bluuebunny/crossref_metadata_2025 huggingface dataset:
Wireless Networking of Rail Sensors on Continuously Welded Rail
Authors: Bilodeau James , Clark Kevin , Gregg David , Pier Heath
Published: November 2010

Railroads around the world are trying to increase hauling capacity on an already over-burdened rail system. This results in increased rail maintenance, increased cost from slow orders and increased risk of track failures. However, monitoring rails for neutral temperature drift, rail buckling and rail breaks is becoming easier and more cost effective with improved sensor technology. One major improvement is the ability to monitor long stretches of rail by networking a series of sensors together. This results in complete track coverage for a reasonable cost. New sensor technology capable of transmitting data wirelessly over several miles of track is presented in this paper. The antenna configuration is a critical factor to achieve adequate signal strength within several inches of the ground. The research presented here shows that it is possible to use the rails themselves as waveguides to help guide wireless signals down the rails to the next sensor.
Revising the UIC 406 Method: Revenue Generating Capacity
Authors: Khadem-Sameni Melody , Landex Alex , Preston John
Published: November 2010

The UIC 406 method has been published by the International Union of Railways (UIC) in 2004 and quantifies capacity utilisation for a given infrastructure. It is generally suitable for capacity analysis in European railways that are focused mainly on passenger operations and run according to exact timetables. This method defines railway capacity as “the total number of possible paths in a defined time window, considering the actual path mix or known developments respectively”. To measure the railway capacity consumption, timetable graphs can be used where by the given infrastructure and the type of rolling stock are implicitly included as they determine the size of the blocking stairs. The capacity consumption is measured by compressing the timetable graphs so that the buffer times are equal to zero. This paper adopts a system approach toward railways and describes the interactions between its different subsystems. Infrastructure management is discussed in the context of performance evaluation. The significance of timetable is stressed as what links all railway subsystems together, determining performance of the whole railway system. Timetable characteristics that affect railway capacity are discussed followed by current theoretical methods to evaluate railway capacity by compressing the timetable. Some of the weaknesses of the UIC 406 method are identified and discussed. To tackle them, the authors define a new term as “Revenue generating capacity” that analyses capacity utilisation according to an estimation of revenue, taking into account wider socio-economic benefits. A weighted UIC method that considers a proper weight for different types of trains that takes into account the revenue generated based on the train type, load factor as well as probability and costs of delays is suggested for further research.
Effect of Flow Arrangements on Thermohydraulic Performance of a Microchannel Heat Sink
Authors: Sehgal Satbir S. , Murugesan Krishnan , Mohapatra S. K.
Published: November 2010

The advancements in fabricating and utilizing microchannel heat sinks (MCHS) for cooling of electronic devices during the last decade has not been matched by corresponding advances in our fundamental understanding of the unconventional micro fluidics. Many theoretical and experimental studies have been reported for the heat transfer analysis along the direction of flow within the microchannels, but to the best knowledge of the authors, the effect of the size of the inlet and outlet plenum and direction of the flow to the plenums was not studied exhaustively till date. The liquid is supplied to the microchannels via the inlet and outlet plenums and this can be achieved by many flow arrangements. Due to the small size of the channel dimensions, the entrance and exit conditions will significantly affect the heat transfer characteristics of the flow field in the channel. Instability effects at the entrance and exit regions of the micro-channel also need to be fully understood for efficient design of microchannel heat sinks. This paper presents an experimental study that has been conducted to explore the effect of entrance & exit conditions of the liquid flow within a copper micro-channel heat sink (MCHS). Three test pieces having inlet & outlet plenum dimensions of 8mm × 30mm, 10mm × 30 mm and 12 mm × 30 mm each with constant depth of 2.5 mm have been selected. Three different flow arrangements (U-Type, S-type and P-type) are studied for each test piece resulting in total nine flow arrangements. Each micro-channel heat sink contains an array of micro-channels in parallel having individual width of 330μm and channel depth of 2.5 mm. A comparison is made based on thermohydraulic performance of MCHS for different flow conditions at inlet and outlet plenums maintaining constant heat flux. Deionised water has been used in the experiments for the Reynolds number ranging from approximately 220 to 1100. The results are interpreted based on pressure drops and maximum temperature variations for these nine flow arrangements. Tests has been conducted to look for optimized dimensions and flow conditions at inlet and outlet plenums for the given fixed length of microchannels under same conjugate heat transfer conditions. Evaluations of experimental uncertainties have been meticulously made while selecting the instruments used in the experimental facility.
Natural Convection With Porous Medium in a Narrow Horizontal Cylindrical Annulus With Periodic Heat Generation
Authors: Mansour Kamyar
Published: November 2010

We consider the two-dimensional problem of steady natural convection in a narrow horizontal cylindrical annulus filled with porous medium due to a constant temperature variation on the outer and at the inner boundaries with periodic volumetric heat flux. The solution is expanded in powers of a single combined similarity parameter, which is the product of the Gap ratio to the power of two, and Rayleigh number. The series is extended by means of symbolic calculation up to 28 terms. Analysis of these expansions allows the exact computation for arbitrarily accuracy up to 50000 figures. Although the range of the radius of convergence is small, but Pade approximation leads our results to be good even for much higher value of the similarity parameter.
Electrokinetic Transport in Micro-Nanofluidic Systems With Sudden-Expansion and Contraction Cross Sections
Authors: Chein Reiyu , Chung Baogan
Published: November 2010

In this study, electrokinetic transport in a micro-nanofluidic system is numerically investigated by solving the transient Poisson, Nernst-Planck, and Navier-Stokes equations simultaneously. The system considered is a nanochannel connected with two microchannels at its ends. Under various applied electric potential biases, the effect of concentration polarization on the fluid flow, induced pressure and electric current is examined. By comparing with the Donnan equilibrium condition and electroosmotic flow in microscale dimension, electric body force due to non-zero charge density is the mechanism for producing vortex flow and inducing positive pressure gradient in the anodic side of the system. The diffusive boundary layer thickness is reduced due to the stirring of the generated vortex flow and results in the over-limiting current when the applied electric potential bias is high.
Aspect Ratio Effect on Adiabatic Two-Phase Flow in Rectangular Microchannels
Authors: Choi Chiwoong , Yu DongIn , Kim Moohwan
Published: November 2010

Most microscale thermal hydraulic systems have been used rectangular microchannels. In a rectangular microchannel, most important parameter is an aspect ratio. In this study, glass rectangular microchannels were fabricated using MEMS (micro-electro-mechanical system) fabrication techniques with a photosensitive glass. The width of all channels is same to approximately 500 μm and the height of rectangular microchannel was changed. The hydraulic diameters of the rectangular microchannels were 490, 322 and 143 μm. Experiments of adiabatic two-phase flow in the rectangular microchannels were conducted using liquid water and nitrogen gas. Pressure drop was directly measured from embedded pressure ports. And the pressure drop results were compared with correlations. Visualization of flow patterns were achieved with a high-speed camera and a long-distance microscope. Bubble behaviors were analyzed using visualized images based on a unit cell concept. As the aspect ratio decreased, a confinement effect was increased. And the thickness of liquid film in the corner of the rectangular cross section was reduced with the aspect ratio decreased. This result affected all phenomena of two-phase flow in the rectangular microchannels.
Non-Fourier Heat Conduction in Carbon Nanotubes
Authors: Wang Hai-Dong , Cao Bing-Yang , Guo Zeng-Yuan
Published: November 2010

Fourier’s law is a phenomenological law to describe the heat transfer process. Although it has been widely used in a variety of engineering application areas, it is still questionable to reveal the physical essence of heat transfer. In order to describe the heat transfer phenomena universally, Guo has developed a general heat conduction law based on the concept of thermomass, which is defined as the equivalent mass of phonon gas in dielectrics according to Einstein’s mass-energy relation. The general law degenerates into Fourier’s law when the thermal inertia is neglected as the heat flux is not very high. The heat flux in carbon nanotubes (CNTs) may be as high as 1012 W/m2. In this case Fourier’s law no longer holds. However, what is estimated through the ratio of the heat flux to the temperature gradient by MD simulations or experiments is only the apparent thermal conductivity (ATC); which is smaller than the intrinsic thermal conductivity (ITC). The existing experimental data of single-walled CNTs under the high-bias current flows are applied to study the non-Fourier heat conduction under the ultra-high heat flux conditions. The results show that ITC and ATC are almost equal under the low heat flux conditions when the thermal inertia is negligible, while the difference between ITC and ATC becomes more notable as the heat flux increases or the temperature drops.
Molecular Dynamics Study on Thermal Conductivity of Single-Walled Carbon Nanotubes
Authors: Cao Bingyang , Hou Quanwen , Guo Zengyuan , Zhang Wusheng
Published: November 2010

In this paper, we study the thermal conductivities of sing-walled carbon nanotubes (CNTs) and CNTs-based nanocomposites using molecular dynamics simulations. Length dependence of the thermal conductivity of (5, 5) carbon nanotube at 300 K and 1000 K is simulated. At room temperature the thermal conductivity shows linear length dependence with the tube length less than 40 nm, which indicates the completely ballistic transport. The thermal conductivity increases with the increase of the nanotube length, but the increase rate decreases as the length increases. It shows that the phonon transport transits from ballistic to diffusive. In the simulations, the power exponent of the thermal conductivity of carbon nanotube to the tube length decreases by decaying exponential function as the tube length increases. We also observe a decrease of the low-dimensional effects by the surrounding matters. A carbon-nanotube-atom-fixed and -activated scheme of non-equilibrium molecular dynamics simulations is put forward to extract the thermal conductivity of carbon nanotubes embedded in solid argon. Though a 6.5% volume fraction of CNTs increases the composite thermal conductivity by about twice larger than that of the pure basal material, the thermal conductivity of CNTs embedded in solids is found to be decreased by 1/8–1/5 with reference to that of pure ones. The decrease of the intrinsic thermal conductivity of the solid-embedded CNTs and the thermal interface resistance are demonstrated to be responsible for the results.
The Effects of Different Doping Pattern on the Lattice Thermal Conductivity of Solid Ar
Authors: Zhao Yanyan , Chen Yunfei , Bi Kedong , Wang Zan , Ge Yanyan , Li Jiapeng
Published: November 2010

Equilibrium molecular dynamics method is performed to calculate the lattice thermal conductivities of solid argon doped with krypton in different geometrical distributions. The effects of centralization doping, monolayer doping, uniform doping, non-uniform doping, random doping and cubic pattern doping on the thermal conductivity of argon crystal are investigated respectively. The results demonstrate that, the uniformity of the impurity distribution plays a critical role in the thermal conductivity of solid argon. It is found that the lowest thermal conductivity could be achieved by organizing the impurity in a cubic pattern. Because both the phonon-impurity scattering and the stronger phonon-interface scattering can destroy the coherence of phonons. Calculation results suggest that the minimum thermal conductivity value among six different kinds of impurity arrangements is roughly 1.90 times lower than that of pure argon under the temperature of 17K. However, the values of thermal conductivity are almost the same as those of pure argon at higher temperatures.
Bubble Dynamics From Artificial Nucleation Sites During Subcooled Pool Boiling
Authors: Lin Xipeng , Christopher David M. , Li Yanshen , Li Hui
Published: November 2010

The bubble dynamics of ethanol vapor bubbles growing, coalescing and condensing in a subcooled ethanol liquid pool were investigated experimentally and numerically for a range of subcoolings and heating rates. The bubbles were generated from an artificial pair of nucleation sites made of microscale tubes mounted flush with the bottom surface of the liquid pool with the vapor supplied by a vapor generator. Observations of the bubble generation with a high speed camera show the various coalescence modes with no coalescence at low heating rates and high subcoolings and horizontal and/or vertical coalescence depending on the heating rate and subcooling. At very low subcoolings, the bubbles grew quite large with various types of coalescence. The numerical results using solutions of the Navier-Stokes equations with the VOF model and using a simplified one dimensional model also describe the bubble dynamics and the conditions for coalescence. The numerical results suggest that the condensation rate at the interface is probably much higher than predicted by the model due to significant convection in the liquid pool or due to significant disturbance of the interface by the vapor jet entering the bubble.
Advanced Thermosyphon Cooling With Nanoporous Structured Mini Channel Evaporators
Authors: Chiu Justin N. W. , Khodabandeh Rahmatollah , Furberg Richard
Published: November 2010

Attention has been given to enhance boiling surfaces in order to decrease the temperature difference and to increase heat transfer coefficient. Structured surfaces may provide both surface enlargement and artificial nucleation sites, thus ameliorate the heat transfer coefficient. The goal of the present experimental work is to analyze the influence on heat transfer coefficient (HTC) of enhanced surface structures coated on mini channel heat exchanger working in a closed loop thermosyphon system. Experimental tests were carried out with three types of surface enhanced mini channel evaporators: smooth surface, threaded structure and nanoporous coating. The evaporators are single channel half circularly shaped, adapted for filming purpose, measuring 30mm in length and 3mm in diameter. Surface areas of channels are 1.41cm2. Experiments were conducted in refrigerant 134a at 4.87bar (reduced pressure pr = 0.12) and at heat fluxes ranging from 0.7W/cm2 to 63.8W/cm2. A high speed video camera was used for visualization of the two-phase flow in the evaporator channel. It is shown that threaded surface provides the highest heat transfer coefficient (HTC) from no load to heat flux of 7.1W/cm2, the nanoporous structure shows the highest performance between 7.1W/cm2 and 49.6W/cm2, and the smooth surface channel exhibits the best HTC from 49.6W/cm2 and higher. In this paper, the influences of heat flux and surface structures on HTC are discussed, and the impact of refrigerant flow regimes on heat transfer performance is also highlighted.
Experimental Researches on Zero Superheat in Refrigeration Cycle
Authors: Wang Yonghong , Tao Leren , Wang Jinfeng , Tao Hong , Huang Lihao , Zheng Zhigao , Yang Zhiqiang , Han Lei
Published: November 2010

In a steam-compression refrigeration cycle, optimum heat exchange efficiency is acquired and compressor liquid hammer can be avoided if “zero superheat” arises at dry-evaporator outlet. Therefore zero superheat control study is of value. since refrigeration cycle will not get stable while it tends to hunt nearby zero superheat, expansion valve-dry evaporator regulation loop have to run at a positive superheat; and no fit theory is able to guide the design on the stability of expansion valve-dry evaporator regulation loop until the cause of refrigeration cycle hunting is found. Flow display experiments reveal the mechanism that refrigeration cycle will hunt next to 0 superheat while vapor/liquid two phase flow alternates at expansion valve exit. on the ground that phases can be told apart by thermal sensing rather than superheat, a specialized sensor has been developed to detect 0 superheat signal which serves as the feedback signal of expansion valve-dry evaporator regulation loop, the experiment results prove that the thermal sensor can afford 0 superheat.
Predicted the Pipe Line Temperature Distributions for the Capillary Pumped Loop
Authors: Lin Hung-Wen , Yong Goh Seng , Fang Yu-Kuen , Lin Wei-Keng
Published: November 2010

Capillary Pumped Loop (CPL) is a high efficiency two-phase heat transfer device. Since it does not need any other mechanical force such as pump, furthermore, it might be used to do the thermal management of high power electronic component such as spacecraft, notebook and computer servers. It is a cyclic circulation pumped by capillary force, and this force is generated from the fine porous structure in evaporator. This research aims to study the CPL pipe line temperature distributions. A steady state heat transfer method was developed to predict the pipeline temperature from evaporator outlet to evaporator inlet. Condenser inlet temperature; condenser outlet temperature; condenser base temperature; pressure drop along the loop could be calculated from the theoretical model. A good agreement between the theoretical results and experimental values were achieved. This theoretical structure provides designer a new design direction and an axial heat transfer method that allows designer more freedom.
Coupling Between Phonons and Fluid Particles in Water/Carbon Nanotube Systems
Authors: McGaughey A. J. H. , Thomas J. A. , Turney J. , Iutzi R. M.
Published: November 2010

We investigate thermal transport in water/carbon nanotube (CNT) composite systems using molecular dynamics simulations. Carbon-carbon interactions are modeled using the second-generation REBO potential, water-water interactions are modeled using the TIP4P potential, and carbon-water interactions are modeled using a Lennard-Jones potential. The thermal conductivities of empty and water-filled CNTs with diameters between 0.83 nm and 1.66 nm are predicted using molecular dynamics simulation and a direct application of the Fourier law. For empty CNTs, the thermal conductivity decreases with increasing CNT diameter. As the CNT length approaches 1 micron, a length-independent thermal conductivity is obtained, indicative of diffusive phonon transport. When the CNTs are filled with water, the thermal conductivity decreases compared to the empty CNTs and transitions to diffusive phonon transport at shorter lengths. To understand this behavior, we calculate the spectral energy density of the empty and water-filled CNTs and calculate the mode-specific group velocities, relaxation times, and thermal conductivity. For the empty 1.10 nm diameter CNT, we show that the acoustic phonon modes account for 65 percent of the total thermal conductivity. This behavior is attributed to their long mean-free paths. When the CNT is filled with water, interactions with the water molecules shorten the acoustic mode mean-free path and lower the overall CNT thermal conductivity.
Convection Heat Transfer of CO2 at Supercritical Pressures in a Vertical Mini Tube
Authors: Jiang Pei-Xue , Li Zhi-Hui , Zhao Chen-Ru
Published: November 2010

This paper presents the experimental and numerical investigation results of the convection heat transfer of CO2 at supercritical pressures in a 0.0992 mm diameter vertical tube at various inlet Reynolds numbers, heat fluxes and flow directions. The effects of buoyancy and flow acceleration resulted from the dramatic properties variation were investigated. Results showed that the local wall temperature varied non-linearly for both upward and downward flow when the heat flux was high. The difference of the local wall temperature between upward flow and downward flow was very small when other test conditions were held the same, which indicates that for supercritical CO2 flowing in a mini tube as employed in this study, the buoyancy effect on the convection heat transfer was quite insignificant, and the flow acceleration induced by the axial density variation with temperature was the main factor that lead to the abnormal local wall temperature distribution at high heat fluxes. The predicted values using the LB low Reynolds number turbulence model correspond well with the measured data. Velocity profiles and turbulence kinetic energy near the wall varying along the tube generated by the numerical simulations were presented to develop a better understanding.
Performances of Flat Plate Pulsating Heat Pipes
Authors: Qu Wei , Yang Bin
Published: November 2010

Flat plate pulsating heat pipe is useful for hot spot heat spreader. Two kinds of flat plate spreader of pulsating heat pipe are designed, fabricated and experimented. For the embedded circular capillary type, the transferred heat flux could reach 32W/cm2, the smallest thermal resistance for acetone, methanol and FC-72 were respectively 0.50, 0.57 and 0.40°C/W. While for the square capillary type, the transferred heat flux could reach 26W/cm2, the equivalent thermal conductivity could reach 3211W/(m. °C). There are ranges of optimal transferred power and filling ratio for different working liquid. If the transferred power is constant, changing the heating area and the place has little effects on the performance.
Analysis of Stress Jump Condition at a Fluid/Porous Interface
Authors: Liu Fang , Chen Baoming , Wang Li
Published: November 2010

Natural convection in partially porous cavities driven by buoyancy force has been given the attention in this paper. Two-domain model with continuous or discontinuous interfacial conditions and One-equation model with heterogeneous interface region were analyzed. FEM with weak constraint condition was applied to solve the differential governing equations. The influence of stress jump conditions at fluid/porous interface on flow and heat transfer in two-domain model was compared with that of heterogeneous interface region in one-domain model. Numerical results showed that vertical velocity was different near the interface for continuous and discontinuous interfacial conditions. And variation of porosity and permeability in the interface region also lead to difference of vertical velocity. The influence on Nusselt number was slight.
A Microfluidic Perfusion Chamber Utilized in the Study of Biophysical Properties of Cell Membrane and Its Fluidic Evaluation
Authors: Chen Hsiu-hung , Gao Dayong
Published: November 2010

A microfluidic system is demonstrated here to measure the kinetic changes of cell volume under various extracellular conditions, in order to determine cell membrane transport properties. The system is comprised of microchannels, a cell immobilization chamber, an inlet and an outlet, and is made of poly(dimethylsiloxane) (PDMS) using softlithographic method. During experiments, mouse dendritic cells (mDCs), mixed with media of known concentrations, are quickly injected to the inlet of such microfluidic device, flow through a microchannel, and are then immobilized by a sieving structure, where kinetic images of cell volume response are captured by a CCD camera lively. The fluid keeps flowing due to the continuous suction from the outlet by a programmable syringe pump. Two sets of experiments have been performed: the cells are mixed with (1) solutions prepared in different concentrations of non-permeating solutes, and (2) solutions containing a permeating cryoprotective agent (CPA) plus non-permeating solute, respectively. Based on the captured images, both cell inactive volumes (Vb), permeability coefficients of water (Lp) and of CPA (Ps) through cell membranes of mDCs at different temperatures (10°C, 22°C, and 34°C) can be determined by least-squared curve fittings, respectively. A quantitative evaluation conducted using ImageJ will be performed in order to validate the microfluidic perfusion system, as well as help us understand the dynamic concentration changes around those immobilized cells. The use of this microfluidic perfusion system enables us to: 1) confine cells in a monolayer channel to prevent image ambiguity, 2) perform cell counting, 3) statistically study cell osmotic response and determine cell membrane transport properties, and (4) lower manufacturing costs.
Numerical Simulation of Geometrical Effects on the Liquid Flow and Heat Transfer in Smooth Rectangular Microchannels
Authors: Yun Heming , Chen Baoming , Chen Binjian
Published: November 2010

The flow and heat transfer characteristics of water in smooth rectangular microchannels had been simulated numerically by using CFD method. Computational results showed that the ratio of the channel length and hydraulic diameter, hydraulic diameter, the ratio of height and width of microchannels, porous ratio had different effects on the flow and heat transfer of microchannels. On the condition of the ratio of the length and hydraulic diameter of channel greater than 70, thereby the entrance effects could be neglected, the effect of hydraulic diameter, the ratio of height and width of microchannels and porous ratio on flow and heat transfer in microchannels had been simulated respectively. The mechanism of flow and heat transfer of each condition had been obtained, which could offer important data to discuss the mechanism of flow and heat transfer in microchannels further and realize the goal of optimizing design of microchannel heat exchanger.
Experimental Investigations on Thermal Performance of a Closed Loop Pulsating Heat Pipe
Authors: Wang Yu , Li Weiyi , Wei Lianyou , Cao Binbin
Published: November 2010

Closed loop pulsating heat pipes (CLPHPs) are complex heat transfer devices having a strong thermohydrodynamic coupling governing the thermal performance. Experimental studies on a CLPHP have focused on visualizing the start-up and operation mode of CLPHP or characterizing the heat transfer capability of CLPHP. In this paper, a visualization setup was established and a series of experimental observations based on the visualization setup were conducted to study the fundamental phenomena and thermal performance in CLPHPs within water. The influence characterization has been studied for the variation of thermal condition in the evaporator section of CLPHPs (large flow rate, little flow rate), inclination angel (30 °, 45 °, 60 °), filling ratio (approximately at 30%, 50%, 70%)of the CLPHP. The thermal performance of CLPHPs was mainly evaluated by calculating the effective conductivity which related to temperature distribution of both evaporator and condenser sections of the CLPHPs, also to the heat transfer between these two sections. The results indicate a strong influence of the filling ratio and the gravity on the CLPHP thermal performance. The filling ratio also affects normal startup and stable operation of the CLPHP.
Investigation on the Viscosity of Lithium-Bromide/Water Solution Added Nano-Particles
Authors: Xie Guozhen , Li Guodong , Liu Lei
Published: November 2010

Viscosity of the suspension fluid, mixed with nano-particles, is an important thermal-physical parameter in researching the flow pattern and heat transfer properties of the fluid, and is closely related to the stability of mineral suspension. Therefore, it is important to study the varying mechanism of the viscosity of lithium-bromide/water solution added some of nano-particles to enhance their heat transfer. This paper investigated the lithium-bromide/water solution’viscosity after adding dispersant and nano-particles by the rotation method. The influence of different adding nano-material content and various temperatures on the viscosity of lithium-bromide/water solution were discussed reasonably. Finally, the relationship between the viscosity of lithium-bromide/water solution and dispersant, nano-particles addition and applied temperature was made.
Development of Silicon Based Heat Spreader for High Power Electronic Devices
Authors: Cai Qingjun , Chen Bing-chung , Tsai Chailun , Zhao Yuan , Chen Chung-lung
Published: November 2010

This article presents the development of silicon based heat spreader devices, called hexcells. Several key technical aspects, including the hexcell MEMS fabrication process, mechanical strength studies, vacuum sealing technique, and phase change and mass transport visualization, have been developed and studied. The hexcell development prototypes are fabricated by MEMS photolithography and dry-etch processes, with eutectic bonding to form a sealed silicon chamber with openings for charging with the working fluid. Using Ansys as the modeling tool, we optimized the hexcell total mechanical strength by incorporating six interior support posts to reinforce the structure. In terms of the optimized design, experimental results on actual hexcell samples show that a well-bonded hexcell can withstand over 60psi without destructive failure. Vacuum sealing are divided into helium and vapor leakage tests. With metalized and solder-sealed sidewalls, both testing results confirm good vacuum sealing. The wick structure used in the present hexcell is silicon pillars with dimensions of 50μm in diameter and 250μm in height. The pillars are etched before the hexcell is bonded and formed. Experiments using the silicon wick structure demonstrate over 300W/cm2 cooling capacity and visualization shows the intensive phase change on the heating area.
Experimental Study of Natural Convective Heat and Mass Transfer With Cross Diffusion Effects in Closed Cavity
Authors: Geng Wenguang , Chen Baoming , Sun Kai , Wang Li , Liu Fang
Published: November 2010

Natural convective heat and mass transfer with Soret effect and Dufour effect is experimental studied in this paper to investigate the diffusion characteristic of volatile organic compounds (VOCs) in multi-physical fields. Firstly, Soret effect (thermal diffusion effect) experiment is conducted. The transfer process of isobutane and nitrogen in two close container connected by a small-diameter pipe is experimental studied. The results show that temperature difference between the two containers would conduct a solute concentration difference. Furthermore, multi-component convective diffusion experiment in a closed cavity which simulate indoor environment is developed under temperature gradient, humidity and propane gas concentration gradients. In this experiment, Temperature, humidity and concentration of propane could be surveyed real-time and do not interfere the natural convection in the closed cavity. The experiment results show that that the temperature gradient and the water vapor concentration gradient have effects on the convective diffusion of VOCs indoor environment. The cross diffusion effects would be taken into consideration for the problem of simultaneous heat and mass transfer especially in the presence of large temperature and concentration gradients.
Lagging Behavior in Biological Systems
Authors: Tzou D. Y.
Published: November 2010

The lagging behavior is first exemplified by a rapidly stretched spring and a one-dimensional fin to illustrate the phase-lag concept via the thermal and mechanical properties that most engineers are familiar with. The second-order lagging model is then introduced to correlate with drug delivery in tumors and bioheat transfer that involve multiple carriers in heat/mass transport. Analytical expressions for the phase lags are derived, aiming toward revealing different physical origins for delays in different systems. For drug delivery in tumors involving nonequilibrium mass transport, the lagging behavior results from the finite time required for the rupture of liposome in releasing the antitumor drug and the finite time required for tumor cells to absorb drugs. For bioheat transfer involving nonequilibrium heat transport, on the other hand, the lagging behavior results from the finite time required for exchanging heat between tissue and blood. Pharmacodynamical and biological properties affecting the phase lags, as well as the dominating parameters over the lagging response are identified through the nondimensional analysis. Involvement of the thermal Mach number, which measures the speed of blood flow relative to the conventional thermal wave speed, is a new feature in this extension of the lagging model. The second order effects in lagging are well correlated with the number of carriers involved in nonequilibrium heat and mass transport.
Thermal Management of On-Chip Hot Spot
Authors: Bar-Cohen Avram , Wang Peng
Published: November 2010

The rapid emergence of nanoelectronics, with the consequent rise in transistor density and switching speed, has led to a steep increase in microprocessor chip heat flux and growing concern over the emergence of on-chip “hot spots”. The application of on-chip high heat flux cooling techniques is today a primary driver for innovation in the electronics industry. In this paper, the physical phenomena underpinning the most promising on-chip thermal management approaches for hot spot remediation, along with basic modeling equations and typical results are described. Attention is devoted to thermoelectric microcoolers — using mini-contcat enhancement and in-plane thermoelectric currents, orthotropic TIM’s/heat spreaders, and phase-change microgap coolers.
A Scale Analysis Based Theoretical Force Balance Model for Critical Heat Flux (CHF) During Saturated Flow Boiling in Microchannels and Minichannels
Authors: Kandlikar Satish G.
Published: November 2010

Accurate prediction of critical heat flux (CHF) in microchannels and small diameter tubes is of great interest in estimating the safe operational limits of cooling systems employing flow boiling. Scale analysis is applied to identify the relevant forces leading to the CHF condition. Using these forces, a local parameter model is developed to predict the flow boiling CHF. The theoretical model is an extension of an earlier pool boiling CHF model incorporating a force balance among the evaporation momentum, surface tension, inertia, and viscous forces. Weber number, capillary number, and a new non-dimensional group K2, representing the ratio of evaporation momentum to surface tension forces, emerged as main groups in quantifying the narrow channel effects on CHF. The constants in the model were calculated from the available experimental data. The mean error with ten data sets is 19.7 percent, with 76 percent data falling within ±30% error band, and 93 percent within ±50% error band. Evaluating individualized set of constants for each data set resulted in mean errors of less than 10 percent for all data sets. The success of the model indicates that flow boiling CHF can be modeled as a local phenomenon and the scale analysis is able to reveal important information regarding fundamental mechanisms leading to the CHF condition. The final equations resulting from this model are given by Eqs. (18–22) along with the transition criteria given by Eq. (28).
Microfluidic Refrigerant Compression and Pumping by Maxwell Pressure Generated at a Nanoporous Monolith
Authors: Chang Hsueh-Chia
Published: November 2010

We introduce a new concept in miniature two-phase cooling with ammonia and other refrigerants. Despite its high heat removal rate density, two-phase cooling has not been attempted for miniature electronic cooling because of the high pressure needed to compress the vapor phase into liquid. We suggest in this short expository that Maxwell pressure generated by an intense DC or AC field across a solid nanoporous monolith can overcome this challenge. The fundamental mechanisms for such miniature pressure source are reviewed and the fabrication challenges discussed.
Developing a 21st Century Energy From Waste Facility in American Samoa
Authors: Rogoff Marc J. , Nicholls Michelle Mullet , Keyser Michael
Published: November 2010

American Samoa is an unincorporated territory of the U.S. roughly 2,300 air miles southwest of Honolulu and about 2,700 miles north of Australia. The largest and most populated island in American Samoa is Tutuila, which is located the territory’s historic capitol of Pago Pago. The territory is home to the world’s largest tuna cannery. Population growth has been dramatic and the island’s energy costs have increased substantially in recent years. The American Samoa Power Authority (ASPA) is responsible for solid waste collection and disposal in the territory with landfilling being the primary mode of waste disposal. However, limited available land on the main island due to volcanic topography limits the long-term use of landfilling as the island’s sole waste management tool. The relative isolated location of American Samoa and the instability of world oil markets have prompted ASPA to look at more environmentally and economically sustainable means of solid waste management. As an outgrowth of its research, ASPA submitted and received a technical assistance grant from the U.s. Department of the Interior to conduct an extensive waste composition study and EfW feasibility study to examine the advantages and disadvantages of efW for American Samoa. The results of these studies have been completed by SCS on behalf of ASPA, which is currently taking steps to permit and procure a 2.0 megawatt, modular efW facility that will go online in 2012 as part of a public private partnership. The lessons learned by SCs and ASPA during the course of the investigations are illustrative of the types of long-term, waste management and energy decision-making that many small communities will have to undertake to attain viable and sustainable alternatives.
DyNOR™ DeNOx Performance Confirmed in Further MSW Plants
Authors: Sigg Fred , Halter Roland , Chromec Peter
Published: November 2010

Von Roll Inova’s innovative new SNCR process is up to the task. This new approach takes the well known Selective non-catalytic reduction process to new heights (lows). By monitoring process conditions very closely and implementing a quick-reacting, highly precise mechanical system for distribution of the reducing agent, emissions can be limited to levels comparable to those demonstrated by SCR. Von Roll Inova’s DyNOR™ (Dynamic NOx Reduction) process takes advantage of fast and precise infrared pyrometer measurements in the exact locations where reagent is needed. Coupled with a patented distribution system, reagent injection is continuously directed to the optimal location in the furnace. The system is capable of responding to changes in a matter of seconds and thus can correct for uneven temperature profiles which are typical in combustion systems with inhomogeneous waste fuel such as MSW. Good combustion control can limit uncontrolled NOx emissions to less than 200 ppmv and forms the platform upon which secondary NOx reduction measures should build. The conventional Von Roll Inova SNCR process limits NOx emissions to 100 ppmv. DyNOR™ pushes the envelope further towards 70 ppmv NOx and less than 10 ppmv ammonia slip and closes the gap towards capital intensive catalytic systems. Long term trials at a full scale industrial installation have demonstrated emission levels well below 75 ppmv with ammonia slip below 15 ppmv. Now this process has successfully been implemented as a retrofit in a commercial unit. Results confirm that these levels can be safely achieved without compromising furnace air distribution and residence time.
Updated Case Study of Fireside Corrosion Management in an RDF Fired Energy-From-Waste Boiler
Authors: Vrchota Stephen , Peterson Tim
Published: November 2010

Fireside corrosion management in energy-from-waste (EfW) boilers is the leading cost of boiler maintenance. The combustion of refuse-derived fuel (RDF) processed from municipal solid waste in a boiler for power generation produces a very corrosive environment for boiler tube materials. Water wall corrosion has been greatly reduced by the use of Alloy 625 overlay in the highest corrosion areas. This paper will describe the progression of water wall corrosion up the boiler walls and novel attempts to reduce this problem. This paper presents an updated case study conducted at the Great River Energy plant in Elk River, MN from 2003–2009 on corrosion management. Areas to be addressed are protection of exposed carbon steel water wall tubes, management of Alloy 625 weld overlay on the water walls and corrosion in the high temperature superheat sections. Methods for testing and maintaining the corrosion resistant Alloy 625 cladding are reviewed. High temperature superheat material selection and shielding are reviewed with information leading to a cost effective solution that requires superheat replacement every three years with very few tube failures between replacements.
Emerging Technology for Multi-Pollutant Control on the Emissions of a Biomass Fired Boiler
Authors: Ginger Bradley
Published: November 2010

Proposed modifications to the laws governing the emissions from biomass fired boilers require more stringent control on emissions. During biomass combustion there are several pollutants produced which require advanced pollution control measures to maintain environmental compliance. These pollutants include Particulate Matter, Hydrogen Chloride, Sulfur Dioxide, Sulfuric Acid Mist, and Oxides of Nitrogen. To ensure operational compliance of the boiler’s stack emissions both now and in the future, proper pollution control technology is paramount. This presentation will address an emerging air pollution control technology that embodies all of these removal steps in a single device specifically designed to meet the needs of biomass fired boilers. Historically, the control strategy for stack emissions from such boilers has included the use of various standalone systems. For example, Dry Electrostatic Precipitators have been used for PM reduction, Selective Non-Catalytic Reduction systems for NOx control, Flue Gas Desulphurization for SO2 removal, and single pass Wet Electrostatic Precipitators for H2SO4 abatement. The consolidation of these multiple, standalone systems into a smaller, less costly alternative tailored specifically for biomass fired boilers can address the new requirements. EISENMANN’s recently patented multi-pollutant control system includes the use of a pre-scrubbing chamber for large PM, SO2, and water soluble NO2 removal. Following the quench and pre-scrubbing region, a specially tuned downflow wet ESP field is responsible for finer PM and Sulfuric Acid aerosol removal, as well as an important Ozone producing stage that oxidizes non-water soluble NO. As the gas continues to travel through the system, a secondary scrubbing chamber is used to further reduce NOx by scrubbing the newly formed NO2 that has been formed from the oxidation of NO through the use of Ozone produced by the electrostatic precipitator. The final polishing stage of the system includes an upflow wet electrostatic precipitator field for the removal of newly oxidized material such as mercury. Research and testing on the aforementioned system took place through the development of a pilot sized unit. Expected performance was validated proving high removal efficiencies for pollutants specifically addressed earlier. Implementation of the technology within the biomass fired area is underway and is currently viewed as an acceptable solution to the environmental regulations associated with a biomass fired boiler because of the smaller footprint, lower operating costs, and overall condensed solution when compared to previously used technologies.
Palm Beach County WTE Expansion Model
Authors: Henderson Thomas M. , Richter Leah K.
Published: November 2010

Palm Beach County (Florida) Solid Waste Authority built an integrated solid waste management system in the 1980s and 1990s around an 1,800 tpd Refuse Derived Fuel (RDF) Waste-to-Energy (WTE) facility. The system included a network of five regional transfer stations, Subtitle D sanitary landfill, recovered materials processing facility, composting facility, metals processing facility and household hazardous waste collection program. The WTE, which became operational in 1989, was built with two 900 tpd RDF combustion units. Space was provided for the addition of a third combustion unit, a second turbine-generator and an extra flue was installed in the facility’s stack. By 2004, the WTE was fifteen years old. It had been running at over 125% availability and well above its nominal capacity for almost a decade. Landfill capacity was being consumed at a rate which would see it filled in less than 20 years. The County had been hit with repeated hurricanes in recent years and the County’s population was continuing to grow making landfill capacity projections far from certain. The Authority began an assessment of its long term capacity options which included renovation of its existing WTE facility, expansion of that facility, development of a new WTE facility, development of a new Subtitle D Landfill and several out-of-county options. This paper will focus on the results of this assessment with emphasis on the current efforts to develop a new Mass Burn WTE facility with a capacity of 3,000 tpd and a commercial operations date of 2015. It will be the largest new WTE built in North America in more than 20 years. The choice of Mass Burn technology, facility and combustion module sizing, air pollution control technology, facility site selection, environmental permitting, public outreach program, project financing and procurement and contracting approach will be discussed.