bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport Phenomena and Droplet Formation During Pulsed Laser Micro-Machining of Thin Films
Authors: Willis David A. , Xu Xianfan
Published: January 2022

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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 < .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.
Supraphysiological Thermal Injury in Dunning AT-1 Prostate Tumor Cells
Authors: Bhowmick Sankha , Bischof John C.
Published: January 2022

Supraphysiological temperatures are generated by radiofrequency and microwave probes used for the treatment of prostate cancer (Montrosi et al., 1992) and benign prostatic hyperplasia (Larson et al., 1996). A quantitative understanding of the cellular mechanisms of tissue destruction due to these supraphysiological temperatures(> 40°C) is necessary for optimal application of clinical therapeutic protocols on the prostate and other tissue systems. A multitude of biophysical and biochemical events take place at the cellular level due to thermal stress (Cravalho et al., 1992). Some of the events include hyperpermeability of the membrane, denaturation of proteins, changes in cytoskeleton, alteration of intracellular ionic concentration and nuclear degradation. This study quantifies membrane injury by measuring the dynamics of vital dye leakage (Calcein) and Propidium Iodide (PI) uptake in the AT-1 Dunning rat prostate tumor cell line. Membrane injury (using these two dyes) is compared to the clonogenicity of these cells after comparable thermal insult. An Arrhenius damage model has been constructed for each of these assays based on a damage parameter to obtain the activation Energy (E) and frequency factor (A), which may prove useful in obtaining insight into the mechanisms of damage associated with thermal injury.
Interstitial Electrolyte Infusion Creates a Liquid Electrode for Controlled Application of High Power Radiofrequency Energy
Authors: Hoey Michael F. , Paul Saurav
Published: January 2022

Conventional application of radiofrequency (RF) energy for thermotherapeutic ablation of pathological tissue is limited by tissue desiccation, high electrical impedance, and small lesion size. A new method has been developed which allows controllable production of small to large lesions. This technique modifies the electric field within the tissue by interstitially infusing hypertonic saline during the application of RF energy. The present study was conducted to determine the spread of saline in prostate and resultant impedance changes. A 26 gauge needle with 5mm exposed metal tip was inserted into the prostate of 10 canines. Impedance measurements were made between the two recording electrodes placed 12mm apart, with the infusion electrode at the center. Hypertonic saline (14.6% NaCl) with a 35% mixture of a radiocontrast agent (Hypaque) was continuously infused at 2 ml/min through the needle electrode into the tissue for 10 minutes. Fluoroscopic images were taken concomitantly with impedance measurements. The images were analyzed for intensity and spread of the saline concentration field. The developed concentration field was observed to modify the impedance characteristics, thereby indicating the creation of the saline-liquid electrode. This research has facilitated the development of RF hyperthermic treatment for benign prostatic hyperplasia in humans.
An Experimental Model for Investigating Mechanotransduction in Cells: Formation of 3-D Colonies and Differentiation of Cells in the Presence of a Force-Conducting Ligand
Authors: Bhatnagar Rajendra S. , Qian Jing Jing , Wedrychowska Anna , Smith Nancy
Published: January 2022

Microgravity profoundly affects the physiology of cells. The formation of 3-D arrays by cells in microgravity environments has provided novel approaches to tissue engineering. In order fully to understand the relationship between cells and their mechanical environment, it is crucial to replicate the physiological pathways involved in the transduction of mechanical energy to chemical work. Cell behavior is modulated by exogenous and biogenic mechanical forces. One of the major mechanisms that couple mechanical signals in these tissues to an intracellular apparatus for the regulation of cell behavior involves the conduction of mechanical signals via an extensive network of collagenous extracellular matrix. Specialized receptors connect cells to collagen fibers. The junction between the ECM, its receptor integrins, and the cells’ cytoskeleton plays a crucial role in cell differentiation and morphogenesis by serving as the agent for sensing the mechanical environment. We have developed an experimental model system that allows the coupling of cells to their mechanical environment through a force transducing ligand. This system has allowed us to construct 3-D colonies of cells in which cells appear to express highly differentiated function. Such systems are likely to be useful in studies on the behavior of biological systems in the microgravity environment of space.
Numerical Study of Mass Transfer Associated With Multiple Microcarriers in a Rotating-Wall Vessel
Authors: Gao Hongxia , Ayyaswamy Portonovo S. , Hu Howard H. , Zhu Mingyu , Ducheyne Paul
Published: January 2022

The motion of multiple microcarriers in the liquid cell culture medium of a NASA designed Slow Turning Lateral Vessel (STLV) has been numerically investigated. The associated mass transfer has been studied using a ‘sink-model’. A finite element method is employed to directly simulate the motion of a number of solid microcarrier particles. The motion of the combined fluid-particle system is simulated by using a procedure in which the positions of the microcarriers and of the unstructured mesh grids are updated explicitly, while the velocity and pressure of the fluid and the velocity of the microcarriers are determined implicitly. The migration of the particles is affected by the interaction between them and with the walls. The hydrodynamic forces on the microcarrier particles are also evaluated. The mass transfer is treated as a post-processing procedure by solving the binary mass transfer equation. We provide results for the oxygen mass fraction distribution as a function of time taking into account its consumption by the cells grown on the microcarriers.
Experimental and Numerical Investigations of Microcarrier Motions in Simulated Microgravity
Authors: Meaney David F. , Johnston Eric D. , Litt Mitchell , Pollack Solomon R.
Published: January 2022

We are interested in studying the cell/microcarrier motions within the NASA rotating bioreactor system, with the eventual goal of using this description to understand the attachment of cells on microcarriers and the assembly of these cell/bead constructs into three dimensional tissue. In this study, we used both experimental imaging tools and numerical analysis to study the motions of typical microcarrier beads used in the High Aspect Ratio Vessel (HARV). Experimental studies demonstrate that physical properties of the microcarrier beads affect directly the primary radial motion of these particles, and also show that these beads interact and aggregate with each other over time. Numerical analyses using the appropriate governing equations and a Runga-Kutta solution method show that computed results agree with experimental observations on both primary and secondary particle trajectories. From the numerical analysis, we develop an analytical description of a typical particle trajectory in the laboratory frame and develop an experimental apparatus to track a single particle temporally in the bioreactor. Results from this study provide insight into the motion and aggregation of particles in the rotary culture bioreactors over time, and can lead to a better control of the bioreactor mechanical environment.
Dynamic Optimization of Start-up and Load-Increasing Processes in Power Plants: Methodology and Application
Authors: Bausa Jens , Tsatsaronis George
Published: January 2022

The fast start-up and load-increasing of power plants is a complex task involving several restrictions that have to be fulfilled simultaneously. An important restriction is the maximum allowed thermal stress of the steam generator pipes and the steam turbines caused by temperature gradients.

In this paper the start-up process is treated as a dynamic optimization problem. Any appropriate objective function can be used in this optimization problem. Examples include the minimization of fuel consumption, or the minimization of the time required to reach the desired load. The maximum allowable temperature and pressure gradients in major plant components appear as additional constraints.

A general methodology for solving these problems is presented: The dynamic process model, consisting of first-order ordinary differential equations (ODEs) and algebraic equations, is discretized over the time horizon using well established methods for the solution of ODEs. Thus, the continuous dynamic optimization problem is transformed into a large-scale non-linear parameter optimization problem with up to 20,000 optimization parameters and constraints. Such parameter optimization problems can be solved with appropriate sequential quadratic programming (SQP) methods that have become available lately.

The application of this method is demonstrated by optimizing the process of rapid load-increase in a single-pressure combined-cycle power plant on the base of a simplified model.
Using Component Effectiveness for a More Comprehensive Analysis of High Temperature Fuel Cells
Authors: Haynes Comas L. , Wepfer William J.
Published: January 2022

High temperature fuel cells will enable power systems to have unprecedented levels of operation. Second Law studies are an effective means of analyzing these promising cells. The “non Carnot-limited” label applied to fuel cells must first be understood in its proper perspective, however. Electric and voltage efficiencies are often used for fuel cell evaluation, but a component effectiveness was developed for better insight into cell performance.

The performance indices were compared via a simulation of Westinghouse Electric’s tubular solid oxide fuel cells. Component effectiveness profiles showed a realistic, decreasing approach to reversible operation. In contrast, electric and voltage efficiencies showed a uniform increase in performance. These latter efficiencies only account for electrochemical losses. High temperature fuel cell operation involves significant heat transfer, however, and thus thermal irreversibilities. Component effectiveness accounts for all forms of entropy generation, and it will be used in subsequent design analyses of high temperature fuel cells.
Modeling of a Heat Pump With Evaporator Air Dehumidification for Reduced Frost Formation
Authors: Martínez-Frías Joel , Aceves Salvador M.
Published: January 2022

This paper presents an analysis of a heat pump that uses a solid desiccant dehumidifier to reduce the humidity of the ambient air that flows into the evaporator, with the purpose of decreasing frost formation on the evaporator. The heat pump is analyzed by adding a dehumidifier model to a previously developed heat pump model that includes frost formation. The dehumidifier reduces the amount of energy required for evaporator defrosting, but introduces the need for energy for regenerating the desiccant. The purpose of the analysis is to search for operating conditions and optimum dehumidifier designs for which the use of the dehumidifier results in energy savings.

The results show that the use of a dehumidifier may result in net energy savings if the energetic cost of defrosting the evaporator is high. Other benefits of dehumidification include an increase of the time intervals between defrost cycles, a better stability in the conditions in the controlled space, and the potential for increased reliability and reduced maintenance of the heat pump.
Comprehensive Modeling of Reed Valve Impact Velocity in Scroll Compressors
Authors: Lifson Alexander , Bush James W.
Published: January 2022

Scroll compressors are becoming popular in refrigeration applications where high pressure ratio operation is required. To achieve competitive efficiency and minimize discharge temperature, a discharge valve is often mandatory in these applications. However, the discharge valve brings with it its own reliability risk. Operation of the valve in scroll compressors in many ways is similar to rotary or reciprocating compressors, but there are specific features of the scroll compression process requiring special consideration in scroll wrap design.

This paper addresses a risk with scroll compressor discharge valve reeds in the form of sudden backflow at the time of porting which occurs at the end of discharge process. The mechanisms responsible for valve impact are evaluated and ways to minimize and to even virtually eliminate them are presented. Computer simulation results quantify the effect of design and application variables on valve impact. Two levels of analysis are presented, first a more rigorous but computationally involved approach, then a simplified method more applicable for a quick estimate or evaluation of trends. A comparison between the two analyses is presented. Effects of clearance volume, discharge pressure, suction pressure, and scroll wrap geometry on valve impact are considered. It is shown that discharge pressure and volumetric flow rate at porting have the greatest effect on the valve impact velocity against the scat. Design tradeoffs for minimizing valve impact also presented.
Refinery Waste Heat Powered Absorption Refrigeration: Cycle Specification and Design
Authors: Erickson Donald C. , Anand G. , Papar Riyaz A. , Tang Jingsong
Published: January 2022

In an effort to increase the energy efficiency and reduce environmental emissions from refineries, the Commerce City Refinery of Ultramar Diamond Shamrock, the Office of Industrial Technologies at the U.S. Department of Energy and a team of contractors have collaborated to implement a novel project. A waste heat fired Absorption Refrigeration Unit (ARU) was designed, fabricated, installed and is currently completing a one year field test at the oil refinery in Denver, Colorado. Data is being gathered to document the performance and compare to the predictions.

The ARU is designed to provide refrigeration for two process streams at the refinery while being powered by waste heat from a third process stream. The refrigeration benefits the refinery by recovering salable product and increasing the capacity of the process units with no additional electrical demand. The constraints to be satisfied by the ARU design were very stringent: low temperature waste heat; very low refrigeration temperature; limited plot space; geographically separated streams; and very limited cooling water. In order to satisfy all these constraints and to make the economics more favorable, several new concepts were developed and incorporated in the ARU. This paper describes the various cycles considered and the qualitative and quantitative considerations involved in screening the cycles. The parametric analysis and optimization of the most promising cycle is presented.
Applications for Advanced Energy Conversion Applications
Authors: Lamp Thomas R.
Published: January 2022

Forest fires that endangered remote US Air Force sites equipped with radioisotope thermoelectric generators (RTGs) prompted the assessment of power generating systems that could be substituted for RTGs in small scale (10–120 watt) applications. Other non-RTG sites were also studied during the assessment. The power system assessment was conducted by the Air Force Research Laboratory (AFRL). The evaluations included engine-driven generators, solar, wind generators, propane thermoelectric generators (TEGs), batteries, fuel cells, and power systems based on advanced conversion technologies; such as, thermionics, free piston Stirling Engines (FPSE), alkali metal thermoelectric conversion (AMTEC), and thermophotovoltaics (TPV). The assessment team concluded that continued use of the RTGs is clearly the safest, most reliable, and most economical approach to supplying electrical power for remote, difficult to access locations. If political considerations force the replacement of the RTGs, the likely replacement is a hybrid system consisting of solar-PV with a propane-TEG for off-solar times. The transport of combustible fuels in Arctic environments is extremely expensive. It is this high logistics cost that signaled the need to consider the option of more efficient and cost effective power sources for the remote, Arctic applications. This paper summarizes AFRL contractual efforts involving two of the more attractive advanced conversion technologies: AMTEC and TPV. The information cited herein is the result of USAF sponsored programs and cooperative efforts with NASA Lewis Research Center (NASA-LeRC). This paper is not intended to reflect the progress and efforts of the energy conversion community as a whole.
Comparison of FEA and LPT Based Failure Analysis of P75 Graphite/934 Epoxy Composites
Authors: Rigas K. , Greif R. , Saigal A.
Published: January 2022

A comparison between a micro-mechanical finite element model (FEM) and the macro-mechanical laminated plate theory (LPT) has been undertaken to investigate the failure of an 8-ply [0/0/90/90]s P75 Graphite/934 Epoxy composite subjected to mechanical and thermal loads. This study deals with the initiation of failure, ultimate failure, and resulting stresses at each failure, as well as the effect of thermal residual stresses on the failure of the composite material. Thermal residual stresses develop as a result of the difference in the coefficients of thermal expansion of the fiber and the matrix, and the operating (75°F) and stress-free or cure temperature (350°F). Relationships between the boundary condition of the FEM and LPT are also explored. The ANSYS finite element program has been used in this research. The initiation of failure is based on the ultimate radial stress criterion developed by Bowles and Griffin. For LPT analysis, the first-ply failure and consequent failures are derived using the Tsai-Wu failure theory. The analyses indicate intermediate degradation of the laminate as the applied stress/strain is increased. This information is used to predict the loss in overall stiffness as a function of loading.
Residual Stress Measurement in Spot Welds and the Effect of Fatigue Loading Using High Sensitivity Moire Interferometry
Authors: Khanna Sanjeev K. , He Canlong , Agrawal Hari N.
Published: January 2022

Residual stress distribution has been determined in spot welds, which are generally used to join mild steel sheets. Various spot weld configurations were investigated using the full-field, experimental, optical technique of high sensitivity moiré interferometry. These stresses were found to be in the range 250–300 MPa (tensile) in the center and decreased to 40–100 MPa (tensile) at the edge of the weld nugget. Low cycle fatigue loading of the spot weld caused the residual stress to drop in the weld center by about 30% and increase at the edges by as much as 100%.
Identification of Free-Free Modes From Constrained Vibration Data for Flexible Multibody Models
Authors: Yi Tong Y.
Published: January 2022

This paper presents a method for identifying the free-free modes of an unconstrained structure by utilizing the available vibration data of the same constrained structure. In modal formulations for flexible body dynamics, modal data are primary known quantities that must be obtained either experimentally or analytically. For vibration measurements, the flexible body may be constrained differently than its actual conditions in the multibody system. To apply the experimentally obtained modal data to the flexible dynamic model, the available vibration data must be properly identified.

For a flexible body model in multibody systems, we may need a set of free-free modal data or constrained modal data depending upon the dynamic formulations. The identification of constrained modes from the free-free vibration data is straight forward, but the reverse process to determine the free-free modes from the constrained vibration data is difficult and expensive. The aim of this study is to extract, based on experimentally obtained vibration data, the necessary free-free frequencies and the associated modes for flexible bodies in multibody systems. In this paper, two different forms of constrained vibration data are considered. The first form is for structures supported by springs, and the second form is for structures supported by kinematic joints. The available vibration data may be either a complete set or an incomplete set.
Implementation and Application of Automatic Parametric Design of 2D Nonlinear FEA
Authors: Verderber Rudy R.
Published: January 2022

This paper presents implementation and application of automatic parametric design of 2D nonlinear FEA. Parametric design involves iterating on a FEA solver and preprocessor. Global quantities and linked database files provide the basis for analyzing the analyses. Parametric analysis of two disks contacting shows an expected relationship between interference, land height, and stress. Lastly, the assembly of press fit tubes shows the relationship between interference, contact area, and normal force.
Probabilistic Estimation of the Effect of Dimensional Tolerance for Turbine/Compressor Blade Attachment
Authors: Singh Murari P.
Published: January 2022

Root attachments of rotating blades of a turbine or a compressor often have multiple lobes. These lobes fit into a matching groove in a rotating disk. Dimension of these lobes, in general, will not be identical for each blade. However, these dimensions will be within manufacturing tolerance. The resulting dimensional fit becomes random in statistical sense within the specified tolerance. Thus precise dimension is unknown even if it is assured to be within the specified tolerance band.

This creates the possibility that for a given blade all the lobes might not be in contact i.e. there might be a gap in the joint. This also means that lobes will carry unequal load. The gap condition may be different for each blade. As the rotational speed increases, each gap will start closing and ideally will eventually close.

Description of a method to assess the influence of manufacturing tolerances on the reliability of such a joint for disk-blade assembly is presented. The resulting estimated stress as a function of rotating speed and tolerance stacking is also presented. The stress result is combined with probabilistic analysis that yields the probability for stress to be within a predetermined amount thus providing a measure of success.
Mechanical Properties of Cellular Polyurethanes Filled With Polyurethane Disperse Filler
Authors: Swisher Karena L. , Shutov Fyodor A.
Published: January 2022

Flexible polyurethane (PUR) foams have been filled with fine PUR powder produced from PUR foam automotive scrap. For pulverization the proprietary non-extrusion and non-cryogenic Pressure Shear Pulverization (PSP) process was used. The PSP process is based on the combined action of high shear stress and compression load at ambient temperatures. Mechanical behavior of filled PUR foams have been studied at various contents (up to 30 percent per polyol component) and size fractions (from 75 to 500 microns) of the PSP powder. Demonstrations showed improvement of compressive and cushioning properties are very critical in terms of size and content of the filler. The mechanism of the reinforcement effect is proposed based on capsulation of the PUR filler into the cell struts and walls of the flexible cellular PUR matrix.
Foam Extrusion Technology of Microcellular Plastics
Authors: Shimbo Minoru , Nishida Kouji , Nishikawa Shigeo , Sueda Takanori , Eriguti Mitio
Published: January 2022

Processing technology was studied basically for microcellular plastics in this paper. The continuous processing system was constructed using extruder and was verified propriety of this system. In order to investigate cell morphology and cell structure, microcellular polystyrene samples were produced under various conditions by the above processing system. Concretely, foaming die which can be varied pressure in die was prepared. The effect of pressure drop in die on cell morphology of microcellular plastics was examined using this changeable die. In addition, the effect of blowing agent contents, temperature in die and besides additioner on that of microcellular plastics were also investigated.