bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Adiabatic Two-Phase Pressure Drops of R134a, R236fa and R245fa in Small Horizontal Circular Channels
Authors: Ong Chin L. , Thome John R.
Published: March 2011

Experimental adiabatic two-phase pressure drops data for refrigerants R134a, R236fa and R245fa during flow boiling in small channels with internal diameters of 1.03, 2.20 and 3.04 mm are presented. The main purpose was to investigate the effects of channel confinement on adiabatic two-phase pressure drops. Thus, the two-phase pressure drop trends were systematically investigated over a wide range of test conditions for all three refrigerants and channel sizes. Statistical comparisons have also been made by comparing the experimental pressure drop data database with various macroscale and microscale prediction methods from the literature. The comparison showed relatively moderate accuracy for three prediction methods developed for macroscale flows, i.e. Baroczy and Chisholm, Friedel and the homogeneous model with the Cicchitti et al. viscosity relation. As for microscale prediction methods, the Cioncolini et al. annular flow model worked best with 68.5% of the data within ± 30%, followed by the Sun and Mishima and the Zhang et al. methods. Combining this database with the LTCM lab’s earlier database for 0.509 and 0.790 mm channels, there appears to be no evidence of a macro-to-microscale transition, at least with respect to two-phase pressure drops.
A Simple Physical Approach to Model Spectral Radiative Properties of Semi-Transparent Dispersed Materials
Authors: Dombrovsky Leonid , Baillis Dominique
Published: March 2011

A novel physical approach based on relative mutual independence of absorption and scattering properties of weakly-absorbing materials is formulated. The resulting simplifications in both experimental characterization and theoretical modeling of spectral properties of dispersed materials are discussed in some details. The suggested approach is verified using the published experimental data for materials of different nature. It is shown that the methods developed enable us to simplify radically the identification procedure for material properties, determine extremely low absorption coefficients of the bulk substance from the measurements for highly-scattering porous material, and estimate the effect of non-uniform distribution of adsorbed water on scattering characteristics of nano-porous super-insulations.
The Constrained Vapor Bubble Experiment: Results From the International Space Station
Authors: Chatterjee Arya , Plawsky Joel L. , Wayner Peter C. , Chao David F. , Sicker Ronald J. , Lorik Tibor , Chestney Louis , Eustace John , Zoldak John
Published: March 2011

The constrained vapor bubble (CVB) experiment is an experiment in thermal fluid science currently operating on the International Space Station. Flown as the first experiment on the Fluids Integrated Rack on the Destiny module of the US part of the space station, the experiment promises to provide new and exciting insights into the working of a wickless micro heat pipe in the micro-gravity environment. The CVB consists of a relatively simple setup — a quartz cuvette with sharp corners partially filled with pentane as the working fluid. Along with temperature and pressure measurements, the curvature of the pentane menisci formed at the corners of the cuvette can be determined using optical measurements. This is the first time the data collected in space environment is being presented to the public. The data shows that, while the performance of the CVB heat pipe is enhanced due to increased fluid flow, the loss of convection as a heat loss mechanism in the space environment, leads to some interesting consequences. We present some significant differences in the operating characteristics of the heat pipe between the space and Earth’s gravity environments and show that this has important ramifications in designing effective radiators for the space environment.
Precise Control Method of Temperature Rising Speed of Wafer During Rapid Thermal Processing With Lamp Heaters
Authors: Hirasawa Shigeki , Kawanami Tsuyoshi
Published: March 2011

In rapid thermal processing of a semiconductor wafer, temperature-rising-time is the same order of heating-time, and so keeping a given temperature-rising-speed of the wafer during the temperature-rising process is important. We made an experimental apparatus to measure the temperature-rising-speed of a ceramic ball of 2 mm in diameter heated with four halogen lamp heaters. The temperature change of the ceramic ball was measured and the heating rate of the halogen lamp heaters was controlled by a personal computer to keep a given temperature-rising-speed 50°C/s with controlling-time-interval 0.1 s. We examined the effect of various heating control methods on the error of the temperature-rising-speed of the ceramic ball. We tested the PID-control, the control with a prepared correlation, and the combined method of control with prepared correlation and PID-control. We found that the combined method is a good method to decease the error of the temperature-rising-speed. The average error of the temperature-rising-speed is 0.5°C/s and the repetition error is almost zero for the temperature-rising-speed 50°C/s during 330°C to 370°C. We also measured the effects of artificial control-delay-time and measuring-error of the monitor temperature on the error of the temperature-rising-speed.
Convective Heat Transfer Enhancement in Nanofluids: Real Anomaly or Analysis Artifact?
Authors: Prabhat Naveen , Buongiorno Jacopo , Hu Lin-wen
Published: March 2011

The nanofluid literature contains many claims of anomalous convective heat transfer enhancement in both turbulent and laminar flow. To put such claims to the test, we have performed a critical detailed analysis of the database reported in 12 nanofluid papers (8 on laminar flow and 4 on turbulent flow). The methodology accounted for both modeling and experimental uncertainties in the following way. The heat transfer coefficient for any given data set was calculated according to the established correlations (Dittus-Boelter’s for turbulent flow and Shah’s for laminar flow). The uncertainty in the correlation input parameters (i.e. nanofluid thermo-physical properties and flow rate) was propagated to get the uncertainty on the predicted heat transfer coefficient. The predicted and measured heat transfer coefficient values were then compared to each other. If they differed by more than their respective uncertainties, we judged the deviation anomalous. According to this methodology, it was found that in nanofluid laminar flow in fact there seems to be anomalous heat transfer enhancement in the entrance region, while the data are in agreement (within uncertainties) with the Shah’s correlation in the fully developed region. On the other hand, the turbulent flow data could be reconciled (within uncertainties) with the Dittus-Boelter’s correlation, once the temperature dependence of viscosity was included in the prediction of the Reynolds number. While this finding is plausible, it could not be conclusively confirmed, because most papers do not report information about the temperature dependence of the viscosity for their nanofluids.
Optimization of the Relationship Between the Two-Phase Friction Factor and Reynolds Equivalent Number Model by Means of Genetic Algorithm
Authors: Bolat Berna , Balcilar Muhammet , Dalkilic¸ Ahmet Selim , Wongwises Somchai
Published: March 2011

The two-phase friction factor of R134a in a copper smooth tube having an inner diameter of 8.1 mm and length of 0.5 m during downward condensation is investigated experimentally and numerically. The test runs were performed at average condensing temperatures of 40–50 °C. The mass fluxes were around 260, 340 and 456 kg m−2s−1 and the heat fluxes were between 11.3 and 55.3 kW m−2. Accuracy of the dataset was proven in many papers in the literature. The quality of the refrigerant in the test section is calculated considering the temperature and pressure obtained from the experiment. The pressure drop across the test section is directly measured by a differential pressure transducer. The equivalent Reynolds number is considered to be the significant variable for the analysis. A Genetic Algorithm (GA), is one of the most successful methods among evolution algorithms, is applied for the optimization of the relationship between the two-phase friction factor and Reynolds equivalent number model in this study. The annular flow condensation process in the vertical test tube is expressed using GA method successfully. Regression analysis was done including the Reynolds equivalent number and other measured values such as pressure drop and mass flux of R134a, and gave a convincing correlation based on 182 smooth tube data points for practical applications. The most suitable coefficients of the proposed correlations are depicted to be compatible with the experiment by way of the algorithm.
Numerical Model of Heat Transfer and Mass Transfer During the Solidification of a Concasting Steel
Authors: Stetina Josef , Kavicka Frantisek
Published: March 2011

The accuracy with which the solidification and cooling of a continuously cast billet is investigated depends on the setting of the boundary conditions of the numerical model of the temperature field. An in-house numerical model of the 3D temperature field of a concast billet had been used. This model enables the analysis of the temperature field of the actual blank as it passes through the zero-, primary-, secondary- and tertiary-cooling zones, i.e. through the entire caster. This paper deals with the derivation of transfer phenomena under the cooling nozzles of the secondary zone. These phenomena are expressed by the values of the heat transfer coefficients (HTCs). The dependences of these coefficients on surface temperature and other operational parameters must also be given. The HTCs beneath the nozzles are given by the sum of the forced convection coefficient and the so-called reduced convection coefficient corresponding to heat transfer by radiation. The definition of the boundary conditions is the most difficult part of the numerical and experimental investigation of the thermokinetics of this process. Regarding the fact that on a real caster, where there are many types of nozzles (with various settings) positioned inside a closed cage, it is practically impossible to conduct measurement of the real boundary conditions. Therefore, an experimental laboratory device was introduced in order to measure the cooling characteristics of the nozzles. It simulates not only the movement, but also the surface of a blank and for the necessary range of water flow in the operation and the casting speeds. The transfer phenomena beneath the water cooling nozzles are presented on a simulated temperature field for a real 150×150 mm steel billet under different operational conditions. This is ensured by the correct process procedure: real process → input data → numerical analysis → optimization → correction of process. The presented model is a valuable computational tool and accurate simulator for investigating transient phenomena in caster operations, and for developing control methods, the choice of an optimum cooling strategy to meet all quality requirements, and an assessment of the heat-energy content required for direct rolling.
Thermal Conductivity of Sol-Gel Amorphous Mesoporous Silica Thin Films: Molecular Dynamics Simulations Versus Experiments
Authors: Coquil Thomas , Pilon Laurent
Published: March 2011

This study reports non-equilibrium molecular dynamics (MD) simulations predicting the thermal conductivity of amorphous mesoporous silica. The heat flux was imposed using the Muller-Plathe method and interatomic interactions were modeled using the van Beest, Kramer and van Santen (BKS) potential. First, simulations were validated against results reported in the literature for dense quartz and amorphous silica. The BKS potential was found to significantly overestimate the thermal conductivity of dense amorphous silica and results depended on the length of the simulation cell. Then, highly ordered pores were introduced in an amorphous silica matrix by removing atoms within selected areas of the simulation cell. Effects of the simulation cell length, pore size, and porosity on the thermal conductivity were investigated at room temperature. Results were compared with predictions from commonly used effective medium approximations as well as with previously reported experimental data for films with porosity and pore diameter ranging from 20% to 48% and 30 to 180 Å, respectively. Predictions of MD simulations overestimated the experimental data and agreed with predictions from the coherent potential model. However, MD simulations confirmed that thermal conductivity in sol-gel amorphous mesoporous materials was independent of pore size and depended only on porosity.
Investigations on Performance of Stirling Engine Regenerator Matrix
Authors: Shendage D. J. , Kedare S. B. , Bapat S. L.
Published: March 2011

Stirling engine technology has attracted attention due to recent environmental and energy problems. The regenerator is the main component in high efficiency Stirling engines. A suitable regenerator must be designed for each Stirling machine to provide high performance. The aim of the present work is to find a feasible number of screens in regenerator by taking into account the pressure drop, dead volume, the thermal penetration depth and geometry of regenerator. The second order cyclic analysis with realistic assumptions is carried out for a single cylinder, beta Stirling engine with rhombic drive for predecided operating conditions, such as pressure of 30 bar, hot side temperature of 750 K, speed of 1440 rpm and hydrogen as the working fluid. It is intended to design and develop the Stirling engine with capacity ≥ 1.5 kWe and the efficiency of drive mechanism and alternator is assumed as 85% each. Miyabe’s and Martini’s approaches are used to simulate regenerator performance considering non-sinusoidal motion of displacer and piston. The results reveal that the flow loss increases remarkably to attain higher value of regenerator effectiveness. However, increase in the speed results into an increase in the mass flow rate of the working fluid. It is observed that regenerator effectiveness decreases only marginally over the range of speeds considered. It is also ensured for selected regenerator screen that the thermal penetration depth (239 μm) should be greater than wire radius of mesh (20.5 μm). For present set of operating and geometrical parameters, length of regenerator is fixed as 22 mm which gives regenerator effectiveness as 0.965. Further, the practice to fill more screens than the designed number of screens in the regenerator, while assembling is not advantageous. It increases pressure drop which results in reduced power output. These are some of the important conclusions.
Aerodynamics of Long Aspect Ratio Fibrous Particles Under Settling
Authors: Qi Guo Q. , Nathan Graham J. , Kelso Richard M.
Published: March 2011

In present study, the aerodynamic behaviour of long aspect ratio fibrous particles has been investigated experimentally whilst settling in air under super dilute conditions without any influence of secondary flows and at particle Reynolds numbers of 30–80 based on fibre length. A method for laser-based measurement of the orientations and velocities of fibrous particles is presented. The experimental apparatus employs Particle Tracking Velocimetry (PTV) to calculate orientation and velocity based on the two end-points. Fibres’ mean vertical and horizontal components of settling velocities, angular velocity, orientation, number density and drag coefficient were calculated to analyze their aerodynamics.
Experimental Investigation of a Scaled-Up Passive Interdigital Micromixer With Circular-Sector Mixing Elements
Authors: Cook Kristina , Fan YanFeng , Hassan Ibrahim
Published: March 2011

Flow patterns and mixing phenomena are investigated qualitatively in a planar passive scaled-up micromixer using flow visualization over 5 ≤ Re ≤ 200. To promote molecular diffusion, the test section utilizes an uneven interdigital inlet which reduces the diffusion path and enhances mixing at the side walls. Five circular sector obstructions located along the channel length serve to divide and recombine the flow, as well as induce Dean vortex formation at high Reynolds numbers. Induced fluorescence is used to provide a quantitative estimate of mixing efficiency at certain Reynolds numbers. A decreasing-increasing trend in mixing efficiency is observed with increasing Reynolds numbers, marking the transition from mass diffusion dominance to mass advection dominance. The design operates well at higher Reynolds numbers, where the dominant mixing mechanism is mass advection.
Transient Heat Transfer From a Horizontal Plate in Forced Flow of Various Gases
Authors: Liu Qiusheng , Shibahara Makoto , Fukuda Katsuya
Published: March 2011

In this research, to obtain fundamental experimental data of transient heat transfer and to clarify the transient heat transfer process at wide experimental conditions for the safety assessment of very high temperature reactor (VHTR), forced convection transient heat transfer coefficients were measured for Helium, Carbon dioxide, Argon and Nitrogen gases flowing over a horizontal plate due to exponentially increasing heat input. The platinum ribbon with a thickness of 0.1 mm and a width of 4.0 mm was used as the test heater and heated by electric current. The heat generation rate was controlled and measured by a heat input control system, it was exponentially increased with a function of Q0exp(t/τ). The periods (e-fold times) of heat generation rate, τ, ranged from 46 ms to 17 s, the gas flow velocities ranged from 1 to 10 m/s, the pressures ranged from 400 kPa to 800 kPa, and the gas temperatures ranged from 290 to 353 K. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period longer than about 1 s, and it becomes higher for the period shorter than around 1 s. The heat transfer coefficient increases with the increases in pressure and velocity, and it shows some dependence on temperature at the experimental range of this research. The dependence of transient heat transfer on the gas flow velocity becomes weaker when the period becomes very shorter. Effect of gas thermal physical properties on heat transfer was investigated, and helium gas shows higher heat transfer coefficients than those of other gases due to its higher thermal conductivity. Empirical correlations for quasi-steady-state heat transfer and transient one for various gases were obtained based on the experimental data.
Flow Boiling Heat Transfer Characteristic of Ternary Mixture in a Micro-Channel
Authors: Park Inmyong , In Sehwan , Jeong Sangkwon
Published: March 2011

This paper describes the flow boiling heat transfer of R123/R134a/R22 mixture in a single round micro-channel with 0.19 mm ID. The flow boiling heat transfer coefficients were measured for ternary mixture (R123/R134a/R22 mole fraction: 0.194/0.62/0.186) at various experimental conditions: mass velocities (314, 392, 470 kg/m2-s), heat fluxes (10, 15, 20 kW/m2) and vapor qualities (0.2–0.8). The heat transfer characteristics of the R123/R134a/R22 mixture are similar to those of the R123/R134a mixture (mole fraction: 0.502/0.498) observed in the previous flow boiling experiment which indicates that major heat transfer mechanism in the microchannel is dominated by evaporation of thin liquid film around the elongated bubbles. The large reduction of heat transfer coefficients compared with pure refrigerant is observed in micro-channel flow boiling by mass transfer effect of mixed refrigerant.
Scale Effects on Thermal-Fluid Performance of Optimized Hierarchical Structures
Authors: Dede Ercan M. , Liu Yan
Published: March 2011

The development of an optimized cooling structure for high heat flux applications is described. A gradient-based method coupled with commercial multiphysics finite element software is used in the optimization process. The results are applied to the design of a combination manifold jet/channel cold plate. Three sizes of the structure ranging from mini to microscale are investigated in a subsequent numerical study, and the effect of size reduction on thermal-fluid performance is explained. It is found that smaller scaling of the cooling structure leads to reduced unit thermal resistance due to a fundamental shift in the behavior that exploits the jet-based characteristics of the design. A relevant application of the microscale technology is discussed.
Mass Transfer From a Bubble in a Vertical Pipe
Authors: Hosoda Shogo , Sakata Ryosuke , Hayashi Kosuke , Tomiyama Akio
Published: March 2011

Mass transfer from single carbon dioxide bubbles in a vertical pipe is measured using a stereoscopic image processing method to develop a mass transfer correlation applicable to a wide range of bubble and pipe diameters. The pipe diameters are 12.5, 18.2 and 25.0 mm and the bubble diameter ranges from 5 to 26 mm. The ratio, λ, of bubble diameter to pipe diameter is therefore varied from 0.2 to 1.8, which covers various bubble shapes such as spherical, oblate spheroidal, wobbling, cap, and Taylor bubbles. Measured Sherwood numbers, Sh, strongly depend on bubble shape, i.e., Sh of Taylor bubbles clearly differs from those of spheroidal and wobbling bubbles. Hence two Sherwood number correlations, which are functions of the Peclet number and the diameter ratio λ, are deduced from the experimental data: one is for small bubbles (λ < 0.6) and the other for Taylor bubbles (λ > 0.6). The applicability of the proposed correlations for the prediction of bubble dissolution process is examined through comparisons between measured and predicted long-term bubble dissolution processes. The predictions are carried out by taking into account the presence of all the gas components in the system of concern, i.e. nitrogen, oxygen and carbon dioxide. As a result, good agreements for the dissolution processes for various bubble sizes and pipe diameters are obtained. It is also demonstrated that it is possible to evaluate an equilibrium bubble diameter and instantaneous volume concentration of carbon dioxide in a bubble using a simple model based on a conservation of gas components.
Quantitative Evaluation of the Thickness of the Free Surface by the Interface-Tracking Method
Authors: Saito Y. , Yasumura K. , Shoji M. , Matsushita Y. , Aoki H. , Miura T. , Ogasawara S. , Daikoku M. , Shirota M. , Inamura T.
Published: March 2011

The numerical diffusion of the discretization of the convection term is investigated. The quantitative evaluation method for the numerical diffusion is proposed. The method evaluates the influence of the numerical diffusion to the shape and the thickness of the free surface by the rate of dullness and blur, respectively. High-order schemes are compared with each other using the proposed method in a two-dimensional simple flow and a two-dimensional collapsing water column. As a result, Chakravarthy-Osher (CO) method and Compressive Interface Capture Scheme for Arbitrary Meshes (CICSAM) are more accurate than other schemes in a two-dimensional simple flow. In the collapsing water column, CICSAM is more accurate than CO. CICSAM with the anti-diffusion operation is lower than CICSAM in the rate of dullness and blur. It is shown that the proposal quantitative evaluation method is able to quantify the numerical diffusion.
Thermal Transport in LEDs for Solid State Lighting
Authors: Su Zonghui , Malen Jonathan A. , Melby Jacob H. , Davis Robert F.
Published: March 2011

Over 20% of electricity in US is used by lighting. Solid state lighting (SSL) efficiency can theoretically surpass that of incandescent and fluorescent lighting techniques. Nonetheless SSL efficiency is greatly reduced at high temperatures that result from inadequate heat dissipation. SSL requires blue and green light emitting diodes (LEDs) made from Gallium Nitride (GaN) and Indium Gallium Nitride (InGaN) to eventually generate white light. Using an infrared thermal imaging camera, temperatures of working blue and green LEDs with different efficiencies were measured. The results show that higher efficiency LEDs have lower active region temperatures when driven with the same power. Further, they motivate our study of thermal properties of the individual thin films that compose the LEDs, since earlier studies show that conduction is the primary dissipative mechanism for heat in LEDs. Bulk thermal properties are poor estimates of thin film properties due to increased boundary and defect scattering of phonons in the films. By examining real LED structures with the 3-omega technique, thin film thermal conductivities can be measured. For this technique, a thin metal line was fabricated onto a smooth dielectric sample surface. This thin metal line works as both a heater and a thermometer. Benchmark studies on Pyrex 7740 were used to validate our 3-omega setup. Data from real GaN/InGaN LED structures show that the effective thermal conductivities of the AlN buffer layer and multi-quantum-well active region are substantially suppressed relative to their anticipated values based on bulk properties.
Thermodiffusion in a Binary Fluid Mixture Subject to External Vibrations: Effect of Variable Physical Properties
Authors: Parsa A. , Saghir M. Z.
Published: March 2011

A microgravity environment is essential for studying the phenomenon of thermodiffusion in order to suppress the microscopic flows in the mixture. It is, however, noted that the residual micro accelerations (g-jitters) in the space laboratories is produced by several sources such as crew activities, mechanical systems, thrusters firing, spacecraft docking, etc. Such external forces lead to significant flows which can induce convection that may affect the accuracy of the experiment. Consequently, an appropriate interpretation of the space experimental results relies on theoretical and numerical studies of the g-jitter effect on the temperature and the concentration fields. In this paper, we have modeled the thermodiffusion experiment subjected to different levels of vibration when the steady gravity is assumed zero. A rectangular cavity that is subjected to a thermal gradient is filled with a binary mixture (water and isopropanol) and put under the influence of different levels of vibrations. The thermal gradient is applied perpendicular to the vibration. All physical properties including density, mass diffusion and thermodiffusion coefficients are assumed variable as function of temperature and concentration using PC-SAFT equation of state. It is found that using variable physical properties including density and diffusion coefficients make the results more realistic in comparison with the constant model especially in cases with higher Rayleigh vibrations.
A Modified 3-Omega Technique to Measure Thermal Conductivity in Liquids, Gases, and Powders
Authors: Schiffres Scott N. , Malen Jonathan A.
Published: March 2011

A novel modified 3ω thermal conductivity measurement technique called metal coated 3ω is introduced for use with liquids, gases, and powders. This technique employs a micron-scale metal coated glass fiber. Metal coated 3ω exceeds alternate 3ω based fluid sensing techniques in a number of key metrics including fraction of heat generated entering fluid, signal strength per temperature oscillation intensity and thermal boundary sensitivity. The advantages of this technique to Transient Hot-Wire (THW) and steady-state techniques are also discussed. A generalized n-layer concentric cylindrical periodic heating solution that accounts for thermal boundary resistance is presented. The technique is validated through a benchmark study of gases and liquids.
Heat Source Localization Sensitivity Analyses for an Ultrasonic Sensor Array
Authors: Myers M. R. , Jorge A. B. , Walker D. G. , Mutton M. J.
Published: March 2011

State estimation procedures using the extended Kalman filter are investigated for a transient heat transfer problem in which a heat source is applied on one side of a thin plate and ultrasonic pulse time of flight is measured between spatially separated transducers on the other side of the plate. This work is an integral part of an effort to develop a system capable of locating the boundary layer transition region on a hypersonic vehicle aeroshell. Results from thermal conduction experiments involving one-way ultrasonic pulse time of flight measurements are presented. Uncertainties in the experiments and sensitivity to heating source location are discussed. Comparisons of heating source localization measurement models are conducted where ultrasonic pulse time of flight readings provide the measurement update to the extended Kalman filter. Two different measurement models are compared: 1) directly using the one-way ultrasonic pulse time of flight as the measurement vector and 2) indirectly obtaining distance from the one-way ultrasonic pulse time of flight and then using these obtained distances as the measurement vector in the extended Kalman filter. For the direct model, the Jacobian required by the extended Kalman filter is obtained numerically using finite differences from the finite element forward conduction solution. For the indirect model, the derivatives of the distances with respect to the state variables are obtained in closed form. Heating source localization results and convergence behavior are compared for the two measurement models. Two areas of sensitivity analyses are presented: 1) heat source location relative to sensor array position, and 2) sensor noise. The direct measurement model produced the best results when considering accuracy of converged solution, ability to converge to the correct solution given different initial guesses, and smoothness of convergence behavior.
Detailed Heat Transfer Measurements Inside Rotating Ribbed Channels Using the Transient Liquid Crystal Technique
Authors: Lamont Justin A. , Ekkad Srinath V.
Published: March 2011

The effects of the Coriolis force and centrifugal buoyancy are well known in rotating internal serpentine coolant channels in turbine blades. As channel flow in rotation is highly complex, detailed knowledge of the heat transfer over a surface will greatly enhance the blade designer’s ability to predict hot spots so coolant may be distributed effectively. The present study uses a novel transient liquid crystal technique to measure heat transfer on a rotating two-pass channel surface with chilled inlet air. The present study examines the differences in heat transfer distributions of three channel types in rotation: smooth wall, 90° ribs, and W-shaped ribs. The two channels in the test section model radially inward and outward flow. To account for centrifugal buoyancy, cold air is passed through a room temperature test section. This ensures that buoyancy is acting in a similar direction to real turbine blades. Three parameters were controlled in the testing: inlet coolant-to-wall density ratio, channel Reynolds number, and Rotation number. Results were compared to previous studies with similar test conditions. The present study shows that the W-shaped ribs enhance heat transfer in all cases (stationary and rotating) approximately 2–3 times better than the 90° ribs. The W-shaped ribbed channel is least affected by rotation due to the complex nature of the flow generated by the geometry.
Contributions of Anharmonic Phonon Interactions to Thermal Boundary Conductance
Authors: Hopkins Patrick E. , Duda John C. , Norris Pamela M.
Published: March 2011

Continued reduction of characteristic dimensions in nanosystems has given rise to increasing importance of material interfaces on the overall system performance. With regard to thermal transport, this increases the need for a better fundamental understanding of the processes affecting interfacial thermal transport, as characterized by the thermal boundary conductance. When thermal boundary conductance is driven by phononic scattering events, accurate predictions of interfacial transport must account for anharmonic phononic coupling as this affects the thermal transmission. In this paper, a new model for phononic thermal boundary conductance is developed that takes into account anharonic coupling, or inelastic scattering events, at the interface between two materials. Previous models for thermal boundary conductance are first reviewed, including the Diffuse Mismatch Model, which only consdiers elastic phonon scattering events, and earlier attempts to account for inelastic phonon scattering, namely, the Maximum Transmission Model and the Higher Harmonic Inelastic model. A new model is derived, the Anharmonic Inelastic Model, which provides a more physical consideration of the effects of inelastic scattering on thermal boundary conductance. This is accomplished by considering specific ranges of phonon frequency interactions and phonon number density conservation. Thus, this model considers the contributions of anharmonic, inelastically scattered phonons to thermal boundary conductance. This new Anharmonic Inelastic Model shows excellent agreement between model predictions and experimental data at the Pb/diamond interface due to its ability to account for the temperature dependent changing phonon population in diamond, which can couple anharmonically with multiple phonons in Pb.
Tunable Thermal Conductivity of TiO2 Films of Close-Packed Nanoparticles
Authors: Hopkins Patrick E. , Mittal Manish , Phinney Leslie M. , Grillet Anne M. , Furst Eric M.
Published: March 2011

We report on the ultra-low thermal conductivity of a series of convectively assembled, anisotropic titania (TiO2) nanoparticle films. The TiO2 films are fabricated on aluminum coated glass substrates by flow coating a suspension of ellipsoidal colloidal nanoparticles, resulting in structured films with tailored order. Time domain thermoreflectance is used to measure the thermal conductivity of the TiO2 films. The thermal conductivities of these nanoparticle films are dependent on nanoparticle orientational order and films with more randomly oriented particles exhibit thermal conductivities less than the amorphous limit.
Coupling of Hydrodynamics, Vaporization and Reaction With Liquid Spray Injection Into a High-Temperature Gas-Solid Reactor
Authors: Wang Dawei , Patel Rajesh , Zhu Chao , Ho Teh C.
Published: March 2011

A mechanistic model that to provide a quantitative understanding of the interplay of hydrodynamics, heat/mass transfer, and cracking reactions in the feed injection zone of a fluid catalytic cracking (FCC) riser reactor with a single nozzle spray. With the injection of an oil spray into a gas-solid flow, the collision between cold oil droplets and hot catalyst particles results in a strong momentum transfer that affects the spray hydrodynamics in terms of penetration and scattering. It also causes a significant heat transfer giving rise to rapid droplet vaporization and the attendant cooling of the catalyst. The presence of cracking reactions introduces volume expansion, changes in gas composition and volume fraction, and a cooling effect due to endothermicity. Accordingly, we in this study present an analysis of chemically-induced “entrance effects” in an FCC riser with a single nozzle spray. The cracking reaction network is described by a four-lump reaction model, while the ambient gas-solid transport is represented by a dense-phase riser flow. A Lagrangian modeling approach is adopted to track the spray trajectory as cracking reactions proceed. It is shown that cracking reactions play an important role in dictating the spray behavior, reaction and heat/mass transfer characteristics in the feed injection zone of an FCC riser.
Decomposition of Toluene as a Biomass Tar Through Partial Combustion
Authors: Nakatsuka Noriaki , Imoto Yasushi , Hayashi Jun , Taniguchi Miki , Sasauchi Kenichi , Matsuda Mayumi , Akamatsu Fumiteru
Published: March 2011

For the electric power generation by the woody biomass gasification, tar is incidentally formed at the same time. Tar means a compound of many kinds of aromatic hydrocarbons and causes some troubles, for example, clogging pipes when it is cooled and condensed before being supplied to the gas engine for electric power generation. One way for reducing tar is oxidative and thermal cracking by partial combustion of the producer gas in the gas reformer that is a stage subsequent to the biomass gasifier. During the partial combustion process of the producer gas, inverse diffusion flame is formed when oxidizer is supplied to producer gas. Cracking and polymerization of tar occur simultaneously at the proximity of the inverse diffusion flame. This polymerization of tar into soot is, however, a significant problem in the gas reformer. Experimental study was performed to clarify the effect of hydrogen concentration in the combustion region on soot formation and the growth of polycyclic aromatic hydrocarbons (PAHs) that is precursor of soot. In the present study, hydrogen concentration at the proximity of the inverse diffusion flame was controlled by the small amount of hydrogen addition to the oxidizer. The main results were as follows. Soot formation was suppressed by the small amount of hydrogen addition (approximately 0.5% to the total enthalpy of the producer gas). The suppression of soot formation was caused by higher concentration of hydrogen at the proximity of the combustion region since the aromatic radicals were neutralized before they could combine together or with acetylene. Carbon yield was increased with the increase in the amount of hydrogen added to the oxidizer as carbon content in the undetectable components by the integrated gas chromatograph such as the soot was decreased. In addition, the increase of carbon yield resulted mainly from the increase in carbon monoxide stemmed from reforming of high-boiling components such as soot.
Radiative Property Measurements of Oxy-Fuel Flames
Authors: Bedick Clinton R. , Beer Stephen K. , Casleton Kent H. , Chorpening Benjamin T. , Shaw David W. , Yip M. Joseph
Published: March 2011

As part of the DOE Existing Plants, Emissions and Capture (EPEC) program, oxy-combustion is being investigated as a method to simplify carbon capture and reduce the parasitic energy penalties associated with separating CO2 from a dilute flue gas. Gas-phase radiation heat transfer in boilers becomes significant when shifting from air-firing to oxy-combustion, and must be accurately represented in models. Currently, radiative property data are not widely available in the literature for conditions appropriate to this environment. In order to facilitate the development and validation of accurate oxy-combustion models, NETL conducted a series of studies to measure radiation properties of oxy-fuel flames at adiabatic flame temperatures of 1750–1950K, and product molar concentrations ranging from 95% CO2 to 100% steam, determined by equilibrium calculations. Transmission coefficients were measured as a function of wavelength using a mid-IR imaging spectrometer and a blackbody radiation source. Additionally, flame temperatures were calculated using data collected within CO2 and H2O absorption bands. Experimental results were compared to two statistical narrow-band models and experimental data from literature sources. These comparisons showed good overall agreement, although differences between the models and experimental results were noted, particularly for the R branch of the 2.7 μm H2O band.
Heat Transfer Between Colliding Surfaces and Particles
Authors: Li Like , Mei Renwei , Klausner James F. , Hahn David W.
Published: March 2011

Collisional heat transfer between two contacting curved surfaces is investigated computationally using the finite difference method and analytically using various asymptotic methods. Transformed coordinates that scale with the contact radius and the diffusion length are used for the computations. Hertzian contact theory of elasticity is used to characterize the contact area as a function of time. For an axisymmetric contact area, a two-dimensional self-similar solution for the thermal field during the initial period of contact is obtained and it serves as an initial condition for the heat transfer simulation throughout the entire duration of collision. A modified 2-D asymptotic result of heat transfer at small Fourier number is obtained. For finite Fourier numbers the heat transfer during the collision has been determined computationally. A closed-form formula is developed to predict the heat transfer as a function of the Fourier number, the thermal diffusivity ratio and conductivity ratio of the impacting particles.
Numerical Simulation on the Instability of Cylindrically Expanding Premixed Flames With Radiative Heat Loss at Low Lewis Numbers
Authors: Kusakai Takafumi , Kadowaki Satoshi
Published: March 2011

The instability of cylindrically expanding premixed flames with radiative heat loss was studied by two-dimensional unsteady calculations of reactive gases, based on the diffusive-thermal model equation. When the Lewis number was unity, instability phenomena were not observed. When the Lewis number was sufficiently low, on the other hand, cellular-shaped fronts on adiabatic and non-adiabatic cylindrical flames were observed, which was due to diffusive-thermal instability. As radiative heat loss increased, the behavior of cellular fronts became more unstable. This indicated that the radiation promoted the unstable behavior of flame fronts at low Lewis numbers. When radiative heat loss was much large compared with the quenching condition of a planar flame, cylindrical flames were broken up and several small flames appeared. This was in qualitative agreement with the experimental results on the dynamic behavior of lean hydrogen-air premixed flames with radiative heat loss under the low gravity condition. Several small flames appeared on the grounds that large curvature of flame fronts was necessary to keep high temperature against radiative heat loss.
Size-Dependent Model for Thin Film Thermal Conductivity
Authors: McGaughey Alan J. H. , Sellan Daniel P. , Landry Eric S. , Amon Cristina H.
Published: March 2011

We present a closed-form classical model for the size dependence of thin film thermal conductivity. The model predictions are compared to Stillinger-Weber silicon thin film thermal conductivities (in-plane and cross-plane directions) calculated using phonon properties obtained from lattice dynamics calculations. By including the frequency dependence of the phonon-phonon relaxation times, the model is able to capture the approach to the bulk thermal conductivity better than models based on a single relaxation time.
Molecular Dynamics Simulation of Vapor Bubble Nucleation in 2D Lennard-Jones Fluid Along Nanometer-Sized Cavities
Authors: Johnston Joseph , Selvam R. Panneer
Published: March 2011

Heterogeneous vapor bubble nucleation was numerically simulated on surfaces containing nanometer-sized rectangular cavities of various sizes (ranging from 2.72–9.36 nm width & 4.09–8.34 nm depth). Non-equilibrium molecular dynamics simulations at constant wall temperature were carried out for the two-dimensional (2D) Lennard-Jones (LJ) fluid which was in thermal contact with LJ solid wall. Nucleation was induced by expanding the system volume to a metastable state while keeping the temperature of the solid wall constant. When the aspect ratio (depth-to-width) of the cavity was large (∼3-to-1), the nucleation rate was increased nearly three-fold compared to the flat surface for relatively large wettability; however, the nucleation rate was nearly the same for lower wettability surfaces. Nucleation was generally favored within the cavities due to the stabilization of the cavity side-walls. The value of cutoff radius, wall temperature, and solid-liquid wettability was varied to determine their effect on nucleation rate. The 2D model was validated by comparing thermodynamic averages of pressure and potential energy to predicted values from a 2D LJ equation of state.
Design and Testing of a High Pressure and High Temperature, Optically Accessible, Entrained Flow Coal Gasifier
Authors: Sircar Indraneel , Gejji Rohan , Sane Anup , Blunck David , Meyer Scott , Gore Jay P.
Published: March 2011

Improved understanding of coal gasification chemical kinetics is needed to increase thermodynamic efficiency and to reduce undesirable CO2 emissions. This work describes an optically-accessible entrained-flow coal gasifier designed and built to allow measurements of the major species at various stages of the chemical reactions. The 2-meter tall gasifier consists of five subsystems: the optical diagnostics, steam generator, coal feeder, external heaters, and gas sampling and analysis. A stoichiometric H2-O2 flame generates superheated steam, the gasifying agent, which reacts with pulverized coal fed from a variable feed-rate pressurized powder feeder. To sustain the endothermic coal gasification reaction, radiant heaters provide 15 kW of external heating. Diagnostics to determine the major species concentrations consist of tunable diode laser absorption spectroscopy (TDLAS) measurements within the reactor vessel assembly and analysis of dry product gases using a gas chromatograph.
Oxygen Supply to Exothermic Combustion Reactions in Compost Heating System (CHS) by Permanent Magnets
Authors: Toriyama H. , Asako Y.
Published: March 2011

The oxygen supply enhancement in a porous compost by permanent magnets have been investigated numerically. The computations were conducted for the cases of neodymium magnet. The magnets were aligned vertically with specified interval in the compost. Darcy model was applied to represent the air flow through the compost and the oxygen concentration was solved by SIMPLE based algorithm, coupled with the fermentation process that occurs in the compost. The following five effects on the oxygen supply enhancement in the compost: 1.permeability through the compost, 2.rate constant of the exothermic reaction in the fermentation process, 3.size of the compost, 4.interval of the magnets and 5.location of the magnets were investigated. As a result, the maximum inlet air velocity reaches 6.4 mm/s when the air permeability is 3.82×10−4 m2. The permanent magnets enhance the air flow and oxygen supply.
The Impact of Converging and Diverging Angle on the X-Shaped Micro-Channels
Authors: Tu Shu-Min , Torii Shuichi , Shih Yang-Cheng
Published: March 2011

Flows in channels and pipes are often used in the chemical and mechanical engineering applications. In the past, several studies of micro-channels have focused on the mixture characteristics in the C-shaped and the T-shaped with complex flow field of temperature gradient, velocity vector, and pressure change. However, the purpose of this study is to research the flow transport phenomenon by employing different angles to the converging and diverging area in X-shaped micro-channels. As the working fluid, water is injected to micro-channel at different mass flow rate. Over a wide range of flow condition, 0.88 < Re < 661, in X-shaped micro-channels, the mixture performances of numerical simulation, flow visualization, and temperature distribution remain the same. At the same mass flow rate, the bigger the angle, the lower the pressure drops and the slower the low velocity becomes. Therefore, it is the biggest angle that has the best mixture of performance and needs the shortest distance in the mixing area. It is clear that the angle plays an important role in both converging and diverging area in the X-shaped micro-channels.