bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Brazing on the Heat Transfer Performance of Fins in Radiators
Authors: Sundén Bengt , Abdon Andreas , Eriksson Daniel
Published: November 2021

The performance of a radiator copper fin is considered as the braze joint between the fin and the brass tube is not perfect. The influence of different thermophysical properties of the brazing materials, created intermetallic compounds and possible air gaps is considered. Numerical methods for both two-dimensional and one-dimensional calculations have been developed. The finite volume technique is applied and in the two-dimensional case, boundary fitted coordinates are used. Heat conduction in the fin and braze joint coupled with convective heat transfer in a gas stream is analysed. Results in terms of fin temperature distributions and fin efficiencies are provided. It is found that the detrimental effect of a poor braze joint is not as large as reported previously in the literature.
Thermodynamic Analysis of a Molten Carbonate Fuel Cell System Using Waste Derived Fuel Gas
Authors: Desideri Umberto , Lunghi Piero , Ubertini Stefano
Published: November 2021

The increasing energy demand along with the growing concern for the environmental issues requires a significant research effort on the development of energy systems with high efficiency and low environmental impact. The use of waste derived fuel in fuel cell systems provides the benefits of high efficiency and very low polluting emissions as well as an effective way of waste disposal.

In the present work an investigation of the potential use of waste derived fuel gas in Molten Carbonate fuel cell systems has been performed. A detailed description of the simulation model developed by the authors with the Aspen Plus thermodynamic flow sheet code is presented. The basic configuration of the plant uses pure methane as fuel. An improved plant configuration has been proposed which allows an optimal exploitation of all the thermal streams giving as an output high electrical yield and heat at high temperature. The plant is then adapted to different gas blends as fuel: landfill gas and gas from the gasification of MSW (Municipal Solid Waste). The analysis is focused on the comparison between different fuel gases plants in terms of efficiency, feasibility and process requirements. Depending on the fuel characteristics, different solutions are applied to the plant in order to achieve optimal exploitation of the thermal streams. A general conclusion is that the use of low BTU gas results in an efficient and environmentally sound power generation but leads to a reduction of the plant net power output especially in the case of using gas derived from existing gasification plants. A consistent research activity is required to identify waste derived fuel processing systems that can yield gases which allow an optimal exploitation in fuel cell systems.
Stationary Electrical Power Generation From an Integrated Fuel Cell System With Thermal Energy Recovery
Authors: Dickman Anthony J.
Published: November 2021

The objective of this paper is to present an overview of design, operating and performance considerations for stationary electrical power generation utilizing a Proton Exchange Membrane (PEM) fuel cell stack integrated with a proprietary IdaTech hydrogen fuel processor. Additionally, electrical and combined (electrical plus thermal) efficiencies of integrated systems are presented.
Energy Efficient and Cool Storage Assisted Air-Conditioning System for Hospital Building
Authors: Maheshwari Gopal P. , Al-Murad Raba’a A. , Al-Hadban Yehya N. , Sebzali Mohammed J.
Published: November 2021

Air-conditioning (A/C) is an important sector for Kuwait. It is not only the single largest consumer of electricity, its yearly import accounts for well over 200 million US dollars. Energy conservation measures have been in practice in Kuwait since 1983 through a well defined code of practice enforced by the Ministry of Electricity and Water (MEW). Additional energy efficient products and techniques developed thereafter, however, have not been introduced as the electricity is highly subsidized and the MEW code has not been modified. Applications of some of the cost effective energy conservation measures and use of cool storage for peak power shaving have been carried out as a demonstration project in a two-story building, housing the Center for Speech and Audio Therapy having 3,180 m2 of air-conditioned space. As a first step, the building cooling load was re-estimated using an energy simulation computer program and proper design specifications. It was found to be 31.4% lower than the original estimated load of 161.3 tons of refrigeration (RT). Use of energy-efficient windows and cooling recovery units that were found to be cost-effective resulted in a final building load of 64.5 RT. Finally, ice storage was incorporated to meet 50% of the peak cooling load. This paper presents the complete design details including the impact of a building load simulation program and cost benefit analysis of important energy conservation measures. It also presents a design and operation scheme for a cool storage, assisted A/C system and its performance results collected during the summer of 1998.
Entropy Generation Maps of a Low-Specific Speed Radial Compressor Rotor
Authors: Iandoli Carmine Luca , Sciubba Enrico
Published: November 2021

The flow field in the rotor of a low-specific speed radial compressor is computed in a fully 3-D simulation and the irreversible entropy generation rates directly calculated from the local velocity- and temperature values. The code used for the simulation is a commercial CFD-finite volumes package, FLUENT™, augmented by an novel entropy generation routine adapted from the original formulation due to Bejan [1]. The model provides the designer with exact and detailed knowledge of the local values of the irreversibility production, allowing for a separate accounting of viscous- and thermal effects and thus resulting in a valuable tool for the search of design improvements. These local entropy generation rates can of course be integrated over the entire flow field to obtain the global irreversibility production, directly linked with the rotor efficiency: but more important is the possibility of obtaining an exact “mapping” of these local values in some particularly “critical” design areas (leading edge of the blade at the inlet, first portion of the channel on the pressure side, last portion of the channel on the suction side, rotor exit). By direct comparison of repeated simulations, the designer can then easily assess the relative performance of different blade arrangements and rotor configurations. In particular, it is possible to compute, via a direct application of the Gouy-Stodola lost work formula, the isentropic efficiency of the rotor.

The possibility is discussed of developing a “configuration optimisation procedure” based on the systematic, iterative and automatic application of this type of analysis.
Study of Lithium Polymer Interface to Enhance Efficiency and Safety in Lithium/Water Batteries
Authors: Cho Jeong-Ju , Urquidi-Macdonald M.
Published: November 2021

New gel electrolytes composed of silica powder and organic electrolytes for the application of lithium/seawater batteries were tested with a porous separator. The maximum current density was ∼25mA/cm2. The discharging current was decreased suddenly because of two reasons. One reason is that the porous separator became clogged with lithium hydroxide and the other is because of the deposition of lithiumsilicate on the lithium surface, which was confirmed using SEM, XPS and hydroxide ion flux measurements. The efficiency (5 ∼ 27%) of the lithium oxidation was also obtained by measuring the hydrogen volume. The efficiency is strongly dependent on the ambient temperature. The effect of additives and other gel systems was also investigated.
Three Dimensional Analysis of Transport and Reaction in Proton Exchange Membrane Fuel Cells
Authors: Um Sukkee , Wang C. Y.
Published: November 2021

A three-dimensional computational study based on the finite volume method is carried out for proton exchange membrane (PEM) fuel cells with a Nation 117 membrane and an interdigitated flow field on the cathode. Emphasis is placed on obtaining a fundamental understanding of fully three-dimensional flow in the air cathode and how it impacts the transport and electrochemical reaction processes. For the first time, fully three-dimensional results of the flow structure, species profiles and current distribution are presented for PEM fuel cells with the interdigitated flow field. The model results show that forced convection induced by the interdigitated flow field in the backing layer substantially improves mass transport of oxygen to, and water removal from, the reaction zone thus leading to a higher cell current density as compared to that of the serpentine flow field. The computations also indicate a need to account for water condensation and ensuing gas-liquid two-phase flow and transport in the porous cathode at high current densities. The present computer model can be used as a design or diagnostic tool for fuel cell cathodes with complex structural flow fields.
Molecular Tagging Fluorescence Velocimetry (MTFV) to Measure Meso- to Micro-Scale Thermal Flow Fields
Authors: Park J. S. , Kihm K. D. , Pratt D. M.
Published: November 2021

The development of a molecular tagging fluorescence velocimetry (MTFV) system is discussed and measurement results are presented for a meso-scale flow field of thermally driven capillary pore of 5-mm inner diameter that is tilted 5° from the horizon. The developed technique uses caged Dextran conjugates of caged fluorescene dyes of less than 10 nm in size for tracers. The frequency-tripled UV band (λ = 355 nm) of a pulsed Nd:YAG laser uncages the molecules by photo-cleaving that is decomposition of a caging chemical group and a fluorescence chemical group. Then a CW blue Argon-ion laser (λ = 488 nm) pumps the fluorescence of only those uncaged molecules, whose emmission band is centered at λ = 518 nm, and a sequential recording of the fluorescence images are digitally recorded and analyzed for Lagrangian velocity field mapping. The use of the technique allows detailed measurements of the thermally driven three-dimensional flow inside a heated capillary pore. The measurement shows that the meniscus surface flow is mainly driven by the thermocapillary stress field, occurring due to the surface temperature gradient, while the bulk flow inside the pore is driven largely by the natural convection buoyancy. The whole capillary flow is made by a combination of these two different flow effects. As to the heater position, above or below the interface, the three dimensional flow patterns are measured totally in the opposite way.
Optical Technique to Measure Transient Interface Temperature During Droplet Impingement on a Cooled Surface
Authors: Li Y. , Longtin J. P.
Published: November 2021

Liquid droplets impinging upon a solid surface are present in many diverse and important engineering and scientific applications. Examples include impingement cooling of surfaces, condensation phenomena in which liquid droplets fall and strike a surface, vigorous mixing of gas-liquid systems, and in manufacturing, e.g., pouring a liquid material onto a cooled surface or mold to form objects. The accurate measurement of the solid-liquid interface temperature of a liquid droplet impinging on a solid surface is extremely difficult to do using traditional, contact-based techniques, however. This work presents a laser-based technique that is capable of resolving the transient interface temperature change as a liquid droplet strikes a surface. The measurement records changes in reflected light from the liquid-solid interface, which is correlated to temperature change. In this work, the substrate is BK7 glass or quartz. The liquid falls from a height of several centimeters, while the laser beam is sent through the transparent solid material from the underside for the measurement. Results are presented for water and glycerin, with good agreement found between predicted and measured temperature histories. Additional features of the technique include extremely fast temporal resolution, which is limited only by the speed of the light-capturing electronics. A temporal resolution of 1 microsecond is readily obtainable with inexpensive electronics. Also, the use of a high-quality Gaussian laser beam from, e.g., a HeNe laser or a single-mode fiber can be focused to a spot size ranging from several millimeters to 10 microns in diameter at the liquid interface, thus providing a wide variety of spatial resolutions, including those in the microscale. Finally, an array of interrogation beams can be employed simultaneously to monitor the spatial temperature history of a droplet as it spreads and cools once striking the surface. Both present and future applications of the technique will be discussed in the talk.
Average Heat Transfer Coefficient Measurements in a Fuel Bundle: Method Development
Authors: Armfield Mary V. , Langford Heather M. , Beasley Donald E. , Conner Michael E.
Published: November 2021

Measurement of single-phase heat transfer rates in a laboratory-scale rod bundle can aid in the design of a full-scale nuclear fuel bundle. It is desirable to obtain heat transfer coefficient measurements as a function of axial position with a high degree of measurement confidence. To achieve this goal, a heated calorimeter is designed and instrumented to measure power input and temperature. Temperature measurement is accomplished using thermocouples embedded in the calorimeter material, and a cartridge heater inserted concentrically in the calorimeter material creates a constant heat flux. The present study examines the contributions of the design parameters and uncertainties in the measurements to the overall uncertainty in the heat transfer coefficient. A design stage uncertainty analysis allows prediction of the required uncertainty in temperature difference measurement to achieve a desired uncertainty in the heat transfer coefficient. The experimental design for differential temperature calibration and representative uncertainty results are presented. All significant contributions to the total uncertainty in heat transfer coefficient are described and quantified.
Characteristics of a Falling Liquid Film on the Outer Surface of a Vertical Pipe: Minimum Wetting Rates and Waves on the Film
Authors: Koizumi Yasuo , Ohtake Hiroyasu , Ikeda Shinichi
Published: November 2021

The minimum wetting rate (MWR) of an isothermal R-113 falling film on an outer surface of a vertical 25 mm OD pipe was examined. The fundamental characteristics of waves (the amplitude, frequency, velocity and wave length) on the falling film were also investigated in the range of the film Reynolds number Ref = 60 ∼ 600. The MWR was not obtained even at extremely small flow rate of 0.38 cc/min (Ref = 0.70). That flow rate was much smaller than the value expected for the smooth surface film although the surface observed was flat. It was pointed out that another factor such as the surface tension or the wettability might need to be included for the MWR expression. The mean film thickness was well represented by the Nusselt film thickness equation although the film surface was covered with many waves. In Ref ≤ 130, the waves were symmetrical and did not deform as the waves proceeded to downstream. When Ref ≥ 300, the waves were like roll waves and the amplitude grew as the waves traveled. The wave amplitude, frequency, velocity and length all showed similar variation tendency that each value changed the trend of variation for Ref across Ref ≅ 300. The waves behaved like theoretical small-perturbation waves in Ref ≤ ∼ 300 and the characteristics of the waves deviated from that when Ref > 300.
Transient Bubble Formation on a Polysilicon Micro Resister
Authors: Tsai Jr-Hung , Lin Liwei
Published: November 2021

Transient bubble formation has been investigated on a polysilicon micro resister of 95μm long, 10μm wide, and 0.5μm thick. The polysilicon micro resister functions as both a heating source and a temperature transducer of thermal bubble nucleation process. At input current of 22 to 30 milliamps, a single spherical bubble is nucleated with a waiting period, when the heating wall temperature drops up to 8°C before a bubble nucleated, of about 1 to 2 seconds depending on the input current. Analytical models are developed to characterize the wall temperature behavior in this micro scale. Substrate warming is found effective to the wall temperature after 0.4 second of heating. Furthermore, evaporation is identified as the major contribution mechanism of the temperature drop before the bubble nucleation. An equivalent heat transfer coefficient is found in the order of 105 W/m2°C with the time constant of 1.25 to 2.5 seconds varying with input current.
Effect of Surface Roughness on Gaseous Flow Through Microchannels
Authors: Turner Stephen E. , Sun Hongwei , Faghri Mohammad , Gregory Otto J.
Published: November 2021

This paper presents an experimental investigation on nitrogen and helium flow through microchannels etched in silicon with hydraulic diameters between 10 and 40 microns, and Reynolds numbers ranging from 0.3 to 600. The objectives of this research are (1) to fabricate microchannels with uniform surface roughness and local pressure measurement; (2) to determine the friction factor within the locally fully developed region of the microchannel; and (3) to evaluate the effect of surface roughness on momentum transfer by comparison with smooth microchannels. The friction factor results are presented as the product of friction factor and Reynolds number plotted against Reynolds number. The following conclusions have been reached in the present investigation: (1) microchannels with uniform corrugated surfaces can be fabricated using standard photolithographic processes; and (2) surface features with low aspect ratios of height to width have little effect on the friction factor for laminar flow in microchannels.
Analysis and Characterization of Thermoelectric Microrefrigerators
Authors: Ju Y. Sungtaek
Published: November 2021

Advances in film growth techniques have sparked a renewed interest in thermoelectric (TE) devices. A previous study suggested that a drastic improvement in the figure of merit can be achieved for superlattices and quantum wells by exploiting phonon scattering/reflection at interfaces [1] or carrier pocket engineering [2]. Thin-film devices are also of great significance because of their capability to handle considerably higher heat flux than conventional bulk modules [3].

Microrefrigerators consist of a single or multiple thin-film thermoelement(s). The use of thin films introduces the full complexity of solid-solid interfaces into any complete discussion of these refrigerators. Many investigators noted that the electrical contact resistance has adverse effects on TE cooling. Less attention has been paid to thermal interface resistance and the boundary Seebeck effects. While previous studies [4] have indicated that the interface effects are related to each other via boundary forms of the Wiedemann-Franz-Lorenz law and the Kelvin-Onsager relation, the impact of their mutual interactions on thermoelectric cooling has remained relatively unexplored.
A Micro-Scale Membrane-Actuated Condenser/Evaporator for Enhanced Thermal Management
Authors: Francois Marianne M. , Shyy Wei , Chung Jacob N.
Published: November 2021

There is a strong need to improve our current capabilities in thermal management and electronic cooling. The present study investigates the feasibility of a micro-scale membrane-actuated dropwise condenser/evaporator. An actuated membrane is adopted as the droplet condensing and ejecting device. Droplets with appropriate dimensions and frequencies are formed and ejected for efficient cooling. The present system requires no mechanical moving parts, and hence is reliable. In addition, it needs little maintenance due to closed recirculation, exhibits favorable packaging scalability in view of the modular concept, and offers high energy transfer effectiveness. In this work, we outline the thermodynamic consideration based on a vapor-compression cycle to assess the performance of such a device. The coefficient of performance of the cycle is estimated for four different fluids: water, R12, R134a and FC-72. The system design parameters and operating performances are estimated for droplet sizes ranging from 10 to 500 micrometers. It is demonstrated that in this operating range, the gravity effect is small, making this device ideal for both earth-bound and spacecraft applications.
Anisotropic Thermal Conductivity of a Si/Ge Quantum Dot Superlattice
Authors: Borca-Tasciuc Theodorian , Liu Weili , Liu Jianlin , Wang Kang L. , Chen Gang
Published: November 2021

In this work, we present experimental results on the in-plane and cross-plane thermal conductivity characterization of a Si/Ge quantum-dots superlattice structure. The quantum-dots superlattice was grown by molecular-beam-epitaxy and self-organization. The anisotropic thermal conductivity measurements are performed by a differential two-wire 3ω method. The measured in-plane and cross-plane thermal conductivity values show a different temperature behavior. The results are compared and explained with heat transport models in superlattices.
Molecular Dynamics Simulation of Hydrogen Storage in Single-Walled Carbon Nanotubes
Authors: Maruyama Shigeo , Kimura Tatsuto
Published: November 2021

The hydrogen storage mechanism of SWNTs was studied through molecular dynamics simulations. Assuming the simple physical adsorption of hydrogen to the surface of SWNTs, potential forms between H2-H2 and C-H2 were both expressed by Lennard-Jones functions. Fixing the relative coordinates of carbon atoms to the center of mass of each SWNT, the center of mass motion was modeled with the van der Waals force between SWNTs. Hydrogen absorption in small bundles of (8,8), (10,10) and (12,12) SWNTs were tested. In order to realize the adsorption between SWNTs within reasonable simulation period, the van der Waals energy between tubes was once decreased and recovered. While the amount of hydrogen adsorption per unit carbon mass inside SWNTs increased with increasing diameter, adsorption between tubes was almost constant. Total amount of hydrogen adsorption for 77 K and 15 MPa system was predicted as 6.9, 7.7, and 8.1 wt % for (8,8), (10,10), and (12,12) bundles, respectively.
Film Cooling on a Flat Surface With a Single Row of Cylindrical Angled Holes: Effect of Discrete Tabs
Authors: Ekkad Srinath V. , Nasir Hasan , Acharya Sumanta
Published: November 2021

The effect of discrete delta-shaped tabs on the film cooling performance from a row of cylindrical holes is investigated. The holes are inclined at 35° along the streamwise direction. Three tab locations are investigated: (1) tabs placed along the upstream edge of the hole; (b) tab placed along the downstream edge of the hole; and (3) tabs placed along the lateral edges of the hole. Measurements were carried out in a low-speed wind tunnel using the transient liquid crystal technique. The mainstream velocity and free-stream turbulence intensity in the low speed wind tunnel are 8.5 m/s and 6% respectively and the Reynolds number based on hole diameter is 6375. Three blowing ratios of 0.56, 1.13, and 1.7 are tested. Results show that the tab placed upstream of the hole covering the 33% of the hole exit provides the highest film effectiveness compared to other tab locations studied. This is because the jet lift-off in the presence of the tabs is reduced and there is greater lateral spreading of the jet.
Influence of Freestream Vortical Structures on Stagnation Region Heat Transfer
Authors: Oo Aung N. , Ching Chan Y.
Published: November 2021

An experimental study was performed to investigate the influence of freestream vortical structures on stagnation region heat transfer. A heat transfer model with a cylindrical leading edge was tested in a low speed wind tunnel at Reynolds numbers ranging from 67,750 to 142,250 based on leading edge diameter of the model. Turbulence generating grids of parallel rods of diameter, 2.86 cm, 1.59 cm and 0.95 cm, were placed upstream of the heat transfer model in horizontal and vertical orientations to generate freestream turbulence with different orientations of vortical structures. The rods in horizontal orientation were perpendicular to the stagnation line and those in vertical orientation were parallel to the stagnation line of the heat transfer model. The distance between the grid and heat transfer model was varied from 25 to 125 rod diameters. The grids with rods in the horizontal orientation, where the primary vortical structures are expected to be perpendicular to the stagnation line, result in higher heat transfer than with the grids where the rods are in the vertical orientation. The difference in heat transfer with the two grid orientations decreases with increasing grid-to-model distance for a given rod-grid. The difference also decreases with decreasing rod size for a given normalized grid-to-model distance. For the 2.86 cm rod-grid, the difference in heat transfer augmentation between horizontal and vertical grid-orientations is highest at the stagnation line and decreases with streamwise distance. This difference, however, remains fairly constant over the whole stagnation region for the 1.59 cm and 0.95 cm rod-grids.
Femtosecond Laser Ablation of Titanium and Silicon
Authors: Ye Mengqi , Grigoropoulos Costas P.
Published: November 2021

Femtosecond laser ablation of titanium and silicon samples has been studied via time-of-flight (TOF), emission spectroscopy and microscopy measurement. Laser pulses of around 100 fs (FWHM) at λ = 800 nm were delivered by a Ti:sapphire femtosecond laser system. A vacuum chamber with a base pressure of 10−7 torr was built for ion TOF measurement. These ion TOF spectra were utilized to determine the velocity distribution of the ejected ions. While nanosecond laser ablation typically generates ions of a few tens of eV, femtosecond laser irradiation even at moderate energy densities can produce energetic ions with energies of up to a few keV. The most probable energy of these fast ions is proportional to the laser fluence. The structure and number of peaks of the TOF spectra varies with the laser fluence. Images of plume emission were captured by an intensified CCD (ICCD) camera. The plume emission spectrum was analyzed by a spectrometer. Laser ablated craters were measured by an interferometric microscope and a scanning electron microscope (SEM). Ablation yield was expressed as a function of laser fluence, and number of shots.
A Parametric Study of the Quasi-Steady State Temperature Field by a Moving Heat Source for Surface Treating
Authors: Bianco Nicola , Manca Oronzio
Published: November 2021

A three dimensional numerical analysis of a solid irradiated by a moving laser heat source in a quasi-steady state is carried out. The thermophysical properties of the material are considered to be temperature dependent. The dependence of the solution on the radiative and convective heat losses, the latter due to an impinging jet on the upper surface, is highlighted; the dependence of the temperature distribution on the Reynolds number of the jet is also presented. Different thicknesses and widths are shown to have discrepant influences on the induced thermal fields for a Gaussian laser source. The parametric analysis shows the thermal profiles to be strongly dependent on the jet Reynolds number. The thermal field is almost symmetric with respect to the spot center for a Peclet number equal to 0.1. The thermal penetration decreases as the Peclet number increases.
Numerical Modeling of Diffusion Boundary Layer in Strip Casting Process of Carbon Steel
Authors: Kuznetsov A. V.
Published: November 2021

This paper is aimed at the investigation of the diffusion boundary layer near the cooled casting surface encountered in the horizontal continuous casting process of carbon steel. The strip casting process is a relatively new continuous casting process. This process makes it possible to produce high-quality flat steel products directly, without using hot rolling. This explains why this process is very attractive for industry. Extensive numerical simulations under equilibrium and nonequilibrium assumptions provide valuable insight into the physics of diffusion boundary layer.
Technical Feasibility of a New Solventless Approach to Manufacture Pre-Pregs and Laminates for Electronic Applications
Authors: Dehnke Lynnette M. , Hogade Ranjeet R. , Castro Jose M.
Published: November 2021

This study refers to the technical feasibility of a continuous process for manufacturing pre-pregs and copper-clad laminates for electronic applications, with the aim to overcome three critical technological challenges, the elimination of environmentally detrimental solvents, elimination of voids and elimination of cure/temperature history variability between laminates. The new approach is based on the concept of injection pultrusion or continuous RTM. The centerpiece of the process is the impregnation die. Glass fabric and resin are fed into the die where impregnation and depending of the design, partial reaction occurs. The B-staging, if not finished in the die, will be done in an oven located immediately after. The final cure and lamination occurs in a continuous belt clamp. In the present paper, we discuss the chemo-rheology of a potential resin system and use it to establish the technical feasibility of the process.
Micro-Scale Aspects of Spray Deposition Processing: A Semi-Analytical Model for Droplet Spreading and Solidification at Off-Normal Impact Angles
Authors: Johnson S. B. , Delplanque J.-P.
Published: November 2021

Droplet impacts are rarely normal to the target substrate during thermal spray processing because of droplet dispersion in the spray cone or because the substrate is moving. A model for droplet spreading and solidification after off-normal impact on a cold substrate was developed. This model is based on Madejski’s energy conservation model but uses a three-dimensional velocity field, which satisfies the no slip condition at the solid front, the no shear condition at the free surface as well as the continuity equation. Furthermore, the present model assumes the shape of the spreading droplet to have a non-axisymmetric shape (limaçon perimeter and a uniform height). Stefan solidification is assumed. A mechanical energy balance is used to describe the deformation of the spreading droplet. The resulting integro-differential equation is solved numerically using a modified Euler predictor-corrector method. This model was validated by comparison with existing energy-conservation models in the case of normal impact. The results indicate both a decrease in the final splat diameter and a decrease in the expansion rate of the spreading droplet as the impact angle increases, as measured from the normal axis. The resulting impacts are therefore less efficient as the impact angle increases.
Theoretically-Based Leidenfrost Point Model
Authors: Bernardin John D. , Mudawar Issam
Published: November 2021

This study presents a theoretically-based model of the Leidenfrost point (LFP); the minimum liquid/solid interface temperature required to support film boiling on a smooth surface. The model is structured around bubble nucleation, growth, and merging criteria, as well as surface cavity size characterization. It is postulated that for liquid/solid interface temperatures at and above the LFP, a sufficient number of cavities (about 20%) are activated and the bubble growth rates are sufficiently fast that a continuous vapor layer is established nearly instantaneously between the liquid and the solid. The model is applicable to both pools of liquid and sessile droplets. The effect of surface cavity distribution on the LFP predicted by the model is verified for boiling on aluminum, nickel and silver surfaces, as well as on a liquid gallium surface. The model exhibits good agreement with experimental sessile droplet data for water, FC-72, and acetone. While the model was developed for smooth surfaces on which the roughness asperities are of the same magnitude as the cavity radii (0.1–1.0 μm), it is capable of predicting the boundary or limiting Leidenfrost temperature for rougher surfaces with good accuracy.
Boiling Incipience in Narrow Channels
Authors: Lakshminarasimhan M. S. , Hollingsworth D. K. , Witte Larry C.
Published: November 2021

Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 1 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mass flux varied from 60 to 4586 kg/(m2s). The inlet subcooling varied from 3.0 to 15.3 °C, and the inlet pressure ranged up to 0.20 MPa. Liquid crystal thermography was used to measure distributions of surface temperature from which the heat transfer coefficients on the heated surface were calculated. Observations of the boiling incipience superheat excursion and the hysteresis phenomenon are presented and discussed.

In laminar flow, a boiling front was observed that clearly separated the region cooled by single-phase convection from the region experiencing nucleate boiling. A prediction for the wall temperature and heat flux at boiling incipience based on nucleation theory compared favorably with the data. An incipience turning angle was defined to describe the transition process from the point of incipience to fully developed nucleate boiling. Fully developed saturated nucleate boiling was correlated well by Kandlikar’s technique.
Experimental Investigation of Condensation Heat Transfer of Refrigerant R-134A in Helicoidal Pipes
Authors: Han J. T. , Lin C. X. , Ebadian M. A.
Published: November 2021

Alternative refrigerant R-134a is considered to be ozone-friendly and a potential candidate for replacing the refrigerant CFC-12 in refrigeration and air-conditioning applications. This paper presents the experimental investigation of condensation heat transfer characteristics of superheated R-134a vapor flowing inside helicoidal pipes with the cooling water flowing through the annular helicoidal passage in a counter-flow direction. The heat transfer experiment was performed for R-134a mass flow flux ranging from 100 to 420 kg/m2s with the superheat of the inlet vapor of 2.8°C and 8.3°C, respectively. The cooling water flow Reynolds Rew ranges from 1500 to 12000. The Nusselt numbers were experimentally determined for a helicoidal pipe with the helix axis of vertical direction. The correlations for Nusselt numbers are developed based on the experimental results, which can be used as a reference in the design of helicoidal pipe condensers.
Analysis and Prediction of Condensation Heat Transfer of the Zeotropic Mixture R-125/236ea
Authors: Cavallini Alberto , Censi Giuseppe , Del Col Davide , Doretti Luca , Rossetto Luisa , Zilio Claudio , Longo Giovanni A.
Published: November 2021

The high temperature glide mixture R-125/236ea at three mass compositions (28/72%, 46/54%, 63/37%) is tested during condensation against water in a tube-in-tube heat exchanger. The experimental runs to measure the heat transfer coefficients are carried out at saturation temperature ranging from 40°C to 60°C and mass velocities ranging from 100 to 750 kg/(m2 s). A gas chromatograph is used for on-line concentration measurements. By comparing the heat transfer performances of the three compositions to the condensation coefficients previously measured for the two pure components inside a smooth horizontal tube [Cavallini et al. (2000)], the dependence of the heat transfer performance on composition during condensation for a non-azeotropic mixture is investigated.

The film method by Colburn and Drew (1937) is applied to predict the experimental coefficients and it is found to underestimate the heat transfer rate, with more conservative results as compared to the equilibrium method by Silver (1947), Bell and Ghaly (1973).
Heat Transfer Characteristics for a Single Fin in a Boiling Liquid
Authors: Bu Yingzong , Kraus Allan D. , Chung Benjamin T. F.
Published: November 2021

This work utilizes the cascade algorithm to predict the heat transfer characteristics of a one-dimensional longitudinal fin of rectangular profile in a boiling liquid. In this analysis, the geometric parameters of the fin, the temperature at the fin base and the saturation temperature of the boiling liquid are assumed. With the utilization of experimental boiling heat transfer coefficient curves, the heat flux, temperature profile, and boiling heat transfer coefficient of each point on the fin are obtained. The effectiveness of the fin in a boiling liquid is plotted for different fin thicknesses. It is found that the fin conductivity, boiling liquid, fin geometry and fin base temperature all affect the effectiveness of the fin in boiling. The effectiveness curves clearly indicate whether a fin should be used or when it is advantageous to use a fin in boiling liquid.
An Analytical and Experimental Model for a Thermosyphon That Employs Solid/Liquid Phase Change Materials
Authors: Nnanna A. G. Agwu , Harris Kendall T. , Haji-Sheikh A.
Published: November 2021

Application of solid/liquid phase change material (PCM) for passive cooling of electronic modules is on the increase. A simplified method of predicting the thermal performance of passive cooling systems is needed for efficient design of thermal storage systems. This paper presents an experimental and approximate analytical method for quick estimation of the rate of thermal transport in solid/liquid PCM during and after the melting process. However, the emphasis of this paper is on the transport phenomena after the melting process is completed. This research is motivated in part by the need for a simplified analytical method of predicting the rate of heat transfer in buoyancy-driven fluids within a partitioned enclosure, and the need for a fundamental understanding of the rate of heat transfer in liquid melt after the phase change phenomena. These needs are of practical importance for efficient design of a thermal energy storage system. The approximate analytical model serves as a quick method of studying the performance of a thermosyphon system.
Modeling and Simulation of Subcooled Turbulent Boiling Flow
Authors: Zarate J. A. , Roy R. P. , Kang S. , Laporta Andre
Published: November 2021

Modeling and numerical simulation of turbulent sub-cooled boiling flow of refrigerant-113 through a vertical concentric annular channel with its inner wall heated are reported. The two-fluid model conservation equations were solved. The Reynolds stresses in the liquid phase momentum equation were closed using the gradient transport approximation. The turbulent viscosity was considered to be comprised of shear-induced and bubble-induced components. Boiling at the inner wall was described by a wall heat transfer model which splits the wall heat flux into convective, quenching, and vaporization heat flux components. This model was modified to reflect our measurement of the radial turbulent heat flux in the liquid phase near the wall. In addition, new wall laws for the liquid phase mean temperature and axial velocity were used. The computational results are compared with our measurements wherever possible.
Methodology for Designing a Hybrid Thermal Energy Storage Heat Sink
Authors: Zheng Ning , Wirtz R. A.
Published: November 2021

A thermal response model for designing a hybrid thermal energy storage (TES) heat sink is developed. The stabilization time and maximum operating (hot side) temperature-to-transition temperature difference are used to characterize the performance of the heat sink. The thermal properties of the PCM employed in the design are investigated. Integration of a design optimization algorithm into a thermal performance model of the TES-hybrid heat sink results in determination of a best design subject to geometric and heat loading constraints. A prototype based on this best design is build and used to benchmark the performance model. The performance measured is consistent with the simulation model predictions of performance.
Structure and Mixing Properties of Unsteady Round Nonbuoyant Turbulent Jets and Puffs in Still Gases
Authors: Sangras R. , Faeth G. M.
Published: November 2021

A theoretical and experimental study of the temporal development of unsteady round nonbuoyant turbulent jets (starting jets) and puffs (interrupted jets) is described, limited to sources in still and unstratified environments. The experiments involved dye-containing fresh water sources injected vertically downward into fresh water within a large windowed tank with injector passage length/diameter ratios of 50. Time-resolved video images of the flows were obtained using a CCD camera. Test conditions were as follows: jet exit diameters of 3.2–12.7 mm, jet exit Reynolds numbers of 1450–11700, volume of injected fluid for puffs up to 80 passage diameters long, and penetration lengths up to 100 source diameters. Near-source behavior varied significantly with source properties but the flows generally became turbulent near the jet exit with self-preserving behavior observed at distances greater than 20–30 source diameters from the source. Within the self-preserving region, both the normalized streamwise penetration distance and the normalized maximum flow radius varied as functions of time to the following powers, in agreement with estimates for self-preserving turbulent flows: 1/2 for starting nonbuoyant jets and 1/4 for nonbuoyant puffs.
Thermal Modeling of the Cavity in Pulsed Excimer Laser Calorimeters
Authors: Chen D. H. , Zhang Z. M.
Published: November 2021

A simplified finite element model is built to study the thermal response of the 193-nm pulsed-laser calorimeter. The nonequivalence between pulsed-laser heating and electrical heating is estimated to be 0.46% at the thermocouple locations by comparing the calibration factors for average-power laser heating and electrical heating. This study should help the development of calibration and measurement standards in pulsed energy measurements for deep ultraviolet excimer lasers that are important for photolithographic and materials processing applications.
The Effect of Wave Number on the Performance of BGT Absorbing Boundary Conditions for Acoustic Scattering
Authors: Harari Isaac , Djellouli Rabia
Published: November 2021

The computation of exterior wave problems at low wave numbers can become prohibitively expensive when higher circumferential modes are significant. An analysis of the effect of wave number on scattering problems, with local absorbing boundary conditions specified on simple shapes as on-surface radiation conditions, provides guidelines for satisfactory performance. Excessive computational cost may be avoided for most practical applications.
Newton-Like Method for Solving Inverse Obstacle Acoustic Scattering Problems
Authors: Djellouli Rabia , Farhat Charbel , Tezaur Radek
Published: November 2021

A Newton-like method is designed for determining the shape or sought-after shape modifications of a scatterer from the knowledge of acoustic far-field patterns at a given number of observation points. This method distinguishes itself from existing numerical procedures by the following features: (a) exact Jacobian matrices for the linearized problems rather than approximate ones, (b) a fast numerical procedure for computing these Jacobian matrices, (c) a computationally efficient absorbing boundary condition for the finite element discretization, and (d) a numerically scalable domain decomposition methods for the fast solution of high-frequency direct acoustic scattering problems.
Time-Dependent Calculation of Acoustic Radiation From Finite Wings Using BEM
Authors: Wood Trevor H. , Grace Sheryl M.
Published: November 2021

The calculation of acoustic radiation from finite wings using a 3D, time-domain Boundary Element Method (BEM) was investigated. Numerical convergence was studied and solutions obtained using an extrapolated convergence method were used to compare to 2D analytical solutions. Frequency-domain lift solutions were found to be accurate to less than 5% using relatively coarse grids (Δx ∼ 0.1) for reduced frequencies above 0.1 and less than approximately 3. The acoustic responses for high aspect ratio wings were found to agree well qualitatively with the 2D results. As an illustration of the capabilities of the method, a full-span, flapped wing configuration undergoing oscillatory motion was considered with a preliminary quantification of the aeroacoustic influence of the flap.
Ultrasound Modulation of Diffusive Optical Waves for Medical Imaging
Authors: Townsend Daniel J. , Stott Jonathan J. , Roy Ronald A. , DiMarzio Charles A.
Published: November 2021

Diffusive optical tomography [DOT] is a technique for imaging within the body. While DOT provides excellent results under good conditions, there are many situations (due to anatomy or other physical limitation) in which it suffers from a “limited view” problem. In this paper we discuss our work on a new technique for combining DOT with focused ultrasound to generate virtual sources of illumination. These virtual sources help overcome the limited view problem. We present our experimental results using laboratory tissue phantoms.
Vibration and Acoustic Evaluation of a Large Centrifugal Wastewater Pump, Part 1: Background and Experiment
Authors: Abbot Philip , Gedney Charles , Morton David , Celuzza Stephen , Dyer Ira , Ehlers Peter , Vaicaitis Rimas , Brown James , Guinzburg Adiel , Hodgson William
Published: November 2021

An extensive series of vibration and acoustic measurements has been conducted on a large (63 inch diameter three-vane impeller) centrifugal wastewater pump at a municipal pump station. Vibration measurements on the pump bearing housing exceeded the design specification at most operating blade-passing frequencies (BPF). The purpose of the testing was to determine the primary mechanisms of the vibration, including contributions from an acoustic resonance (within the piping system) and the pump’s hydrodynamic near-field. In Part 1, the physical mechanisms of pump vibration and overall experimental results are presented.
Sensitivity of Stiffness and Damping to Various Aspects of Material and Structural Behavior
Authors: Gibson Ronald F.
Published: November 2021

This paper reviews research which has demonstrated the use of nondestructive measurements of stiffness and damping to characterize some interesting aspects of both micromechanical and macromechanical behavior in materials and structures. The sensitivity of stiffness and damping to material microstructural detail, macroscopic defects and damage, degradation due to environmental conditions such as temperature and moisture, and other mechanical properties is examined. Observed changes in stiffness and damping can be particularly useful when measured by using nondestructive vibration tests, and there are potential applications of such measurements in both manufacturing quality control and in-service evaluation of materials and structures. A particularly attractive method for fast, low cost nondestructive measurement of stiffness and damping is based on the use of impulsive excitation, non-contacting response measurement, and data analysis with PC-based virtual instruments.