bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Theoretical Treatment of Critical Heat Flux on Metal-Graphite Composite Heating Surfaces
Authors: Yang Wen-Jei , Zhang Nengli 
Published: December 2021

Abstract
This paper presents a theoretical treatment of the critical heat flux on metal-graphite composite surfaces. A previous study found that the tips of graphite-fibers act as bubble nucleation sites. Throughout the transition boiling regime, vapor rises into liquid on the nodes of the Taylor waves in reference to the Rayleigh-Taylor instability theory. At the critical (i.e., maximum) heat flux, this rising vapor forms into jets. These jets come from the graphite fiber tips that are arranged in an equilateral triangular grid in the metal matrix. The basic spacing of the grid is the two-dimensional Taylor wavelength, which is the spacing of the most basic module of jets. At the peak heat flux, the Kelvin-Helmholtz instability causes the jets to become unstable and brings about burnout. In other words, this instability theory predicts when the vapor velocity in the jet will reach a critical value to cause the vapor jets to cave in. The existing empirical results indicate that the nucleate pool boiling curves for metal-graphite composites of different graphite concentrations (i.e., area fractions) congregate near the critical heat flux of the composite for the optimum performance as the degree of superheat increases. With this particular graphite-fiber concentration known, a balance of the heat flux by the latent heat carried away in the jets when the liquid is saturated yields the maximum (i.e., critical) heat flux equation. Both copper-graphite and aluminum graphite composites are treated.
Study on Enhancement of Critical Heat Flux by Supplying Liquid-Jets to Heating Surface
Authors: Ohtake Hiroyasu , Yamamoto Noriyuki , Koizumi Yasuo 
Published: December 2021

Abstract
The enhancement of a critical heat flux in pool boiling was investigated by supplying liquid-jets to a heated surface, as a proposal of the high heat removal technology for future. Experiments were conducted using a pure copper block and saturated water for a pool condition at atmospheric conditions. Two or three jet-nozzles were set away a certain distance from the test surface for supplying liquid-jets to the heated surface. In the present study, the effects of the distance between the nozzles and the test surface, the diameter of jet-nozzles, the liquid flow rate and the jet-velocity on the enhancement rate of the critical heat flux were examined experimentally.
The critical heat flux obtained in the present experiments was enhanced a factor of about two for the flow rate per nozzle of 2.5 × 10−6 m3/s by supplying two liquid-jets. However, it was little affected for the supplied liquid when the distance between the jet-nozzles and the heated surface was 15 mm. The enhancement rate increased with the liquid flow rate and liquid jet velocity except for the 15 mm nozzle distance. The dependency of the enhancement rate on the flow rate for the nozzle-diameter of 0.9 mm was similar to that for the 0.5 mm in diameter. The dependency on the jet-velocity for the case of 0.9 mm, however, was difference to that of 0.5 mm. In other words, the enhancement rate of the critical heat flux is related to the flow rate of the liquid-jets. These results suggest that the enhancement of the critical heat flux is affected additionally by the quantity of supplied liquid to the macrolayer on the heated surface.
Numerical Study of Spray Parametric Effects on Gas Turbine Combustion Performance
Authors: Su K. , Zhou C. Q. 
Published: December 2021

Abstract
A numerical study was conducted to determine the effects of fuel spray characteristics on the gas turbine combustion performance including the combustion efficiency and the overall temperature distribution factor (OTDF) at the exit of the combustor using the KIVA-3V code. A model of a typical annular combustor was used in the computations. Operating conditions were varied with inlet pressure from 0.1 to 1.2 MPa, inlet temperature from 400 to 650 K, and air fuel ratio from 0.015 to 0.024. A log-normal spray distribution was assumed to simulate a real fuel spray distribution at injection. The droplet mean diameter as well as injection velocity and angle were independently varied to distinguish the separate effects of variables involved. Flow fields and temperature distributions in the combustor were analyzed. The results reasonably agreed with those from a semi-empirical approach. It is found that the overall temperature distribution deteriorates as the Sauter mean diameter of fuel spray increases. There is an optimum range of the Sauter mean diameters for the efficient combustion of fuel sprays. The overall temperature distribution is improved as the injection velocity of fuel sprays increases, but the combustion efficiency does not change much with it. It appears that the KIVA-3V code can be used to guide the design and improvement of the gas turbine combustor.
An Unstructured-Mesh Methodology for Computation of Reacting Sprays in Industrial Combustors
Authors: Giridharan M. G. , Sheu J. C. , Bayyuk S. A. , Presser C. 
Published: December 2021

Abstract
This paper reports the progress made in developing a state-of-the-art, unstructured-mesh code for simulating reacting two-phase flows for general-purpose industrial applications. The code has been created by combining a finite-volume solver for computing flow, heat-transfer, and chemical reaction in the gas phase with a new object-oriented module specifically designed and developed to provide a framework for solving the system of equations governing the motion of spray droplets and their interactions with the gas phase. The gas phase equations are solved in an Eulerian frame while the droplet equations are solved in a Lagrangian frame. The paper presents the equations for droplet transport and behavior, describes the coupling models between the gas and liquid phases, and outlines the overall solution technique. Much of the paper is devoted to verification and validation of the computational models. The verification studies include comparison of computational results for particle motion under the influence of gravity and for solutions. The validation studies include comparison of predictions with published experimental data on behavior of evaporating and non-evaporating sprays. All comparisons show good qualitative and quantitative agreement. A 2-D axisymmetric simulation of methanol combustion in the N1ST reference spray combustor is also presented, and the results are compared with the NIST flow visualization data. Relevant ongoing work and future plans for incorporation of advanced spray models are briefly described.
Fabry-Perot Resonators Built With YBa2Cu3O7-δ Films on Si Substrates
Authors: Kumar A. Ravi , Boychev Vladimir A. , Zhang Zhuomin M. , Tanner David B. 
Published: December 2021

Abstract
Fabry-Perot (F-P) resonators were built from two superconductive YBa2Cu3O7-δ (YBCO) films separated by a spacer. Each film of 35 nm thickness was deposited on a Si substrate ≈0.2 mm thick. A slow-scan Michelson interferometer was employed to measure the transmittance of the resonator in the far-infrared frequency region from 10 to 90 cm−1 at temperatures between 10 and 300 K. Measurements showed that in the normal state the peak (or resonant) transmittance decreases with temperature, whereas in the superconducting state it can increase with decreasing temperature. The transmittance of the resonator was calculated using properties of individual reflectors obtained previously. When the effect of partial coherence is taken into consideration, the calculated transmittance is in good agreement with the experiments. Furthermore, the maximum possible resonant transmittance was predicted based on an optimization analysis considering the interference effects. The effect of the YBCO film thickness on the transmittance peaks was also studied, showing that the resonant transmittance decreases but the finesse increases as the film thickness is increased. This study should help improve the future design of F-P resonators based on HTSC thin films.
Computations of Low Pressure Fluid Flow and Heat Transfer in Ducts Using Direct Simulation Monte Carlo Method
Authors: Yan Fang , Farouk Bakhtier 
Published: December 2021

Abstract
High Knudsen (Kn) number flows are found in vacuum and micro-scale systems. Such flows are characterized by non-continuum behavior. For gases, the flows are usually in the slip or transition regimes. In this paper, the direct simulation Monte Carlo (DSMC) method has been applied to compute low pressure, high Kn flow fields in partially heated channels. Computations were carried out for nitrogen, argon, hydrogen, oxygen and noble gas mixtures. Variation of the Kn is obtained by reducing the pressure while keeping the channel width constant. Nonlinear pressure profiles along the channel centerline are observed. Heat transfer from the channel walls is also calculated and compared with the Graetz solution. The effects of varying pressure, inlet flow and gas transport properties (Kn, Reynolds number, Re and the Prandtl number, Pr respectively) on the wall heat transfer (Nu) were examined. A simplified correlation for predicting Nu¯ as a function of Pe¯ and Kn¯ is presented.
Experimental and Numerical Study of Conjugate Heat Transfer in a Horizontal Channel Heated From Below: Applications to CVD Processing
Authors: Chiu Wilson K. S. , Richards Cristy J. , Jaluria Yogesh 
Published: December 2021

Abstract
A detailed experimental and numerical study is carried out to investigate conjugate heat transfer in a horizontal channel with a heated section which simulates Chemical Vapor Deposition (CVD) processing. Since film quality, uniformity and deposition rate have strong dependence on temperature, the role of conjugate heat transfer in influencing temperature distribution is significant in thin film production. Experimental data obtained from this study provides physical insight into conjugate heat transfer effects and allows for comparison and validation of numerical conjugate heat transfer models. The basic characteristics of the flow and the thermal transport are studied. The numerical model is used to perform a parametric study of operational parameters, allowing for the characterization of conjugate heat transfer effects on temperature at the susceptor surface, reactor walls and the gas phase. The study yields valuable guidelines for the thermal design of CVD reactors.
A Study of Particle Growth Using Light Scattering and Local Sampling in Flame Synthesis of Nano Particles
Authors: Cho Jaegeol , Lee Jeonghoon , Kim Hyun W. , Choi Mansoo 
Published: December 2021

Abstract
The growth of silica particles in coflow diffusion flames has been studied experimentally using light scattering and local thermophoretic sampling techniques. The number densities and volume fractions of both aggregates and spherical particles have been determined calculated by a novel method of using the scattering cross section measured from 90° light scattering with the combination of particle sizes and morphology measured from the localized sampling and TEM image analysis under the assumption of monodisperse distribution of primary particles in an aggregate. Rayleigh-Debye-Gans and Mie theories have been applied to the calculations for fractal aggregates and spherical particles, respectively. Of particular interests are the effects of carrier gas flow rates on the evolution of silica particles and the roles of radial heat and H2O diffusion have been studied when using N2 or O2 as a carrier gas.
Benchmark Boundary Element Solutions for Some Problems Governed by the Boussinesq Equations
Authors: Grigoriev Mikhail M. , Dargush Gary F. 
Published: December 2021

Abstract
The boundary element formulation developed previously by the authors for incompressible isothermal viscous fluid flows is extended for non-isothermal flows governed by Boussinesq equations. The new boundary element method is applied to the classical Rayleigh-Benard problem and to a stratified flow over a backward-facing step. In all cases, the boundary element results are in good agreement with published finite element solutions. However, in some instances, the boundary element solutions are more accurate, particularly in terms of resolving surface tractions and heat fluxes.
Wavelets and the Numerical Solution of Heat Transfer Problems: A Discussion of Two Methods
Authors: Sowayan A. S. , Bénard A. , Díaz A. R. 
Published: December 2021

Abstract
Two methods for solving heat transfer problems using wavelets are reviewed and discussed, namely the so-called “Fictitious Boundary” and “Fictitious Domain/Penalty” methods. Evaluation of the two methods is performed by solving simple two-dimensional heat conduction problems using fixed scale expansion of the unknowns. A discussion on the implemention of the boundary conditions and the ease of solving the resulting system of equations is presented. For each problem the error is computed so that the accuracy of the solution can be evaluated. It is found that the Fictitious Domain/Penalty method shows better agreement with the exact solutions than the Fictitious Boundary method as it introduces less computational errors due the methodology used to implement the boundary conditions in the extended domain.
Simulation of Flow and Heat Transfer With Phase Boundaries and Complex Geometries on Cartesian Grids
Authors: Udaykumar H. S. , Mittal R. , Shyy W. 
Published: December 2021

Abstract
This paper is an extension of our previous work on simulation of complex phase front evolution in the diffusion-dominated situation. The Navier-Stokes equations are solved using a finite-volume method based on a second-order accurate central-difference scheme in conjunction with a two-step fractional-step procedure. The key aspects that need to be considered in developing such a solver are imposition of boundary conditions on the immersed boundaries and accurate discretization of the governing equation in cells that are cut by these boundaries. A new interpolation procedure is presented which allows systematic development of a spatial discretization scheme that preserves the second-order spatial accuracy of the underlying solver. The presence of immersed boundaries alters the conditioning of the linear operators and this can slow down the iterative solution of these equations. The convergence is accelerated by using a preconditioned conjugate gradient method where the preconditioner takes advantage of the structured nature of the underlying mesh. The accuracy and fidelity of the solver is validated and the ability of the solver to simulate flows with very complicated immersed boundaries is demonstrated. The method will be useful in studying the effects of fluid flow on the evolution of complex solid-liquid phase boundaries.
Three-Dimensional Thermal Model of Resistance Spot Welding in Aluminum
Authors: Kabir A. A. S. Arefin , Khan Jamil A. , Broach Kirk 
Published: December 2021

Abstract
A 3-D thermal model for resistance spot welding in aluminum is presented. The numerical model, validated with experimental findings, considers phase change and the associated weld-pool convection. A parametric study is performed to determine the influence of welding features such as faying surface (work-piece contact surface) contact resistance, current, electrode-work-piece surface-thermal-contact-conductance and electrode tip diameter. These parameters have significant effects on the nugget and heat-affected-zone geometry. The phase change morphology, including melting and solidification rates and weld pool dynamics, is also significantly influenced by the parameters studied. The strongest convection was observed at the center of the molten pool in a plane aligned with gravity. Although two prominent convection cells develop, the phase change morphology is not significantly affected due to the short welding time (less than 0.05 seconds) and low fluid velocity (smaller than 1 × 10−2 mm/s). The nugget grows nonlinearly with increasing current and faying surface contact resistance while diminishing with increasing electrode work-piece surface-thermal-contact-conductance. The influence of faying surface contact resistance on nugget size is less than that of the other parameters. Optimum selection of electrode tip diameter provides the best possible nugget. The duration of weld pool existence increases with the increasing current but decreases with the increasing electrode work-piece surface-thermal-contact-conductance.
Data Reduction Methodology for Fast-Response Schmidt-Boelter Heat-Transfer Gages
Authors: Adams John C. , Kidd Carl T. 
Published: December 2021

Abstract
Transient heat-transfer data have recently been obtained in hypersonic wind tunnels at the Arnold Engineering Development Center (AEDC) with miniaturized fast-response Schmidt-Boelter gages. These sensors have time constants in the 10- to 15-msec range, but have response characteristics that are usually less than first-order. This presents a requirement for a general data reduction method to prevent degradation of the accuracy of the experimental data. A consistent nonambiguous data reduction methodology for fast-response Schmidt-Boelter heat-transfer gages is presented which is easy to implement in an algorithmic fashion. Timewise correction of measured Schmidt-Boelter gage heat flux is no more difficult than that involved in a classical first-order system (Gardon gage), and only involves the determination of a characteristic time measure of the integrated energy deficiency inherent in the gage response. This characteristic time measure is easily determined from the gage response characterization to a step input heat flux by numerical integration of the response versus time data.
A Comparison of Radiation Versus Convection Calibration of Thin-Film Heat Flux Gauges
Authors: Smith D. E. , Bubb J. V. , Popp O. , Diller T. E. , Hevey Stephen J. 
Published: December 2021

Abstract
A transient, in-situ method was examined for calibrating thin-film heat flux gauges using experimental data generated from both convection and radiation tests. Also, a comparison is made between this transient method and the standard radiation substitution calibration technique. Six Vatell Corporation HFM-7 type heat flux gauges were mounted on the surface of a 2-D, first-stage turbine rotor blade. These gauges were subjected to radiation from a heat lamp and in a separate experiment to a convective heat flux generated by flow in a transonic cascade wind tunnel. A second set of convective tests were performed using jets of cooled air impinging on the surface of the gauges. Direct measurements were simultaneously taken of both the time-resolved heat flux and surface temperature on the blade. The heat flux input was used to predict a surface temperature response using a one-dimensional, semi-infinite conduction model into a substrate with known thermal properties. The sensitivities of the gauges were determined by correlating the semi-infinite predicted temperature response to the measured temperature response. A finite-difference code was used to model the penetration of the heat flux into the substrate in order to estimate the time for which the semi-infinite assumption was valid. The results from these tests showed that the gauges accurately record both the convection and radiation modes of heat transfer. The radiation and convection tests yielded gauge sensitivities which agreed to within ±11%.
Instability of Flame Spread in Microgravity
Authors: Oravecz Lisa M. , Wichman Indrek S. , Olson Sandra L. 
Published: December 2021

Abstract
Results from the first part of an experimental study of flame spread instability are presented. The instabilities were investigated in the NASA drop facilities because the particular instabilities being examined were most pronounced in microgravity, when the influences of buoyancy were minimized. The flame front over thin cellulosic samples broke apart into separate flamelets which interacted with one another and oscillated (frequency ∼ 1 Hz). Different heat-sink backings, which were used to promote flame instability and flamelet productions are examined and described. Preliminary experiments in the NASA 5 second drop tower (Zero-G) drop facility are discussed.
Thermal Analysis of an Absolute Radiometer Designed for the Future Satellite Mission of Total Solar Irradiance Measurement
Authors: Shen Y. J. , Chen D. H. , Zhang Z. M. 
Published: December 2021

Abstract
This work employs finite element (FE) software to perform a thermal modeling of a proposed absolute radiometer designed for the future satellite mission of total solar irradiance measurement. Both steady-state and transient analyses have been performed to obtain the temperature distribution and history. The cavity-type absolute radiometer employs the electrical-substitution technique and active temperature control to determine the radiant power entering the receiving cavity. The nonequivalence between the shutter-open mode and shutter-closed mode due to different temperature distributions is a major factor that affects the radiometric accuracy. The steady-state analysis shows that the nonequivalence is a function of sensor positions and can be minimized by properly choosing the electrical heating method and the temperature sensor location. The transient analysis provides the temperature response for a step power input. In order to reduce the computational time, simplified lumped-heat-capacity models have been developed by applying the least-squares fitting technique to the transient result of the FE model. The two-lumped-heat-capacity model demonstrates a better accuracy than the single-lumped-heat-capacity model and will facilitate the controller design.
Surface Deformation and Thermal Convection in Electrostatically-Positioned Droplets Under Microgravity
Authors: Song Suping , Li Ben Q. 
Published: December 2021

Abstract
Electrostatically positioned droplets are very useful for the fundamental study of solidification phenomena and the measurement of thermal physical properties. This paper descries a numerical analysis of surface deformation and surface tension driven flows in electrostatically positioned droplets in microgravity. The analysis is based on a fully coupled boundary element and finite element solution of the Maxwell equations, the Navier-Stokes equations and the energy balance equation. Results show that an applied electrostatic field results in a nonuniform electric stress distribution along the droplet surface, which, combined with surface tension, causes the droplet to deform into an ellipsoidal shape in microgravity. Laser heating induces a non-uniform temperature distribution in the droplet, which in turn produces Marangoni convection in the droplet. It is found that the viscous stress contribution to the deformation is small for a majority of cases. Also, a higher temperature gradient produces a stronger Marangoni convection in droplets with higher melting points that require more laser power. The internal recirculating flow may be reduced by more uniform laser heating. During the undercooling of the droplet, both temperature and fluid flow fields evolve in time such that the temperature gradient and the tangential velocities along the droplet surface subside in magnitude and reverse their directions.
Safety Analyses at the Idaho National Engineering and Environmental Laboratory Test Reactor Area: Past to Present
Authors: Ambrosek Richard G. , Ingram Fred W. 
Published: December 2021

Abstract
Test reactors are unique in that the core configuration may change with each operating interval. The process of safety analyses for test reactors at the Idaho National Engineering and Environmental Test Reactor Area has evolved as the computing capabilities, software, and regulatory requirements have changed. The evaluations for experiments and the reactor have moved from measurements in a set configuration and then application to other configurations with a relatively large error to modeling in three-dimensions and explicit analyses for each experiment and operating interval. This evolution is briefly discussed for the Test Reactor Area.