bluuebunny/crossref_metadata_2025 huggingface dataset:
The Influence of Sweep on Axial Flow Turbine Aerodynamics at Mid-Span
Authors: Pullan Graham , Harvey Neil W.
Published: September 2008

Sweep, when the stacking axis of the blade is not perpendicular to the axi-symmetric streamsurface in the meridional view, is often an unavoidable feature of turbine design. Although a high aspect ratio swept blade can be designed to achieve the same pressure distribution as an unswept design, this paper shows that the swept blade will inevitably have a higher profile loss. A modified Zweifel loading parameter, taking sweep into account, is first derived. If this loading coefficient is held constant, it is shown that sweep reduces the required pitch-to-chord ratio and so increases the wetted area of the blades. Assuming fully turbulent boundary layers, and a constant dissipation coefficient, the effect of sweep on profile loss is then estimated. A combination of increased blade area and a raised pressure surface velocity means that the profile loss rises with increasing sweep. The theory is then validated using experimental results from two linear cascade tests of highly loaded blade profiles of the type found in low pressure aeroengine turbines: one cascade is unswept, the other has 45 degrees of sweep. The swept cascade is designed to perform the same duty with the same loading coefficient and pressure distribution as the unswept case. The measurements show that the simple method used to estimate the change in profile loss due to sweep is sufficiently accurate to be a useful aid in turbine design.
CFD Analysis Prediction of Heat Transfer Coefficient in Rotating Cavities With Radial Outflow
Authors: Wu Charles , Vaisman Boris , McCusker Kevin , Paolillo Roger
Published: September 2008

This paper documents two related investigations. The first investigation was to benchmark commercial CFD code Fluent in rotating cavities for velocity profiles and beat transfer coefficients. The second investigation was to evaluate the methods of extracting heat transfer coefficients from CFD solution with direct method and Reynolds analogy approach. The rotating cavities examined include rotor-stator, contra-rotating and co-rotating disks. The velocity profiles benchmark was conducted prior to heat transfer coefficient benchmark. Several turbulence models were compared for closed rotating cavity flows. The comparisons between test data and CFD results of tangential and radial velocity profiles showed that the SST k-ω turbulence model performed the best among turbulence models tested. Hence, the SST k-ω model was chosen for heat transfer coefficient benchmarking. The comparisons of heat transfer coefficients between test data and CFD results were presented in the form of local Nusselt number. The thermal wall boundary conditions applied to all the computations were curved-fitted wall temperature distributions from available test data. The wall temperature distributions include approximately constant, positive and negative profiles. It was found that the accurate information of the thermal wall temperature distribution was critical to the benchmark and that only the CFD results with well defined information of wall temperature distributions matched well with test data. The Nusselt number extracted from the CFD solution with the Reynolds analogy approach tends to over predict the heat transfer coefficient on the higher radii and only matched test data at low Reynolds number with positive wall temperature profile. The error increases with higher Reynolds number and decreases with larger flow rate.
Curtis Stage Nozzle/Rotor Aerodynamic Interaction and the Effect on Stage Performance
Authors: Rashid Stephen , Tremmel Matthew , Waggott John , Moll Randall
Published: September 2008

Curtis, or velocity compounded, stages commonly don’t achieve the same accuracy of performance prediction expected of most other turbine stages. A review of Curtis stage design practices, field wear, and dirt patterns, in conjunction with performance testing and CFD modeling, determined that the nozzle/rotor aerodynamic interaction is far more complex than typical design and performance calculations assume. Understanding this nozzle/rotor interaction is key to obtaining both improved performance, and a more accurate performance prediction. This paper discusses the nature of this interaction, and it’s implications to Curtis stage performance prediction.
A Diagnostic and Design Approach of Axial Compressor Based on Local Dynamics
Authors: Guo Ming , Li Qiushi , Hou Anping , Yuan Wei
Published: September 2008

The vortex separate flow that exists on the wall surfaces of blade, shroud, and hub is a major source of the performance loss for the modern axial fans/compressors. To-date the principal diagnostic and redesign approaches to reducing the vortex separate loss have been based on the principal parameters such as pressure, velocity, or Mach number. The original vortex separate flow may be decreased, but a new vortex separate flow which emanates from an else area may be produced, thus the whole course of designing a high performance axial compressor becomes more slowly. This paper presents a novel diagnostic approach based on Local Dynamics, which probes into physical sources of dynamic process and is quite different from principal methods, and a design scheme incorporating new restraint conditions, which depends less on the empirical formulas or models. As examples, one transonic fan rotor is diagnosed, and another low-speed compressor is diagnose and inverse-designed. The examples show that the new approach can enhance the load capability of the axial compressor and provide the high efficiency in a relatively wide working range.
Upgrade of a 16-Stage Industrial Compressor: Part I — Development of an Innovative Performance Analysis Method
Authors: Attia Magdy S.
Published: September 2008

The compressor belonging to a 165 MW-class gas turbine engine designed in the 1970’s with initial operation starting in the early 1980’s, is to be upgraded. The goal of the redesign is to develop a retrofittable upgrade which will deliver a 6% increase in flow and a 2-point increase in adiabatic total-to-total efficiency. The desired increase in compressor efficiency is equivalent to a 0.7-point increase in simple cycle efficiency, approximately. To initiate the upgrade process, a thorough performance evaluation of the existing configuration was needed using the current technology. In this case, the S1S2 prediction did not match measured performance to within an acceptable band. Therefore, a new and innovative system was developed to overcome the existing limitations. This paper presents a simple, physically sound, reliable, and efficient method for predicting axial compressor performance using a combination of single-row CFD and Streamline Curvature (Throughflow) codes. The method has been developed and tested on several industrial multi-stage compressors including this 16-stage compressor with excellent results.
Gas Turbine Performance Simulation Using an Optimized Axial Flow Compressor
Authors: Bringhenti Cleverson , Tomita Jesui´no Takachi , de Sousa Ju´nior Francisco , Barbosa Joa˜o R.
Published: September 2008

Gas turbines need to operate efficiently due to the high specific fuel consumption. In order to reach the best possible efficiency the main gas turbine components, such as compressor and turbine, need to be optimized. This work reports the use of two specially developed computer programs: AFCC [1, 2] and GTAnalysis [3, 4] for such purpose. An axial flow compressor has been designed, using the AFCC computer program based on the stage-stacking technique. Major compressor design parameters are optimized at design point, searching for best efficiency and surge margin. Operation points are calculated and its characteristics maps are generated. The calculated compressor maps are incorporated to the GTAnalysis computer program for the engine performance calculation. Restrictions, like engine complexity, manufacture difficulties and control problems, are not taken into account.
On Near-Wall Dynamic Coupling of LES With RANS Turbulence Models
Authors: Daeninck Goe´ric , Medic Gorazd , Templeton Jeremy A. , Kalitzin Georgi
Published: September 2008

In this paper, the RANS/LES coupling formulation proposed in [1–3] is adapted for various RANS turbulence models. In that formulation, the LES subgrid-scale eddy-viscosity is replaced in the near-wall region with a RANS eddy-viscosity dynamically corrected with the resolved turbulent stress. The RANS eddy-viscosity is first obtained from precomputed tables. To further generalize the approach, RANS turbulence model equations (for Spalart-Allmaras and k-ω) are then solved simultaneously with the LES. Detailed results are presented for channel flow at Reτ = 395 and compared to traditional LES. The method is then applied to a serpentine passage and compared with DNS computations [4] at Reτ = 180.
Aerodynamics of a Family of Three Highly Loaded Low-Pressure Turbine Airfoils: Measured Effects of Reynolds Number and Turbulence Intensity in Steady Flow
Authors: Popovic I. , Zhu J. , Dai W. , Sjolander S. A. , Praisner T. , Grover E.
Published: September 2008

The steady, midspan aerodynamic performance of a family of three low pressure (LP) turbine airfoils has been investigated in a low-speed cascade wind tunnel. The baseline profile has a Zweifel coefficient of 1.08. To examine the influence of increased loading as well as the loading distribution, two additional airfoils were designed, each with 25% higher loading than the baseline version. All three airfoils have the same design inlet and outlet flow angles. The aerodynamic performance was investigated for Reynolds numbers ranging from 25,000 to 150,000 (based on the axial chord and inlet velocity) and for values of freestream turbulence intensity of 1.5% and 4%. The flow field was measured with a three-hole pressure probe. Also, detailed loading distributions were obtained for all three airfoils using surface static pressure taps. The baseline airfoil and the new aft-loaded airfoil showed a separation bubble on the suction side of the airfoil under most of the conditions examined. In addition, a sudden and intermittent stall was observed at low Reynolds numbers for the new aft-loaded airfoil. The relatively short separation bubble would abruptly “burst” and fail to reattach. As the Reynolds number was decreased over a narrow range, the percentage of time that the flow was fully-separated increased to 100%. By comparison, the separation bubble on the baseline airfoil gradually increased in size in an orderly way as the Reynolds number was decreased. The new front-loaded airfoil provided the most encouraging performance: no separation bubble was present except at the very lowest Reynolds numbers. The absence of a separation bubble also had a favourable effect on the loss behaviour of this airfoil: despite its much higher aerodynamic loading, it exhibited very similar midspan losses to those observed for the baseline airfoil.
Transport of Particulates in an Internal Cooling Ribbed Duct
Authors: Shah Anant , Tafti Danesh K.
Published: September 2008

A ribbed square duct (P/e = 10, e/Dh = 0.10) subjected to sand ingestion is studied using an Eulerian-Lagrangian framework. Particle sizes of 10μm, 50μm, and 100μm with response times (normalized by friction velocity and hydraulic diameter) of 0.06875, 1.71875, and 6.875 respectively are considered. The calculations are performed for a nominal bulk Reynolds number of 20,000 under fully-developed conditions. It is found that at any given instant in time about 40% of the total number of 10 micron particles are concentrated in the vicinity (within 0.05 Dh) of the duct surfaces, compared to 26% of the 50 and 100 micron particles. The 10 micron particles are more sensitive to the flow features and are prone to preferential concentration more so than the larger particles. At the side walls of the duct, the 10 micron particles exhibit a high potential to erode the region in the vicinity of the rib due to secondary flow impingement. The larger particles are more prone to eroding the area between the ribs and towards the center of the duct. At the ribbed walls, while the 10 micron particles exhibit a fairly uniform propensity for erosion, the 100 micron particles show a much higher tendency to erode the surface in the vicinity of the reattachment region. The rib face facing the flow is by far the most susceptible to erosion and deposition for all particle sizes. While the top of the rib does not exhibit a large propensity to be eroded, the back of the rib is as susceptible as the other duct surfaces because of particles which are entrained into the recirculation zone behind the rib.
A Criterion for Axial Compressor Hub-Corner Stall
Authors: Lei V. M. , Spakovszky Z. S. , Greitzer E. M.
Published: September 2008

This paper presents a new criterion for estimating the size and strength of three-dimensional hub-corner stall in rotors and shrouded stators of multi-stage axial compressors. A simple, first-of-a-kind description for the formation of hub-corner stall is derived, consisting of (i) a stall indicator, which quantifies the extent of the reversed flow via the local blade loading and thus indicates whether corner stall occurs, and (ii) a diffusion parameter which defines the diffusion limit. The stall indicator can be cast in terms of a Zweifel loading coefficient. The diffusion parameter is based on preliminary design type flow variables and geometry. Computational simulations and single and multi-stage compressor data are used to show the applicability of the criterion over a range of blade design parameters. The criterion also enables determination of specific flow control actions needed to mitigate hub-corner stall. To illustrate the latter a flow control blade, designed using the ideas developed, is seen to achieve a substantial reduction in the flow non-uniformity associated with hub-corner stall.
A PZT Insulin Pump Integrated With Silicon Needle Array for Transdermal Delivery
Authors: Ma Bin , Liu Sheng , Gan Zhiyin , Liu Guojun , Cai Xincia , Zhang Honghai , Yang Zhigang
Published: September 2008

Many of the compounds in drugs cannot be effectively delivered using current drug delivery techniques (e.g., pills and injections). Transdermal delivery is an attractive alternative, but it is limited by the extremely low permeability of the skin. Because the primary barrier to transport is located in the upper tissue, Micro-Electro-Mechanical-System (MEMS) technology provides novel means in terms of both micro needle array and PZT pump, with the former one to increase permeability of human skin with efficiency, safety and painless delivery, and the latter one to decrease the size of the pump. Micro needle array has many advantages, including minimal trauma at penetration site due to the small size in needle, no condition limit, painless drug delivery for penetration depth with few nerves, and precise control of penetration depth for micro needle extension length. The micro needle array drug delivery is precise, painless, effective, clean and neatness, without any inconvenience. This will promote the development of biomedical sciences and technology and makes medical devices more humanized. So far most of the insulin pump has been using mechanical pump. We present the first development of this novel technology which can assemble the PZT pump and the micro needles together for diabetes mellitus. The micro needle array based on a flexible substrate can be mounted on non-planar surface or even on flexible objects such as a human fingers and arms. The PZT pump can pump the much more precision drug accurately than mechanical pump and the overall size is much smaller than those mechanical pumps. The hollow wall straight micro needle array is fabricated on a flexible silicon substrate by inductively coupled plasma (ICP) and anisotropic wet etching techniques. The fabricated hollow micro needles are 200μm in length and 30μm in diameter. The micro needle array, which may be built with on-board fluid pumps, have potential applications in the chemical and biomedical fields for localized chemical analysis, programmable drug-delivery systems, and very small, precise fluids sampling. The micro needle array has been installed in an insulin pump for demonstration and a leak free packaging is introduced.
Effect of Actuation Frequency on the Performane of Diffuser Micropumps
Authors: Mehrabian Amin , Ahmadian M. T.
Published: September 2008

Valveless piezoelectric micropumps are in wide practical use due to their ability to conduct particles with absence of interior moving mechanical parts. The objective of this paper is to obtain the fluid flow response to actuation frequency of a passive diffuser valve under harmonic pressures. In this regards a 2D model of a micropump valves and chambers is analyzed. The analysis is performed for 10Kpa back pressure on micropump chamber and actuation frequencies within the range of 1 Hz to 10 KHz. Results show the highest velocity in the direction of diffuser axis occurs at the narrow diffuser neck while flow direction reverses every half period. For low frequencies, a parabolic velocity profile is observed at the valve midway while, instabilities with the tendency of transition to boundary layer dominant profile is observed for high actuation frequencies. Oscillating flow in diffuser indicates existence of high shear stress regions near the wall along with the flow reversal in the center at high frequencies. Both valve and pump net flow rate decrease drastically as the frequency approaches a certain value. From electrical analogy viewpoint, nozzle/diffuser passive valves can be modeled as Low Pass Filters (LPF). The results are in good agreement with the relevant analytical findings. Similar to analytical results, flow rate is approximately in phase with actuation at low frequencies but phase shift ascends as actuation frequency is increased. The main head loss of flow occurs at the diffuser valves while sudden contraction and expansion of streamlines at the diffuser entrance and exit involve only 22% of the total energy.
Studying Inflammatory Responses of Endothelial Cells and Leukocytes in Perfused Microchannels
Authors: Nash Gerard B.
Published: September 2008

Circulating leukocytes must adhere to the endothelial cells (EC) that form the lining of blood vessels, and migrate through them to carry out their protective immune functions. During inflammation this recruitment is typically controlled by cytokines released from tissue that act on the EC. The endothelial cells respond by increasing the expression of adhesion molecules on their surface (to capture flowing leukocytes), and also by presenting chemotactic agents (to induce the captured cells to migrate). This recruitment process is influenced by the local haemodynamic milieu in several ways: interactions with red cells modify the distribution of leukocytes in the blood stream; flow velocity and shear stress influence the formation and breakage of adhesive bonds; flow forces act on EC and modify their responses to inflammmatory cytokines. Microchannels have been widely used to study these processes, especially the specific receptors required for capture of isolated flowing leukocytes and their ability to support adhesion as a function of fluid shear stress. We developed a versatile system based on pre-fabricated glass capillaries with rectangular cross-section (microslides) in which we cultured EC, and which could also be coated with purified adhesion receptors for reductive studies. We also developed fluoresence-microscope-based systems for using these microslides to observe adhesion in flowing whole blood, and multiple parallel cultures for studying the effects of conditioning the EC by growth at different levels of shear stress before investigations. The microslides are available in various dimensions, and smaller versions can be used to generate high circulatory stresses when small volumes of materials (such as blood from genetically modified mice) are available. With these systems, we have for instance, been able to show how varying the concentration and aggregability of red blood cells alters leukocyte adhesion, and how expression levels of endothelial genes which underly inflammatory responses are modified by culture at a range of shear stresses mimicking different regions of the circulation.
Electrically Tunable Superhydrophobic Nanostructured Surfaces
Authors: Krupenkin Tom , Taylor J. Ashley , Kolodner Paul , Hodes Marc
Published: September 2008

In this work, we discuss dynamic electrical control of the wetting behavior of liquids on nanostructured surfaces spanning the entire possible range from superhydrophobic behavior to nearly complete wetting. It is demonstrated that a droplet of liquid can be reversibly switched between the superhydrophobic “rolling ball” state and the hydrophilic immobile droplet state by the application of electrical voltage and current. The nature of the transition mechanism is studied both experimentally and theoretically. The reported results provide novel methods of manipulating liquids at microscale.
Microfluidics and Personalised Medicine
Authors: Davies Mark , Dalton Tara
Published: September 2008

Personalized medicine is set to transform the diagnosis and treatment of many of the most prominent and dangerous diseases. By analyzing a patient or population’s genome, transcriptome or proteome, complete patient profiling is possible. For the engineer the key issue is to process the biomolecules so that they can be read into an electronic transducer. From then modern computing methods are sufficient to process and analyze the data. Microfluidics will be the key technology in overcoming the present bottleneck, providing a high throughput, low cost method to presenting molecular data to the transducer.
Numerical Mixing Analysis of a Vaned Circular Micromixer
Authors: Bergman Richard , Efremov Alexander , Woehl Pierre
Published: September 2008

Mixing of fluids is a common and often critical step in microfluidic systems. In typical large scale processes turbulence greatly speeds the mixing process. At the mini and micro-scales, however, the flow is laminar and the benefits of turbulent mixing are not present. Mixing at the mini- and micro-scales tends to become a more highly engineered process of bringing fluids together in predictable ways to achieve a predetermined and acceptable level of mixing. This paper summarizes a numerical analysis of the mixing performance of a vaned circular micromixer. A newly developed mixing metric suitable for reacting fluids is developed for this study. Applying the basic steps of stretching, cutting, and stacking to effect mixing, a useful micromixer is analyzed numerically for its mixing efficiency. A parametric study of flow and viscosity indicate that a flow Re of 12 or higher is sufficient to achieve effective and rapid mixing in this device.
Microstructure Heat Exchanger Applications in Laboratory and Industry
Authors: Brandner Juergen J. , Bohn Lothar , Henning Torsten , Schygulla Ulrich , Schubert Klaus
Published: September 2008

In this publication heat transfer in microstructure devices and its application in laboratory and industry will be described. Basic principles of microstructure heat exchangers made of metal, ceramics and polymers will be presented. A variety of laboratory prototype applications will be shown as well as some examples for industrial use of not only microstructure heat exchangers but also microstructure devices as chemical reactors. A brief outlook will describe possible future application fields.
Enhanced Condensation Heat-Transfer on Mini or Low Fin Tubes
Authors: Briggs Adrian
Published: September 2008

This paper presents an overview of the use of low or mini-fin tubes for improving heat-transfer performance in shell-side condensers. The paper concentrates on, but is not limited to, the experimental and theoretical program in progress at Queen Mary, University of London. This work has so far resulted in an extensive data base of experimental data for condensation on single tubes, covering a wide range of tube geometries and fluid thermophysical properties and in the development of a simple to use model which predicts the majority of this data to within 20%. Work is progressing on the effects of vapor shear and on three-dimensional fin profiles; the later having shown the potential for even higher heat-transfer enhancement.
EWOD Digital Microfluidics for Lab on a Chip
Authors: Fouillet Y. , Jary D. , Brachet A. G. , Berthier J. , Blervaque R. , Davous L. , Roux J. M. , Achard J. L. , Peponnet C.
Published: September 2008

This paper presents a brief overview of Electro Wetting On Dielectric (EWOD) microdroplet actuation technology fluidic behaviour. EWOD specifics are compared with other digital microfluidics actuation modes. In particular ease of integration with complex protocols is emphasized. After reviewing the electro-wetting principle and various Electro-Hydro-Dynamic (EHD) phenomena; we compare various EWOD configurations for Lab on a Chip. Two fluid functionalities will be detailed: on-chip droplet dispensing, and mixing. We cover chip architecture and the benefits of organizing these chips as fludic microprocessors. Finally, real time PCR (Polymerase Chain Reaction) within a 64 nl droplet is described as an illustration of a biological application using EWOD.
Sensing and Modeling Techniques for Micro and Nano Scale Transport
Authors: Kim Sung Jin , Kim Dong-Kwon
Published: September 2008

In the present study, three types of micro-sensors developed for experimental investigation of fluid flow and heat transfer in microstructures are introduced. The micro-sensors can be used to measure temperature distributions at the surface of a microstructure and mass flow rates passing through it. It is followed by a description of a method for modeling transport phenomena in microstructures is introduced. The modeling technique, based on the averaging method, is illustrated in thermal design and optimization of a microstructure.
Micro Process Engineering: Actual State and Challenges
Authors: Kockmann Norbert
Published: September 2008

For process industries the enhanced performance of key processes is crucial for their economical development. The process intensification benefits from the miniaturization of channels and conduits within devices, where the characteristic lengths are reaching into the order-of-magnitude of boundary layers or transport lengths. The fast transport rates can be used for many different purposes like fast and mixing sensitive reactions, temperature homogenization or nanoparticle precipitation. This review gives an overview of miniaturization effects and beneficial phenomena in microchannels with characteristic dimension from 10 to 1000 μm. Actual research projects in Germany in the Microsystems Technology program 2004–2009 are described as well as the actual EU projects. Further emphasis is laid on industrial projects in Europe, in the States and in Far East for laboratory or production purposes. Characteristic examples illustrate the first successful applications, the crucial drawbacks, but also the needs and demands for future research and development. The integration of micro structured devices together with sensing and actuating elements as well as with the “macro world” will be one of the key issues for the future development.
Novel Hybrid Simulations for Heat Transfer at Atomistic Level
Authors: Nedea S. V. , Frijns A. J. H. , van Steenhoven A. A. , Markvoort A. J. , Hilbers P. A. J.
Published: September 2008

Hybrid simulations are used to overcome length and time scale limitations of atomistic simulations for problems involving multi-fluid dynamics in the presence of multi-fluid interfaces. An overview of hybrid atomistic-continuum for the treatment of dense fluid problems with emphasis on the coupling of molecular dynamics (MD) with continuum methods is given. A new hybrid approach coupling MD with a stochastic particles simulation approach based on Monte Carlo (MC) simulation is further described. The coupling in the hybrid MD-MC method is presented and simulation results are validated by comparing with pure MD simulation results of a system consisting of dense gas molecules confined between the walls of a micro/nano-channel. In the end, comparisons between accuracy and computational costs of MD, MC and hybrid MD-MC simulations are outlined. Flow and no-flow regimes are considered for comparisons and the predictions for heat transfer in micro/nano-channel cooling applications are discussed.
Advanced Micro Heat Exchangers for High Heat Flux
Authors: Yang Chien-Yuh , Yeh Chun-Ta , Liu Wei-Chi , Yang Bing-Chwen
Published: September 2008

Owing to the rapid development of semiconductor industry, the heat dissipated from electronic devices increases drastically with increasing device logic gate number and operation speed. The cooling technologies have undergone evolutionary changes from air cooled fin geometry to copper base and vapor chamber heat spreader and to more thorough methods such as forced convective liquid cooling in recent years. Three micro heat exchangers with long offset strip, short offset strip and chevron flow path based on the conventional heat transfer enhancement concepts were designed, fabricated and tested. A straight channel heat exchanger was also made for comparison. The test results show that there is no significant difference of the thermal resistance at various heating power for each heat exchanger. The chevron channel heat exchanger provides the lowest thermal resistance. However, its pressure drop is also the highest. It is approximately 250% higher than that for other three heat exchangers. The offset strip heat exchangers provide better thermal performance than the straight channel heat exchanger does. The performance of heat exchanger with shorter strip is better than that of heat exchanger with longer strip. Further improvement such as optimum strip length design or streamlined strip shape may be applied to reduce its flow pressure drop.
Hydrodynamical Theoretical Solutions for Peristaltic Microchannels.
Authors: Merlen Alain
Published: September 2008

Three analytical solutions describing the 2D Stokes flow in a peristaltic micro-channels are presented. The paper is concerned with pure hydrodynamics discarding any other physical phenomenon like electrical forces. This allows the derivation of analytical results when the problem is share into three main parts: the effect of the contraction on its vicinity, the squeezing of the fluid near the contraction and the effect of wavy walls that is related to the problem of the wall quality which depends on the elaboration process. The results can be considered as reference touch stones for these flows at Reynolds number smaller than one. They allow some physical discussions on the phenomena.
Carbon Nanotubes, Synthesis, Growth and Orientation Control
Authors: Kennedy Lawrence A.
Published: September 2008

The combustion synthesis of carbon nanotubes is reviewed, examining their formation and control in diffusion flames. The production of CNTs in the absence of a catalyst, the range of morphology of nanostructures when a catalyst is employed, control of the growth and orientation of CNTs and their arrays through the use of electric fields and the functional coating of CNTs with polymers using supercritical CO2 are discussed. Application of these techniques to other materials is discussed.
Ceramic Microjet Cooling Device
Authors: Natarajan Govindarajan , Bezama R. J.
Published: September 2008

This paper details the technology elements developed to design and manufacture a liquid microjet array cooling device, for thermal management of very high power dissipating electronic chips. Multilayer ceramic technology (MLC) is used to build the cooling device with microns size jet arrays, which include distributed return network for the spent fluid. Intertwined microchannel flow networks inside the cooler body distribute the flow in and out of the device. A cooler with 1600 jets and 1681 interstitial returns for the drains built using Glass Ceramic material is discussed. The device when tested with an 18 mm heated silicon chip and an average convection coefficient of 0.052 MW/m2K demonstrated a cooling capability greater than 2.5 MW/m2, with a water pressure drop of < 70 kPa. Further extension of the cooling capability to greater than 6 MW/m2, as predicted by the simulation is also discussed.
A Procedure for Calculating Wall Distance in Arbitrary Microchannel Geometries
Authors: Scanlon Thomas J. , Reese Jason M. , O’Hare Lynne
Published: September 2008

This paper describes a continuum-based CFD solution for flow in a microchannel using near-wall scaling and first-order slip conditions. This near-wall scaling approach is used in an attempt to capture the Knudsen layer effects. The near-wall scaling itself requires the distance to the nearest wall as an input parameter and this distance is calculated using a simple technique which involves the solution of a diffusion equation for a scalar value φ of the form div(gradφ) = −1. The wall distance is then deduced for this scalar field and implemented in the near-wall scaling function. In order to demonstrate the efficacy of the wall distance/near-wall scaling technique the methodology is applied to two practical cases. The first case describes Poiseuille flow in a microchannel (for which analytical solutions exist) and the second considers flow in a microchannel with two 90° bends. The results show that the implementation of the wall distance procedure is relatively straightforward and that the use of the near-wall scaling increases the mass flow rates in both of the cases considered.
Experimental Study on Saturated Flow Boiling Critical Heat Flux in Microchannels
Authors: Kuan Wai Keat , Kandlikar Satish G.
Published: September 2008

The saturated flow boiling critical heat flux in microchannels is investigated using water as the working fluid. The experimental test section has six parallel microchannels with each having a cross sectional area of 1054 × 157 micrometers. The mass flow rate, inlet temperature of the working fluids, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative information near the CHF condition in microchannels. The trends in present CHF with mass flux and quality are similar to those obtained by Qu and Mudawar [1] and earlier investigators.
Experimental Study on the Effect of Stabilization on Flow Boiling Heat Transfer in Microchannels
Authors: Kuan Wai Keat , Kandlikar Satish G.
Published: September 2008

The effect of flow instabilities on flow boiling heat transfer in microchannels is investigated using water as the working fluid. The experimental test section has six parallel rectangular microchannels with each having a cross sectional area of 1054 × 197 microns. Flow restrictors are introduced at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. The mass flow rate, inlet temperature of water, and the electric current supplied to the resistive cartridge heater are controlled to provide quantitative heat transfer information. The results are compared with the unrestricted flow configuration.
Film Condensation in Microchannels: Effect of Tube Inclination
Authors: Wang Hua Sheng , Rose John W.
Published: September 2008

A recent model for condensation in microchannels by the authors has been modified to investigate the effect of channel inclination. Provisional results are obtained for the case studied earlier for horizontal channels i.e. for R134a with saturated vapour at inlet and prescribed uniform wall temperature. Calculations give distributions around the channel perimeter of condensate film thickness and heat flux from which the mean (around the channel perimeter) heat flux and heat-transfer coefficient are found. Results are presented for square channels with side 0.5, 1.0 and 3.0 mm.
Is It Possible to Control Air Flow by Using Laser Photon Pressure?
Authors: Shiraishi Masatake
Published: September 2008

Extremely low-velocity airflow fluctuations around precision equipment is a primary cause of diminished accuracy of such systems. Unfortunately, there is currently no effective means to control these air fluctuations. Assuming that airflow dynamics can be approximated by a linear equation under low-velocity viscous flow conditions, this paper shows that airflows around equipment can be controlled. A series of experiments is then performed to corroborate the theoretical findings. In the experiments, smoke particles are excited by the photon pressure of an argon laser beam. The behavior of the particles is regulated by an optical system consisting of a convex lens and a neutral density filter. The experimental findings demonstrate that it is indeed possible to control the airflow in the recessed parts of precision equipment using photon pressure of a laser beam.
Visualization of Boiling in Inclined Rectangular Narrow Long Channels
Authors: Noh Sang W. , Yoo Jae S. , Suh Kune Y.
Published: September 2008

During the Three-Mile Island Unit 2 (TMI-2) accident, the lower part of the reactor pressure vessel had been overheated and then rather rapidly cooled down, as it was later found out in a vessel investigation project. These findings triggered a great deal of investigations to determine the critical heat flux (CHF) in narrow channels. Experiments were conducted to determine the CHF on a long downward heated rectangular narrow channel by changing the orientation of a copper crevice (5×105 mm2) type heater assembly. The test heater was placed in a demineralized, saturated water pool at atmospheric pressure. This work aims also to investigate the general boiling phenomena and the triggering mechanism for the CHF in the narrow channel through visualization of the bubble behavior in the vicinity of CHF. The test parameters include the channel size of 5 mm and the surface orientation angles from the downward facing position (180°) to the vertical position (90°). It was found that the CHF decreases as the surface inclination angle increases and as the gap size decreases. It was also shown that there exists a transition angle at which the CHF changes with a rapid slope, and that the inclination angle affects the bubble layer and the bubble discharge from the narrow gap.
Flow in 2D-Nanotubes by Stochastic Rotation Dynamics Algorithm
Authors: Madadi Mahyar , Mehrabi Marjan
Published: September 2008

We use the Stochastic Rotation Dynamics (SRD) to simulate the fluid flow in 2D Carbon Nanotubes. The SRD algorithm is able to simulate flow in different length scale of the fluids. First of all, we use SRD algorithm to simulate the macroscopic Helium flow as a simple interacting system. Using Green-Kubo formula, viscosity of the system as a macroscopic quantity has been calculated. Then, we apply our algorithm to simulate the Helium flow through the Carbon Nanotube in two dimensions. Finally, we find the effect of interaction of Carbon Nanotube with viscosity as a function of temperature. Also, our simulation shows the viscoelastic effects in 2D flow.
Computational Investigation of a Non-Newtonian Fluid Flow in a Microchannel Using Surface Micro Waves
Authors: Dharmalingam Sugumar , Shi Yanru , Yu Zhenxian , Kong Lingxue , She Feng Hua
Published: September 2008

One of the methods of transporting fluid in microchannels without employing high voltage or syringe pump is the surface micro waves. The micro surface waves are able to move the fluids in the channels in the direction of wave propagation. In this study, computational investigations are made to analyse the behaviour of a Non-Newtonian fluid flow under the surface micro wave in a square microchannel. The analysis is restricted to 5 wave lengths due to the constraints in the computation for longer wave lengths. The results show that surface waves are able to make the fluid flow in the direction of the wave propagation. By altering the wave parameters, the mass flow rate of the fluid can be increased or reduced in real time. However, there are several observations that need to be taken into consideration in using the surface waves as mean for fluid flow in microchannels (not clear here). Pressure and velocity difference across the cross section of the microchannels might cause flow instabilities which might affect the intended use of the system.
Preliminary Numerical Modelling of Non-Newtonian Fluid Behaviour Under Surface Microwaves
Authors: Shi Yanru , Dharmalingam Sugumar , Yu Zhenxian , Kong Lingxue , Hsu Hung-Yao
Published: September 2008

This paper presents the numerical simulation of a non-Newtonian fluid under the effect of moving sinusoidal surface micro waves generated by a micro actuator. The blood is used as the fluid in the simulation, which is confined between the actuator and the substrate, within a channel of 20 micron high. The simulation was solved using the finite element method by utilizing the commercially available software ANSYS. A mathematical model is developed to convert the non-Newtonian fluid to equivalent Newtonian fluid to estimate the traction force. The results show that a stable thrust force is generated by the moving sinusoidal waves. The magnitude of the thrust force is increasing while the fluid viscosity and the wave frequency are increasing. The results also show that the thrust force is highly predictable and controllable. A surface thrust force of 19.71 micro-Newton per centimetre for the frequency of 1 kilohertz can be obtained in blood by using an actuator of one millimeter diameter. The direction of the force can be changed by changing the wave propagation direction.
Integrated Nanofluidic Devices and Circuits
Authors: Majumdar Arun
Published: September 2008

The fundamental length scales related to ions and molecules in liquids fall in the range of 1–100 nm. These involves the range of intermolecular forces due to steric interactions, electrostatic forces between charged species, and van der Waals interactions. This talk will focus on how confinement of aqueous solutions in the range of Debye screening length (1–50 nm) in nanochannels can lead to formation of unipolar ionic solutions. The ionic current in such nanochannels is found to several orders of magnitude higher than that predicted by macroscopic theories, and is extremely sensitive to surface charge, which can be used to study surface biomolecular reactions. Furthermore, this phenomenon can be exploited to develop nanofluidic transistors, diodes, and integrated circuits, which is now forming the basis for manipulating and analyzing complex mixtures of biomolecules in ultrasmall volumes.
Measurement of Transient Electrokinetic Flow in Microchannels Using Micro-PIV Technique
Authors: Yan Deguang , Yang Chun , Nguyen Nam-Trung , Huang Xiaoyang
Published: September 2008

Measurement of the steady-state electroosmotic velocity distributions in microchannels has been reported in the literature. Characterizing time-dependent electrokinetic flows is of importance to the development of microfluidic devices such as rapid capillary electrophoretic separation systems, AC pumps, novel micromixers etc. In this paper, we report a novel technique for studying and quantifying the transient electrokinetic flow phenomena in microchannels using the micro-PIV system with an ordinary PIV CCD camera. This is achieved by synchronizing different trigger signals for the laser, CCD camera, and custom high-voltage switch. Using the transient micro-PIV technique, we further propose a method to determine the electrophoretic component in the particle velocity and the zeta potential of the channel wall. Then the time evolution of the full-field, electroosmotic velocity distributions in both open- and closed-end rectangular microchannels is obtained from the micro-PIV measurement data. Using the slip velocity approach and the measured channel zeta potential, the theoretical predictions of the transient electroosmotic flow in the open- and closed-end microchannels are obtained, and they are found in good agreement with the experimental results.
The Optimized Analysis of Electronic Cooling by CFD Methods
Authors: Cheng Lin , Yun Heming
Published: September 2008

The heat dissipation of electronic elements in a mini-space is investigated by using Computational Fluid Dynamics (CFD) methods in this paper. The velocity and temperature fields of mini-space are simulated on the condition of several schemes with air as fluid. The synergetic effects of temperature and velocity field for mini-space have been analyzed by field coordination principle. Then a cooling effect number has been put forward to evaluate the cooling effects of electronic elements. The optimized scheme of mini-space has been obtained by comparing the cooling effect number of different schemes, which has established a solid foundation for discussing the cooling techniques of micro-electronic elements further.
Numerical Computation of Roughness Effects on Heat Transfer and Hydrodynamic Characteristics in Microchannels
Authors: Yun Heming , Cheng Lin , Wang Liqiu , Chen Binjian
Published: September 2008

In the present paper we focus our attention on the analysis of surface roughness effects. In the process of numerical simulation, a finite-volume method was used to solve the three-dimensional Navier-Stokes equations and energy equation. In turbulent region, wall-function was used to solve the temperature and velocity of coolant in the area near the wall. In all computational regions, the fluid-solid Conjugate heat transfer is used to solve the microchannel heat transfer problems. In conclusion the effect of surface roughness on heat transfer and pressure drop can not be neglected. And one should be very careful in ascribing the roughness effect to the discrepancies between experimental heat transfer and the prediction for standard macro scale channels.
From Macro to Micro Scales: Identifying and Measuring Scaling Effects
Authors: Herwig H. , Gloss D.
Published: September 2008

Scaling effects in continuum flows can be identified that characterize flow and heat transfer in small, micro-sized devices compared to the same geometries but on a macro-sized scale, when the underlying continuum equations (Navier-Stokes and first law of thermodynamics) are subject to a dimensional analysis. In order to identify micro scaling effects experimentally, measured flow quantities are compared to numerically calculated results, based on a theoretical model that is appropriate for macro scale channels (no scaling effects, continuum approach). They have to be interpreted carefully, including a thorough error analysis of experiments as well as the theoretical model. Instead of trying to experimentally identify scaling effects in fixed geometries we suggest to combine macro parts in a way that micro channels emerge. Then, continuously adjustable sizes of the channels can be realized that go from macro to micro dimensions. Equally important, the surfaces of the channels are freely accessible when the macro parts are disjoined. Two such facilities are shown and discussed.
Rarefaction, Temperature Jump, and Viscous Dissipation Effects on Heat Transfer in Rotating Micro Devices
Authors: Jiji Latif M.
Published: September 2008

This paper examines the effects of rarefaction and dissipation on flow and heat transfer characteristics in rotating micro devices. The housing is assumed to be at uniform temperature while the rotating surface is insulated. Thus heat generation and transfer are due to viscous dissipation only. An analytic solution is obtained for the velocity and temperature distribution in the gas filled concentric clearance between a rotating shaft and its stationary housing. The solution is valid in the slip flow and temperature jump domain defined by the Knudsen number range of Kn < 0.1. The Nusselt number was found to depend on three parameters: the Knudsen number Kn, ratio of housing to shaft radius ro / ri, and Prandtl number-specific heat ratio group γ/(γ + 1) Pr. Results indicate that curvature and Knudsen number have significant effect on the Nusselt number. However, fluid temperature rise due to dissipation is negligible.