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Proceedings Papers

*Proc. ASME*. HT2021, ASME 2021 Heat Transfer Summer Conference, V001T01A006, June 16–18, 2021

Paper No: HT2021-62998

Abstract

Estimating the parameters that describe a thermal problem using Bayes statistics requires the specification of appropriate prior probabilities. That is p(P|D) = p(D|P)p(P)/p(D) where P = parameters, D = data and p(P) is the prior probability. For thermal problems this requires prior probabilities for density, specific heat, thermal conductivities, surface convective coefficients, radiative properties, and local heat release, Q. For many problems it is common to choose Gaussian probabilities to represent the errors. If the standard deviation is large, then the predictions can lead to negative values — a result that is not possible except for Q. Variational Bayes (VB) is an alternative to Markov Chain Monte Carlo (MCMC) and assumes that complex distributions p(a,b) can be replaced by factorization, p(a,b) = p(a)p(b), the mean field theory of physics. Overall Variational Bayes is particularly important for posterior probabilities, p(a|D), that have multiple maxima distributions.

Proceedings Papers

*Proc. ASME*. HT2013, Volume 3: Gas Turbine Heat Transfer; Transport Phenomena in Materials Processing and Manufacturing; Heat Transfer in Electronic Equipment; Symposium in Honor of Professor Richard Goldstein; Symposium in Honor of Prof. Spalding; Symposium in Honor of Prof. Arthur E. Bergles, V003T20A002, July 14–19, 2013

Paper No: HT2013-17159

Abstract

In this study the effect of randomness of blowing ratio on film cooling performance is investigated by combining direct numerical simulations with a stochastic collocation approach. The geometry includes a 35-degree inclined jet with a plenum attached to it. The blowing ratio variations are assumed to have a truncated Gaussian distribution with mean of 0.3 and the standard variation of approximately 0.1. The parametric space is discretized using Multi-Element general Polynomial Chaos (ME-gPC) with five elements where general polynomial chaos of order 3 is used in each element. A fast convergence of the polynomial expansion in the random space was observed. Direct numerical simulations were carried out using spectral element method to sample the governing equations in space and time. The probability density function of the film cooling effectiveness was obtained and the standard deviation of the adiabatic film cooling effectiveness on the blade surface was calculated. A maximum standard deviation of 15% was observed in the region within a four-jet-diameter distance downstream of the exit hole. The spatially-averaged adiabatic film cooling effectiveness was 0.23 ± 0.02 . The calculation of all the statistical properties were carried out as off-line post-processing. Overall the computational strategy is shown to be very effective with the total computational cost being equivalent to solving twenty independent direct numerical simulations that are performed concurrently.

Proceedings Papers

*Proc. ASME*. HT2012, Volume 2: Heat Transfer Enhancement for Practical Applications; Fire and Combustion; Multi-Phase Systems; Heat Transfer in Electronic Equipment; Low Temperature Heat Transfer; Computational Heat Transfer, 1095-1104, July 8–12, 2012

Paper No: HT2012-58523

Abstract

In recent years, there has been interest in employing atomistic computations to inform macroscale thermal transport analyses. In heat conduction simulations in semiconductors and dielectrics, for example, classical molecular dynamics (MD) is used to compute phonon relaxation times, from which material thermal conductivity may be inferred and used at the macroscale. A drawback of this method is the noise associated with MD simulation, which is generated due to the possibility of multiple initial configurations corresponding to the same system temperature; for phonon relaxation times, the spread may be as high as 20%. In this work we propose a method to quantify the uncertainty in thermal conductivity computations due to MD noise, and its effect on the computation of the temperature distribution in heat conduction simulations. Bayesian inference is used to construct a probabilistic surrogate model for thermal conductivity as a function of temperature, accounting for the statistical spread in MD relaxation times. The surrogate model is used in probabilistic computations of the temperature field in macroscale Fourier conduction simulations. These simulations yield probability density functions of the spatial temperature distribution. To allay the cost of probabilistic computations, a stochastic collocation technique based on generalized polynomial chaos (gPC) is used to construct a response surface for the variation of temperature (at each physical location in the domain) as a function of the random variables in the thermal conductivity model. Results are presented for the spatial variation of the probability density function of temperature as a function of spatial location in a typical heat conduction problem to establish the viability of the method.

Proceedings Papers

*Proc. ASME*. HT2012, Volume 2: Heat Transfer Enhancement for Practical Applications; Fire and Combustion; Multi-Phase Systems; Heat Transfer in Electronic Equipment; Low Temperature Heat Transfer; Computational Heat Transfer, 205-212, July 8–12, 2012

Paper No: HT2012-58311

Abstract

Secondary atomization is one of the most attractive and misunderstood effects in the combustion of microemulsified fuel blends. The occurrence of secondary atomization has been studied to determine its effects on improved combustion efficiency especially when low vapor pressure fuels are used. Several methods to detect microexplosion as alternative to secondary atomization have been considered including acoustic signal processing. As part of the physical characterization of an emulsified vegetable oil-methanol blend, microexplosion behavior of fuel blend droplets has been observed to take place under certain environmental conditions. Droplets microexplode as methanol surrounded by vegetable oil molecules flashes or microexplodes under intense temperature and intense droplet pressure. The droplets of emulsified methanol-in-oil break up forming tiny droplets with greater surface-to-volume ratio in the process. To understand the effects of emulsification on microexplosion, characterization of secondary atomization has been performed using a temperature probe, a high-speed camera and an acoustic sound signal processor. Experiments have been conducted at temperatures similar to those encountered in liquid fuel boilers. The acoustic signal data were analyzed using Fast Fourier Transform (FFT) to define and understand the overall microexplosion process. Also, the effect of temperature, droplet sizes and the percentage of methanol in the vegetable oil blend have been studied to understand what leads to a higher probability of microexplosion occurrence. A correlation between the analyzed acoustic signal data and high speed images were used to differentiate between the different microexplosion events. The results of the study can be useful in predicting the occurrence of microxplosion in liquid fuel boiler which should result in more complete combustion processes, reducing contaminant levels significantly.

Proceedings Papers

*Proc. ASME*. HT2012, Volume 1: Heat Transfer in Energy Systems; Theory and Fundamental Research; Aerospace Heat Transfer; Gas Turbine Heat Transfer; Transport Phenomena in Materials Processing and Manufacturing; Heat and Mass Transfer in Biotechnology; Environmental Heat Transfer; Visualization of Heat Transfer; Education and Future Directions in Heat Transfer, 601-607, July 8–12, 2012

Paper No: HT2012-58445

Abstract

We determine how the natural distributions of phonon-phonon and phonon-boundary scattering free paths affect the prediction of thermal conductivity for thin films, nanowires, and porous nanofilms. Using Monte Carlo sampling, the effective mean free path for each phonon mode is calculated using a Poisson distribution for the phonon-phonon free path and assuming an equal probability of the phonon originating at any point in the nanostructure. We find our predictions to be consistent with an analytical result for the in-plane direction in the thin films, as opposed to the Matthiessen rule, which leads to an under-prediction by up to 10 %. Furthermore, we are able to use our approach to predict the thermal conductivities of complex nanostructures, where correct application of the Matthiessen rule is challenging.

Proceedings Papers

*Proc. ASME*. HT2009, Volume 3: Combustion, Fire and Reacting Flow; Heat Transfer in Multiphase Systems; Heat Transfer in Transport Phenomena in Manufacturing and Materials Processing; Heat and Mass Transfer in Biotechnology; Low Temperature Heat Transfer; Environmental Heat Transfer; Heat Transfer Education; Visualization of Heat Transfer, 527-535, July 19–23, 2009

Paper No: HT2009-88626

Abstract

In the current work, the mixing of a diffusive passive-scalar, e.g., thermal energy or species concentration, driven by electro-osmotic fluid motion being induced by an applied potential across a micro-channel is studied numerically. Secondary time-dependent periodic or random electric fields, orthogonal to the main stream, are applied to generate cross-sectional mixing. This investigation focuses on the mixing dynamics and its dependence on the frequency (period) of the driving mechanism. For periodic flows, the probability density function (PDF) of the scaled passive scalar (i.e., concentration), settles into a self-similar curve showing spatially repeating patterns. In contrast, for random flows there is a lack of self-similarity in the PDF for the interval of time considered in this investigation. The present study confirms an exponential decay of the variance of the concentration for the periodic and random flows.

Proceedings Papers

*Proc. ASME*. HT2009, Volume 1: Heat Transfer in Energy Systems; Thermophysical Properties; Heat Transfer Equipment; Heat Transfer in Electronic Equipment, 77-91, July 19–23, 2009

Paper No: HT2009-88078

Abstract

The transported PDF method coupled with a detailed gas-phase chemistry, soot model and radiative transfer equation solver is applied to various turbulent jet flames with Reynolds numbers varying from ∼ 6700 to 15100. Two ethylene–air flames and four flames with a blend of methane–ethylene and enhanced oxygen concentration are simulated. A Lagrangian particle Monte Carlo method is used to solve the transported joint probability density function (PDF) equations, as it can accommodate the high dimensionality of the problem with relative ease. Detailed kinetics are used to accurately model the gas-phase chemistry coupled with a detailed soot model. Radiation is calculated using a particle-based photon Monte Carlo method, which is coupled with the PDF method and the soot model to accurately account for both emission and absorption turbulence–radiation interactions (TRI), using line-by-line databases for radiative properties of CO 2 and H 2 O; soot radiative properties are also modeled as nongray. Turbulence–radiation interactions can have a strong effect on the net radiative heat loss from sooting flames. For a given temperature, species and soot distribution, TRI increases emission from the flames by 30–60%. Absorption also increases, but primarily due to the increase in emission. The net heat loss from the flame increases by 45–90% when accounting for TRI. This ixs much higher than the corresponding increase due to TRI in nonsooting flames. Absorption TRI was found to be negligible in the laboratory scale sooting flames with soot levels on the order of a few ppm, but may be important in larger industrial scale flames.

Proceedings Papers

*Proc. ASME*. HT2007, ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 1, 47-51, July 8–12, 2007

Paper No: HT2007-32590

Abstract

The dependence of molecular motion on the dissociative adsorption mechanism of hydrogen molecule (H 2 ) on platinum (Pt) surface was studied by Molecular Dynamics (MD) method. An interaction between atoms was considered by the Embedded Atom Method (EAM). A potential between an H atom and a Pt atom was determined from results of Density Functional Theory (DFT). Dissociation probabilities of three surface conditions, that is, (1) when the surface temperature is 300 K, (2) when the surface temperature is 0 K with allowing motion of the surface atoms and (3) when the surface temperature is 0 K with prohibiting motion of the surface atoms, were obtained. From results of the simulations, the effect of surface motion on dissociation probability was analyzed as a function of initial energy of the dissociating molecule or the surface conditions. First, it was concluded that the increase in the dissociation probability of the case (3) by the increase in the initial translational energy of H 2 molecule is gentle compared with those of the other cases. Additionally, the minimum initial translational energy of H 2 molecule of case (3) at which the H 2 molecule can dissociate is the smallest among all of three cases. It was found that this is because the range of the dissociation barrier distribution for the case (3) is wider than those for the other cases due to the thermal motion of surface atoms. Moreover, the effect of translational and rotational motion of molecule on the dissociation probability was analyzed. It was concluded that the dissociation probability increases with the increase in the translational energy while it decreases with the increase in the rotational energy when the rotational energy is small.

Proceedings Papers

*Proc. ASME*. HT2007, ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 1, 585-589, July 8–12, 2007

Paper No: HT2007-32646

Abstract

Numerical simulation based on a moment method is conducted to investigate the feasibility of an assumed probability density function (PDF) approach in the configuration of a turbulent jet nonpremixed flame. In this study, a multivariate β-PDF is employed to account for turbulence-chemistry interaction. The multivariate β-PDF approach has an advantage that only one additional transport equation of sum of composition variances is solved to determine the shape of species PDF to transport equations of mean compositions. The numerical simulation is carried out for H3 flame. Reaction mechanism is a single-step irreversible reaction including H 2 , O 2 and H 2 O species. The results are compared with those from measurements and a combined PDF/moment method that detailed reaction mechanism is applied. Velocity distributions obtained by the multivariate β-PDF approach show good agreement with measurements and combined PDF/moment results, which indicates that the present approach can predict the flow pattern of nonpremixed flames. The present approach also provides good predictions in terms of mean temperature and mass fraction. PDFs of mass fraction obtained by the present approach are similar to those by the combined PDF/moment method. On the other hand, the variance of temperature is underpredicted, which is attributed to an approximation of temperature variance. In order to achieve a good prediction of the reaction rate, a PDF approximation of enthalpy is proposed for the evaluation of mean reaction rate.

Proceedings Papers

*Proc. ASME*. HT2008, Heat Transfer: Volume 1, 99-108, August 10–14, 2008

Paper No: HT2008-56077

Abstract

Thermo-mechanical failure of components in a compact steam reformer is a major obstacle to bring this technology to real-life applications. The probability of material degradation and failure depends strongly on the convective heat transfer in the fuel gas flow duct and local temperature distribution in multifunctional materials. It is of significant importance to accurately predict the convective heat transfer coupled with catalytic reactions within the reformer components. In this paper, the simulation and analysis of combined chemical reactions and transport processes are conducted for a duct relevant for compact design steam reformer, which consists of a porous layer for the catalytic reforming reactions of methane, the fuel gas flow duct and solid plates. A fully three-dimensional computational fluid dynamics (CFD) approach is applied to calculate transport processes and effects of thermal conductivities of the involved multi-functional materials on convective heat transfer/temperature distributions, in terms of interface temperature gradients/heat fluxes and Nusselt numbers. The steam reformer conditions such as mass balances associated with the reactions and gas permeation to/from the porous anode are implemented in the calculation. The results show that the classic thermal boundary conditions (either constant heat flux or temperature, or combined one) may not be applicable for the interfaces between the fuel flow duct and solid plate/porous layer.

Proceedings Papers

Tae-Woo Lee, Himanshu Tyagi, David Sonenschein, Patrick E. Phelan, Ravi Prasher, Robert Peck, Paul Arentzen

*Proc. ASME*. HT2008, Heat Transfer: Volume 3, 243-248, August 10–14, 2008

Paper No: HT2008-56466

Abstract

Basic ignition, evaporation and combustion behavior of liquid fuel droplets containing metal nanoparticles is experimentally investigated. The addition of metal nanoparticles enhances the ignition and evaporation of the liquid fuel droplets, even at low volume fraction of the nanoparticles (0.1% to 0.5%). These enhancements were, however, independent of the amount, type and size of the nanoparticles and limited to ignition and low temperature evaporation conditions. At higher temperatures, evaporation and combustion rates of the liquid droplets were not significantly affected by addition of nanoparticles. The data suggest, therefore, that the primary role of nanoparticles is in enhancing the thermal diffusion during initiation phase (ignition and low-temperature evaporation) where even in very small amounts addition of nanoparticles increases the ignition probability and evaporation rates.

Proceedings Papers

*Proc. ASME*. HT2008, Heat Transfer: Volume 3, 199-206, August 10–14, 2008

Paper No: HT2008-56310

Abstract

In the present work, line-of-sight spectral radiation intensities ( I λ ) were measured in a 7.1 cm ethylene (C 2 H 4 ) buoyant diffusion flame, designed to mimic pool fires. Various time series statistics were calculated using the radiation data. Both soot and gaseous species had significant radiation emissions, emphasizing the need for spectrally-resolved radiation measurements. Significant fluctuations were observed in the radiation intensities from the fire, especially at higher elevations and near the flame edges. In addition, root-mean-square (rms) and probability density functions (PDF) of I λ indicated higher fluctuations in soot compared to gaseous species. Autocorrelations of I λ showed periodic oscillations due to the puffing phenomenon typically seen in pool fires. The observed oscillation frequencies ranged from 7.47 to 7.86 Hz and are in excellent agreement with empirical correlations based on past data. Characteristic frequencies of these oscillations were also reflected in the power spectral densities (PSD) of I λ . Based on the measured autocorrelations of I λ , it was observed that the integral time scales decrease with increasing height above the burner exit, which is expected since mean velocities increase with height due to combustion-induced buoyancy in pool fires and buoyant flames.

Proceedings Papers

*Proc. ASME*. HT2008, Heat Transfer: Volume 3, 331-340, August 10–14, 2008

Paper No: HT2008-56259

Abstract

In this paper a computational heat transfer model for prediction of the temperature distribution within the human eye during laser surgery is presented. The heat transfer within a tissue is described by the classic Pennes bioheat transfer equation. The intraocular temperature distribution is calculated using finite-difference method. Two types of computational domain have been considered: (i) rectangular parallelepiped and (ii) cylindrical. The eye is modeled as a composite layered structure consisting of four different ocular tissues, namely, cornea, aqueous, lens and vitreous. It is assumed that the eye is symmetrical about the pupillary axis. The absorption probability of ocular tissue is modulated based on the Lambert-Beer’s law to reproduce the exponential attenuation of the laser light with depth within a biomaterial. The heat flow is modeled as transient and three-dimensional for rectangular parallelepiped geometry and two-dimensional (axi-symmetric) for the cylindrical geometry. The results indicate that for the insulation condition imposed on the periphery of the eye the model based on rectangular parallelepiped geometry of the eye at no laser power and at the initial temperature of 25°C predicts temperature closer to in-vitro experimental measurements reported in literature whereas the model based on cylindrical geometry predicts higher temperature. The opposite is true (that is, lower temperature is predicted by the model based on cylindrical geometry) for high laser heat flux (2000 W/m 2 ) and higher initial temperature (37°C). This study also presents changes in eye temperature subjected to intermittent laser source used in laser surgery techniques such as PRK and LASIK. A comparison of the results based on three different boundary conditions such as convection (h b = 10 W/m 2 K), constant temperature (37°C) and insulation on the eye periphery reveals that the model based on insulation condition predicts results closer to that of in-vitro experiment at no laser power and initial temperature of 25°C whereas at a laser power of 200 W/m 2 and at the initial temperature of 37°C insulation boundary condition produces highest temperature followed by that produced by convection and constant temperature conditions. The heat transfer is one-dimensional for the insulated eye periphery whereas multi-dimensional heat flow takes place when the circumferential boundary condition is either convective or isothermal.

Proceedings Papers

*Proc. ASME*. HT2005, Heat Transfer: Volume 1, 397-402, July 17–22, 2005

Paper No: HT2005-72377

Abstract

One-dimensional (1D) materials such as various kinds of nanowires and nanotubes have attracted considerable attention due to their potential applications in electronic and energy conversion devices. The thermal transport phenomena in these nanowires and nanotubes could be significantly different from that in bulk material due to boundary scattering, phonon dispersion relation change, and quantum confinement. It is very important to understand the thermal transport phenomena in these materials so that we can apply them in the thermal design of microelectronic, photonic, and energy conversion devices. While intensive experimental efforts are being carried out to investigate the thermal transport in nanowires and nanotube, an accurate numerical prediction can help the understanding of phonon scattering mechanisms, which is of fundamental theoretical significance. A Monte Carlo simulation was developed and applied to investigate phonon transport in single crystalline Si nanowires. The Phonon-phonon Normal (N) and Umklapp (U) scattering processes were modeled with a genetic algorithm to satisfy both the energy and the momentum conservation. The scattering rates of N and U scattering processes were given from the first perturbation theory. Ballistic phonon transport was modeled with the code and the numerical results fit the theoretical prediction very well. The thermal conductivity of bulk Si was then simulated and good agreement was achieved with the experimental data. Si nanowire thermal conductivity was then studied and compared with some recent experimental results. In order to study the confinement effects on phonon transport in nanowires, two different phonon dispersions, one based on bulk Si and the other solved from the elastic wave theory for nanowires, were adopted in the simulation. The discrepancy from the simulations based on different phonon dispersions increases as the nanowire diameter decreases, which suggests that the confinement effect is significant when the nanowire diameter goes down to tens nanometer range. It was found that the U scattering probability engaged in Si nanowires was increased from that in bulk Si due to the decrease of the frequency gap between different modes and the reduced phonon group velocity. Simulation results suggest that the dispersion relation for nanowire solved from the elasticity theory should be used to evaluate nanowire thermal conductivity as the nanowire diameter reduced to tens nanometer.

Proceedings Papers

*Proc. ASME*. HT2005, Heat Transfer: Volume 3, 563-570, July 17–22, 2005

Paper No: HT2005-72313

Abstract

This work presents a Lagrangian approach to simulate convective heat transfer in small scales. The fully developed flow field, simulated by a Lattice Boltzmann Method, is combined with Lagrangian tracking of thermal markers to determine the behavior of an instantaneous scalar line source located at the wall of a channel. The resulting probability density functions are used to calculate the behavior of continuous line sources of heat at the wall of the channel, as well as the temperature for the case of constant temperature or constant heat flux from the wall. This method is resourceful in terms of computational efficiency, in that it can be used to simulate various thermal boundary conditions and Prandtl number fluids with a single flow field resulting from a Lattice Boltzmann simulation.

Proceedings Papers

*Proc. ASME*. HT2005, Heat Transfer: Volume 4, 947-954, July 17–22, 2005

Paper No: HT2005-72530

Abstract

In this work we model uncertainty propagation in heat transfer via the multi-element generalized polynomial chaos (ME-gPC) method by focusing on the stochastic heat-transfer enhancement in a two-dimensional grooved channel. Based on the global energy balance, a similar technique as in [1] is employed to develop proper numerical schemes for the fully developed flow. The velocity and temperature field are expressed by the ME-gPC. Using a Galerkin projection, we reduce the stochastic PDE system to a high-dimensional deterministic one, which is solved by the spectral/ hp element method. A time, spaced-averaged Nusselt number with error bars is obtained at different excitation frequencies. The probability density function (PDF) of the Nusselt number is also presented.

Proceedings Papers

*Proc. ASME*. HT-FED2004, Volume 4, 503-504, July 11–15, 2004

Paper No: HT-FED2004-56556

Abstract

Understanding thermal boundary resistance (TBR) is becoming increasingly important for the thermal management of micro and optoelectronic devices. The current understanding of room temperature TBR is often not adequate for the thermal design of tomorrow’s complex micro and nano devices. Theories have been developed to explain the resistance to energy transport by phonons across interfaces. The acoustic mismatch model (AMM) [1, 2], which has had success at explaining low temperature TBR, does not account for the high frequency phonons and imperfect interfaces of real devices at room temperature. The diffuse mismatch model (DMM) was developed to account for real surfaces with higher energy phonons [3, 4]. DMM assumes that all phonons incident on the interface from both sides are elastically scattered and then emitted to either side of the interface. The probability that a phonon is emitted to a particular side is proportional to the phonon density of states of the two interface materials. Inherent to the DMM is that the transport is independent of the interface structure itself and is only dependent on the properties of the two materials. Recent works have shown that the DMM does not adequately capture all the energy transport mechanisms at the interface [5, 6]. In particular, the DMM under-predicts transport across interfaces between non Debye-like materials, such at Pb and diamond, by approximately an order of magnitude. The DMM also tends to over-predict transport for interfaces made with materials of similar acoustic properties, Debye-like materials. There have been several explanations and models developed to explain the discrepancies between the mismatch models and experimental data. Some of these models are based on modification of the AMM and DMM [7–9]. Other works have utilized lattice-dynamical modeling to calculate phonon transmission coefficients and thermal boundary conductivities for abrupt and disordered interfaces [3, 6, 10–13]. Recent efforts to better understand room temperature TBR have utilized molecular dynamics simulations to account for more realistic anharmonic materials and inelastic scattering [14–18]. Models have also been developed to account for electron-phonon scattering and its effect on the thermal boundary conductance for interfaces with one metal side [19–22]. Although there have been numerous thermal boundary resistance theoretical developments since the introduction of the AMM, there still is not an unifying theory that has been well validated for high temperature solid-solid interfaces. Most of the models attempt to explain some of the experimental outliers, such as Pb/diamond and TiN/MgO interfaces [6, 23], but have not been fully tested for a range of experimental data. Part of the problem lies in the fact that very little reliable data is available, especially data that is systematically taken to validate a particular model. To this end, preliminary measurements of TBR are being made on a series of metal on non-metal substrate interfaces using a non-destructive optical technique, transient thermal reflectance (TTR) described in Stevens et al. [5]. Initial testing examines the impact of different substrate preparation and deposition conditions on TBR for Debye-like interfaces for which TBR should be small for clean and abrupt interfaces. Variables considered include sputter etching power and duration, electron beam source clean, and substrate temperature control. The impact of alloying and non-abrupt interfaces on the TBR is examined by fabricating interfaces of both Debye-like and non Debye-like interfaces followed by systematically measuring TBR and altering the interfaces by annealing the samples to increase the diffusion depths at the interfaces. Inelastic electron scattering at the interface has been proposed by Hubermann et al. and Sergeev to decrease TBR at interfaces [19–21]. Two sets of samples are prepared to examine the electron-phonon connection to improved thermal boundary conductance. The first consists of thin Pt and Ag films on Si and sapphire substrates. Pt and Ag electron-phonon coupling factors are 60 and 3.1×10 16 W/m 3 K respectively. Both Pt and Ag have similar Debye temperatures, so electron scattering rates can be examined without much change in acoustic effects. The second electron scattering sample series consist of multiple interfaces fabricated with Ni, Ge, and Si to separate the phonon and electron portions of thermal transport. The experimental data is compared to several of the proposed theories.

Proceedings Papers

*Proc. ASME*. HT-FED2004, Volume 3, 837-842, July 11–15, 2004

Paper No: HT-FED2004-56826

Abstract

Bubble nucleation and growth of formed nuclei are investigated by molecular dynamics simulation in Lennard-Jones liquid with gas impurities. For the onset of nucleation from bulk, it has been found that a dissolved gas whose interaction is very weak and whose diameter is larger than that of solvent molecules makes the action to cause composition fluctuation or local phase separation so strong that the nucleation probability predicted from pressure change becomes qualitatively wrong. It has been confirmed that this wrong prediction is generally explained by introducing the superheat ratio nondimensionalized by saturation pressure and spinodal pressure. For the growth stage of formed bubble nuclei, it is observed that the coalescence of nuclei occurs when a weak-interaction gas is dissolved at a high concentration while the competition between neighbor nuclei is dominant in the case of pure liquid.

Proceedings Papers

#### A Sensitivity Study of NOx Emission to the Change in the Input Variables of a FGR Industrial Furnace

*Proc. ASME*. HT2003, Heat Transfer: Volume 2, 95-102, July 21–23, 2003

Paper No: HT2003-47315

Abstract

Preliminary study has shown that the flue gas recirculation (FGR) is one of the effective ways to reduce the Nitric Oxides (NOx) emission in industrial furnaces. The research reported in this paper concentrates mainly on the development of dynamic models suitable for on-line and real-time feedback control to reduce the NOx emission in industrial furnaces with FGR. To construct an appropriate dynamic model, the relationship between the NOx emission and the furnace input variables, such as the inlet combustion air mass flow rate, inlet combustion air temperature, and the pressure head of the FGR fan, has been investigated. A moment closure method with the assumed β probability density function (PDF) for the mixture fraction is used to model the turbulent non-premixed combustion process in the furnace. The combustion model is derived based on the assumption of instantaneous full chemical equilibrium. The discrete transfer radiation model is chosen as the radiation heat transfer model, and the weighted-sum-of-gray-gases model is used to calculate the absorption coefficient.