bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurements of Rewetting Temperatures of Hot Dry Surface in Saturated and Subcooled Film Boiling
Authors: Nagashima Nozomi , Ohtake Hiroyasu , Koizumi Yasuo
Published: March 2011

The behavior of rewetting on a high superheated and dry surface, focusing on rewetting temperature just as collapse of saturated and subcooled film boiling was investigated experimentally by using a commercial separated-type infrared thermometer. Saturated and subcooled impingement jet experiments were conducted by using a silicon wafer with 20 mm length, 20 mm width and 0.5 mm thickness and pure water at atmospheric condition. Temperature of the test heater was measured by using a commercial separated-type infrared thermometer from a back side of it. The present experimental results showed that as the liquid subcooling was high, Minimum Heat Flux temperature (i.e., Minimum Film Boiling, rewetting temperature or quenching temperature) was higher. Furthermore, the effect of the rewetting temperature on liquid subcooling was similar to that of Dhir-Purohit’s correlation quantitatively.
Large Eddy Simulation of Film Cooling With Swirling Coolant Flow
Authors: Oda Yutaka , Takeishi Kenichiro , Shimizu Dai
Published: March 2011

LES (Large Eddy Simulation) of a film cooling with a swirling coolant jet has performed for a circular hole at the blowing ratios of M = 0.5 and 1.0. For the LES of film cooling flows, a film-hole model based on a RFG (Random Flow Generation) technique was proposed to simulate turbulent fluctuating flows at the exit plane of film cooling hole as a boundary model. As a result, film cooling with a swirling coolant jet is confirmed to be effective to reduce net heat transfer from the hot gas to the wall at given uniform temperature conditions by about 6% and 12% at the blowing ratio of M = 0.5 and 1.0, respectively, compared to nonswirling cases. In a swirling film coolant jet case at M = 1.0, penetration of coolant jet is suppressed. It seems that one of the two jet core regions is pressed against the bottom wall by the primary swirl of the coolant jet itself, and this seems to prevent the detachment of the film coolant from the wall. In addition, the proposed film-hole model for LES was validated by the comparison of predicted center-line film effectiveness with a known experimental result.
Characteristics of Air-Oil Slug Flow in Inclined Pipe Using Tomographic Techniques
Authors: AbdulKareem Lokman A. , Hernandez-Perez V. , Sharaf S. , Azzopardi Barry J.
Published: March 2011

The structure of gas liquid flow in horizontal and vertical pipes to some extent is well understood. However, the situation in inclined pipes is much more difficult with very little work published in literature. Changes in physical phenomena occur as the pipe inclination angle varies from the vertical through to inclined and then to horizontal. This work describes a study carried out at the University Of Nottingham on the effects of inclination on gas / liquid slug flow. Two advanced tomography techniques were applied simultaneously to the flow of a mixture of air and silicone oil in a 67 mm internal diameter pipe and the pipe was inclined at angles 0, 5, 10, 30, 45, 60, 80, 90 degrees. This paper reports on the use of twin plane electrical capacitance tomography (ECT) system developed by TomoFlow electronics Ltd to measure flow characteristics in gas-liquid flows. We report measurements over a range of liquid superficial velocities from 0.05 m/s to 0.5 m/s and gas superficial velocities from 0.06 m/s to 6 m/s at all the above angles in a pipe 6 m long. A second technique, Capacitance Wire Mesh Sensor (WMS) developed at Forschungszentrum Rossendorf-Dresden/Germany was also present in the tests, The results for the two sensors are shown to be within 1% of each other in some instances when comparing cross-sectional averaged void fraction. The data was recorded at an acquisition frequency of 1000 Hz over an interval of 60 seconds. This enabled an examination of the flow to be carried out at several levels of complexity. Both measuring sensors provide time and cross-sectionally resolved information about the spatial distribution of the phases. In present paper, the effect of inclination on the characteristics of slug flow is presented. Radial gas volume fraction profiles and bubble size distributions were also processed from the wire-mesh sensor output. The results indicate that the pipe inclination has a significant effect on the slug flow characteristics.
Comparisons Between Integral Transform, Finite Volumes and Combined Solution Strategies for Convective Heat Transfer Problems
Authors: Chalhub D. J. N. M. , Sphaier L. A.
Published: March 2011

Both traditional discretization-based numerical methods and alternative hybrid analytical-numerical techniques have been successfully applied for solving a considerable number of convective heat transfer problems. Despite the number of studies dedicated to separately solving a given problem by one methodology or the other, there are very few studies dedicated to comparing the computational solution performance of these approaches. In this context, this paper presents a comparison of solutions using the Finite Volumes Method (FVM) and the Generalized Integral Transform Technique (GITT) for a three dimensional steady-state convective heat transfer problem. The selected problem is that of thermally developing laminar flow within a square duct. The flow is considered kinetically developed and a constant wall temperature condition is employed. Both solutions are computationally implemented using the Mathematica system and, in order to guarantee a fair comparison, both implementations employ the same numerical ODE integrator to handle the solution in the flow direction. The comparisons are made by observing the convergence behavior of the Nusselt number for different positions along the flow direction, for both methodologies. In addition to these comparisons, combined solution strategies are analyzed, in which the velocity is obtained by one methodology and the temperature by the other.
Laminar Natural Convection From Isothermal Vertical Cylinders: A Revisit to a Classical Subject
Authors: Day Jerod C. , Traum Matthew J. , Boetcher Sandra K. S.
Published: March 2011

Laminar natural convection heat transfer from the vertical surface of a cylinder is a classical subject, which has been studied extensively. Furthermore, this subject has generated some recent interest in the literature. In the present investigation, numerical experiments were performed to determine average Nusselt numbers for isothermal vertical cylinders (103 < RaL < 109, 0.5 < L/D <10, and Pr = 0.7) situated on an adiabatic surface in a quiescent ambient environment which will allow for plume growth. Results will be compared with commonly used correlations and a new average Nusselt number correlation will be presented. Furthermore, the limit for which the heat transfer results for a vertical flat plate may be used as an approximation for the heat transfer from a vertical cylinder will be investigated.
Thermal Conductivity Measurement of Vertically Aligned Single-Walled Carbon Nanotubes Utilizing Temperature Dependence of Raman Scattering
Authors: Ishikawa Kei , Chiashi Shohei , Badar Saifullah , Thurakitseree Theerapol , Hori Takuma , Xiang Rong , Watanabe Makoto , Shiomi Junichiro , Maruyama Shigeo
Published: March 2011

We present a method for measuring the thermal conductivity and the thermal contact resistance between the film and the substrate of vertically-aligned single-walled carbon nanotubes (VA-SWNTs) grown on Si substrate by ACCVD (Alcohol Catalytic Chemical Vapor Deposition) method, utilizing temperature dependence of the Raman spectrum obtained from SWNTs. The method utilizes the excitation laser of the Raman system to heat the VA-SWNT film and measure the temperature simultaneously. The method finds the thermal conductivity of the VA-SWNT film to be around 1 Wm−1K−1 and the thermal contact resistance between the substrate and the film to be around 10−5∼10−6 m2KW−1. The obtained film thermal conductivity is converted into equivalent thermal conductivity of an individual SWNT, whose value is several tens of Wm−1K−1, and is more than an order of magnitude smaller than the reports on individual SWNTs.
Validation of a Thermal Conductivity Measurement System for Fuel Compacts
Authors: Jensen Colby , Xing Changhu , Ban Heng , Phillips Jeffrey
Published: March 2011

A high temperature guarded-comparative-longitudinal heat flow measurement system has been built to measure the thermal conductivity of a composite nuclear fuel compact. It is a steady-state measurement device designed to operate over a temperature range of 300 K to 1200 K. No existing apparatus is currently available for obtaining the thermal conductivity of the composite fuel in a non-destructive manner due to the compact’s unique geometry and composite nature. The current system design has been adapted from ASTM E 1225. As a way to simplify the design and operation of the system, it uses a unique radiative heat sink to conduct heat away from the sample column. A finite element analysis was performed on the measurement system to analyze the associated error for various operating conditions. Optimal operational conditions have been discovered through this analysis and results are presented. Several materials have been measured by the system and results are presented for stainless steel 304, inconel 625, and 99.95% pure iron covering a range of thermal conductivities of 10 W/m*K to 70 W/m*K. A comparison of the results has been made to data from existing literature.
Thermal Effects During Hollow Polymer Fiber Drawing
Authors: Grange Spencer , Dillon Heather , Mescher Ann , Emery Ashley
Published: March 2011

Cylindrical hollow polymer fibers are drawn in an environment in which the heat transfer is approximately half radiative and half convective. A preform is introduced into the drawing furnace through an iris, travels vertically downward through the furnace, and fiber of reduced diameter exits through a bottom iris. For photonic crystal and biomedical applications one or more circular channels are drilled longitudinally in the preform. Challenges arise in the manufacture of hollow polymer fibers because the hole to outer diameter (aspect) ratio of the preform can change as the material is heated and drawn into fiber. Experiments to quantify the trends in aspect ratio changes have been performed. The results indicate that further study of the drawing process for hollow fiber is needed. Experiments with thick walled hollow fibers show poor repeatability even at stable drawing conditions, and the trends were not captured well by existing models. A simple 1-D model is presented and compared to the experimental results.
Combining Meshless Analysis and Kalman Filters to Estimate Parameters When System Models are Inaccurate
Authors: Emery A. F. , Pepper D. W.
Published: March 2011

Parameter estimation assumes that the model is an accurate representation of the system being studied and that any deviations are caused by measurement noise. For real experimental data this is often not the case. Clearly, the model will constructed to the highest fidelity by the analyst but when it is deficient, the remedy is not always obvious. One approach is to include a discrepancy function which one hopes will resolve any differences. The paper describes the use of such a function combined with Kalman filtering and meshless FEA.
Thermal Fluctuations and Heat Transfer Measurements in an Externally Heated Rotary Cylinder
Authors: Sunkara Koteswara Rao , Herz Fabian , Specht Eckehard
Published: March 2011

Rotary cylinders are widely used in the industries for thermal processing of granular materials. It is highly important to maintain the uniform temperature throughout the solid bed during this process. In the current study, the temperature fluctuations in the bed and the wall to bed heat transfer coefficients (HTC) are estimated. A pilot plant rotary steel cylinder of length 45 cm and internal diameter of 60 cm has been designed and fabricated with industrial norms. Two rods, each assembled with 16 thermocouples of k-type are arranged in the cylinder, one fixed and another rotates with the drum to measure the temperature variations along the radial and circumferential direction respectively. Experiments have been performed with various materials such as Quartz sand (0.2 mm) and Glass beads (0.7 mm) to measure the effect of filling degree and rotational speed on mixing time and wall-solid contact coefficient. Thermal variations in the bed have been studied thoroughly and it is found that, as the time interval increases the gradients in the bed becomes closer. Contact heat transfer has been investigated from the heat balance between wall and solid. The effect of rotational speed, filling degree on the contact coefficient have been estimated. It shows that as the rotational speed increases, the contact coefficient also increases. The heat transfer measurements show good agreement with the proposed models.
Flow Pattern Dynamics Around a Vertical Dividing Junction
Authors: Alamu Mhunir B. , Azzopardi Barry J.
Published: March 2011

Liquid hold-up and phase split have been measured to study flow pattern dynamics around a vertical dividing junction with 0.005 m internal diameter pipes. Liquid phase viscosities were varied systematically between 1 mPa s and 36 mPa s. Test matrix implemented varied between 0–32 m/s for gas superficial velocity and 0.003–1.3 m/s for liquid superficial velocity respectively. Dynamic signals were acquired during the passage of gas–liquid two-phase flow employing electrical resistance between pairs of flush-mounted ring conductance probes located around the junction. The time varying void and phase split data have been examined at a number of levels. First, information about distribution of phases and flow pattern classification along each segment of the pipe is presented using probability Density Function (PDF) generated from time varying void fraction. PDF characteristic signature exhibits lower peaks and a marked shift towards decreasing void fraction as liquid viscosity increases. For a viscous liquid phase, bubbly flow approaching the junction changes to slug flow pattern after splitting at the junction in the vertical direction. Flow pattern in the horizontal side arm remains inevitably stratified irrespective of increase in liquid viscosity. At another level, liquid hold-up and phase split were examined. This analysis reveals additional flow assurance details. Liquid hold-up was seen to increase with increase in both liquid viscosity and gas take-off at the horizontal segment of the junction. However, effect of liquid viscosity only become significant when gas take-off exceeds a threshold of 0.40. Plot of the liquid hold-up against mixture velocity at various take-offs and different liquid viscosities fingerprints churn-annular transition boundary around gas superficial velocity of 15 m/s.
Comparison of Accuracy and Computational Expense of Radiation Models in Simulation of Non-Premixed Turbulent Jet Flames
Authors: Pal Gopalendu , Gupta Ankur , Modest Michael F. , Haworth Daniel C.
Published: March 2011

The accuracy and computational expense of various radiation models in the simulation of turbulent jet flames are compared. Both nonluminous and luminous methane-air non-premixed turbulent jet flames are simulated using a comprehensive combustion solver. The combustion solver consists of a finite-volume/probability density function-based flow–chemistry solver interfaced with a high-accuracy spectral radiation solver. Flame simulations were performed using various k-distribution-based spectral models and radiative transfer equation (RTE) solvers, such as P-1, P-3, finite volume/discrete ordinates method (FVM/DOM), and Photon Monte Carlo (PMC) methods, with/without the consideration of turbulence-radiation interaction (TRI). TRI is found to drop the peak temperature by close to 150 K for a luminous flame (optically thicker) and 25–100 K for a nonluminous flame (optically thinner). RTE solvers are observed to have stronger effects on peak flame temperature, total radiant heat source and NO emission than the spectral models. P-1 is found to be the computationally least expensive RTE solver and the FVM the most expensive for any spectral model. For optically thinner flames all radiation models yield excellent accuracy. For optically thicker flames P-3 and FVM predict radiation more accurately than the P-1 method when compared to the benchmark line-by-line (LBL) PMC.
Analysis of Thermocouple Responses to Turbulent Radiating Environments
Authors: Weinschenk Craig , Ezekoye O. A.
Published: March 2011

With increasing requirements for model validation when comparing computational and experimental results, there is a need to incorporate detailed representations of measurement devices within the computational simulations. Thermocouples are the most common temperature measurement transducers in flames and fire environments. Even for the relatively simple thermocouple transducer, the coupling of heat transfer mechanisms particularly under unsteady flow conditions leads to interesting dynamics. As experimentalists are well aware, the experimentally determined thermocouple values are not the same as the local gas temperatures and corrections are often required. From the computational perspective, it is improper then to assume that the predicted gas temperatures should be the same as the temperatures that an experimentalist might measure since the thermal characteristics of the thermocouple influence the indicated temperature. In this study we investigate the thermal characteristics of simulated thermocouples in unsteady flame conditions. Validation exercises are presented to test the underlying thermocouple model. Differences are noted between the predicted thermocouple response and expected response. These differences are interpreted from the perspective of what modeling artifacts might drive the differences.
Water Vapor Adsorption–Desorption Behavior of a Small Piece of Desiccant Rotor in Temperature Swing
Authors: Kodama Akio , Washio Yasuko , Okamoto Kumiko , Osaka Yugo
Published: March 2011

This study aims to clarify the adsorption / desorption behavior of water vapor onto / from a desiccant rotor in temperature swing. A magnetic suspension balance followed time variations of the weight of a small piece of desiccant rotor at various desorption temperature, adsorption / desorption time and their duration time ratio. Adsorption-desorption swing in steady state settled down at certain amplitude of the amount adsorbed keeping the balance of the adsorption and desorption rates averaged over each period. At low regeneration temperature around 40–50°C, adsorption and desorption rates were affected considerably by the change of driving force of adsorption q*-q rather than the temperature dependence of the mass transfer coefficient. At constant adsorption and desorption air conditions, the adsorption /desorption rates could be summarized by the amount of adsorption and temperature, independently of the length of cycle time. Also, region of the amount of adsorption at which adsorption–desorption swing occurred was predicted considering the adsorption / desorption rates – amount adsorbed relationship and the adsorption / desorption duration ratio.
Enhancement of Pool Boiling and Critical Heat Flux in Self-Rewetting Fluids at Above Atmospheric Pressures
Authors: Morovati Mostafa , Bindra Hitesh , Esaki Shuji , Kawaji Masahiro
Published: March 2011

Pool boiling experiments have been conducted with a self-rewetting fluid consisting of an aqueous butanol solution to study the boiling heat transfer enhancement at pressures of 1 ∼ 4 bars. Although self-rewetting fluids have been used to enhance the performance of heat pipes, boiling heat transfer characteristics are yet to be fully understood especially at pressures above atmospheric. Pool boiling experiments with aqueous butanol solutions were performed using an electrically heated platinum wire to obtain pool boiling heat transfer data up to the Critical Heat Flux (CHF). Aqueous butanol solutions with butanol concentrations 2–7% showed enhanced heat transfer coefficients and CHF data at various pressure levels. In comparison to water, aqueous butanol solutions showed 20–270% higher values of CHF at pressures up to 4 bars. The bubble sizes were also observed to be significantly smaller in self-rewetting fluids compared to those in water at the same pressure. This observation was consistent even at higher pressures. However, for the highest butanol concentration tested (7%), the CHF enhancement was diminished at higher pressures.
A Study of Fine Particle Spheroidization Process by Elevated-Pressure Pure Oxygen Flame
Authors: Suzuki Shingo , Sasaki Koji , Nakatsuka Noriaki , Hayashi Jun , Akamatsu Fumiteru , Hagiwara Yoshiyuki , Iino Kimio
Published: March 2011

Particle spheroidization by using the flame method is an effective process to produce spheroidized particles, which have high fluidity and filling fraction, from mechanically-pulverized materials. Although it has been reported that ultra fine particles attached on the surface of spheroidized particles after the spheroidization process, the physics underlying the formation of the ultra fine particles in the flame have not been clarified. In consequence, the techniques to control the amount of the attached ultra fine particles on spheroidized particles have not been established yet. The purpose of the present research is, therefore, to control the amount of the ultra fine particles attached on spheroidized particles after the spheroidization process and to clarify the effect of pressure of the combustion field on the amount of the attached ultra fine particles. In order to clarify the effect of pressure of the combustion field, the SEM photographs, particle size distribution and the specific surface area with BET method are measured. These results clearly show that the ultra fine particles attached on the spheroidized particles were reduced with the increase in pressure of the combustion field. This can be derived from inhibited vaporization of the particles because of the shortened flame length and the subsequent reduced heat quantity added to particles whereas the flame temperature rises with the increase in pressure of the combustion field.
Condensation/Collapse of Vapor Bubble Injected to Subcooled Pool
Authors: Ueno Ichiro , Hosoya Ryota , Hong Chungpyo
Published: March 2011

We focus on condensation and collapse processes of vapor bubble(s) in a subcooled pool. We generate the vapor in the vapor generator and inject it/them to form vapor bubble(s) at a designated temperature into the liquid at a designated degree of subcooling. In order to evaluate the effect of induced flow around the condensing/collapsing vapor bubble, two different boundary conditions are employed; that is, the vapor is injected through the orifice and the tube. We also focus on interaction between/among the condensing/collapsing vapor bubbles laterally injected to the pool. Through this system we try to simulate an interaction between the vapor bubble and the subcooled bulk in a complex boiling phenomenon, especially that known as MEB (microbubble emission boiling) in which a higher heat flux than critical heat flux (CHF) accompanying with emission of micrometer-scale bubbles from the heated surface against the gravity is realized under a rather high subcooled condition.
Molecular Dynamics Simulation of Quasi-Two-Dimensional Water Network on Ice Nucleation Protein
Authors: Murakami Daisuke , Yasuoka Kenji
Published: March 2011

An ice nucleation protein induces a phase transition from liquid water to ice in air. A specific hydrophilic surface of the protein may have an influence on the network of hydrogen bonds touching on the protein. However, microscopic characteristics of the ice nucleation protein and behavior of water molecules on it have not been clarified. So we carried out molecular dynamics simulations in various quasi-two-dimensional densities of water molecules on the ice nucleation protein. The percolation threshold of water clusters was confirmed. Comparing another hydrophilic protein, the threshold density in both cases had nearly the same value. But percolation probabilities and mean cluster sizes near the threshold were different between both cases. Those results implied that the threshold density was consistent with the conventional theory, but the forming of water clusters near the threshold was influenced by the hydrophilicity on the ice nucleation protein.
Significance of Micro-Scale Mass Transport Phenomena on Fuel Cells and CO2 Sequestration
Authors: Hirai Shuichiro , Tsushima Shohji , Uemura Suguru
Published: March 2011

We describe micro-scale mass transport plays a key role for R&D of the two realistic countermeasures of global warming, hydrogen fuel-cell energy system and CO2 capture and sequestration (CCS). Understanding of the phenomena based on in-situ measurements leads to the implementation and practical use of these systems. Water inside the fuel cells plays a key role for both cell performance and durability. We have been developing magnetic resonance imaging (MRI) and also soft X ray techniques as in-situ visualization methods for water transport in operational fuel cells. MRI visualization of water content in membrane achieved high spatial resolution, 5 μm, to obtain fundamental insights on water transport process in membrane of 50 μm thickness. Soft X ray has been firstly introduced to measure water transport phenomenon in gas diffusion layer. On the other hand, we clarified CO2 distribution and its behavior by micro-focus X-ray CT and LBM simulation for CCS.
Low-Emissions Renewable Power Generation Using Liquid Fuels
Authors: Eskin Leo D. , Klassen Michael S. , Roby Richard J. , Joklik Richard G. , Holton Maclain M.
Published: March 2011

A Lean, Premixed, Prevaporized (LPP) combustion technology has been developed that converts liquid biofuels, such as biodiesel or ethanol, into a substitute for natural gas. This fuel can then be burned with low emissions in virtually any combustion device in place of natural gas, providing users substantial fuel flexibility. A gas turbine utilizing the LPP combustion technology to burn biofuels creates a “dispatchable” (on-demand) renewable power generator with low criteria pollutant emissions and no net carbon emissions. Natural gas, petroleum based fuel oil #1 and #2, biodiesel and ethanol were tested in an atmospheric pressure test rig using actual gas turbine combustor hardware (designed for natural gas) and achieved natural gas level emissions. Both biodiesel and ethanol achieved natural gas level emissions for NOx, CO, SOx and particulate matter (PM). Extended lean operation was observed for all liquid fuels tested due to the wider lean flammability range for these fuels compared to natural gas. Autoignition of the fuels was controlled by the level of diluent (inerting) gas used in the vaporization process. This technology has successfully demonstrated the clean generation of green, dispatchable, renewable power on a 30kW Capstone C30 microturbine. Emissions on the vaporized derived from bio-ethanol are 3 ppm NO(x) and 18 ppm CO, improving on the baseline natural gas emissions of 3 ppm NO(x), 30 ppm CO. Performance calculations have shown that for a typical combined cycle power plant, one can expect to achieve a two percent (2%) improvement in the overall net plant heat rate when burning liquid fuel as LPP Gas™ as compared to burning the same liquid fuel in traditional spray-flame diffusion combustors. This level of heat rate improvement is quite substantial, and represents an annual fuel savings of over five million dollars for base load operation of a GE Frame 7EA combined cycle plant (126 MW). This technology provides a clean and reliable form of renewable energy using liquid biofuels that can be a primary source for power generation or be a back-up source for non-dispatchable renewable energy sources such as wind and solar. The LPP technology allows for the clean use of biofuels in combustion devices without water injection or the use of post-combustion pollution control equipment and can easily be incorporated into both new and existing gas turbine power plants. No changes are required to the DLE gas turbine combustor hardware.
Unsteady Conjugate Heat Transfer Analysis of an Air Immersed Solid Particle With Application to an Innovative Heat Exchanger
Authors: Nettis Leonardo , De Bellis Fabio , Catalano Luciano A. , Verzicco Roberto
Published: March 2011

The improvement of both heat recovery Joule-Brayton cycles and closed cycle (externally fired) gas turbine plants is strongly limited by the availability of high efficiency heat exchangers. In such a scenario, a non conventional heat exchanger was recently proposed; this device employs falling solid particles to perform heat transfer between two separate gas flows and was designed with a 1D model neglecting conduction within the particles. Although experimental reliability of this assumption was already obtained, there is no proof available of the quantitative effect introduced by the above mentioned simplification. In this work, Direct Numerical Simulation (DNS) of a solid particle immersed in a gas flow has been performed in order to further validate the hypothesis of negligible conduction and to enhance the design of the proposed heat exchanger. Unsteady Conjugate Heat Transfer (CHT) has been used to predict the final temperature of the solid sphere for Reynolds numbers ranging from 30 to nearly 300, the computational grid being generated with the Immersed Boundary (IB) technique. A validation of the study is presented, together with grid independence and boundary independence assessment. The results fully confirmed the worthiness of the initial assumption, with a 1.4% maximum error for high Reynolds conditions (large diameter particles) with respect to the 1D model. Additionally, the code has been employed to explore the influence both of several particles disposed in a row and of the distance between successive particles.
Control of Radiative Properties of Coatings Pigmented With Fe2O3 Nanoparticles
Authors: Gonome Hiroki , Baneshi Mehdi , Komiya Atsuki , Maruyama Shigenao
Published: March 2011

This study describes nanoparticles pigmented coatings used in controlling the radiative properties of surfaces exposed to sunlight. An optimization method that embraces both thermal and aesthetic requirements has been proposed. The proposed coatings maximize the reflectivity of the near infrared (NIR) region to reduce thermal heating, while for aesthetic appeal they minimize the visible (VIS) reflected energy. This spectral behavior can be achieved by controlling the size and concentration of pigment particles and coating thickness. In this study, both experimental and numerical approaches are applied on Fe2O3 pigmented coating samples with 0.2 μm and 1 μm of average particle size and different particle concentrations and coating thicknesses. For numerical part the radiation analysis using the Radiation Element Method by Ray Emission Model (REM2) in a one dimensional parallel plane model is conducted. From the numerical results, it is shown that the optimum size of Fe2O3 particles for our desired spectral behavior is about 0.8 μm. The experimental results also show that the samples made from 1 μm particles have better performance for our objective.
Interaction Between Two Falling Droplets in the Liquid-Liquid Two Phase Flow
Authors: Ninomiya Nao , Mori Takeshi
Published: March 2011

Although the phenomena related to the multiphase flow can be found in many kinds of industrial and engineering applications, the physical mechanism of the multiphase flow has not been investigated in detail. The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. The difference in the refractive indices makes the visualization in the vicinity of the boundary of the multiple phases almost impossible. In this study, the refractive index of the aqueous phase has been equalized to that of the oil phase by adjusting the concentration of aqueous solution. Presently, the simultaneous visualization and the PIV measurement have been carried out about the both phases of the liquid-liquid two-phase flow. The measurement has been carried out for the flow field around and inside of two falling droplets interacting each other while they travel.
Influence of Surface Emissivity and of Low Emissivity Shields on the Thermal Properties of Low Density Insulating Materials
Authors: Arduini Mariacarla , Campanale Manuela , Moro Lorenzo
Published: March 2011

The theory of heat transfer through low density insulating materials explains the importance of thermal radiation in the overall heat transfer. As a matter of fact, in many semitransparent insulating materials, radiation has a considerable influence on measured thermal conductivity. In this work we continue the investigation (both experimentally and theoretically) on the heat transfer through low density insulating materials that we started some years ago and whose results have been presented in some International Conferences. Test have been done on low density insulating materials: expanded polystyrene with a density of 10 kg/m3 and polyester fibres with a density of 9 kg/m3 (these last tests are not yet completed and will not be discussed in this paper). The transfer factor T was measured in the heat flow meter apparatus of our laboratory [1]. The first measurements have been done with the two surfaces of the apparatus uncoated (emissivity ε = 0.91) at a mean test temperature of 283 K (10 °C) and then with the specimens enclosed in the aluminium foils (emissivity ε = 0.045) at the same mean test temperature. The results obtained from the measurements of the transfer factor T pointed out that a change of the emissivity ε of the surfaces from 0.91 to 0.045 caused a considerable decreasing of the transfer factor. Then the same panels have been cut into two slices and the aluminium foil has been interposed also between the slices, as shield, and the transfer factor was measured again in both cases: at first with the surfaces of the apparatus uncoated and then with the surfaces of the apparatus coated with the aluminium foils. In both cases the decreasing of the transfer factor τ was not negligible. The radiation extinction parameters have been then measured with a spectrometer and a model has been found to predict the transfer factor T in function of the testing conditions. We can conclude that in presence of a thin reflective metal cover placed on a low density insulating material, the thermal conductivity decrease immediately (about 7%) with a significant improvement of the thermal characteristics of the insulating material. If we put then some low emissivity foils between the slices of the material, another considerable decreasing of the thermal conductivity can be obtained (about 10%) and in presence of both aluminum foils (inside and outside). This fact confirms the importance of the contribution of radiation in thermal transmissivity of low density insulating materials and gives the possibility to reduce and to predict the thermal performances of such a material.
Fluid Flow Characteristics in Microchannels With Rib-Patterned Surface
Authors: Yamada Toru , Hong Chungpyo , Gregory Otto J. , Faghri Mohammad
Published: March 2011

The effects of rib-patterned surfaces and surface wettability on liquid flow in microchannels were experimentally investigated in this study. Microchannels were fabricated on single-crystal silicon wafers by photolithographic and wet-etching techniques. Rib structures were patterned in the silicon microchannel, and the surface was chemically treated by trichlorosilane to create the hydrophobic condition. Experiments with water as the working fluid were performed with these microchannels over a wide range of Reynolds number between 110 and 1914. The results for the rib-patterned microchannels showed that the friction factor with the hydraulic diameter based on the rib-to-upper-wall height was lower than that for the incompressible theory with the same height. The friction factor-Reynolds number products for the hydrophobic condition increased as Reynolds number increased in the laminar flow regime. The experimental results were also compared with the predictive expressions from the literature, and it was found that the experimental data for the small rib/cavity geometry was in good agreement with those in the literature.
Performance Characterization of a Microscale Integrated Combustor Recuperator Oil Heat Exchanger
Authors: Ghazvini Mohammad , Narayanan Vinod
Published: March 2011

A two-dimensional numerical model of an integrated microscale hydrogen-air combustor, recuperator, and oil heat exchanger is presented. The recuperator is used to preheat the incoming reactant gases entering the combustor. Heterogeneous catalytic combustion occurs on the walls of the microchannel in the presence of platinum catalyst. The maximum oil temperature was constrained based on the properties of the fluid used. The recuperator gas outlet temperature was constrained to be larger than the saturation temperature for water to avoid condensation in the exhaust gas stream. The performance of the combustor is documented for variations in geometric and fluidic parameters. The geometric parameters include the length and location of the catalyst bed, and the length of the device. Varied fluidic parameters include the oil inlet temperature, flow rates of oil and reactants, and the equivalence ratio of the reactants. For the range of parameters studied, results indicate that increasing the catalytic surface length as well as the channel length increases the efficiency.
A 3D Numerical Simulation of a Cylindrical Towel Heater With Symmetric and Asymmetric Heating
Authors: Murray Daniel , Lage Jose´ L.
Published: March 2011

In this study a cylindrical towel heater filled with air is simulated numerically in three-dimensions, with the cylinder being heated electrically from the side. The objective is to investigate the efficiency of the heating process as to maintain the towel at a certain temperature, higher than the ambient temperature (ambient temperature outside the heating cylinder), with the heating being symmetric or asymmetric. The process is modeled analytically assuming the towel as a homogeneous and isotropic porous medium, saturated with air, and enclosed by the cylinder. The cylinder wall is heated with a constant, symmetric or asymmetric heat flux, with the bottom surface assumed adiabatic and the top isothermal in equilibrium with the ambient air. The porous-continuum mass, momentum and energy equations for the natural convection inside the cylinder, derived through volume averaging the continuum equations with appropriate closure equations, are written in nondimensional form and solved numerically using the finite-volume method. A parametric study is then performed, after identifying suitable ranges for the parameters involved, to identify the effects of the several controlling parameters, namely the cylinder heating strength (the Rayleigh number), the towel permeability (the Darcy number), form coefficient (the dimensionless form coefficient), and thermal diffusivity (modified Prandtl number). The results, in terms of volume-averaged and surface-averaged temperatures and Nusselt numbers, indicate that the Darcy and Rayleigh numbers have a predominant effect on the natural convection process inside the cylinder, with the inertia coefficient and the modified Prandtl number having lesser influence on the results. For the asymmetric heating configuration, the resulting Nusselt number is higher while the volume-averaged temperature is lower, as compared to the symmetric heating. Hence, a symmetric heating is preferable if a high average towel temperature is the objective of the heater. If a more efficient heating process is sought, on the other hand, than the asymmetric option should be the best alternative.
Magnetic Resonance Imaging Techniques for Measuring Film Cooling Flow Velocity and Effectiveness
Authors: Elkins Christopher J. , Issakhanian Emin , Eaton John K.
Published: March 2011

Film cooling of gas turbine engine components directly influences the efficiency and lifetime of the engine. Prediction of the film cooling surface effectiveness remains a problem area for engine designers. Magnetic Resonance Imaging (MRI) measurements of the surface film cooling effectiveness can be made using the analogy between temperature and passive scalar concentration in which the concentration of scalar marked cooling fluid is measured as it mixes with the main flow. The present work specifically addresses refinements to MR imaging techniques needed to accurately measure the concentration of a scalar contaminant at a flow-bounding surface. Anecdotal data are presented from experiments in which a single film jet exits into the boundary layer on one wall of a square channel. Data are presented for hole angles α = 30° and 60° and blowing ratios BR = 0.5 and 1.0. The Reynolds number of the main channel based on hydraulic diameter and bulk velocity is 400,000 and the jet Reynolds number at BR = 1.0 is 5300.
Thermal Dispersion in Metal Foams
Authors: Hoberg Teresa B. , Muramatsu Kenshiro , Cherry Erica M. , Eaton John K.
Published: March 2011

Open-cell metal foams are of interest for a variety of thermal engineering applications because of their high surface-to-volume ratio and high convective heat transfer coefficients relative to conventional fins. The tortuous flow path through the foam promotes rapid transverse mixing, a fact that is important in heat exchanger applications. Transverse mixing acts to spread heat away from a heated surface, bringing cooler fluid to the foam elements that are in direct contact with the surface. Heat is also spread by conduction in the foam ligaments. The present work addresses fully-coupled thermal dispersion in a metal foam. Dispersion of the thermal wake of a line source was measured. A conjugate heat transfer model was developed which showed good agreement with the data. The validated model was used to examine the complementary effects of the mechanical dispersion, molecular diffusion in the gas, and conduction in the solid.
A Quantum Mechanical Study of the Thermal Conduction Across a ZrB2-SiC Interface as a Function of Temperature and Strain
Authors: Samvedi Vikas , Tomar Vikas
Published: March 2011

Studies on nanocomposites have proven them to be a promising option for various applications based on their excellent thermal and mechanical properties, especially at high temperatures. Such materials consist of heterogeneities in the form of interfaces, grain boundaries, triple junctions, and second phase dispersion. It is, therefore, important to understand the effect of heat transfer across a nanocomposite interface on its thermal conduction behavior. Analyses need to take into account possible phase changes as a function of changes in temperature and thermal stress levels. In the present research, atomistic analyses of thermal conduction across a nanocomposite interface are performed using quantum simulations based on plane-wave basis sets combined with the density function theory (DFT). Analyses of the effect of straining on the nanocomposite property changes are performed to study it as a promising means to obtain nanocomposites with tailored properties.
Development and Experimental Validation of a Micro/Nano Thermal Ground Plane
Authors: de Bock H. Peter J. , Chauhan Shakti , Chamarthy Pramod , Eastman Chris , Weaver Stanton , Whalen Bryan P. , Deng Tao , Russ Boris , Gerner Frank M. , Johnson Douglas , Courson David , Leland Quinn , Yerkes Kirk
Published: March 2011

Heat pipes are commonly used in electronics cooling applications to spread heat from a concentrated heat source to a larger heat sink. Heat pipes work on the principles of two-phase heat transfer by evaporation and condensation of a working fluid. The amount of heat that can be transported is limited by the capillary and hydrostatic forces in the wicking structure of the device. Thermal ground planes are two-dimensional high conductivity heat pipes that can serve as thermal ground to which heat can be rejected by a multitude of heat sources. As hydrostatic forces are dependent on gravity, it is commonly known that heat pipe and thermal ground plane performance is orientation dependent. The effect of variation of gravity force on performance is discussed and the development of a miniaturized thermal ground plane for high g operation is described. In addition, experimental results are presented from zero to −10g acceleration. The study shows and discusses that minimal orientation or g-force dependence can be achieved if pore dimensions in the wicking structure can be designed at micro/nano-scale dimensions.
Two-Phase Cooling Characteristics of Mono-Dispersed Droplets Impacted on a Heated Surface
Authors: Mahmoudi S. R. , Adamiak K. , Castle G. S. P.
Published: March 2011

Droplet impact cooling has been shown to be a promising method for high heat flux removal applications. Recent experimental studies have revealed that even higher heat transfer at low mass fluxes and low Weber number can be achieved with only few degrees of superheat. In the present work, mono-dispersed droplet cooling of a horizontal upward facing heated surface was investigated at low Weber numbers. The impact velocity and frequency of free falling stream of droplets were varied dependently through changing the gap between the heated surface and tip of different capillaries and variation of volumetric flow rate (0.5–4.7 cc/min).The range of impact velocity and droplet frequency was ranged between 0.28 to 1.3 m/s and 0.5 Hz to 5 Hz, respectively using different capillaries size between 17g to 22g. The coolant was 25°C deionized water and all the experiments were performed at atmospheric pressure. The time-averaged two-phase characteristic curves were obtained up to Critical Heat Flux (CHF)-regime. Through the extensive set of experiments, two separate correlations are proposed to predict the average CHFs based on the Weber between 3<We<10, 10<We<100 and Strouhal number ranged and 6.35×10−3<St<3.88×10−2 1.81×10−3<St<3.86×10−2, respectively. The correlation predicts the average CHFs with absolute errors less than 20% and 25%, respectively.
Atomistic Scale Thermal Transport in Amorphous Materials and Its Interfaces
Authors: Roy Ajit K. , Varshney V. , Ganguli S. , Sihn S. , Lee J. , Farmer B.
Published: March 2011

The thermal loads (excess heat) in all DoD systems (aircrafts and spacecrafts) have steadily been increasing at an alarming rate. The current practice is use fuel as the heat sink to dump the excess heat. This operational approach currently is not adequate to sufficiently cool the electronics and thermal devices, and thus limiting the system performance and its system readiness. Amorphous materials system (polymers, adhesive, etc.), which is known to be thermally non-conductive material, is prevalent in almost all DoD systems. So, there is a big incentive in tailoring its thermal transport characteristics to meet the system requirements. Advent of the conductive nano material constituents (such as, carbon nanotubes, graphite platelets, graphene, etc.) and its adaptation in polymers provides us such opportunity. The success of adapting the nano constituents in polymers in providing the conductive pathways through the polymer phase solely lies on the extent how the interface thermal transport characteristics are tailoring between the polymer and nano constituent interfaces. In order to understand the thermal transport phenomena is amorphous materials and to design its interface consistent to the nano constituent morphology scale, computational methodology using atomistic molecular dynamics (MD) is developed. Examples for tailoring thermal interface of nano constituents with polymer will be presented.