bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transport Phenomena and Droplet Formation During Pulsed Laser Micro-Machining of Thin Films
Authors: Willis David A. , Xu Xianfan 
Published: January 2022

Abstract
This work investigates the transport phenomena and the mechanisms of droplet formation during a laser-based, thin film micro-machining process. The surface of the target material is altered through laser-induced material flow in the molten phase induced by a tightly-focused laser energy flux. Experimental and numerical investigations of the laser-induced fluid flow and topography variations are carried out for a better understanding of the physical phenomena involved in the processes.
As with many machining techniques, debris is often generated during the laser machining process. Experimental parametric studies are carried out to correlate the laser parameters with the topography and droplet formations. It is found that a narrow range of operation parameters and target conditions exist for ‘clean’ structures to be fabricated.
The stop action photography technique is employed to capture the surface topography variation and the melting development with a nanosecond time resolution and a micrometer spatial resolution. Numerical simulations of the laser-induced surface deformation are also performed to obtain the transient field variables and to track the deforming surface. The comparison between the numerical and experimental work shows that, within the energy intensity range investigated in this work, the surface deformation is attributed to the surface-tension-driven-flow, and the recoil pressure effect plays an insignificant role in surface topography variation. Instability of the fluid flow in the laser-induced molten pool is shown to be a possible cause of debris formation.
Molecular Dynamics Simulation of Thermal Conductivity in Bulk Silicon and Nanowires
Authors: Volz Sebastian G. , Chen Gang 
Published: January 2022

Abstract
With the advancement of nanofabrication technologies, nanowires may be produced for both fundamental studies and practical applications. Understanding the heat conduction mechanisms in these nanodevices is important for a number of technological areas such as electronics and thermoelectrics. In this work, we investigate the thermal conductivity of silicon single crystals and silicon nanowires based on molecular dynamics (MD) simulations and the Stillinger-Weber potential. Although the simulated crystal size is much smaller than the phonon mean free path and shorter than a range of the bulk phonon wavelengths, we show that the periodic boundary conditions together with a spectral analysis lead to reasonable values of the thermal conductivity in bulk silicon. The simulated thermal conductivity of a 2.14nm × 2.14nm square cross-sectional nanowire with rigid boundaries is found to be 40 times smaller than bulk Si at 500 Kelvin. In addition to the MD simulations, the BTE is solved under the relaxation time approximation by considering various specular/diffusive scattering rates of phonons at the surfaces. Through a comparison of the nanowire thermal conductivity obtained by both methods, we quantify the surface scattering properties and give explanations to the observed discrepancies.
Application of Block-Implicit Multigrid Approach to Heat Transfer Problems Involving Discrete Heating
Authors: Tang Lan , Joshi Yogendra K. 
Published: January 2022

Abstract
In this study, the performance of Symmetrically Coupled Gauss-Seidel (SCGS) based multigrid method was investigated by applying it to three-dimensional conjugate heat transfer in two different configurations with discrete heat sources. These include a natural convection cooled rectangular enclosure with a discrete heat source mounted on one vertical wall, and a mixed/forced convection cooled channel with a discrete heat source on the bottom wall.
The convergence rates by using SIMPLER (Semi-Implicit Method for Pressure-Linked Equations Revised), SCGS, and Multigrid SCGS (MG-SCGS) were compared for both configurations. The performance of MG-SCGS was tested for variations in Rayleigh number, Reynolds number, and boundary conditions. It is shown that faster convergence rate can be achieved by applying multigrid technique with only two grid levels. With MG-SCGS, significant and consistent performance enhancement over SIMPLER was obtained for the conjugate natural, mixed, and forced convection problems considered.
Finite Element Simulation of Turbulent Heat Transfer in Mold-Filling Problems
Authors: Ilinca Florin , Hétu Jean-François , Audet Martin 
Published: January 2022

Abstract
This paper presents a finite element solution algorithm for solving the turbulent heat transfer and fluid flow on three-dimensional industrial mold-filling problems. The problems of interest present unusual challenges for both the physical modeling and the solution algorithm. The heat transfer on high Reynolds number transient turbulent flow with free surfaces has to be computed on complex 3D geometries. In this work a segregated algorithm is used to solve the Navier-Stokes, energy, turbulence and front tracking equations. The Streamline Upwind Petrov-Galerkin method is used to obtain stable solutions to convection dominated problems. Turbulence is modeled using a one-equation turbulence model and the k-ϵ two-equation model with wall functions. Turbulence equations are solved for the natural logarithm of the turbulence variables. The change of dependent variables allows for good predictions even on coarse meshes. The forced heat transfer in the cavity partly filled with fluid and partly filled with air is coupled with the solution of the conduction equation in the mold. The position of the flow front in the mold cavity is computed using a level set approach. Finally, equations are integrated in time using second order accurate schemes. The methodology presents the robustness and cost effectiveness needed to tackle such complex industrial applications.
Finite Volume TVD Algorithm for Computation of Aerodynamic Heating
Authors: Dong Wei , Fan H. T. 
Published: January 2022

Abstract
In the design of high speed vehicle, in order to ensure safety of flight, its surface pressure, density of heat flow distributions must be given accurately. Many computational schemes based on either the inviscid Euler equations or various forms of the Navier-Stokes equations can give out satisfied results in the predictions of pressure distributions. However computations of skin friction and in addition heat transfer particularly at high speeds have been a source of considerable difficulty. This paper adopts the finite volume method to solve the conservative type of Navier-Stokes equations simulating supersonic and hypersonic flow, for the aerodynamic heating problem. For the calculation of inviscous flow fluxes passing every surface element, the second order precision TVD scheme developed by Harten is adopted, the viscous flow fluxes are treated with centered differences of upwinded/downwinded averaged flow varibles. Numerical experiments show that the proposed schemes are quite robust and accurate.
Thermal Properties of Honeycomb Panels: Analysis of Transient Experiments With One-Dimensional Models
Authors: Cole Kevin D. 
Published: January 2022

Abstract
This work is motivated by the need for thermal properties in order to perform thermal stress analysis of aircraft structural members. For the particular titanium-core honeycomb panels of interest, the effective conductivity was previously underpredicted by established theory compared to a steady experiment. In the present study the thermal properties panel were measured by transient heating experiments. The transient data is analyzed with a parameter estimation method, in which a non-linear regression is carried out between the experimental data and a transient finite-difference model of the heat transfer in the honeycomb panel. A lumped-parameter analytical model is also discussed. The experimental results show that effective thermal conductivity agrees with the previous steady measurement, which indicates that additional work is needed to understand why the steady predictive method underestimates the effective conductivity of this type of honeycomb panel.
The Integration of Design of Experiments, Surrogate Modeling and Optimization for Thermoscience Research
Authors: Queipo Néstor V. , Arévalo Carlos J. , Pintos Salvador A. 
Published: January 2022

Abstract
This paper presents an integrated approach for the solution of complex optimization problems in thermoscience research. The cited approach is based on the design of computational experiments (DOE), surrogate modeling, and optimization. The DOE/Surrogate modeling techniques under consideration include: A-Optimal/Classical Linear Regression, Latin Hypercube/Artificial Neural Networks, and Latin Hypercube/Sugeno-type Fuzzy Models. These techniques are coupled with both local (modified Newton’s method) and global (Genetic Algorithms) optimization methods. The proposed approach showed to be an effective, efficient, and robust, modeling and optimization tool in the context of a case study, and holds promise to be useful in larger scale optimization problems in thermoscience research.
Bubble Swarm Velocity in Two Phase Flows
Authors: Schlueter M. , Raebiger N. 
Published: January 2022

Abstract
The mass transfer in two-phase flows depends significantly on the concentration gradient around the dispersed particles and the contact time between the two phases due to the local hydrodynamics of the system which are closely related to the rising velocity of the gas bubbles in the swarm.
The common equations for calculating the slip velocity which take into account the gas void fraction and the velocity of a single free-falling (or rising) particle lead to differences between the theoretical and the measured slip velocity of up to 40 percent. The investigation show that the bubble rise path, expressed by a special tortuousity number for the 3D-bubble trajectory, is totally different from the bubble rise path of a single, free-rising bubble. Furthermore it should be possible to find a relationship between the swarm velocity, the flow velocity and the gas void fraction of the two-phase flow, correlated to the swarm turbulences.
Interface Shape and Wave Velocities of Air-Water Flows in a Vertical Duct
Authors: Gottmann Matthias , Oishi Tomomi , Sridhar K. R. , Kumar Ranganathan 
Published: January 2022

Abstract
This paper describes the experimental investigation of an upward annular air-water flow in a duct with a 6.35 mm by 63.5 mm rectangular cross section. The test section was instrumented to study the shape of the interface and the interfacial wave velocity. Flush-wire electrical conductivity probes were used to obtain local film thickness measurement with a spatial resolution of 200 μm or better and a temporal resolution greater than 2 kHz. The probe design and a statistical calibration method are discussed. Two flush-wire probes which allow the determination of wave propagation velocities have been implemented. Pressure drop in the channel was measured to provide a measure of averaged momentum transfer in the channel. A simple model for the prediction of interfacial wave velocities is presented, and it matches the data favorably.
Characterization of Chaos Suppression in Fluidization Through Instantaneous Heat Flux and Pressure
Authors: Pence Deborah V. , Beasley Donald E. 
Published: January 2022

Abstract
Gas-solid fluidized beds have been shown to be consistent with deterministic chaos, and are appropriately termed a self-excited nonlinear system. The present study examines chaos suppression resulting from an opposing oscillatory flow in gas-solid fluidization. Recent studies of a new fluidization concept, termed pulse-stabilized fluidization, have shown promising results for heat transfer enhancement in fluidized bed combustors. Pulse stabilized fluidization is accomplished through a secondary flow that is oriented vertically downward in the fluidized bed, and is characterized by a mean and a sinusoidally oscillating component. This opposing oscillatory flow significantly alters the hydrodynamics of fluidization.
Chaos suppression may result from the systematic perturbation of a system variable or control parameter. In the present study, chaos suppression is demonstrated in the hydrodynamics of a bubbling fluidized bed through local instantaneous pressure measurements. Quantitative chaos measures are presented to demonstrate the degree to which chaos is suppressed in the fluidized system under specific operating conditions. The chaos, which is clearly suppressed in the pressure time-series data, is at times distinctly different from measured instantaneous heat flux data under the same operating conditions. Entropy values determined from phase-space attractors are contrasted between pressure and heat flux data to infer aspects of the physics.
A Software for Forecasting the Flow Patterns in Microgravity
Authors: Diev Mikhail D. , Leontiev Alexander I. , Shchetinin Alexey V. 
Published: January 2022

Abstract
The problem of two-phase flow regime diagnostics and prediction remains one of the most complicated problems in modern thermodynamics and hydrodynamics. Despite the great importance of the flowing regime proper choice, it is still based on empirical or semi-empirical approaches, and analytical studies are mainly rather superficial. At the present, due to joint efforts of Russia and the USA, a new two-phase Thermal Control System (TCS) has been developing for the International Space Station «Alpha» (ISSA). Anhydrous ammonia is chosen as a TCS’ working fluid. TCS includes Evaporative Heat Exchangers (EHE) that are assigned to collecting heat escaped during functioning of different equipment in different ISSA modules. To the inlet of EHE, a subcooled ammonia is supplied. Ammonia is then heated and boils in internal EHE channels, and at vapor quality x ≫ 0.6 ... 0.8, it enters the Adiabatic Transportation Tube (ATT). Vapor quality in ATT may vary in a wide range in respect to the level of heat load in EHEs. That is why the forecasting of the two-phase flow pattern is an important problem in a pressure drop prediction.
Fuel Spray Characteristics and Their Effect on Diesel White Smoke Emissions
Authors: Jawad Badih A. , Yassine Mahmoud K. 
Published: January 2022

Abstract
The growing interest in diesel engines and vehicles has put more concern on the environmental issues especially the small particles coining out of the diesel exhaust. This has resulted in regulatory efforts to reduce emissions of these fine particles. Particulates, a main constituent of white smoke poses a big problem for the diesel engine manufacturers and has triggered a heavily focused research in the automotive and aftertreatment industry. One aspect goes into the basics of the diesel fuel spray formation and characteristics and looks at the influence of the different parameters affecting fuel particle size and distribution and the other aspect looks at the actual measurement of white smoke under cold starting of diesel engine. The effect of ambient temperature and fuel properties on white smoke is investigated. The effect of engine speed and ignition delay is discussed. The breakdown of white smoke in terms of gaseous hydrocarbons, liquid and solid particulates is studied. A comparative study is made between white smoke and in it’s three forms for diesel fuel (DF2) and jet fuel (JP8). The fuel accumulated in the engine during cranking plays a major role in the emission of white smoke under cold starting conditions.
Effect of Dimensions and Thermal Properties of Heat Flux Gage on Local Heat Flux
Authors: Sengupta-Deo Indrani , Karwe Mukund V. 
Published: January 2022

Abstract
Steady-state errors in the output in a thin foil-type heat flux gage have been calculated using conduction heat transfer analysis. These errors are a result of differences in the thermal properties and the geometry of the substrate and the gage. It was shown that the error in measuring steady state heat flux is affected by the ratio of the substrate to gage thickness ratio, substrate to gage thermal conductivity ratio, and the surface heat transfer coefficient. The amount of error varied between +40% to −20% for the cases considered. However, the errors were within 4% in most cases with a surface heat transfer coefficient was less than 10 W/m2K.
Blood Vessel Network Generation for Thermal Modeling of Living Tissue
Authors: Gutierrez-Croft Gabriela , Blanchard Curtis H. , Roemer Robert B. 
Published: January 2022

Abstract
A flexible network generation package for use in modeling and thermal analysis of tissue vasculature has been developed. This package can be used to simulate a wide variety of vascular networks with the long range goal being to simulate any tissue in the body. This modular package consists of four programs that are used interactively to generate network models. The first program (Unit Cell) creates individual vascular network “unit cells” of a user specified vascular anatomy distributed throughout a specified unit cell parallelpiped. The second program (Pack) then “packs” any three-dimensional space with these unit cell parallelpipeds (UCP’s) in a user specified manner. The third program (Connect) then connects the vessels of the various unit cell parallelpipeds that have been packed into the tissue. Finally, the fourth program (Flow Rates) assigns blood flow rates to each vessel. The network generation package produces files which are compatible with a hybrid finite-element / finite-difference based program which automatically generates finite-element meshes and computes the complete temperature fields. The network generation package allows the operator to create highly detailed, continuous vessel networks in a short amount of time.
Cellular Signaling Mechanisms Involved in the 3-Dimensional Assembly and Differentiation of PC12 Pheochromocytoma Cells Under Simulated Microgravity in NASA Rotating Wall Vessel Bioreactors
Authors: Lelkes Peter I. , Unsworth Brian R. 
Published: January 2022

Abstract
Rotating Wall Vessel (RWV) Bioreactors simulate microgravity and facilitate 3-D tissue-like assembly through spatial co-localization and cell-cell interactions. This unique cell culture venue is well suited to assess the role of micro-environmental cues in the assembly and tissue-specific differentiation of cells in culture. Our long term goal is to use RWV Bioreactors for generating functional neuroendocrine 3-D constructs which may be useful as clinical replacement tissue in treating neurodegenerative diseases. As a model we are using PC12 pheochromocytoma cells, a bipotential rat adrenal medullary tumor cell line. PC 12 cells differentiate, depending on exogenous factors, either along the neuronal or the neuroendocrine pathway. PC12 cells, when maintained for up to 20 days in RWV Bioreactors, form macroscopic tissue-like aggregates which exhibit enhanced expression of neuroendocrine, adrenergic differentiation markers (Lelkes et al., In Vitro Devel. Biol, 1998, 34: 316–325). We hypothesized that exposure of PC12 cells to the “simulated microgravity” culture conditions in the RWV Bioreactors, might selectively activate signal transduction pathways leading to enhanced neuroendocrine adrenergic differentiation. Using quantitative RT-PCR we demonstrated rapid upregulation of an adrenergic marker, phenylethanolamine-N-methyl transferase (PNMT), in short term RWV cultures. Concomitantly, we found, by electrophoretic mobility shift assays, differential induction of nuclear transcription factors, such as GRE and SP-1, which are known to be involved in the glucocorticoid-induced activation of PNMT. Conversely, upon short term culture of PC12 cells in RWV, the neuronal traits of the cells were impaired. Upon exposure to simulated microgravity, MAPK signaling (erk and jnk) was constitutively activated, while nerve-growth factor (NGF)-induced activation of erk, was abrogated. These results suggest that the culture conditions in the RWV Bioreactors are sufficient to induce PC12 cell differentiation towards the neuroendocrine, phenotype by upregulating “adrenergic” gene expression, while downregulating neurotrophin signaling pathways.
Flight Studies of Particle Trajectories in the NASA/JSC RWPV Bioreactor
Authors: Begley Cynthia M. , Kleis Stanley J. 
Published: January 2022

Abstract
The NASA/JSC rotating wall perfused bioreactor vessel was designed to provide a controllable low shear environment for the culture of mammalian cells on microcarriers in the microgravity environment of space. Sufficient mass transport of nutrients and waste products is essential for the growth and differentiation of cell assemblages. In order to accurately predict the mass transport characteristics of the bioreactor vessel and determine appropriate operating conditions for the proper suspension of the cells, detailed knowledge of the motion of the cell assemblages relative to the fluid phase is required. In the microgravity environment, cell assemblages move under the influence of the pressure gradient, viscous shear, and centripetal acceleration fields. A numerical simulation of the trajectories of spherical particles has been used to predict operating conditions that will adequately suspend the cells while minimizing fluid shear stresses on the cells.
A study of the particle trajectories in the NASA/JSC rotating wall perfused bioreactor vessel was performed aboard STS-85 in August, 1997. Spherical beads of various sizes and densities were used to simulate assemblages of cells on microcarriers in the bioreactor. Bead trajectories were videotaped for numerous operating conditions. A split image optical corrector was used to more accurately determine particle positions in three dimensions.
Results from the flight experiments are compared to numerical solutions. For the moderate Reynolds numbers of interest, the history and lift effects were found to be particularly significant.
Strain and Strain Rate Dependent Changes in Cytosolic Calcium of Cultured Neurons Subjected to Mechanical Stretch
Authors: Lusardi Theresa A. , Wolf John , Smith Douglas H. , Meaney David F. 
Published: January 2022

Abstract
In this study, we examined the response of cultured neurons to mechanical stretch, varying the rate and magnitude of mechanical stretch to encompass both physiological and non-physiological levels. Fully differentiated NTera2 cells, a human-derived neuronal cell line, were cultured on a flexible substrate and a uniaxial strain was applied to the neurons at a specified magnitude and rate. Using rates representing non-physiologic (rapid onset time of 20ms and intermediate onset time of 85 ms), and physiologic levels (slow onset time of 1.5sec), we measured the intracellular calcium transient using the calcium indicator dye Fura-2.
Immediately following the stretch, intracellular calcium concentration increased, then decreased as the cells attempted to restore pre-stretch cytosolic calcium levels. Statistical analysis using ANOVA showed that normalized peak [Ca+2]i immediately following stretch, average [Ca+2]i following the stimulation, and the final [Ca+2]i value at 4 minutes post-stretch had a significant (p &lt; .0005) dependence on the rate and magnitude at which stretch was applied. At the physiologic rate cell response was minimal, while cell response was maximal at the severe onset rate. Unexpectedly, we observed an attenuation in the response in high stretch, high rate group.
At the highest stretch rate studied, these data provide insight into the response of neurons to deformations associated with mechanical trauma. Since calcium is an important cation for processes that can remodel the cytoarchitecture, affect cell signaling, and influence gene expression, the changes associated with the high rates provide at least one pathway for influencing both acute and chronic changes in neuronal behavior following traumatic injury.