bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Performance Evaluation of a High Temperature PEM Fuel Cell at Different Temperatures and Pressures
Authors: Ubong Etim U. , Das Susanta K. , Berry K. J. , Reis Antonio
Published: June 2009

The high temperature proton exchange membranes (HT-PEM) attract growing interests due to its enhanced electrochemical kinetics, simplified pinch technology and utilization of higher CO-rich reformed hydrogen as the fuel. From the technological point of view, using pure hydrogen as fuel seems highly restrictive because hydrogen with high purity may not always be readily available. As an attractive alternative to compressed hydrogen, it is preferred to use hydrogen-rich gases as fuel. On-site generation of hydrogen using reformed fuels can be directly fed to the high temperature proton exchange membrane fuel cells (HT-PEMFCs) without first preheating the cell with external heat source to raise the temperature to its operating temperature. Since the HT-PEMFCs performance depends strongly on temperature, the cell temperature plays an important role in its operation. The purpose of this research is to experimentally study a high temperature PEM fuel cell at steady operating conditions. In this work, the performance of the fuel cell has been experimentally examined to unravel the steady-state effects of changes in temperature and pressure at a fixed hydrogen stoichiometry and variable air stiochiometries In particular, the effects that changes in temperature and pressure have on the voltage-current characteristics. Experimental data of this type is needed to develop and validate the fuel cell models, and to help understand and optimize the operation of these devices. In this study, a cell with an active cell area of 45 cm2 based on polybenzimidazole (PBI), doped with phosphoric acid is examined over the entire temperature range of 120°C–180°C with hydrogen of 99.999% purity. The quantitative results obtained from the experiments showed variations in current-voltage characteristics at different pressure and temperatures. The results will be used as a baseline value to under-study the performance of a high temperature PEM fuel cell in terms of current-voltage characteristics, when fueled with a reformate with higher CO concentrations in our future study.
Criteria for Characterizing the Performances of Fuel Cell Humidifiers: Theoretical Approach and Experimental Results
Authors: Dalet Corinne , Lottin Olivier , Maranzana Gae¨l , Diny Mouad
Published: June 2009

In a proton exchange membrane fuel cell (PEMFC), humidification of reactant gases must be carefully optimized. Extremes in humidity levels at the low end (membrane dehydratation) and at the high end of the range (cathode flooding) can seriously reduce PEMFC performances. Various devices already exist to humidify and to adjust the temperature of gas streams. Criteria for the evaluation of their performances depend on the technology and/or differ from one manufacturer to the other, which makes comparison difficult. A fortiori, there is no consensus regarding their ideal values and no general method for their evaluation. The purpose of this article is to define two parameters (efficiencies) suitable for all humidification technologies and characterizing air humidifier performances in term of mass and heat transfer. These parameters allow to compare the different technologies and to define, for all of them, the range of performances required to supply fuel cells with properly humidified gases.
Hydrogen Sulfide Induced Nickel Depletion of SOFC Anodes
Authors: Lussier Alexandre , Dvorak Joseph , Sofie Stephen , Idzerda Yves U.
Published: June 2009

Our results reveal a mechanism for permanent degradation of solid oxide fuel cells (SOFCs) by which hydrogen sulfide leads to nickel migration and depletion of the anode, thereby compromising electrical conductivity and cell operation. Additionally, we find that this process is accentuated at higher temperatures and causes depletion of near surface nickel, while deeply buried or trapped nickel remains in the anode.
Fuel Cell Distributed Generation System for Cooling
Authors: ElSherbini A. I. , Al-Qattan A. M.
Published: June 2009

Air conditioning (A/C) systems are the major consumers of power in hot climates. In a country like Kuwait, A/C accounts for 85% of power supplied to homes during peak hours and 55% of annual energy consumption by the residential sector. A fuel-cell-based cogeneration system is proposed to improve the efficiency of generating and utilizing power for cooling in residential buildings. Distributed electric power is generated by a solid oxide fuel cell (SOFC). The electricity is used to operate high-efficiency water-cooled chillers in a district-cooling setup, which replaces packaged A/C units typically used for homes. The exhaust fuel and heat from the SOFC operate a gas turbine and an absorption chiller. A thermal energy storage tank is used for storing chilled water to reduce the total capacity of the system and, hence, capital investment. The integrated fuel-cell air-conditioning (FCAC) system improves the cooling-to-fuel efficiency, expressed as coefficient of performance, by 375%. The peak power requirement is reduced by 65% and the total fuel energy is reduced by 58%. An example system of 2 MW delivers 3750 RT (13.2 MW) of cooling to a district. Over a 9-month period, it saves 94 TJ of fuel energy and feeds 5.21 GWh of electricity to the grid as a surplus.
A Dynamic Model of PEMFC System for the Simulation of Residential Power Generation
Authors: Yu S. , Kim H. S. , Lee Y. D. , Ahn K. Y.
Published: June 2009

A PEMFC System of residential power generator (RPG) has different operating strategy from the PEMFC system of transportation application because of its environmental difference. In this study, a dynamic simulation model of PEMFC system is introduced which has model for a turbo blower, a membrane humidifier, two cooling circuits, and a PEMFC stack. The thermal efficiency of the PEMFC system for the RPG is very high because it supplies the electricity and hot water to the house. This study is designed to study the dynamic response of individual components during the dynamic change of current density. In particular, since the operation of turbo blower is very sensitive at low current density, the parasitic power consumption of blower is significant. Additionally, the system performance and the operating strategy are also presented.
A Computational Analysis to Identify the Current Density Characteristics of a Micro-Tubular Solid Oxide Fuel Cell
Authors: Serincan Mustafa F. , Pasaogullari Ugur , Sammes Nigel M.
Published: June 2009

A computational fluid dynamics model is developed to study the effects of operational parameters on the performance of a micro-tubular SOFC. Coupled partial differential equations for heat, momentum, species and charge balances are solved with a commercial software using finite element method. Effect of temperature on the power characteristics of the system is addressed. Current density distributions for different temperatures are compared with the inclusion of electronic leakage currents in the electrolyte. Current density profiles for different conditions are examined thoroughly and related to the transport properties.
Design of a Double-Ejector Oxygen Recirculated System for Large-Scale Submarine Fuel Cell
Authors: Kim Minjin , Sohn Young-Jun , Kim Kyoungyoun , Lee Won-Yong
Published: June 2009

In terms of the system efficiency, it is very useful to apply the ejector into the fuel recirculation system of a fuel cell system since the ejector need no parasitic power to operate. Since the conventional automotive fuel cell use hydrogen and air as their fuel, the only hydrogen is needed to be recirculated for the better fuel efficiency. On the other hand, the submarine fuel cell needs both hydrogen and oxygen recirculation systems because the submarine drives under the sea. In particular, the cathodic recirculation has to meet the tougher target since the oxygen based pressurized stack generally used in the submarine applications generates the significant amount of the water in the stack during the operation. Namely, the oxygen utilization has designed less than 50% in the whole operating range for the better exhausting of the generated waters. The target of the oxygen utilization forces that the entrainment ratio of the ejector to be more than one in the whole range. However, the conventional ejector using a constant nozzle can not afford to satisfy the mentioned critical requirement. To overcome the problem, the double-ejector and its control strategy are designed. The performance of the proposed double-ejector is verified by the experiments based on the real operating conditions of the target submarine system. Furthermore, the proposed design method can be used for the other fuel recirculation system of a large-scale fuel cell system with the critical requirement of the fuel utilization.
Mechanical Properties of Ceria Based Oxygen Ionic Conductors for SOFC
Authors: Yugami Hiroo , Iguchi Fumitada , Sato Kazuhisa , Hashida Toshiyuki
Published: June 2009

The fracture strength and creep rate of rear earth (Y and Gd) doped ceria are systematically studied from the viewpoints of dopant concentration, oxygen partial pressure and temperature dependences. Fracture strength and creep rate are measured by modified small punch test and four point bending method, respectively. From results of fracture test, the highest fracture strength is obtained on the samples sintered at 1600 °C for Y and Gd-doped CeO2. The unique temperature dependence of fracture strength on doped CeO2 is observed. It shows the local minimal value at around 600 °C and the fracture strength increases with increasing temperature. The fracture surface structure drastically changes with changing temperature observed by SEM. Since we observed the close coincidence between the fracture strength and the ratio of transcrystalline fracture surface for all samples, it is concluded that the increase of fracture strength at high temperature in doped CeO2 can be attributed to the temperature dependence of transcrystalline fracture strength. Typical creep curves of 2, 5, 10 and 20 YDC were measured under constant load in air. The creep rate decreases with increasing the dopant concentration. From the analysis of creep properties, the creep is controlled by cerium vacancy diffusion and change of ceria vacancy concentration decreases creep rate.
A Comprehensive Analysis Procedure for Predicting the Performance of a Molten Carbonate Fuel Cell
Authors: Choi D. H. , Kim H. S.
Published: June 2009

A three-dimensional numerical procedure to predict the performance of a molten carbonate fuel cell has been developed. The Navier-Stokes, energy, and species equations are solved to obtain the velocity, temperature, pressure, and concentration distributions in the cathode/ anode channel. The channel with the trapezoidal supports is approximated by an anisotropic porous medium, of which the effective permeability and conductivity are obtained by separate 3D FVM calculations. For a given average current density, the local current density, which is directly related to the rate of chemical reaction and heat generation on the reaction surface, and the cell voltage are determined to satisfy the electrochemical relations at the electrode surface. The process is iterative and the solution is assumed to have converged when the cell voltage and the local current density fall within the specified convergence limits. The unit cell characteristics, such as current-density distribution, and average current density vs. cell voltage are presented and discussed. Once the relation between the flow rate and the pressure loss in a unit cell are known, the mass flow to each cell of a MCFC stack is estimated by coupling the manifold flow and the flow within the unit cell. The stack performance is then calculated by integrating the individual cell performance using this information.
Experimental Evaluation of Air Flow Effect in Gas Diffusion Layer on PEM Fuel Cell Performance
Authors: Tabe Yutaka , Yoshida Daisuke , Kikuta Kazushige , Chikahisa Takemi , Kozakai Masaya
Published: June 2009

This paper investigated the effects of gas and liquid water flow on the performance of a polymer electrolyte membrane (PEM) fuel cell using cells to allow direct observation of the phenomena in the cell and measurements of the local current density and the local pressure loss. The experimental results to compare the separator type indicated the effect of cross-over flow in the gas diffusion layer (GDL) under the lands of serpentine separators on cell performance and the potential of straight channel separator to achieve a relatively-uniform current density distribution. To evaluate the cross-over flow under the land of serpentine separators, a simple circuit model of the gas flow was developed. This analysis showed that slight variations in oxygen concentration caused by the cross-over flow under the land affect the local and overall current density distributions. It was also shown that the establishment of gas paths in the deep layer of GDL by the channels filled with condensed water is effective for stable operation at low flow rates of air in the straight channels.
CFD Analysis of a Two-Phase Flow Model for a Low Temperature Proton Exchange Membrane Fuel Cell
Authors: Das Susanta K. , Berry K. J.
Published: June 2009

To understand heat and water management phenomena better within an operational proton exchange membrane fuel cell’s (PEMFC) conditions, a three-dimensional, two-phase flow model has been developed and simulated for a complete PEMFC. Both liquid and gas phases are considered in the model by taking into account the gas flow, diffusion, charge transfer, change of phase, electro-osmosis, and electrochemical reactions to understand the overall dynamic behaviors of species within an operating PEMFC. The model is solved numerically under different parametric conditions in terms of water management issues in order to improve cell performance. In this paper, mostly cathode side results of a complete PEMFC are presented. The results obtained from two-phase flow model simulations show improvement in cell performance as well as water management under PEMFCs operational conditions as compared to the results of a single phase flow model available in the literature. The quantitative information obtained from the two-phase model simulation results will help to open up a route in designing improvement of PEMFC for better operational efficiency and performance.
On-Board Hydrogen for High Temperature PEM Fuel Cell Stack by Methane and Methanol Steam Reforming
Authors: Kolavennu Panini , Das Susanta K. , Berry K. Joel
Published: June 2009

In this study, an in-house testing facility was used to examine the effect of CO concentration on the high temperature PEM fuel cells. Using the CO tolerance as a design parameter, a fuel processor based on steam reforming is designed using both methane and methanol as fuel. A simulation analysis based on a kinetic model is performed to investigate both methane and methanol as fuel for a potential source of hydrogen. Using simulation results, an analysis of the fuel processor and fuel cell stack is performed. The effect of steam to carbon ratio and reformer operating temperature on the overall reformer system’s performance is studied. The system was designed for a 5kWe auxiliary power unit (APU) which can be used as a combined heat and power generation system.
Ethanol Transport and Chemistry in Solid Oxide Fuel Cells
Authors: Daggett James M. , Sullivan Neal P. , Kee Robert J. , Zhu Huayang , Dean Anthony M.
Published: June 2009

Biofuels are receiving significant interest as a source for sustainable, locally produced hydrocarbon fuels. While solid-oxide fuel cells (SOFCs) can operate efficiently on biomass fuel streams, their use can prove problematic if process conditions are not carefully monitored, as carbon-deposit formation presents a significant risk. In this study, we examine the chemistry and transport processes underway when SOFC anodes are exposed to ethanol-steam mixtures. Through use of a unique Separated-Anode Experiment, this study decouples anode chemistry processes from charge-transfer, cathode-activation, and other electrochemical processes in an effort to focus on ethanol decomposition in SOFC environments. Experiments are combined with numerical simulations that include Dusty-Gas transport modeling within the anode pore structure, and elementary, multi-step heterogeneous and homogeneous chemical kinetics mechanisms representing fuel conversion within the anode. Process windows for deposit-free operation are postulated, and alternate anode architectures that minimize the risk of deposit formation are discussed.
Hexaaluminate Catalysts for Fuel Reforming
Authors: McGuire Nicholas E. , Sullivan Neal P. , Kee Robert J. , Zhu Huayang , Nabity James A. , Engel Jeffrey R. , Wickham David T. , Kaufman Michael
Published: June 2009

Hexaaluminate catalysts offer excellent high-temperature stability compared to the equivalent metal-based catalysts. Their stability also lends well to use as a catalyst support. However, use of novel hexaaluminates is limited in fuel processing for fuel-cell applications. In this paper, we report on the performance of hexaaluminates as a catalyst support in the steam reforming of methane. The hexaaluminates are synthesized by a metal-exchange process using alumoxane precursors that enable a wide range of metal substitutions. Performance is evaluated using a unique stagnation-flow reactor that enables detailed probing of the boundary layer above the catalyst-impregnated stagnation surface. Experimental results are compared with models to understand fundamental reaction kinetics and optimize catalyst performance. RhSr-substituted hexaaluminates with a Rh impregnation are shown to yield the best performance. Scanning- and Transmission-Electron Microscopy are used to characterize the different types of hexaaluminates, and to examine the effect of aging on catalyst structure.
Water Management Scheme for a 3-kW JP-8 Steam Reformer-SOFC Power System
Authors: Sishtla Chakravarthy , Wangerow James R. , Hill Andy H. , Onischak Michael , Holcomb Franklin H.
Published: June 2009

Diesel or JP-8 fueled SOFC power systems are envisioned for both critical and non-critical military use such as auxiliary power units (APUs), portable power, tent cities, camp kitchens, and permanent stationary power [1]. A system that eliminates or minimizes the addition of make-up water is a great advantage in these applications. This paper presents an approach for water recovery from the spent anode exhaust gas for use in the JP-8 steam reformer [2]. A key objective of this on-going effort is to configure an internal water management scheme for the system to recover water for the JP-8 fuel processor steam-reforming requirements. The approach used was to combust the water-laden SOFC anode exhaust gas (AEG), condense and recycle the water to the reformer. HYSYS simulation performed on the configured system indicated that over 91% of fuel processor water requirements can be obtained in this approach to maintain a steam-to-carbon (S/C) ratio of 4. The S/C ratio was set at 4 to ensure a high JP-8 conversion and prevent carbon formation in the reformer. Operational tests at simulated system conditions confirmed >91% water recovery as predicted. System tests of this scheme indicate that it is feasible to combust and recover product water for reforming, minimizing makeup water requirements. The results from the system tests are promising for configuring stationary power systems for military use where water availability is limited.
Numerical Simulation of SOFC Performance Affected by Cathode Mesoscale-Structure Control
Authors: Konno Akio , Iwai Hiroshi , Saito Motohiro , Yoshida Hideo
Published: June 2009

Increase of the current density is one of the most important topics in the development of solid oxide fuel cells. In this study we focus on the possibility of the current density enhancement by controlling the mesoscale structure of the electrodes. Modifications of the mesoscale structures increase the area of electrode-electrolyte interface and the volume of the electrode, reduce the electrolyte thickness, affect gas diffusion in the porous electrode and consequently influence the cell performance. To evaluate its effect on the cell performance, two-dimensional numerical simulation for SOFC with and without mesoscale grooves on the cathode-electrolyte interface is conducted to understand the effects of such cathode mesoscale structure on the cell performance. It is found that the electrochemical reaction in porous electrodes takes place in the region close to the electrode-electrolyte interface and the cell performance can be improved by applying cathode mesoscale structures.
Determination of the Relationship Between Capillary Pressure and Saturation in PEMFC Gas Diffusion Media
Authors: Sole Joshua D. , Ellis Michael W.
Published: June 2009

This paper describes a method of measuring the relationship between capillary pressure and porous media saturation in the gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEMFC). Such a relationship is commonly used to model the liquid water flow in the GDL. The method utilized to characterize the GDL behavior mimics the actual transport of liquid water within the GDL by utilizing the actual fluids of interest in a PEMFC cathode (water and air), and by introducing all water from a single face to simulate the water production at the catalyst layer. Other porosimetry methods rely on totally non-wetting or totally wetting fluids to achieve saturation and consequently the resulting capillary pressure measurements must be scaled to the emulate the situation in the PEMFC GDL. Capillary pressure versus saturation curves for two different GDL materials (one paper, one cloth), each with four different bulk loadings of PTFE (0, 10, 20 and 30 wt%), were measured. Results show that the PTFE loading has a relatively small effect on the capillary pressure within the pressure range normally associated with PEMFC water transport. The results also show that carbon cloth based GDL materials require greater capillary pressures than paper materials to achieve significant saturation and that compression has a homogenizing effect on the pore structure and the slope of the capillary pressure – saturation Pc(S) behavior of both materials. Representative curves for the derivative of the Pc(S) function are developed for each type of diffusion media within the appropriate saturation range.
Fabrication of Anode-Supported Micro-Tubular Solid Oxide Fuel Cell Using an Extrusion and Vacuum Infiltration Technique
Authors: Song Jung-Hoon , Sammes Nigel M. , Zhang Xiaoyu
Published: June 2009

A simple and mass productive extrusion technique was applied to fabricate anode-supported micro-tubular solid oxide fuel cells (SOFCs). A standard NiO/8YSZ (Nickel oxide/8 mol % yttria stabilized zirconia) cermets anode, 8 YSZ electrolyte, and LSM (Lanthanum strontium manganite) cathode were used as the materials components. SEM (secondary electron microscopy) images indicated vacuum infiltration method successfully generated the thin electrolyte layer (10∼15 μm) with a structurally effective three phase boundaries. Fabricated unit cell showed the open circuit voltage of 1.12 V without any fuel leaking problems. Electrochemical tests showed a maximum power density up to 0.30 W/cm2 at 800 °C, implying the excellent performance as micro-tubular SOFCs. This study verified that the extrusion aided by vacuum infiltration process could be a promising technique for mass production of microtubualr SOFCs.
Mixing Enhancement by Induced-Charge Electrokinetic Flow
Authors: Wu Zhemin , Li Dongqing
Published: June 2009

The induced-charge electrokinetic flow (ICEKF) in a rectangular micorchannel with conducting hurdles embedded in the middle is investigated in this paper. A correction method is suggested to numerically estimate the induced zeta potential on the conducting surface. Two-dimensional pressure-linked Navior-Stokes equation is used to model the flow field in the channel. The numerical results show flow circulations generated from the induced non-uniform zeta potential distribution along the conducting hurdle surfaces. It is demonstrated numerically that the local flow circulations provide effective means to enhance the flow mixing between different solutions; the degree of enhancement depends on the hurdle geometries and hurdle numbers. The mixing using ICEKF described in this paper can be used in various microfluidics and lab-on-a-chip applications.
Design of Wavelength-Selective Surfaces for Mid-Infrared Detectors Using Heavily Doped Silicon Complex Gratings
Authors: Chen Y.-B. , Zhang Z. M.
Published: June 2009

The feasibility of using complex gratings for mid-infrared wavelength-selective absorbers is investigated. Nano/microscale surface features are employed for tailoring thermal radiative properties, which are much different from those of plain surfaces. High absorptance from heavily doped ( > 1×1020 cm−3) silicon for the transverse magnetic wave incidence can be achieved with one-dimensional periodic gratings by exciting surface plasmon polaritons. For simple binary gratings, the associated absorptance peak is narrowband and directional sensitive. These drawbacks can be remedied by using complex gratings, whose features are a superposition of multiple simple surface-relief gratings. The spectral absorptance displays a peak whose full-width-at-half-maximum (FWHM) exceeds 1.5 μm and is less sensitive to the angle of incidence. Moreover, the peak wavelength can be adjusted by varying the doping concentration and grating geometry. This study demonstrates that the use of complex gratings may significantly enhance the performance of infrared detectors.
Growth of Micro Bubbles on Micro-Configured Metal-Graphite Composite Surfaces and Boiling Enhancement
Authors: Chao David , Zhang Nengli , Yang Wen-Jie
Published: June 2009

A series of studies in nucleate boiling phenomena on metal-graphite composite surfaces has been investigated by Prof. Wen-Jei Yang and their associates. It has been discovered that the unique micro-configured construction of the composite surfaces plays a crucial role in the enhancement of boiling heat transfer. The present paper focuses on the formation and growth processes of micro bubbles and the micro/nano scale boiling behavior to reveal the mechanism of boiling heat transfer enhancement on the unique surfaces. The growth processes of the micro and macro bubbles are analyzed and formulated followed by an analysis of bubble departure. Based on these analyses, the enhancement mechanism of the pool boiling heat transfer on the composite surfaces is clearly revealed. The micro-configured composite surfaces provide more even distribution of a great number of stable boiling active sites through the graphite fibers. Consequently, the heat conduction through the layers is increased, which provides the power of phase change at the interfaces on bubble bottoms. Experimental results convincingly demonstrate the enhancement effects of the unique structure of metal-graphite composite surfaces on boiling heat transfer.
Numerical Investigation of a Novel Grooved Vapor Chamber
Authors: Zhang Ming , Liu Zhongliang , Ma Guoyuan
Published: June 2009

An effective thermal spreader can achieve more uniform heat flux distribution and thus enhance heat dissipation of heat sinks. Vapor chamber is one of highly effective thermal spreaders. In this paper, a novel grooved vapor chamber was designed. The grooved structure of the vapor chamber can improve its axial and radial heat transfer and also can form the capillary loop between condensation and evaporation surfaces. A two dimensional heat and mass transfer model for the grooved vapor chamber is developed. The numerical simulation results show the thickness distribution of liquid film in the grooves is not uniform. The temperature and velocity field in vapor chamber are obtained. The thickness of the liquid film in groove is mainly influenced by pressure of vapor and liquid beside liquid-vapor interface. The thin liquid film in heat source region can enhance the performance of vapor chamber, but if the starting point of liquid film is backward beyond the heat source region, the vapor chamber will dry out easily. The optimal filling ratio should maintain steady thin liquid film in heat source region of vapor chamber. The vapor condenses on whole condensation surface, so the condensation surface achieves great uniform temperature distribution. By comparing the experimental results with numerical simulation results, the reliability of the numerical model can be verified.
Investigation on the Steady Thermal Resistance of Axial Grooved Heat Pipe (AGHP)
Authors: Tao Hanzhong , Zhang Hong , Zhuang Jun
Published: June 2009

According to the classic thermal resistance network model of the heat pipe, a quasi-two-dimensional theoretical thermal resistance model for the horizontal axial grooved heat pipe (AGHP) under normal conditions is presented. The contact type between liquid working fluid and groove wall at various axial positions are considered. The two-dimensional mass balance equation and momentum equation are adopted to predict the contact type between liquid working fluid and groove wall, contact point position and the radius of curvature of liquid pool. For the condensate thickness and liquid pool depth, three cases are discussed. The liquid pool depth and circumference radius of curvature of each element along the axial direction can be obtained based on the force balance. The elemental thermal resistance is obtained by superposing the compound layer thermal resistance of liquid working fluid and wick, and conductivity thermal resistance of container wall. Paralleling connection the element thermal resistance at the evaporator and the condenser of the AGHP respectively, the thermal resistance of evaporator and condenser are obtained respectively. The overall thermal resistance of the AGHP can be gotten by adding the two parts thermal resistance. The filling amount of working fluid is the sum of vapor and liquid inner the AGHP. The amount of liquid working fluid is the sum of each element in all the grooves. The results from the model are matched the testing results and the traditional semi-empirical correlation.
The Enhancement of Marangoni Condensation Heat Transfer by Addition of Additives
Authors: Peng Baohong , Yang Li
Published: June 2009

This paper investigated the heat transfer process that the condensing occurred on the tube and the vapor has been added with effective additives. The effective additives trigger interfacial convection that leads to loss of hydrodynamic stability at the liquid/vapor interface and produce a spontaneous disturbance in the condensate liquid. As a result, condensation heat transfer is significantly increased. Both physical models included the condensate liquid film and mathematical model based on the boundary layer equation were given and then transformed to a non-dimensional form by applying the similarity theory. The main concept of developing the model is to understand the basic mechanism of surface tension effect on the process of steam condensation.
Optofluidics: Fluidics Enabling Optics and Optics Enabling Fluidics
Authors: Erickson David , Mandal Sudeep , Yang Allen , Goddard Julie , Cordovez Bernardo
Published: June 2009

Optical devices which incorporate liquids as a fundamental part of the structure can be traced at least as far back as the 18th century where rotating pools of mercury were proposed as a simple technique to create smooth mirrors for use in reflecting telescopes. Modern microfluidic and nanofluidics has enabled the development of a present day equivalent of such devices centered on the marriage of fluidics and optics which we refer to as “Optofluidics.” In this review paper we will present an overview of our approach to the development of three different optofluidic devices. In the first of these we will demonstrate how the fusion of novel nanophotonic structures with micro- and nanofluidic networks can be used to perform ultrasensitive, label free biomolecular analysis. This will be done in the context of our newly developed devices for screening of Dengue and Influenza virus RNA. For the second class of device I will discuss and demonstrate how optical forces (scattering, adsorption and polarization) in solid and liquid core nanophotonic structures can be used to drive novel microfluidic processes. Some of the advanced analytical, numerical and experimental techniques used to investigate and design these systems will be discussed as well as issues relating to integration and their fabrication.
Parametric Study of the Porous Cathode in the PEM Fuel Cell
Authors: Zhang Zhuqian , Jia Li
Published: June 2009

The electrochemical behavior and the reactant transport in the porous GDL and CL are controlled by a large number of parameters such as porosity, permeability, conductivity, catalyst loading, and average pore size etc. A three-dimensional PEM fuel cell model is developed. The model accounts for the mass, fluid and thermal transport processes as well as the electrochemical reaction. Using this model, the effects of the various porous electrode design parameters including porosity, solid electronic conductivity and thermal conductivity of cathode GDL, and the catalyst loading, average pore size of cathode CL are investigated through parametric study. The model is shown to agree well with experimental data over a substantial range of the porous electrode specifications. In addition, the model shows promise as a tool for optimizing the design of fuel cells.
A Thermal Lattice Boltzmann Model for Micro/Nano-Flows
Authors: Zhang Y.-H. , Gu X.-J. , Barber R. W. , Emerson D. R.
Published: June 2009

With the development of micro/nano-devices, low speed rarefied gas flows have attracted significant research interest where successful numerical methods for traditional high speed flows, including the direct simulation Monte Carlo method, become computationally too expensive. As the Knudsen number can be up to the order of unity in a micro/nano flow, one approach is to use continuum-based methods including the Navier-Stokes-Fourier (NSF) equations, Burnett/super Burnett equations, and moment models. Limited success has been achieved because of theoretical difficulties and/or numerical problems. The recently developed lattice Boltzmann equation (LBE) offers a fundamentally different approach which is close to kinetic methods but with a significantly smaller computational cost. However, success of LBE methods for rarefied gas motion has been mainly on isothermal flows. In this paper, thermal rarefied gas flows are investigated. Due to the unique features of micro/nano flows, a simplified thermal lattice Boltzmann model with two distribution functions can be used. In addition, kinetic theory boundary conditions for the number density distribution function can be extended to construct a thermal boundary condition. The model has been validated in the slip-flow regime against solutions of the NSF equations for shear and pressure driven flows between two planar plates. It is shown that the present thermal LBE model can capture some unique flow characteristics that the NSF equations fail to predict. The present work indicates that the thermal lattice Boltzmann model is a computationally economic method that is particularly suitable to simulate low speed thermal rarefied gas flows.
Coupling Effect of Interfacial Transport on Particle-Surface Capillary Forces
Authors: Gao Bo , Peng Xiaofeng
Published: June 2009

In this investigation, an interest is addressed on getting some fundamental insights on the theoretical analysis of inter-particle forces and interfacial evaporation induced by the existence of liquid at pore level. The imbalance of capillary attractive forces and great potential of heat/mass transport at interfaces are found to be most important in driving the dynamic evolution of the system. Connected by micro liquid layer lying among particle(s) and supporting plate, the particle-surface system can experience both repulsion and attraction interactions. Based on the theoretical model proposed in current investigation, the particle’s mechanical status is found to be closely dependent on particle-surface distance, contact line radius, contact properties and mean curvature of the interface. Meanwhile, geometrical information and governing equations bridge interfacial transport together with possible particle movements.
Solutions of SAT Problems Solved by a SPR-Based DNA Processor
Authors: Chang Tsung-Yao , Lin Chii-Wann
Published: June 2009

DNA computation has shown its potential not only on mathematics, but on various practical areas such as diagnosis, single nucleotide polymorphism (SNP) detection, smart amplification, encryption and drug delivery etc. However, most previous researches about DNA computation possess a couple of weaknesses, including time-wasting, effort-wasting, lack of reusability and no miniaturization. In order to address this issue and improve weaknesses mentioned above, we built up a surface plasmon resonance (SPR) system for the detection on the DNA array chip to solve a 3-clause satisfiability (SAT) problem with 3 variables x, y and z. Every variable is defined as a 15-nt single strand DNA (ssDNA) which is immobilized on one spot of the gold surface. We further define SPR reflective intensity changes 0, 0.2 and 2 A.U. caused by changes of molecular weight on surface as Boolean signals False, True and None, respectively. Moreover, False signal represents a positive hybridization reaction via the hydrogen bond that binds the complementary ssDNA conjugating to IgG (150 kDa) by the crosslinker Sulfo-SMPB which can links thiol group labeled on ssDNA and amine group existed on IgG; True signal represents the hybridization reaction that binds the complementary ssDNA-IgG-Antigen which can result in a much larger intensity change. For a SAT problem F = (XT ∪ YF)∩(XF ∪ ZT)∩(YT ∪ ZT), there are 8 possible answers. Therefore, we established a 3-spot array as a set which is immobilized sequence x, y and z. After one calculation, we read out the solution of this set and then regenerate it by injecting 0.05 N sodium hydroxide solution. In this work, we used 200 ng/ml Xc-Human IgG, Yc-Rabbit IgG and Zc-Goat IgG as reaction agents for hybridization which represent False signal. Furthermore, 100 ng/ml Anti-Human IgG, Rabbit IgG and Goat IgG were taken as True signal agents. A full reaction can be completed within 30 minutes at room temperature. The buffer in the study is 1 x phosphate buffered solution (PBS) with 100 mM sodium chloride. The proposed platform has improved drawbacks that occurred in previous researches about DNA computer. Besides, it is provided with abilities a processor should have which are recalculable and realtime measurement so that provides us a novel approach for addressable and reusable diagnosis.
An Electromagnetic Actuator in Lab-on-a-Chip Systems
Authors: Lee Chia-Yen , Chen Zgen-Hui , Wen Chih-Yung
Published: June 2009

A novel technique for the fabrication of electromagnetic micro actuators was proposed and a prototype was designed and fabricated in this study. The constituent parts of the designed actuator are comprised of the diaphragm, the micro coils, and the magnet. When an electrical current was applied to the micro coils, the magnetic force between the magnet and the coil is produced, causes the diaphragm to deflect and becomes the source of actuation. The fabrication process of the actuator combines Optical Lithography, Electron Beam Evaporation, and Electroplating. The structure of the actuating device uses PDMS as the vibrating diaphragm and electroplated copper as the coils. The diaphragm deflection can be regulated by varying the electrical current passed through the micro coil and hence the actuating effects can be controlled. The experimental results show that the maximum diaphragm deflection within elastic limits is 150 μm at an electrical current of 0.6 A for a micro coil of 100 μm line width. The micro electromagnetic actuator proposed in this study is easily fabricated and is readily integrated with Lab-on-a-Chip systems due to its planar structure.
Prediction of Bulk Density of Microencapsuated Phase Change Material Slurry
Authors: Dai Chuanshan , Wang Huajun , Zhang Liang
Published: June 2009

The use of phase change material (PCM) particles suspended in a liquid-phase carrying fluid can provide additional thermal capacity from the latent heat associated with the solid-liquid phase changing process. It has the advantages of capable flowing and simultaneously a high effective heat capacity in a certain temperature range. However, the bulk thermophysical properties are very specific and may vary with many parameters such as particle geometry, chemical component, fabrication technology and temperature. This paper proposed a theoretical model for predicting the bulk density of microencapsulated PCM slurry in solid-liquid phase changing process basing on a thermodynamic analysis of free energy and Gibbs-Thomson theory. The effects of particle size and distribution, mass concentration and surface tension of PCM on the bulk slurry density were investigated.
Molecular Dynamics Simulations of Nanoscale Water Jet
Authors: Lin Jau-Wen , Chu Shu-Xian
Published: June 2009

This paper represents molecular dynamics simulations of pressurized ejection of water nanojet and water droplet formation process. In the simulations, the effects of nozzle opening size, pressing force and temperature on the nano water droplet formation are investigated. The relation of droplet shape with flow rate at the nozzle opening is also discussed. The data from these simulations are analyzed to get a physical insight view of nano water droplet formation.
DNA Amplification Efficiencies of PCR Chips Using Different Heaters and Channels
Authors: Chung Yung-Chiang , Ye Chuan-You , Lai Li-Wei
Published: June 2009

This paper presents the effect of temperature distributions in different heaters and channels on DNA amplification for polymerase chain reaction biochip. We utilized the Micro-Electro-Mechanical System to complete biochip accuracy. The TPX (Poly-4-methyl-pentene-1) was used as the polymer material. The microchip composed of two parts. One is the heater and temperature sensor on a top cover, the other is the microchannel and reaction chamber on a bottom substrate. Then we designed two kinds of chip materials: 1. a glass cover and a TPX substrate, 2. a TPX cover and a TPX substrate. Temperature is the most important in PCR, so the more uniform one is better. And we designed two kinds of heater. According to heat conduction simulation, we can find the best heater pattern. The simulation result is that the design of long inside distance and short outside distance between heater columns was the best one. The reagent of 10 μL was repeated twenty-five cycles to complete PCR process. The temperature controller could reach the speed of heating 20° C /sec and the speed of cooling 5°C /sec. Thus the PCR process could be achieved for twenty-five cycles within 35 minutes. Finally we used the instruments to check DNA amplification result qualitatively and quantitatively. The DNA amplification length was 108 bps. The DNA amplification of long inside distance and short outside distance between heater columns was 90.17 ng/μL, and was larger 12 ng/μL than that of equally distances. Excellent correlation between simulation analysis and experimental result was obtained in this study.
Flow Characteristics and Convection Heat Transfer in Microporous Media
Authors: Jiang Pei-Xue , Xu Rui-Na , Zhao Chen-Ru
Published: June 2009

The flow characteristics of water and air in micro porous tubes with average diameters of 200 μm ∼ 10 μm were studied experimentally and numerically. The results showed that compressibility significantly influence the air flow in porous media with the particle diameters of 200 μm ∼ 10 μm, which increases the friction factor in porous media. Rarefaction effects occur in air flows in the microporous media with particle diameters less than 90 μm. New correlations for K and F were proposed with consideration of Kn. The numerically predicted friction factors for the slip-flow regime in the micro-porous media with 90 μm ∼ 10 μm diameter particles were less than the known correlation and close to the experimental data. The internal convection heat transfer coefficients between particles and fluid in the micro porous media were determined experimentally and numerically. The experimental data for the micro porous media with particle diameters of 20 and 10 μm are much lower than the previously published results. A new correlation for Nusslet number was proposed with consideration of the influence of Kn. Numerical calculation with consideration of slip-flow and temperature jump in micro porous media can properly simulate internal convection heat transfer.
Design and Fabrication for Coplanar Type of Micro-DMFC
Authors: Yao Da-Jeng , Hsu Chih-Peng
Published: June 2009

This research is to fabricate μ-DMFC (micro direct methanol fuel cell) by using MEMS technology. A novel concept of design, compared with the traditional type of DMFC, has been designed and fabricated, which anode and cathode are made in the same plane so called coplanar type of DMFC. In this coplanar type of DMFC, we can also integrate the current collectors and catalyst layer on the flow channels. In order to improve the performance of entire system, we also integrate the fuel preheat device on the chip, so heater was put on the flow channels. By the heating effect, we apply voltage on both sides to increase operation temperature. The experiment results show that when we apply 41 volts on the pads, system average temperature will reach 70°C. Then the fuel (2M CH3OH / 2.5M H2SO4 / H2O) was fed into anode, and (O2-sat. / 2.5M H2SO4 / H2O) was fed into cathode, operating under 70°C. The maximum power was reached around 0.956mW/cm2 at 4.978 mA/cm2.
Flow Characteristics of Rarified Gases in Micro-Grooved Channels by the Lattice-Boltzmann Method
Authors: Guzma´n Amador M. , Di´az Andre´s J. , Sanhueza Luis E. , Escobar Rodrigo A.
Published: June 2009

The flow characteristics of a rarified gas have been investigated in microgrooved channels. The governing Boltzmann Transport Equation (BTE) is solved by the Lattice-Boltzmann method (LBM) for the Knudsen number range of 0.01–0.1. First, the compressibility and rarified effects are investigated in a plane channel by performing numerical simulations for different Knudsen numbers, pressure ratio and accommodation coefficients with the objective of validating the computational code used in this investigation and determining the transition characteristics from the macro to microscale. The numerical predictions are compared to existing analytical and numerical results. Then, numerical simulations are performed for microgrooved channels for the Knudsen numbers range of [0.01–0.1]. Different meshes are used for preserving numerical stabilities and obtaining accurate enough numerical results. For the microgrooved channel configuration, the fluid characteristics are determined in terms of pressure ratio and Knudsen numbers. The numerical results are compared to existing analytical predictions and numerical results obtained from plane channel and one cavity simulations.