bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Simulation of Mark Formation/Erasure in Phase Change Recording
Authors: Small Evan , Reifenberg John , Yang Yizhang , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: April 2009

Design/optimization of the phase change recording media to create proper marks, in size, shape, and quality, needs a robust modeling tool to predict temperature distribution in the constituting layers and model the phase formation during writing/erasure of the information bits. This requires a modeling of the heat transfer (thermal performance) and the crystallization processes. The thermal modeling, which is based on the solution of the heat diffusion equation for finding temperature distribution in the multilayer media, has been done before, using the finite difference techniques. These techniques have limited potentials for modeling real phase change recording media that have a rather more complex geometry. The finite elements method has, on the other hand, the required flexibility for such applications. In this work, we are reporting on development of a numerical simulation tool that uses the finite elements method for heat transfer simulation. ANSYS is used as the source code for the heat transfer simulation, in this application, with the crystallization model then being built into this media. This code has been used to simulate mark formation during writing on grooved plain and planer patterned media. Patterning the phase change material layer looks very promising in controlling the mark size and the mark edge irregularity which lead to timing jitter.
Thermal Management of a Fast UV Slitless Spectrometer for a Meteor Research Experiment
Authors: McAssey E. V. , Vahadat Vahid , LeMunyan Greg , Renda George
Published: April 2009

This paper presents the proposed thermal management design for an ultra-violet slitless spectrometer to be flown on either the Space Shuttle or on the International Space Station as a scientific experiment to capture the ultraviolet spectrum of meteors as they are heated by the Earth’s atmosphere. The proposed telescope was initially planned as a Hitchhiker experiment for the Space Shuttle. The Space Station environment is thermally more critical than the Hitchhiker application. The final thermal design is essentially passive; however, heaters will be used to maintain the component temperatures at acceptable levels during telescope nonoperating conditions. The major difference between the Space Station design and the Hitchhiker design is the use of external multi-layer insulation and thermal strapping on the former application.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Fast Transient Micro-Boiling Characterization
Authors: Escobar-Vargas Sergio , Fabris Drazen , Gonzalez Jorge E. , Sharma Ratnesh , Bash Cullen , Ortiz Lester , Cartagena Julio
Published: April 2009

The dynamics of Thermal Ink Jet (TIJ) micro-bubble life cycles is characterized through bubble area measurements for small planar heaters (41 μm × 45 μm). A laser visualization technique is used to measure the bubble area viewed from above. The bubbles are generated in water by 2–4 μs heating pulse and survive for 8–10 μs after the pulse. The bubble life-cycle consists of a short initiation time, fast growth, a period of maximum size, and a rapid collapse. Effect of the power inputs (2–4 W) total energy releases (8.8–13.3 μJ) and operational frequencies of 2–3 kHz is observed. Direct observations of bubble area indicate that bubble initiation time and initial growth rate correlates to the input power. The maximum bubble size and overall longevity correlates to the total energy release.
Nanoscale Heat Conduction Across Metal-Dielectric Interfaces
Authors: Ju Y. Sungtaek , Hung Ming-Tsung , Usui Takane
Published: April 2009

Energy transport across solid-solid interfaces is a critical consideration in various micro- and nanoscale devices and structures. The impact of the thermal interface resistance is most pronounced at cryogenic temperatures. Heat conduction in Josephson junctions is analyzed to illustrate the significance of thermal interface engineering in the thermal management of superconducting devices. In nanolaminates and nanoscale thin films the thermal interface resistance plays a critical role even at elevated temperatures. Experimental studies using nanolaminates provide further insight into heat conduction across interfaces. An approximate theoretical model is presented to elucidate the effect of electron-phonon nonequilibrium on heat conduction across nanolaminates.
Pool Boiling Heat Transfer of Alumina-Water, Zinc Oxide-Water and Alumina-Water+Ethylene Glycol Nanofluids
Authors: Moreno Gilbert , Oldenburg Steven J. , You Seung M. , Kim Joo H.
Published: April 2009

This investigation conducts pool boiling experiments under saturated conditions (Tsat = 60 °C) using nanofluids as the coolants. Three different nanofluids were tested including zinc oxide (ZnO)-water, aluminum oxide (Al2O3)-water and aluminum oxide (Al2O3)-water+ethylene glycol (ethylene glycol solution). At saturation (Tsat = 60°C), the pool boiling performance of the two pure water based nanofluids were similar. The maximum CHF enhancement as compared to the predicted Zuber’s [1] CHF evaluated at an equivalent saturation temperature is ∼180% for Al2O3-water nanofluids and ∼240% for ZnO-water nanofluids. In both cases, no degradation in the boiling heat transfer rate was observed for lower nanoparticle concentrations. However, higher nanoparticle concentrations demonstrate nucleate boiling heat transfer degradation at high heat fluxes. The dispersion of Al2O3 nanoparticles in various ethylene glycol solutions is also found to enhance CHF by as much as ∼130%. A significant difference in the diameter of individual grains/particles (27 ± 16.3 nm) and the volume weighted average diameter of particles in solution (155 ± 80 nm) indicates that the Al2O3-water nanofluids consist primarily of nanoparticle agglomerates. Gravimetric fractionation of the nanofluid produced nanofluids with particle/particle aggregate average diameters that ranged from 69–346 nm. Over the size range tested, there was no significant CHF dependence on the average particle diameter.
A Novel Quick Qmax Test Method and Experimental Investigation of Heat Pipes
Authors: Chan Yao-Chen , Lin Wei-Keng
Published: April 2009

In traditional heat pipe performance test, to keep an adiabatic temperature at a constant value, the evaporator wall temperature would be slowly increased when the thermal power was step input to the evaporator of the heat pipe. The maximum heat transfer rate (Qmax) was then defined that when the evaporator wall temperature rapidly increased at a certain amount of power input to the heat pipe. However, it is not easy to distinguish this sharp increased curve and sometimes result in the wrong Qmax data. In addition, it took too long for waiting the evaporator temperature approach to a steady state, thus this process could not use be for the fully check Qmax of the heat pipe. In this paper, we propose a novel quick test method to predict the maximum heat dissipation of the heat pipes namely Dynamic-Temperature-Tracing (D.T.T). The concept of the D.T.T was when we tracing the evaporator and the adiabatic wall temperature, these two temperature curves should be the same trend before the dry-out phenomena was occurred. Theoretically, when the dry-out start to occur in the heat pipe, the adiabatic temperature profile was no longer kept the same temperature profile as that of the evaporator. Hence, the maximum heat dissipate ability of the heat pipe was then easy to obtained at this measuring adiabatic temperature. The data were also compared with those obtained from the traditional standard method at the same equivalent evaporator length, condenser length and adiabatic temperature. In this experiments, sinter powder and groove heat pipes with diameter 6mm 8mm and 200mm length were selected as the capillary wick structure. Comparing with traditional method results, the errors of maximum heat transfer rate are less than 15%. The results also shown D.T.T. method is much fast and reliable compare with the traditional test method.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
On the Influence of Gas Mixture Composition on Gas Quenching Uniformity and Mean
Authors: Macchion O. , Zahrai S. , A˚stro¨m A.
Published: April 2009

The use of gas mixtures is widely spread in today’s industry. The fields of application go from cooling within refrigerators to the deep freezing of meat balls. One particular application is within the industry of gas heat treating of metal pieces. Such heat treatment involves the cooling of metal pieces, called quenching. The present work investigates the dependence of the performance of a given gas mixture on the geometry of the metal pieces to quench. The heat transfer coefficient and the convection Nusselt number across a short cylinder (D = 150 mm, L = 300 mm) in axial flow for mixtures of hydrogen and nitrogen were computed for six Reynolds numbers in the range 2.0 104 to 2.0 105. The Nusselt number decreased continually with increasing hydrogen content. Since the existing correlations did not adequately represent the calculated data, modified correlations were developed to describe the influence of transport properties and flow parameters on the convective heat transfer over the front and lateral surfaces of the cylinder. These correlations are valid for the range of Reynolds numbers 2.0 104 to 2.0 105 and in the range of Prandtl numbers 0.4 to 0.73. A relation giving the heat transfer uniformity as a function of the Reynolds number and Prandtl number of the gas mixture flowing around the cylinder in axial flow has been developed. This correlation is valid within the same range of Reynolds and Prandtl numbers previously given.
Cryo-Preservation and Biophysical Properties of Articular Cartilage Chondrocytes
Authors: Wu W. T. , Hsieh W. H. , Lyu Shaw-Ruey
Published: April 2009

In order to successfully cryopreserve articular cartilage chondrocytes, it is important to characterize their osmotic response, during the cryopreservation process, as the ice forms and the solutes concentrate. In this study, an experimental work was undertaken to determine the osmotic parameters of articular cartilage chondrocytes. The osmotically inactive volume of articular cartilage chondrocytes was determined to be 44% of the isotonic volume. The membrane hydraulic conductivity parameters for water were determined by fitting a theoretical water transport model to the experimentally obtained volumetric shrinkage data; the membrane hydraulic conductivity parameter LPg was found to be 0.0633 μm3/μm2/min/atm, and the activation energy E, 8.23 kcal/mol. The simulated cooling process, using the osmotic parameters obtained in this study, suggest an optimal cooling rate of 80 °C /min in the cryopreservation of the articular cartilage chondrocytes of hogs.
Experimental Investigation of the Heat Transfer Performance of Arrays of Round Jets With Sharp-Edged Orifices and Peripheral Effluent: Convective Behavior of Water on a Heated Silicon Surface
Authors: Campbell Levi A. , Ellsworth Michael J. , Iyengar Madhusudan , Simons Robert , Chu Richard
Published: April 2009

In the present work, deionized water is impinged onto a heated silicon surface using square arrays of round jets. Various numbers of jets and jet diameters are used over a heated area of constant size with the orifice plate height above the heater held constant. In these experiments, the jet orifices are sharp-edged and the fluid exhaust direction is parallel to the heated surface and leaves the chip periphery through a manifold. The resulting temperature and flow data are presented in physical units as well as in groups of dimensionless parameters. A correlation is presented to reasonably predict the experimental results of this study. The techniques used for data reduction and for experimentation, including the construction of the test module, are given in detail, including a numerical conduction simulation based data reduction technique and uncertainty analysis. The results shown include flow rates ranging from 6.1 cc/s to 63.18 cc/s resulting in Reynolds numbers based on orifice diameter ranging from 141 to 6670. Jet diameters investigated in this study range from 377 μm to 1.01 mm, in square arrays of 16 to 324 orifices on an area of 18.52 mm × 18.59 mm. The resulting maximum spatially averaged effective heat transfer coefficient achieved is 7.94 W/cm2K, and the maximum spatially averaged Nusselt number based on jet diameter is 79.4.
Effects of Multiple Reflections on Hole Formation During Short-Pulsed Laser Drilling
Authors: Modest Michael F.
Published: April 2009

Beam guiding effects during laser drilling due to multiple specular reflections inside the hole are analyzed for the case of very short laser pulses (ns range). Specular reflections are valid for materials that retain a smooth surface during laser evaporation (small optical roughness compared to the laser wavelength). The problem is assumed to be 2D axisymmetric (unpolarized laser), with the hole geometry denned by nodal values connected through a cubic spline. The net radiative flux onto a surface node is determined through ray tracing methods. The resulting absorbed laser flux is combined with a simple quasi-one-dimensional conduction model (to assess the minor conduction losses) and an Arrhenius evaporation rate model, to predict hole development as a function of time through iteration. To stabilize this highly nonlinear and thus unstable problem (in numerical analysis as well as in experiments) the laser beam is diffused a small amount from the specular direction (to also account for the limitation that no beam can be focused down to a point), and by periodic slight smoothing of the irradiation levels. Results show that drilling rates are increased dramatically due to beam trapping for highly reflective materials, resulting in a more pointed hole profile.
Simplified Thermal Analysis of the SOFC Transients During Startup/Shutdown
Authors: Damm David L. , Fedorov Andrei G.
Published: April 2009

Transient thermal analysis plays the central role in the design and optimization of high temperature solid oxide fuel cells (SOFCs) during startup/shutdown, because of the potential for damaging thermal gradients to develop within the SOFC components. To this end, we consider the SOFC unit cell, which is heated by hot air supplied into the oxidizer channel at a specified, time-dependent inlet temperature. Closed-form analytical solutions are obtained for two simplified 1-D models of the SOFC unit cell: (1) purely convective heating, assuming thermally-thin cell components, and (2) convective-conductive heating, under the assumption of local thermal equilibrium in the direction normal to flow. Given thresholds of maximum allowable temperature gradients, the optimal design is one that minimizes the total time required to reach a prescribed final operating temperature. With appropriate scaling, the models we developed predict the maximum temperature gradients and heating time requirements for various operating conditions, and the results are generalized by presentation in terms of the effective cell Peclet number and inlet temperature function. Finally, these predictions are used to identify favorable trends and design rules for optimizing the transient heating process. The simplicity, computational savings, and ability to capture the essential physics of the transient process demonstrated by application of the analytical models provide compelling justification for their use over more accurate, highly detailed, numerical/CFD schemes.
Confined Liquid Jet Impingement on a Plate With Discrete Heating Elements
Authors: Rahman Muhammad M. , Mukka Santosh K.
Published: April 2009

The primary focus of this paper is the conjugate heat transfer during vertical impingement of a two-dimensional (slot) submerged confined liquid jet using liquid ammonia as the working fluid. Numerical model for the heat transfer process has been developed. The solid region has been modeled along with the fluid region as a conjugate problem. Discrete heat sources have been used to study the overall effect on convective heat transfer. Simulation of discrete heat sources was done by introducing localized heat fluxes at various locations and their magnitudes being varied. Simulations are performed for two different substrate materials namely silicon and stainless steel. The equations solved in the liquid region included the conservation of mass, conservation of momentum, and conservation of energy. In the solid region, only the energy equation, which reduced to the heat conduction equation, had to be solved. The solid-fluid interface temperature showed a strong dependence on several geometric, fluid flow, and heat transfer parameters. The Nusselt number increased with Reynolds number. For a given flow rate, a higher heat transfer coefficient was obtained with smaller slot width and lower impingement height. For a constant Reynolds number, jet impingement height and plate thickness, a wider opening of the slot provided higher average heat transfer coefficient and higher average Nusselt number. A higher average heat transfer coefficient was seen at a smaller thickness, whereas a thicker plate provided a more uniform distribution of heat transfer coefficient. Higher thermal conductivity substrates also provided a more uniform heat distribution.
Thermal Conductance Measurement Techniques for High-Speed Bearings in Vacuum
Authors: Demsky Steven M. , Takeuchi Yoshimi R. , Dickey James T.
Published: April 2009

An experimental method has been developed at The Aerospace Corporation to determine the thermal conductance of moving bearings in vacuum. The test involves the measurement of thermal conductance of a single bearing under controlled inner race rotational speed, axial load, and thermal environment. Applications of interest include high-speed momentum wheels and flywheels. This paper covers the experimental method developed for this purpose and the techniques used to establish measurement uncertainty.
Heat of Reaction Measurements of Sodium Borohydride Alcoholysis
Authors: Zhang Jinsong , Fisher T. S. , Gore Jay P. , Ramachandran P. Veeraraghavan
Published: April 2009

On-board hydrogen storage has been identified as one of the most challenging technical barriers to the transition from gasoline to hydrogen powered vehicles. The Hydrogen-On-Demand™ system patented by Millenium Cell Inc. uses sodium borohydride and water to generate hydrogen when needed. The system has many advantages over other types of storage methods such as compressed hydrogen, liquid hydrogen and metal hydrides. Nevertheless, the cost of making and regenerating sodium borohydride is too high. A recently filed patent indicates that sodium borohydride alcoholysis (e.g. using ethylene glycol) may offer some advantages over the aqueous system in terms of regeneration, which may significantly reduce the cost to regenerate sodium borohydride. To begin evaluating the energy efficiency of this new approach, this work experimentally characterizes the heat of reaction of sodium borohydride with ethylene glycol. The heat of reaction was measured to be approximately 220 kJ/mol (exothermic). For the sodium borohydride and water reaction, two different heat of reaction values have been reported in prior literature. The present work shows that the heats of reaction for both sodium borohydride hydrolysis and alcoholysis are both near 220 kJ/mol exothermically.
Optimization of an Effervescent Atomizer to the Combustion of Residue Oils
Authors: Ferreira Manuel E. C. , Martins Jorge J. G. , Teixeira Jose´ C. F.
Published: April 2009

This paper reports the geometrical optimization of an effervescent atomizer used in the combustion of used recycled oils. The objective was to obtain stable flames while minimizing the emission levels. A test facility was designed and constructed, which included: a furnace rated at a thermal input of 300 kW and a swirl generator as a part of the burner setup for the application of the effervescent atomizer. Other auxiliary facilities were also included, such as: cooling system, air supplies and pre-heating gas burner. Combustion tests were carried out with used recycled oil having a viscosity of 46 mm2/s (50°C) and a higher heating value of 44.6 MJ/kg. Results included qualitative observations of the ignition and flame stabilization, emission concentrations and LDA velocity measurements of the flow field produced by the swirl generator with and without flame. The results show a good performance of the swirl generator in the process of fuel/air mixing inside the furnace, which results in very low emission levels. The various tests carried out with different geometric configurations of the burning facility clearly suggest that the high velocity and penetration of the spray require an adequate design of the swirl generator and the nozzle orifice, in order to obtain a good air/fuel mixture inside the furnace.
Experimental Study of Thickness Effects on Evaporation/Boiling on Thin Sintered Copper Mesh Surfaces
Authors: Li Chen , Peterson G. P. , Wang Yaxiong
Published: April 2009

Evaporation/boiling from surfaces coated with multiple, uniform layers of sintered, isotropic, copper-mesh is studied experimentally. The investigation focuses on the effect of the wick thickness on the steady-state evaporation/boiling heat transfer coefficient and the critical heat flux under atmospheric pressure conditions. An optimal sintering process was developed and employed to prepare the test articles. This process minimizes the interface thermal contact resistance between the heated wall and wick, as well as enhancing the contact conditions between the layers of copper mesh. Due to the reduction in the thermal contact resistance between the wall and copper mesh, extremely high evaporation/boiling heat transfer coefficients were achieved. These values, which varied with input heat flux and wick thickness, were from 5 to 20 times higher than those previously reported by other researchers. The critical heat flux (CHF) was also significantly enhanced. The experimental results also indicated that while the evaporation/boiling heat transfer coefficient is not affected by wick thickness, the CHF for steady-state operation is strongly dependent on the wick layer thickness. In addition, the CHF increases proportionally with the wick thickness when the wick structure, porosity and pore size are held constant. Sample structure and fabrication processes as well as test procedures are described and discussed in detail and the experimental results and observations are systematically presented and analyzed. Evaporation/boiling Heat transfer regimes from these wick structures are identified and discussed based on the visual observations of the phase-change phenomena and the relative relationship between the heat flux and superheat.
Analysis of Thermal Comfort and Contaminant Removal in an Office Room With Underfloor Air Distribution System
Authors: Ho Son H. , Rosario Luis , Rahman Muhammad M.
Published: April 2009

The study of human thermal comfort requires detailed information about distributions of air velocity, air temperature and relative humidity in an occupied zone. Air quality is related to the contaminant distributions and contaminant removal effectiveness in indoor environment. This paper presents an evaluation of thermal comfort and contaminant removal for an office setting with underfloor air distribution system by the use of computational fluid dynamics modeling. A typical single cubicle in a large office floor in steady state condition of airflow as well as heat and mass transfer is investigated for both cooling and heating scenarios. The model includes a typical cubicle in a large office floor with a chair, a desk with a personal computer on its top, and heat sources such as seated people, computer monitor and CPU, and lights. Air enters the occupied zone through an inlet located at the floor level supplying a vertical upward inflow. Five different locations of the inlet diffuser, three different inlet air speeds, and four different loads of heat loss through the floor slab in heating case scenario were considered. Distributions of velocity, temperature, relative humidity, and contaminant concentration in such cases were computed. The results were compared among various simulation cases and showed reasonable agreement with experimental data taken from related literature.
Mathematical Imaging of Piloted Diffusion Methane-Air Flames Under Anisotropic Scalar Dissipation Rates
Authors: Abou-Ellail Mohsen M. , Beshay Karam R. , Halka David R.
Published: April 2009

The present work is a numerical simulation of the, piloted, non-premixed, methane–air flame structure in a new mathematical imaging domain. This imaging space has the mixture fraction of diffusion flame Z1 and mixture fraction of pilot flame Z2 as independent coordinates to replace the usual physical space coordinates. The predications are based on the solution of two–dimensional set of transformed second order partial differential conservation equations describing the mass fractions of O2, CH4, CO2, CO, H2O, H2 and sensible enthalpy of the combustion products which are rigorously derived and solved numerically. A three–step chemical kinetic mechanism is adopted. This was deduced in a systematic way from a detailed chemical kinetic mechanism by Peters (1985). The rates for the three reaction steps are related to the rates of the elementary reactions of the full reaction mechanism. The interaction of the pilot flame with the non-premixed flame and the resulting modifications to the structure and chemical kinetics of the flame are studied numerically for different values of the scalar dissipation rate tensor. The dissipation rate tensor represents the flame stretching along Z1, the main mixture fraction, and in the perpendicular direction, along Z2, the pilot mixture fraction. The computed flame temperature contours are plotted in the Z1-Z2 plane for fixed values of the dissipation rate along Z1 and Z2.These temperature contours show that the flame will become unstable when the dissipate rates along Z1 and Z2 increase, simultaneously, to the limiting value for complete flame extinction of 45 s−1. However, the diffusion flame will extinguish for dissipate rates less than 20 1/s, if unpiloted. It is also noticed that the flame will remain stable if the dissipation rate along Z2 is increased to the limiting value, while the dissipation rate, along Z2, remains constant at a value less than 30 s−1.
Flow Regime Analysis of Forced Flow Boiling Hydrogen Subjected to High Heat Flux
Authors: Pasch James , Popp Michael , Anghaie Samim
Published: April 2009

This paper presents an analysis of forced flow two-phase hydrogen heat transfer data for the purpose of interpreting the various flow regimes of inverted annular flow. Hydrogen heat transfer data available from an early 1960s NASA experimental investigation were used for the analysis. The data was evaluated in light of a heat transfer characteristics map and related flow pattern map which were established by more recent work on inverted flow film boiling of freon R113. It was shown that the hydrogen data exhibit the same three flow patterns as found in the R113 data. This may allow the use of film boiling heat transfer models developed for such fluids to be used for hydrogen film boiling heat transfer predictions.
Experimental Investigations Into Mixed Convection About a Horizontal Cylinder: Part A — Heat Transfer Using Digital Speckle Pattern Interferometry
Authors: Egan Vanessa , Dalton Tara , Davies Mark R. D. , Whelan Maurice
Published: April 2009

Mixed convection heat transfer is commonly found in many engineering applications and is particularly relevant to the cooling of electronic components but despite this, the physics of this heat transfer regime is not fully understood. This paper presents an experimental study into buoyancy opposing cross flow, a commonly found mixed convection regime. The experimental configuration comprised a long heated cylinder suspended in a glass walled enclosure. The airflow within the enclosure was controlled using a baffled axial fan to give Reynolds numbers in the range of 32–89. The mean Nusselt numbers were measured about the cylinder for Rayleigh numbers between 1.7E+04–4.0E+04. For the acquisition of full field data the optical techniques, digital speckle pattern interferometry (DSPI) and phase measurement interferometry (PMI), were employed. Buoyancy opposing cross flow created an unsteady flow field about the cylinder at low Reynolds numbers and steady state temperatures. DSPI enabled real-time interferograms to be recorded and results are presented in the form of instantaneous interferograms showing the high frequency fluctuations of the temperature field about the cylinder. Attention is focused on understanding the trend in mean heat transfer values resulting from an increased inertia force and thus providing a significant insight into unsteady mixed convection flow.
Mitigation of Bending Stress and Failure Due to Temperature Differentials in Piping Systems Carrying Multiphase Fluids: Using CFD and FEA
Authors: Diwakar Philip , Mehrotra Vibhor , Richardson Frank
Published: April 2009

The bending of large pipes due to temperature differentials between the bottom and top of the pipe is a very serious problem. The temperature differentials can either be caused by extremely cold liquids (such as methane or ethylene flowing from a lateral into a flare header) or hot liquids flowing at the bottom of a piping system (such as in a Vacuum transfer line) while the top is exposed to atmospheric conditions. In some cases liquids may be produced by Joule-Thompson cooling of high pressure cold gas as it expands through a safety-relief or emergency depressurization valve. The liquid so formed can accumulate, for example, on the dead leg side of a flare header. The differential expansion can deform the pipe so that it lifts off its supports. It takes a finite amount of time for the heat transfer by conduction to equilibrate the temperature to a more benign level. The initial stresses induced due to large thermal differential may even cause the pipe to crack in the region of the supports and T-joints to the laterals. This phenomenon has been observed in several industries, most predominantly in the petrochemical industry. This paper recounts the use of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) to study this important phenomenon. The liquid flowing from the lateral into the main header pipe is multiphase in the dispersed, stratified, slug or annular flow re´gime. Multiphase flows with heat transfer are analyzed using CFD. The temperatures on the walls of the pipe system are then transferred to the FEA and analyzed for heat transfer and thermal stresses. These stresses are compared to ASME standards to see if they are within allowable limits. This paper also recounts efforts to reduce the bending effect by preventing liquid accumulation on the dead leg side. Other methods that provide better supports for bent piping are studied. Further, methods of equilibrating the temperature faster to prevent the bowing of the pipe are also studied. It is hoped that this presentation will benefit people designing piping networks with varying liquid and vapor traffic.
Performance Evaluation of Prototype Microchannel Evaporators for the Residential Air-Conditioning Application
Authors: Cho Honggi , Cho Keumnam
Published: April 2009

The present study was aimed to evaluate the performance of prototype microchannel evaporators for the residential air-conditioning application using R-22 refrigerant under wet condition. Eight prototype evaporators were manufactured and tested using psychrometric calorimeter test facilities. Each evaporator consisted of two or three parallel flow heat exchangers connected with return pipes. The parallel flow heat exchanger had 41 parallel microchannel tubes that brazed into the inlet and outlet headers. The tube had 8 rectangular ports with the hydraulic diameter of 1.3 mm. The louvered fin had louver angle of 27°, louver pitch of 1.4 mm and flow depth of 18.8 mm. It was found that the flow area ratio had a great effect on the cooling capacity of the microchannel evaporator from experimental results of prototypes 4, 5 and 6, and there was an appropriate range for cooling capacity. The flow distribution characteristics were slightly affected by the pressure drop resulting from the configuration of the refrigerant flow at the exit of the evaporator like merging manifold, which means that it could be possible to reduce the manufacturing cost of the microchannel evaporator. Both refrigerant and air-side pressure drops for the best prototype evaporator were 28.6 kPa and 2.53 mmAq, respectively, which could be affordable for the residential air-conditioning application.
Enhancement of Thermal Bubble Nucleation From Micro Cavity Filled With Porous Materials
Authors: Chang Young-Soo , Lee Heon Ju , Kim Ho-Young , Oh Sang-Youp , Lee Yoon-Pyo
Published: April 2009

In many applications, the study of nucleation of thermal bubble is requisite for design of micro geometry such as micro-actuator, chip cooling system and ink-jet device operation and so on. In heterogeneous nucleation boiling, a bubble generally initiated from a small gas trapped cavity on heated surface. Experimental observations were undertaken on the bubble generation phenomena from fabricated micro-cavity on the silicon wafer, which is immersed in FC-72. Especially, the nucleation of thermal bubble is much enhanced in the case of the cavity filled with porous material compared to vacant cavity. Incipience boiling occurs much less degree of superheat, which is the difference of surface temperature and bulk fluid temperature. It is also observed that the generated bubble size and frequency are dependent on the specifications of cavities. In this study, we performed various experiments to minimize the degree of superheat and to generate specific bubble size and purposed frequency by modification of cavity size and filling porous materials.
On Treatment of Negative Pressures in Fluid Dynamics
Authors: Tiselj Iztok , Gale Janez
Published: April 2009

Rapid depressurization of a cold single-phase liquid leads to the onset of a vaporisation, i.e. the phase transition phenomena. Prior to the start and in the very first moment of the phase transition, pressure in the liquid may briefly drop to negative values, when initial liquid temperature is low enough. Metastable liquid in a state of tension is well known in static experiments, but is less known in the fluid dynamics. The present paper discusses some preliminary findings in the field of modeling of the negative pressures in transient water flows and subsequent phase transition with a single-pressure two-fluid model. A highly simplified single-pressure two-fluid model is used in the present work to describe the two-phase flow with negative liquid and positive vapor pressure. The assumption used at negative liquid pressures is equal temperature of liquid and newly generated vapor phase, while the gas pressure is assumed to be the saturation pressure at that temperature. Rather rough models seem to be sufficiently accurate due to the large uncertainty in the modeling of the single-to-two-phase flow transition, which strongly depends on the density of the nucleation sites in the liquid and at the wall.
Analysis on the Glass Panel Heating in the Vacuum Sealing Chamber for a Plasma Display Panel
Authors: Lee Kong Hoon , Kim Ook Joong
Published: April 2009

Numerical analysis has been carried out to find optimum parameters for the infrared heating of the glass panel in the vacuum sealing chamber for a Plasma Display Panel (PDP). The glass panel is composed of two sheets of glass plates and both 42 and 60 inch panels are used for the analysis. The glass panel is assumed to be opaque to radiation for the simplification and thermal conduction in the direction normal to the glass surface is neglected since the thickness of the panel is much smaller than other dimensions. Heat is transferred only by conduction within the panel and heat transfer between the panel and heaters in the vacuum chamber is analyzed with the surface-to-surface radiation exchange model. Wall reflectivity is used as a parameter in the analysis. When the reflectivity of the chamber wall is high, the temperature uniformity of the panel is improved but rapid heating might not be possible since it requires a long heating time. When the reflectivity is low, rapid heating is possible but temperature uniformity is degraded and the electric power applied to heaters increases due to large heat loss through the wall.
Critical Heat Flux in Tubes With Cosine Axial Heat Flux
Authors: Shim W. Jaewoo , Park Joo-Yong , Lee Ji-Su , Kim Dong Kook
Published: April 2009

In this study a method to predict CHF (Critical Heat Flux) in vertical round tubes with cosine heat flux distribution was examined. For this purpose a uniform correlation, based on local condition hypothesis, was developed from 9,366 CHF data points of uniform heat flux heaters. The CHF data points used were collected from 13 different sources had the following parameter ranges: 1.01 ≤ P (pressure) ≤ 206.79 bar, 9.92 ≤ G (mass flux) ≤ 18,619.39 kg/m2s, 0.00102 ≤ D (diameter) ≤ 0.04468 m, 0.0254 ≤ L (length) ≤ 4.966 m, 0.11 ≤ qc (CHF) ≤ 21.42 MW/m2, and −0.87 ≤ X (exit qualities) ≤ 1.58. The result of this work showed that the uniform CHF correlation could be used to predict CHF accurately in a non-uniform heat flux heater for wide flow conditions. Furthermore, the location, where CHF occurs in non-uniform heat flux distribution, can also be determined accurately with the local variables: the system pressure (P), tube diameter (D), mass flux of water (G), and true mass flux of vapor (GXt). The new correlation predicted CHF with cosine heat flux, 297 data points from 5 different published sources, within the root mean square error of 12.42% and average error of 1.06% using the heat balance method.
Extending the 3 Omega Method to Measure Thermal Conductivity Anisotropy in Three Dimensions
Authors: Olson Brandon , Graham Samuel
Published: April 2009

A simplified method of measuring three-dimensional thermal conductivity anisotropy has been developed around the popular 3ω method. This approach utilizes a pair of surface mounted test elements as both heating and sensing probes. 3ω has historically been used to measure thermal conductivity in homogeneous, low conductivity substrates and thin surface films. The present technique employs a combination of broad band frequency measurements and directionally oriented test elements to extract property information that was previously inaccessible. Data reduction is dramatically improved through the use of a full accuracy analytical solution that replaces the heavily approximated original 3ω solution. Anisotropic degrees of freedom are optimized using an efficient gradient based algorithm that can be coded using any number of commercially available software packages. Test element design guidelines are presented to help insure that optimal experimental conditions exist during material testing. Comparative experimental results are presented for an aligned graphite fiber / epoxy composite.
Electromagnetic-Thermal Responses of Tissues During Microwave Hyperthermia
Authors: Lee H. K. , Li B. Q. , Huo Y.
Published: April 2009

A numerical model is developed to study the electromagnetic and thermal responses of normal and cancerous tissues under microwave hyperthermia. The numerical model is 3-D dimensional with full integration of electromagnetic and thermal phenomena. The model development employs a finite difference time domain (FDTD) method for electromagnetic calculations and an implicit transient node finite element (FEM) method for thermal calculations. The multi-scale microwave-propagation and thermal diffusion phenomena are coupled either directly or indirectly, depending up of the properties of the tissues. The calculated quantities include the absorbed source distribution, heating pattern, and temperature distributions within the tissues consisting of skin, fat, muscle and blood flows. The calculated results are compared with experimental measurements.
Heat Transfer Increase by Flow Structures Modifications
Authors: Lemarie´ Charles-Andre´ , Bourabaa Nachida , Monnoyer Franc¸ois , Benazzouz Tewfik
Published: April 2009

This paper makes use of a new methodology for heat transfer increase through flow structures modifications. Intended to help railway designers in handling cooling issues, it is applied to improve the roof-mounted equipment design of a modern railway coach, namely the CORADIA TER 2N NG produced by the ALSTOM Transport company. The brake resistor, a key equipment in charge of dissipating the train kinetic energy as heat into the surrounding air during braking phases, has been particularly considered. To do so, a simple model including a heated obstacle inside a three-sided lead-driven cavity is used, and simple geometry variations are suggested. Their impact on heat transfer is then estimated through numerical simulations while experimental tests validate the results obtained.
Thermal Stress Analysis During the Czochralski Melt Growth of Optical Crystals
Authors: Xu F. , Li B.
Published: April 2009

This paper presents a finite element method for studying Czochralski melt growth of optical crystals with an emphasis on thermal and stress analyses of axisymmetric problems. A heat transfer analysis is performed to determine the temperature distribution in the crystal. The heat transfer problem is solved with a mixed computational model including the hybrid finite/boundary element for electromagnetism, the Galerkin finite element method for transport equations, the Galerkin boundary element method for external surface energy exchanges and the discontinuous finite element method for internal radiation. The temperature results are directly input as loads to determine the stresses caused by the temperature loading. Thermal stress analyses of a Gadolinium gallium garnet (Gd3Ga5O12) crystal are performed in the cases of the [100] pulling direction. Then, we can evaluate the crystal quality based on the thermal stress analysis. Three real operating cases for Gadolinium gallium garnet crystal growth processes are studied with the method presented in this paper.
Comparison of Temperature Measurements in Fire Test Furnaces Using Aspirated Thermocouples
Authors: Mammoser John H. , Jimenez Aldo
Published: April 2009

There are numerous thermocouple types which are used to measure temperature in experimental fire environments including bare bead, plate, sheathed (grounded and ungrounded) and aspirated thermocouples (suction pyrometers). Furnaces used to test fire resistive construction, as specified in the Standards ANSI/UL 263, ASTM E119 and NFPA 251 employ sheathed, ungrounded thermocouples to measure gas temperatures, while room fire experiments, such as ASTM E603-01, employ bare bead and aspirated thermocouples to measure hot gas temperature layers. Shielded, aspirated thermocouples are quite inexpensive and easy to make, however, the suction needed to create velocities in excess of 10 m/s at the tip is quite a difficult challenge. A commonly used method to create suction includes multiple gas traps to cool and dehumidify the hot gas before passing through a pump rated for high temperatures. This method can be costly, time consuming to maintain and cannot operate for multiple hours at high temperature without damaging the pump. An investigation has been undertaken to determine a cost effective method to measure gas temperatures in fire test furnaces for long durations at high temperatures. A comparison of bear bead, plate and double shielded, aspirated thermocouples will be presented. A low cost, durable aspirated thermocouple will be shown to continuously endure temperatures in excess of 1040°C for multiple hours.
Investigating the Effect of Power Distribution on Cooling a Double-Sided PCB: Numerical Simulation and Experiment
Authors: Johansson Jonas , Belov Ilja , Leisner Peter
Published: April 2009

An experimental procedure for investigating the effect of power distribution on the cooling of a double-sided PCB is implemented. A number of computational fluid dynamics (CFD) models are validated by laboratory experiments performed in 19.5°C temperature environment. Case temperatures of surface-mounted components fully populating the PCB sides are measured and monitored in simulations. Different combinations of power distribution with other cooling methods, such as a heatsink tooled on a sealed or open enclosure, at natural or forced convection, are studied. Thermally efficient uniform and non-uniform power configurations are determined on a double sided PCB. It is concluded that managing power distribution on a double-sided PCB can be considered as a measure to improve the thermal performance of electronic modules.
Interfacial Energy and Micelle Conditions of Ternary Mixtures for Improved Heat Transfer
Authors: Reynoso G. , Marti´nez P. , Reyes R.
Published: April 2009

The search for suitable mixtures as boiling fluids leads to the development of ternary liquid mixtures that could handle even higher heat fluxes than binary mixtures through the formation of stable bubble-micelles departing from the heater’s surface. The amount of experimental work for testing the combinations is reduced using the interfacial tension prediction capabilities of simulation software, although it is not possible to predict singularities in the interfacial tension behavior of the mixtures. The ethanol aqueous mixture shows a singularity in its interfacial tension value at 16% ethanol by weight. In this work was combined with glycols for enhancing boiling heat transfer by decreasing the mixture interfacial tension. Also, the effect of the surfactants Dodecyl Benzene Sodium Sulfonate (DBSS) and Sodium Lauryl Sulfonate (SLS) in the mixture interfacial tension was studied. The measurements of sessile drop contact angles of mixtures with added surfactant allowed finding the singularities in the surface tension values that are related to critical micelle concentrations and the increment in boiling heat transfer. The propilenglycol-ethanol-water mixture produced the lowest values of contact angles, while for the etilenglycol-ethanol-water mixtures no such reduction was obtained with the same amount of the glycol. The use of DBSS and SLS at their critical micelle concentration decreased further the interfacial tension of the propilenglycol ternary mixture to generate a mixture that could improve the convective heat transfer coefficient.
Molecular Dynamics Simulation of the Density and Surface Tension of Water by PPPM Method
Authors: Shi Bo , Sinha Shashank , Dhir Vijay K.
Published: April 2009

This paper presents a molecular simulation study of the density and surface tension of a water film for a range of temperatures from 300K to 600K. The extended simple point charge (SPC/E) [1] interaction potential for water is used with full Ewald summation. The PPPM method, which automatically include untrucated the long-range terms, is applied instead of using the tail correction. The normal and tangential components of the pressure tensor were calculated and are presented at 352K. Results show that the calculated density and surface tension of water fit well with experimental data for temperatures less than 500K.