A nine-velocity model and an internal energy distribution model are used to obtain the mass, momentum and temperature distributions. It is shown that for small Knudsen numbers (Kn), the current results are in good agreement with those obtained from the traditional Navier-Stokes equation with non-slip boundary conditions. As the value of Kn is increased, it is found that the non-slip condition may no longer be valid at the wall boundary and that the flow behavior changes to one of slip-flow. In slip flow regime, the present results is still in good agreement with slip-flow solution by Navier Stokes equations. The non-linear nature of the pressure and friction distribution for micro-channel flow is gieven. Finally, the current investigation presents a prediction of the temperature distribution for micro-channel flow under the imposed conditions of an isothermal boundary.
Numerical Simulation on Micro Flow-Through PCR Chip
Authors: Wang Wei , Li Zhi-Xin , Guo Zeng-Yuan
Published: March 2009

The miniaturization of clinical analysis device by microfabrication technology has great impact on medical and biological fields. In the present work, a two dimensional model has been put forward to numerically analyzing the thermal cycling of the micro flow-through PCR chip, which is different from the conventional PCR instruments and micro chamber PCR chip. In the micro flow-through PCR chip, sample and reagent continuously flow through a microchannel in the chip with three different temperature regions (denaturation, annealing and extension) to realize the nucleic acid amplification. Two parameters, U and D, are adapted to describe the temperature uniformity and deviation from the target temperature of the sample and reagent. Effects of the microchip’s geometrical structure, materials, designed temperatures of the three temperature regions, flow rate of the samples and reagents and the thermal boundary conditions around the microchip on the thermal cycling of micro flow-through PCR chip were numerically studied. Based on the simulation results, the silicon-glass-bonding micro PCR chip is recommended, and the optimally designed temperatures of the heaters in the three regions are given. The applicability of silicon-glass-bonding micro flow-through PCR chip with denaturation region heated alone is examined.
Gaseous Flows in Rectangular Microchannels: Experimental Validation of a Second-Order Slip Flow Model
Authors: Colin Ste´phane , Lalonde Pierre , Caen Robert
Published: March 2009

A precise analytical model for gaseous flows in microchannels is of great interest for various applications, as for example when these microchannels are parts of a complex fluidic microsystem. However, a decrease in the channel hydraulic diameter leads to an increase in the rarefaction effects. If the Knudsen number becomes higher than about 0.1, it is generally admitted that the Navier-Stokes equation, even with first-order slip flow boundary conditions, are no longer valid. In order to keep an analytical model for higher Knudsen numbers, a resolution of the Navier-Stokes equation with second-order boundary conditions has been proposed in rectangular microchannels. An experimental setup has been designed for the measurement of gaseous microflows under controlled temperature and pressure conditions. Data relative to nitrogen and helium flows through rectangular microchannels are presented and analyzed. The microchannels have been etched by DRIE in silicon and closed with Pyrex by anodic bounding. Their depths range from 4.5 to 0.5 μm, with aspect ratios from 1 to 9%. It is shown that for aspect ratios higher than 1%, a plane flow model is no longer accurate, and that the proposed rectangular model should be used. The different sources of uncertainty that could occur during the experiments are discussed. A method is proposed to eliminate the principal one, that is the uncertainty when measuring the dimensions of the microchannel cross-section. Theoretical and experimental mass flow rates are compared, and it is shown that in rectangular microchannels, the second-order model is valid up to about 0.25, whereas the first-order model is no longer accurate for Knudsen numbers higher than 0.05. The best fit has been found for a tangential momentum accommodation coefficient σ = 0.93 , both with helium and nitrogen. Perspectives of this work are also presented.
Flow Through Rough Microchannels: A Lubrication Perspective
Authors: Boedo S.
Published: March 2009

This paper provides concise specifications where idealized Poiseuille flow is applicable in representing one-dimensional flow through wide, thin, rough microchannels subjected to prescribed pressures at the channel ends. Starting with the general (compressible) form of the Navier-Stokes equations, new expressions which discuss the effect of body forces on flow through thin channels are first presented, leading to upper and lower bounds on channel reference velocity where idealized Poiseuille flow dominates. These results are combined with previously published studies related to the predicability of flow through stochastically rough surfaces. An arbitrarily chosen microchannel model based loosely on a previously published experimental test setup is used as a sample application.
The Thermocapillary Convection in Locally Heated Laminar Liquid Film Flow Caused by a Co-Current Gas Flow in Narrow Channel
Authors: Gatapova E. Y. , Lyulin Y. V. , Marchuk I. V. , Kabov O. A. , Legros J.-C.
Published: March 2009

A two-dimensional model of a steady laminar flow of liquid film and co-current gas flow in a plane channel is considered. It is supposed that the height of a channel is much less than its width. There is a local heat source on the bottom wall of the channel. An analytical solution for the temperature distribution problem in locally heated liquid film is obtained, when the velocity profile is linear. An analytical solution of the linearized equation for thermocapillary film surface deformation is found. A liquid bump caused by the thermocapillary effect in the region where thermal boundary layer reaches the film surface is obtained. Damped oscillations of the free surface may exist before the bump. This is obtained according to the solution of the problem in an inclined channel. It depends on the forces balance in the film. The defining criterion is found for this effect. The oscillations of free surface do not exist for horizontally located channel.
Two-Phase Flow Pattern and Pressure Drop in a Microchannel
Authors: Kabov O. A. , Iorio C. S. , Colinet P. , Legros J.-C.
Published: March 2009

An experimental investigation has been carried out on two-phase flow characteristics in a 10 μm circular gap. The inlet of the gap is formed by two circular surfaces with radius 10 mm. The pressure drop is measured between two points placed — respectively — at the inlet and at the outlet of the gap. The upper and lower plates of the test section are transparent. Two-phase flow patterns were determined by video recording. The single flows of liquid FC-72 and nitrogen gas, as well as two-phase flow are investigated. In two-phase flow experiments the gap is filled by liquid. Liquid is maintained continuously by surface tension in the gap and in the meniscus formed between two inlet circular surfaces. The pressure difference includes two components, surface tension component in the meniscus and viscous one. Instability appears at the entrance of the gas into the gap. At small flowrate the gas flows in the gap has the form of chains of bubbles. Part of investigation was done in microgravity during a Parabolic Flights. In order to better understand experimental results, some numerical simulations have been done both in two and three dimensions for the real geometrical configuration for one-phase flows only.
Observation of Low Bond Number Two-Phase Flow Regime Transition From Slug to Annular Wavy Flow in a Microchannel
Authors: Allen Jeffrey S. , Son Sang Young
Published: March 2009

An understanding the physics behind the flow transition when capillary forces are important is critical to the development of many technologies; both for terrestrial- and space-based applications. The flow transition of greatest concern is that between slug, or plug, flow and core-annular flow. The transition of plug flow to core-annular flow in a low-Bond number configuration is experimentally observed in a novel capillary configuration. The effect of variations in mass flow rate of each phase (gas and liquid) on the overall system dynamics is discussed for both flow regimes.