bluuebunny/crossref_metadata_2025 huggingface dataset:
Three Dimensional Effects in Composite Plates
Authors: Prabhu Santosh , Lambros John
Published: December 2021

In this study, a finite element investigation of the three dimensional nature of stress fields in the near tip region of a cracked orthotropic plate was conducted. Two and three dimensional finite element analyses were used to investigate the relative extent of regions of three dimensional to two dimensional (plane stress or plane strain) deformation in the cracked plate. The material properties used in the simulations corresponded to those of a graphite/epoxy composite. A three point bend loading geometry, with the fiber directions either parallel or perpendicular to the crack, was simulated. In analogy to isotropic materials, it was observed that a plane stress K-dominant region does not arise arbitrarily close to the crack tip because of the existence of a three dimensional zone. However, it was seen that the shape and the size of this three dimensional zone in the cracked composite plate is substantially different from that of an isotropic plate, and depends intimately on material properties. For a crack parallel to the fiber direction the three dimensional zone extends to 0.46h (h = specimen thickness) ahead of the crack tip but only to 0.27h at 30°. Fibers perpendicular to the crack produce a highly elongated three dimensional zone in the direction of the fibers (up to 0.78h). The zone is also sensitive to the variations in the Poisson’s ratio’s of the orthotropic solid.
Thermal Issues That Arise due to Manufacturing Processes: Evaluation and Measurement Techniques
Authors: Sammakia Bahgat , Sathe Sanjeev
Published: December 2021

This paper describes the methodology used to design and evaluate the strength and reliability of the thermal interface between the chip and heat sink (coverplate) in a TBGA first level package. TBGA is a new technology that is part of the new generation of organic ball grid array chip carriers that are quickly gaining popularity for packaging various microprocessors and memory in portables, desktops, mid-range and high-end mainframes. The package consists of a Kapton or Upilex dielectric layer with one signal plane and one ground plane on either side, as shown in Figure 1. The chip is attached to the package with the signal side ‘down’, that is, facing the card. This leaves the backside of the chip available for coverplate (flat copper heat sink) attach. This direct access to the chip allows for a very effective thermal path from the chip directly to the heat sink, resulting in outstanding thermal performance. It is therefore essential to ensure that the interface between the chip and the heat sink remains intact through the end of the assembly processes for the package, including second-level attach to the board and rework. The interface must also remain intact through the life of the product. It is also necessary to ensure that the interface survives all of the necessary qualification stresses including accelerated thermal cycling, thermal age and deep thermal cycling, to name a few. First the results of a numerical analysis are presented showing the impact of surface de-lamination upon the thermal performance of the package. The model used is a full three-dimensional conjugate model accounting for conduction and radiation effects in the package, as well as the natural convection flow in the surrounding air. The results confirm that delamination of the interface degrades the thermal performance of the package. The model and test results also indicate that, due to the robustness of the package, voids or incomplete coverage of the chip with the thermal adhesive results in a relatively small degradation of the thermal performance of the package, provided total de-lamination of the chip or coverplate does not occur. The methodology used in evaluating different design options, such as adhesive material and heat sink surface treatment, is then described in detail. The primary method used for evaluating interfacial strength is a modified fracture toughness test (MFTT). This is the best measure of resistance to crack propagation. In conjunction with the MFTT, a sonographic technique was used to evaluate the integrity of the interface as a function of stress. Finally, a laser moiré tool is employed to evaluate the strains in the package due to thermal stress. The moiré results are shown for an intact package as well as for a completely de-laminated package, showing the differences in the mechanical response of the package due to delamination.
Towards the Development of a Comprehensive HIC: Predicted Injury – Brain Material Dependency
Authors: Taleb L. , Brown M. J. , Sadeghi M. M.
Published: December 2021

This study proposes a systematic computer simulation technique, using strain as a criterion to assess the severity of brain damage under rotational loading, in particular diffuse axonal injury (DAI). A plane strain model representing realistically a section of the brain in the frontal plane (coronal section) is used in this investigation. The Brain-Skull interface has been modelled using a new representation, allowing the brain to move in a true bio-fidelic way, as well as taking into account the damping role of the Cerebrospinal Fluid (CSF), which acts as a buoy forming a protective cushion around the brain. Based on accident reconstruction data from the literature, the model is validated against the injury observed on the victims. Furthermore, this study proposes a parametric study of brain material properties to assess their effect on the brains’ dynamic response and suggests a new injury criterion for the DAI. It appears that the need to develop a comprehensive head injury criterion (CHIC) which takes into account head injuries caused by non-direct impact or by inertial loading becomes crucial.
Natural Convective Heat Transfer Through a Liquid Between a Heated Horizontal Surface and a Vertical Fin Attached to a Cooled Surface
Authors: Oosthuizen Patrick H.
Published: December 2021

Natural convective heat transfer from a heated horizontal surface directly exposed to a liquid into which vertical fins, attached to a cooled horizontal surface, project vertically downwards has been numerically studied. It has been assumed that the flow is steady, laminar and two-dimensional. The governing equations have been written in terms of dimensionless variables and have been solved using the finite element procedure. The solution has the following parameters: the Rayleigh number, the Prandtl number, the dimensionless half-width i.e. the ratio of the half-distance between the fins to the liquid depth, the dimensionless gap between the bottom of the fin and the lower surface, and the ratio of the thermal conductivity of the fin material to that of the liquid. Because of the application being considered, the Prandtl number has been taken as 5. Solutions have been obtained for Rayleigh numbers of between 10 and 1,000,000 for dimensionless half-widths of between 1 and 0.2 for thermal conductivity ratios of 20, 10 and 4 for a range of dimensionless fin gaps and widths.
Transitions and Bifurcations to Chaos in Combined Radiation and Natural Convection in a Two-Dimensional Participating Medium
Authors: Lan Chao-Ho , Ezekoye Ofodike A. , Howell John R.
Published: December 2021

Combined radiation and natural convection in a square cavity with emitting and absorbing participating medium is studied numerically. The equation of radiation transfer is analyzed by the P-1 approximation. The momentum and energy balance equations are calculated using spectral methods. The presence of a radiation source increases the bulk temperature of the fluid, and has a significant influence on the flow pattern and temperature distribution. In this work, the flow is initially stationary, and is simulated from transition to chaos by varying with Rayleigh numbers of 104, 105, 106, 107, and 108. The conduction-radiation parameter ranges from 100 to 0.1, and optical thickness ranges from 10 to 0.01. Comparisons are made with some existing results. The influence of the conduction-radiation parameter, Rayleigh numbers and optical thickness on flow instabilities and bifurcations is discussed.
The Effect of Streamwise Diffusion on Natural Convection From Isothermal, Vertical Parallel Plates
Authors: Li H. H. , Chung B. T. F.
Published: December 2021

More and more evidence has shown that, at low Rayleigh numbers, the natural convective heat transfer from vertical isothermal channel walls is higher than the widely accepted fully-developed asymptote. This paper attempts to analyze the reason for this discrepancy by numerically solving the full Navier-Stokes equations and comparing with the results obtained from the parabolic type of equations. Calculations are made for the air on a wide range of the Rayleigh number and the channel aspect ratio. It is found that the vertical diffusion contained in elliptic formulation becomes important at a low Rayleigh number and cannot be neglected. The fully-developed asymptote supported by the parabolic solution appears to underpredict the Nusselt number except for special conditions.
Features of Natural Convective Air Flows Inside Vertical Parallel-Plate Channels Subject to Step Heat Fluxes: Insulated Upstream and Heated Downstream
Authors: Campo Antonio , Manca Oronzio , Morrone Biagio
Published: December 2021

This paper addresses the impact of adding insulated extensions at the entrance of a parallel-plate channel in which the plates receive a uniform heat flux and a natural convection air flow is responsible for the cooling. The full elliptic conservation equations are solved numerically in a composite I-type computational domain. It was found that the wall temperatures increase when the channel extensions are appended at the inlet. The pertinent results are reported in terms of maximum wall temperatures, induced mass flow rates, as well as velocity, pressure and temperature profiles of the fluid.
Large Eddy Simulations of Jets in Crossflow: Large Scale Turbulence Effects
Authors: Tyagi Mayank , Acharya Sumanta
Published: December 2021

Large eddy simulations of jets in crossflow are performed to study the effect of energy containing scales present in the freestream on the penetration and spread of the coolant jet. Two specific freestream turbulence conditions are examined, one corresponding to 15% small scale Gaussian turbulence, and the other corresponding to a 15% freestream turbulence that satisfies the Von-Karman spectrum and has its peak energy specified in the small wave number range (large scales). The small-scale freestream turbulence can be viewed to be similar to grid generated turbulence. The large scale freestream turbulence spectrum has energy peak at a small wave number (corresponding to a specified length scale taken to be 4 hole diameters in this study) and has energy in the inertial subrange for large wave numbers. In the present study, the jets are issued through a row of square holes into the main crossflow. The jet to crossflow blowing ratio is 0.5 and the jet Reynolds number is approximately 4,700.

Greater jet penetration and jet-mainstream mixing, in both the vertical and lateral directions, are observed for large-scale turbulence. The energy contained in large scales is mostly preserved although the energy carrying scales themselves undergo subsequent breakdown process due to the effect of the jet. In the nearfield of the jet, the large scales play a major role in enhancing the turbulent stresses, and the near wall transport. In the presence of the large scales, the horseshoe vortex is energized, and there is greater crossflow entrainment into the wake region. These large scale effects lead to significantly greater wall friction.
Influence of Cross-Flow Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil
Authors: Ekkad Srinath V. , Pamula Gautam , Acharya Sumanta
Published: December 2021

Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The crossflow is generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The communicating holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180° U-bend. The holes direct the flow laterally from one passage to another, and depending on the injection angle, cause impingement and generate swirl. The heat transfer enhancement in the second pass is achieved by the combination of impingement and crossflow-induced swirl. Heat transfer distributions are presented on the sidewalls of the passages. Three different hole configurations are tested for three flow channel Reynolds numbers (Re = 10000–50000). The hole configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is applied to measure the detailed heat transfer coefficient distributions inside the passages. Results for the three hole supply cases are compared with the results from the traditional 180° turn passage. Results show that the new feed system, from first pass to second pass using crossflow injection holes, produces significantly higher Nusselt numbers on the second pass walls. The enhancement is as high as 7–8 times greater than obtained in the second pass for a channel with a 180° turn. The additional pressure drop (rise in friction factor) caused by flow through the crossflow holes is compensated by the significant heat transfer enhancement obtained by the new configuration.
Effect of Humidity on PEM Fuel Cell Performance: Part II — Numerical Simulation
Authors: Shimpalee S. , Dutta S. , Lee W. K. , Van Zee J. W.
Published: December 2021

Experiments have shown that the inlet humidity has a significant influence on the performance of a polymer electrolyte membrane (PEM) fuel cell, and theory indicates that the ionic resistivity of the electrolyte membrane is dependent on the activity of water at the membrane surface. Water flux and activities change along the flow field direction. To understand the inner flow and mass transfer processes, a numerical model is developed to predict the flow inside a single fuel cell. Detailed velocity fields, pressure profiles, and current density distributions are obtained and predictions from the full-cell model are compared with the experimental data. Predictions indicate that flow inter-linkage between side-by-side flow channels occurs through the porous diffusion layer. Results also indicate that the diffusion of hydrogen is aided by the flow toward the membrane in the anode side and diffusion of oxygen is opposed by the flow direction present in the cathode side.
An Investigation of Local Degassing Effects on Heat Transfer During Gas-Saturated Boiling From a Small Cylinder
Authors: Hong Y. S. , Ammerman C. N. , You S. M.
Published: December 2021

Boiling heat transfer from a 50-μm-diameter wire immersed in FC-72 is examined. Effects of pressure, subcooling, and dissolved gas concentration on nucleate boiling heat transfer and critical heat flux (CHF) are investigated. The current study is an ongoing effort to systematically quantify dissolved gas content effects on boiling heat transfer. The present investigators previously determined that gas-saturated boiling efficiency is affected by local degassing of the working fluid near the heater surface. This local degassing effect is further investigated in the present study using helium, air, and carbon dioxide as dissolved gases. In addition, the limits of gas-saturated boiling enhancement are determined by varying system pressure.
Stability of Heat Pipes in Vapor-Dominated Systems
Authors: Amili Pouya , Yortsos Yanis C.
Published: December 2021

We study the linear stability of a two-phase heat pipe zone (vapor-liquid counterflow) in a porous medium, overlying a superheated vapor zone. The competing effects of gravity, condensation and heat transfer on the stability of a planar base state are analyzed in the linear stability limit. The rate of growth of unstable disturbances is expressed in terms of the wave number of the disturbance, and dimensionless numbers, such as the Rayleigh number, a dimensionless heat flux and other parameters. A critical Rayleigh number is identified and shown to be different than in natural convection under single phase conditions. The results find applications to geothermal systems, to enhanced oil recovery using steam injection, as well as to the conditions of the proposed Yucca Mountain nuclear waste repository. This study complements recent work of the stability of boiling by Ramesh and Torrance (1993).
Prediction of Frost Height on Heat Exchanger Fins
Authors: Chen Hong , Thomas Leena , Besant Robert W.
Published: December 2021

Frost growth on heat exchanger fins under freezer operating conditions reduces the heat rate and increases the airflow pressure drop across heat exchangers.

In this paper, a numerical model is presented to predict the height of frost growing on the heat exchanger fins under freezer operating conditions where the frost is treated as a porous media and includes coupling with heat conduction in the fins. The simulation results are compared to the experimental data for frost height measured using a specially designed laser scanning system. The frost height data on two-dimensional fins agree well with the simulation results and are generally within the experimental uncertainty.
NMR Technique for Multiphase Fluid Study Involving Melting Phenomena
Authors: Ni Q. , King J. D. , Tao Y.-X.
Published: December 2021

Nuclear magnetic resonance (NMR) sensors are used to determine the time variation of solid mass for a packed ice bed in an experiment of convective melting under non-thermal equilibrium conditions. The paper describes the basic experimental technique for NAFTM apparatus and feasibility for determining the solid volume fraction and ultimately the melting rate. The NMR technique provides an effective, non-destructive method for multiphase fluid study where phase change is one of the important physical phenomena. The results show a good agreement of data obtained by the NMR method with those from image-analysis method.
Micro Thermal Engines: Is There Any Room at the Bottom?
Authors: Peterson Richard B.
Published: December 2021

Richard P. Feynman introduced the field of microscale and nanoscale engineering in 1959 by giving a talk on how to make things very small. Feynman’s premise was that no fundamental physical laws limit the size of a machine down to the microscopic level. Is this true for all types of machines? Are micro thermal devices fundamentally different than mechanically-based machines with respect to their scaling laws? This paper demonstrates that micro thermal engines do indeed suffer serious performance degradation as their characteristic size is reduced. A micro thermal engine, and more generally, any thermally-based micro device, depends on establishing a temperature difference between two regions within a small structure. In this paper, the performance of a micro thermal engine is explored as a function of the characteristic length parameter, L. In the development, the important features of thermal engines are discussed in the context of developing simple scaling laws predicting the dependency of the operating efficiency on L. After this is accomplished, a general model is derived for a heat engine operating between two temperature reservoirs and having both intrinsic and extrinsic sources of irreversibility, i.e. thermal conductances and heat leakage paths for the heat flow. With this model and typical numerical values for the conductances, micro heat engine performance is predicted as the characteristic size is reduced. This paper demonstrates that under at least one particular formulation of the problem, there may indeed be some room at the bottom. However, heat transfer does play a critical role in determining micro engine performance and depending on how the heat transfer through the engine is modeled, vanishingly small efficiencies can result as the characteristic engine size goes to zero.
Temperature Dependent Thermal Conductivity of Symmetrically Strained Si/Ge Superlattices
Authors: Borca-Tasciuc Theodorian , Liu Jianlin , Zeng Taofang , Liu Weili , Song David W. , Moore Caroline D. , Chen Gang , Wang Kang L. , Goorsky Mark S. , Radetic Tamara , Gronsky Ronald
Published: December 2021

Experimental evidence for a significant thermal conductivity reduction has been reported in recent years for GaAs/AlAs, Si/Ge, and Bi2Te3/Sb2Te3 superlattices. Previously reported experimental studies on Si/Ge superlattices are based on samples grown by metal oxide chemical vapor deposition (MOCVD) on GaAs substrates with Ge buffers. In this work, we present experimental results on the temperature dependent thermal conductivity of symmetrically strained Si/Ge superlattices grown by molecular beam epitaxy (MBE) as a function of the superlattice period and the growth temperature. Thermal conductivity measurements are performed using a differential 3ω method. In this technique, the temperature drop across the superlattice film is experimentally determined and used to estimate the thermal conductivity of the film. Transmission electron microscopy (TEM) is employed to study the quality of the superlattice and the influence of the growth temperature on the superlattice structure. For all the superlattices studied, the measured thermal conductivity values are lower than that of the Si0.5Ge0.5 alloy. Furthermore, the measured thermal conductivity of a 40Å period Si/Ge superlattice with high dislocation density is comparable to the calculated minimum thermal conductivity of the constituent bulk materials.
Theoretical and Experimental Study of Heating/Drying of Paper Sheet With Gas Heated Infrared Emitter
Authors: Husain A. Nadir , Seyed-Yagoobi Jamal , Wirtz Jefferson W.
Published: December 2021

Infrared (IR) radiation is used for heating/drying of moist paper owing to its penetration characteristic inside porous media, and a high absorptivity of water in the infrared wavelength range. A series of experiments has been conducted along with the development of a theoretical model to study IR drying characteristics. Paper samples are instrumented with thermocouples in the thickness direction to obtain transient temperature profiles along with moisture data. The experimental results confirm IR energy penetration into the paper sheet. The numerical model predicts the experimental transient temperature profile for thinner samples fairly well but tends to under predict the temperatures with progressively thicker samples. Theoretical depth of IR penetration, as a function of sample initial moisture content, has been calculated and was found to decrease with increasing moisture content.
Direct Numerical Simulation of Mixing of a Passive in Decaying Turbulence
Authors: Deb P. , Majumdar Pradip
Published: December 2021

Research on turbulent mixing processes is of great interest to those working on turbulent-reactive flows. In this paper, a detailed study has been performed for the evolution of scalar fields of different initial integral scales in decaying, homogeneous and isotropic turbulence using DNS technique. Passive scalar mixing in a cubical decaying, homogeneous, isotropic turbulence field is considered. The three-dimensional incompressible Navier-Stokes equations together with scalar equation are solved using Fractional Step Method. The convective and diffusive terms in governing equations are discretised by Compact Finite Difference Scheme. The 32 × 32 × 32 uniform staggered grids are used. The present simulation is performed at Taylor Reynolds number of 28.83. In this paper, the evolution of scalar RMS and scalar dissipation rate for different integral length scales has been presented. The initial velocity vector and Probability Density Function (PDF) of scalar at different eddy turn over time have also been presented.
Design Analysis of an Electroless Plating Bath Using CFD Technique
Authors: Lee Tien-Yu Tom , Lin Jong-Kai
Published: December 2021

The fluid field of the electroless plating bath was analyzed using a Computational Fluid Dynamics Tool. By solving continuity and momentum equations, the pressure and velocity distributions in the plating bath were predicted. The analysis was performed under various design options: flow direction, flowrate, diffuser plate design, and wafer cassette design. It was found that with the reverse flow option; it seems to deliver uniform flow as compared to the forward flow option. Flow pattern was similar among different flowrates and diffuser designs. Low velocity flow always existed at the top portion of the wafer and near the last row of the wafer cassette. With the hypothesis that slower flowrate results in higher plating rate; a qualitative agreement has been observed between the predicted flow pattern and the plated nickel height uniformity.
Temperature/Heat Flux Errors Caused by High Temperature Resistive Shunting Along Mineral-Insulated, Metal-Sheathed Thermocouples
Authors: Gill Walter , Nakos James T.
Published: December 2021

Commercially manufactured, mineral-insulated, metal-sheathed (MIMS) thermocouples (TCs) have been used at Sandia National Laboratories (Sandia) and other experimental laboratories for many years to measure temperatures in fires and high-temperature (e.g., 1200°C) radiant-heat environments. These TCs are rugged and relatively inexpensive, which make them ideal for large-scale outdoor testing where factors such as weathering and rough handling are important.

A particularly insidious source of TC error is thermal shunting of the TC assembly. This error is caused by a sharp drop in the electrical resistivity of the mineral insulation at elevated temperatures. When a TC assembly is subjected to high temperature along its length, the lower resistivity of the mineral insulation can cause shorting or shunting to occur.

This paper describes several cases demonstrating the seriousness of the shunting problem at temperatures previously thought to be immune. Some preliminary experiments designed to clarify the thermal shunting problem are presented. A model developed under previous work but modified specifically for Type K TCs is discussed. Comparisons of measured and predicted temperature error data in additional thermal shunting experiments provide some degree of confidence in the model’s predictive capability. Predictions for several common field test configurations used in Sandia experiments are shown in the hopes of sensitizing other researchers in the field to this problem.
Design and Uncertainty Analysis of a Second-Generation Convective Heat Flux Calibration Facility
Authors: Holmberg David G. , Womeldorf Carole A. , Grosshandler William L.
Published: December 2021

The National Institute of Standards and Technology has developed a convective heat flux facility to allow calibration of heat flux sensors. The facility consists of a small wind tunnel that produces a two-dimensional laminar boundary layer across a heated isothermal copper plate. Sensors are mounted flush in the copper plate alongside a reference to measure the heat leaving the plate. Convective calibrations up to 5 kW/m2 are possible. Sensor output is compared with the reference value, and contrasted with a standard radiation calibration. Recognizing that many sensors are used in mixed radiation and convection environments, this facility provides a unique opportunity to assess a sensor’s convective response. This report describes a second-generation heated plate and provides an analysis of the system uncertainty. Redundant references, improved sensor heating and mounting, improved reference isolation, and a minimized radiation component has reduced the combined relative expanded uncertainty of the reference to ±2.5 %. The benefits of an embedded temperature sensor in the heat flux sensor are described. The facility is available for comparative calibrations and for heat transfer studies by individual researchers.
Survey of Research Activities for Passive Safety System of AC600
Authors: Chen Bingde , Yang Zhumao , Ji Fuyun
Published: December 2021

The use of passive safety system in AC600, the Chinese advanced 600 MWe PWR proposed by NPIC, together with other improvements, such as simplification and advanced I&C etc., makes the plant more safe, economic and reliable. The core damage frequency (CDF) decreases from less than 10−4 of conventional PWR to less than 10−5 to 10−6 and the plant available factor increases to ∼90%.

The passive safety system of AC600 consists of three complete independent systems. They are passive containment cooling system (passive CC system), passive core residual heat removal system (passive CRHR system) and passive safety injection system (CMT). To verify and demonstrate the AC600’s innovative passive safety features and to obtain an experimental database for system design modification and optimizing, and for computer code development and assessment, the experimental studies on these systems were finished in NPIC during the eighth national Five Year period under the national support.

In this paper, the experimental research activities on passive containment cooling system, passive CRHR system and CMT injection system, including test rigs and main results are summarized. These experiments proved the design of all these passive systems are feasible and reliable and can meet basically the required safety functions. Some undesired thermal hydraulic phenomena, for example, “water hammer”, which may have bad impacts on its safety functions and to which high attention should be given, was found and identified in these studies. All data obtained have already been used in the design improvement and next R&D program planning.
An Experimental Correlation of Quenching Temperature Under Top-Down Reflooding in a Vertical Tube
Authors: Huang Yanping , Lang Xuemei , Chen Bingde
Published: December 2021

A quenching experiment under top-down reflooding in a vertical tube was performed by adopting the transient hot block quenching test technique. The temperature history on the inner wall of test tube was calculated by using a quasi-steady-state two-dimension numerical technique, and the intersection of double tangent lines was used to determine the location and the time of the quench front. Based on some theoretical models of quenching temperature, at the same time, the effect of flow parameters in the tube during quenching was taken into account, a semi-empirical correlation for quenching temperature under the low pressure and low mass flow rate is presented in this paper. It is as follows:Tq−TsTo−Ts=11.8362(Ts−Tf,inTo−Ts)−0.0714[(cρk)w]0.2938×G0.0251×(Ts−Tf,in)−0.3145 The parameter range of this correlation is as follows: system pressure: 0.31∼0.88MPa: mass flux: 17.7∼902.kg/m2s; inlet subcooling: 3∼77°C; initial hot-wall temperature: 450∼600 °C.
A Method for Estimating Acoustic Implosion Efficiencies for Collapsing Cavities in Nuclear Reactor Systems
Authors: Kullberg C. M.
Published: December 2021

For the last several decades, condensation induced water hammer events have been a concern i n the nuclear industry. With the arrival of passive reactor designs, concerns have arisen about the natural inception of vapor cavity formation in these systems. Several aspects of subcooled bubble cavity implosions are examined. In particular, this paper will focus on spherical cavity implosion transients. Numerical scoping calculations were performed with the compressible version of the Rayleigh-Plesset equation. The calculations revolved around predicting two key parameters, the peak pressure and the net acoustic energy release. Both of these parameters are relevant in quantifying the damage potential of a spherical water hammer event.
Approximate Temperature Profiles and Companion Heat Transfer Rates of Uniform Annular Fins Using Finite-Differences Instead of Bessel Functions
Authors: Campo Antonio
Published: December 2021

The temperature variation along annular fins of uniform thickness and constant thermal conductivity is governed by a differential equation of second order with variable coefficients which is called the modified Bessel equation of zero order. This educational paper addresses a simplistic finite-difference procedure for solving this kind of Bessel equation employing a reduced system of algebraic equations. Approximate temperature distributions and companion heat transfer rates have been computed with the elimination of unknowns by hand and also with the Gauss elimination method using the symbolic algebra software Maple V (Char et al., 1991) on a personal computer. Instructors and students of heat transfer courses may benefit from this alternative computational procedure that seeks to avoid the use and operations with Bessel functions and still produce numerical results of good quality. Rudimentary knowledge of numerical techniques is the only mathematical background that students need to possess in order to implement the computational scheme explained here.
Rheological Measurements on Molten Metals
Authors: Bakhtiyarov Sayavur I. , Overfelt Ruel A.
Published: December 2021

The rotational measurement technique has been developed to measure the dynamic viscosity of liquid metals. A special procedure is accomplished to eliminate both end and eccentricity effects. The technique was calibrated and tested with liquids of known rheology. The apparent viscosity of low melting alloy composite is measured by means of the technique.
Plastic Flow in Confined Porous Media of Complex Contours
Authors: Letelier Mario F. , Rosas César E.
Published: December 2021

A theoretical study of the fully developed fluid flow through a confined porous medium is presented. The fluid is described by the Bingham plastic model for small values of the yield number. The analysis allows for many admissible shapes of the wall contour. The velocity field is computed for several combination of relevant parameters, i.e., the yield number, Darcy resistance coefficient and the boundary perturbation parameter. The wall effect is especially highlighted and the characteristics of the central plug region as well. Plots of isovel curves and velocity profiles are included for a variety of flow and geometry parameters.
Elasto-Plastic Finite Element Analysis of Metal-Matrix Composite Plates With Hole Under Plane Loading
Authors: Okumuş Fuat , Turgut Aydın , Sancaktar Erol
Published: December 2021

The elasto-plastic stress analysis of composite plates with hole has been carried out by the finite element method.

For this purpose, an isoparametric rectangular element with nine nodes has been chosen and the lagrange polynomial has been used as interpolation function. Steel-aluminum composite has been manufactured by using mould under the action of 30 MPa pressure and heating up to 600 °C. Mechanical properties and yield strength of the composite material have been obtained experimentally by using a strain gauge in the tensile testing machine. The composite plates in various dimensions have been. obtained by changing the diameter of the hole. The various tension loads which are increased step by step from beginning of the yield have been applied to these plates. The expansions of plastic regions have been illustrated for various cases. According to orientation angle and applied loads, elastic, plastic and residual stresses have been obtained.
Stress Analysis of Bolted Joints of Flat Cover With Tap Bolts in a Pressure Vessel
Authors: Sawa Toshiyuki , Karasawa Akihiro , Shimizu Akihiro
Published: December 2021

Bolted joints with gaskets have been designed empirically, and the sealing performance is not made clear by theoretical analyses because the contact stress distribution between the gasket and the flanges are not clarified when an internal pressure is applied to the joint. The present paper, discusses the distribution of contact stresses in the bolted joints fastened with tap bolts, when a clamped part with a gasket is the cover of a pressure vessel and is a circular flange. The distribution of contact stresses is analyzed as a three-body contact problem, using the three-dimensional theory of elasticity. Moreover, the contact stress is measured by means of ultrasonic waves. In addition, the load factor (the ratio of an increment of the axial bolt force to an external load) and the maximum stress caused in bolts are analyzed taking into account the bending moment. For verification, experiments are carried out, and the analytical results are found in fairly good agreement with the experimental ones. It was found that the sealing performance was improved when Young’s modulus of the gaskets was decreased and the gasket thickness was increased.
Examining Multiaxial Impact Behavior of Polymer Materials
Authors: Lawrence G. E. , Saigal A. , Zimmerman M. A. , Greif R. , Duan Y.
Published: December 2021

The analysis of multiaxial impact of polymer disks is considered. The calculation of impact displacements and stresses is provided. Finite element simulation results are compared to experimental data. The results from simulations of various impact velocity and mass are given for a constant disk thickness. Results from simulations of various disk thickness for constant impact mass and velocity are shown as well. The plasticity failure model used in FEA simulation of impact is quantified for the application with the tested polymers. It is shown that strain rate material dependence is an important factor in accurately modeling impact response of polymers.
Structure Analysis of a Turbulent Jet by Means of Multiresolution Fluctuating Velocity Decomposition
Authors: Li Hui , Takei Masahiro , Ochi Mitsuaki , Saito Yoshifuru , Horii Kiyoshi
Published: December 2021

To evaluate coherent structures in the dimension of time and scale, a new procedure based on the multiresolution analysis and multiresolution auto-correlation analysis is developed in this paper. By analyzing u- and v-components of fluctuating velocity, the coherent structure and its scales can be identified when larger amplitude fluctuation and stronger autocorrelation are appeared at same wavelet level. For a turbulent jet at position of x/d = 6, the larger coherent structures with frequency 39Hz can be deduced around times 0.29, 0.53, 0.6 and 0.67s. This also represent the passing of eddies through the shear layer and concentration of the energy of the flow at these instants.
Numerical Investigation of Flow Field at the Rotor-Stator Gap Entrance
Authors: Tong Wei
Published: December 2021

The turbulent flow field at the rotor-stator gap entrance of a generator was investigated numerically. Predictions of the fluid dynamics characteristics for the present problem were made by adjusting boundary pressure conditions to match the prescribed flowrate allocation. The velocity field and pressure distribution at the rotor-stator gap entrance were presented. The mean values of pressure and velocity, obtained by integrating the local values across the flow cross-sectional lines, were applied to calculate pressure loss coefficient ß at the gap entrance.

Results show that because of the complex geometry at the air gap entrance and flow splits through the stator cooling ducts, the display of ß is rather complicated. Rotating body windage losses for the rotor and retaining rings were determined from calculated friction factors on these surfaces.
Experimental Study of Aerodynamics Around Co-Rotating Blades in a Lawn Mower Deck
Authors: Chon W. , Tetzlaff P. , Amano R. S. , Triscari A. , Torresin J. , Johnson K.
Published: December 2021

A combination of computational and experimental studies was performed on a 1.1m wide side discharge double-spindle lawn mower deck. For the experimental portion of the study air velocities were measured by using a forward-scatter LDV system. Velocity measurements were collected at several different tangential and axial sections inside the deck. In order to simulate the flow in real operating conditions, a grass feeding system was constructed in the laboratory. LDV test data were also validated by the conducting high-speed video taping of the experiments in several different running conditions.

In the computational fluid dynamics (CFD) work, 2-D blade shapes at several arbitrary radial sections have been selected for flow computations around the blade model. The 2-D computational results were compared with the experimental results obtained in this study.
Prediction and Test Verification of Liquid Hammer in De-Energized Hydraulic Reaction Turbines
Authors: Kikuchi Hirohiko , Kimmel Hans E. , Smith Donald R.
Published: December 2021

The transient behavior of radial inflow turbine generators for the case of a power failure during operation is studied for a performance model of a variable speed hydraulic reaction turbine and verified in full scale tests. Liquid hammer effects due to the change of rotational speed are studied and measured.

The performance model transforms into a nonlinear system of differential equations, which can be explicitly solved by quadrature. The analytical solution predicts the change of the turbine speed during the time after a power failure had occurred, and the predictions of the model are compared with measured test results on a cryogenic turbine generator with 1.0 MW rated power output. The predicted and the measured test results deviate with a maximum error of 1.5%.
Numerical Simulation of Two Phase Flows in a Bath With Top-Blowing Lance Injection
Authors: Xia J. L. , Ahokainen T. , Holappa L.
Published: December 2021

Numerical simulation of two phase flows in a bath agitated by top blowing lance injection is carried out using the CFX code. An Eulerian-Eulerian two phase flow model is used. The drag, lift and turbulent dispersion forces are taken into account for the interface interactions. Calculations show that there exist different flow patterns with changing the operational conditions (Q, dn, and hn/H). The gas-liquid plume spreads radially, gradually in most of the plume region and extensively near the free surface. For the cases considered, bubbles in the central plume (r = 0.006 m) accelerate up to their terminal rising velocity, then move at this rising velocity, and thereafter decelerate when they approach the surface. A similar behaviour is demonstrated for the liquid rising velocity. Numerical results are compared with available experimental data, and a good agreement is achieved. Predictions provide insight into the flow behaviour and useful information for engineering design.
Using CFD to Improve Stall Margin
Authors: Hardin James R. , Boal Charles F.
Published: December 2021

Centrifugal compressors for multi-stage industrial applications must have both high efficiency and stable operation over a wide flow range. CFD analyses were used to evaluate the stall margins of candidate impeller designs compared to a baseline semi-inducer design. With this guidance, a new full-inducer impeller was designed with predicted wider operating range and slightly higher peak efficiency. Prototype tests confirmed these predictions. This paper presents predictions from two CFD codes and test results, for both the original and the redesigned impeller, and discusses the application of CFD for predicting impeller stall.
New Design Features of Centrifugal Blower Systems to Improve its Airflow Performance and Power Consumption
Authors: Botros Monier B. , Beaudoin Thomas M. , Lai Ming-Chia
Published: December 2021

A parametric study is carried out to screen the effects of HVAC blower housing volute, scroll, design parameters on its performance. The results of statistic regression analysis, mathematical models and prediction correlation to test data are included and discussed.

Blower airflow field is inspected by computational fluid dynamics (CFD) and Laser Doppler velocimetry (LDV) to define its deficiencies. New design features for blower scrolls are developed to resolve the flow deficiencies, in order to minimize the blower energy losses, vibrations and air-rush noise. Flow field improvements are illustrated.

Blower performance with the new design features is compared to the performance of the previous design art known as “standard blower” designs. Airflow capacity of the new designs is higher than that of a standard design of one degree larger in size, within the operating range of automotive air-handling systems. Blower efficiency is increased by 3 to 8% over a wider airflow range. The effects of scroll size and exit design on the performance of the new scroll designs are illustrated and discussed.
High Performance Computing: Analytical Aerodynamics for Automotive Vehicles
Authors: Miller Ronald H. , Strumolo Gary S. , Hytopoulos Evangelos , Remondi Stephen A. , Watson Samuel M.
Published: December 2021

High Performance Computing (HPC) represents a significant resource whereby automotive manufacturers can utilize analytical methodologies to reduce experimental testing and design time, resulting in lower costs and higher quality. Optimization of styling and aerodynamics requires multiple CFD simulations which have been enabled by the commercial availability of parallel algorithms, as well as enhancements in computer architectures. We have developed a Virtual Aerodynamic Wind Tunnel (VAWT) which uses PowerFLOW® and can simulate conditions similar to experimental wind tunnels. One key element of this methodology is the use of PowerFLOW. Two of the major attributes of PowerFLOW are its inherent parallelization and automeshing capabilities. In this paper, we will focus on the scalability and feasibility of PoweFLOW, which is essential for the optimization of styling and aerodynamics. Timing and scalability results on an Origin 2000 server are presented for a number of different configurations.
Detection of Wrap-Up Incidents in a Napping Machine
Authors: Dad Shahzad A. , Kamarthi Sagar V. , Cullinane Thomas P.
Published: December 2021

In the textile industry, a napping machine is used to raise pile on the surface of the web (knit or woven fabric). As a result of the napping machine’s high speed planetary motion, the web can get tangled in the machine and induces damage to both the machine and the web. By averting wrap-up incidents, it is possible to save maintenance costs, reduce machine downtime, and make the work environment safer. This paper introduces a method for predicting wrap-up incidents in a napping machine to avoid costly damage to the machine.

The task of detecting wrap-up incidents is achieved by using indirect sensing of vibration signals from the napping machine. The data collected from the napping machine are represented by discrete wavelet transforms. The features extracted from the coefficients of the discrete wavelet transforms are used as inputs to a multilayer neural network. Once the neural network is trained by using the data specific to the napping machine, data from the machine are processed and fed to the neural network for online wrap-up incident prediction.

Several experiments are conducted on a test napping machine, to verify and validate the proposed wrap-up detection scheme. It was found that the vibration signals along the horizontal direction of the main shaft of the napping machine provides an impressive 100% correct wrap-up detection signal.
1-Propyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (Solarpur®) analyzed by hard x-ray photoelectron spectroscopy
Authors: Knigge Xenia , Radnik Jörg
Published: December 2021

1-Propyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (Solarpur®), an ionic liquid was purchased from Merck (formerly Sigma Aldrich), was analyzed using hard x-ray photoelectron spectroscopy (HAXPES). The liquid is UHV stable, vertically and laterally homogeneous, and is easy to clean; thus, it can be used as a reference material. The HAXPES spectra of Solarpur® obtained using monochromatic Cr Kα radiation at 5414.8 eV include a survey scan, high-resolution spectra of C 1s, O 1s, N 1s, S 2p, S 1s, S 2s, F 1s, and S KLL.