bluuebunny/crossref_metadata_2025 huggingface dataset:
Probabilistic Mesomechanics for High Cycle Fatigue Life Prediction
Authors: Tryon Robert G. , Cruse Thomas A.
Published: March 2022

This paper presents an analytical modeling approach to characterize and understand high cycle fatigue life in gas turbine alloys. It is recognized that the design of structures subjected to fatigue cannot be based on average material behavior but that designs must consider −3σ or some other appropriate extreme value (tail of the distribution) loading and/or material properties. Thus, a life prediction capability useful in a design application must address the scatter inherent in material response to fatigue loading. Further, the life prediction capability should identify the key micromechanical variables that are critical in the tail of the scatter in the materials durability distribution. The proposed method addresses the scatter in fatigue by investigating the microstructural variables responsible for the scatter and developing analytical and semi-analytical models to quantitatively relate the variables to the response. The model is general and considers the entire range of damage accumulation sequences; from crack nucleation of the initially unflawed structure to final fast fracture.
Numerical Simulation of Instability of Interfaces Between Superposed Layers With Application to Phase Change Processes
Authors: Dhir V. K. , Son G. , Banerjee D.
Published: March 2022

The past efforts on the use of linear Taylor instability theory to predict heat transfer and minimum heat flux during film boiling on flat plates are briefly reviewed. This is followed by a review of recent work on numerical evaluation of non-linear growth of the interface between superposed layers of immiscible fluids. In these studies the numerical results were obtained for the temporal and the spatial variation of the heat transfer rate and the interface shape during saturated film boiling on a horizontal surface at low and near critical pressures, and during melting of a substrate supporting a pool of warmer liquid. New physical insights gained from the analysis are discussed.
Experiments on Liquid Surface Deformation Upon Impingement by a Gas Jet
Authors: Eletribi S. , Mukherjee D. K. , Prasad V.
Published: March 2022

The impingement of a gas jet on a liquid surface has several applications including electric arc furnace steel-making, top blown copper converting, welding and dust removal from the producer gas obtained from biomass gasification. An experimental model has been developed to study the effect of a circular air jet impinging upon a liquid surface. Experiments are conducted with variations in the type of liquid, jet velocity, and separation distance between the nozzle and the liquid surface. Upon jet impingement a cavity (depression) is created on the surface of the liquid. The width and height of this cavity have been determined using sophisticated image processing and edge detection software. The shape of the cavity is either parabolic or Gaussian depending on the conditions of the jet flow and the liquid bath. The shear of the impinging air jet causes recirculatory flow patterns within the liquid that are visualized using aluminum particles as tracers. The measurements show that the previously reported theoretical analysis cannot make accurate predictions of the width and height of the cavity unless surface tension and viscous effects of the liquid are properly accounted for.
Studies on Flow Pattern Transitions and Wavy Films in Gas-Liquid Two-Phase Flows in Microgravity
Authors: Jayawardena Subash S. , Balakotaiah Vemuri
Published: March 2022

Two phase flows are important in both normal and microgravity operations. Using our recently proposed dimensionless flow pattern maps for microgravity flows, we develop system specific flow pattern maps which can be used in designing such systems.

In the second part, we compare the characteristics of micro-gravity annular flows with normal gravity downward co-current annular flows. It is found that the proper length scale for normalization in microgravity is the length scale defined using the friction velocities based on the pressure gradients. Using the universal velocity profile, we present a correlation for the mean film thickness h+ and the standard deviation h+rms for microgravity annular flows. A comparison of the interfacial friction factors and wave celerities shows that a higher friction factor and a larger celerity are observed in microgravity flows.
Turbulent Boundary Layer of Vapor Phase on a Wavy Falling-Film Condensation of Steam-Air Mixture
Authors: Park Su-Ki , Kim Moohwan
Published: March 2022

The wave structure of condensate film and the characteristics of boundary layer flow in the vapor phase were investigated experimentally for condensation of steam-air mixture on a vertical surface. The instantaneous film thickness and the fluctuating temperature in the boundary layer were measured simultaneously. Also the heat transfer coefficient across the condensate film and the diffusion layer formed by air (noncondensable gas) was obtained at various film Reynolds numbers and vapor velocities. The influence of the wavy interface on the temperature field and the heat transfer depend strongly on film Reynolds number and vapor velocity. The condensation heat transfer coefficient increases more than several tens percents with the increase of film Reynolds number depending on the vapor velocity. The fluctuating temperature correlates strongly with the waviness of condensate film corresponding to film Reynolds number. The RMS (root-mean-square) of the temperature fluctuation increases considerably due to the waviness and shows a maximum value around the crest of large amplitude waves.
Heat Transfer Characteristics in Partial Boiling, Fully Developed Boiling, and Significant Void Flow Regions of Subcooled Flow Boiling
Authors: Kandlikar Satish G.
Published: March 2022

Subcooled flow boiling covers the region beginning from the location where the wall temperature exceeds the local liquid saturation temperature to the location where the thermodynamic quality reaches zero, corresponding to the saturated liquid state. Three locations in the subcooled flow have been identified by earlier investigators as the onset of nucleate boiling, the point of net vapor generation, and the location where x = 0 is attained from enthalpy balance equations. The heat transfer regions are identified as the single phase heat transfer prior to ONB, partial boiling (PB), and fully developed boiling (FDB). A new region is identified here as the significant void flow (SVF) region. Available models for predicting the heat transfer coefficient in different regions are evaluated and new models are presented based on our current understanding. The results are compared with some of the experimental data available in the literature.
A Study of Droplet Vaporization in a Longitudinal Acoustic Field Using Exciplex Vapor/Liquid Visualization
Authors: Ondas Michael S. , Santavicca Domenic A.
Published: March 2022

Droplet vaporization has been targeted as one of the primary mechanisms for initiating and sustaining combustion instability. Past research has studied droplet vaporization in the presence of an acoustic field to determine if the acoustic field has an influence on the vaporization rate. These studies looked for an increase or decrease in the time averaged vaporization rate due to the acoustic field by measuring droplet diameter as a function of time. This research focuses on the fuel vapor wake as a means to reveal the instantaneous perturbation in the droplet vaporization due to an imposed acoustic field. An exciplex vapor/liquid visualization technique is used to image the fuel vapor wake downstream of a vaporizing droplet at discreet phases of a longitudinal acoustic field. The results indicate that longitudinal acoustic waves can couple with the vaporization process and cause perturbations in the spatial distribution of the fuel vapor that occur at the same frequency of the imposed acoustic field.
Coalescence of Droplets of an Ink Jet
Authors: Watanabe Keizo , Che Feng , Mutoh Masayuki
Published: March 2022

Measurements of the velocity of ink jet droplets were made using a microscope in an experimental apparatus in which the nozzle is about 18 μ m in diameter. It was shown that the distance for the coalescence of droplets from the liquid jet increases with the increase of density of liquid.

The equation of motion for the droplet is analyzed numerically by assuming the air velocity around a droplet, and trajectories are obtained. The results of numerical simulation for the coalescence correspond to the experimental results well. It is pointed out that the droplet stream stability is affected by the surface tension of the jet.
Gas-Solid Suspension Flow in a Nozzle and the Overexpanded Free Jet
Authors: Ben-Dor G. , Elperin I. , Igra O. , Vasiliev E.
Published: March 2022

Two-phase gas-solid particles nonstationary axisymmetric flows through converging-diverging nozzles and the free overexpanded jets emerging from the nozzles are studied numerically. The solution of the flowfield is carried out until a steady flow is established. The Eulerian approach is used to describe the flowfield and both phases are treated in the homogeneous mixtures approximation. A monotone second order accurate in space and time W-modification of Godunov’s scheme is applied for the numerical solution of the governing equations. The evolution of the discontinuities is investigated as well as the effects of the particle size and the loading ratio on the flow pattern. The two-phase flowfield is compared with a similar pure gas flowfield in a two-dimensional nozzle and in the plume. Limiting cases of the two-phase flow, frozen and equilibrium, are considered. Intermediate regimes of the two-phase flow are compared with the frozen and the equilibrium flows.
Industrial Applications of Spray Technology
Authors: Chigier Norman
Published: March 2022

Spray Systems are used very extensively in a wide range of industrial applications. Injection of liquid fuel in gasoline and diesel automotive engines, gas turbine aircraft and land-based engines, rocket engines and a wide variety of industrial furnaces and boilers, require improved control of atomization and spray characteristics to improve performance and efficiency and to reduce emission of pollutants to satisfy EPA regulations. Spray painting of automobiles, aircraft, bridges and a large range of manufactured products results in the waste of large proportions of paint that does not hit the target and is carried away by offspray, which requires expensive treatment to prevent pollution. In manufacturing processes, molten metal sprays are used for direct manufacture, using near net shaping, high temperature arc spray coatings (thermal spraying) and for coatings. The need to achieve uniform thickness film layers with low porosity, requires control of drop size, velocity, temperature and number density in the spray. More than 80% of agricultural crops are sprayed with herbicides, fungicides and insecticides, using aircraft and tractors. Drop size needs to be maintained sufficiently large during evaporation to prevent drift by wind away from the target crop. Drops that are too large cause wastage and low target transfer efficiencies. Control is required of initial drop size distributions and subsequent changes of spray characteristics from nozzle to target crops. Many industrial chemical and food processes use spray drying where liquid slurries, colloids and solutions are injected into heated gas (air) environments. Control of atomization and spray characteristics is required in order to meet the end product specifications, of particle size, agglomeration, porosity and friability. In the field of medicine, inhalation therapy is used for treatment of respiratory diseases. New developments include inhalation of cyclosporin to prevent rejection after lung transplants, deep lung inhalation of insulin as a more effective and comfortable treatment for diabetics and inhalation of chemotherapy for prevention of lung cancer for heavy smokers. The generation of monosize particles in nebulizers targeted to particular locations in the respiratory tract and lung surfaces requires accurate control of particle size and velocity during inhalation. Control of all these spray processes is achieved by improved atomizer design and accurate measurement of spray characteristics by phase Doppler, diffraction and imaging laser diagnostic instruments.
Visualization and Measurement of Automotive Electrostatic Rotary-Bell Paint Spray Transfer Processes
Authors: Lai Ming-Chia , Im Kyoung-Su , Liu Yi , Skender Margie M. , Nivi Hossein
Published: March 2022

In order to improve the transfer efficiency and finish quality in automotive spray painting, a better understanding of the paint spray structure and transfer processes of the electrostatic rotary bell applicators is needed. This paper briefly reviews the current technological challenges and research issues, then describes the spray visualization, droplet size, and velocity measurement results of a water-borne paint spray system under various operating parameters. The optical techniques used are copper vapor laser light sheet visualizations and phase Doppler particle analyzer. Four main operating parameters are varied in this study: liquid flow rate (100 ml/min to 250 ml/min), shaping air flow rate (120 l/min to 180 l/min), bell rotational speed (20,000 rpm 50,000 rpm), and high voltage setting (60 kV to 90 kV, and 0 V for comparison). For simplicity, water is used as paint surrogate, and a flat metallic panel is used as the target surface. The results show that bell speed dominates the atomization, but high voltage and flow rate settings significantly modify the spray transport. The results of this study also provide detailed information on the paint spray structure and transfer processes, which can be used in future model development and validation.
Experimental Study on the Spray Cooling of a Heated Solid Surface
Authors: Cho Chris , Ponzel Rainer
Published: March 2022

Spray cooling of a heated solid surface using water spray was investigated. In this experiment, uniform heat flux condition was assumed, and the liquid flow rates and nozzle orifice diameter were selected as main variables. Two water spray temperatures were used for the tests. Saturated water spray was used to measure the wall superheat temperature. Subcooled water was used to measure the effect of water spray in the single-phase regime. Tests using the saturated water showed that the heat transfer rate was a function of Weber number and the superheat temperature. The surface temperature was related to the characteristic velocity and the droplet diameter. On the other hand, tests using the subcooled water spray showed little dependence on the liquid flow rate and the nozzle orifice diameter in the single-phase regime. A correlation was obtained in terms of Reynolds number and Prandtl number. Test results indicated that the spray cooling was more effective during the evaporation of the thin liquid film above the saturation temperature.
Tomographic Identification of Bubbles in Two-Phase Flows Using a Genetic Algorithm
Authors: Lyons Donald P. , Kihm Ken D.
Published: March 2022

Genetic algorithm (GA)-based tomographic reconstruction algorithm is examined to use for nonintrusive optical or acoustic imaging of bubbles in two-phase flows. Individual bubble boundaries are described by elliptical basis functions whose major and minor axes specify the bubble shape and sizes. Genetic algorithm, a robust combinatorial non-linear optimization based on fittest survival principle, allows a regressive determination of the bubble center locations, shape and sizes simultaneously by maximizing the fidelity of guessed images compared with measured images. Preliminary results indicate a strong potential of GA-based tomography for accurate reconstruction of two-phase flow images.
An Alternative Modeling Procedure for Describing Coupled Heat and Mass Transfer in Semi-Dry Porous Media Samples
Authors: Rieder William G. , Prunty Lyle D.
Published: March 2022

An alternative modeling approach is described for unsaturated porous-media samples, where both irreversible and equilibrium thermodynamic arguments are used to set up a simple coupled differential equation set. Predictions based on numerical evaluations of the foregoing set demonstrate the nonlinear temperature and fluid profiles that have been observed in experiments with unsaturated water-in-soil samples. Minimal literature and empirical input is required to quantify parameters. Comparisons with data from small scale experiments show good agreements. It is argued that such an approach could lead to acceptable simulation schemes for poorly-defined media containing several nonreacting fluids.
Thermal Dispersion in Thermally-Developing Region of a Porous Channel
Authors: Hsieh W. H. , Lu S. F.
Published: March 2022

The thermal dispersion and heat-transfer processes in the thermally-developing region of a sintered porous channel with asymmetric heating are analyzed by a two-equation model. The thermal dispersion conductivity is modeled as the product of an entrance-effect function, the dispersive length and the Peclet number. The empirical coefficients in the entrance-effect function are determined by matching the experimental data. The calculated distributions of wall temperature and local Nusselt number are in good agreement with experimental data. From the calculated results it is found that most of the energy at the heated wall is absorbed by the solid. The heat transfer between the solid and the fluid reaches a maximum and then drops in the transverse direction; in the axial direction it increases due to the enhanced local heat transfer coefficient caused by the flow acceleration.
A Parallel Programming Model for Industrial CFD Applications on Microprocessor Based Systems
Authors: Wang G. , Tafti D. K.
Published: March 2022

In this paper, we examine the performance of typical CFD kernels on five major microprocessor-based systems, and show that, for large problem sizes, performance is bounded by the speed of main memory. We further show that, for the solution of large sparse linear systems, preconditioning with a multilevel additive Schwarz method, not only enhances convergence, but also, improves performance by a factor of two to three. This is a direct result of better cache utilization. Further, we show the excellent parallel performance of this method. Finally, we apply the parallel solution technique developed to the unsteady Navier-Stokes equation in the study of transitional heat transfer in louvered fin heat exchangers.
Assessment of Chip-Scale Package Design Options
Authors: Teng Sue Y. , Guo Yifan , Sarihan Vijay
Published: March 2022

The trend in portable products continues towards shrinking size, faster speeds, increased functionality, and, above all, low cost. Chip-scale packages are able to meet these demands of reduced board space consumption, increased functional density, and low cost while still maintaining compatibility with the existing assembly infrastructure.

A chip-scale package development effort for low to moderate I/O count devices has been initiated within Motorola using a flip-chip interposer type of design. This CSP design has been coined the JACS-Pak (Just About Chip Size Package). This work outlines a comparative analysis of various interconnect design schemes being evaluated for future versions of the JACS-Pak. Experimentally validated finite element simulation is used to predict the thermal stresses and strains induced by the manufacturing and assembly processes and thermal cycling tests. Various package design parameters are evaluated in terms of their impact on the mechanical performance of the package, and design enhancements are recommended for enhanced mechanical integrity of the chip-scale package under consideration.

This work illustrates the application of simulation during the initial design stages of the JACS-Pak, demonstrating its importance in contributing to the overall direction and success of the program.
Assessment of an Axisymmetric Analytical Model of a Square Areal Array Assembly
Authors: Shakya S. , Heinrich S. M. , Liang J. , Lee P. S.
Published: March 2022

Three-dimensional (3-D) finite element analyses have been performed for square assemblies, each with a homogeneous component attached to a homogeneous substrate by an areal array of solder joints to test the assumption of replacing the square geometry of the component, substrate, and joint array by equivalent circular disks. Three different square assemblies, namely a Plastic Ball Grid Array (PBGA), a Ceramic Ball Grid Array (CBGA), and a Flip-Chip package have been considered for comparing the maximum shearing displacement, obtained from the 3-D numerical model, with the analytical estimate, which is based on an axisymmetric model. Comparison of the analytical and the finite element results indicates excellent agreement in estimating maximum shearing displacement, provided that the array stiffness is sufficiently smaller than the Young’s moduli of the component and substrate materials. These convincing comparison results indicate that the analytical approach may in some applications provide a useful alternative to the more expensive and time-consuming finite element method.
Low Cost Plastic Packaging of the Network Interface Unit
Authors: Zimmerman M. A.
Published: March 2022

The Network Interface Unit is a module of electronics mounted on the side of homes which carries broadband information, including voice, video, and data. The packaging goals are to provide for environmental protection along with EMI shielding for the electronics with inherent reliability’s providing for up to 20 years in life, at extremely low costs.

The packaging approach involves providing a double enclosure concept utilizing injection molded plastics. The design provides for snap-fit features which allows for mounting of the printed circuit board and a one-time-only snap-fit of the inside enclosure with no seals, screws, or gaskets to minimize assembly costs. The inside plastic components provide for fire resistance (UL-94-5VA), high heat resistance, and shielding while the outside plastic enclosure provides for chemical resistance, impact resistance, (low temperature) and ultraviolet resistance. The outside enclosure provides for a hinge and skirt which allows for shielding of the internal plastic components against ultraviolet exposure. There is also a tongue and groove seal which provides for moisture resistance.
“Thick” Plastic Packages With “Small” Chips vs “Thin” Packages With “Large” Chips: Experimental Evaluation of Their Propensity to Moisture-Induced Failures
Authors: Ilyas Qazi S. , Suhir Ephraim
Published: March 2022

A simple model reflecting the combined effect of the chip width, the pad with, and the underchip thickness of the molding compound on the propensity of a plastic electronic package to a moisture-induced failure was presented last year in the ASME conference (EEP-Vol. 16, Structural Analysis in Microelectronics and Fiber Optics - 1996). In this model, it was shown that “thick” packages (such as MQFP, SQFP) with “small” or “medium” size chips are less prone to moisture induced failure than “thin” packages (such as TQFP) with relatively large chips. An experiment was performed to examine the validity of this theoretical model. The purpose of this paper is to document the experimental data. The obtained results appear to support the suggested model.
Comparison of Different Solder Systems Based on Propensity for Damage
Authors: Sarihan Vijay
Published: March 2022

Very often need arises for evaluation of solder systems based not just on their reflow temperatures but on their capacity to withstand damage. Is there an inherent advantage from fatigue considerations in choosing one system over another? If so can we predict this difference.

Damage and it’s accumulation resulting in fatigue failure of solder interconnects is difficult to predict because of complex time and temperature dependence of solder behavior. Strain based solder fatigue description, like Coffin Manson, is not adequate as the fatigue life of the solder may also be a function of stresses. To circumvent the inherent drawback of the strain-based approach and for a more accurate prediction of stresses and inelastic strains, a dissipated energy based damage index approach, using a finite strain, nonlinear Finite Element Method (FEM), has been developed by the author for damage and fatigue life prediction. Instead of looking at complex tensorial responses of stress and strain it is proposed to look at the response in terms of the scalar damage.

The damage index method based approach is used here for comparing two different solder systems. The solder systems chosen are a high lead Pb97Sn3 system and the Sn60Pb40 eutectic alloy. In order to avoid biasing the evaluation for the melting point of the solder alloy, a new equivalent temperature cycle method is proposed. The response of the solder system to this equivalent temperature cycle is proposed as a fair methodology to distinguish the inherent differences in solder systems based on their propensity for damage.
Experimental Observation of Fatigue-Creep Fracture Development in Solder Joints of Different Standoffs
Authors: Liu D. R.
Published: March 2022

During its service, an electronic module often experiences a wide range of temperature variations. This would cause a large thermal strain in the solder joints which connect components to a printed wire board (PWB) in the electronic module if the difference of the coefficients of thermal expansion between the components and the PWB is large. On the other hand, the temperature range experienced by the solder material is typically about 50% to 80% of its melting temperature. Under this circumstance, the solder joints would experience repeated creep. The accumulation of the creep damage would fracture the joints. Eventually, they would fail by the separation of the joint.
Mechanism of Thermo-Solutal Transport and Segregation in High Pressure Liquid-Encapsulated Czochralski Crystal Growth
Authors: Zou Y. F. , Wang G.-X. , Zhang H. , Prasad V.
Published: March 2022

The mechanism of dopant transport and segregation in high pressure liquid-encapsulated Czochralski (HPLEC) grown III-V compound crystals (e.g., GaAs, InP) has been numerically studied using an integrated model, MASTRAPP. Based on the physics of the growth processes, a two-time-level scheme has been implemented where dopant transport and growth are simulated at a small time-scale while flow and temperature solutions are obtained from quasi-static calculations. Detailed numerical analyses are performed under the conditions of pure crystal rotation, pure thermally-driven natural convection, and pure crucible rotation as well as for mixed flow with all of these forces present simultaneously. The dopant transport and segregation in these cases are well correlated to the corresponding melt flow pattern. Very weak radial segregation is predicted for pure crystal rotation because the resulting melt flow leads to a fairly flat solute boundary layer. The natural convection, on the other hand, produces a non-uniform boundary layer along the melt/crystal interface. This leads to a strong radial segregation with a high concentration along the central axis of the crystal. The crucible rotation has a similar effect. The combined effect of all of these flow mechanisms produces a strong radial segregation, whose extent depends on the relative strength of the driving forces. The crystal rotation is helpful in suppressing the radial segregation. In all of these cases, strong melt flows lead to thin boundary layers that result in decreased longitudinal segregation. The pulling rate also has a strong influence on segregation and the slower the crystal is grown, the lesser is the effect. On the other hand, the effect of variation in partition coefficient is weak when its value is low. The predictions agree well with the experimental observations reported in the literature.
Interface Propagation and Free Convection in Alloy Solidification
Authors: Simpson James E. , Garimella Suresh V.
Published: March 2022

The unidirectional solidification of a dilute alloy (tin-bismuth) in a two-dimensional rectangular cavity is investigated. A uniform computational grid is employed. A vorticity-vector potential representation is used for the governing equations for the velocity field. The interface compatibility conditions for vorticity and vector potential are developed and discussed. The energy equation is solved for the temperature field, while the species equation is solved for the solute distribution. The constitutive equations are solved using a true transient method. The solution scheme incorporates an Alternating Direction Implicit (ADI) approximation for the vorticity while the conjugate gradient method is employed for the vector potential equation. The results obtained from the numerical simulations compare very well with experimental results for directional solidification in the literature in terms of the propagation of the solidification front as well as the free convection flow patterns in the liquid.
Numerical Simulation of Continuous Microwave Hybrid Heating Process
Authors: Zhang Qiong , Jackson Tom H. , Ungan Aydin
Published: March 2022

This study developed a numerical model to simulate a continuous hybrid microwave heating process using a single-mode microwave resonant cavity. A hybrid heating process combines the volumetric energy deposition from microwaves with a convective heat flux at the surface. This combination of heating mechanisms may be used to produce more uniform temperature distributions than either method alone. A Finite Difference Time Domain (FDTD) technique was used to model the electric field distribution. The field strength data allowed power deposition to be approximated and the control volume method was used to solve the energy equation. Temperature dependence of dielectric properties was simulated through an iterative process. This simulation showed that hybrid heating schemes can be used to increase uniformity of the temperature distribution and reduce incidences of thermal runaway.
Pulsed Laser-Induced Ablation of Absorbing Liquids and Acoustic-Transient Generation
Authors: Kim Dongsik , Grigoropoulos Costas P.
Published: March 2022

The mechanisms of pulsed laser-induced ablation of strongly absorbing solutions and generation of acoustic transients are described in this paper. Aqueous solutions of K2CrO4 are irradiated by a KrF excimer laser (λ = 248 nm, FWHM = 24 ns) with moderate energy density below the plasma-formation threshold. The ablation process including the vapor cavity formation and the acoustic-wave propagation is visualized by laser flash photography. The generated pressure transients are measured using a broadband piezoelectric pressure transducer. Simultaneous optical transmission detection is also carried out in order to elucidate the vapor-phase kinetics. The mechanisms of liquid ablation and acoustic-pulse generation are investigated based on the thermoelastic behavior of the liquid medium and the evaporation dynamics. The results show that the ablation is initiated by cavitation driven by the tensile component of the produced thermoelastic stress. Three distinct stages are identified in the ablation process: the initial stage with negligible surface deformation and ejection of a small amount of vapor, the second stage with violent vapor plume and bulk liquid jet ejection that is accompanied by significant surface deformation, and the final stage of large scale hydrodynamic motion. The pressure transient is generated thermoelastically at low laser fluences, but the contribution of the vapor phase expansion and / or recoil momentum exerted by the ablation plume becomes dominant at high laser fluences.
Laser Heating of Metal Targets Including the Influence of the Background Pressure
Authors: Jeong S. H. , Greif R. , Russo R. E.
Published: March 2022

Unsteady vaporization of a metal target due to nanosecond pulsed laser heating when an ambient gas of finite pressure exists was studied numerically. A one dimensional model for target heating and for the gasdynamic flow of the vapor was employed including an analysis of the vapor motion inside the Knudsen Layer (KL). For single pulse laser heating of an aluminum target, it was found that the threshold laser fluence for evaporation of the target is greatly dependent upon the target surface reflectivity. The threshold laser fluence predicted by a thermal evaporation model is larger than the values obtained experimentally. The local Mach number of the vapor at the edge of the KL becomes equal to unity at the beginning of evaporation only when the ambient pressure is sufficiently small; for large ambient pressures, the Mach number of the vapor during the early period of evaporation decreases first and then increases to a local sound velocity. An acceleration of the gasdynamic flow during the early period of evaporation was found and attributed to the unsteady adiabatic expansion.
Condensation Heat Transfer of R-134a in Helicoidal Pipe
Authors: Zaki M. , Liu Y. Z. , Xin R. C. , Dong Z. F. , Ebadian M. A.
Published: March 2022

Following the Montreal Act/Protocol of 1990, which calls for the complete phase out of chloroflorocarbon (CFC) production by the year 2000, increasing attention has been placed in recent years to improving the thermodynamic performance of heat exchangers by using non-azeotropic refrigerant as the working fluid. As a result, the currently used refrigerant, R-12, should be replaced with R-134a. However, R-134a is thermodynamically about 20 to 30 percent less efficient than R-12 in heat exchangers. Helically coiled tubes provide a simple and effective means of augmenting heat transfer. However, the effective design of a helically coiled condenser for refrigeration and air conditioning applications requires knowledge of the optimum configuration of helical coil geometry and the data on condensation heat transfer coefficients to achieve the maximum heat transfer rate. Therefore, an experimental study of condensation of pure R-134a refrigerant inside a helicoidal pipe has been carried out. Experimental heat transfer data are reported in this paper for the condensation of R134a in a helicoidal pipe that measured 12.7 mm at the inner tube and 25.4 mm at the outer tube. The test section was well insulated from the surroundings by two layers of fabric glass. The heat transfer coefficient was calculated from the measured fluid temperatures based on the energy conservation principle.
Experimental Study of Two-Phase Flow in a Hemispherical Annular Gap With Boiling on One Side of the Channel
Authors: Liu Y. C. , Shih Y. C. , Cheung F. B.
Published: March 2022

The phenomenon of nature convection boiling on the outer surface of a heated hemispherical vessel surrounded by a thermal insulation structure was investigated experimentally. The objectives were to observe the behavior of the boiling-induced two-phase motion in the annular gap between the vessel and the insulation structure and to determine the flow effect on the rate of boiling. High-speed photographic records revealed the presence of violent cyclic ejection of the vapor masses generated by boiling on the vessel outer surface which resulted in a buoyancy-driven, upward, concurrent two-phase flow through the channel. When boiling was taking place at high heat flux levels, the flow was found to be three-dimensional with swirl formation. Measurements of the local boiling heat fluxes and the local wall superheats were made under steady-state boiling conditions covering the entire range of nucleate boiling with special emphasis on the high-heat-flux regime.
Thermal Hydraulic Instabilities During Startup Transients in Two Heated Parallel Channels
Authors: Paniagua J. C. , Rohatgi U. S. , Prasad V.
Published: March 2022

In multiple channel systems, channel dynamics can be coupled to one another and be independent of the remaining flow loop or one unstable channel may dominate the transients and make the multiple parallel channel system behave as one single channel. In the single channel case, the whole loop participates in the flow oscillations, whereas in a two parallel channel system the flow oscillations occur in the channels and can be out-of-phase. Previous studies indicated the instabilities are due to condensation in a low pressure natural circulation two parallel channel loop at low powers and inlet subcoolings. A thermal hydraulics computer code was developed to simulate the geysering instability and is based on integral methods where local properties are based on local pressures and the vapor generation model is adjusted accordingly to reflect the vapor generation rate necessary to initiate the instability. This is an important modeling feature since local vapor generation rate depends on local saturation temperature. The code is designed to simulate startup transients in two heated parallel channel natural circulation systems with subcooled water as an initial condition. The numerical simulations illustrated flow reversal in the individual channels, which is a thermal hydraulic feature of condensation-induced geysering.
Evaluation of Prompt Nucleation of Bubbles in Annular Fuel Elements During the Initial Depressurization Transient of a DEGB LOCA
Authors: Smith Allen C.
Published: March 2022

In the first moments of a DEGB LOCA, the depressurization wave may result in the system pressure falling below the saturation pressure of the coolant resulting in bubble formation. Immediate formation of bubbles might result in flow instability, with the affected fuel element unable to survive the LOCA. Nucleation of bubbles can occur by either pressure undershoot, or liquid superheat in the boundary layer adjacent to hot surfaces. This investigation developed a method for evaluating the possibility of occurrence of bubble formation as a result of this initial depressurization. The method developed was based on bubble nucleation models and experimental results. The results show that the superheat required for prompt nucleation, within the initial period between the depressurization wave and the re-pressurization wave, is much greater than the available superheat in the subject fuel element, either measured experimentally or calculated by RELAP. Accordingly, prompt nucleation would not occur in the subject fuel element in this initial time period.
Flow Boiling Heat Transfer of Kerosene Inside Ribbed Tube
Authors: Cheng Lixin , Chen Tingkuan , Luo Yushan
Published: March 2022

Results of a study on flow boiling heat transfer enhancement of kerosene with ribbed tube (rib pitch 9 mm, rib height 0.4 ∼ 0.6 mm, rib width 3.9 mm) are reported. Experiments of upward flow boiling heat transfer in smooth tube and ribbed tube at a pressure 2 bar were performed for a range of heat flux (28.5 ∼ 93.75 kW/m2), mass flux (410 ∼ 810 kg/m2 s) and equilibrium mass quality (0 ∼ 0.3) respectively. Heat transfer coefficients in the ribbed tube are improved by a factor of 1.4 ∼ 1.6 as compared with the smooth tube. A correlation of flow boiling heat transfer coefficients is proposed for the enhanced ribbed tube. Phenomenon and mechanism of flow boiling heat transfer with kerosene are discussed.
Experimental Investigation of Metallic Fibrous Heat Sinks for External Cooling of an Electronic Package
Authors: Angirasa D. , Pyrtle F. , Peterson G. P.
Published: March 2022

Preliminary results of an experimental study to test the effectiveness of metallic fibrous heat sinks for electronic cooling applications are presented. In these initial measurements, low heat inputs were employed. Within a higher range of porosity of the aluminum fibrous sinks, lower porosities lead to lower thermal resistance and higher heat transfer rates. Over a range of Reynolds number, the surface to ambient temperature difference remains fairly constant indicating the possibility that, with the use of fibrous heat sinks, low velocities are enough to keep the surface temperature to a desired value.
An Experimental Study of Upward Flame Spread in a Vertical Corner Wall Fire
Authors: Powell Amy M. , Kulkarni Anil K.
Published: March 2022

This paper presents results of an experimental investigation of upward flame spread on a vertical corner wall. The corner wall flame spread phenomenon differs from that for a plain vertical wall primarily because of the radiative and flow interaction between the walls. An experimental apparatus, capable of being set at corner angles of 60°, 90°, and 135° was designed and constructed. Samples, measuring 1.20 m by 0.30 m, of plywood, particle board, and hardboard were tested. Three burner configurations were used during experimentation — an arrow configuration, a line configuration, and a point source. Flame height as a function of time was measured during each run. Several trends were observed including — the significance of the burner configuration when determining flame shapes; the relationship between radiative interaction and different corner angles; and the capability of each material to sustain flame growth once the burner was turned off. Also, the pyrolysis front was noted at the conclusion of each test run using the charred region apparent on the sample, which revealed the dependence of the shape of pyrolysis front on the burner configuration. The study allows insight into various aspects of corner fire spread and provides data for validating flame spread models.
A Numerical Analysis of a Conical Swirl-Stabilized Spray Burner
Authors: Stojkovic Boris D. , Acharya Sumanta , Morgan Tim G. , Zanca Kevin J. , Graf Michael J. , Gutmark Ephraim
Published: March 2022

Numerical calculations of the droplet dispersion in a conical spray burner are presented. A commercial CFD code, FLUENT, is used to execute the numerical calculations. The burner has the shape of a cone, which is offset in four places. These four gaps allow for secondary air injection into the burner region, and provide a high level of swirl. The fuel spray, together with coaxial primary air, in both co-swirl (primary air swirling in the same direction as the secondary air), and counter-swirl configuration are introduced at the base of the burner. Results indicate that the counter-swirl configuration leads to uneven fuel distribution and local pockets of high stoichiometry. Increasing the swirl ratio between the primary and secondary stream enhances the central recirculation region that is likely to promote flame stability, but adversely affects the mixing and fuel distribution. Increasing air to fuel flow momentum ratio leads to low droplet dispersion but higher turbulent level.
Vapor Condensation Processes Associated With Premixed Flame Quenching
Authors: Ezekoye O. A.
Published: March 2022

Although unsteady flame quenching is a classical combustion problem, several key features of the process have yet to be understood. As an example, for an unsteadily propagating flame (away from the flammability limits) stagnating on a cold wall, there has not been conclusive experimental and theoretical agreement on the effects of varying the thermal boundary conditions on the flame extinction process. Characterization of the flame quenching problem is exacerbated by the length scales over which it occurs. The flame quenching distance for single sided flame quenching at atmospheric pressures is on the order of hundreds of micrometers, and thus few diagnostics can be used to determine the extent to which the flame propagates towards a specified temperature wall. The most meaningful diagnostics to date for such processes have been heat transfer measurements of the wall heat flux as the flame quenches. These diagnostics although second hand, provide information about the flame trajectory during a given quenching process. Even in the absence of detailed species description of the quenching process, several interesting features are noted as a result of the evolution of major species. The effect of water condensation during flame quenching which is examined in this study has been neglected in many studies of flame quenching. It is shown that coupling water condensation to the quenching process modifies both the extinction chemistry and also the wall heat flux measurement.
The Measurement of Transient 2-D Profiles of Velocity and Fuel Concentration Over Liquids
Authors: Ito Akihiko , Narumi Akira , Konishi Tadashi , Tashtoush Gassan , Saito Kozo , Cremers Clifford J.
Published: March 2022

We recently developed two different optical techniques in order to simultaneously measure transient 2-D profiles of velocity, temperature and fuel concentration that were generated by a spreading flame over liquid fuels. One technique employs a particle-track system combined with a laser-sheet system (PTLS) and a high speed camera, while the other technique employs a dual wavelength holographic interferometry (DWHI). The PTLS system revealed transient 2-D profiles of flame induced flow, while DWHI revealed 2-D profiles of fuel concentration over liquids. In this paper we present a series of velocity profiles for a pulsating flame spread over propanol and concentration profiles for gaseous propanol determined with PTLS and DWHI respectively. Other researchers have predicted the formation of small twin circulations, one a gas-phase circulation just ahead of the flame’s leading edge, and the other a small liquid circulation just underneath the gas-phase circulation. Our PTLS results confirmed these predictions, i.e., the formation of 5–10 millimeter diameter circulation in the gas phase and an accompanying approximately 20 millimeter diameter liquid circulation. Based on these data, we offer a phenomenological explanation of the mechanism of pulsating flame spread. In addition, we show that DWHI is a very promising technique for measuring transient fuel-concentration profiles over liquids.
Moving Matrix Reactor for Biomass and Organic Waste Gasification
Authors: Goldman Y. , Timnat Y. M. , Arfi P.
Published: March 2022

An organic waste gasification scheme based on the use of a new reactor concept has been investigated. The gasifier includes an intermediate heat carrier matrix, moving opposite to the gas stream. A technical embodiment of the concept is presented and a computational model for the description of the process in the reactor is developed. The first stage of the experimental study demonstrates the possibility of a two-phase counter-flow concept as a mean of providing super-adiabatic conditions, which are expected to enhance weak exothermic reactions and endothermic gasification reactions in the reforming zone. To perform a parametric study, the mathematical model was run in a simplified case with a single source of reaction-liberated energy. Temperature profiles were obtained and from our first predictive results, one can conclude that there is a broad range of combinations of gas velocity, matrix velocity and oxygen addition to control the gasification process. A feeding system and atomization into the moving matrix is currently developed to feed the reactor with an organic solid fuel downstream of the steam addition. The next stage of the research will allow us to test the complete gasification scheme with a selected biomass material. The simulation model will permit to evaluate anticipated performance of the moving matrix reactor and thus optimization of the process.