bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive Transport Modelling of the Interaction of Fission Product Ground Contamination With Alkaline and Cementitious Leachates
Authors: Kwong S. , Small J.
Published: June 2009

The fission products Cs-137 and Sr-90 are amongst the most common radionuclides occurring in ground contamination at the UK civil nuclear sites. Such contamination is often associated with alkaline liquids and the mobility of these fission products may be affected by these chemical conditions. Similar geochemical effects may also result from cementitious leachate associated with building foundations and the use of grouts to remediate ground contamination. The behaviour of fission products in these scenarios is a complex interaction of hydrogeological and geochemical processes. A suite of modelling tools have been developed to investigate the behaviour of a radioactive plume containing Cs and Sr. Firstly the effects of sorption due to cementitious groundwater is modelled using PHREEQC. This chemical model is then incorporated into PHAST for the 3-D reactive solute transport modeling. Results are presented for a generic scenario including features and processes that are likely to be relevant to a number of civil UK nuclear sites. Initial results show that modelling can be a very cost-effective means to study the complex hydrogeological and geochemical processes involved. Modelling can help predict the mobility of contaminants in a range of site end point scenarios, and in assessing the consequences of decommissioning activities.
Waste Treatment by Selective Mineral Ion Exchanger
Authors: Polito Aure´lie
Published: June 2009

STMI, subsidiary company of the AREVA Group with over 40 years in the D&D business, has been continuously innovating and developing new decontamination techniques, with the objectives of achieving more efficient decontaminations on a growing spectrum of media. In the field of liquid waste treatment, STMI manufactures uses and commercialises selective inorganic ion exchangers (RAN). These are hydrated synthetic inorganic compounds prepared from very pure raw materials. Different types of RANs (POLYAN, OXTAIN, Fe-Cu, Fe-CoK, Si-Fe-CoK) can be used to trap a large number of radioactive elements in contaminated effluents. Different implementations could be applied depending on technical conditions. STMI’s offers consist in building global solution and preliminary design of installation either in dispersed form (batch) or in column (cartridge filtration). Those products are used all over the world not only in the nuclear business (Canada, US, Belgium, France…) but also in other fields. Indeed, it provides competitive solutions to many domains of application especially water pollution control, liquid waste treatment in the nuclear business by decreasing the activity level of waste. The following paper will focus on the theoretical principle of the mineral exchanger, its implementation and the feed back collected by STMI.
Developing Satisfied and Talented Consultants
Authors: Greenwood Sarah , Higgs Helen
Published: June 2009

It has been well documented that the ageing, male dominated profile of the workforce in the UK nuclear industry will not support the forecasted nuclear renaissance. Based upon the aspects of age, gender and level of education, there is an existing shortfall in available knowledgeable resource to undertake and manage the extensive new build, operational and decommissioning programmes. The 2005 Nuclear Employers Survey advised the industry to recruit and train more: • young and qualified people. • experienced and qualified people from outside the industry. The future for the UK nuclear industry lies with people in their 20s and 30s. It is essential that not just technical talent but also managerial talent be identified early and that they are nourished and allowed to flourish.
In-House Developed Methodologies and Tools for Decommissioning Projects
Authors: Detilleux Michel , Centner Baudouin
Published: June 2009

The paper describes different methodologies and tools developed in-house by Tractebel Engineering to facilitate the engineering works to be carried out especially in the frame of decommissioning projects. Three examples of tools with their corresponding results are presented: - The LLWAA-DECOM code, a software developed for the radiological characterization of contaminated systems and equipment. The code constitutes a specific module of more general software that was originally developed to characterize radioactive waste streams in order to be able to declare the radiological inventory of critical nuclides, in particular difficult-to-measure radionuclides, to the Authorities. In the case of LLWAA-DECOM, deposited activities inside contaminated equipment (piping, tanks, heat exchangers ...) and scaling factors between nuclides, at any given time of the decommissioning time schedule, are calculated on the basis of physical characteristics of the systems and of operational parameters of the nuclear power plant. This methodology was applied to assess decommissioning costs of Belgian NPPs, to characterize the primary system of Trino NPP in Italy, to characterize the equipment of miscellaneous circuits of Ignalina NPP and of Kozloduy unit 1 and, to calculate remaining dose rates around equipment in the frame of the preparation of decommissioning activities; - The VISIMODELLER tool, a user friendly CAD interface developed to ease the introduction of lay-out areas in a software named VISIPLAN. VISIPLAN is a 3D dose rate assessment tool for ALARA work planning, developed by the Belgian Nuclear Research Centre SCK·CEN. Both softwares were used for projects such as the steam generators replacements in Belgian NPPs or the preparation of the decommissioning of units 1&2 of Kozloduy NPP; - The DBS software, a software developed to manage the different kinds of activities that are part of the general time schedule of a decommissioning project. For each activity, when relevant, algorithms allow to estimate, on the basis of local inputs, radiological exposures of the operators (collective and individual doses), production of primary, secondary and tertiary waste and their characterization, production of conditioned waste, release of effluents, ... and enable the calculation and the presentation (histograms) of the global results for all activities together. An example of application in the frame of the Ignalina decommissioning project is given.
The Long-Term Storage of Radioactive Waste and Spent Fuel: Safety and Policy Considerations
Authors: Rowat J. , Metcalf P.
Published: June 2009

Storage is a necessary step in the overall management of radioactive waste. In recent years, due to the unavailability of disposal facilities, storage facilities intended originally as temporary, have had their lifetimes extended and consideration has been given, in some countries, to the use of long term storage (LTS) as a management option. In 2003, the IAEA published a position paper titled “The Long Term Storage of Radioactive Waste: Safety and Sustainability”. The position paper, which written for a non-specialist audience, focused on seven key factors for safety and sustainability of LTS, namely: safety, maintenance/institutional control, retrieval, security, costs, community attitudes and retention of information. The Agency is preparing a follow-up report to the position paper that elaborates in a more technical manner upon the issues raised in the position paper and issues important for implementation of LTS. It also provides some discussion of the reasons for implementing a LTS option and contrasts LTS with aspects of other management options. The present paper provides an overview of the draft follow-up report.
Vision for the Development of an International Nuclear Fuel Recycling Program
Authors: Kok Kenneth D.
Published: June 2009

The purpose of the development of an international nuclear fuel recycle program is to: • Demonstrate advanced recycling by working to prove the technologies needed to close the fuel cycle, minimize waste, and obtain more energy benefit for each unit of fuel. • Build a global vision by enlisting partners to limit the spread of sensitive nuclear technologies in a way that enables nuclear power to meet global challenges. The program will begin with the establishment of a smaller scale secure fuel cycle facility that would serve as a model for international nuclear fuel reprocessing centers that would eventually be built in several countries world wide. The operating process plants will provide the secure and safe guarded environment for the recycle of spent fuel from nuclear power stations around the world. The demonstration site will provide for developing and testing processes that would lead to the more complete use of the energy available in nuclear fuels and the minimization of long lived nuclear waste.
Radioactive Waste Treatment Technologies and Environment
Authors: Horva´th Ja´n , Krasny Dusan
Published: June 2009

The radioactive waste treatment and conditioning are the most important steps in radioactive waste management. At the Slovak Electric, plc, a range of technologies are used for the processing of radioactive waste into a form suitable for disposal in near surface repository. These technologies operated by JAVYS, PLc. Nuclear and Decommissioning Company, PLc. Jaslovske´ Bohunice are described. Main accent is given to the Bohunice Radwaste Treatment and Conditioning Centre, Bituminization plant, Vitrification plant, and Near surface repository of radioactive waste in Mochovce and their operation. Conclusions to safe and effective management of radioactive waste in the Slovak Republic are presented.
Synthesis of Yttria-Stabilised Zirconia Matrices for Immobilisation of Actinides by Internal Gelation Method
Authors: Benay G. , Modolo G. , Odoj R.
Published: June 2009

In the scope of the co-conversion of actinides solutions obtained from partitioning spent nuclear fuel, the internal gelation of ceria-doped yttria-stabilized zirconia was investigated. This dust-free method to fabricate kernels, which can be used as fuel or pressed into pellets, is technically easy to implement and compatible with remote handling. The effects of the quantity of reactants used on the properties of the material were studied. Gels, kernels and pellets were analyzed by thermal analysis, electron microscopy and X-ray diffraction. It was found that the initial broth composition played an important role in the structure of kernels and the formation of cracks during thermal treatment. Pellets obtained with a repressing method were found to present densities up to 86% TD.
Numerical Assessment of the Origin of Deep Salinity in a Low Permeability Fractured Medium
Authors: Guimera` Jordi , Ruiz Eduardo , Luna Miguel , Arcos David , Dome`nech Cristina , Jordana Salvador , Saegusa Hiromitsu , Iwatsuki Teruki
Published: June 2009

Many possible origins have been proposed for the saline groundwater observed in many deep geological environments. In particular, samples obtained from deep boreholes located in granite at the Mizunami Underground Research Laboratory in Central Japan show total dissolved solids increasing to 50 mmol/L at depths below 800 m. Different hypothesis have been formulated to explain the observed fluid composition, among them, long-term water-rock interaction, mixing with residual fluids of magmatic origin and relict seawater dating from Miocene times. A review of the hydrochemical and isotopic data suggests that the three above hypotheses may be valid, at least to different degrees, or that processes acting over more recent geological times may be involved. The origin of the salinity was assessed by simulating land emersion by means of changing the upper recharge boundary. In this manner the Miocene seawater was modeled as being continually mixed with fresh water until the present time. The effects of different retardation processes were considered by varying factors such as matrix diffusion and fracture conductivity. Finally, geochemical reactions reproduced trends in major ions and master variables. This study shows that the salinity observed in the boreholes can be explained qualitatively as residual Miocene age seawater subjected to alteration due to long-term contact with the host material and continuous mixing with meteoric groundwater.
Utilizing the Right Mix of Environmental Cleanup Technologies
Authors: Whitaker Wade , Bergren Chris , Flora Mary
Published: June 2009

The Savannah River Site (SRS) Figure 1 is a 310-square-mile United States Department of Energy nuclear facility located along the Savannah River near Aiken, South Carolina. During operations, which started in 1951, hazardous substances (chemicals and radionuclides) were released to the environment. The releases occurred as a result of inadvertent spills and waste disposal in unlined pits and basins which was common practice before environmental regulations existed. The hazardous substances have migrated to the vadose zone and groundwater in many areas of the SRS, resulting in 515 waste units that are required by environmental regulations, to undergo characterization and, if needed, remediation. In the initial years of the SRS environmental cleanup program (early 1990s), the focus was to use common technologies (such as pump and treat, air stripping, excavation and removal) that actively and tangibly removed contamination. Exclusive use of these technologies required continued and significant funding while often failing to meet acceptable clean-up goals and objectives. Recognizing that a more cost-effective approach was needed, SRS implemented new and complementary remediation methods focused on active and passive technologies targeted to solve specific remediation problems. Today, SRS uses technologies such as chemical / pH-adjusting injection, phytoremediation, underground cutoff walls, dynamic underground stripping, soil fracturing, microbial degradation, baroballs, electrical resistance heating, soil vapor extraction, and microblowers to more effectively treat contamination at lower costs. Additionally, SRS’s remediation approach cost effectively maximizes cleanup as SRS works proactively with multiple regulatory agencies. Using GIS, video, animation, and graphics, SRS is able to provide an accurate depiction of the evolution of SRS groundwater and vadose zone cleanup activities to convince stakeholders and regulators of the effectiveness of various cleanup technologies. Remediating large, complex groundwater plumes using state of-the art technologies and approaches is a hallmark of years of experience and progress. Environmental restoration at SRS continues to be a challenging and dynamic process as new cleanup technologies and approaches are adopted.
Modified Microspheres for Cleaning Liquid Wastes From Radioactive Nuclides
Authors: Danilin Lev , Drozhzhin Valery
Published: June 2009

An effective solution of nuclear industry problems related to deactivation of technological and natural waters polluted with toxic and radioactive elements is the development of inorganic sorbents capable of not only withdrawing radioactive nuclides, but also of providing their subsequent conservation under conditions of long-term storage. A successful technical approach to creation of sorbents can be the use of hollow alumosilicate microspheres. Such microspheres are formed from mineral additives during coal burning in furnaces of boiler units of electric power stations. Despite some reduction in exchange capacity per a mass unit of sorbents the latter have high kinetic characteristics that makes it possible to carry out the sorption process both in static and dynamic modes. Taking into account large industrial resources of microspheres as by-products of electric power stations, a comparative simplicity of the modification process, as well as good kinetic and capacitor characteristics, this class of sorbents can be considered promising enough for solving the problems of cleaning liquid radioactive wastes of various pollution levels.
Single-Phase Friction Factor in Micro-Tubes: A Critical Review of Measurement, Instrumentation and Data Reduction Techniques From 1991-2006
Authors: Krishnamoorthy Chandramoulee , Ghajar Afshin J.
Published: June 2009

The objective of this paper is to provide a state-of-art review in the field of single-phase pressure drop (friction factor) measurements in micro-tubes. Twenty-three experiments from 1991 to 2006 are reviewed critically in areas of different measurement techniques, instrumentation used and the various data-reduction methods employed. The review confirms that researchers unanimously agree that friction factor in micro-tubes can be predicted by using macro-scale theory and that there is a need to investigate certain issues like (a) the effect of roughness on friction factor and transition and (b) the effect of micro-tube diameter on transition Reynolds number. The state-of-art review thus provides the contemporary experimenters in the field of mini-micro channel fluid flow this vast amount of tabulated data on experimental set-up, results, instrumentation and uncertainties for all twenty-three experiments. The data can be used to investigate how the different parameters affect the fluid flow in these small scales and to validate future numerical and experimental work. Moreover, the review observes that smooth micro-tubes follow classical laws while roughness does seem to play a major role in the dynamics of smaller diameter tubes.
Deviation of Electroosmotic Flow From Plug-Like Profile: The Effect of Reservoir Size
Authors: Yan Deguang , Yang Chun , Huang Xiaoyang
Published: June 2009

In electrokinetically-driven microfluidic applications, reservoirs are indispensable and have finite sizes. During operating processes, as the liquid level in reservoirs keeps changing as time elapses, a backpressure is generated. Thus, the flow in microfluidic channels actually exhibits a combination of the electroosmotic flow and the time-dependent induced backpressure-driven flow. In this paper, a model is presented to describe the effect of the finite reservoir size on electroosmotic flow in a rectangular microchannel. Important parameters that describe the effect of finite reservoir size on flow characteristics are discussed. A new concept termed as “effective pumping period” is introduced to characterize the reservoir size effect. The proposed model identifies the mechanisms of the finite-reservoir size effects and is verified by experiment using the micro-PIV technique. The results reported in this study can be used for facilitating the design of microfluidic devices.
Further Evaluation of a Flow Boiling Correlation for Microchannels and Minichannels
Authors: Peters Julian V. S. , Kandlikar Satish G.
Published: June 2009

Flow boiling in microchannels and minichannels is being investigated for its potential for high heat flux removal in electronics and other devices. The small channel dimensions characteristic of these channels result, under most circumstances, in laminar flow at the flow rates used in these applications. The present work investigates the applicability of the correlation developed by Kandlikar and Balasubramanian [1] to some of the recent data for plain as well as enhanced microchannels using artificial nucleation cavities. The correlation is able to provide insight into the effect of the nucleation cavities on the heat transfer coefficient during flow boiling in microchannels. Modifications to the use of the correlation with deep laminar flows are suggested based on comparison with new data.
Micro Channel Roughness Effects: A Close-Up View
Authors: Gloss D. , Ko¨cke I. , Herwig H.
Published: June 2009

The effect of wall roughness on laminar flows may be important in micro sized channels though it is often neglected in macro sized flow geometries. Based on entropy production considerations we show how its influence can be determined theoretically. It is also discussed how different ways to define the actual wall location influence the pressure drop results in terms of a Poiseuille number.
Reactive Precipitation in Microchannels: Impact of Convective Mixing on Particle Formation
Authors: Kastner Johannes , Fedier Sara , Kockmann Norbert , Woias Peter
Published: June 2009

Reactive precipitation in micro- and minichannels currently draws attention of both, chemists and engineers in the field of micro process engineering. Due to intensified mixing and improved heat and mass transfer, fast chemical and thermodynamical processes involved in precipitation can be controlled readily in micro or mini structures. Particularly microchannels are a promising technology for particulate processes allowing continuous operation along with little or no backmixing. However, the sensitivity of microscale channels to blocking and fouling requires careful design and appropriate peripheral equipment. This study presents experimental results of barium sulfate precipitation from barium chloride solution and sulfuric acid in both, T-shaped and injection micromixers. The measured particle size distributions (PSD) are characterized by their first and second moment, reflecting the correlation between fluidic mixing and precipitation: faster mixing results in smaller mean particle sizes (1st moment of the PSD). The homogeneity of the mixing process on the other hand should have impact onto the width of the distribution (2nd moment of the PSD) due to superposition of locally formed particles to the global size distribution. The experimental particle size distributions are compared with simulations based on reduced-order modeling of the diffusive mixing process, coupled with the population balance for particle nucleation and growth. While the simulated size distributions have mean diameters between 40 nm and 68 nm, experimental data are between 90 nm and 130 nm.
Experiments on the Laminar/Turbulent Transition of Liquid Flows in Rectangular Micro Channels
Authors: Wibel Wolf , Ehrhard Peter
Published: June 2009

The advances of micro-fabrication techniques allow for the manufacturing of micro heat exchangers or micro reactors. These micro devices are characterized by a large surface-to-volume ratio and, hence, allow for the transfer of large heat fluxes or offer large catalytic surfaces for reactions. The design and optimization of such micro devices heavily relies on correlations for pressure drop and heat transfer, as well as on information on the laminar/turbulent transition. As these questions are still discussed controversially in literature, a careful investigation appears highly desirable. We concentrate onto rectangular stainless steel micro channels with a hydraulic diameter of dh ≅ 133 μm. Three aspect ratios are engaged, namely 1:1, 1:2, 1:5, whereas the hydraulic diameter is kept constant. The average roughness depth of the channel walls is r ≅ 1–2 μm in general, specific channels are of roughness r ≅ 25 μm. Filtered and degassed deionized water is driven at pressure differences up to 20 bar through the channels, allowing for Reynolds numbers up to Re = 4000. The measuring techniques allow for a highly-accurate determination (i) of the mass flow rate (precision weighting), (ii) of the temperatures at inlet and outlet, (iii) of the pressure drop, and (iv) of the time-resolved velocity field (μPIV). We find from all measured quantities — consistently — the laminar/turbulent transition for smooth channels in the range Rec = 1900–2200, in agreement with findings for macroscopic channels. The influence of rough channel walls appears particularly strong for the micro channels of aspect ratio 1:5 (Rec = 1000). This raises the question, whether the dimensionless group (r/dh) remains the relevant parameter at extreme aspect ratios. In this article we focus on the μPIV results.
Investigation of Heat Transfer and Flow Characteristics in Heat Exchanger With Microscale Channels
Authors: Xu Shaokun , Chen Baoming , Ji Shui , Zhao Shiqi
Published: June 2009

The experimental study of heat transfer and flow characteristics are conducted for water and ethylene-glycol solution flowing in the heat exchanger with rectangular or triangular microscale channels, which have equivalent diameter of 0.55mm, 0.91mm, 1.38mm and 5mm. During experiments, the Reynolds number ranges from 300 to 2500. The experimental results show that: at a fixed Reynolds number, the Nusselt number increases along with increasing equivalent diameter, the Nusselt number for ethylene-glycol solution with larger Prandtl number is greater than that for water, the geometrical configuration of the microscale channels have a significant effect on the heat transfer; the flow friction factors of microscale channels are smaller than that of normal channels, flow characteristics of rectangular channels are evidently better than that of triangular, the flow friction factor decreases with increasing Reynolds number, the experiment also show that the flow friction factor is independent of Prandtl number; The critical Reynolds number at which the flow transiting to turbulent flow is 700∼1200.
Transport Phenomena Through Gaseous Mixtures in Microchannels
Authors: Sharipov Felix
Published: June 2009

In practice, one deals with gaseous mixtures more frequently than with a single gas. However, very few papers about the transport phenomena through a mixture of rarefied gases were published. The aim of this work is to present a general approach to calculations of mass, heat and momentum transfer through gaseous mixtures over the whole range of the gas rarefaction. Results on some classical problems such as slip coefficient, Poiseuille flow, Couette flow and heat transfer are given for a gaseous mixture. A comparison with results corresponding to a single gas is carried out. Such a comparison shows the peculiarities of the transport phenomena in mixtures.
Flow Boiling in Minichannels Under Normal, Hyper and Microgravity: Frictional Pressure Loss and Flow Patterns
Authors: Brutin D. , Luciani S. , Rahli O. , LeNiliot Ch. , Tadrist L.
Published: June 2009

We present in this paper, flow boiling results obtained during parabolic flights campaigns. The experimental aim is to obtain the local heat transfer coefficient and the influence of gravity on HFE-7100 flow boiling in minichannels. The hydraulic diameter investigated is: 0.84 mm. The influence of hypergravity and microgravity solely on the frictional pressure loss is evidenced in this paper, and explained using the flow patterns.
Investigation of Three-Dimensional Flow in Microchannels With Patterned Surfaces
Authors: Saha Auro Ashish , Mitra Sushanta K.
Published: June 2009

A three-dimensional numerical simulation of flow in patterned microchannel with alternate layers of hydrophilic and hydrophobic surfaces at the bottom wall is studied here. Surface characteristics of the microchannel are accounted by specifying the contact angle and the surface tension of the fluid. Meniscus profiles with varying amplitude and shapes are obtained under the different specified surface conditions. Flow instability increases as the fluid at the bottom wall traverses alternately from hydrophilic region to hydrophobic region. To understand the surface tension effect of the side walls, a two-dimensional numerical study has also been carried out for the microchannel and the results are compared with three-dimensional simulation. The surface tension effect of the side walls enhances the capillary effect for three-dimensional case.
Design Optimization of Micro-Channel for Micro Electronic Cooling
Authors: Husain Afzal , Kim Kwang-Yong
Published: June 2009

A numerical optimization of a rectangular micro-channel has been performed. Navier-Stokes and energy equations for laminar flow and conjugate heat transfer are solved using a finite volume solver. Solutions are first carefully validated with available analytical and experimental results; the shape of the micro-channel is then optimized using surrogate method. Ratios of the micro-channel width to depth and the width of the fin to the depth are selected as design variables. Design points are selected through a four-level full factorial design. A single objective function thermal resistance, formulated using pumping power as a constraint, is optimized. Mass flow rate is adjusted by the constant pumping power constraint. Kriging method is applied to construct surrogate and the optimum point is searched by sequential quadratic programming.
Design of a Micromixer With Herringbone Grooves Using Numerical Optimization Techniques
Authors: Ansari Mubashshir Ahmad , Kim Kwang-Yong
Published: June 2009

Optimization of a staggered herringbone groove micromixer has been performed by using three-dimensional Navier-Stokes analysis. The analysis of the degree of mixing is performed by the calculation of spatial data statistics. The calculation of the variance of the mass fraction at various nodes on a plane in the channel is used to quantify mixing. A numerical optimization technique is applied to optimize the shape of the grooves on a single wall of the channel. Two design variables, namely, the ratio of the groove depth to channel height and the angle of the groove, are selected for optimization. A mixing index is used as the objective function. The results of the optimization show that the mixing is very sensitive to the shape of the groove which can be used in controlling mixing in microdevices.
Friction Factor Correlations of Slip Flow in Micro-Tubes
Authors: Hong Chungpyo , Asako Yutaka , Faghri Mohammad
Published: June 2009

Poiseuille number, the product of friction factor and Reynolds number (f·Re) for quasi-fully developed flow in a micro-tube was obtained in slip flow regime. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. Two-dimensional compressible momentum and energy equations were solved for a wide range of Reynolds and Mach numbers with two thermal boundary conditions: CWT (constant wall temperature) and CHF (constant heat flux), respectively. The tube diameter ranges from 3 to 10μm and the tube aspect ratio is 200. The stagnation pressure, pstg is chosen in such away that the exit Mach number ranges from 0.1 to 1.0. The outlet pressure is fixed at the atmospheric pressure. In slip flow, Mach and Knudsen numbers are systematically varied to determine their effects on f·Re. The correlation for f·Re is obtained from numerical results. It was found that f·Re is mainly a function of Mach number and Knudsen number and is different from the values obtained by 64/(1+8Kn) for slow flow. The obtained f·Re correlations are applicable to both no-slip and slip flow regimes.
Visual Experimental Study of Flow Field in Rectangular Microchannels With Different Surface Roughness
Authors: Zhang Chunping , Tang Dawei , Han Peng , Hu Xuegong
Published: June 2009

A new visual experimental study is performed on flow field for laminar to turbulent transition in three different roughness microchannels with almost the same aspect ratio. The red trace is a thin straight line in microchannels at the low Reynolds number. The exit, middle and entrance region become diffuse and transitional flow occurs successively with increasing Reynolds number. The transition Reynolds number is about 1700 for relative roughness smaller than 3%, but the transition Reynolds number is about 1500 with relative roughness is 3.15%, which show that transition occurs earlier than the traditional values. The friction factor and Poiseuille number were also measured in microchannels. It is found that the friction factor and Hagen-Poiseuille number increased with surface roughness, and were significantly greater than the classical values.
Surface Deposition of Nanoparticles During Pool Boiling of Nanofluids and Its Effects on CHF Enhancement Using Nanofluids
Authors: Kim Hyung Dae , Kim Moo Hwan
Published: June 2009

This paper is concerned about mechanism of outstanding CHF enhancement phenomena using nanofluids, a subject with academically and industrially remarkable interest. Pool boiling experiments using an electrically heated horizontal wire were carried out with various water-based nanofluids containing Ag, Al2O3, SiO2, and TiO2 nanoparticles. The results showed that nanoparticle deposition on the heater surface occurred during pool boiling of nanofluids, and that the effect of nanoparticle porous layer on CHF could explain enough the CHF enhancement of nanofluids. Then the porous surface was characterized using surface wettability and capillary wicking performance, which are the significant properties of boiling surface influencing CHF. Discussion of the results suggested that the outstandingly enhanced CHF performances of nanofluids under the nucleate pool boiling were associated with enhanced surface wettability and liquid suction effect due to capillary wicking on the nanoparticle-deposited surface.
Effect of Channel Length on the Flow Cross-Over Through Gas Diffusion Layer and Pressure Distribution in a PEM Fuel Cell Flow Plate With Serpentine Channels
Authors: Sun L. , Oosthuizen P. H. , McAuley K. B.
Published: June 2009

A numerical model was developed to study the effects of channel length and bend shape on the flow cross-over through the porous gas diffusion layer (GDL) and the pressure distribution in a PEM fuel cell flow plate with a serpentine channel flow system. Usually, on the cathode side of a PEM fuel cell, air flow through a flow plate with serpentine channels with certain lengths, to supply the oxygen to the catalyst layer for the chemical reaction. There is a porous GDL between the flow plate and the catalyst layer. Flow cross-over of air through the porous GDL from one part of the channel to another can occur because of the pressure differences existing between different parts of the channel. This cross-over causes the flow rate through the channel to vary with distance along the channel, and also has an influence on the pressure distribution through the plate and, eventually, the fuel cell performance. For the conventional channel flow, the pressure drop is proportional to the channel length. To study the importance of this channel length effect on the PEM fuel cell flow field with cross-over, the pressure distribution and flow rate variation along the channels have been examined by numerically solving for the flow through the plate and porous GDL assembly. Attention has been given here to serpentine channel flow systems with single and parallel channel patterns and with different numbers of passes. A 3-D, single-phase flow has been considered. It was assumed that the flow is steady and incompressible, and the flow through the porous diffusion layer can be described using the Darcy law. The governing equations have been written in dimensionless form using the channel width as the length scale and the mean velocity at the channel inlet as the velocity scale. The resulting set of dimensionless governing equations has been solved using the commercial finite element method (FEM) software package, FIDAP. The solution was obtained by simultaneously solving the equations for the flow in the channels and for the flow through the porous GDL. The solution depends on the following parameters, (1) the Reynolds number, Re, based on the channel width and on the mean velocity at the channel inlet, (2) the dimensionless GDL permeability, (3) the dimensionless channel length, (4) the bend shape, and (5) channel configurations. The main emphasis of this study was on the effect of channel length. The numerical results obtained indicate that the channel length has a significant effect on the flow cross-over through porous GDL and the pressure distribution in the flow plate.
Experimental Investigation on Geometric Effect on Micro Fluidic Diodicity
Authors: Fadl Ahmed , Zhang Zongqin , Faghri Mohammad , Meyer Donna , Simmon Eric
Published: June 2009

The Micro pump is an essential component in a Micro Total Analysis System (μTAS). A feasible and reliable design of the micro pump is a key for the development of the μTAS. The Valve-less Rectification Micro Pump (VRMP) has many advantages, such as: non-moving parts, independent of fluids and channels properties, reliable, and easy to fabricate. Fluid diodicity is an essential parameter of the VRMP design. In this study, we investigate the fluid diodicity (the ratio of forward to reverse flow’s pressure drop) of micro rectifying geometries for more effective design of VRMPs. An experimental apparatus is designed and constructed. In our preliminary experiments, we measured diodicities of four different rectifying geometries, including bifurcation, heart shape, semi-circle and triangle. Experimental results demonstrate that rectifying geometries can take different designs that differ from the conventional diffuser-nozzle and Tesla’s designs; therefore, there is an opportunity to enhance the performances of VRMP by choosing the application-specific rectifying geometries.
Conceptual Design of Industrial Inkjet Head for Micro Patterning on Printed Circuit Boards
Authors: Kim Changsung Sean , Park Sung-Jun , Shim Wonchul , Kim Young-Jae , Park Jung Hoon , Park Chang-Sung , Yoo Youngseuck
Published: June 2009

A conceptual design using computational fluid dynamics and experimental fabrication has been performed to develop an industrial inkjet head for micro-patterning on printed circuit boards. The measured displacement waveform from piezoelectric actuator by Laser Doppler Vibrometer was used as input data for the three-dimensional flow solver to simulate the droplet formation. The mechanism of droplet ejection from piezoelectric-type inkjet heads was investigated by simulating two-phase flows of the air and metal inks. As a preliminary approach, liquid metal jetting phenomena are identified by simulating droplet ejection, droplet formation, and wetting on the substrate in a consequent manner. Parametric studies are followed by the design optimization process to deduce key factors to inkjet head performance: nozzle geometry, droplet size, ejecting speed, ejecting frequency, and ink viscosity. The present design tool based on two-phase flow solver and experimental measurements has shown its promising applicability to various concept designs of industrial inkjet system for micro-patterning on electronic chips and boards.
Transient Thermoreflectance Measurement of Thermal Conductivity of Nanoscale Silicon Nitride Thin Films
Authors: Bai SuYuan , Tang ZhenAn , Huang ZhengXing , Wang JiaQi
Published: June 2009

The present work measured the thermal conductivities of the silicon nitride films prepared by lower pressure chemical vapor deposition (LPCVD) with thicknesses ranging from 100 nm to 200 nm. The measurements were made at room temperature using the transient photothermal reflectance technique, which is a non-contacting and non-destructive optical approach. The data measured were fitted by genetic algorithm to get the thermal conductivity of thin films and interfacial thermal resistance simultaneously. The results show that thermal conductivities of these films are lower than corresponding bulk material values. The interfacial thermal resistances are in the order of 10−8 m2K/W. It cannot be neglected for the very thin films. Some comparison and analysis for the results were discussed.
Mathematical Modeling of Binary Nano Scale Diffusion of Molecular Gas Suspensions in Liquid Media
Authors: Groll Rodion
Published: June 2009

A model describing the suspension diffusion process of gas molecules in liquid media is presented in this paper. This process is not yet solved by a satisfactory model for micro-scale applications at this time. The new model allows the simulation of diffusion processes in continuous media considering the molecular mass flux in a suspension/carrier phase mixture. Modelling the diffusion of gas suspensions in liquid media the saturation mass ratio is reached near the liquid/gas surface very quickly. The increase of gas concentration in the liquid domain depends on the elapsed time and the physical properties of gas and liquid media. The molecular gas velocity is described by a Maxwell probability density function. Based on this spectral method macroscopic physical values are modelled to describe time-dependent global concentration changes. Modelling the gas species diffusion the molecular convection is considered. Modelling the mass flux of the molecular gas suspension characteristic time scales are developed describing the completion level of the saturation progress based on non-dimensional formulations of the molecular convection equation. The present model is implemented in a CFD code and validated by a family of parametric simulation results depending on the saturation mass ratio of the suspended gas phase. This simulation result array shows the dependency of saturation time and saturation mass ratio of the suspended gas molecules. Based on this relation macroscopic diffusion processes in micromixers and microchannels are described with this model and without an extra solution of molecule trajectories or spectral fields of molecule velocity.
New Derivation of a Particle Wall Boundary Condition in Molecular Dynamics
Authors: Spijker Peter , Markvoort Albert J. , ten Eikelder Huub M. M. , Nedea Silvia V. , Hilbers Peter A. J.
Published: June 2009

In this paper a new particle wall boundary condition to replace explicit solid walls in molecular dynamics (MD) simulations is proposed. This new wall potential reduces the computational complexity considerably and allows the investigation of larger channels without compromising macroscopic quantities, such as density, temperature, pressure and heat flux. Since it is common practice in MD to truncate pair interaction potentials, an alternative and explicit derivation of the wall potential is possible, which is in contrast to previous work. Moreover, different types of crystal lattices can be included in the new potential. To demonstrate the applicablity of the method, MD simulations of a gas between two parallel plates at different temperatures and densities have been performed. The results of these simulations are compared to explicit wall simulations and previously proposed wall potentials. Although differences with other wall potentials are minor, some superior aspects of the new potential are addressed.
Heater Size Effect on 3D Liquid Film Flow
Authors: Kabova Yu. O. , Kabov O. A.
Published: June 2009

Thin liquid films may provide very high heat transfer intensity and may be used for cooling of microelectronic equipment. Investigation of the influence of size of hot spots on 3-D structures, occurring at the film surface, is the main objective of the present work. Calculations were carried out for a rectangular heater of different width. It was obtained that there is a heater size effect on 3D liquid film deformations. Film pattern changes in spanwise direction with the heater size. Calculations have been done for various liquid Reynolds numbers.
The Effects of Cross Links on Adiabatic Two-Phase Flow Characteristics in Scaled Microchannel Heat Sinks
Authors: Dang Minh N. , Hassan Ibrahim G.
Published: June 2009

The effects of cross-links, introduced in the channel core of an array of parallel scaled microchannels, were investigated by comparison of the flow distribution in six different multichannel configurations. A standard straight channel test section and five other test sections, which incorporated cross-links were used. One case includes two cross-links located at 1/3 and 2/3’s of the channel length, with their width varied by one, two, and three times the channel width. Whereas, four and six cross-links were used for the other case. All test sections had 45 parallel rectangular channels, with a hydraulic diameter of 1.59 mm, and were fabricated from clear acrylic to enhance flow visualization. The flow distribution was monitored at four select channels. The working mixture was air and water with superficial velocities ranging from 0.03 to 9.93 m/s, and 0.04 to 0.83 m/s, respectively. This corresponds to an observed range of flow quality between 0 and 0.25, whereby the mass flux range is from 42 kg/m2s to 834 kg/m2s. The cross-linked designs permit fluid communication between channels, and the results showed that there is a significant impact on flow distribution when compared to the straight channel design. This is due to flow sharing between neighboring channels. Flow patterns were presented in terms of fractional time function, and provided further insight to flow characteristics. Comparing with a single channel flow regime map, the expected intermittent flow regime was observed 84% to 90% of the time for the cross-linked designs, whereas 65% to 80% of that for the straight channel design.
Numerical Models of Gas Flow and Heat Transfer in Microscale Channels: Capturing Rarefaction Behaviour Using a Constitutive Scaling Approach
Authors: O’Hare Lynne , Reese Jason M.
Published: June 2009

In this paper we discuss the physics of rarefied gas flows at the micro-scale, including discontinuities of momentum and energy at solid boundaries, and the Knudsen layer (a region within one to two mean free paths of any solid surface where non-equilibrium flow features are dominant.) We describe how scaling the constitutive relations of the Navier-Stokes-Fourier equation set can capture key rarefaction behaviour observed in gas microsystems, and how a new implementation of this approach in fully compressible, non-isothermal CFD facilitates the analysis of “real-world” engineering problems. Details of our implementation are given, as are the results of a compressible Couette flow case study, successfully validated against available data sources. We also discuss the relative merits of two published constitutive scaling models, comparing their micro-flow predictions for half-space problems, and contrasting their individual means of application. Some practical implications of using constitutive-relation scaling are explained, and some advantages of the technique compared to alternative methods are outlined. To conclude, we examine some limitations of the method, and outline avenues of research that could potentially broaden the scope of what is a flexible and efficient approach to gas microsystem design using CFD.
Micron-Level Actuators for Thermal Management of Microelectronic Devices
Authors: Erbas Nurhak , Baysal Oktay
Published: June 2009

Failure rates of electronic equipment depend on the operating temperature. Although demand for more effective cooling of electronic devices has increased in the last decades because of the microminiaturization in device sizes accompanied by higher power dissipation levels, there is still a challenge for engineers to attain improved reliability of thermal management for intermediate and low-heat-flux systems. In the present study, an innovative alternative method is proposed and a computational parametric study has been conducted. A single microchip is placed in a two-dimensional channel. Different synthetic jet configurations are designed as actuators in order to investigate their effectiveness for thermal management. The effect is that the actuator enhances mixing by imparting momentum to the channel flow thus manipulating the temperature field in a positive manner. The best control is achieved when the actuator is placed midway of the chip length and increasing the throat height. Also, using nozzle-like throat geometry increases the heat transfer rate from the microchip surface. Doubling the number of the actuators, optimally placing them, and phasing their membrane oscillations all improve the cooling.