bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated Undergraduate, Graduate, and Professional Student (Distance Learning) Education in Thermal Systems Design
Authors: Garimella Srinivas
Published: November 2021

This paper describes an educational program in practical thermal systems design that encompasses design project-oriented teaching of undergraduate, graduate and off-campus professional students, industry-university collaboration, and community outreach. The program uses an integrated approach that treats thermodynamics, fluid mechanics, and heat transfer as parts of one interconnected area, in which solutions to real-life design problems can be obtained only when all these aspects are considered simultaneously. Cooperation between students at various stages of their educational and professional careers is fostered to maximize the synergy that results from combining insights gained in industry and those developed in structured classroom instruction.

The program consists of a comprehensive portfolio of Thermal Systems Design Instruction Initiatives. An interactive design laboratory format is used for cooperative execution of open-ended mini-projects spanning two-to-three weeks, and a semester-long project. The use of virtual project groups through the web removes geographical barriers. Computer programs for the solution of projects are placed on-line to create a design library for use by students in future semesters as case studies. An Energy-Efficient Environmentally-Safe Design Studio is planned where projects on environmental responsibility, and energy efficiency can be conducted for the local community. Annual design studio conferences will be held to foster K-12 and community involvement, and to demonstrate sustainable technologies. Collaboration with local thermal systems related organizations such as the Iowa Energy Center is also being pursued, which will provide inherent mechanisms for technology transfer from course-related projects to industry and the community.
Convective Heat Transfer in Micro and Nano Channels: Nusselt Number Beyond Slip Flow
Authors: Hadjiconstantinou Nicolas G.
Published: November 2021

We present calculations of the constant-wall-heat-flux Nusselt number for fully developed transition flow in two-dimensional microchannels. The Nusselt number cannot be obtained by a continuum analysis since the continuum description breaks down in the transition regime. We have used a molecular simulation technique known as the direct simulation Monte Carlo (DSMC). DSMC is a stochastic simulation technique previously shown to capture the hydrodynamic behavior of hard sphere gases. A wide range of Knudsen numbers is investigated: a channel height range of approximately 50 is analyzed starting from the micrometer scale that corresponds to slip flow. The channels have a length/height ratio of 20 to ensure fully developed flow, and care was taken to ensure that the Brinkman number is always small. The Nusselt number is found to decrease with increasing rarefaction (Knudsen number). The effects of thermal creep are discussed.
Mixed Convection Adjacent to 3-D Backward-Facing Step
Authors: Li A. , Armaly B. F.
Published: November 2021

Results from three-dimensional numerical simulation of laminar, buoyancy assisting, mixed convection airflow adjacent to a backward-facing step in a vertical rectangular duct are presented. The Reynolds number, and duct geometry were kept constant at Re = 200, AR = 8, ER = 2, and S = 1 cm. Heat flux at the wall downstream from the step was kept uniform, but its magnitude was varied to cover a Grashof number (Gr) range between 0.0 to 4000. All the other walls in the duct were kept at adiabatic condition. The flow, upstream of the step, is treated as fully developed and isothermal. The relatively small aspect ratio of the channel is selected specifically to focus on the developments of the three-dimensional mixed convection flow in the separated and reattached flow regions downstream from the step. The presented results focus on the effects of increasing the buoyancy force, by increasing the uniform wall heat flux, on the three-dimensional flow and heat transfer characteristics. The flow and thermal fields are symmetric about the duct’s centerline. Vortex generated near the sidewall, is the major contributor to the three dimensional behavior in the flow domain, and that feature increases as the Grashof number increases. Increasing the Grashof number results in an increase in the Nusselt number, the size of the secondary recirculating flow region, the size of the sidewall vortex, and the spanwise flow from the sidewall toward the center of the channel. On the other hand, the size of the primary reattachment region decreases with increasing the Grashof number. That region lifts away and partially detaches from the downstream wall at high Grashof number flow. The maximum Nusselt number occurs near the sidewalls and not at the center of the channel. The effects of the buoyancy force on the distributions of the three-velocity components, temperature, reattachment region, friction coefficient, and Nusselt number are presented, and compared with 2-D results.
Radiation Effects on Natural Convection Between Horizontal Walls With Heated Upper Plate
Authors: Guidotti Giuseppe , Manca Oronzio , Nardini Sergio , Morrone Biagio
Published: November 2021

Radiation heat transfer affects natural convection of air inside an open ended cavity with a heated horizontal upper plate and an unheated lower parallel plate. The influence is mainly due to radiative heating of the lower plate, and plane fluid layer secondary motion could arise. In this paper an experimental study is carried out to describe and to detect the influence of radiation on air flow and on heat transfer coefficient by means of wall temperature profiles, smoke visualization, and air temperature measurements. The analysis is obtained for an emissivity of the horizontal plates equal to 0.8, for distances between the plates of 20.0, 32.3, and 40.0 mm. By means of flow visualization and local air temperature measurements in the cavity as a function of time, remarkable secondary motion in the cavity is observed when qΩ is equal to 120 W/m2. Measurement of the air temperature in the cavity also shows that radiation causes and damps secondary motion at the same time. Profiles of the mean value of the air temperature as a function of the x and y coordinates confirm both the main flow path inside the cavity and radiation effects on convective heat transfer. Finally, correlations related to average Nusselt number are proposed for natural convection as well as for heat transfer as a whole, that is convection along with radiation.
Motion of Liquid Drops on an Inclined Solid Surface
Authors: Kim H.-Y. , Lee H. J. , Kang B. H.
Published: November 2021

The shape and motion of sliding drops on an inclined plane have been studied experimentally. In the experiments, various volumes of water, ink, ethylene glycol, and glycerin drops are placed on solid surfaces and the substrate is tilted to record the motion of the drops. A scaling law is provided to predict the steady-state velocity of the drop. It is shown that Poiseulle flow analysis cannot describe the steady-state motion of a drop. Instead, much stronger dissipation arising near the contact line is shown to play a major role in determining the speed of the drop. The scaling analysis agrees with experimental results using highly viscous liquid drops of ethylene glycol and glycerin. On the other hand, relatively inviscid drops of water and ink more slowly before abruptly accelerating to a high speed. This suggests that there exist two jumps in the dynamic state of those drops, one corresponding to initiation of movement and the other to a subsequent transition to a steady motion.
An Investigation of Microscale Explosive Vaporization of Water on an Ultrathin PT-Wire
Authors: Glod S. , Poulikakos D. , Zhao Z. , Yadigaroglu G.
Published: November 2021

The present study investigates at the microscale level the explosive vaporization of water close to its superheat limit. In the course of the research, it was possible to obtain simultaneously unique results of visualization, temperature and pressure of the vapor microregion, thus accomplishing a marked step forward in understanding the complex behavior of explosive vapor nucleation growth and subsequent collapse, despite the very small time and length scales of the phenomena of interest. To this end, a short (1 mm in length) and ultrathin (10 μm in diameter) Pt-wire is very rapidly heated by imposing a short and intense current pulse. Deionized and degassed water in contact with the wire is, as a consequence, also rapidly heated during the time of application of the current (in the range of 6 to 50 μs) and vaporizes explosively.

For the visualization of the very short boiling process, a strobe microscopy technique was developed and employed. The dynamic interaction between the exploding vapor microlayer and the surrounding liquid can be quantified and further characterized by measuring the acoustic pressure wave in the liquid during the boiling process. A fast pressure transducer allows us to capture the acoustic emission from the expanding vapor volume. From these data, the pressure inside the growing vapor layer and the mechanical energy released from its rapid expansion can be estimated.

An important result of the present experiments is the determination of the vapor nucleation temperature. The method for measuring the maximum superheat temperature of the water involves measuring the change in resistance of the Pt-wire during a heating pulse and relating the change in resistance to the change in temperature. The slope of the temperature curve changes shape when the fluid in contact with the wire changes phase, because when the vapor phase covers the wire, it reduces the rate of heat transfer to the fluid. This produces an inflection point in the temperature curve. A curve-fitting method was developed, which enabled us to define the vapor transition point and thus to determine the temperature of the heater surface, when explosive boiling is initiated. In the present study we were able to operate with the shortest heating pulses (<4.5 μs) for an electrically heated body reported (to the best of our knowledge) and thus apply more electric power to the Pt-wire. The shorter the heating pulse, the more unlikely it is that nucleate boiling is promoted by gases trapped on the surface of the wire. It was shown that with a shorter pulse and higher power, the maximum attained superheat temperature increases. To the best of our knowledge, the superheat temperatures obtained for water (∼305 °C) in this study are higher than those reported in previous experiments in the open literature.
Heat Transfer for Gaseous Flow in Microtubes With Viscous Heating
Authors: Tunc Gokturk , Bayazitoglu Yildiz
Published: November 2021

Convective heat transfer for steady state, laminar, hydrodynamically developed flow in microtubes with a boundary condition of constant temperature is solved by the integral transform technique. Temperature jump condition at the wall and viscous heating within the medium are included. For a given Brinkman number, at specified axial lengths, the viscous effects are presented for the developing range, reaching the fully developed Nusselt number. In previous studies without temperature jump condition at the wall, a 22% increase in the Nusselt number was found for Knudsen numbers ∈ [0,0.12]. In this work we have found that for the same range of Knudsen numbers, the Nusselt number decreases by 35.6%. In addition, as we increase the Prandtl number the temperature jump effect diminishes.
Thermal Conductivity of Nanochanneled Alumina
Authors: Kumar A. R. , Achimov D.-A. , Zeng T. , Chen G.
Published: November 2021

We present an experimental study on the thermal conductivity of anodized alumina with regular nanochannels. Thermal conductivity values in both directions parallel and perpendicular to the nanochannel axis are measured at room temperature using the 3ω technique. An anisotropic heat conduction model is developed to analyze the experimental data.
Flow Characteristics in a Three-Dimensional Rectangular Channel With a Pair of Ribs Placed Symmetrically at the Channel Walls
Authors: Singh M. , Panigrahi P. K. , Biswas G.
Published: November 2021

A numerical study of rib augmented cooling of turbine blades is reported in this paper. The time-dependent velocity field around a pair of symmetrically placed ribs on the walls of a three-dimensional rectangular channel was studied by use of a modified version of Marker-And-Cell algorithm to solve the unsteady incompressible Navier-Stokes and energy equations. The flow structures are presented with the help of instantaneous velocity vector and vorticity fields, FFT and time averaged and rms values of components of velocity. The spanwise averaged Nusselt number is found to increase at the locations of reattachment. The numerical results are compared with available numerical and experimental results. The presence of ribs leads to complex flow fields with regions of flow separation before and after the ribs. Each interruption in the flow field due to the surface mounted rib enables the velocity distribution to be more homogeneous and a new boundary layer starts developing downstream of the rib. The heat transfer is primarily enhanced due to the decrease in the thermal resistance owing to the thinner boundary layers on the interrupted surfaces. Another reason for heat transfer enhancement can be attributed to the mixing induced by large-scale structures present downstream of the separation point.
Adaptive Neurocontrol and Minimization of Energy Consumption of a Heat Exchanger Test Facility
Authors: Díaz Gerardo , Sen Mihir , McClain Rodney L.
Published: November 2021

It has been shown that artificial neural networks (ANNs) can be used to simulate and control thermal systems such as heat exchangers. It is known that the characteristics of thermal components such as heat exchangers vary with respect to time mainly due to fouling effects. There is a need of a model that can adapt to the new characteristics of the thermal system. In this work adaptive artificial neural networks are used to control the outlet air temperature of a heat exchanger test facility. The neurocontrollers are adapted on-line on the basis of different criteria. The parameters of the ANNs are modified considering target error and stability conditions of the closed loop system analyzed as a nonlinear iterative map. We also implement a minimization of a performance index that quantifies the energy consumption. It is shown numerically and experimentally that the neural network is able to control the thermal facility, and is also able to adapt to different disturbances applied to the system, while minimizing the amount of energy used.
An Economical Method for Artificial Neural Network Process Modeling by the Model-Modifier Approach
Authors: Bhatikar Sanjay
Published: November 2021

In this paper we present our model-modifier approach as an economical method for the development of accurate manufacturing equipment models. The model modifier method leverages knowledge from one ANN model to another of a similar type, thus reducing the development effort required as compared to starting from scratch. The economy afforded by this knowledge-sharing technique was evaluated on a Chemical Vapor Deposition (CVD) reactor. The results show that the model-modifier approach is a valid method for transferring knowledge between similar ANN models and that significant savings in training data accrue from this approach. In our case, a highly accurate ANN model was developed with a mere one-fifth of the data that would have been required without this approach. Further, we have also shown that an ANN model developed by the model-modifier approach can be easily and reliably utilized for process optimization.
Modeling of Moving Breakdown by Femtosecond Laser Pulses in Dielectrics
Authors: Fan C. H. , Longtin J. P.
Published: November 2021

Laser ablation is becoming increasingly important in the fields of micromaching, thin film formation, and bioengineering applications. In laser ablation, the ablation rates and feature quality strongly depend on the size of the breakdown region in the material. This region is characterized by a high density of free electrons, which absorb a large fraction of energy from the laser pulse that results in material vaporization in solids or liquids. For nanosecond- and picosecond pulses, the breakdown region tends to form near the beam focus and then expand back along the beam path toward the laser; this phenomenon is called moving breakdown. For femtosecond pulses, however, breakdown begins up the beam path and then propagates toward the focal point. A moving breakdown model presented by Docchio et al. (1988a) successfully explains and predicts the time-dependent breakdown region in the nanosecond regime, however it does not adequately describe propagation of the breakdown region at pico- and femtosecond time scales. In the present work, a modified moving breakdown model is proposed that includes the pulse propagation and small spatial extent of ultrafast laser pulses. This revised model shows that pulse propagation becomes significant for pulsewidths less than 10 picoseconds. The new model characterizes the pulse behavior as it interacts with a material within the focal volume in both solids and liquids. The model may also be useful in estimating the time- and space-resolved electron density in the interaction volume, the breakdown threshold of a material, shielding effectiveness, energy deposition, and the temperature increase in the material.
Numerical Simulation of Dendritic Solidification
Authors: Jung Jin-Young , Chen Michael M.
Published: November 2021

It is well known that the dendritic microstructure of alloys is a consequence of morphological instability of the solidification process, which is a result of the coupling of heat and mass transfer with the composition-dependent phase equilibrium condition mediated by the surface energy. There have been many numerical simulations of dendritic solidification. However, many successful simulations of dendritic growth have used non-discrete front tracking method such as artificial source method or phase field method, with demonstrably first order accuracy. Many also found it necessary to continuously inject random noise during simulation. The continuous injection of random noise raises the suspicion that the numerical schemes used may be overly dissipative. The noise is apparently capable of creating nonuniform solidification, but not sufficient to ensure growth with a clear dendritic pattern. In the present study, to rule out the numerical diffusivity as a cause of the damping of dendritic perturbations, artificial perturbations are either not used, or injected only as initial conditions. Under the unstable solidification mode, the initial perturbation triggers the onset of interface instability. Computations were performed for both sub-cooled pure material as well as directional solidification of alloys. The successful simulation of dendritic solidification without the intentional injection of random noise provided evidence that the present method has less numerical diffusion than many existing front tracking methods.
A Volume Radiation Heat Transfer Model for Czochralski Crystal Growth Processes
Authors: Nunes Edmundo M. , Naraghi Mohammad H. N. , Zhang Hui , Prasad Vishwanath
Published: November 2021

Thermal modeling of Czochralski (CZ) crystal growth processes is a challenging task owing to the complex interaction of heat conduction, convection, thermal radiation, fluid flow, and other transport phenomena. A highly innovative, general-purpose computer model for phase-change and free-surface problems, utilizing a multi-zone adaptive grid generation and curvilinear finite volume scheme, is linked to a spectral, volume and surface thermal radiation algorithm to predict the temperature distribution within a Czochralski growth furnace. The radiative transfer model, based upon the Discrete Exchange Factor (DEF) method, is capable of addressing the complexities due to irregularly-shaped axisymmetric geometries and shadowing effects. A unified exchange factor model is used to account for multiple reflection/scattering of radiation within the enclosure. Several numerical trials are performed to simulate the CZ growth of yttrium aluminum garnet (YAG). The effect of the top surface boundary condition on temperature profile, crystal/melt interface shape, and process stability is studied to examine the applicability of this model to control the growth conditions and interface shape. The results show that there exists a temperature range for this surface for which the desirable conditions for crystal growth are possible. This limiting temperature range is, however, dynamic and changes as the growth progresses.
Improved Thermoplastic Composite by Alignment of Vapor Grown Carbon Fiber
Authors: Kuriger Rex J. , Alam M. Khairul , Anderson David P.
Published: November 2021

This paper discusses the properties of an improved thermoplastic composite by alignment of vapor grown carbon fiber (VGCF) suspended in a polypropylene matrix. VGCF provides improved mechanical and electrical properties in composites. In this study an extruder was used to shear mix and extrude VGCF/polypropylene mixtures containing fiber volume fractions of 2.5%, 7% and 11% through a converging-annular die which produces a high degree of fiber alignment along the flow direction. X-ray diffraction analysis performed on the extruded composite strands showed that the fibers were oriented approximately ± 23.7, ± 28.15 and ± 30.0 degrees along the preferred direction for the 2.5%, 7% and 11% specimens, respectively. Tensile tests were done in both the preferred and transverse directions of samples reinforced with pyrolytically stripped VGCF. When compared to polypropylene, there was a 36.5%, 69.4% and 82.0% increase in tensile strength, and a 94.9%, 173.7% and 218.2% increase in modulus for the 2.5%, 7% and 11% VGCF mixtures along the preferred direction, respectively. The tensile strength and modulus in the transverse direction increased as the fiber volume content increased, however, all values were well below that of polypropylene. This behavior could be attributed to stress concentrations in the composite material. Electrical resistivity measurements were made on samples reinforced with two types of VGCF. The results concluded that the electrical conductance of the polymer strands reinforced with a heat-treated VGCF was far superior to those reinforced with a pyrolytically stripped VGCF.
Mechanism and Modeling of Micro-Droplet Impact, Fragmentation, and Solidification
Authors: Zhang H.
Published: November 2021

New applications have been identified for thermal spraying using micro-droplets. Mechanisms of impact, fragmentation, and solidification developed for millimeter size droplets are no longer applicable for micro-droplets due to the significance of the surface tension and wall interaction. New fragmentation mechanisms and advanced numerical modeling are required to develop a better understanding of the transport phenomena for droplet spreading and solidification. In this paper, the existing fragmentation mechanisms have been reviewed, and a new mechanism is proposed. The proposed mechanism considers the effects of flow instability, wettability, surface roughness, surface chemistry, and moisture absorption. This mechanism has been incorporated into an advanced numerical model that consists of a multizone adaptive grid generation used for tracking the movement of the solidification interface and a curvilinear level-set method for capturing the movement of free surface. Impact, fragmentation, and solidification of a molybdenum micro-droplet has been simulated, and the fragmentation morphology has been predicted.
System Characterization and Plasma-Particle Distribution Analysis for Development of a Closed Loop Control for Plasma Spray
Authors: Gevelber M. , Wroblewski D. , Fincke J. , Swank W. D.
Published: November 2021

This paper investigates the need to develop an advanced control system for plasma spray deposition. The limitations and performance capability of both feed forward and real-time control are evaluated. Critical system characteristics for developing such controllers are experimentally identified including dominant nonlinearalities; dynamics, cross-coupling, distributions, and sensor issues.
Pool Boiling Critical Heat Flux on a Downward-Facing Convex Surface
Authors: Howard Alicia H. , Mudawar Issam
Published: November 2021

Heat transfer measurements and photographic studies were performed to capture the detailed evolution of liquid-vapor interfacial behavior near critical heat flux (CHF) for a 90-degree downward-facing convex surface. The test surface, with a width of 3.2 mm and a 102.6-mm radius, consisted of a series of nine heaters which dissipated equal power. Instrumentation within each heater facilitated localized heat flux and temperature measurements along the convex surface, and transparent front and back windows enabled optical access to a fairly two-dimensional liquid-vapor interface. Near CHF, vapor behavior along the convex surface was cyclical in nature and somewhat similar to that observed in pool boiling on horizontal downward-facing flat surfaces. The vapor repeatedly formed a stratified layer at the bottom of the convex surface, which stretched as more vapor was generated, and then departed from the surface. Subsequently, the bottom (downward-facing) heaters, followed by the other heaters, were wetted with liquid before the nucleation/coalescence/stratification/release process repeated itself. Prior to CHF, the surface was adequately cooled by the liquid wetting. At CHF, the surface was still wetted for a brief period, but the wetting time was too short to allow adequate cooling of the downward-facing heaters, and the temperature of these heaters began to rise. This study proves that despite the pronounced thickening of the vapor layer as it propagates upwards along the convex surface, CHF always commences on the downward-facing heaters.
Transient Convective Heat Transfer in a Helical Tube With Steam-Water Two-Phase Flow Under Pressure Drop Type Oscillations
Authors: Guo Lie-Jin , Feng Zi-Ping
Published: November 2021

In the present paper the experiments for subcooled water flow and steam-water two-phase flow were conducted to investigate the effects of pulsation upon transient heat transfer characteristics in a closed-circulation helical-coiled tube steam generator. The non-uniform property of local heat transfer with steady flow was also examined. The secondary flow mechanism and the effect of interaction between the flow oscillation and secondary flow were analyzed on the basis of the experimental data. Some new phenomena were observed and explained. A series of correlations were proposed for the average and local heat transfer coefficients both under steady and oscillatory flow conditions. The results showed that there were considerable variations in local and peripherally time-averaged Nusselt numbers for pulsating flow in a wide range of parameters. Systematic investigations of pressure drop type oscillations and their thresholds for steam-water two-phase flow in a uniformly heated helical tube were also reported.
Subcooled Boiling of Surfactant Solutions
Authors: Hetsroni G. , Gurevich M. , Mosyak A. , Rozenblit R. , Yarin L. P.
Published: November 2021

During subcooled boiling of pure water and water with cationic surfactants, the motion of bubbles and the temperature of the heated surface were recorded by both a high-speed video camera and an infrared radiometer. The results show that the bubble behavior and the heat transfer mechanism for the surfactant are quite different from those of clear water. Bubbles formed in Habon G solutions were much smaller man those in water and the surface was covered with them faster. Boiling hysteresis is found for degraded solutions. Dependencies of heat transfer coefficient for various solutions were obtained and compared. The boiling curves of surfactant are quite different from the boiling curve of pure water. Experimental results demonstrate that the heat transfer coefficient of the boiling process can be enhanced considerably by the addition of a small amount of Habon G. The experiments show that the limitations of the ER technique with respect to frequency response are outweighed by its unique capacity to measure wall temperature distribution with high spatial resolution over an area encompassing many nucleation sites and over long periods.
Some Aspects of Critical-Heat-Flux Enhancement in Tubes
Authors: Doerffer S. S. , Groeneveld D. C. , Rudzinski K. F. , Pioro I. L. , Martin J. W.
Published: November 2021

This paper summarizes the effects of various types or numbers of critical-heat-flux (CHF)-enhancing inserts in tubular geometries. The impact of inserts on CHF is frequently expressed by an enhancement ratio K: the ratio of CHF with an insert to the CHF in a bare tube for the same local flow conditions. The impact on K of the following parameters was investigated: (i) fluid type (Freon-134a, water), (ii) axial spacing between inserts, (iii) shape of the insert, (iv) flow blockage of the insert, (v) number of similar/dissimilar insert planes upstream, and (vi) impact of flow conditions. The spacing and flow-obstruction area were found to be the major geometric factors that affected K: by decreasing the relative spacing, L/D, to 16, K can reach a value of from 2 to 3, depending on the flow-obstruction area. Among flow parameters, the critical quality, xc, usually has a strong effect on K: K can increase from a value of 1 to 3, when xc increases from 0 to 0.4 for a mass flux G ≥ 2 Mg/m2s. For G < 2 Mg/m2s, CHF enhancement can disappear or become negative (K < 1). No cumulative effect was found on K for a series of upstream insert planes. CHF enhancement does not depend on fluid type, provided that the conditions in the fluids meet the CHF fluid-to-fluid modelling requirements.
Shock Waves in Liquids With Bubbles Containing Evaporating Drops
Authors: Khabeev Nail S. , Bertelsen Arnold F. , Ganiev Oleg R.
Published: November 2021

An investigation of wave processes in liquids with bubbles containing evaporating drops is presented. A model is used which takes into account both the liquid radial inertia due to medium volume changes, and the temperature distribution inside and around the bubbles. An analysis of the microsopic fields of physical parameters is aimed at closing the system of equations for averaged characteristics. The evolution of non-steady shock waves in liquids with bubbles containing evaporating drops is studied by numerical methods. The effect of the initial conditions, shock strength, volume fraction, dispersity of the vapor phase, initial static pressure and of the thermophysical properties of the phases on shock-wave structure and evolution is studied.

The possible enhancement of disturbances in the region of their initiation is shown. The phenomenon of the nonlinear anomalous enhancement of waves reflected from a wall is established.
Stacked Microchannel Heat Sinks for Liquid Cooling of Microelectronic Components
Authors: Wei X. , Joshi Y.
Published: November 2021

A novel heat sink based on a multi-layer stack of liquid cooled microchannels is investigated. For a given pumping power and heat removal capability for the heat sink, the flow rate across a stack of microchannels is lower compared to a single layer of microchannels. Numerical simulations using a computationally efficient multigrid method [1] were carried out to investigate the detailed conjugate transport within the heat sink. The effects of the microchannel aspect ratio and total number of layers on thermal performance were studied for water as coolant. A heat sink of base area 10 mm by 10 mm with a height in the range 1.8 to 4.5 mm (2–5 layers) was considered with water flow rate in the range 0.83×10−6 m3/s (50 ml/min) to 6.67×10−6 m3/s (400 ml/min). The results of the computational simulations were also compared with a simplified thermal resistance network analysis.
Fire Resistance Characteristics of Fire Protection Materials With High-Water Content
Authors: Asako Y. , Otaka T. , Yamaguchi Y.
Published: November 2021

It is well known that moist fire protection materials show good fire resistance characteristics. For this reason, these materials are usually made of mixtures of cement mortar and high-water content materials such as silica gels or moist perlites. The latent heat of water plays an important role in the resistance of heat propagation in these materials. In this study, the thermal conductivity of mixtures of perlite-mortar and super-absorbent polymer gel to increase its water storage capacity, were measured. Also, the water content of the test materials was measured. Using the measured thermal properties of such fire protection materials, the numerical simulation for the fire resistant test were conducted. The effects of mixing ratio of the gels and the perlite-mortar on the fire resistance characteristics are discussed.
Simulation of Turbulent Flow Through Hybrid Porous Medium: Clear Fluid Domains
Authors: de Lemos Marcelo J. S. , Pedras Marcos H. J.
Published: November 2021

Turbulent flow in a channel, totally and partially filled with a porous medium, is simulated with a proposed turbulence model. Two cases are analyzed, namely clear flow past a porous obstacle and flow through a porous medium having a cavity with a higher porosity. Mean and turbulence quantities were solved within both computational domains using a single numerical technique. The control volume approach was used to discretize the governing equations. In the first case analyzed, the flow penetration into the porous substrate is accompanied by generation of turbulence kinetic energy within the obstacle. In the second geometry, the flow is pushed towards the cavity as porosity increases.
Measurement and Prediction of Temperature Distributions in Optical Elements in the Millikelvin Regime
Authors: Ambrose Jay , Hashemi Ab , Schneider Julie , Stubbs Dave , Aaron Kim , Shao Michael , VanZandt Tom
Published: November 2021

This paper describes analytical and experimental thermal results for a 33.5 cm diameter plano mirror under conditions of small thermal perturbations (steady-state temperature gradients of 10–100 mK). These tests are intended to support verification of specific thermal requirements for a space interferometer. The primary thermal requirement is knowledge/control of temporal changes in mirror gradients to the 1 mK (0.001 K) level. Tests were performed with small heat inputs to the back of the mirror, which was suspended in a thermally-uniform shroud. Correlation of thermal models for both conductively and radiatively-heated test configurations were performed, and results indicate very good agreement between the thermal model predictions and the temperature measurements. The modeling uncertainty based on the test correlation is estimated to be ±3 mK for absolute temporal comparisons. Comparisons for temporal change of gradient are shown to be within 1 mK for small perturbations. The paper describes the test setup, test results, model correlation and uncertainty estimates.
Application of Computational Fluid Dynamics to Protective Clothing System Evaluation
Authors: Gibson Phillip W. , Charmchi Majid
Published: November 2021

Convection, diffusion, and phase change processes influence heat and mass transfer through textile materials used in clothing systems. For example, water in a hygroscopic porous textile may exist in vapor or liquid form in the pore spaces or in bound form when it has been absorbed by the solid phase, which is typically some kind of hydrophilic polymer. Phase changes associated with water include liquid evaporation/condensation in the pore spaces and sorption/desorption from hydrophilic polymer fibers. Certain materials such as encapsulated paraffins may also be added to textiles; these materials are designed to undergo a solid-liquid phase change over temperature ranges near human body temperature, which influences the perceived comfort of clothing. Additional factors such as the swelling of the solid polymer due to water imbibition, and the heat of sorption evolved when the water is absorbed by the polymeric matrix, can all be incorporated into the appropriate conservation and transport equations describing heat and mass transfer through clothing layers. These physical factors, nonlinear material properties, and complex multiphase flows make the task of modeling and predicting levels of protection and comfort of various clothing designs difficult and elusive. Computational fluid dynamics (CFD) has proven to be useful at several levels of material and system modeling to evaluate and design protective clothing systems and material components. This paper summarizes current and past work aimed at utilizing CFD techniques for protective clothing applications.
Development of Finite Volume Shell Conduction Model for Complex Geometries
Authors: Mathur S. R. , Lim C. K. , Nair R.
Published: November 2021

Thin, plate-like structures are often encountered in industrial heat transfer applications. Discretizing them as volumetric elements along with the rest of the domain results in a large number of elements and significantly increases the cost of computational analysis of such problems. It can also cause numerical errors and convergence difficulties because of the large aspect ratios and skewness of the mesh. On the other hand, treating the conduction in such regions separately is also unattractive because the inherent coupling of the two problems makes for very slow convergence. In this paper we present an alternative approach which treats such structures as planar elements while still maintaining full coupling between the temperature fields in the two regions. Consequently the solution for the entire domain can be obtained simultaneously without significant increase in problem complexity. The method is validated using canonical problems as well as solutions obtained by full discretization of the thin structures. Compared to the latter, the present approach is found to be significantly more efficient and robust.
Buoyancy Effect on Developing Turbulent Flow and Heat Transfer in a Helical Pipe With Finite Pitch
Authors: Zheng B. , Lin C. X. , Ebadian M. A.
Published: November 2021

Numerical modeling was performed to investigate the buoyancy effect on developing turbulent flow and the heat transfer characteristics of saturated water in a helical pipe with finite pitch. The renormalization group (RNG) κ–ε model was used to account for the turbulent flow and heat transfer in the helical pipe at a constant wall temperature with or without buoyancy force effect. A control volume method with second-order accuracy was used to numerically solve the three-dimensional full elliptic governing equations for this problem. The O-type nonuniform structured grid system was adopted to discretize the computation domain. The Boussinesq approximation was applied to deal with the buoyancy. This study explored the influence of buoyancy on the developing heat transfer along the helical pipe. Based on the results of this research, the velocity, temperature, and Nusselt number are presented graphically and analyzed.
Modelling of Convective Melt Flow and Interface Shape in Commercial Bridgman-Stockbarger Growth of CdZnTe
Authors: Rule Toby D. , Li Ben Q. , Lynn Kelvin G.
Published: November 2021

CdZnTe single crystals for radiation detector and IR substrate applications must be of high quality and controlled purity. The growth of such crystals from a melt is very difficult due to the low thermal conductivity and high latent heat of the material, and the ease with which dislocations, twins and precipitates are introduced during crystal growth. These defects may be related to solute transport phenomena and thermal stresses associated with the solidification process. As a result, production of high quality material requires excellent thermal control during the entire growth process. A comprehensive model is being developed to account for radiation and conduction within the furnace, thermal coupling between the furnace and growth crucible, and finally the thermal stress fields within the growing crystal which result from the thermal conditions imposed on the crucible.

As part of this effort, the present work examines the heat transfer and fluid flow within the crucible, using thermal boundary conditions obtained from experimental measurements. The 2-D axisymetric numerical model uses the deforming finite element method, with allowance made for melt convection, solidification with latent heat release and conjugate heat transfer between the solid material and the melt. Results are presented for several stages of growth, including a time-history of the solid-liquid interface (1365 K isotherm). The impact of melt convection, thermal end conditions and furnace temperature gradient on the growth interface is evaluated. Future work will extend the present model to include radiation exchange within the furnace, and a transient analysis for studying solute transport and thermal stress.
Dispersion Analysis of Stabilized Finite Element Methods for Acoustic Fluid-Structure Interaction
Authors: Thompson Lonny L. , Sankar Sridhar
Published: November 2021

The application of stabilized finite element methods to model the vibration of elastic plates coupled with an acoustic fluid medium is considered. New stabilized methods based on the Hellinger-Reissner variational principle with a generalized least-squares modification are developed which yield improvement in accuracy over the Galerkin and Galerkin Generalized Least Squares (GGLS) finite element methods for both in vacuo and acoustic fluid-loaded Reissner-Mindlin plates. Through judicious selection of design parameters this formulation provides a consistent framework for enhancing the accuracy of mixed Reissner-Mindlin plate elements. Combined with stabilization methods for the acoustic fluid, the method presents a new framework for accurate modeling of acoustic fluid-loaded structures. The technique of complex wave-number dispersion analysis is used to examine the accuracy of the discretized system in the representation of free-waves for fluid-loaded plates. The influence of different finite element approximations for the fluid-loaded plate system are examined and clarified. Improved methods are designed such that the finite element dispersion relations closely match each branch of the complex wavenumber loci for fluid-loaded plates. Comparisons of finite element dispersion relations demonstrate the superiority of the hybrid least-squares (HLS) plate elements combined with stabilized methods for the fluid over standard Galerkin methods with mixed interpolation and shear projection (MITC4) and GGLS methods.
Introduction to Acoustic Compressors
Authors: Lipkens Bart , Lalande Fred , Perkins David
Published: November 2021

The emergence of acoustic compressors has been made possible by the development of a new technology called Resonant MacroSonic Synthesis (RMS). RMS allows the creation of macrosonic standing waves in acoustic resonators. The shape of the resonator controls the nonlinear fluid dynamic processes by which energy is transferred to higher harmonics. Through this process resonators have been designed that allow high-amplitude shock-free waveforms. A variable reluctance driver is used to transfer energy into the resonator. The entire resonator is oscillated along its axis at the fundamental acoustic resonance frequency. This process is called entire resonator drive. The valve technology used in these compressors is similar to that of conventional reciprocating compressors. Acoustic compressors are inherently variable capacity and oil-free. Other unique characteristics are flexible orientation and low profile packaging option. Development focuses on vapor-compression applications. The application discussed here is spot-cooling.
Response to an Induced Flow/Pressure Transient During Well Fracturing
Authors: Loth John L. , Echavarria Erika , Stephenson Stan
Published: November 2021

Hydraulic fracturing of oil and gas wells is often needed to increase well production. The fluid pumping schedule is designed to control the fracture growth in length, width and height. This paper investigates the potential for using the fracture fluid acoustic properties to measure, on-line, the length of the fracture and or reduce the enormous pumping power required. This preliminary study shows that most induced flow or pressure transients are critically damped inside the fracture. Pulses with pressure rising or dropping faster man the time required for the wave to travel the length of the fracture, behave differently. Those pulses excite the natural frequency of the fracture, which is about 10 Hertz for a 100 ft. (30 m) long fracture. If the fracture natural frequency can be detected at the surface, it provides an on-line insight into the length of the fracture created.
Non-Linear Least-Squares Estimation of Material Properties and Structural Intensity in Non-Uniform Beams
Authors: Halliday Peter J. , Grosh Karl
Published: November 2021

Algorithms for determining material properties and power flow in vibrating structures are presented. The new techniques are achieved by synthesizing wave component identification methods developed previously (Halliday and Grosh, 2000) with new methods targeted towards material property and structural intensity estimation. The effectiveness of this nonlinear least-squares approach is investigated through laboratory and numerical experiments on a non-uniform structure, yielding guidelines for spatial sampling and the effects of noise.
Modelling of Rigid-Frame Porous Materials: A Simple Approach
Authors: Brennan M. J. , To W. M.
Published: November 2021

This paper is concerned with the modelling of rigid-frame porous materials. Currently there are very simple models which describe the acoustic behaviour of such materials, and there are also very complicated models. The aim of this paper is to present a model which occupies the “middle ground”, but is simple enough to be used by practising noise control engineers. Using concepts of acoustic mass, stiffness and damping, non-dimensional expressions for the acoustic wavenumber and the characteristic impedance of a rigid-frame porous material are derived. These expressions are used to give a “rule of thumb” for the optimum flow resistivity for a given thickness of material.
Low-Velocity Impact Response and Dynamic Characteristics of Glass-Resin Composites
Authors: Mantena P. Raju , Mann Richa , Nori Chandrasekhar
Published: November 2021

This paper describes a test methodology used for characterizing different glass-resin composite systems with respect to their low-velocity impact response, dynamic modulus and inherent damping properties. Impact tests were conducted on SMC plaque samples in an instrumented impact test machine. A Dynamic Mechanical Analyzer was used for testing small rectangular samples in the fixed frequency mode of operation. An impulse-frequency response vibration technique was used for obtaining the dynamic modulus and loss factor of cantilever beam specimens at ambient conditions. The dynamic modulus, glass transition and damping peak intensities obtained from the DMA and the vibration techniques are correlated with the impact test data. The potential application for screening glass-resin formulations with respect to their impact performance is discussed.