bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of Compressed Air Hybrid Operation for a Heavy Duty Diesel Engine
Authors: Wang Xiaoyong , Tsao Tsu-Chin , Tai Chun , Kang Hyungsuk , Blumberg Paul N.
Published: June 2009

Internal combustion engines can be modified to operate regenerative braking cycles by using compressed air power. This paper presents a particular air hybridization design from among many possible configurations. The engine cycles are enabled by a highly flexible engine valvetrain, which actuates engine valves to generate desired torque with optimal efficiency. A lumped parameter model is developed first to investigate the cylinder-tank mass and energy interaction based on thermodynamic relationships and engine piston kinematics. Special consideration is given to the engine valve timing and air flow. A high fidelity, detailed model using the commercially available GT-Power software is developed for a commercial 10.8 liter heavy-duty diesel engine with a 280 liter air tank in order to capture the effects of engine friction, heat transfer, gas dynamics, etc. The model is used to develop optimal valve timing for engine control. The established engine maps are incorporated into the ADVISOR vehicle simulation package to evaluate the potential fuel economy improvement for a refuse truck under a variety of driving cycles. Depending on the particular driving cycle, the simulation has shown a potential 4% – 18% fuel economy improvement over the truck equipped with the conventional baseline diesel engine.
Dual-Stage Turbocharger Matching and Boost Control Options
Authors: Lee Byungchan , Jung Dohoy , Assanis Dennis , Filipi Zoran
Published: June 2009

Diesel engines are gaining in popularity, penetrating even the luxury and sports vehicle segments that have traditionally been strongly favored gasoline engines as the performance and refinement of diesel engines have improved significantly in recent years. The introduction of sophisticated technologies such as common rail injection (CRI), advanced boosting systems such as variable geometry and multi-stage turbocharging, and exhaust gas after-treatment systems have renewed the interest in Diesel engines. Among the technical advancements of diesel engines, the multi-stage turbocharging is the key to achieve such high power density that is suitable for the luxury and sports vehicle applications. Single-stage turbocharging is limited to roughly 2.5 bar of boost pressure. In order to raise the boost pressure up to levels of 4 bar or so, another turbocharger must be connected in series further multiplying the pressure ratio. The dual-stage turbocharging, however, adds system complexity, and the matching of two turbochargers becomes very costly if it is to be done experimentally. This study presents a simulation-based methodology for dual-stage turbocharger matching through an iterative procedure predicting optimal configurations of compressors and turbines. A physics-based zero-dimensional Diesel engine system simulation with a dual-stage turbocharger is implemented in SIMULINK environment, allowing easy evaluation of different configurations and subsequent analysis of engine system performance. The simulation program is augmented with a turbocharger matching program and a turbomachinery scaling routine. The configurations considered in the study include a dual-stage turbocharging system with a bypass valve added to the high pressure turbine, and a system with a wastegate valve added to a low-pressure turbine. The systematic simulation study allows detailed analysis of the impact of each of the configurations on matching, boost characteristics and transient response. The configuration with the bypass valve across high pressure turbine showed better results in terms of both steady state engine torque and transient behavior.
Engine-Component Wear Modeling With Consideration of Growth and Removal of Surface Films: Computational Framework and Preliminary Results
Authors: Thomas B. C. , Wong Victor W.
Published: June 2009

The life of an automotive engine is often limited by the ability of its components to resist wear. The ability to predict wear, particularly for the effects of lubricant and additive characteristics, would greatly aid the development process of both engine components and lubricants. This paper addresses the development and function of thin solid films on rough surfaces and their effect on surface wear, as that occurring between contacting engine component surfaces. Completely deterministic modeling of such films may not be possible due to the complex interactions between the numerous mechanical, thermal, and chemical variables over disparate magnitudes of time and length scales. However, it is believed that useful predictions can be made by constructing a mechanistic model in which all of the most important effects are included, even if only at an approximate level. This work outlines the early stages of such a modeling effort in the context of zinc dialkyl-dithiophosphate (ZDDP) antiwear films on iron surfaces. The key concepts behind the theoretical model will be introduced, while its numerical implementation will be the focus of the discussion. Preliminary results from this effort are presented to illustrate feasibility and functionality on a qualitative level.
A ‘New Twist’ on Twisted Rings
Authors: Sytsma Steve , Carson Mike , Karrip Kimm , Lunsford Randy
Published: June 2009

Facing monumental challenges in the tightening constraints of friction reduction, oil control, and blowby, piston ring designs are becoming intricately more complex. Within this complex matrix of design criteria, minute changes can have a big impact on the performance of engines, which are operating under conditions of higher temperatures and speeds. At the same time there is a general requirement to reduce the overall mass of the components. Thus, the piston rings must have inherent design properties (more finely tuned) to withstand the elevated operations of the engine, maintain longevity, and perform within the expected performance criteria. To help meet these challenges, this paper gives a brief introduction to the axial formed process as an improvement of the twist characteristic on the upper compression ring (UCR) design, along with representative supporting performance data based on engine tests and computer simulation. The goal is to show some successes across different engine types involving the axial formed process. The main topics covered include a) historical role and design of twisted rings in the engine, b) advantages of improved twisted rings, c) example of engine test data and d) example simulation results.
Experimental Investigation of Surface Modifications for Piston-Ring/Cylinder-Liner Friction Reduction
Authors: Cater Marko S. , Bolander Nathan W. , Sadeghi Farshid
Published: June 2009

Micro-dimples on the surface of lubricated sliding contacts can act as mini-hydrodynamic bearings. The pressure generated within these dimples tends to separate the surfaces and reduce the number of asperities in contact, thereby lowering the average coefficient of friction and moving the lubrication condition to the more stable hydrodynamic lubrication regime. An experimental study on the effects of laser surface modifications for friction reduction is presented through the use of several experimental test rigs. Micro-dimples were generated with an Nd-YAG laser on the surface of flat samples for testing in constant speed and reciprocating motion test rigs. These simple geometries were used to investigate the phenomenon and validate existing analytical models. Modifications to the top dead center region of an actual cylinder liner were evaluated with a motored, small-engine dynamometer. The results demonstrated that measurable friction reductions can be achieved using this approach.
Lean-Burn Stationary Natural Gas Reciprocating Engine Operation With a Prototype Miniature Diode Side Pumped Passively Q-Switched Laser Spark Plug
Authors: McIntyre Dustin L. , Woodruff Steven D. , McMillian Michael H. , Richardson Steven W. , Gautam Mridul
Published: June 2009

To meet the ignition system needs of large bore lean burn stationary natural gas engines a laser diode side pumped passively Q-switched laser igniter was developed and used to ignite lean mixtures in a single cylinder research engine. The laser design was produced from previous work. The in-cylinder conditions and exhaust emissions produced by the miniaturized laser were compared to that produced by a laboratory scale commercial laser system used in prior engine testing. The miniaturized laser design as well as the combustion and emissions data for both laser systems was compared and discussed. It was determined that the two laser systems produced virtually identical combustion and emissions data.
Blow-By Vapour Impact on Flexible Fuel Applications
Authors: Fusco Rovai Fernando , Milanez Ju´nior Cla´udio , Cawsey Paul Edward
Published: June 2009

The flexible fuel vehicles (FFV) are definitely a reality in Brazil. Most of the cars currently produced in Brazil are flexible fuel with fuel range from gasohol (E22) to hydrated ethanol (E100). All of these Brazilian applications are fuel sensor less. It means that the fuel inference is based on lambda sensor only. This fuel inference approach takes the intake air mass over the calculated mass of fuel delivered through the injectors in account to calculate the air fuel ratio (AFR) which points out the fuel blend in tank. One of the disadvantages of this inference strategy is that all the fuel considered for AFR calculation must come from injectors. Considering that the cold start and warm-up phases should operate in a richer mixture (choke operation), part of this fuel is delivered to the lubricant which is know as fuel dilution phenomenon in lubricant. According to the fuel properties and the lubricant temperature the diluted fuel evaporates and is mixed in intake air through blow-by system. This extra fuel source is considered in AFR calculation and can, in some conditions, distort the fuel blend inference. In order to prevent this blow-by vapour negative impact on flexible fuel inference logic a mathematical model was developed and calibrated for a 1.6 liter engine FFV application. Many test results with different blends and conditions are discussed. This study confirmed that this mathematical model presented positive results and some improvement opportunities were commented as well.
3-D Numerical Simulation of Structure Optimization of Rectangular Fin Tube Economizer
Authors: Lu¨ Yu-Kun , Lu Quan
Published: June 2009

The FLUENT6.2 software is adopted for numerical simulating heat transfer and flow characteristic of the gas when it flow through rectangular tube bundles in transverse direction, the array separation of tubes effected to heat transfer and flow is analyzed, the correlation equation of heat transfer characteristic is derived, and bases on the velocity distributing the rational tube arrangement is adopt to optimize economizer. Taking a certain power plant’s 200MW boiler economizer as an example, the porous medium model and heat exchanger model are employed for simulating. The study result indicates that: the heat-exchange performance of the economizer taking variable-pitch tube arrangement is excelled than the primary one, the discrepancy of gas pressure drop of them is narrow. The essay has direct significance for the structure optimizing and increasing heat exchange efficiency of power plant economizer.
Computational Modeling of Molecular Gas Convection With a c2-z2 Model
Authors: Groll Rodion
Published: June 2009

Modelling micro channel flows momentum and heat diffusion / convection are recent parameters modelling the molecule velocity distribution. Macroscopic models describe velocity and energy / enthalpie with integrals of mass increments. Using microscopic models motion and forces of a molecular flow have to be computed by models of physical properties, whose are described by statistical power moments of the molecule velocity. Therefore dilute flows have to be investigated in small channels with a mean free path length of molecules higher than the channel width of the the micro channel itself (λ0 ≥ H0). Modelling this process by a continuous flow the boundary conditions have to be modified (e.g. [9]). Instead of a simple Dirichlet boundary condition with a neglecting velocity directly at the channel wall, given slip models define a slip velocity of the ducted fluid depending on the shear stress at the wall. The present model uses the statistical approximation of the molecule velocity distribution to simulate the behaviour of this discrete flow with a weighted averaged molecule velocity ξ˜i, its standard deviation σ and the characterisic molecule collision rate z. The number density n of molecules N per volume V near one position is used for the weighting factor averaging method describing the mean molecule velocity. The present model is validated computing Poiseuille and Couette flows with different Knudsen numbers. Showing the advantages of the present model the simulation results are compared with simulation results of the wall-distance depending diffusivity model of Lockerby and Reese [5] and BGK results of a Lattice-Boltzmann simulation.
The CFD Simulation and Experimental Study of the Plate-Type Evaporative Condenser
Authors: Zhu Dongsheng , Li Yuanxi , Zhang Jingwei , Jiang Xiang
Published: June 2009

This paper presents a simulation of two operations—upwind, downwind with two-phase flowing in the plate bundles of the plate-type evaporative condenser, by means of the FLUENT software, which provide a direct illustration of the influence of the water film flowing on spray water flow, air velocity, air direction in the plate bundles. The result of simulation demonstrates the advantages of air-water parallel-flow over countercurrent in making use of enhanced heat transfer and mass transfer of fluid film.
Microchannel Fluorescent Melting Curve Analysis
Authors: Kinahan David J. , Dalton Tara M. , Davies Mark R.
Published: June 2009

In recent years, Fluorescent Melting Curve Analysis (FMCA) has become an almost ubiquitous feature of commercial quantitative PCR (qPCR) thermal cyclers. Here a microfluidic device is presented capable of performing droplet based Fluorescent Melting Curve Analysis within a microchannel. The device consists of modular thermally conductive blocks which can sandwich a microfluidic substrate. Opposing ends of the blocks are held at differing temperatures and a linear thermal gradient is generated along the microfluidic channel. Fluorescent measurements taken from a sample as it passes along the micro-fluidic channel permits fluorescent melting curves be generated. In this study we demonstrate the capability of measuring fluorescent melt curves from DNA passing through the device in a serial flow of sample plugs buffered by mineral oil.
Specific Heat of Individual Silicon Nanowires
Authors: Feng Bo , Li Zhixin , Zhang Xing
Published: June 2009

The elastic continuum model is resorted to study the lattice specific heat of individual crystalline silicon nanowires with 22 and 37 nm in diameter. Incorporating both longitudinal and transverse modes, a model based on the power-law phonon dispersion is developed to illustrate the characteristics of phonon density of states (DOS) in bulk and low-dimensional systems. The results show that there exist multiple and explicit van Hove singularities for thin wire and step-like enhancement for thin film, attributing to the quantized phonon modes in the particular dimensionality. Furthermore, we examine the phonon dispersion and DOS of silicon nanowires and find infinite phonon branches. A cutoff frequency based on the reduced phonon group velocity is defined to guarantee that the phonon wavelength can not be shorter than the lattice constant. The softening of vibrational modes in low-frequency region and the deficit in high-frequency region occur, resulting in the excess specific heat of silicon nanowire compared with that of bulk silicon. This phenomena becomes more significant at low temperatures. In addition, the dependence of specific heat of nanowires on temperature departs from that of bulk material in view of the quasi one-dimensional feature. Qualitative support is presented to our present work.
An Electroosmotically Stirred Continuous Micro Mixer
Authors: Beskok Ali
Published: June 2009

A continuous microfluidic mixer concept is developed by superposition of time-periodic electroosmotic flow on zeta potential patterned surfaces and pressure driven flow. Finite time Lyapunov exponents and filament stretching are utilized to quantify the chaotic strength, and to identify the chaotic and regular zones in the mixer at various operation conditions. Numerical solutions of the species transport equation are performed as a function of the Peclet number (Pe) at fixed kinematic conditions. Mixing efficiency is quantified using mixing index that is based on standard deviation of the scalar species distribution. The mixing length (lm) is characterized as a function of the Peclet number, and lm ∝ ln (Pe) scaling is observed under locally-optimum stirring conditions.
Micro/Nano-Scale Fluid Flows on Structured Surfaces
Authors: Chen Min , Cao Bing-Yang , Guo Zeng-Yuan
Published: June 2009

Understanding the effects of surface nanostructures on fluid flow in micro- and nano-channels is highly desirable for micro/nano-electro-mechanical systems. By way of equilibrium and non-equilibrium molecular dynamics simulations, wetting on nano-structured surfaces and liquid flow in nano-channels with structured surfaces are simulated. The surfaces show dual effects on the boundary slip and friction of the liquid flow in nano-channels. Generally, the nanostructures enhance the surface hydrophilicity for a hydrophilic liquid-solid interaction, and increase the hydrophobicity for a hydrophobic interaction. Simultaneously, the nanostructures distort the nanoscale streamlines of the liquid flow near the channel surface and block the flow, which decreases the apparent slip length. The twofold effects of the nanostructures on the surface wettability and the hydrodynamic disturbance result in a non-monotonic dependence of the slip length on the structure’s size. However, the surface structure may lead to a very high contact angle of about 170° in some cases, which cause the surface show super-hydrophobicity and lead to a remarkable velocity slip. The surface nanostructures can thus be applied to control the friction of micro- and nano-flows. In addition, the gaseous flows in micro- and nano-channels with structured surfaces are simulated. The geometry of the surface is modeled by triangular, rectangular, sinusoidal and randomly triangular nanostructures respectively. The results show that the velocity slips, including negative slip, depend not only on the Knudsen number but also the surface structure. The impacts of the surface nanostructure and the gas rarefaction are strongly coupled. In general, the slip length of a gaseous flow over a structured surface is less than what predicted by the Maxwell model, and depends not only on the Knudsen number but also the size of the surface nanostructures.
Shear and Pressure Driven Flow and Thermal Transport in Microchannels
Authors: Jaluria Yogesh
Published: June 2009

In many practical circumstances, the flow in microchannels is driven by moving surfaces that impart shear to the fluid. The shear may generate a pressure differential or the pressure may be imposed to affect the resulting flow and heat transfer. Processes where such flows arise include coating, cooling and thermal treatment of moving wires, fibers, and microscale devices. One particularly important circumstance is the optical fiber coating process, where both the entrance of the moving surface into a reservoir of fluid, as well as the exit, are of interest, since the thermal transport in the relevant microchannels influences the resulting coating very substantially. Similarly, the drawing of microscale fibers and the cooling of fibers after drawing are important in the overall manufacturing process and involve microchannel transport. This paper discusses the basic considerations in such processes, particularly the flow that arises in drawing and coating and the menisci that are observed at the inlet and outlet regions of the two microchannels. Experimental and analytical/numerical work has been carried out on these flows and the results obtained are presented. An important aspect is the pressure rise in the channel for narrowing flow domains, such as those employed in dies, and a comparison with imposed pressures. It is found that, in many practical problems, the shear generates much higher pressures than the typically imposed pressures and, thus, the flow is largely dominated by the shear effects due to the moving surfaces. It is also found that the flow develops very rapidly in forced convective cooling by gases, such as nitrogen and helium, resulting in thermal transport in a largely developed flow region. Comparisons between experimental and numerical results show fairly good agreement, indicating the validity of the model for such complex microchannel flows.
Flow Boiling Heat Transfer and Two-Phase Flow Pressure Drop in Thin-Rectangular Channels
Authors: Koizumi Yasuo , Yamada Tomonari , Ohtake Hiroyasu
Published: June 2009

Heat transfer and pressure drop of single- and two-phase flow in thin-rectangular channels of the width of 10 mm have been examined. The gap clearance δ of the flow channel covered a range from 0.6 mm to 0.1 mm. In the water single-phase flow condition, the narrowness effect came out around δ = 0.37 ∼ 0.35 mm. Below that value, the friction factor became lower than the value of the usual size in the laminar flow region and the transition from the laminar flow to the turbulent flow was delayed. The Nusselt number also showed dependency on the Reynolds number even in the laminar flow region and became lower than the value for the usual size over the whole Reynolds number region. Bubbly flow, slug flow, semi annular flow and annular flow were observed in boiling flow. The flow pattern transition agreed well with the Baker flow pattern map for the usual size. The Martinelli and Nelson method for the two-phase pressure drop of the boiling flow predicted well present experimental results. Boiling was dominant during the forced flow boiling. The heat transfer coefficient of the boiling flow was larger than the value of the usual sized flow channel. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments.
Indirect Fluorescence Detection of Non Fluorescent Analytes Using Isotachophoretic Mobility Markers
Authors: Khurana Tarun K. , Bercovici Moran , Santiago Juan G.
Published: June 2009

We have developed a method to detect non-fluorescent analytes on standard microfluidic chip platforms equipped with fluorescence detection. We leverage isotachophoresis (ITP) to electrophoretically segregate both analytes and fluorescent species termed mobility markers into distinct zones. The fluorescent marker zones bound analyte zones, so that gaps in the fluorescent signal indicate the presence and concentration of analytes. We here demonstrate separation and indirect detection of amino acids, serine and phenylalanine and organic acids, acetic acid and phenylpropionic acid (∼10 μM) using this technique. We also present an indirect detection of the environmental toxin phenol [1][2] (∼10 μM) using two mobility markers. We show preliminary numerical simulation results that provide useful guidelines in design and optimization of our indirect detection assay.
From Batch to Continuous Production Through Micro Process Technology: Chances and Challenges
Authors: Scholl Stephan
Published: June 2009

The majority of the manufacturing processes in the chemical, pharmaceutical, food or cosmetics industry is operated as batch processes. This is economically advantageous in cases where - capacities per product are low, in the range of 10 kg/a to 1000 t/a - many different educts have to be mixed and processed for the product, i.e. a recipe-based manufacturing, - many different but similar products have to be produced, - educts have to be fed at different times and with varying quantities, - educts show problematic properties such as high viscosity, solids or stickiness, - problematic processing behaviour such as fouling, foaming, viscous intermediate phases or undesired precipitation, is found, - manufacturing has to meet a sometimes stochastic market demand or - the process consist of only a few process steps like mixing, heating, reaction and cooling.
Bubble Dynamics and Boiling Heat Transfer in Microsystems
Authors: Xu Jinliang , Zhang Wei , Li Yuxiu , Gan Yunhua , Tang Qionghui , Liu Guohua
Published: June 2009

Understanding of micro boiling systems requires multiscale modeling, linking nanoscale fluid-surface interactions and micrometer channels. We present a multiscale model, successfully used for analysis of boundary conditions in microchannels. Slip lengths are found to be mainly dependent on the surface-fluid interactions, weakly on the channel sizes from nanometer to micrometer. The multiscale model is expected to be extended for bubble dynamics in microsystems, considering wall surface roughness, nano bubbles tripped in the cavities of the surface, etc. The second part gives a review on the micro bubble dynamics of pool boiling under pulse heating conditions. The third part reviews boiling heat transfer in silicon microchannels. Bubbles are being nucleated in the channel corners. Flow patterns are repeated in millisecond time-scale. Explosive boiling was found to be triggered by the higher liquid superheat, pushing liquid plugs out of microchannels. Depending on boiling numbers, three distinct heat transfer regions are identified. Heat transfer displays the nucleate boiling behavior at medium boiling numbers, and the convective heat transfer one at higher boiling numbers. The available heat transfer correlations over-predict the heat transfer performance in silicon microchannels, due to lack of nucleation sites in smooth silicon microchannels.
Development of Unsteady Flow in a Wavy Minichannel System
Authors: Oosthuizen Patrick H.
Published: June 2009

Flow through a minichannel with a square cross-sectional shape whose center-line follows a wavy path has been numerically studied. The wavy center-line path is defined by a series of circular arcs. Now when a fluid flows through such a wavy channel unsteady flow can develop at Reynolds numbers that are far below the value at which transition to turbulence occurs. The development of this unsteadiness can lead to increases in the pressure losses in the channel and to significant increases in the heat transfer rate when the channel wall is heated or cooled. To study the conditions under which unsteady flow develops with a wavy, circular arc center-line shape attention has been given to flow through a channel system in which there is a short straight entrance section followed by a wavy channel section with four full waves followed by a short straight outlet section. It has been assumed that the flow is incompressible and that there is no slip at the channel walls. The unsteady form of the governing equations have been written in dimensionless form and solved using a commercial finite-element based software package, FIDAP. The solution has the following parameters: the Reynolds number, the Prandtl number, and the dimensionless radius of the wavy portion of the channel system. Results have only been obtained for a Prandtl number 0.7 for Reynolds numbers of between 10 and 500 for various dimensionless wave radii. The solution shows that steady exists at low Reynolds numbers but that at a critical Reynolds unsteady flow exists, this critical Reynolds number depending on the dimensionless wave radius. The major concern in this work is with defining the conditions under which this unsteady flow develops and with the effect of the development of this unsteadiness on the pressure drop in the channel system.
Flow Morphology and Heat Transfer During Subcooled Flow Nucleate Boiling of HFE-7000 in Microchannels
Authors: Kuo Chih-Jung , Peles Yoav
Published: June 2009

Flow boiling was experimentally studied in parallel microchannels using coolant HFE-7000. Subcooled nucleate boiling was achieved under various thermal-hydraulic conditions for mass velocities ranging from G = 164 kg/m2·s to G = 3025 kg/m2·s. Local surface temperatures were measured and flow visualizations were conducted to obtain flow morphologies, boiling curves, and heat transfer coefficients during boiling process. It was found that heat transfer was significantly enhanced during subcooled flow boiling by bubble agitation of the liquid.
Investigation of Fouling and Its Mitigation in Silicon Microchannels
Authors: Perry Jeffrey L. , Kandlikar Satish G.
Published: June 2009

Particulate fouling studies with 4.0-μm silica and 1.25-μm alumina dispersions in water were performed in rectangular, silicon microchannels having a hydraulic diameter of 225 μm with a Reynolds number of 17. Data show the absence of particle deposition within the microchannels. The primary reason for this is the relatively high wall shear stress at the microchannel walls of 2.3 Pa compared to conventional size passageways. In contrast, the headers for the microchannels are quite susceptible to particulate fouling under the same conditions. This is because the shear stress in the header region is lower. Moreover, there is a secondary effect in particulate fouling when fibrous elements exist within the particle dispersion. The fouling behavior due to fibrous material is quite different. In fact, the presence of fibers is extremely detrimental to pressure drops within a microchannel device.
Thermal Model of Disk Coil With Directed Oil Flow
Authors: Khalil Aria Shahram , Samsami Sahar
Published: June 2009

In this paper, a developed mathematical model for temperature rise calculation is briefly described. In this model, at first, load loss of a transformer winding with forced directed oil is calculated and the winding temperature rise along the horizontal ducts and vertical ducts is computed. Then hot spot temperature and its exact location is determined. The model can also be used for optimal design of winding in size and cooling. Finally the results are given and compared with experiment values.
Energy Dissipation During Liquid Adsorption/Desorption In/From Liquid-Repellent Nanochannels
Authors: Suciu Claudiu Valentin
Published: June 2009

Ability of viscous fluids, flowing in narrow interstices, to dissipate the mechanical energy of shock and vibration is well known. In recent years, connected to the nano-technological development, solid-liquid interfaces have been used to dissipate surface energies, in systems where the solid is liquid-repellent; such interfaces are able to store, release or transform the energy. Thus, the contact angle hysteresis can be applied to dissipate the mechanical energy, and this kind of energy loss, in which not the viscosity but the surface tension of the liquid plays the main role, is called surface dissipation. In fact a liquid nano-porosimeter that exhibits nano-damping ability, when applied to mechanical systems is called colloidal damper. Concretely, during the cyclical adsorption/desorption of the liquid (e.g., water or aqueous solutions) in/from the liquid-repellent nanochannels (e.g., modified nanoporous silica gel) the energy is dissipated. Such absorber is convenient from the ecological standpoint since it is oil-free and since both the silica gel (artificial sand with controlled architecture) and the liquid are environment-friendly. Connected to this attractive kind of energy loss, one of the problems awaiting solution is that a theoretical model of the surface dissipation remains to be developed and validated by tests. Accordingly, in this work, based on a detailed discussion of the mechanism of surface dissipation one reveals that the parameters which determine the magnitude of the energy loss are the silica gel mass, the liquid and solid surface tensions, and an integral function (specific pore surface) which is related to the nano-architecture of the liquid-repellent coating, to the silica gel pore architecture and to the maximum applied pressure. Silica gel particles are supposed to be obtained through the aggregation of nano-particles, producing rough nanochannels of variable radius, and normal distribution fits quite well the measured pores size distributions. Heterogeneous molecules of the liquid-repellent coating have a methyl group as head, and a body consisted of methylene groups; they produce a nanopillar structure on the silica gel surface. Maximization of the surface dissipation for imposed working liquid or imposed coating molecule is discussed. Test rig is a compression-decompression chamber used to validate the theoretical findings. Results obtained are useful in general for the appropriate design of liquid-repellent nanochannels with technological applications, and in particular for the absorber optimum design under imposed requirements.
Pressure Drop and Heat Transfer of Fully Developed, Laminar Flow in Rough, Rectangular Microchannels
Authors: Shokouhmand Hossein , Aghvami Maziar , Afshin Mohammad Javad
Published: June 2009

In this paper, a Gaussian, isotropic distribution has been applied to model the wall roughness in microchannels of rectangular cross-section in order to investigate the friction factor and convection coefficient of fully developed, laminar and incompressible flows. As the hydraulic diameter of (micro-) channels decreases, the surface to volume ratio increases rapidly. As a result, the surface phenomena and the effect of roughness become more significant. There is a need for a better understanding of the effect of wall roughness on fluid flow characteristics in microchannels which make them well suited for a wide variety of unique cooling applications. The results of this research indicate that the friction factor and convection heat transfer coefficient increase by increasing the relative roughness of channel. The effect of changing the aspect ratio has also been investigated in this research. In addition, results are compared with experimental data obtained by different researchers.
The Principle of Nanoengines as a Tool for Designing Alloys and Controlling Corrosion Phenomena
Authors: Reda M.
Published: June 2009

Nanoengine principle is new idea that can be used to design new alloys with any desired properties, simply explain corrosion phenomenon and suggest new solutions and can help understand why alloys and composite undergo failure. Nanoengine principle is based on the simple fact that when alloys are made by mixing different metal and nonmetals together at certain ratio of these components, this will enable the formation of Nanoengine crystal structure both at the interface and at the grain-boundary. It is shown that the polarity and the size of the reactant molecule is important variable for the performance of the Nanoengine as well as the choice of the counter cation of the Heteropolyacid (Nanoengine) can determine the mechanical and thermal stability. For example, for industrial alloys, the protective mechanism of alloying using chromium, Nickel and Molybdenum is mis-understood because it will be shown that for example using about 20% chromium, almost 20% Nickel in combination with roughly 6% molybdenum (Alloy AL-6XN and 254 SMO used in space shuttle) is way too much and such a high content of chromium, Nickel and Molybdenum are not needed. The objective her is to show that it is the ratio of Ni:Cr:Mo:P:Si, the choice of counter cation, as well as the water of hydration are the important factors. This ratio and proper choice of counter cation in combination with proper alloys preparation method (water of Hydration during annealing) should be able to produce the right Nanoengine which has the desired mechanical, chemical and thermal properties. This should help in designing alloys at lower chromium and nickel content. This is based on assuming that the protective mechanism of the Nanaoengines is due to both their ability for Redox transformation combined with heterogeneous catalysis. The principle of Nanoengines can give a very precise scientific definition for the phenomena of passivity.
Laminar Convective Heat Transfer in a Microchannel With Internal Fins
Authors: Narayanaswamy Ramesh , Chandratilleke Tilak T. , Foong Andrew J. L.
Published: June 2009

A numerical study was conducted to investigate the fluid flow and heat transfer characteristics of a square microchannel with four longitudinal internal fins. Three-dimensional numerical simulations were performed on the microchannel with variable fin height ratio in the presence of a hydrodynamically developed, thermally developing laminar flow. Constant heat flux boundary conditions were assumed on the external walls of the square microchannel. Results of local Nusselt number distribution along the channel length were obtained as a function of the fin height ratio. The analysis was carried out for different fin heights and flow parameters. Interesting observations that provide more physical insight on this passive enhancement technique, and the existence of an optimum fin height is brought out in the present study.
Interfacial Flow Visualization in Microfluidic Channels
Authors: Saha Auro Ashish , Mitra Sushanta K.
Published: June 2009

Study of capillary driven flow is important in microfluidic devices. Capillary driven flows are often accompanied by formation of interface between phases of fluid participating in the flow. Interfacial flow visualization becomes necessary for tracking the transient flow in the microfluidic devices. A novel method for visualization of the meniscus interface using a standard micro particle image velocimetry (micro-PIV) apparatus is presented in this paper. The modifications carried out in the existing micro-PIV apparatus for interface tracking is described. Test samples of microfluidic channels made of glass and polydimethylsiloxane (PDMS) with different geometrical dimensions are visualized and reported. Different test fluids like DI water, isopropyl alcohol have been used in the microchannels. The parameters such as optical properties of the test sample and physical properties of the test fluid influence greatly on the resolution of the interface images. Open channel microfluidic study is also done by studying the interface phenomena of an evaporating droplet on a PDMS microchannel. The effect of the surface properties on the visualization of the evolution of the meniscus interface is emphasized. The intent of the study is to demonstrate and show how the versatility of micro-PIV can be extended for interfacial flow visualization.
A Micropatterned Surface for the Assessment of Relative Two-Dimensional Molecular Selectin Kinetics in Flow
Authors: Lawrence Michael B. , Schmidt Brian J.
Published: June 2009

Recruitment rate measurements of micro-scale particles, such as cells or microbeads, to biofunctional surfaces is difficult because factors such as uneven ligand distributions, particle collisions, variable particle fluxes, and molecular-scale surface separation distances that combine to obfuscate the ability to link the observed particle behavior with the governing nanoscale biophysics. We report the development of a hydrodynamically-conditioned micropattern catch strip assay to measure microparticle and cellular recruitment kinetics. The assay exploited patterning within microfluidic channels and the mechanostability of selectin bonds to create reaction geometries that confined a microbead flux to within 200 nm of the surface under flow conditions. Systematic control of capillary action enabled the creation of homogenous or gradient ligand distributions. The method enabled the measurement of particle recruitment rates (keff, s−1) that were primarily determined by the interaction of the biomolecular pair being investigated. The method may be well suited for analysis of reaction rates between surface-bound molecules in the presence of convective flow patterns.
Heat Capacity of Copper Thin Films Measured by Micro Pulse Calorimeter
Authors: Yu Jun , Tang Zhen’an , Zhang Fengtian , Ding Haitao , Huang Zhengxing
Published: June 2009

Thermal properties of thin films may differ from the bulk value due to the differences in microstructure, such as the grain size, impurities and defects. Heat capacity is one of the thermophysical properties and it is measured by calorimetry. However, traditional calorimeters can’t measure heat capacity of thin films which are quasi-2D and has small heat capacity. Recently, micro calorimeters with suspending membrane structure have been developed to measure the heat capacity of ultra thin films with thickness of sub-micrometer to nanometer scale. Efforts are focused on reducing heat capacitance of the addenda and minimizing the thermal link so as to permit an adiabatic measurement of the heat capacity of thin film. In this paper, a micro pulse calorimeter was developed and heat capacities of the copper thin films were measured by the micro pulse calorimetry. The heating rate of the micro calorimeter is up to 200K/ms with heating power of 4.5mW, and the heat capacity of the calorimeter is about 23.4nJ/K at 300K. Heat capacities of polycrystalline copper thin films with thickness from 20nm to 340nm were measured in the temperature range from 300K to 420K in vacuum of 1mPa. In order to extract the specific heat of the Cu films, mass of the films was calculated with volume and density of the sample film. The specific heat of the Cu films was compared with the literature values of bulk Cu. The specific heat of the 340nm Cu film is close to the literature data of bulk Cu. For the thinner films, enhanced specific heat was observed, and the data shows that the specific heat increases with the decreasing of crystalline size and film thickness.
Multifunctional Microfluidic Device Utilizing Unsteady Flow
Authors: Lee Ching-Jiun , Sheen Horn-Jiunn
Published: June 2009

This study describes experimental results for a multifunctional microfluidic device with fluid pumping, mixing and particle removal. The obstacle-type valveless micropump, micromixer and particle separator are further integrated into the proposed multifunctional device. The process for fabricating this device is simple as only 1 photo mask, 1 inductively coupled plasma (ICP) etching step and anodic glass bonding are required. This novel device was developed utilizing an unsteady flow in a microchannel induced by the piezoelectric zirconium titanate (PZT) membrane oscillation of an obstacle-type valveless micropump. Flow direction is controlled by the amplitude and frequency of power driving the vibrating membrane. The optimal operational frequency for this device is 1.0 kHz. Very high mixing (>95%) and particle removal efficiency (close to 100%) exist at the inlet region and trifurcate zone, respectively. Image processing is utilized to count the number of particles and assess removal efficiency.
Analytical Solution of Hyperbolic Heat Conduction Equation for a Finite Slab With Arbitrary Boundaries, Initial Condition, and Stationary Heat Source
Authors: Shokouhmand Hossein , Mahmoudi Seyed Reza , Habibi Kaveh
Published: June 2009

This paper presents an analytical solution of the hyperbolic heat conduction equation for a finite slab that sides are subjected to arbitrary heat source, boundary, and initial conditions. In the mathematical model used in this study, the heating on both sides treated as an apparent heat source while sides of the slab assumed to be insulated. Distribution of the apparent heat source for a problem with arbitrary heating on two boundaries is solved. The solution obtained by separation of variable method using appropriate Fourier series. Being a Sturm-Liouville problem in x-direction, suitable orthogonal functions can be allocated to hyperbolic heat conduction equation depending on the type of boundary conditions. Despite ease of proposed method, very few works has been done to solve hyperbolic heat conduction problems using this method by authors. The main feature of the method is straightforward formulation. In the analysis of heat conduction involving extremely short times, the parabolic heat conduction equation breaks down. By increasing the applications of the fast heat sources such as laser pulse for annealing of semiconductors and high heat flux applications, the need for adequate model of heat conduction has arisen. The hyperbolic heat conduction equation eliminates the paradox of an infinite speed of propagation of thermal disturbances which contradicts with Einstein’s theory of relativity. Moreover, it describes the highly transient temperature distribution in a finite medium more accurately.
Novel Design, Fabrication, and Characterization of an ElectroHydroDynamic Conduction-Micropump Using LCP MEMS Technology
Authors: Mahmoudi Seyed Reza
Published: June 2009

This paper demonstrates the design, Fabrication, and characterization of a novel electrohydrodynamic (EHD) conduction micropump. The device is based on LCP MEMS microfabrication technology. The novelty of design is due to its micro scale space between two electrodes. The pump consists of high voltage electrode, ground electrode, gasket, input/output ports, and electrical connections. The high voltage electrode consists of 75 centric annulus that were patterned on a 1.5mm LCP film with 30 μm copper clad layer as a substrate. The ground electrode was patterned using the same technology in the shape of a single circular plane avoiding any sharp point. A 230 μm -annuals liquid crystal polymer (LCP) gasket was used to fix the distance between the two substrates. Using 56 μm -resin epoxy film, two substrates are bonded together with constant distance 286 μm. The overall dimension of the micro pump is 65mm × 70mm. The flow direction in the pump was from ground electrode toward positive voltage electrode. In the absence of net flow, the device tests showed a maximum head of 105 Pa with 18 mW power consumption in absence of direct ion injection. The low level of power consumption with this pressure head generation promises a good chance to use the micropump in microgravity micro lubrication applications.
Microfabrication of Bubble Cavities in PDMS for Cell Sorting and Storage Applications
Authors: Giang Ut-Binh T. , King Michael R. , DeLouise Lisa A.
Published: June 2009

We describe a novel technique, low surface energy gas expansion molding (GEM), to fabricate microbubble arrays in polydimethylsiloxane (PDMS) which are incorporated into parallel plate flow chambers and tested in microcell culture and cell sorting applications. This architecture confers several operational advantages that distinguish this technology approach from the current state. Here in we describe the GEM molding process and the parameters that are used control microbubble formation. We introduce a vacuum-assisted coating process developed to selectively and spatially alter the PDMS surface chemistry in the wells and on the microchannel surface. We describe results from preliminary microparticle image velocimetery (μPIV) studies conducted to investigate fluid streams above and within microbubble wells and conclude with a discussion of our initial efforts to integrate optical sensors in PDMS.
Optofluidic Trapping and Transport Using Optically Resonant and Non Resonant Structures
Authors: Erickson David , Yang Allen , Moore Sean
Published: June 2009

Recently, we have demonstrated the ability to perform optically driven trapping and transport of dielectric nanoparticles using the electromagnetic energy in the evanescent field of an optically excited microphotonic waveguide. The advantage of such structures is that they allow us to condense the optical energy down to extremely small cross sectional areas (on the order of 1μm2) while simultaneously applying the impulse over indefinitely long distances (as much as several centimeters). Ultimately however both the trapping stability and transport velocity of such systems are limited by the amount of optical energy coupled into the system. In this work we review of past work and present our new work demonstrating on the use of optically resonant structures to trap and transport particles. As will be shown optically resonant structures can locally amplify the amount of electromagnetic energy, thereby enabling faster transport and greater trapping stability.