bluuebunny/crossref_metadata_2025_split huggingface dataset:
Freezing of Molten Solder Droplets Impacting Onto Flat Substrates in Microgravity
Authors: Haferl Stephan E. , Butty Vincent , Poulikakos Dimos , Giannakouros Johannes , Boomsma Kevin , Megaridis Constantine M. , Nayagam Vedha 
Published: November 2021

Abstract
The axisymmetric impingement of solidifying molten solder droplets onto smooth metallic substrates in a microgravity environment is investigated numerically to provide basic information of the heat and fluid flow phenomena and to determine the governing parameters of the process. The numerical predictions are also tested against experimental data. Millimeter-sized droplet impact events in reduced gravity are employed for scale up modeling of the impingement of picoliter size droplets of molten eutectic 63%Sn-37%Pb solder used in electronic chip packaging. The present article reports on both numerical (the main focus of the paper) as well as experimental work. To this end, the employed numerical model considers the axisymmetric impact and subsequent solidification of an initially spherical, molten solder droplet on a flat, metallic substrate. The laminar Navier-Stokes equations, combined with the energy transport equations are solved simultaneously in the liquid region (melt) using a Lagrangian approach. In the solid (substrate and solidified droplet material) the heat conduction equation is solved. A time and space averaged model of the thermal contact resistance between the impacting droplet and the substrate, is also incorporated in the model. The numerical model is solved using a Galerkin finite element method, where a deforming, adaptive triangular-element mesh is employed to accurately simulate the large-domain deformations caused by the spreading and recoiling of the impinging droplet. The experimental work has been conducted in reduced gravity with technically relevant impact velocities of ∼0.2m/s, in order to provide validation of the numerical predictions. In reduced gravity of 2×10−4g to 5×10−4g, the impact conditions correspond to Re = O(100), We = O(1), and Fr = O(10000), Ca = O(0.001). Presentation of the numerical results in terms of the Froude and the Ohnesorge numbers aided their interpretation Among the results that stand out is the formation of a large number of frozen ripples on the droplet surface as a result of the simultaneous manifestation of rapid oscillations and solidification. Furthermore, a non-intuitive behavior of the solidification times is reported. To this end, the dependence of the final solidification time on the Froude number (representing the variation of the impact velocity) was not monotonic and featured a distinct minimum for all values of Ohnesorge numbers in this study. Despite the complexity of the phenomenon, the numerical model captures well the main features of the experimental results. In addition, it gives key insights on the influence of the Ohnesorge and Froude numbers on the solidification process.
Thermal Characteristics of a Compact, Passive Thermal Energy Storage Device
Authors: Bauer Candice A. , Wirtz R. A. 
Published: November 2021

Abstract
A Thermal Energy Storage (TES) system uses a Phase Change Material (PCM) to store heat during peak power operation of variable power dissipating devices via the latent heat effect. The TES composite developed is a plate-like structure that consists of a central core of foamed aluminum that is packed with a PCM. By considering the elements of the composite to be thermal resistors and constructing a flat-plate thermal conductivity apparatus, the plate-to-plate effective thermal conductivity is determined. The composite effective thermal conductivity is primarily composed of the thermal conductivity of the aluminum foam which is reduced by the effect of the aluminum foam-to-plate bond resistance. Heat flow through the PCM slightly augments the effective thermal conductivity. An increase in aluminum foam metal fraction results in an increase in the effective thermal conductivity of the composite because only about 2% of the heat flow is through the PCM, and the interfacial bond resistance decreases due to increased contact area. The trade-off is that as there is an increase in aluminum foam metal fraction, the volumetric latent heat decreases; thus, the storage time is reduced.
The Design of a Thermochromic Liquid Crystal Based Flow Visualization Surface
Authors: Lussier Brett A. , Lupino Gina , Anderson Ann M. 
Published: November 2021

Abstract
This paper describes the design, construction and testing of a thermochromic liquid crystal based, non-intrusive, surface flow visualization system. The system uses a pin-finned heat sink in contact with a thin sheet of liquid crystals and is easily mounted in a wind tunnel. When heated and placed in a fluid flow, the pin-finned heat sink produces teardrop-shaped thermal wakes that indicate the direction of the flow. We performed an optimization experiment and determined that the best flow visualization images are achieved for heat sink base temperatures that are 10–20 °C above the liquid crystal activation temperature. Under these conditions, the full range of the liquid crystals is utilized. We present liquid crystal flow visualization results for flow about streamlined and blunt objects and demonstrate the performance of the liquid crystal surface. We also compare liquid crystal images for flow about a blunt body to PIV data and show good qualitative agreement. The technique is repeatable, non-intrusive and instructive for learning about surface flow characteristics.
A Comparative Case Study in the Development of Thermal Manufacturing Curricula
Authors: Smith R. N. , Doumanidis H. C. 
Published: November 2021

Abstract
A collaboration between faculty at Tufts University and Rensselaer Polytechnic Institute has initiated a research-curriculum development program to promote high level technology transfer both with the classroom and through other educational venues in the area of Thermal Manufacturing and Materials Processing. One central aspect of this collaboration is the concurrent development of two new graduate courses at these respective institutions. The specific content of each of the two courses will be described in some detail in addition to some of the developmental background that constrained them. In particular, the technology transfer issue will be discussed, including a goal to communicate to a much wider audience some of the advances in this technical area without requiring a graduate level heat transfer background. Additional issues include our experiences with distance learning in thermal manufacturing and with the development of curriculum materials for use in other courses, at the graduate and undergraduate level, at both institutions.
Heat Transfer Coefficients for Simultaneously Developing Flow in Rectangular Tubes
Authors: Garimella Srinivas , Dowling William J. , Van derVeen Mark , Killion Jesse D. 
Published: November 2021

Abstract
A study of heat transfer in simultaneously developing flow through rectangular tubes is presented in this paper. Heat transfer coefficients were measured for three different tube sizes and shapes (Dh = 2.21 mm, α = 0.050; Dh = 3.02 mm, α = 0.108; and Dh = 1.74 mm, α = 0.029), which correspond to typical dimensions used in automotive heat exchangers. For each of these tubes, several different tube lengths were tested to measure the effect of developing flow on the Nusselt number. The study primarily focussed on the laminar and transition regimes, with some data in the turbulent regime, which is typical of the operating conditions for many automotive heat exchangers. The results demonstrate that developing flow enhances Nusselt numbers, especially for the short tubes used in heater cores, although for the geometry range studied, the effect of aspect ratio was not very significant. Heat transfer correlations were developed from the data, with excellent agreement between the data and the values predicted by these correlations. These correlations accounted for the effects of Reynolds number (118 &lt; Re &lt; 10671) Prandtl number (6.48 &lt; Pr &lt; 16.20), and bulk-to-wall property variations (0.243 &lt; μb/μw &lt; 0.630), and geometric features such as tube length, hydraulic diameter, and aspect ratio.
Fluid Mechanics and Biological Interaction in a Tubular Nitrifier Designed for Use in Space
Authors: Pickering Karen D. , Ungar Eugene K. , Vega Leticia M. , Campbell Melissa L. 
Published: November 2021

Abstract
Biological processes are currently being investigated for use in spacecraft wastewater treatment. In a biological wastewater processor, microorganisms are used to degrade organic and inorganic contaminants to carbon dioxide, water, and other metabolic products. One step in the process is nitrification, in which ammonium ions in the wastewater stream are converted to nitrate ions. Traditional reactor designs for nitrification, which include continuously stirred tank reactors and trickling filters, are unsuitable for use on spacecraft due to their reliance on gravity for aeration. A tubular reactor for aerobic nitrification in a microgravity environment has been developed to allow use of biological systems for wastewater treatment on spacecraft. The tubular reactor uses a 3.2 mm ID tube 305 m long with co-current air and wastewater flow. Aerobic microbes grow on the tube walls. Because of the small tube diameter and the high surface tension of the wastewater, the air/wastewater flow is gravity independent. Thus it is expected that the fluid flow and biological performance will be identical in Earth-normal gravity and in flight.
Uncertainty Estimation in the Determination of Thermal Conductivity of 304 Stainless Steel
Authors: Blackwell Bennie F. , Gill Walter , Dowding Kevin J. , Easterling Robert G. 
Published: November 2021

Abstract
The thermal conductivity of 304 stainless steel has been estimated from transient temperature measurements and knowing the volumetric heat capacity. Sensitivity coefficients were used to guide the design of this experiment as well as to estimate the confidence interval in the estimated thermal conductivity. The uncertainty on the temperature measurements was estimated by several means, and its impact on the estimated conductivity is discussed. The estimated thermal conductivity of 304 stainless steel is consistent with results from other sources.
Direct Refrigeration by Electron Field Emission From Diamond Microtips
Authors: Fisher T. S. , Walker D. G. 
Published: November 2021

Abstract
This paper describes a concept for creating high-capacity, direct electrical-to-thermal energy conversion for compact cooling based on electron field emission. Electron field emission involves the transport of electrons that tunnel through a potential barrier. The thermodynamics of field emission have remained relatively unexplored. However, emission from wide-band-gap semiconductors, such as diamond, is known to produce an energy filtering effects such that high-energy electrons possess higher probabilities of emission. Lower energy electrons replace the emitted electrons, and thus, this process can produce a refrigeration effect. The refrigeration capacity is proportional to the emission current density, which is very high for diamond emitters. This high electrical current density implies that high thermal current densities are possible. The present work provides a thermodynamic analysis and energy conversion predictions based on experimental current-voltage data from diamond tip emitters. Energy fluxes in excess of 100 W/cm2 are predicted by the theory for room-temperature operation.
Modeling Film-Coolant Flow Characteristics at the Exit of Shower-Head Holes
Authors: Garg Vijay K. 
Published: November 2021

Abstract
The coolant flow characteristics at the hole exits of a film-cooled blade are derived from an earlier analysis where the hole pipes and coolant plenum were also discretized. The blade chosen is the VKI rotor with three staggered rows of shower-head holes. The present analysis applies these flow characteristics at the shower-head hole exits. A multi-block three-dimensional Navier-Stokes code with Wilcox’s k-ω model is used to compute the heat transfer coefficient on the film-cooled turbine blade. A reasonably good comparison with the experimental data as well as with the more complete earlier analysis where the hole pipes and coolant plenum were also gridded is obtained. If the 1/7th power law is assumed for the coolant flow characteristics at the hole exits, considerable differences in the heat transfer coefficient on the blade surface, specially in the leading-edge region, are observed even though the span-averaged values of h match well with the experimental data. This calls for span-resolved experimental data near film-cooling holes on a blade for better validation of the code.
A Numerical Analysis of Gas Turbine Disks Incorporating Rotating Heat Pipes
Authors: Cao Y. , Ling J. , Rivir R. , MacArthur C. 
Published: November 2021

Abstract
Radially rotating heat pipes have been proposed for cooling gas turbine disks working at high temperatures. A disk incorporating the heat pipe would have an enhanced thermal dissipation capacity and a much lower temperature at the disk rim and dovetail surface. In this paper, extensive numerical simulations have been made for heat-pipe-cooled disks. Thermal performances are compared for the disks with and without incorporating the heat pipe at different heating and cooling conditions. The numerical results presented in this paper indicate that radially rotating heat pipes can significantly reduce the maximum and average temperatures at the disk rim and dovetail surface under a high heat flux working condition. In general, the maximum and average temperatures at the disk rim and dovetail surface could be reduced by above 250 and 150 degrees, respectively, compared to those of the disk without the heat pipe. As a result, a disk incorporating radially rotating heat pipes could alleviate temperature-related problems and allow a gas turbine to work at a much higher temperature.
Neural Network Based Control of Preform Permeation in Resin Transfer Molding Processes With Real-Time Permeability Estimation
Authors: Nielsen David , Pitchumani Ranga 
Published: November 2021

Abstract
Variabilities in the preform structure in situ in the mold are an acknowledged challenge to effective permeation control in the Resin Transfer Molding (RTM) process. An intelligent model-based controller is developed which utilizes real-time virtual sensing of the permeability to derive optimal decisions on controlling the injection pressures at the mold inlet ports so as to track a desired flowfront progression during resin permeation. This model-based optimal controller employs a neural network-based predictor that models the flowfront progression, and a simulated annealing-based optimizer that optimizes the injection pressures used during actual control. Preform permeability is virtually sensed in real-time, based on the flowfront velocities and local pressure gradient estimations along the flowfront. Results are presented which illustrate the ability of the controller in accurately steering the flowfront for various fill scenarios and preform geometries.
Parametric Study of the Ablation Characteristics of Absorbing Dielectrics by Short Pulse Laser
Authors: George Samuel , Mitra Kunal 
Published: November 2021

Abstract
This paper investigates the effect of ablation of absorbing dielectrics by two successive ultra short pulses from an excimer laser source. The numerical model is based on two photon absorption followed by thermal degradation and diffusion. Unlike most previous studies the present formulation considers the transient nature of laser propagation within the medium. Heating of the material is dependent on light absorption by chromophores while ablation occurs through sublimation of the material from the surface. The mathematical formulation takes into consideration the saturation effects within the framework of a three level system of the electronic structure of chromophores. This involves solving a set of coupled rate equations, heat diffusion equation, and the transient radiative transport equation, using Fromm’s scheme. Results for the temperature distribution and ablation depth are obtained for different laser parameters and material properties. Parametric study of the delay time between two successive pulses, laser pulse width, laser fluence, activation energy, and the relaxation time is only performed in this paper for the purpose of brevity. The results obtained by the consideration of the transient radiative transfer equation are compared with the steady state formulation and significant differences are observed in the temperature profiles and the ablation depth.
Effective Thermal Conductivity of Compressed Woods
Authors: Asako Y. , Nishimura H. , Kamikoga H. , Yamaguchi Y. 
Published: November 2021

Abstract
The total amount of lumbers consumed in Japan during a year, reaches to 1.1 billion cubic meter. However, 75 percent of them are imported. The resource of same 1.1 billion cubic meters is growing up every year in the domestic forest. This is due to the price difference between the domestic and imported lumbers. It is strongly required to improve the quality of the domestic lumber. One solution of the improvement of the domestic lumber is the compression of the wood. It results in a good strength characteristics. However, the thermal characteristics of the compressed wood has not been reported yet. In this study, the effective thermal conductivity of compressed Japanese cedar (cryptomeria japonica) were measured. And the characteristics of the effective thermal conductivity are discussed.
Optimization of Vacuum Assisted Resin Transfer Molding for Sandwich Panels
Authors: Dai Jean , Pellaton Dominique , Hahn H. Thomas 
Published: November 2021

Abstract
The vacuum assisted resin transfer molding (VARTM) of sandwich panels may be facilitated by using high permeability layers over the skins or adding grooves in the surfaces of the core. The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. Before comparison, each method is optimized through simulations. The panel geometry and the injection pressure are held constant. The design parameters are the number of high permeability layers, and the number and size of grooves. The optimized processes are finally compared with each other in terms of the aforementioned cost and time. Meanwhile, the sensitivities of several important parameters in the cost model to the optimal result are studied.
Study on the Behavior of a Wetted Area Right After Liquid-Wall Contact in Pool Film Boiling
Authors: Ohtake Hiroyasu , Satoh Hiroyuki , Koizumi Yasuo 
Published: November 2021

Abstract
The behaviors of the rewetting on pool film boiling, focusing on observations of a collapse of a vapor film, a wetted area and a contact angle on a superheated surface were investigated experimentally. Using a U-shaped platinum wire with 2 mm diameter and 140 mm long, pool film-boiling experiments were performed for saturated water at atmospheric pressure. After a stable film-boiling state at a prescribed initial wall temperature was established, saturated water from a nozzle, set above the test wire, was injected on the superheated surface in the stable film-boiling, then artificial rewetting was forced on the superheated surface. During forming the artificial rewetting, the temperature fluctuation right under the liquid injection and the behavior of the rewetting were obtained for the initial wall temperatures of 600, 420, 400 and 300 degree-C, respectively. The present experimental results showed that the propagative collapse of the vapor film occurred when the initial wall superheat was below 300 K. On the other hand, above the initial wall superheat of 320 K, the rewetting declined after liquid injection was finished then film boiling recovered. The temperature was related to the thermodynamic limit of superheat, according to the measured temperature fluctuation during supplying the liquid. The wetted area right after liquid-wall contact and the advancing velocity of the rewetting front increased as the initial wall superheat decreased. The measured angles between the liquid-vapor interfacial line and the heated wall corresponded to dynamic contact angles were close to the dynamic advancing contact-angles in room temperature.
Mixing of Two Streams, Steam and Water, in a Converging Nozzle
Authors: Aybar Hikmet S. 
Published: November 2021

Abstract
Mixing of two fluid streams can be seen in many applications in chemical processing and energy generation industries. The supersonic steam blows into the cold water in the mixing nozzle. When the steam condenses, steam transfers to water heat and mass (because of the temperature difference and condensation) and momentum (because of the velocity difference). The condensation should be fully completed before the end of mixing nozzle. Thus, the length of the mixing nozzle is important parameter. After the condensation is completed, the flow is single phase, that is, liquid water, and the subsonic water flows in the converging nozzle. In this study, the mixing of the supersonic steam and subsonic water in a converging nozzle is investigated. The problem is modeled using one-dimensional continuity, momentum and energy equations, and solved numerically. For the calculation of the rate of condensation, a correlation for the contact heat transfer coefficient is used.
Thermal Spreading Resistance of Eccentric Heat Sources on Rectangular Flux Channels
Authors: Muzychka Y. S. , Culham J. R. , Yovanovich M. M. 
Published: November 2021

Abstract
A general solution, based on separation of variables method for thermal spreading resistances of eccentric heat sources on a rectangular flux channel is presented. Solutions are obtained for both isotropic and compound flux channels. The general solution can also be used to model any number of discrete heat sources on a compound or isotropic flux channel using superposition. Several special cases involving a single and multiple heat sources are presented.
Transient Axial Free Jet Impinging Over a Flat Uniformly Heated Disk: Solid–Fluid Properties Effects
Authors: Bula Antonio J. , Rahman Muhammad M. , Leland John E. 
Published: November 2021

Abstract
Transient conjugate heat transfer process during axial free jet impingement on a solid disk of finite thickness was considered. As the fluid reached steady state, power was turned on and a uniform heat flux was imposed on the disk at its opposite surface. The numerical model considered both solid and fluid regions. Equations for conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries, as well as at the solid-liquid and liquid-gas interfaces. Inside the solid, only the heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. A non-uniform grid distribution, captured from a systematic grid-independence study, was used to adequately accommodate large variations near the solid-fluid interface. Computed results include the simulation of six different substrate materials namely, aluminum, constantan, copper, diamond, silicon, and silver, and three different impinging liquids, FC - 77, Mil - 7808, and water. The solids and fluids selected covered a wide range of possibilities of conjugate heat transfer phenomena. The analysis performed showed that the thermal storage capacity, defined as density times specific heat, is an important factor defining which material will attain steady state faster during conjugate heat transfer process, like the thermal diffusivity does it for pure conduction heat transfer.