bluuebunny/crossref_metadata_2025 huggingface dataset:
Supercritical Speed Stability of an Axially Moving String on an Elastic Foundation
Authors: Parker Robert G.
Published: January 2022

The stability of an axially-moving string supported by a discrete or distributed elastic foundation is examined analytically. Particular attention is directed at the distribution of the critical speeds and identifying divergence instability of the trivial equilibrium. In contrast to the unsupported axially-moving string, the elastically supported string shows considerably different stability behavior. In particular, any elastic foundation (discrete or distributed) leads to multiple critical speeds and a single region of divergence instability above the first critical speed, whereas the unsupported string has one critical speed and is stable at all supercritical speeds. Additionally, the elastically supported string critical speeds are bounded above, and the maximum critical speed is the upper bound of the divergent speed region. The analysis draws on the self-adjoint eigenvalue problem for the critical speeds and a perturbation analysis about the critical speeds. No numerical approximation is required and the identified stability phenomena apply to general elastically supported traveling strings.
Turbulent Heat-Transfer Characteristics in Flow Networks
Authors: Shin Jongmin , Yang Wen-Jei , Wu Chung-Sheng
Published: January 2022

A numerical analysis is performed to investigate turbulent heat-transfer characteristics in flow networks. The Renormalization Group Theory k-ε model is employed to describe turbulent behavior in the flow. A flow network with a higher intersecting angle and a smaller length-to-width ratio yields a higher heat transfer performance, especially in those units with an intersecting angle between 30° and 45°. It is disclosed that the presence of two flow separation zones causes three maxima in the local Nusselt number on the outer walls and a maximum value on the downstream inner wall, resulting in an average heat transfer coefficient much higher than that of a straight channel. A correlation equation similar to the Dittus-Boelter equation is derived to predict the average Nusselt number. This formula can be used in designing a flow network as a heat exchanger.
Heat Transfer in the Confined Impingement of Multiple Air Jets
Authors: Schroeder Vincent P. , Garimella Suresh V.
Published: January 2022

Heat transfer from a discrete heat source to multiple, normally impinging, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with still-developing velocity profiles on to a foil heat source which produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was measured in fine increments over the entire heat source. Experiments were conducted for different jet Reynolds numbers (5000 < Re < 20000), orifice-to-target spacings (0.5 < H/d < 4), and multiple-orifice arrangements. The results are compared to those previously obtained for single air jets. A reduction in orifice-to-target spacing was found to increase the heat transfer coefficient in multiple jets, with this effect being stronger at the higher Reynolds numbers. With a nine-jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet. For a four-jet arrangement, however, each jet was found to have stagnation-region heat transfer coefficients that were comparable to the single-jet values. The effectiveness of single and multiple jets in removing heat from a given heat source is compared at a fixed total flow rate. Correlations are proposed for single and multiple jet impingement heat transfer.
Heat Transfer by a Two-Dimensional Air Jet Impinging Obliquely on a Flat Surface
Authors: Beitelmal Abdlmonem H. , Saad Michel A. , Patel Chandrakant D.
Published: January 2022

An experimental study was performed to determine the effect of the inclination of an impinging two-dimensional air jet on the heat transfer from a uniformly heated flat plate. The impingement surface was a stainless steel plate of the same width as the jet nozzle. Local Nusselt numbers were determined as a function of three parameters: a) inclination angle of the air jet relative to the plate in the range of 90° to 40°, b) nozzle exit-to-plate spacing, z/Dh, in the range of 4 to 12 and c) Reynolds number based on the hydraulic diameter of the slot nozzle in the range of 4049 to 12020. The results are presented in the form of graphs showing the variation of the local Nusselt number as a function of these parameters. The point of maximum heat transfer shifts towards the uphill side of the plate and the maximum Nusselt number decreases from its value at θ = 90° as the inclination angle decreases. The location of the maximum heat transfer region lies between 0 and 3Dh away from the geometrical impinging point and appears to be insensitive to the Reynolds number in the range used in this study. For lower values of inclination angle, the local Nusselt number downstream from the maximum heat transfer point was insensitive to jet exit-to-plate spacing.
Representation of Local Heat Transfer Coefficient for Slot and Radial Jet Reattachment Nozzles
Authors: Narayanan Vinod , Seyed-Yagoobi Jamal , Page Robert H.
Published: January 2022

A scheme to represent local heat transfer data in submerged two-dimensional (slot) and axisymmetric (radial) reattachment jet flows is presented. A characteristic length that relates to the jet path length facilitates the representation of heat transfer results in a proper form. A detailed parametric study of the 0° Slot Jet Reattachment (SJR) nozzle is initially presented. The parameters varied are nozzle to surface spacing, exit opening, and the flow exit Reynolds number. Correlations for the location of peak Nusselt number, and local Nusselt number distribution along the minor axis of the 0° SJR nozzles are provided. The dimensionless scheme is then extended to incorporate the effects of different exit angles. A modified correlation to represent the location of peak local Nusselt number to account for changes due to exit angle is determined. The same length scale is also shown to adequately represent the heat transfer data for a Radial Jet Reattachment (RJR) nozzle.
Modeling of Solid Particle Flows, Heat Transfer, and Mass Transfer in Rotary Kilns
Authors: Yang Lei , Farouk Bakhtier , Boateng Akwasi A.
Published: January 2022

Results from a computational model are presented in this paper for material flow, and heat and mass transfer in a rotary kiln. A kinetic theory based granular flow model has been employed to establish the particle flow field in a two-dimensional plane to predict the rotation induced flow of the solid particles. A pseudo three-dimensional model for heat and mass transfer and kinetics was developed as an extension to one-dimensional models which are usually used to predict thermal or concentration gradients in the bulk bed. To validate the model, limestone calcination is predicted and compared with available experimental data from a pilot kiln.
Kinetic Theory Analysis of Thermal Conductivity in Granular Material Flows
Authors: Hsiau Shu-San
Published: January 2022

The effective thermal conductivity is developed by employing the dense-gas kinetic theory. The free path used in the theory varies with the particle velocity. The analytical results can be used for the whole range of the product of Biot number and Fourier number provided that the Biot number is less than 0.1. For the very small Biot-Fourier numbers, the conductivities are found to increase with the particle diameters and the square root of granular temperatures. For the limit of very large Biot-Fourier numbers, the two effective thermal conductivities are found to be linearly proportional to the granular temperature.
The Concentration of a Spent Liquor in an Experimental Falling Film Evaporator With Plastic Heat Transfer Surfaces
Authors: Hughes D. T. , Bott T. R. , Pratt D. C. F.
Published: January 2022

A low pH spent sulphite liquor with a dissolved solids content of 16% has been experimentally evaporated in a single tube falling film evaporator with a small temperature driving force of 1.4°C. Nylon and polyethylene tubes 4m in length with an internal diameter of 6mm were used in the study.

The measured heat transfer coefficients at the initial concentration of 16wt% solids were in the range 900–1000 W/m2K. At the final concentration at 45 wt% solids the heat transfer coefficients were approximately 250–300 W/m2K.
Stability Analysis of an Evaporating and/or Condensing Thin Liquid Film
Authors: Chai L. H. , Peng X. F. , Ochterbeck J. M.
Published: January 2022

A perturbation analysis of a simplified set of the Navier-Stokes equations was conducted to investigate the transport process of an evaporating and/or condensing thin liquid film. Expression of the wave growth rate was obtained by accounting for the phase transition at the interface and surface tension gradients. Effects of the surface tension gradient and phase transition on the stability were investigated by introducing two dimensionless parameters, the Marangoni number, Ma, and the phase transition number, ζ, respectively. The present investigation also provides several reasonable theoretical explanations of the fundamental characteristics of dropwise and pseudo-dropwise condensation.
Heat Transfer Enhancement With Falling Film Evaporation on Vertical Tubes Using Electric Fields
Authors: Darabi Jafar , Ohadi Michael M. , Dessiatoun Serguie V.
Published: January 2022

The objective of this work is to characterize the phenomena and to identify the feasibility of the EHD technique for falling film evaporation on geometries of practical significance to industrial chillers. Single-tube experiments are conducted with refrigerants R-123 and R-134a on the outside of three commercially available vertical, electrically heated tubes. Tests are conducted with a 19 mm (3.4″) smooth tube, a 19 fpi tube, and a Turbo BIII tube. The effect of heat flux, refrigerant mass flow rate, and applied potential are investigated. Up to a 7 fold enhancement in heat transfer coefficient with R-123 and 2.1 fold with R-134a are documented. EHD power consumption in all cases is less than 0.15% of the total energy exchange rate in the test section.
Two-Dimensional Transient Analysis of Absorbing Thin Film in Laser Treatments
Authors: Bianco Nicola , Manca Oronzio
Published: January 2022

Conjugate optical-conductive analysis is of main importance in thin film processing applications. Several studies have been carried out by making use of the one-dimensional model. In this paper the transient conjugate conductive-radiative field has been solved in the hypothesis of one-dimensionality of the optical field and of two-dimensionality of the thermal field. Results have been obtained with the matrix method for the optical field and the finite volume method for the thermal field. The results show that when the investigation is localized to the center of the spot, the one-dimensional model describes the thermal field quite well. Instead, if knowledge of the temperature is required elsewhere the two-dimensional model is needed. The investigation herein presented shows that for low-conductivity materials (a – Si) the temperature peaks are placed inside the thin film for the absorption function distribution, determined by interference phenomena. For higher-diffusivity materials (c – Si), both the thermal gradient components are of the same order of magnitude. The laser irradiation wavelength is 1.064 μm for a – Si and 0.532 μm for c – Si.
Directional Spectral Emittance of a Packed Bed: Correlation of Theoretical Prediction and Experimental Data
Authors: Lopes Rogério , Moura Luís M. , Baillis Dominique , Sacadura Jean-François
Published: January 2022

Directional spectral emittance of absorbing and scattering isotherm packed spheres system is predicted by a radiative model based on the discrete ordinates method associated with the control volume technique to solve the radiative transfer equation. Radiative properties for the packed opaque spheres bed are computed by the large size parameter factor scaling model. This model requires the knowledge of several parameters. Particle diameter and porosity can be easily obtained, but particle hemispherical spectral reflectivity is very difficult to obtain directly. It is determined by an identification method (Gauss method of linearization) applied to bidirectional spectral reflectance data obtained from an experimental device using a Fourier transform infrared spectrometer. Results obtained from this approach are consistent. Directional spectral emittance of absorbing and scattering isotherm packed spheres system is predicted using a radiative model based on the discrete ordinates method to solve the radiative transfer equation. Directional spectral emittance is measured using a direct radiometric technique which has been recently proposed. A good agreement is observed between experimental results of directional spectral emittance packed opaque spheres system at high temperature and theoretical data computed.
Foundations of Thermal-Fluid Sciences: An Introductory Sophomore Course for Mechanical Engineering Majors
Authors: Gaddis J. L. , Ochterbeck J. M.
Published: January 2022

As part of an overall revision of the mechanical engineering curriculum at Clemson University, a new introductory course in thermal-fluid sciences was developed.1 This course is situated in the second semester, sophomore year for mechanical engineering majors, and is a prerequisite for the junior-level courses in thermodynamics and fluid mechanics. The new course introduces the mass, momentum, and energy conservation laws in addition to defining work and heat and use of thermodynamic properties. Included in the paper is information on the new curriculum, motivation for new course and sequence, decisions interacting with the curriculum, implementation of textbooks, and early results.
Towards an Integrated Thermal/Fluids Engineering Curriculum
Authors: Jensen Michael K. , Smith Richard N. , Kaminski Deborah A. , Hirsa Amir
Published: January 2022

We present a new approach to teaching the core thermal/fluids curriculum for undergraduate programs in engineering. Traditional thermodynamics, fluid mechanics, and heat transfer classes are being replaced with two integrated courses and a laboratory in which the three disciplines are taught simultaneously to show interconnections and transferability of concepts and ideas, with an emphasis on the way they occur in engineering practice. This approach seeks to improve both the context and manner in which the subject matter is covered. Our goals are to enhance the physical intuition of our students, to stimulate their ability to think critically and synthesize information, and to make clearer the relevance of the fundamentals to advanced analytical and computational tools.
An Integrated Thermal Science Course for Third-Year Mechanical Engineering Students
Authors: Noymer Peter D. , Hazen Megan U. , Yao S. C.
Published: January 2022

A new course in the thermal science discipline was introduced in 1998 in the Mechanical Engineering Department at Carnegie Mellon University. The course was titled “Thermal Fluids Engineering” and some of the specific aims were to integrate and extend the students’ knowledge in the areas of heat transfer, thermodynamics and fluid mechanics and provide better preparation for their post-graduate endeavors. The development of this course was part of a larger curriculum re-design within both the Mechanical Engineering Department and the College of Engineering at Carnegie Mellon.

The course was offered to students in the second semester of their third year, after they have taken thermodynamics, fluid mechanics and heat transfer in each of the previous three semesters. In addition to integrating the three basic thermal science disciplines, other novel aspects of this course included: a series of computational assignments in which finite-element models were applied to solve conjugate heat transfer problems; a series of laboratory experiments, one of which was used as the basis for the computational assignments; and a series of in-class “case studies” in which the students applied their integrated knowledge to the design and analysis of a complex system. Feedback from the students indicated that the integration aspect of the course was successful although there was still room for improvement in the structure and presentation of the material.
Electro-Hydrodynamic Augmentation of Heat Transport in Micro Heat Pipe Arrays
Authors: Hallinan Kevin P. , Bhagat Wilber , Kashaboina Balamurali , Kashani A. Reza
Published: January 2022

Research is reported on a novel use of electrostatic fields to both enhance the effectiveness of heat transport and the maximum heat transfer throughput of micro heat pipe devices. This research has sought to make practical the electro-hydrodynamic heat pipe concept proposed by T. Jones in the early 1970s, but which never was successfully developed at macroscales.

Experiments are reported which conclusively demonstrate the viability of using electrostatic fields to augment heat transfer in micro heat pipe devices. An n-pentane filled glass heat pipe array comprised of 1mm width grooves having 1mm of ‘land’ between each groove was fabricated from quartz. The heat pipe array was 25.4 mm long. Gold-palladium electrodes, approximately 100 microns in thickness, were vapor deposited on both sides of the heat pipe to allow for the application of an electrostatic field across the grooves of up to 10 kV/mm. The electrodes were semi-transparent, thereby permitting visual observation of the liquid orientation within the micro heat pipe. For a majority of experiments, however, the micro heat pipes were contained in an insulated enclosure.

The experiments indicated little difference in the micro heat pipe temperature at low heat inputs (less than 0.3 W/groove). At heat inputs sufficient to cause the onset of dry-out of the evaporator without application of the electric field, the presence of the electric field was noticeable in producing a more uniform micro heat pipe temperature and a relatively lower evaporator temperature. At increasing heat inputs, the presence of the electric field was shown to prevent evaporator dry-out for the heat inputs considered. Further, at heat inputs sufficient to cause dry-out of the evaporator without an applied electric field, the electric field contributed to an increasing heat transfer effectiveness in the evaporator as the heat input was increased.
Flow Profile Simulation of Heated Copper Films on Substrates With Micro-Trenches
Authors: Hirasawa Shigeki , Saito Yoko , Saito Tatsuyuki , Yamaguchi Hizuru
Published: January 2022

It is important that copper films fill the sub-micron trenches on silicon substrates in order to produce high-density electronic devices. In this paper, changes of the copper film profiles in trenches on silicon substrates during the reflow process were numerically calculated by 2- and 3-dimensional analyses. Calculation results from a model of atomic surface diffusion in a thin layer on the film were similar to experimental results. The relationship between the change of the film profile and the geometric parameters was determined. The results show that a uniform and thick initial film on the side walls of a trench is important to avoid film-bridge and void formation in the trench. In order to increase flow rate into the trenches, narrow trenches with a thick initial film on the bottom of the trench are effective.
Technique for Measuring Surface Temperature Fluctuations on a Silicon Wafer During Boiling
Authors: Kim Jungho , Whitten Matthew , Quine Richard W. , Kalkur T. S.
Published: January 2022

A method of measuring temperature fluctuations on a silicon wafer during boiling is described. The technique consists of building an array of diodes on a silicon wafer using VLSI techniques, and exploiting the fact that the forward voltage drop across a silicon diode typically is approximately proportional to the inverse of the absolute temperature of the diode. Once a calibration of voltage drop vs. temperature is obtained, the temperature of each diode can be obtained by scanning across the diode array. A 32 × 32 array of diodes (1024 diodes) has been built. Each diode in the array is nominally 100 μm × 100 μm in size. A circuit capable of scanning this diode array at speeds up to 2.5 MHz was also designed, built, and tested. The entire array can be sampled at speeds up to about 2.5 kHz. Construction of the diode array, the circuit, and some preliminary results are described.
Coupled Liquid and Vapor Flow in Miniature Passages With Micro Grooves
Authors: Khrustalev Dmitry , Faghri Amir
Published: January 2022

Friction factor coefficients for liquid flow in a rectangular microgroove coupled with the vapor flow in a vapor channel of a miniature two-phase device were calculated using finite element analysis. The results show that the effect of the vapor-liquid frictional interaction on the liquid flow decreases with curvature of the liquid-vapor interface. Shear stresses at the liquid-vapor interface are significantly non-uniform, decreasing towards the center of the liquid-vapor meniscus.
Effectiveness of Open-Cell Metallic Foams for High Power Electronic Cooling
Authors: Bastawros Ashraf-F.
Published: January 2022

The effectiveness of metallic foams in forced convection heat removal is studied. The metallic foam showed an improved heat removal rate with a moderate increase in the pressure drop. The hydraulic and thermal characteristics are analyzed experimentally. The measurements are used in conjunction with a model based on a bank of cylinders in cross-flow to understand the effect of various foam morphologies. The model prediction is extrapolated to examine the trade-off between heat removal and pressure drop. For a particular working fluid, the model provides two sets of design parameters; (i) a preferred foam morphology which will provide the required heat flux at a competitive pressure drop and (ii) the circulating fan characteristics as an output flow rate vs. the static pressure drop.
Design Analysis of the Stirling Engine Using an Equation Solver
Authors: Farley Jove S. , Ibrahim Osama M.
Published: January 2022

A typical undergraduate course in thermal-fluids design sees the unfolding of important concepts in heat transfer, thermodynamics, and fluid mechanics and associated governing laws. Unfortunately, up until the recent past students have largely been asked to study fundamental, but often elusive, topics in these areas by means of simplified problems mostly resulting in the solution of elementary sets of algebraic equations. More complex problems involving higher order equations and ordinary differential equations are left unexamined, due mostly to the time consumption and difficulty level of programming, which may detract from the scope of the class.

Fortunately, there now exists prewritten software (i.e. EES, Matlab, Mathematica, etc.) which numerically allows students to solve more challenging problems with relative ease. Thus allowing thermal-fluids design courses to focus on more challenging projects.

This paper illustrates the use of a program, written for an equation solving software package that solves the ordinary differential equations governing the processes of the Stirling engine. Stirling engines, their history and present applications along with the methods EES software uses to allow for the engine’s study is briefly described. A step by step development of the general equations concerning mass, energy, entropy balances, and the Nusselt number for approximating the heat transfer coefficient is given and discussed. Results are shown through plotting numerical solutions of various points of interest. Lastly, a list of the program’s equations will be supplied in an appendix at the end of the paper.
Field Test of a Drag-Reducing Surfactant Additive in the Hydronic Cooling System of a Building: Phase 2 — Heat Transfer Control
Authors: Gasljevic K. , Hoyer K. , Matthys E. F.
Published: January 2022

A field test was conducted recently in the hydronic cooling system of a medium-size building. This test was the second phase of a study of the possible use of drag-reducing additives in hydronic systems for pumping power reduction. In the first phase of the field test we measured how much pumping power savings was achievable in this system, regardless of heat transfer reduction in the heat exchangers. We measured about 30% of pumping power savings. The recent second phase of the field test work had a different goal, namely to ascertain whether it is possible to control or eliminate the heat transfer reduction in the heat exchangers. This is an important issue because a loss in heat transfer capacity would lead to reduced chiller efficiency and therefore reduced net energy savings. We did indeed show in the second test that the use of an improved non-ionic surfactant did in fact allow us to control fully the heat transfer in the heat exchangers (both evaporator and cooling coils) by means of intentional temporary degradation of the drag-reducing properties of the solution. Even with full elimination of heat transfer reduction, we still achieved an overall 12% (limited by the small size and the configuration of the system) in pumping power savings, with no measurable effect on the heat transfer capacity of the evaporator or on the compressor power, even at full load. Furthermore, it was possible to eliminate the heat transfer reduction by degradation induced by components already existing in the system (pump and control valves). These issues and other aspects of the test strategy, implementation, and measurements are described.
Computer Simulation of the Thermal Performance of a Parallel/Countercurrent Flow Heat Exchanger for Patient Thermal Comfort in Medical Applications
Authors: Moujaes Samir , Oliver Dana
Published: January 2022

A computer simulation is proposed for a specialized heat exchanger used in the medical field which provides thermal comfort to potentially hypothermic patients whose bodies can provide a very limited amount of body heat. The model describes the thermal performance of the heat exchanger using a one-dimensional finite difference technique and solving a two-point boundary value problem to obtain the solution. It was found that the model predicts the thermal performance of the heat exchanger quantitatively when compared with the experimental data provided. The errors in predicting the difference between infusate inlet and outlet temperatures experimentally and theoretically were within 10% of experimental values and it is concluded that the program can be used for future design purposes.
Direct Numerical Simulation of a Coolant Jet in a Periodic Crossflow
Authors: Sharma Chirdeep , Acharya Sumanta
Published: January 2022

A Direct Numerical Simulation of a coolant jet injected normally into a periodic crossflow is presented. The physical situation simulated represents a periodic module in a coolant hole array with a heated crossflow. A collocated finite difference scheme is used which is fifth-order accurate spatially and second-order accurate temporally. The scheme is based on a fractional step approach and requires the solution of a pressure-Poisson equation. The simulations are obtained for a blowing ratio of 0.25 and a channel Reynolds number of 5600. The simulations reveal the dynamics of several large scale structures including the Counter-rotating Vortex Pair (CVP), the horse-shoe vortex, the shear layer vortex, the wall vortex and the wake vortex. The origins and the interactions of these vortical structures are identified and explored. Also presented are the turbulence statistics and how they relate to the flow structures.
A Study of Film Cooling Injection Geometries: Measured Flow and Thermal Fields With Lateral, Compound and In-Line Injection
Authors: Oke Rohit A. , Simon Terrence W.
Published: January 2022

Temperature field measurements taken with a traversing thermocouple are presented for compound angle injection with Φ = 45°. These are compared with data from lateral injection, Φ = 90°, and in-line injection, Φ = 0, cases. Near-wall values of these measurements, which are adiabatic effectiveness values, η, show the effect of Φ on film cooling performance. Complementary velocity field measurements, including streamwise and cross-stream velocity components, taken with triple-wire anemometry, are also presented for compound angle injection. These are compared with similar data for lateral and in-line injection cases presented in the literature. The main feature of the flow pattern with compound angle injection is the presence of an asymmetrical pair of counter-rotating vortices of unequal strength, the nature of which depends on the ratio of the momentum flux of the coolant and the mainstream and the injection angle, Φ. For compound angle injection, the stronger vortex appears to draw free stream fluid towards the wall, as with lateral injection, but to a lesser degree. Triple-sensor anemometry measurements also yield turbulent Reynolds stress distributions which allow discussion of anisotropy of turbulent transport. Eddy diffusion in cases of isotropic turbulence would follow the gradient diffusion model in which the shear stress vectors are perpendicular to the velocity gradients. Due to anisotropy, this is not the case over most of the flow field, however.
Running a Small Gas Turbine With and Without a Recuperator: Comparisons of Efficiency at Various Loads
Authors: Rosén Per , von Heiroth Paul , Lindquist Torbjörn
Published: January 2022

An advanced integrated humidification gas turbine process based on an Evaporative Gas Turbine cycle (EvGT), is being built at Lund University in Sweden. The pilot plant is based upon a new 600 kW gas turbine engine. The building of the complete cycle is done in steps, the first step is to run and record measurements from the simple open gas turbine cycle. The next step is to add a compact heat exchanger, a recuperator, to the process and repeat the measurements. This enables an evaluation of the performance of the recuperator in the gas turbine cycle. The result of this comparison is that the efficiency increase is lower than predicted in an earlier stage due to large heat losses of the inner cone extension of the combustion chamber and also because a large amount of compressed air is being used as dilution air just before the expansion take place in the expander.
Enhancing Small-Channel Convective Boiling Performance Using a Microporous Surface Coating
Authors: Ammerman C. N. , You S. M.
Published: January 2022

Performance characteristics are experimentally determined for enhanced convective boiling of FC-87 in horizontal, small-cross-sectional-area, single-channel heaters. Two different channels are tested which have square cross sections with side lengths of 2 and 0.5 mm, respectively. Each of the channels are 8 cm in length. The heated surface of each of the two channels is tested both with, and without, a microporous surface coating. Although few studies have been performed to quantify the effects of internal porous coatings on flow boiling, their application in this area is promising. The coating is shown to provide increases in both heat transfer coefficient and critical heat flux. Convective boiling curves are generated for mass fluxes from 500 to 5000 kg/m2s and for inlet subcooling levels ranging from 2 to 31°C.
A Stagnation Flow Analysis of Keyhole Formation in Laser Drilling
Authors: Batteh John J. , Chen Michael M. , Mazumder Jyoti
Published: January 2022

This paper presents a quasi-steady stagnation flow analysis for keyhole initiation processes in high intensity laser materials processing, such as laser drilling. The governing stagnation flow equations are normalized, and the important problem parameters are identified. The simple model accounts for conduction in the solid, conduction and convection in the melt layer, and the latent heats of melting and vaporization. The stagnation flow governing equations and boundary conditions are appropriately normalized and solved, and the important combinations of material properties and independent laser parameters are identified. This semi-quantitative analysis yields quasi-steady estimates for the penetration velocity, the thickness of the melt layer, the velocity profiles in the melt layer, and the fraction of melt that is vaporized for varying absorbed laser power and beam radii. Results from inviscid stagnation flow analyses are shown and compared for four different materials: aluminum, low carbon steel, stainless steel, and titanium.
A Fuzzy-Neural Controller for Film Extruding Processes
Authors: Andersh Jonathan , Axelrod Anthony , Stachowicz Marian
Published: January 2022

This paper presents a new method for controlling thickness in film extruding processes. The proposed architecture uses fuzzy logic and neural network techniques to achieve a MIMO controller that accounts for strong interactions between the thickness in different lanes and for the time delay between the actuators and the sensor. Experimental results demonstrate the performance of the controller.
An Approximate Analysis of the Melt Flow and Heat Transfer in Deep Penetration Laser Welding
Authors: Bos Jeannine A. , Chen Michael M.
Published: January 2022

Deep penetration welding, also called Keyhole welding, is one of the most interesting flow and heat transfer phenomena in laser welding. Once a threshold power density is reached a small diameter vapor cavity, which is characteristic of keyhole welding, is formed. Understanding the fundamental aspects of deep penetration welding will aid in the design and control of welding processes. Of particular interest is the prediction of penetration depths given certain process parameters such as material velocity and laser power.

The present investigation focuses attention on the lower portion of the keyhole where the essential features of the flow are primarily two-dimensional in the plane perpendicular to the axis of the laser. Further it is proposed that by focusing on the stagnation region an approximate solution can be obtained which would capture the essential features of the problem for large Peclet numbers. This work can later be used as a basis for more exact methods of solving the Navier-Stokes equations.
Modeling of Powder Particle Heating, Melting and Evaporation in Plasma Spraying Processes
Authors: Wan Y. P. , Prasad V. , Wang G.-X. , Sampath S. , Fincke J. R.
Published: January 2022

A comprehensive model is developed to study the heating, melting and evaporation of powder particles in plasma flames. The well-established LAVA code, a CFD software specially designed for plasma flame simulation, is used to predict the plasma gas field under given power conditions, and provide inputs to the particle model. The particle is assumed to be spherical and one-dimensional heat conduction equation with phase change within the particle is solved numerically using an appropriate coordinate transformation and finite difference method. Melting and vaporization interfaces are tracked and the particle vaporization is accounted for by the mass diffusion of vapor through the boundary layer around the particle. The model also takes into account of both the convective and radiative heat transfer between the particle and the plasma. The effect of mass transfer on convective heat transfer is also included. Calculations have been carried out for a single particle injected into an Ar-H2 plasma jet from outside the DC-plasma gun. Zirconia and nickel are selected as solid particles because of their widespread industrial applications as well as the apparent difference in their thermal properties. Numerical results show strong non-isothermal effect of heating, especially for materials with low thermal conductivity, such as Zirconia. The model also predicts strong evaporation of the material at high temperatures. A parametric study has been performed to examine the physical mechanisms of particle melting and evaporation in plasma and the effect of vaporization on convective heat transfer.
Heat Transfer Enhancement by Fins in the Microscale Regime
Authors: Chou Fu-Chu , Lukes Jennifer R. , Tien Chang-Lin
Published: January 2022

The current literature contains many studies of microchannel and micro-pin-fin heat exchangers, but none of them considers the size effect on the thermal conductivity of channel and fin walls. The present study analyzes the effect of size (i.e., the microscale effect) on the microfin performance, particularly in the cryogenic region where the microscale effect is often appreciable. Due to the size effect, the thermal conductivity of microchannel and microfin walls is reduced, so is the heat transfer rate. The heat transfer enhancement becomes even more important. This study resolves three basic issues. First, it is found that the heat flow choking can occur even in the case of simple plate fins or pin fins in the microscale regime, although choking is usually caused by the accommodation of a cluster of fins at the fin tip. Second, this paper shows that the use of micro-plate-fin arrays yields a higher heat transfer enhancement ratio than the use of the micro-pin-fin arrays due to the stronger reduction of thermal conductivity in micro-pin-fins. The third issue is how the size effect influences the fin thickness optimization. For convenience in design applications, an equation for the optimum fin thickness is established which generalizes the case without the size effect as first reported by Tuckerman and Pease.
Anisotropic Thermal Conductivity of Si/SiGe Superlattice
Authors: Zhou S. Q. , Chen G. , Liu J. L. , Zheng X. Y. , Wang K. L.
Published: January 2022

Recent experimental and theoretical studies demonstrate that the thermal conductivity of superlattices can be significantly reduced due to the interface phonon scattering. These studies raise the interesting possibility of phonon engineering to control the thermal conductivity of nanostructures for thermoelectric, thermionic, and microelectronic applications. Experimental evidences of a significant thermal conductivity reduction have been reported for GaAs/AlAs, Si/Ge, and Bi2Te3/Sb2Te3 superlattices. In this work, we present experimental results on the anisotropic thermal conductivity of a Si/Si0.71Ge0.29 (50Å/10Å) superlattice measured by a 2-wire 3ω method. The experimental results show that both the cross-plane and the in-plane thermal conductivities of the Si/Si0.71Ge0.29 superlattice are reduced by a factor of three compared to the predictions of the Fourier heat conduction theory. These reductions are not as large as that observed in pure Si/Ge superlattices of comparable thickness, which can be explained by the smaller mismatch in material properties between Si and Si0.71Ge0.29 than those between Si and Ge. This work provides preliminary experimental evidence supporting the idea of controlling the thermophysical properties of low-dimensional structures through phonon engineering.
Grain Growth Following Recrystallization in Reactive Spray Deposited Al-Mg-Mn Alloys
Authors: Dai Shenlong L. , Delplanque Jean-Pierre , Lavernia Enrique J.
Published: January 2022

This paper focuses on the quantitative investigation of grain growth at 500, 530, and 560 °C in reactive spray deposited Al-Mg-Mn alloys after thermo-mechanical processing and recrystallization. Results show that reactive spray deposited 5083 alloy processed using N2-5%O2, in which no significant volume fraction of oxide particles was found, experienced significant grain growth when annealed at 500, 530 and 560°C following recrystallization. On the other hand, the reactive spray deposited 5083 alloy atomized with N2-10% O2 and the 5083+Zr alloy atomized with N2-5% O2 exhibit very slow grain growth below 530°C and limited grain growth at 560°C. This behavior is attributed to the retardation effect of the second phase particles that were formed in these alloys. The grain growth exponent of the two alloys are found to depend on the annealing temperature, with a value of n = 6 at 530°C and n = 5 at 560°C. The retardation effect of the oxide particle and the grain growth kinetics are analyzed in the context of the model developed by Anderson and Grong (Acta Met., 43:2678, 1995).
An Eulerian-Lagrangian Front Tracking Method for Immersed Boundaries
Authors: Udaykumar H. S. , Mittal R. , Shyy Wei
Published: January 2022

In tracking moving boundaries that arise in several flow problems, a mixed Eulerian-Lagrangian algorithm can prove quite useful. In such a method, the grid on which the flow computations are performed remains stationary, while the interface is immersed in and moves through the grid. In this report we present a finite-difference based formulation for a scalar transport equation, which will be designed to alleviate some of the concerns associated with interface tracking on a fixed underlying grid. By performing truncation error analysis, the presentation of the method also sheds light on the expected accuracy of the solutions. The finite-difference operations are performed to maintain nominal global second-order accuracy. To demonstrate the second-order accuracy of the solutions, we present grid refinement studies preformed for some test problems.
Utilization of Sensitivity Coefficients to Guide the Design of a Thermal Battery
Authors: Blackwell Ben F. , Dowding Kevin J. , Cochran Robert J. , Dobranich Dean
Published: January 2022

Equations are presented to describe the sensitivity of the temperature field in a heat conducting body to changes in the volumetric heat source and volumetric heat capacity. These sensitivity equations, along with others not presented, are applied to a thermal battery problem to compute the sensitivity of the temperature field to 19 model input parameters. Sensitivity coefficients, along with assumed standard deviation in these parameters, are used to estimate the uncertainty in the temperature prediction. From the 19 parameters investigated, the battery cell heat source and volumetric heat capacity were clearly identified as being the major contributors to the overall uncertainty in the temperature predictions. The predicted operational life of the thermal battery was shown to be very sensitive to uncertainty in these parameters.
Determination of Interfacial Heat Fluxes During Casting of Aluminum in Resin-Bonded Sand Molds
Authors: Woodbury Keith A. , Chen Yuhui , Ke Quanpeng
Published: January 2022

This paper presents the results from an experiment to determine the heat transfer from aluminum castings during solidification. An aluminum plate (alloy A356 600 mm by 600 mm) was cast in two different thicknesses (6.25 mm and 25 mm) in a horizontal configuration. An inverse analysis, using a sequential function specification method, was used to compute the surface fluxes from the solidifying metal to the mold. The inverse analysis accounted for temperature-dependent thermal properties of the mold sand. Special attention is devoted in this paper to selection of the appropriate value of regularization parameter and suitable error estimation for thermal experiments utilizing measurements from off-the-shelf thermocouples in an inverse estimation procedure.
Numerical Estimation of Heat Transfer and Thermal Stresses in Water Cooling of Shipbuilding Profiles
Authors: Sørli Karstein , Olden Vigdis
Published: January 2022

In this paper a numerical procedure for estimation of heat transfer coefficients based on temperature measurements during the cooling of ship building profiles is described. Results on running a software implementation of the procedure for selected time series of laboratory measurements are presented. The paper also includes computational results of thermal stresses based on the established heat transfer coefficients.
Electrical Capacitance Tomography of Horizontal Two-Phase Flow
Authors: Moura Luiz F. M. , Tambellini Flavio , Belo Francisco A.
Published: January 2022

This paper describes an electrical capacitance tomography (ECT) system for imaging of two-phase flows. The capacitance sensor was built with eight electrodes around an insulating pipe. In the proposed capacitance measurement system, when an electrode is an emitter, the seven other electrodes are receivers, leading to a parallel reading tomography type. For a 8-electrode sensor, there are 28 independent readings. In order to improve the measurement system time response, a new electronic transducer was developed that supports excitation frequency up to 16 MHz. The proposed ECT system was tested for stratified air-water flows, with void fraction ranging from 0.1 to 0.9. A linear back projection algorithm was used to reconstruct the cross section image of the two-phase flow from the measured capacitance values. The reconstructed flow images obtained using this algorithm were compared to the real two-phase distributions. Filtering techniques were applied to the back projection algorithm in order to improve the reconstructed flow image quality. Limitations and possible future improvements of this technique are also discussed.
Characteristics of the Liquid Slug and the Taylor Bubble in a Vertical Slug Flow
Authors: Pedroso Daniel C. , França Fernando A. , Rosa Eugenio S.
Published: January 2022

Measurements in vertical upward concurrent slug flows are presented. The experiments, carried with mixtures of air and water and a viscous aqueous solution, were aimed to the characterization of the structures that form the slug flow. Double-wire conductive probes were carefully designed and calibrated to identify and to measure the slug flow and the structures that constitute the so-called slug-cell model. The variables measured were: the frequency of the slug-cell, the length of the liquid slug, the velocity and the length of the elongated bubble, the thickness of the liquid film surrounding the elongated bubble and the void fraction in the liquid slug. Comparisons between these measured quantities and results of correlation frequently adopted in the literature are presented and discussed.
Flow Regimes and Equations for Predicting Capsule Flow Through Pipe
Authors: Liu Henry , Gao Xiang , Xu Wenwei
Published: January 2022

The motion of cylindrical capsules in pipe can be classified into four regimes. The characteristics of each regime are described and analyzed in this paper. In each of the four regimes, the pressure drop across a capsule or capsule train (comprising a number of capsules with zero spacing or very small spacing between neighboring capsules) can be predicted by using the one-dimensional energy, momentum and continuity equations with proper consideration for the headloss including entrance and exit effects. The effect of eccentric annulus is taken into account. In predicting the capsule velocity, equations are derived by applying the overall force balance to both the capsule train and the annular flow surrounding the capsule train. Comparison with experimental data shows the incipient velocity, the capsule velocity, and the drag coefficient can be determined accurately from the theory.
Annular Flow of R-134A in a Vertical Duct: Local Void Fraction, Droplet Velocity and Droplet Size Measurements
Authors: Trabold Thomas A. , Kumar Ranganathan , Vassallo Peter F.
Published: January 2022

Local measurements were made in annular flow of R-134a through a high aspect ratio vertical duct. Using a gamma densitometer, hot-film anemometer and laser Doppler velocimeter, profiles of void fraction, liquid droplet frequency and droplet velocity were acquired across the narrow test section dimension. Based upon these results, data for liquid droplet size were obtained and compared to previous experimental results from the literature. These data are useful for developing an improved understanding of practical two-phase refrigerant flows, and for assessment of advanced two-fluid computer codes.