bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Induced Thermal and Fluid Transport Phenomena in Laser Assisted Chemical Vapor Deposition
Authors: Yu D. , Duncan A. B.
Published: January 2022

Laser-assisted Chemical Vapor Deposition (LCVD) utilizes a focused laser beam to induce a chemical vapor deposition process upon a substrate material. By moving either the substrate or the focal plane of the laser beam LCVD may be used to produce three dimensional structures having characteristic lengths on the order of μm. The physical phenomena associated with LCVD also occur on length scales of μm. For this reason, with the exception of the observation of bulk properties, detailed experimental observations of the fluid flow and heat transfer phenomena associated with the LCVD process do not exist. The LCVD process is characterized by the inter-relating fluid flow, chemical reaction and mass and heat transfer phenomena. In addition, the characteristics of the laser and the deposited material morphology influence the overall process.

The current research effort has developed a mathematical model and employed a numerical technique to characterize the three-dimensional natural convection induced by an incident laser beam around a fiber. This effort has not accounted for the effects of the chemical reactions associated with the LCVD process. The laser irradiance characteristics and the absorption by the fiber material have been incorporated into the energy equation. The velocity and temperature profiles in the boundary layer demonstrate the existence of a small area in which large temperature gradients and a chemical reaction occur. This effort has laid the foundation for an investigation of the one-dimensional diffusion controlled chemical vapor deposition process model. Additionally, it will facilitate the modeling of the three-dimensional homogeneous and heterogeneous reactions in the buoyancy driven flow produced in LCVD fiber formation.
Molecular Dynamics Study of Solid Thin-Film Thermal Conductivity
Authors: Lukes Jennifer R. , Liang Xin-Gang , Tien Chang-Lin
Published: January 2022

This study explores the feasibility of using the molecular dynamics computational technique to predict the thermal conductivity of solid thin films in the direction perpendicular to the film plane. The results show that thermal conductivity, as expected from thin-film experimental data and theoretical predictions, decreases as film thickness is reduced. In the large-size limit, this method yields thermal conductivities which asymptote to a value comparable to experimental data. The calculations modestly overpredict thermal conductivity, probably due to the use of a too-steep intermolecular potential. Most interestingly, an unusual wave effect is revealed for thin film thermal conductivity. This effect may be a manifestation of phonon wave interference analogous to the interference of light which determines the radiative properties of thin films.

It is also found that there are some temperature and computational domain size limitations on the applicability of molecular dynamics to the study of solid systems. A regime map is developed which delineates the conditions necessary for molecular dynamics to produce physically meaningful results. This work shows that molecular dynamics, applied under the correct conditions, is a viable tool for calculating the thermal conductivity of solid thin films. More generally, this work demonstrates the potential of molecular dynamics for ascertaining microscale thermophysical properties in more complex structures.
Heat Transfer and Solidification Model for a Droplet Impinging on a Solid Substrate
Authors: Canton A. , Delplanque J.-R. , Rangel R. H.
Published: January 2022

Spray deposition is an efficient means of manufacturing materials. It requires fewer manufacturing steps than conventional methods, saves energy, and reduces costs. Various experimental and theoretical studies have been conducted to investigate spray deposition processes. They generally focus on the fluid dynamics and/or heat transfer aspects of these processes. The effort discussed herein is dedicated to including a thermal solver into an existing Navier-Stokes solver for free surface flows (RIPPLE) in order to allow detailed numerical simulations of droplet impact, spreading, and solidification. The new model solves the thermal energy equation over the complete domain (droplet and substrate) using the enthalpy method. The enthalpy method is preferred to a temperature formulation because it does not require the tracking of the solid/liquid interface during the solidification process. The numerical procedure developed to this end is described herein, and test cases (with and without solidification) are presented.
Inverse Heat Conduction Problems and Generalisation of Experimental Results
Authors: Raudenský Miroslav , Druckmüller Miloslav , Horský Jaroslav
Published: January 2022

The paper describes the process of data evaluation for the experimental study of cooling by means of water and mist jets. The relative movement of nozzles and the cooled surface are characteristic of these experiments. The speed of movement and the relative position of the nozzle to the cooled surface are additional parameters to the standard thermal parameters. Two types of experiments are mentioned. Both are based on the same principle — a hot steel plate is cooled, temperature in several points of the plate is measured by embedded thermocouples and the temperature records are evaluated by an inverse heat conduction task. Using these results in mathematical models shows certain disadvantages. The data are influenced by noise from both the thermal and the spatial point of view. The data are rare in certain surface temperature areas due to the fast temperature changes during the quenching process. A numerical interpolating procedure has been developed to compute the general parameters describing the cooling and to reduce the amount of the experimental data.
Application of the Function Decomposition Method to Design of Solidification Processes
Authors: Hale S. W. , Keyhani M. , Frankel J. I.
Published: January 2022

In a unidirectional solidification design problem, the solidification velocity and liquid-side interfacial temperature gradient are of principle interest due to their effect on the morphology of the cast structure. The design challenge is the prediction of the temporal conditions at the boundaries such that the solidification velocity and liquid-side temperature gradient at the solid-liquid interface follow a prescribed scenario. This design problem requires the resolution of two inverse heat conduction problems: one in an expanding solid domain and the second in a shrinking liquid domain. Resolution of the solid domain results in a transient boundary condition that yields the prescribed solidification velocity, while resolution of the liquid domain results in a transient boundary condition that yields the prescribed interfacial temperature gradient.

An innovative and robust solution technique is proposed and demonstrated for resolution of the liquid-side temperature gradient design problem during unidirectional solidification. The technique, termed the Function Decomposition Method (FDM), is an innovative combination of function decomposition for the superposition of direct solutions, continuous least squares, and the weighted residual method which transforms the mildly ill-posed inverse heat conduction problem in the shrinking liquid region into a set of well-posed direct problems. To demonstrate its application, a set of test cases are presented which provide illustrative results highlighting the flexibility of the methodology.
Estimation of Transient Boundary Conditions in a Multimaterial: Computational and Experimental Analysis
Authors: Abboudi S. , Artioukhine E. A. , Riad H.
Published: January 2022

The goal of the proposed study is to analyze numerically and experimentally transient flux densities absorbed by specimen which is a typical thermal barrier. The studied composite material is obtained by thermal projection of a deposit of MCrAlY on a substrate in Copper. To solve this inverse heat conduction problem, we have used the implicit finite difference method for the direct problem and the iterative regularization method for the inverse problem. The developed numerical algorithm is based on the minimization of the residual functional which is the integrated difference between temperature histories measured and those calculated by solving the direct problem. The conjugate gradient method is used to solve the inverse problem. The residual functional gradient is computed by solving the adjoint problem and the optimal descent parameter is calculated by solving the problem for temperature variations. The heat flux evolution is approximated by cubic B-splines. The method is first validated with simulated numerically data and second validated experimentally by thermal cycling device. Temperature evolutions measured inside the specimen are used to solve the inverse problem.
Two-Phase Flow Pattern Identification From Fluctuating Components of Pressure and Void Fraction Signals
Authors: Teyssedou Alberto , Han Yanjie
Published: January 2022

This paper presents results on air-water flow pattern identification. The fluctuating components of void fraction are analyzed using the Probability Density Function (PDF). For bubbly and annular flows, the PDF’s show a single mode distribution. Double mode type PDF’s dominate the slug and churn flow regimes. Differential pressure and void signals are also analyzed using Power Spectrum Distribution Function (PSDF). The normalized PSDF’s for bubbly flows are broadband. For slug and churn flows, the PSDF’s show one dominant frequency with several smaller peaks.

For the churn-to-annular flow transition, the signals become more random with their spectrum shifting toward higher frequencies A single high frequency component characterizes annular flows. The average energy dissipation rate and the amplitude of the frequency components are used to develop a new flow pattern representation. This kind of representation allows different flow regime transitions to be better identified. Furthermore, by using an appropriate pressure transducer it should be possible to extend the application of the present technique to high-pressure steam-water systems.
Determination of Local Two-Phase Variables and Flow Pattern Characterization in an Upward-Flow, Rectangular Channel
Authors: Moujaes Samir F. , Sparks Jonathan C.
Published: January 2022

Local, time-averaged measurements of gas void fraction, gas velocity, gas bubble diameter, and bubble passage frequency in a rectangular channel (15.0 × 1.25 cm) are presented. Profiles of the gas velocity and the void fraction were characterized for the different flow regimes along the cross-sectional, transverse axes. Use of the average slug interval technique and a flow regime map, generated on coordinates of superficial velocities have been determined to be useful tools for characterizing two-phase flows and are in good agreement with established flow regime maps for both round and rectangular channels, especially for the bubble-to-slug transition. An alternative method using the centerline gas void fractions is also used to characterize the flow regimes and shows some promise where these values range from 8.0% to 57.0%.
Flow Pattern of Gas-Liquid Two-Phase Annular Flow in a Spiral Tube
Authors: Asano Hitoshi , Takenaka Nobuyuki , Fujii Terushige , Arakawa Tetsuya , Matsubayashi Masahito
Published: January 2022

To clarify the effect of the centrifugal force on the phase distribution of gas-liquid two-phase flow in a coiled tube, air-water two-phase annular flows in a spiral tube were visualized by a thermal neutron radiography method, and the two-dimensional void fraction distributions were measured from the obtained images by some image processing methods. An aluminum tube coiled in a plane and placed vertically was used as the test section. As a result, inversion, that is whether the liquid phase tends to flow at the inside or outside, of the spiral tube, could be determined. The condition of the inversion was correlated by body force on the gas and the liquid phases, that is, the centrifugal force and gravity.
Tomographic Measurement of the Liquid Hold-Up in a Structured Packing
Authors: Schmitz D. , Petritsch G. , Mewes D. , Moser F.
Published: January 2022

The high resolution which can be obtained by computer assisted tomography is used to investigate the liquid distribution and void fraction of the structured packing OPTIFLOW by Sulzer CHEMTECH. With a spatial resolution of 0.4 mm it is possible to detect the thin liquid films on structured packings. The experimental set-up consists of a custom-built second generation tomograph. The liquid and void fraction distribution in the structured packing with a quiescent gaseous phase is visualized. The water/air system is used. The liquid distributor consists of a perforated plate. The measured average hold-up of the packing is in good agreement with empirical correlations.
Monitoring Fluidization Dynamics for Detection of Changes in Fluidized Bed Composition and Operating Conditions
Authors: van Ommen J. Ruud , Schouten Jaap C. , van den Bleek Cor M.
Published: January 2022

In many industrial applications of gas-solids fluidized beds, the hydrodynamics of the bed can change over time, either by imposed alterations (e.g., a grade change) or by unwanted phenomena (e.g., agglomeration). In both cases, it is worthwhile to have an on-line monitoring method for detecting these changes quickly. In this paper, such a method, based on the short-term predictability of fluidized bed pressure fluctuations, is examined. Its sensitivity has been investigated by experiments with small step changes in the superficial gas velocity and by experiments with a gradual change in the particle size distribution of the solids in the bed. For both types of experiments, it is shown that the monitoring method detects changes in the excess gas velocity as small as 0.01 m/s. Furthermore, it is demonstrated that the method is well able to indicate if a stationary hydrodynamic state has been reached after a change in the particle size distribution (a ‘grade change’).
A Multi-Phase Flow Research Facility to Study Oil-Water-Gas Flow Systems
Authors: Ching Chan Y. , Wang Guanjun , Marshall Alfred R.
Published: January 2022

A new flow loop has been constructed at Memorial University of Newfoundland (MUN) to investigate oil-water-gas flows. The facility will initially support the development of an electroquasistatic multiphase flow meter (MPFM) to measure the individual oil-water-gas flow rates of unprocessed oil well streams. The flow loop is a 65 m recirculating open circuit system, and is constructed of 3-inch diameter pipe. There are clear horizontal and vertical test sections for flow visualization. Instrumentation includes several pressure and temperature transducers, and flow meters on the gas and liquid lines to measure the individual gas and liquid flow rates. Electro-pneumatic control valves arc installed on the liquid and air lines to facilitate control of the flow conditions, and a wide range of flow regimes can be generated. Operational control of the loop is implemented through a fully integrated computer system, which also handles the data acquisition. Quantitative flow visualization techniques, in combination with hot-film anemometry measurements are being used to study and characterize the different flow regimes. A new way of presenting flow maps that incorporates the pipe diameter and loop pressure is discussed. Preliminary results indicate that hot-film anemometry is a viable technique to obtain local volume fraction, and convection velocities of the gas slugs/bubbles. A block matching correlation technique is being developed to identify the different flow regimes, and estimate the velocity vectors of the different phases using consecutive frames from flow visualization.
Liquid-Liquid and Gas-Liquid Flow Patterns in a Torus Reactor
Authors: Benzemel Hafid , Rosant Jean-Michel , Legrand Jack
Published: January 2022

Two-phase liquid/liquid and gas/liquid flows in a circular torus reactor have been experimentally studied. The goal was to determine the flow structure inside the torus for various volume ratios of the two phases and various circulation velocities. The observed flow patterns are either stratified, dispersed or mixed flows. For the lower rotational speeds, stratified flow is obtained. For the higher speeds, one phase is dispersed within the other, corresponds to the dispersed flow regime. For the moderate speeds, both stratified and dispersed flows coexist in the torus reactor; this defines the mixed flow regime.
Measurement of Temperature Distribution of a Flat-Plate Heat Pipe Using Thermochromic Liquid Crystal and Color Imaging Techniques
Authors: Sun Jinhui , Liu Chang Yu
Published: January 2022

An experimental study on the performance of a flat-plate heat pipe was conducted by measuring the surface temperature distribution using thermochromic liquid crystals (TLC). Single wide-band liquid crystals were coated on the heat pipe and the colors exhibited by the liquid crystals were captured using a color video camera and calibrated using thermocouples. Comparative experiments were performed on the heat pipe and a heat pipe shell (without working fluid) under steady state and transient conditions. The full-field temperature visualization revealed a number of hot spots in the condenser section under both steady state and transient operation conditions. These hot spots are caused by non-uniformity in the wick structure of the heat pipe.
Frequency Response Calibration of Cold-Wire Sensors
Authors: Wroblewski Donald E. , Xie Qi
Published: January 2022

Cold-wire sensors, used for measurements of temperature fluctuations in turbulent flows, can suffer greatly from reduced frequency response, at high frequencies as a result of the wire’s thermal inertia and at low frequencies as a result of end conduction between the wire and the thermally massive support prongs. The frequency response of two platinum cold wires (1.27 μm diameter, 0.8 mm length and 1.27 μm, 0.76 mm length) was measured using the movement of the instantaneous hot-cold interface of a heated turbulent boundary layer, combined with a conditional sampling and averaging technique. The method proved suitable for measuring the plateau-level response due to end conduction, but exhibited significant scatter in the indirect measurements of the wire time constant. Variations of the time constant with velocity, over the range 5 to 15 m/s, were consistent with the thermal behavior exhibited by hot-wire sensors. For situations in which the cold wire will be used in boundary-layer applications, this method is attractive since the response can be determined in situ, without the need for specialized equipment or facilities.
Numerical Analysis of a Radiant Heat Flux Calibration System
Authors: Jiang Shanjuan , Horn Thomas J. , Dhir V. K.
Published: January 2022

A radiant heat flux gage calibration system exists in the Flight Loads Laboratory at NASA’s Dryden Flight Research Center. This calibration system must be well understood if the heat flux gages calibrated in it are to provide useful data during radiant heating ground tests or flight tests of high speed aerospace vehicles. A part of the calibration system characterization process is to develop a numerical model of the flat plate heater element and heat flux gage, which will help identify errors due to convection, heater element erosion, and other factors.

A 2-dimensional mathematical model of the gage-plate system has been developed to simulate the combined problem involving convection, radiation and mass loss by chemical reaction. A fourth order finite difference scheme is used to solve the steady state governing equations and determine the temperature distribution in the gage and plate, incident heat flux on the gage face, and flat plate erosion. Initial gage heat flux predictions from the model are found to be within ±7% of experimental results.
Discussion of Non-Equilibrium Heat Transfer in Biological Systems
Authors: Xu Lisa X. , Liu Jing
Published: January 2022

To study the nature of the previously observed wave like behaviors of heat propagation in biological materials, the approach of simulating the non-homogeneous biological material as a de-formable porous medium was taken. It was shown that, the wave-like heat conduction in the bologna meat can be caused by the propagation of water in the porous medium due to thermal expansions and pressure gradients applied to the meat during measurements. Thus, in contrast to the previous thermal wave interpretation, the mechanisms of the observed phenomena may be attributed to the thermal non-equilibrium between solid and liquid in the biological material rather than the pure conduction.
Growth and Differentiation of Osteoblasts on Hollow Biocompatible Ceramic Microcarriers Under Microgravity Conditions
Authors: Qiu Qing-Qing , Ducheyne Paul , Ayyaswamy Portonovo S.
Published: January 2022

In our recent studies with osteoblasts in the simulated microgravity environment of rotating-wall vessels (RWVs), we have observed the formation of cell aggregates and glass surface layers. In those studies, surface modified bioactive glass particles were employed as microcarriers. The growth and coverage of cells on the glass microcarriers were observed to be limited. We have also studied this problem from a numerical modeling viewpoint. Our numerical analysis of the particle dynamics in RWVs has revealed that the limited coverage noted in the experiments may be attributable to both the high shear stress imparted to the particle surface and the collisions experienced by the microcarrier with the outer wall of the vessel. The high shear stress and wall collisions arise primarily as a result of the high density of the microcarrier material. Here, we report the development of novel hollow bioceramic microspheres with an apparent density in the range 0.8 ∼ 1.0 g/cm3. These microcarriers alleviate the aforementioned problems. The hollow ceramic microspheres have an inner shell with composition of 58–72% SiO2, 28–42% Al2O3 (in % by weight) and a porous calcium phosphate surface. This surface was deposited using a fine particle sedimentation method. The hollow microspheres were sintered at 800°C for 1h. FTIR analysis indicated that crystalline calcium hydroxyapatite (HA) was present in the porous surface. Particle trajectory analyses in both an inertial frame and a rotating frame have shown that these microspheres remain suspended in the RWV environment during the entire cell culture period without experiencing collisions with the outer wall of the vessel. Furthermore, the shear stress imparted on the microsphere surface is low (∼ 0.6 dyn/cm2. Our cell culture studies in the HARV employing the hollow microcarriers have shown that osteoblastic cells form 3-D aggregates. Extensive extracellular matrix and mineralization were also observed in these aggregates.
Temperature Distribution in Prostate During Transurethral Radio Frequency Thermotherapy Treatment of Benign Prostatic Hyperplasia
Authors: Zhu Liang , Mi Zhengxin , Xu Lisa X.
Published: January 2022

The heating pattern of a radio frequency (RF) electrode catheter and its induced temperature field in prostate during transurethral thermal therapy treatment were investigated in this study. Experiments were performed in a tissue-equivalent phantom gel to quantitatively examine the volumetric heating produced by a RF electrode catheter for transurethral prostatic thermotherapy. The specific absorption rate (SAR) of RF energy in the gel was measured from the initial transient temperatures at various locations within the gel. An expression for the SAR was proposed and its unknown parameters in this expression were determined by comparing the predicted and measured SAR values. The SAR distribution was then used in conjunction with the Pennes bioheat transfer equation to model the temperature field in prostate during the thermotherapy treatment. The prostatic tissue temperature rise and its relation to the effect of blood perfusion were analyzed. Blood perfusion is found to be an important factor for removal of heat especially at the higher RF heating level. The minimum RF power required to achieve a maximum tissue temperature above 45 °C is in the range from 14 W to 60 W depending on the local blood perfusion rate (0.2 ∼ 1.5 ml/gm/min). An empirical expression for the detailed temperature field within the prostate for various blood perfusion rates and RF power levels was also provided for clinical purposes.
Protective Clothing Containing Encapsulated Phase Change Materials
Authors: Colvin David P. , Bryant Yvonne G.
Published: January 2022

Based upon experimental results from numerous Small Business Innovation Research (SBIR) programs for USAF, NASA, NAVY, NSF and USMC, new protective clothing are being developed that provide significant enhancements in thermal storage and comfort using encapsulated phase change material With a paraffinic phase change core and a polymer outer shell whose latent phase change can be designed to occur at a selected temperature, particles of microencapsulated phase material (microPCM) can range from 3–100 microns in diameter and be added to textile fibers, composites, foams, coatings and liquid coolants. Much larger 1–3 mm macroencapsulated phase change material (macroPCM) particles can also be included within clothing to provide significant improvements in breathable thermal cooling under conditions of high humidity. When microPCM particles of 10–50 microns diameter are added to a flexible matrix such as foams, new materials are created that can provide both enhanced thermal storage and insulation within the same thickness. Enhancements of thermal capacitance of textile fibers and foams can reach 10X or 1,000 % compared to unfilled fibers and materials. The resulting clothing can provide greatly enhanced thermal protection in both hot and cold environments with both low bulk and thickness. Firefighters, race drivers, skin divers and snow skiers are discovering significant protective advantages with these new materials. For example, waterproof and breathable arctic gloves have been shown to provide superior protection to commercially-available ski wear that is less susceptible to loss of thermal resistance with localized compression.
Breast Tissue Cryosurgery With Antifreeze Proteins
Authors: Pham Linda D. , Rubinsky Boris
Published: January 2022

Antifreeze proteins (AFP) are chemical compounds which can modify ice crystal structure to a needle-like form. They have been shown to enhance destruction of frozen cells. The goal of this study was to determine if these antifreeze proteins can destroy cells in frozen breast tissue and thereby serve as chemical adjuvants to breast cryosurgery. Fresh, normal human breast tissue was injected with solutions of phosphate buffered saline (PBS) or PBS with 10 mg/ml antifreeze protein of type I (AFP-I) then frozen with a cooling rate of 5 °C/min to various subzero temperatures, on a special cryosurgery apparatus. Cell viability was examined with a two stain fluorescent dye test. The results show that a significant percentage of breast cells survive freezing to high subzero temperatures, typical of the temperature on the margin of a frozen cryolesion. The results also show that AFP have the ability to significantly increase cellular destruction in the high subzero temperature range.
Modular Dynamic Model of Multi-Shaft Gas Turbine and Validation Test
Authors: Bianchi M. , Peretto A. , Spina P. R.
Published: January 2022

The paper deals with the development of a component module library necessary to study multi-shaft gas turbine power plants.

In particular the paper presents:

- the features of the software environment used to develop the gas turbine modular dynamic model;

- for each gas turbine component, the whole form of the dynamic physical equations and their simplified final expression suitable for the software environment requirements;

- the procedure relative to the building of the gas turbine modules.

In order to validate the created gas turbine modules, the transient behavior of a twin-shaft industrial gas turbine, simulated by connecting the new modules, was compared with experimental data available in literature. The values obtained by the simulation turn out to be in agreement with the experimental data.
Modified Forms of the First and the Second Law of Thermodynamics
Authors: Sohrab Siavash H.
Published: January 2022

A scale-invariant statistical theory of fields is presented that leads to invariant definition of density, velocity, temperature, and pressure. The definition of Boltzmann constant is introduced as kk = k = mkvkc = 1.381 × 10−23 J/K, suggesting that Kelvin absolute temperature scale is equivalent to a length scale. Two new state variables called the reversible Qrev = TS and the reversible work Wrev = PV are introduced. The modified forms of the first and second law of thermodynamics are presented. The microscopic definition of heat (work) is presented as the kinetic energy due to random (peculiar) translational, rotational, and pulsational motions. The Gibbs free energy of an element at scale β is identified as the total system energy at scale (β-1), thus leading to an invariant form of the first law of thermodynamics Uβ = Qβ − Wβ + NeβUβ-1.
Adiabatic Availability
Authors: Metghalchi Mohamad
Published: January 2022

Adiabatic availability, a property, is defined as the largest work that can be done by a system in an adiabatic, constant mass and volume process. Adiabatic availability of all systems at any state is larger than or equal to zero. Adiabatic availability of a system in stable equilibrium state is zero. Adiabatic availability of a composite made of a system and a reservoir is the same as the available energy of the system with respect to the given reservoir. Change of adiabatic availability, transfer of adiabatic availability and destruction of adiabatic availability due to irreversibility for few processes have been investigated.
Improving the Performance of an Existing Air-Cooled Binary Geothermal Power Plant: A Case Study
Authors: Kanoğlu Mehmet , Çengel Yunus A.
Published: January 2022

An existing air-cooled binary geothermal power plant in Northern Nevada with an average net power output of 27 MW is studied. The current performance of the plant is analyzed with an emphasis on the effects of seasonal climate changes. Two potential sites have been identified to improve the performance of the plant. Northern Nevada has a dry climate particularly in hot summer months, and the temperature of cooling air can be decreased considerably by evaporative cooling. When the air temperature is decreased to the wet-bulb temperature, the decrease in the condenser temperature is determined to increase the power output by up to 29%. The required amount of water for this case is calculated to be about 200,000 tons per year. Several parametric studies are performed by simulating the operation of the plant with an equation solver with built-in thermophysical property functions. It is determined that the net power output of the plant can be increased by 2.8 percent by optimizing the maximum pressure in the cycle. Also, replacing the existing working fluid isobutane by other commonly used binary fluids such as butane, R-114, isopentane, and pentane can increase the net power output by up to 2.5 percent.
Exergy and Pinch Analysis of an Advanced Ammonia-Water Coal-Fired Power Cycle
Authors: McIlvried Howard G. , Ramezan Massood , Enick Robert M. , Venkatasubramanian Srikanth
Published: January 2022

An exergy analysis of a power system identifies the location, type, and magnitude of losses of the potential to do work, while a pinch analysis examines a heat exchange network efficiency. A complete exergetic analysis of Kalina cycle System 19, an advanced binary fluid (ammonia-water working fluid) power cycle, is presented along with a combined pinch/exergy analysis of the Kalina cycle heat exchanger/furnace/cooling utility network. The Kalina cycle System 19 has a net thermal efficiency (net work/furnace duty) of 43% (HHV), a furnace exergetic efficiency of 77.4%, and an exergetic plant efficiency (net work/exergy of flue gas) of 61.6%. Most of the exergy losses (21.5%) occur in the furnace; 9.6% of the exergy is lost in pumps, turbines, throttles, mixers, and the stack gas; and 7.3% of the exergy loss occurs in heat exchanger/cooling utility network. The System 19 total exergy loss in all heat exchange equipment is only 7.2% greater than its minimum value. Thus, the analysis indicates that the Kalina cycle System 19 is efficiently designed.
The Rational Efficiency of Fossil-Fuel Power Plants
Authors: Horlock J. H. , Young J. B. , Manfrida G.
Published: January 2022

The definition of open cycle rational efficiency is unequivocally based on the ratio of the actual shaft work output from a power plant to the maximum work that could be obtained in a reversible process between prescribed inlet and outlet states. However, the specification of this ideal process remains a matter for discussion. The “classical” definition specifies the outlet state as a “standard” atmosphere (p0,T0) with a given composition of constituent gases and an exergy of zero. The ideal work output is then the exergy of the fuel supplied, which is the sum of the Gibbs function change in reversible combustion at (p0,T0) and the work of extraction and delivery of the reactant and product species.

However, two other ideal processes may be considered in which different outlet states are specified leading to alternative definitions of rational efficiency. In one process all species enter and leave the ideal plant individually at (p0,T0) in thermal and mechanical (but not chemical) equilibrium with the environment. In the other, the exhaust is at (p0,T0) but the gas composition is the same as in the real process. A further complication occurs when water or steam is injected into a gas turbine plant. In such cases the exergy of the added water must be considered within any definition of rational efficiency. The three definitions of rational efficiency are discussed and compared and some illustrative calculations presented.
The Pressure-Exchange Ejector Heat Pump
Authors: Garris Charles A. , Hong Woo Jong , Mavriplis Catherine , Shipman Jeremy
Published: January 2022

The pressure-exchange ejector offers the possibility of attaining a breakthrough in the level of performance of ejectors by means of utilizing non-dissipative non-steady flow mechanisms. Yet, the device retains much of the mechanical simplicity of conventional steady-flow ejectors. If such a substantial improvement in performance is demonstrated, its application to ejector refrigeration will be very important. Such a development would provide significant benefits for the environment in terms of both CFC usage reduction and greenhouse gas reduction.

The current paper will discuss in detail the concept of pressure-exchange ejector refrigeration, compare it with existing technologies, and discuss the potential impact that might be derived if certain levels of ejector performance can be achieved. Since the limiting issue on the system performance is in the fluid dynamics of non-steady flow induction, research issues and recent progress will be discussed.
Valve Opening and the Onset of Flow in a Reciprocating Compressor Cylinder
Authors: Overfield Norbert W.
Published: January 2022

This paper describes ongoing development work on a new class of compressor valves. The significant feature of the new valve is that it opens promptly upon pressure reversal. This response differs markedly from conventional valves, which do not start to open until a substantial pressure difference (approximately ten percent of upstream pressure) is established. Improved adiabatic efficiency and reduced valve velocity at first contact with the lift stop were noted during the initial prototype tests of the new valve.

The current work is an attempt to gain a better understanding of the causes of these improvements. Specifically, the effects of valve spring pre-load and rate on the opening valve velocity and stop impact arc explored.

The results of a time domain study of valve opening are presented. Opening dynamics of both conventional plate valves and equivalent valves of the new design are investigated. The specific goals are to determine the effects of differing rates and pre-loads in the plate return springs.
Study of Heated Accumulator in Air-Source Heat Pump With Binary Mixture
Authors: Sami Samuel M. , Desjardins Daniel E.
Published: January 2022

In this paper, an experimental study is presented on the behavior of zeotropic versus azeotropic binary mixtures in heated accumulator air-source heat pump during heating mode. The experimental set up was composed of a fully instrumented air-source heat pump with a capacity of 36,000 BTUH and equipped with a heated suction accumulator.

Standard heating mode test conditions were used at the condenser inlet; however, the refrigerant temperatures were varied at the evaporator entrance from 5 to −40 °C, to simulate various conditions encountered in air-source heat pump applications. The primary parameters observed during the course of this study were mass flux, heat flux, quality, thermal capacities, power consumption and pressure ratios for the refrigerants under investigation.

The test results showed that a heated suction accumulator helps to evaporate the more volatile component of the binary mixture, thus, increasing the mixture thermal capacity. Furthermore, experiments have also shown capacity increases of 27% with heated accumulator over unheated accumulator at −30 °C outside air temperatures.
Heat Exchanger Mean Temperature Differences for Refrigerant Mixtures
Authors: Schaefer Laura A. , Shelton Samuel V.
Published: January 2022

Many of the refrigerants that have been examined as replacements for hydrochlorofluorocarbons (HCFCs) are zeotropic mixtures. The temperature of a zeotropic mixture does not remain constant throughout a heat exchanger, and zeotropes often exhibit a nonlinear temperature/enthalpy relationship. These factors contradict some assumptions that are made in deriving the Log Mean Temperature Difference (LMTD), a calculation that is used to compute the size of a heat exchanger (UA). Since the temperature is not an easily-determined function of enthalpy, in order to find a more accurate UA, the heat transfer process must be discretized and the properties determined at each point. An ammonia-water mixture and synthetic mixtures that are being studied as HCFC-22 replacements are analyzed. In each case, the actual UA is compared to the UA found using the LMTD. It is found that these errors can cause a heat exchanger to be undersized by as much as a factor of fifty.
Preliminary Secondary Power System Thermodynamic Analysis for Tactical Aircraft Pulsed Loads
Authors: Lykins Richard , Ramalingam Mysore L. , Donovan Brian D. , Cloyd James S. , Beam Jerry E.
Published: January 2022

A computerized thermodynamic analytical program has been developed to investigate the impact of secondary power system improvements on mission effectiveness and efficient pulsed power generation in a conventional tactical aircraft. Besides indicating that the engine performance in a conventional aircraft was more sensitive to pneumatic bleed than to shaft power extraction, the analysis also revealed a 5% improvement in fuel consumption with the use of a more electric secondary power system. Using the total fuel consumed by the conventional aircraft for a typical tactical mission as a baseline, several investigative options were considered for the excess fuel availability, for an identical situation with the more electric secondary power system. The result was the availability of multiple combat mission legs or an equivalent of 24 kW of pulsed power that could potentially be used for communications purposes or as a weapon load. The improvements in the quality of the pulsed power with the incorporation of cryogenic technologies and a trade study between open and closed cryogenic cooling systems are also presented in this investigation.
The Effects of Channel Height on Flow Boiling of Liquid Nitrogen
Authors: Lu W. , Chow L. C.
Published: January 2022

The quest for high-power electronics operating in a cryogenic environment has given rise to the need for very effective cryogenic cooling of the electronic devices. Electronic chips are usually mounted on the circuit boards. Those boards are stacked one above or next to the others. For the electronic engineers who design the electronic systems, how close the circuit boards can be stacked together is very important. This paper presents an investigation of effects of flow channel heights on flow boiling heat transfer with liquid nitrogen from small, discrete heat sources that simulate electronic chips. The experimental apparatus is designed to allow visual observation of the phase-change phenomena of cryogen (liquid nitrogen) at the heat sources. Experiments with different flow channel heights have been conducted. It is noted that the channel height has little effect on the CHF until the channel height is decreased to approximately 1.6 mm. The critical heat flux (CHF) and the heat transfer coefficient decreases significantly. There is no significant difference between the heat transfer conditions in flow channel heights of 6.35 mm and 3.18 mm, which indicates that distance between the multi-layer-stacked electronic boards should be larger than the critical height (1.6 mm) in order to obtain optimum cooling results. A model to describe the heat transfer mechanism near CHF was developed using the present results and those of previous investigators. A correlation was established using this model and the experimental data. This correlation provides a good fit to the experimental data from various flow channel heights.
Heat Spreaders for High-Power Electronics Employing Boiling Mechanisms in a Narrow Space
Authors: Gao M. , Cao Y.
Published: January 2022

To achieve a high heat-flux level and reduce manufacturing costs associated with conventional heat pipes, the concept of network heat spreaders employing boiling heat-transfer mechanism in a narrow space has been proposed and several flat-plate wickless heat spreaders have been designed and fabricated. The heat spreaders have been tested under different working conditions and orientations relative to the gravity with very good results. The previously tested network heat spreaders, however, were based on plates with a relatively large size for general heat spreading purposes. In the present study, network heat spreaders with overall dimensions of 78 × 62 × 3.2 mm are designed and fabricated. The spreaders with this size are intended for use as heat sinks of high-power electronic components. External cooling fins are attached to enhance air-cooling heat transfer rate. The network heat spreaders are tested under various working conditions with water as the working fluid. The maximum heat input rate achieved is about 150 W with a corresponding heat flux of 60 W/cm2. Compared to the performance of a solid copper plate having the same overall size as the spreader, the maximum temperature difference over the surface is reduced from about 32 °C to 3.3 °C. The heat transfer performance of the spreader is also largely dependent on the filling ratio of the working fluid and the boiling heat transfer in the narrow space. For these reasons, boiling heat transfer mechanisms in a narrow space are analyzed, and a spreader design that would improve the performance in a horizontal position is described.
Processing Induced Warpage in Composite Cylindrical Shells
Authors: Meink Troy E. , Shen M.-H. Herman
Published: January 2022

This paper investigates a cause for warpage in structures manufactured using filament winding or fiber placement. This warpage phenomena has been determined to be caused by fiber/resin consolidation resulting from manufacturing parameters including: cure pressure, winding tension, and material system characteristics. This is a non-thermal phenomena and is independent of cure temperature, or finished part operational environments. A novel theory has been developed to predict the warpage or “springback” resulting from the processing induced strain gradient that develops in laminates due to the consolidation. This paper utilizes a strain model derived previously to develop a warpage prediction model utilizing Classical Laminated Plate Theory (CLT). This theoretical solution is than compared to experimental results for hoop wound test specimens. The end goal of the research is to develop a springback prediction model that can be applied to large scale parts utilizing consolidation parameters measured at the coupon level.
Micro Instabilities in a System of Particles in Silos During Filling Process
Authors: Gavrilov Dmitri , Vinogradov Oleg G.
Published: January 2022

The process of filling a silo with particles is simulated by placing them one-by-one at random locations. In simulations, a plane problem is considered and the particles are represented by disks. After each disk is placed on the system of disks already in a silo, the distribution of normal and shear stresses is recalculated. If any shear stress exceeds the predetermined limit, then a slip takes place. It is found that a slip can occur between a few particles simultaneously. Such a micro-slip reflects a physical instability in the system. It also results in a numerical instability. A Recursive Inverse Matrix Algorithm (RIMA) is implemented to account for the topological changes in the system during the loading. It allows efficient addition/removal of contact interfaces between the particles by updating the inverse matrix of the system rather then generating and solving a system of equations after each topological change. The extent of instabilities is determined numerically using RIMA update algorithm iteratively. As a result of irreversible events taking place during the filling operation, the final stress distribution in a filled silo is loading history-dependent. A numerical example of filling a silo with 500 particles is given as an illustration.
Biomechaimical Study of Ballistic Impact on Helmets: Injury of Head and Neck
Authors: Kwon Y. W. , King Q. M.
Published: January 2022

Technology has improved dramatically over the last quarter century. It has allowed the development of personal body armor capable of preventing penetration of fragments traveling in excess of 609 m/s (2000 ft/s). However, these strides have also exposed the body to greater impact energies without a lethal penetration. The objective of this study was to examine how the body, in particular the head-neck complex, responds to these impacts. A finite element model was developed to characterize the behavior of this biomechanical system. This model was validated against experimental work. The validated model was then subjected to impacts at different positions to induce different load cases. Each set of results was then compared to Head Injury Criteria (HIC), Abbreviated Injury Scale (AIS), and the Injury Assessment Reference Values (IARVS) for evidence of injury potential. Disc stiffness was found to be proportional to the injury potential. Rupture of the disc was considered likely for most cases considered. Fracture of the vertebral body was considered likely in a half of the cases under study.