bluuebunny/crossref_metadata_2025 huggingface dataset:
An Integrated Model for Electromagnetic Field and Heat Transfer in a Cylindrical Silicon Tube Growth System
Authors: Roy A. , Chen Q.-S. , Zhang H. , Prasad V.
Published: December 2021

Edge-defined Film-fed Growth (EFG) processes are widely used to grow silicon sheets and hollow cylinders of different shapes, e.g., octagon, nonagon and circular. Growth of large diameter silicon tube can bring further advancements in the photovoltaic technology. In the present investigation, a two dimensional axisymmetric numerical model has been developed for a cylindrical silicon tube growth system. The growth furnace is inductively heated. Magnetic vector potential equation and energy equation are solved to obtain the induced magnetic field and temperature distribution in the system. Selected results for magnetic and thermal fields have been presented for a range of parameters. The effect of using graphite afterheater in the system has also been investigated. The goal of the investigation is the system optimization with respect to the temperature field in the global system and the thermal profile in the grown tube.
High-Resolution Wafer Surface Topology Measurement Using Phase-Shifting Shadow Moiré Technique
Authors: Wei Songbin , Guan E. , Kao Imin , Chiang Fu-Pen
Published: December 2021

The traditional shadow moiré technique has been employed, using the fringe pattern information and numerical interpolation, to construct the wafer surface topology. In this paper, phase-shifting shadow moiré technique is discussed and applied to the measurement of wafer surface topology with high resolution. The phase-shifting technique takes advantage of the gray level information to increase the physical resolution of the measurement. A series of fringe patterns are recorded while they are shifted by moving the wafer along the direction perpendicular to wafer surface. The phase is encoded in the variations in the intensity pattern of the recorded fringe images, and a simple point-by-point calculation recovers the phase. The needs to locate the fringe centers and interpolation are eliminated. Since the depth variation of wafer surface is very small, usually within the range of 0.1 to 20 microns, very fine grating is required in order to capture the small depth variation. However, very fine grating will introduce strong diffraction effect which blurs the fringe patterns. In this study, the Talbot distance is applied to obtain images with good contrast. The phase shift is realized by moving the wafer to change the distance between the wafer surface and the reference grating. A four-step phase wrapping algorithm is used to calculate the phase. The phase pattern recovered from four fringes patterns is presented. Future work such as how to reduce the noise, how to do phase unwrapping and calibration is also discussed.
Fundamental Analyses of Smart Tooling for Assembly of Thin Flexible Circuit and Board Systems
Authors: Chen Ruijun , Baldwin Daniel F.
Published: December 2021

Flexible nature of flexible circuits/boards poses new fixture tooling challenges for standard surface mount assembly equipment. The flexible substrates experience significant transverse displacements under perpendicular assembly forces during solder paste printing and component placement processes. The displacements result in misregistration of the component leads and substrate bond pads, leading to assembly process defects. Solder reflow process further complicates the issue due to the thermo-mechanical warpage induced. Reengineered and specialized dedicated tooling for fixturing flexible substrates in standard assembly equipment is becoming extremely important. This paper focuses on developing analysis methodologies and theories for implementing Smart Tooling. The primary goals being to determine the impact of fixturing on assembly process quality and to determine optimum fixturing configurations for thin flexible circuit board assemblies based on circuit board design data. A mathematical model to describe both transverse and perpendicular displacements of flex substrates is developed, and its close-form solution for transverse displacements is obtained. Using a “near” optimum fixturing configuration to minimize transverse displacements is verified.
A Study of the Aperture Filling Process in Solder Paste Stencil Printing
Authors: Pan Jianbiao , Tonkay Gregory L.
Published: December 2021

Stencil printing has been the dominant method of solder deposition in surface mount assembly. With the development of advanced packaging technologies such as ball grid array (BGA) and flip chip on board (FCOB), stencil printing will continue to play an important role. However, the stencil printing process is not completely understood because 52–71 percent of fine and ultra-fine pitch surface mount assembly defects are printing process related (Clouthier, 1999). This paper proposes an analytical model of the solder paste deposition process during stencil printing. The model derives the relationship between the transfer ratio and the area ratio. The area ratio is recommended as a main indicator for determining the maximum stencil thickness. This model explains two experimental phenomena. One is that increasing stencil thickness does not necessarily lead to thicker deposits. The other is that perpendicular apertures print thicker than parallel apertures.
Constitutive and Cyclic Damage Model of 63Sn-37Pb Solder
Authors: Stolkarts V. , Keer L. M. , Fine M. E.
Published: December 2021

The proposed model describes constitutive behavior of 63Sn-37Pb solder including effects of size, thermomechanical loading and cyclic damage. Its application to the uniaxial fatigue data shows a good agreement with the experiments.
A Dual-Phase-Lag Diffusion Model for Predicting Thin Film Growth
Authors: Chen J. K. , Beraun J. E. , Tzou D. Y.
Published: December 2021

A dual-phase-lag diffusion (DPLD) model, which extends Fick’s law by including two lagging times, τj for the mass flux vector and τρ for the density gradient, is developed to predict thin film growth. Depending upon the phase lag ratio τρ/τj, the proposed model uniquely characterizes four types of growth kinetics as reported in the literature. The model validation with the experimental data of silicon oxidation and Hg1-xCdxTe film deposition demonstrates that the DPLD model captures the anomalous behavior of thin film growth from the very beginning of the process to relatively long times very well.
Effect of Volume on Ceramic Ball-Grid Array Solder Life
Authors: McKeown Stephen A. , Sahay Chittaranjan
Published: December 2021

Paper describes the effect of solder volume on solder life based on linear finite element analysis using ANSYS. The results indicate an optimal volume for the solder life. Any increase or decrease in the solder volume from the optimum volume decreases the fatigue life of solder joints. Solder joint life was also experimentally determined for the same temperature excursion with a 2-hour thermal cycle. The experimental results compare well with the results estimated by finite element modeling. Studies for one elastic-plastic analysis has also been carried out. Initial results indicate substantial increase in strain concentration factor.
In-Situ Warpage Measurement During Thermal Cycling of Dielectric Coated SS Substrate for Large Area MCM-D Packaging
Authors: Dang Anh X. H. , Ume I. Charles , Bhattacharya Swapan K.
Published: December 2021

Feasibility of using stainless steel (SS) as a base substrate material for a large area MCM-D packaging is reported in this paper. A test vehicle was fabricated using 0.008 inch thick and 12-inch × 12-inch SS panel with laser drilled 0.01-inch vias. A dielectric material (Parylene N) was deposited on the SS panel and around the inside via walls in order to electrically isolate the via filling material from the body of the SS substrate and also making the SS surface non-conductive. Vias were filled using a commercially available conductive via-plug material. The test structure was exposed to elevated temperatures to simulate the thermal excursion the substrate would be subjected to during the MCM-D thin film process. The end objective of this work is to be able to fabricate large area (24 inch × 24 inch) SS substrates for the next generation MCM-D packaging with reduced warpage. This paper reports results of the dynamic warpage measurement during thermal cycling of a 12-inch × 12-inch SS substrate.
Changes due to Scission in an Elastomeric Cylinder Undergoing Circular Shear and Heat Conduction
Authors: Wineman Alan
Published: December 2021

Research in the prediction of durability and service life for elastomeric products has been actively pursued over the past decade because these materials are finding increasingly abundant applications in the automotive, aerospace and medical industries. Elastomers are used in many critical service applications that require long trouble free life, such as gaskets, seals, bridge pad bearings, tires, medical components and rocket fuel binders. For example, elastomeric seals are used in many applications where seals are relatively inaccessible and cost of replacement is too great. Thus, a fifty year service life for seal life is now a clearly stated objective for the energy industry (Hertz, 1997). The life expectation for elastomeric components on vehicles has changed dramatically over the past few years. Previously, many rubber components were viewed as items that would be replaced once or more during the life of a vehicle. Now, elastomeric components are expected to last the life of the vehicle, which is currently defined as 10 years/150,000 miles for both passenger cars and light trucks (Pett, 1997).
Prediction of the Initial Crack Tip Microstructure in a Single Crystal of CuAlNi
Authors: Vasko Galyna M. , Leo Perry H. , Shield Thomas W.
Published: December 2021

The austenite to martensite pseudoelastic transformation induced by the anisotropic elastic crack tip stress field in a single crystal of shape memory alloy is considered. It is proposed that the orientation of the initial austenite-martensite interface that forms can be predicted based on knowledge of the stress field, the crystallography of the transformation and one of two selection criteria. These criteria are based on the work of formation of the martensite in stress field and the crack opening displacement the martensite causes at the crack. Predictions of the criteria are compared to experiments on three single edge notched CuAlNi single crystal specimens. Results indicate that the maximum work criterion accurately predicts the orientation of the austenite-martensite interfaces that initially form near a crack.
Adiabatic Processes and Constraints in Thermoelasticity
Authors: Rajagopal Kumbakonam R. , Srinivasa Arun R.
Published: December 2021

The aim of this paper is to briefly outline an approach to the thermomechanics of thermoelastic solids based on the notion of multiple natural states and the use of adiabatic processes. We use a statement of the second law attributed to Kelvin for certain special cycles and show that the work done in adiabatic cycles of deformation is non-positive. With these and other assumptions on the nature of thermoelastic solids, we demonstrate the existence of an entropy function and the absolute temperature scale. In this, we closely follow the arguments of Caratheodory (1976). Finally, we briefly address the issues of a class of thermomechanical constraints and show that they naturally lead to considering constraints on adiabatic processes.

The principal results are the following:

1. Demonstration of the existence of the absolute temperature and entropy functions based on the consideration of adiabatic processes

2. A one-to-one correspondence between the stress-free states and the entropy, leading to a “decomposition” of the deformation gradient as Fκr = FκnG(η).

3. Physical interpretation of the constraints of the form f(Eκr,η) = 0.
Shocks in Thermoelastic Rods
Authors: O’Reilly Oliver M. , Varadi Peter C.
Published: December 2021

A theory of a thermoelastic rod is presented in this paper. The theory is based on the work of Green and Naghdi, supplemented by singular supplies of momenta, energy and entropies at a discontinuity. In addition, several aspects of the theory in the presence of internal constraints are presented. The theory is suited to the study of numerous applications, including studies of phase transformations, propagation of shock and acceleration waves and axially moving rods.
A Numerical Evaluation of Protection Strategies for Cab Car Crashworthiness
Authors: Stringfellow Richard , Mayville Ronald , Rancatore Robert
Published: December 2021

The operator and passengers in cab cars are particularly vulnerable to collisions with objects or with other trains because of their proximity to the point of collision. We present one part of a larger study in which we examined several strategies for improving the protection afforded to the operator and the passengers in cab car collisions. These strategies include: strengthening key cab-end structural elements, such as corner posts, collision posts and end beams; locating the operator between the collision posts rather than to one side of the control cab; and implementing crush zones into the ends of the cab as part of a crash energy management design for the entire train. Here we focus on the first of these strategies, evaluating the effectiveness of strengthened cab-end structures through explicit dynamic finite element-based calculations simulating the crush behavior of the cab car. There calculations were made for conditions representative of a number of collision scenarios based upon recent accidents, including several oblique collisions. The results of these calculations suggest that such strengthening can significantly increase the tolerable collision speeds that can be withstood without compromising the operator and passenger volumes.
Simulation of an Oblique Collision of a Locomotive and an Intermodal Container
Authors: Tyrell David C. , Severson Kristine J. , Marquis Brian P. , Perlman A. Benjamin
Published: December 2021

This paper presents an approach to modeling an oblique collision of a locomotive and an intermodal container. Previous studies of offset and oblique train collisions have used one and two-dimensional models to determine the trajectories of the equipment during the collision (Mayville, et al. 1995, Tyrell, et al, 1997). This analysis uses a three-dimensional model to determine the trajectories of the equipment.

In the collision scenario of concern, an intermodal container impacts the outboard corner of the short hood of a wide-nose locomotive above the deck. An impact element has been used in the collision dynamics model to transfer contact load to the short hood of the locomotive. A detailed non-linear finite element model has been developed to characterize the force-crush behavior of the short hood. These results determine the parameters that connect the impact element to three-dimensional lumped-masses that represent vehicles in the consist. The collision dynamics analysis includes the influence of the locomotive suspension and the trailing locomotive.

The model has been used to evaluate the influence of short hood design on intrusion into the operator’s cab, the deceleration of the locomotive during the collision, and whether derailment of the locomotive occurs as a consequence of the collision. Results indicate that short hood strength can be increased significantly above the strength of the current design without derailing the locomotive in this collision scenario. More short hood strength increases the maximum closing speed that can be sustained without intrusion into the operator’s cab, while the deceleration of the operator’s cab remains relatively low.
A Semi-Empirical Method for Estimating the Effective Leak and Vent Areas of an Airbag
Authors: Anagonye Aloysius U. , Wang J. T.
Published: December 2021

A semi-empirical method that utilizes tests from a small fabric specimen to quantify the effective leak and vent areas of an entire airbag is developed in this paper. The test setup and procedure used in the airbag material coupon tests are similar to the standard method used in determining air permeability of fabrics. A test apparatus for measuring the deflection of the fabric coupon was devised. Finite element analysis is used to compute the expanded vent and airbag surface areas of the coupon under various deformations. The leak and vent models were developed based on the results of a regression analysis. The effective vent area of a fabric coupon is a function of the ratio of the pressures across the fabric and the expanded vent area. Similarly, the effective leak area of a fabric coupon is a function of the ratio of the pressures across the fabric and the expanded surface area. The tested airbag materials were characterized with these models for use with finite element airbag models.
The Relationship of Driver Airbag Design Parameters to an Out-of-Position Small Female Thorax Injury
Authors: Mu William , Sheng Jianping , Chen Chao
Published: December 2021

Airbag related out-of-position occupant (OOPO) thorax injury was investigated for many years. However, little study was published to address how to reduce the OOPO related thorax injury from the point of view of restraint system design. The objective of this investigation is to utilize both experiment and computer simulation approaches to study the OOP small female thorax injury mechanism and its relationship to the restraint system design parameters. Coupled structure, computational fluid dynamics (CFD) and rigid multi-body dynamics simulations were performed to investigate the effect of airbag deployment on OOPO thorax injury. The laboratory experiments are performed to validate the simulation results. Then the relationship of airbag design parameters on OOPO thoracic injury risk is characterized. The outcomes of this study lay down the foundations for advanced restraint system development.
The Effects of Common Misuses of a Child Safety Seat in an Automobile Crash
Authors: Canha Joseph , Greif Robert , Neat George
Published: December 2021

This paper investigates the effects the four most common misuses of a child safety seat (CSS) have on a toddler involved in a motor vehicle crash using a validated MADYMO model. These misuses involved a locking clip, shoulder harness chest clip and straps, and vehicle safety belt. A properly seated toddler in a forward-facing CSS was secured to a standard vehicle seat in a 48-kph frontal collision. The new proposed injury criteria (HIC, chest acceleration, and maximum axial neck load) and other occupant responses were used for model evaluation. For a CSS with as little as 3 centimeters of excessive slack in the vehicle safety belt, the child dummy exceeds each of the injury threshold values. Although some misuses provide a significant increase in injury response, the other misuses either individually or combined did not increase the injury potential of the child dummy in this CSS to unacceptable levels.
A Constriction Resistance Model in Thermal Analysis of Solder Ball Joints in Ball Grid Array Packages
Authors: Ying T. M. , Toh K. C.
Published: December 2021

The constriction resistance model is employed for the thermal analysis at the solder ball joint of a Ball Grid Array (BGA) package. The behavior of heat dissipation in solder joint is also analyst through Finite Element Modeling (FEM) and compared with the analytical model. The principle of constriction and spreading resistances is analyzed in detail because of the geometrical complexity encountered in BGA solder joints. The total resistance across the solder joint includes the internal resistance and external resistance. The internal resistance, which is the main focus of the analysis, consists of material resistance and constriction resistance. It is a function of material conductivity, thermal boundary conditions and geometric parameters. FEM solutions are in good agreement with analytical results of thermal resistance for single solder ball joint and multiple solder ball joints. The analytical resistance provides an accurate prediction on the temperature drop across the array of solder balls and hence the overall performance of the BGA packages. The pitch size is the main parameter in the investigation to study the heat dissipation of solder ball joints.
Inverse Heat Source Design Combining Radiation and Conduction Heat Transfer
Authors: França Francis H. R. , Ezekoye Ofodike A. , Howell John R.
Published: December 2021

This work investigates solutions of inverse heat source problems for combined-mode radiation and conduction. The problem consists of finding the heat source distribution in an absorbing-emitting medium that satisfies both the temperature and the heat flux distributions prescribed on the surfaces of a two-dimensional rectangular enclosure. The participating medium is gray, the walls are gray emitters and absorbers, and all the thermal properties are uniform. The combined heat transfer mode problem is described by a system of non-linear equations, which is solved by an iterative procedure. At each iteration a system of linear equations is solved, but, as often occurs in inverse problem, the system of equations is ill-conditioned, and the number of equations and the number of unknowns are not necessarily the same. The solution is obtained by regularizing the system by truncated singular value decomposition (TSVD). It is also discussed how to impose additional conditions to satisfy physical constraints that govern the heat source itself.
Investigation of Conjugate Heat Transfer in Interim Storage of High Level Radioactive Waste
Authors: Sizgek G. Devlet
Published: December 2021

Solidified high level radioactive wastes generate decay heat that must be taken into account during interim storage in engineered facilities prior to geological disposal. The continual heat generation within the canisters necessitates reliable heat removal to avoid overheating of the stored material and the surrounding safety barriers. This paper is concerned with the modelling and computation of heat transfer in one of the storage cells, based on the conceptual design study for natural convection cooled high level radioactive waste storage. All internal features of the storage cell have been explicitly modelled to analyse the internal heat transfer process by conduction and natural convection coupled with thermal radiation. One of the major objectives of the current study was to assess the contribution of radiation heat transfer in altering temperature profiles in the storage cell. Furthermore the model has been used to predict the effects of surface radiative properties, canister filling material conductivities and waste loading on the temperature and velocity fields. A variation in the enclosed air gap width and also cooling air channel width has also been performed to see their potential effect on temperature profiles of the storage cell.
Natural Convection Heat Transfer in a Vertical Square Duct With Radiation Effects
Authors: Yan Wei-Mon , Lee Kuan-Tzong
Published: December 2021

The present work investigates numerically the natural convection heat transfer with radiation effects in an open vertical square duct. The integro-differential radiative transfer equation is solved by discrete ordinates method. The vorticity-velocity formulation is applied to solve for the coupled momentum and energy equations. The effects of five major parameters, Grashof number Gr, conduction-to-radiation parameter Nc, optical thickness τ, single scattering albedo ω and temperature ratio Tr, on the combined natural and radiation heat transfer are discussed in detail. The numerical results of the dimensionless induced volume flow rate and average Nusselt numbers show that the thermal radiation would enhance the heat transfer rate. Additionally, the variations of the induced volume flow rate and total Nusselt number are independent of radiative parameters under fully-developed flow limit.
The Application of a Hue-Based Liquid Crystal Technique to Determine Convective Heat Transfer Downstream of Non-Axisymmetric Circular-to-Square Expansions
Authors: Guile Anthony W. , Garwood Roy , Ward John
Published: December 2021

A liquid crystal technique has been applied to the problem of convective heat transfer downstream of a circular to square abrupt expansion. This configuration is similar to that found with a burner firing into a furnace or boiler. There is little data available in the literature for these expansions as most previous investigations have concentrated on a simple circular to circular geometry.

Liquid crystals were selected for the tests because of their ability to provide a full surface temperature map with a high spatial resolution. With the progress of image capture and processing technology a transient test method was preferred as it makes the construction of models very simple by eliminating the need to heat the surface with the inherent problem of uniformity and the difficulty in viewing the surface.

The application of liquid crystals produced results which were found to be accurate and repeatable, when compared with results obtained from other investigations in the area. It gave quantitative data, allowing spanwise and axial distributions of heat transfer to be calculated in these geometries.

The hue capturing technique thus provides quantitative, accurate and repeatable temperature measurements, and when applied to heat transfer problems is a powerful experimental tool.
Heat Transfer Enhancement by Imposed Pulsation in a Channel With Sudden Expansion
Authors: Tandogan E. , Mitra N. K.
Published: December 2021

A numerical investigation of laminar pulsating flows in a channel with sudden expansion in the cross section has been performed by solving two dimensional Navier-Stokes and energy equations for an incompressible fluid. A sinusoidal pulsation has been imposed on the axial velocity at the inlet. Results show that the flow field symmetry at the channel axis vanishes at even a Reynolds number of 100. The time averaged Nusselt number of pulsating flow increases sharply over the nonpulsating flow in the Reynolds number range of 400 and 500. The time averaged Nusselt number on the two walls can be different.
Turbulent Boundary Layer Subjected to a Sudden Change in Surface Roughness and Temperature
Authors: Guimarães João Henrique D. , dos Santos Sergio J. F. , Su Jian , Silva Freire Atila P.
Published: December 2021

In present work, the dynamic and thermal behaviour of flows that develop over surfaces that simultaneously present a sudden change in surface roughness and temperature are discussed. In particular, the work is concerned with the physical validation of a newly proposed formulation for the near wall temperature profile. The theory uses the concept of the displacement in origin, together with some asymptotic arguments, to propose a new expression for the logarithmic region of the turbulent boundary layer. The new expressions are, therefore, of universal applicability, being independent of the type of rough surface considered. The present formulation may be used to give wall boundary conditions for two-equation differential models. The theoretical results are validated with experimental data obtained for flows that develop over flat surfaces with sudden changes in surface roughness and in temperature conditions. Measurements of mean velocity and of mean temperature are presented. A reduction of the data provides an estimate of the skin-friction coefficient, the Stanton number, the displacement in origin for both the velocity and the temperature profiles, and the thickness of the internal layers for the velocity and temperature profiles. The skin-friction co-efficient was calculated based on the chart method of Perry and Joubert (J.F.M., 17, 193–211, 1963) and on a balance of the integral momentum equation. The same chart method was used for the evaluation of the Stanton number and the displacement in origin.
A Numerical Study of Three-Dimensional Natural Convection in a Low Aspect Ratio Horizontal Enclosure With a Uniform Heat Flux on the Lower Surface
Authors: Oosthuizen Patrick H.
Published: December 2021

Flow in a rectangular enclosure with a square horizontal cross-section and with a uniform heat flux applied across the lower horizontal surface and with the upper horizontal surface cooled to a uniform low temperature has been numerically studied. The vertical side-walls of the enclosure are adiabatic. It has been assumed that the flow is laminar and that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces. The unsteady form of the governing equations, written in terms of the vector potential and vorticity vector functions and expressed in dimensionless form, have been solved using a finite-difference procedure based on the equations. The solution was started with no flow in the enclosure. The solution, in general, has the following parameters: the heat flux Rayleigh number Raq, the Prandtl number and the size A of the square cross-sectional shape compared to the height of the enclosure. Results have only been obtained for a Prandtl number of 0.7. Results for values of A between 0.5 and 3 for various relatively low and moderate values of Rayleigh number (up to 40000) have been obtained. The results have been used to determine the effect of A on the value of Raq below which there is no fluid motion in the enclosure and to examine the various flow patterns that arise as the value of Raq is increased with various values of A. The effect of A on the variation of the mean dimensionless lower surface temperature with Ra has also been examined.
Natural Convection to Power-Law Fluids From a Heated Vertical Plate Under Mixed Thermal Boundary Conditions
Authors: Büyük Elif , Ece Mehmet C.
Published: December 2021

Steady free convection laminar boundary-layer flow subject to mixed thermal boundary conditions along a heated vertical plate immersed in a quiescent power-law fluid is investigated. Similarity solutions are obtained numerically for the boundary-layer velocity and temperature profiles. The effects of flow behavior index and the generalized Prandtl number on the surface shear stress and heat flux are determined.
Retrieval of Multidimensional Heat Transfer Coefficient Distributions Using an Inverse BEM-Based Regularized Algorithm: Numerical and Experimental Results
Authors: Divo Eduardo , Kassab Alain J. , Kapat Jay S. , Chyu Ming-King
Published: December 2021

Surface maps of heat transfer coefficients (h) are often determined by transient liquid crystal or other similar transient experimental techniques. This involves (1) conducting an experiment with an impulsively imposed convective boundary condition on an initially isothermal test object, (2) measuring the resulting time-dependent surface temperature distributions, and (3) solving the one-dimensional transient heat conduction equation for different points on the convective surface. There are many practical cases where this approach fails to adequately model the temperature field and, consequently, leads to erroneous h values. In this paper, we present an inverse boundary element method (BEM)-based approach for the retrieval of spatially varying h distributions from surface temperature measurements. In this method, an efficient numerical algorithm requiring only a surface mesh is used to solve the conduction problem. At each time level, a regularized functional is minimized to estimate the time-dependent heat flux and simultaneously minimize the effect of experimental measurement uncertainties in surface temperature values on the calculated heat flux. Newton’s cooling law is then invoked to compute h. Results are presented from several numerical simulations and from a laboratory experiment. The method is applicable to unsteady as well as to steady-state convective systems.
Dynamics of Heat Transfer in the Melt Pool at Nuclear Severe Accident Conditions
Authors: Horvat Andrej , Kljenak Ivo , Marn Jure
Published: December 2021

Prediction of thermal loads on nuclear reactor vessel lower plenum after core melting and relocation during a severe accident requires knowledge about the core melt behavior, especially the circulation pattern. To analyze the heat transfer dynamics on the lower plenum walls, two-dimensional numerical simulations of a fluid flow with internal heat generation were performed for Rayleigh numbers 106, 107, 108, 109, 1011 and 1013 at Prandtl number 0.8. For subgrid motion modeling, a Large-Eddy Simulation Smagorinsky model was implemented.

The minimum, time-average and maximum Nusselt numbers on the boundaries were calculated. The dynamics of fluid structures were analyzed to reveal the instability mechanisms and transition to turbulence. Results disclose Rayleigh-Taylor instabilities as a dominant mechanism for turbulence appearance, which occurs when the Rayleigh number is increased over 108.

The structure dependence of fluid motion at high Rayleigh numbers makes the time-average of heat transfer hard to assess. The time-average values should be supplemented with probability distributions of related variables.
New Model of Higher Moments for Describing Stratified and Swirled Turbulent Flows
Authors: Ilyushin Boris B. , Yakovenko Sergey N.
Published: December 2021

A new model of the fourth-order cumulants has been elaborated for describing non-local turbulent transfer in stratified flows allowing the field of applicability of turbulence model to be significantly widened. An algebraic version of the fourth-order cumulants model does not require additional empirical information. An algebraic model for third-order moments is also formulated on the base of standard models correction for buoyancy and swirl effects. The models have been tested for a turbulent flow in a rotating pipe. These results and results of modelling turbulent transfer in the convective atmospheric boundary layer let us conclude that the developed algebraic approximations for higher moments can be applied for both parameterization of turbulent diffusion processes in the transport equations and computation of higher-order moments in turbulent stratified and swirled flows.
Thermal Analysis of Stacked Ni-MH Battery
Authors: Hisano Katsumi , Iwasaki Hideo , Ishizuka Masaru , Yamane Tetsuya
Published: December 2021

Numerical analysis was carried out to evaluate the temperature rise and charge retention of Ni-MH batteries as pallet loads. In this paper, thermal analysis of pallet loads which contain 2400 mAh Ni-MH batteries is considered as a test case. To reduce computational load, thermal analysis was performed in three stages. Measured and calculated temperature rise of the load showed good agreement, and it can be observed that there exists an appropriate charge retention of the battery to sustain high retention during transportation.
Condensation of R134a Flowing Inside Horizontal and Vertical Helicoidal Pipe
Authors: Kang H. J. , Lin C. X. , Ebadian M. A.
Published: December 2021

Condensing heat transfer characteristic of an ozone-friendly refrigerant HFC-R134a (Hydrofluorocarbon R134a) flowing inside a 12.7mm helicoidal tube was investigated experimentally to obtain heat transfer data and correlations. For this long helicoidal pipe at horizontal and vertical helicoidal positions, heat transfer measurements were performed for the refrigerant flow mass fluxes from 100 to 400 kg/m2/s, in the cooling water flow Reynolds number range of 1500 < Rew < 9000 at fixed system temperature (33°C) and cooling tube wall temperature (12°C and 22°C). Experimental results show that, with the increase of mass flux, the overall condensing heat transfer coefficients of R134a increase. However, with the increase of mass flux (or the cooling water flow Reynolds number), the refrigerant side heat transfer coefficients decrease. The effects of cooling wall temperature on heat transfer coefficients were considered. Predictive correlations valid over the above water flow Reynolds number ranges and refrigerant flow mass fluxes were proposed. Helicoidal pipe heat transfer characteristics were compared with data from literature reports for horizontal straight tube. Experimental results show that helicoidal pipe, especially at horizontal position, conducts a much better heat transfer characteristic than that of horizontal tube even it was grooved. The helicoidal pipe’s position plays a very great role on heat transfer characteristic with 100 percent higher results at a horizontal position than that of vertical position.
Thermal-Hydraulic Behavior and Prediction of Heat Exchanger for Latent Heat Recovery of Exhaust Flue Gas
Authors: Osakabe Masahiro
Published: December 2021

In order to improve the boiler efficiency, latent heat recovery from the flue gas is very important concept. Three kinds of countercurrent cross-flow heat exchangers, which consist of bare tubes, spirally finned tubes of fin pitch 5 and 10mm, were designed and used for the experiment. The heat exchanger of the bare tubes consists of a staggered bank of 5-4 rows and 50 stages. The length, outer and inner diameter of the bare tube is 482, 27.2 and 23.2mm, respectively. The heat exchangers of finned tubes consist of staggered banks of 3-2 rows, 34 stages for the fin pitch 10mm and 20 stages for the pitch 5mm. The length, outer and inner diameter of the base tube welded with the fins is 482, 34 and 28.8mm, respectively. The thickness and height of the plate fin are 1 and 12mm, respectively. The parametric study varying the flue gas flow rate, feed water temperature and flow rate was conducted. The temperature distributions of water and flue gas in the heat exchanger were measured with sheath K-type thermocouples of 1.6 mm in diameter. The pressure loss and the total amount of condensate generated in the heat exchanger were also measured.

Based on the previous basic studies, a prediction method for the heat exchanger was proposed. In the prediction, the flue gas was treated as a mixture of CO2, CO, O2, N2 and H2O, and the one-dimensional heat and mass balance calculation along the flow direction of flue gas was conducted. The heat and mass transfer on tubes was evaluated with a simple analogy correlation. For the finned tubes, the fin efficiency at the condensing region was calculated with a semi-empirical correlation obtained in the previous basic study. The effect of condensate film on the tubes was considered to be negligibly small for the heat transfer and pressure loss calculation. The experimental results for the temperature distributions of water and flue gas in the test heat exchangers with bare and finned tubes agreed well with the prediction.
Simulation of Subcooled Nucleate Boiling in a Vertical Tube With a Bubble-Tracking Model
Authors: Kljenak Ivo , Mavko Borut
Published: December 2021

A three-dimensional bubble-tracking model was developed to simulate subcooled nucleate boiling in a heated vertical cylindrical tube. The behavior of the liquid-vapor system results from motion, interaction and heat transfer mechanisms prescribed mostly at the level of individually-tracked vapor bubbles. The model takes into account bubble nucleation and liquid heating caused by wall heat flux, bubble sliding on tube walls, bubble condensation in the low-temperature tube core region, bubble interaction through wake drift, bubble collisions and coalescence, bubble radial migration towards the tube core region, and turbulent dispersion in the liquid phase. The agreement between calculated void fraction and liquid temperature radial profiles along the flow with experimental results from other authors is promising.
Water Flow Distribution in Horizontal Protruding-Type Header Contaminated With Bubbles
Authors: Horiki Sachiyo , Osakabe Masahiro
Published: December 2021

Flow header for small multiple pipes is commonly used in boilers and heat exchangers. The system contributes to raise the heat transfer efficiency in the components. The flow distribution mechanism of the header for water has been studied and the calculation procedure for the design has been recommended for a single-phase condition. It is also recommended to avoid the bubbles in the header to obtain a uniform water flow rate to each small pipe. But in some cases, the header has to be used to distribute a flow containing bubbles. Distribution behavior of water with a gas-phase was studied experimentally in a horizontal header with four vertical pipes. In the present experimental header, it was possible to protrude the branch pipes inside of the header and the effect of protruding length on the water distribution behavior was studied.

When the protruding length was 0, the water distribution rate to the first pipe rapidly increased and the rates to the others decreased with a small amount of bubbles. As the bubbles in the header were absorbed only into the first pipe, the average two-phase density in the first pipe decreased. The decreased pressure head promotes the rush of water into the first pipe such as in an airlift pump. By increasing the air flow rate in the header inlet further, the flow rate to the first pipe took a maximum and then tended to decrease. The increased air flow rate in the first pipe increased the pressure loss in the pipe and resulted in a reduction in the water flow rate. The more important and serious behavior could be seen in the other pipes where the water flow rate decreased to 1/5 of the uniform distribution rate. By increasing the protruding length, the non-uniform distribution of water was suppressed because the gas-phase entered not only the first pipe but also the others. The best result was obtained when the four branch pipes were protruded into the center of header.
Experimental Study on the Hydraulic Characteristics of Solid-Liquid Slurry Two-Phase Flow in Horizontal Pipelines
Authors: Xu J. L. , Lin C. X. , Ebadian M. A.
Published: December 2021

A flow loop that contains a mixing tank, pump, horizontal pipeline, and corresponding measurement transducers has been constructed at Florida International University’s Hemispheric Center for Environmental Technology (FIU-HCET). Several slurry simulants that include liquid and five or six chemical solid species were applied in the tests. New data were provided on the pressure gradient and volume concentration across a vertical cross-section. It was found that the flow characteristics are quite distinct from the classical characteristics of coal-water or sand-water slurry flowing in horizontal pipelines. An apparent transition point occurs in the curve of the pressure gradient versus velocity. Flow observation identified that the solid particles settle down at the velocities of the corresponding transition points. The velocities at the transition points are classified as the limit deposition velocity. Lower velocity than the limit deposition velocity will result in a stationary bed flow. Weight concentration measurements in a heterogeneous flow regime indicate that there is no weight concentration gradient along the axial distance. However, within the present parameter range, the weight concentration is always higher at the top point than that at the bottom point.
Analysis of Fluid Flow in Composite Channels: Comparision of Analytical and Numerical Approaches
Authors: Kuznetsov A. V. , Xiong Ming
Published: December 2021

In this work, comparisons between the numerical solutions for forced convective flow in composite channels, partly occupied by a homogeneous (clear) fluid and partly by a fluid saturated porous medium, and the exact solutions for the same problems are carried out. This is done to establish limitations of the single-domain approach utilized to obtain the numerical solutions. These limitations result from the assumptions which are implicitly invoked once the single-domain approach is utilized to model fluid flow in the interface region between the porous medium and a clear fluid. It is shown that the single-domain approach results in correct matching of the shear stress at the porous/fluid interface only if the adjustable coefficient in the representation for the excess stress equals zero and also if the effective viscosity of the porous medium equals to the fluid viscosity.
A Hyperbolic Phase-Field Approach for Solidification With Supercooling
Authors: Chen Yuqi , McDonough James M. , Tagavi Kaveh A.
Published: December 2021

This report concerns the solidification of a “supercooled” liquid, whose temperature is initially below the equilibrium melt temperature, Tm of the solid. A new approach, the phase-field method, will be applied for this Stefan problem with supercooling, which simulates the solidification process of a pure material into a supercooled liquid in a spherical region. The advantage of the phase-field method is that it bypasses explicitly tracking the freezing front. In this approach the solid-liquid interface is treated as diffuse, and a dynamic equation for the phase variable is introduced in addition to the equation for heat flow. Thus, there are two coupled partial differential equations for temperature and phase field. In the reported study, an implicit numerical scheme using finite-difference techniques on a uniform mesh is employed to solve both Fourier phase-field equations and non-Fourier (known as damped wave or telegraph) phase-field equations. The latter gurantees a finite speed of propagation for the solidification front. Both Fourier (parabolic) and non-Fourier (hyperbolic) Stefan problems with supercooling are satisfactorily simulated and their solutions compared in the present work.
A Numerical Study of the Development of Convective Motion in a Bottom Heated Square Enclosure Containing Ice and Water
Authors: Oosthuizen P. H.
Published: December 2021

A numerical study of the steady state flow in a square enclosure with two vertical walls which are adiabatic and with two horizontal isothermal walls has been undertaken. The enclosure contains water and the upper wall is maintained at a uniform temperature that is below the freezing point of water while the lower wall is maintained at a uniform temperature that is above the freezing point of water. The upper portion of the enclosure is thus filled with ice and the lower portion is filled with water. The conditions considered in the present study are such there can be significant natural convection in the water and the effect of the density maximum that exists in the water at approximately 4°C can have a significant effect on this flow. The main aim of the study was to determine how far above 4°C the hot wall temperature can be before significant convective motion develops in the water. The governing equations have been expressed in dimensionless form and solved using a finite element procedure. The effect of the various governing parameters on the mean Nusselt number has mainly been considered and the effect of the lower surface temperature has, in particular, been studied. The results obtained, which indicate that convective motion does not occur until the lower hot wall temperature is well above the maximum density temperature, can be used to determine the actual hot wall temperature at which significant convective motion develops.