bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Temperature Computation of Spheres in Packings With Multi-Neighbors
Authors: Siu W. W. M. , Lee S. H.-K.
Published: December 2021

Packed sphere systems commonly involve heat transfer processes, such as catalytic beds and insulations. Most of the time, these types of systems were considered as porous media. In fact, porous medium approach has been successfully used for application involving considerable amount of spheres with corresponding resolution and, typically in geothermal system study. In recently years, researchers have started to investigate the problem in a finer length scale formulation because of the relevant application requirement, such as powder sintering processes. Using thermal constriction resistance for solving transient temperature of individual sphere in a packing was one of the attempt to achieve the finer resolution of temperature. It has been found that a special formulation is required in order to take care the finite heat diffusion mechanism between spheres. However, available correlations and governing equations from literature were only applicable for spheres with two neighbors. It is obviously not sufficient for solving temperatures of spheres within realistic packing. Furthermore, the interaction of the finite diffusion amoung spheres should be more complicated in three dimensional packing situation. Therefore, this work focuses on the enhancement of the approach of using constriction resistance for realistic packing of spheres. The formulation of the governing equation with the consideration of multi-neighbor arrangement was performed. A finite difference code was developed and using for solving the governing equation. It has been verified to be applicable to multi-neighbor situation few regular packing situations. Computation of sphere temperatures of a packing involving a thousand of spheres was also performed for illustrating the application.
Microscale Permeability Predictions of Porous Fibrous Media
Authors: Ngo Nam D. , Tamma Kumar K.
Published: December 2021

A good understanding of woven fiber preform permeabilities is critical in the design and optimization of the composite molding processes, yet these issues remain unresolved in the literature. Many have attempted to address permeability predictions for flat undeformed fiber preform, but few have investigated permeability variations for complex three-dimensional molds. In this study, the objectives are to: (i) first provide a brief review of existing methods for the prediction of the fiber mat permeability; (ii) postulate a more realistic representation of a unit cell to account for such fabric structures as crimp, tow spacing and the like; and (iii) apply computational approximations for predicting effective permeabilities for use in the modeling of structural composites processes. The Stokes equation is used to model the flow in the inter-tow region of the unit cell, and in the intra-tow region, the Brinkman’s equation is used. Preliminary permeability prediction calculations are performed for a three-dimensional unit cell model representative of PET 61 woven fabric. The results showed good agreement with experimental data published in literature.
Non-Isothermal “2-D Flow/3-D Thermal” Developments Encompassing Process Modeling of Composites: Flow/Thermal/Cure Formulations and Validations
Authors: Ngo Nam D. , Tamma Kumar K.
Published: December 2021

In the manufacturing process of large geometrically complex components comprising of fiber-reinforced composite materials by Resin Transfer Molding (RTM), the process involves injection of resin into a mold cavity filled with porous fiber preforms. The overall success of the RTM manufacturing process depends on the complete impregnation of the fiber mat by the polymer resin, prevention of polymer gelation during filling, and subsequent avoidance of dry spots. Since a cold resin is injected into a hot mold, the associated physics encompasses a moving boundary value problem in conjunction with the multi-disciplinary study of flow/thermal and cure inside the mold cavity. Although experimental validations are indispensable, routine manufacture of large complex structural geometries can only be enhanced via computational simulations, thus eliminating costly trial runs and helping the designer in the set-up of the manufacturing process. This study describes the developments towards formulating an effective simulation based design methodology using the finite element method. The specific application is for thin shell-like geometries with thickness being much smaller than the other dimensions of the part. Due to the highly advective nature of the non-isothermal conditions involving thermal and polymerization reactions, special computational considerations and stabilization techniques are also proposed. Validations and comparisons with experimental results are presented whenever available.
Mesoscale Machines and Electronics: “There’s Plenty of Room in the Middle”
Authors: Warren William L. , Dubois Lawrence H. , Wax Steven G. , Gardos Michael N. , Fehrenbacher Lawrence L.
Published: December 2021

Machine properties optimized in the mesoscale size regime include improved heat transfer, macroscopic electrostatic actuation, and chemical mixing. This manuscript describes the origin of these advantages along with the development of several energy-efficient meso-machines that exploit these properties. The advantages of direct-write mesoscale electronics are also presented. These include the ability to place the electronics on the physical structure of a machine to improve performance, reduce size and weight, and enhance durability.
State-of-the-Art in Micro- and Meso-Scale Heat Exchangers
Authors: Shekarriz Reza , Call Charles J.
Published: December 2021

A review of the literature and the state-of-the-art in research and development of miniature heat exchangers is presented in this paper. The authors provide a discussion of what makes the micro- and meso-scales important, highlight the design constraints and challenges that surface when miniaturizing a heat exchanger, and outline and discuss the outstanding practical and scientific issues in this area. Finally, the most recent advances in manufacturing processes and application of these miniature heat exchangers are covered in this article.
Integrated Mesoscopic Cooler Circuits (IMCCs)
Authors: Shannon Mark A. , Philpott Mike L. , Miller Norman R. , Bullard Clark W. , Beebe David J. , Jacobi Anthony M. , Hrnjak Predag S. , Saif Taher , Aluru Narayan , Sehitoglu Huseyin , Rockett Angus , Economy James
Published: December 2021

This paper presents the design, fabrication approach, and initial results on the development of an active composite fabric comprising a system of energy-efficient micro-miniature vapor-compression heat pumps to form integrated mesoscopic cooler circuits (IMCCs). Wafer-scale microfabrication, traditional volume processes such as injection molding, and new layered fabrication techniques have been combined with a scale-efficient vapor-compression cycle. The resulting IMCC offers significant improvements in cooling efficiency over normal-scale refrigeration. The flexible polymer-based IMCC patches may be interconnected to form distributed fault-tolerant refrigeration circuits for a wide variety of applications. Potential applications include microclimate control for military, space, and fire fighting personnel, on-board/chip cooling of electronic devices, medical applications requiring highly localized and/or efficient temperature control, and automotive comfort control devices.
The Use of a Psychrometric Chart in the Absorption-Evaporative Cooling Refrigerator
Authors: Morales G. Juan R. , Lara V. Araceli , Lizardi R. Arturo , López C. Raymundo , Díaz C. Alen
Published: December 2021

In the absorption-evaporative cooling refrigerator, the evaporator works with liquid butane and a gaseous ammonia-butane mixture. In order to design such a refrigerator the mixture behavior has to be known. In this paper such behavior is determined first considering an ideal gases mixture and no ammonia in the liquid butane. For this purpose a psychrometric chart for a pressure of 105 kPa is obtained. To validate these assumptions a second model is chosen that considers a certain amount of non-ideality. The selected model is represented by the equations of Peng-Robinson. The results obtained for the equilibrium conditions are compared with the 100% relative humidity of the psychrometric chart. A satisfactory agreement is found.
A Latching Mechanism for Unloading a Rotary Compressor
Authors: Smith Joseph L. , Webb Michael D. , Umans Stephen D.
Published: December 2021

A vane latching mechanism for unloading a rotary vane compressor is described. Mechanical unloading is proposed as a potential alternative to electronic control of motor speed for variable compressor capacity. Performance of a demonstration compressor operating at part capacity in a residential air conditioning system is described.
Profile Generation and Analysis for Twin Screw Multiphase Compressor/Pump
Authors: Cao Feng , Xing Ziwen , Peng Xueyuan , Shu Pengcheng
Published: December 2021

Multiphase transportation technology enables to transfer the mixture of crude oil, gas, water and sand in a single pipeline. Compared to the conventional method, it is more efficient since the multi-pipelines are not required.

Multiphase compressor is the key machine in a multiphase transportation system, and the twin screw multiphase compressor/pump has proved to be a suitable machine for this application. This paper investigates the twin screw multiphase compressor, mainly focusing on the rotor profile. The calculating methods for mesh line length and blow hole area between the two rotors are presented. The geometrical characteristics of the rotor profile are also discussed in the paper.
Modeling and Analysis of the Air Cooled Ammonia-Water Triple Effect Cycle
Authors: Shelton Sam V. , Jacob David , Schaefer Laura A.
Published: December 2021

Development of air-cooled absorption cycles appropriate for residential applications has been problematic. This study examines an ammonia-water triple effect cycle known as the kangaroo cycle, and investigates its limitations when used as an air-cooled space air conditioner. The triple effect absorption processes were modeled and a methodology for optimizing the design was developed. The arrangement and relative sizes of the heat exchangers thermally coupling the upper and lower loops were studied. The thermal coupling involves the upper rectifier, condenser, and absorber rejecting heat to the lower generator. Contrary to other triple effect studies, internal generator heat exchangers were incorporated in both the upper and lower generators and their optimum relative positions were studied. Also, errors of up to 150 percent were shown to result from conventional LMTD and pinch point analysis due to the highly non-linear temperature-enthalpy relationship in the upper condenser. Three configurations for the upper heat exchangers coupling the upper loop to the lower generator were analyzed, and their relative sizes were optimized. The cycle’s performance was shown to depend on the exit temperature of the lower loop generator, and the COP optimization was demonstrated with respect to this design variable. Operation at air-cooled ambient conditions was investigated. At lower ambient temperatures that are heavily weighted in air conditioning rating standards, the efficiency is very favorable. Equipment development and cost issues need to be addressed.
Modeling an Integral Dual Solar/Gas Fired Generator for a Water-Lithium Bromide Absorption Chiller
Authors: Cao Jiming , Christensen Richard N.
Published: December 2021

This paper presents a design process for a dual solar/gas fired generator. A generator fired by solar energy and/or natural gas for a water-lithium bromide absorption chiller of 25 refrigeration tons (RT) was modeled. The natural gas is considered as the backup heat when the solar energy is unavailable or insufficient. The flue gas and the water-lithium bromide solution are in co-current flow, while the solar fluid and the water-lithium bromide solution are in counter-current flow. Fifty fluted tubes were installed vertically between two concentric cylindrical tubes. A solid ceramic insert was used to enhance heat transfer on the gas side that is considered as having the dominant heat transfer resistance. The burner is installed inside the smaller cylindrical tube. The solar fluid from the solar collector enters the generator through the fluted tubes while the water-lithium bromide mixture flows in the annular channel around the fluted tubes as a subcooled liquid. The generator is divided into two regions according to the heat transfer mechanism: subcooled liquid region and desorption region. In this model, a simultaneous solar and gas fired desorption process was investigated. The amount of makeup heat needed from natural gas was determined as a function of the solar fluid flow rate. Local temperature profiles were predicted by the model.
The Correlation of Coupled Heat and Mass Transfer Experimental Data for Vertical Falling Film Absorption
Authors: Miller William A. , Keyhani Majid
Published: December 2021

Absorption chillers are gaining global acceptance as quality comfort cooling systems. These machines are the central chilling plants and the supply for comfort cooling for many large commercial buildings. Virtually all absorption chillers use lithium bromide (LiBr) and water as the absorption fluids. Water is the refrigerant. Research has shown LiBr to be one of the best absorption working fluids because it has a high affinity for water, releases water vapor at relatively low temperatures, and has a boiling point much higher than that of water. The heart of the chiller is the absorber, where a process of simultaneous heat and mass transfer occurs as the refrigerant water vapor is absorbed into a falling film of aqueous LiBr. The more water vapor absorbed into the falling film, the larger the chiller’s capacity for supporting comfort cooling. Improving the performance of the absorber leads directly to efficiency gains for the chiller.

The design of an absorber is very empirical and requires experimental data. Yet design data and correlations are sparse in the open literature. The experimental data available to date have been derived at LiBr concentrations ranging from 0.30 to 0.60 mass fraction. No literature data are readily available for the design operating conditions of 0.62 and 0.64 mass fraction of LiBr and absorber pressures of 0.7 and 1.0 kPa.

Experiments were conducted on an internally cooled smooth tube 0.01905 m in outside diameter and 1.53 m in length. Tests were conducted with no heat and mass transfer additive. The data, for testing at 0.62 and 0.64 mass fraction of LiBr, were scaled and correlated into both Nusselt (Nu) and Sherwood (Sh) formulations. The average absolute error in the Nusselt correlation is about ±3.5% of the Nu number reduced from the experimental data. The Sherwood correlation is about ±5% of the reduced Sh data. Data from the open literature were reduced to the authors’ Nu and Sh formulations and were within 5% of the correlations developed in the present study. Hence, this study provides correlations for the complex heat and mass transfer process that is validated against extensive experimental data. The study therefore contains useful information for the design of a vertical column absorber operating with no heat and mass transfer additive.
Theory of Heat/Mass Transfer Additives in Absorption Chillers
Authors: Kulankara S. , Verma S. , Herold K. E.
Published: December 2021

A new theory is presented, termed the vapor surfactant theory, which explains the heat and mass transfer enhancement mechanism of additives in absorption chillers. The vapor surfactant theory holds that the enhancement additives are surfactants delivered to the surface of the solution film from the vapor and that they produce enhancement by generating intense secondary flows on the film. The secondary flows, driven by surface tension gradients (Marangoni convection), augment the transfer process by providing mixing of the film. The primary variable in the enhancement is the surface concentration distribution of the surfactant additive since the surface tension gradients arise due to non-uniformities in the surface concentration. The vapor surfactant theory is found to explain all observations from several different types of experiments. The new theory is a significant departure from past theories in its emphasis on the primary role of the vapor in the process.
Entropy: Part I — Statistics and its Misleading Disorder
Authors: Gyftopoulos Elias P.
Published: December 2021

The overwhelming majority of scientists, engineers, and other professionals believe that: (a) statistical mechanics explains thermodynamics, and provides explicit expressions of entropy (for example, S = k ln Ω); and (b) in general, each entropy represents disorder in a system and, in particular for given values of energy, volume, and amounts of constituents, the largest value of the entropy represents the ultimate disorder (thermodynamic equilibrium state). The purposes of this paper are to present both theoretical and experimental evidence that refutes these beliefs and to show that the spontaneous increase in thermodynamic entropy represents a nonstatistical, natural tendency to perfect order rather than disorder. The arguments are presented in two parts. Brief discussions of the premises and conclusions of the statistical interpretation of thermodynamics, the association of the statistical entropy with disorder, and inconsistencies that arise from such an association are presented in Part I. A nonstatistical exposition of thermodynamics, the interpretation of entropy as a measure of the quantum-theoretic shape of molecules, and the association of the entropy of classical thermodynamics with perfect order are presented in Part II.
Modeling of Incomplete Equilibria in Industrial and Environmental Systems and Processes: A Theoretical Framework
Authors: Filippov Sergei P. , Kaganovich Boris M. , Yablonsky Gregory S.
Published: December 2021

The paper presents the models of the regions of thermodynamic accessibility and incomplete equilibria in physico-chemical systems that are intended to study diverse industrial and environmental processes. The models are compared with the traditional ones of classical equilibrium thermodynamics. Peculiarities of the presented mathematical problems are analyzed and the ways for devising relevant algorithms are outlined. The gains of the approach suggested are discussed.
Fuel Processing and Combustion: An Extreme Thermodynamic Analysis
Authors: Filippov Sergei P. , Keiko Alexandre V. , Pavlov Peter P.
Published: December 2021

The paper concerns application of the extreme thermodynamics approach within the analysis of chemically reacting systems. Some principal techniques of the approach are shown on simplified examples of coal processing and nitrogen oxides formation. The analyses are based on the investigation of incomplete chemical equilibria using the models of extreme intermediate states (MEIS). The close correspondence between the MEIS statement and graphical interpretations is shown and used.
Trade-Off Design Analysis of Operating Pressure and Temperature in PEM Fuel Cell Systems
Authors: Barbir Frano , Balasubramanian Bhaskar , Neutzler Jay
Published: December 2021

The paper presents the results of an optimization study of an automotive fuel cell propulsion system equipped with a fuel reformer. Based on a set of fuel cell polarization curves determined experimentally by running a prototype fuel cell stack at a variety of operating pressures and temperatures, a numerical steady state model was used to determine the optimal operating pressure and temperature. The optimization criteria were the size of individual components and the entire propulsion system as well as its total efficiency at both full power and partial load. The results suggested that an automotive system should be operated at relatively high pressure (308 kPa), but an expander must be used to recover most of the power used for compression. A surprising result of this analysis is that a relatively low temperature (∼60°C) results in smallest heat rejection equipment if neutral water balance is mandated. The efficiency of the system is about 33% at full power and about 38% at 25% of the load. Higher efficiencies may be achieved by selecting a higher fuel cell operating voltage, but that would result in larger fuel cell stacks, which may be a limiting factor for automotive application with the state-of-the-art fuel cells.
On-Particle EDS Analysis of PtRu/C DMFC Catalysts Using High-Resolution TEM
Authors: Boxall Deborah L. , Lukehart Charles M. , Kenik Edward A.
Published: December 2021

On-particle energy dispersive x-ray spectroscopy (EDS) was performed on direct methanol fuel cell (DMFC) anode catalysts in order to measure the Pt:Ru ratio of individual catalyst particles in Pt1Ru1/C and Pt3Ru1/C composite materials. It was found that the Pt:Ru ratio increased as the diameter of the particles decreased. The curvature observed in the plots of the integrated intensities of the two metals is consistent with loss of Ru from the surface of the metal particle. Compensation for this Ru loss computationally results in a Pt:Ru ratio that is within experimental error of the targeted alloy composition.
Analysis of a Large Scale Liquid Hydrogen Dispersion Using the Multi-Phase Hydrodynamics Analysis Code (CHAMPAGNE)
Authors: Chitose K. , Takeno K. , Okamoto M. , Hayashi K. , Hishida M.
Published: December 2021

It is planned to use hydrogen extensively as a source of clean energy in the next century. As part of our investigation for an International Clean Energy Network Using Hydrogen Conversion (WE-NET), we have been studying to establish a safety scheme to ensure that both existing and new hydrogen technologies are implemented without endangering public safety. In this plan, we consider the transport and storage of a large quantity of hydrogen in a large tank. First we must evaluate the consequence of the postulated accident of liquid hydrogen. Since we have developed the multi-phase hydrodynamics analysis code (CHAMPAGNE), we apply the code to simulate the formation and dispersion of hydrogen vapor clouds.

In the present paper we have improved the calculation model in two ways. We added a function to CHAMPANGE for solving evaporation phenomena realistically, made many parametric calculations and planned the small-scale hydrogen dispersion experiments for the validation of this model. Another improvement is the turbulent mixing of evaporated liquid hydrogen.

Now we have completed the basic functions of our simulation code. And these models of CHAMPANGE code must be verified by the experimental data.
Improvement of the Exergoeconomic “Fuel-Impact” Analysis for Acceptance Tests in Power Plants
Authors: Zaleta-Aguilar Alejandro , Gallegos-Muñoz Armando , Valero Antonio , Royo Javier
Published: December 2021

This work builds on the previous work on “Exergoeconomics Fuel-Impact” developed by Torres (1991), Valero et. al. (1994), and compares it with respect to the Performance Test Code (PTC’s) actually applied in power plants (ASME/ANSI PTC-6, 1970). With the objective of proposing procedures for PTC’s in power plant’s based on an exergoeconomics point of view. It was necessary to validate the Fuel-Impact Theories, and improve the conceptual expression, in order to make it more applicable to the real conditions in the plant. By mean of a program using simulation and field data, it was possible to validate and compare the procedures. This work has analyzed an example of a 110 MW Power Plant, in which all the exergetic costs have been determined for the steam cycle, and a fuel-impact analysis has been developed for the steam turbines at the design and off-design conditions. The result of the fuel-impact analysis is compared with respect to a classical procedure related in ASME-PTC-6.
Exergetic and Thermoeconomic Analyses of a Combined Cycle Plant
Authors: Kim Duck-Jin , Jeon Jin-Seok , Kwak Ho-Young
Published: December 2021

Exergetic and thermoeconomic analyses were performed for a 500-MW combined cycle plant systematically. In this analysis, the mass and energy conservation laws were strictly applied to each component of the system. Careful attention was also paid to the quantitative balances of the exergy and exergetic cost for each component as well as the whole system. The exergoeconomic model employed provided, which is self-consistent the productive structure of the system considered, consequently could visualize the cost formation process and the productive interaction between components clearly. The computer program developed in this study may apply to determine the production cost of any power plant such as gas turbine and gas-turbine cogeneration systems and to study the thermodynamic performance and the sensitivity of such plants to changes in process and/or component design variables.
A Thermodynamic Approach for Conceptual Design of Chemical Processes
Authors: Sorin M. , Hammache A. , Diallo O.
Published: December 2021

The purpose of this paper is to develop a new thermodynamic approach for conceptual design of chemical processes. The approach is based on a concept of reducible superstructure and exergy load distribution analysis. It starts by building a specific reducible structure of the process flowsheet called the “competitive process” superstructure. A two-step exergy analysis is carried out on the superstructure to reduce it to a final optimal flowsheet topology. In the first step, only the design options with the highest impact on the utilizable exergy coefficient of the overall flowsheet is kept for subsequent analysis. In the next step, the distribution of exergy loads from the less efficient units to the more efficient ones makes it possible to relocate the units inside the flowsheet. The new approach was applied for the design of a gas separation section within a benzene synthesis chemical plant. It has been found that the overall exergy efficiency of the benzene synthesis is highest with the design option using a membrane for hydrogen recuperation and an absorber for benzene recuperation. The final step is the relocation of the absorber achieved through the application of the exergy load distribution analysis. Compared with the previous solutions obtained by the hierarchic and mathematical approaches, a new flowsheet for benzene synthesis has been proposed. It consumes the least amount of raw materials, such as hydrogen and toluene, and produces the least amount of discharged gas as waste.
A Simulation Code for Single Phase Geothermal Fields
Authors: Maria Francesco Di , Desideri Umberto
Published: December 2021

This paper presents a design and off-design study of a geothermal field consisting of a number of wells, a steam network which collects the geothermal fluid, and a power plant to generate electricity. The geothermal field considered is located in Italy and the fluid is a mixture of steam and non-condensable gases. The power plant is a conventional type for vapor dominated fields and has a compressor-extractor to remove non-condensable gases from the condenser. The condenser has wet cooling towers to remove heat.

In this study, computer codes developed at the University of Perugia were used to simulate the behavior of geothermal field as a whole. The wells are modeled with second order functions in order to describe pressure-flow rate and temperature-flow rate correlations. The geothermal fluid network is calculated by setting pressures and thermal losses in all the branches. The power plant is simulated with all its components: steam turbine, condenser, gas extractor, cooling towers and auxiliaries. All the components of the geothermal field are simulated at both design and off-design conditions.

The fluid network is solved with an algorithm developed by the authors, which allows the definition of boundary conditions by means of curves based on experimental data. The advantage in comparison with conventional techniques, requiring a fixed pressure or flow rate as boundary condition, is that the solution of the network and the power plant is always a real solution.

The results show how changes in ambient conditions or in the characteristic curve of one or more plant components may influence power production and the exploitation of the geothermal source.
Preliminary Thermodynamics of a Practical Hot Air Power System With Isothermal Combustion and Expansion
Authors: Fineblum Solomon S.
Published: December 2021

The potential benefits of external combustion hot air engines: quietness, combustion cleanliness and combustion efficiency, as well as multi-fuel usage, can be realized only if the heat of the combustion gases is efficiently transferred into the working fluid. Heat transfer in external combustion power systems is usually accomplished by a single, relatively large heat exchanger and by a large delta T across the heat exchanger, which leads to poor First and Second Law efficiencies. The basic flaw in the conventional analysis of externally heated power cycles is identified. A novel open cycle external combustion power system described here incorporates constant pressure recuperation and isothermal expansion for power generation, as in a classical Ericsson cycle. The cycle is improved by the use of exhaust heated isothermal combustion and heat transfer into an immediately adjacent isothermally heated expander. Isothermal expansion is compared with adiabatic expansion. It is shown that a fixed value of specific work can be produced at a lower expander inlet temperature with isothermal expansion than with adiabatic expansion. The thermodynamic as well as practical advantages of this lower temperature are noted. The cycle efficiency is shown to be further improved by isothermal combustion. A practical embodiment of the proposed power system in the form of a hot air turbine will be described. Engine performance, in terms of specific power and system efficiency as a function of temperature and expansion ratio, is predicted with realistic assumptions of component efficiencies and system losses.
The Impact of Reference Environment Selection on the Exergy Efficiencies of Aerospace Engines
Authors: Etele Jason , Rosen Marc A.
Published: December 2021

An exergy analysis is applied to a turbojet engine over a range of flight altitudes ranging from sea level to 15,000 m (∼50,000 ft), to examine the effects of using different reference-environment models. The results of this analysis using a variable reference environment (equal to the operating environment at all times) are compared to the results obtained using two constant reference environments (sea level and 15,000 m). The actual rational efficiency of the turbojet decreases with increasing altitude, ranging from a value of 16.9% at sea level to 15.3% at 15,000 m. In the most extreme cases considered, the rational efficiency value calculated using a constant reference environment varies by approximately 2% from the variable reference environment value.
“Life-Time Oriented” Design and Operation of Energy Conversion Plants: Criteria and Procedures
Authors: Lazzaretto Andrea , Macor Alarico , Mirandola Alberto , Stoppato Anna
Published: December 2021

The design, operation, control and diagnosis of energy conversion systems are different aspects of an integrated approach, which considers the whole life-time of the plants and brings about different skills:

- applied thermodynamics and its various methods of analysis and assessment of functional performances;

- machine design, stress analysis and mechanical control of components, to assess their health state and expected durability;

- diagnosis methods, to check the departures from the expected performances and identify their causes;

- economics, in both designing the plant and deciding if and when it is advisable to do maintenance or an overhaul on machines to restore them to expected performance.

Different methods, procedures and techniques are discussed here, in order to select the most suitable approach to the “life time oriented” design and operation. The following base points have been identified and are presented in this paper:

- to implement efficient operation models of the plants and employ suitable computer codes able to simulate the nameplate and off-design operation as well as to check the consistency of the data coming from the measurement systems;

- to apply the traditional first-law analysis for preliminary thermodynamic calculations and on-line checks;

- to use the exergetic and exergoeconomic analyses to obtain further and more valuable results, both in the design of the plants and during their operation as well as in the diagnosis of departures from the reference values of the parameters (due to malfunctions or change in boundary conditions).

Some results coming from the application of these procedures to a cogenerative plant are shown.
Performance Characteristics of a Combined Ejector-Absorption Heat Pump Using NH3-H2O
Authors: Kouremenos D. A. , Rogdakis E. D. , Alexis G. K.
Published: December 2021

Absorption system have been investigated for many years. However, coefficient of performance COP or heat gain factor HGF for absorption systems are significantly lower than those for conventional compression systems. This has restricted their wide application.

This paper discusses the behavior of mixture NH3-H2O through of an ejector, operating in an absorption heat pump system. This combination improves the performance of conventional absorption system and with the phasing out of ozone-damaging refrigerants, absorption refrigerators, heat pumps and air-conditioning now provide a potential alternative.

For the detailed calculation of the proposed system a method has been developed, which employs analytical functions describing the thermodynamic properties of die mixture. The influence of three major parameters: generator, condenser and evaporator temperature, on ejector efficiency and heat gain factor of the system is discussed.

Also the maximum value of HGF was estimated by correlation of above three temperatures.
Localization of One-Dimensional Thermoelastic Waves in Layered Structures
Authors: Cetinkaya Cetin , Li Chen
Published: December 2021

Including the second sound effect, a transfer matrix formulation based on the generalized dynamical theory of thermoelasticity is developed for longitudinal wave component propagation in a thermoelastic layer. The attenuation and propagation properties of one-dimensional thermoelastic wave in both continuum and layered structures are studied using this formulation and the periodic systems framework. Localization of thermal waves is demonstrated in the time-spacial domain by an FFT-based transient analysis. A perturbation analysis tor identifying leading terms in thermal attenuation is performed, and the role of the thermal elastic coupling term in attenuation is determined. The reflection and transmission coefficients between half-spaces are calculated to evaluate the potential practical use of the approach in laser-based nondestructive testing.
Ultrasonic Signals Generated by a Laser Source in Film/Substrate Systems
Authors: Murray T. W. , Guo Z. , Krishnaswamy S. , Achenbach J. D.
Published: December 2021

A model for the pulsed laser generation of ultrasound in an isotropic film on a semi-infinite substrate is presented. The model gives the time domain displacement of the system as a function of the density and mechanical properties of the film and substrate and the thermal properties of the film. Theoretical signals are calculated and analyzed for both a slow layer on a fast substrate and a fast layer on a slow substrate. The model has been verified experimentally using a 1 ns Nd:YAG laser source for acoustic wave generation and a stabilized Michelson interferometer for detection. Experimental and theoretical signals agree well for both fast on slow and slow on fast systems.
Guided Waves in Thin-Walled Structural Members
Authors: Rogers J. B. C. , Zhuang W. , Shah A. H. , Popplewell N.
Published: December 2021

Infrastructures are deteriorating and billions of dollars are spent to rehabilitate them. Civil structures usually comprise of pavements and bridge decks (plates), pipelines (cylinders), and structural members having, say, I, L, etc. cross sections. The deterioration of these structures causes flaws arising from factors such as the severity of the weather, aging, corrosion, fatigue cracks, etc... The flaws degrade the stiffness (material properties) of a structure and severe conditions eventually can result in a catastrophic failure. Thus, the detection and characterization of the flaws is important in evaluating and monitoring the integrity of existing structures and determining the viability of their continued use or a change in use. Therefore, it is necessary to employ a reliable and effective, quantitative nondestructive evaluation (QNDE) to characterize the mechanical properties and identify defects in the structures. Ultrasonic waves provide such a technique but a knowledge of guided elastic waves is required. Considerable information is available for waves in plates and cylinders but very little work has been reported in the literature on the waves in thin-walled, structural members.

In this paper, a semi-analytical finite element (SAFE) formulation is proposed to study the wave propagation characteristics of thin-walled members. Common structural members are considered as an assemblage of thin plates. The members are assumed to be infinitely long in the longitudinal (axial) direction. The ratio of the thickness of the plate to the wavelength in the axial direction is assumed to be small so that the plane-stress assumption is valid. Employing a finite element modeling in the transverse direction circumvents difficulties associated with the cross-sectional profile of the member. The dynamic behavior is approximated by dividing the plates into several line (one-dimensional) segments and representing the generalized displacement distribution through the segment by polynomial interpolation functions. By applying Hamilton’s principle, the dispersion equationis obtained as a standard algebraic eigenvalue problem. The accuracy of the proposed method is demonstrated by comparing the results with analytical solutions. Detailed numerical results are presented for an I shaped cross section.
Variable Frequency Microwaves (VFM) for Non-Destructive Testing and Evaluation of Adhesively Bonded Polymers
Authors: Siu F. , Siores E. , Basu A.
Published: December 2021

This paper presents a novel microwave assisted nondestructive evaluation system for industrial applications. The technique provides rapid, on-line, non-intrusive, non-destructive, and volumetric monitoring of adhesively bonded polymer materials. When a microwave signal of a given frequency is launched into a metallic cavity which is fully or partially filled with a material, the microwaves reflect back and forth between cavity walls and travel through the material many times until a final standing wave condition is established. Material property variables such as physical geometry, chemical and physical properties, internal or surface defects, and dielectric properties can contribute to its unique output characterisation. The established reflected and the input signals form a ratio, which can be monitored and plotted as a function of the frequency. The signal ratio versus frequency curve is called the microwave reflective spectrum. The spectrum generated can be used as a signature curve for assessing bond quality during processing. This way, the same material under the same processing environment provides a common characteristic curve, which can be traced. Therefore, the quality of adhesively bonded products can be detected by the intrinsic spectrum signals generated.
Elastic Guided Waves in a Pre-Stressed Compressible Layer Imbedded in a Pre-Stressed Two-Material Structure
Authors: Sotiropoulos D. A.
Published: December 2021

Elastic guided waves in a pre-stressed compressible layer imbedded in a pre-stressed two-material structure are examined. The waves propagate parallel to the planar layer interfaces as a superposed dynamic stress state on the statically pre-stressed layer. The stress condition in the layer and in the surrounding materials is arbitrary as are their strain energy functions. To gain understanding of the propagation characteristics, the mathematically tractable model of the materials having common principal axes of strain, one of which is perpendicular to the layering, is employed. The dispersion equation is derived in explicit form yielding guided wave phase and group speeds in terms of wavelength, stress and elastic parameters, and mass densities of the three materials. Limiting cases of the above dispersion equation give the dispersion equation of guided waves in a pre-stressed surface layer overlying a pre-stressed half space, the secular equation of interfacial waves in two semi-infinite pre-stressed materials, the secular equation of non-dispersive Rayleigh surface waves in a half-space, and the frequency equation of guided elastic waves in a pre-stressed compressible plate. Analysis of the dispersion equation reveals the propagation characteristics and their dependence on material and stress parameters. For small interlayer thickness the phase and group speeds are obtained in explicit form. This yields parameter conditions under which the structure acts as a mechanical filter to guided wave propagation. For arbitrary layer thickness, material parameter combinations are also found for which propagation cannot occur. Special attention is paid to the possible existence of interfacial standing waves as a limiting solution of the dispersion equation. Regions of material and stress parameters are defined in which standing waves exist. Numerical computations complement the analytical results for several classes of materials.
On the Steady-State Characteristics of Circumferential Waves in a Two-Layered Cylinder
Authors: Valle Christine , Qu Jianmin , Jacobs Laurence J.
Published: December 2021

A two dimensional, infinitely long hollow cylinder with an inner shaft is considered in this paper. The interface is assumed to be a perfect, infinitely thin layer of inviscid fluid, and the outer surfaces of the cylinder are traction free. Thus the shear stress is assumed to be zero at the interface, but the normal stress and radial displacements are continuous. The problem of steady state, time harmonic waves propagating along the circumference is studied. The dispersion equation is obtained through the exact equations of elasticity and the dispersion curves are calculated for the first five propagating modes. Displacement profiles along the radial direction are included for those same modes. Comparisons are made with the dispersion curves of a full cylinder of same outer radius, and a hollow cylinder of the same dimensions as the one holding the inner shaft. The material is the same for all cases, and assumed to be isotropic and linearly elastic.

It is found that the Rayleigh wave mode is almost identical for the full cylinder and the hollow cylinder with the shaft, and in fact those two cases have mostly similar dispersion branches, except for low frequencies. However the dispersion curves of the hollow cylinder by itself are quite different from the other two, especially at low frequencies.
Failure of a Fiber Composite Lamina Under Three-Dimensional Stresses
Authors: DeTeresa Steven J.
Published: December 2021

The efficient use of thick-section fiber composites requires a proven three-dimensional failure model. Numerous failure criteria have been proposed, but the lack of critical experimental results makes it difficult to assess the accuracy of these models. It is shown that the various predictions for failure of a lamina due to the simple state of uniaxial stress plus superposed hydrostatic pressure are disparate. These differences are sufficient to allow evaluation of failure criteria using data that has the normal scatter found for composite materials. A high-pressure test system for fiber composites is described and results for the effects of pressure on the transverse and longitudinal compression strengths of a carbon fiber/epoxy lamina are discussed. Results are compared with a few representative failure models.
Subsonic and Intersonic Dynamic Crack Growth in Unidirectional Composites
Authors: Coker Demirkan , Rosakis Ares J. , Huang Yonggang Y.
Published: December 2021

Some recent experimental observations of highly dynamic crack growth events in thick unidirectional graphite fiber-reinforced epoxy matrix composite plates are presented. The composite plates were symmetrically (mode-I) and asymmetrically (mode-II) loaded in a one-point bend configuration with an edge pre-notch machined in the fiber direction. The lateral shearing interferometric technique of coherent gradient sensing (CGS) was used in conjunction with high-speed photography. Symmetric, mode-I cracks initiated at 1300 m/s and subsequently accelerated up to the Rayleigh wave speed but never exceeded it. For asymmetric, Mode-II types of loading, the results reveal highly unstable and intersonic, shear-dominated crack growth along the fibers. The intersonic cracks propagated with unprecedented speeds reaching 7400 m/s, more than three times the shear wave speed of the composite, and featured a shock wave structure typical of disturbances travelling with speeds higher than one of the characteristic wave speeds in the solid.
Influence of Delamination on Strength of Externally Pressurized Glass/Epoxy Cylinders
Authors: Davies Peter , Carlsson Leif A.
Published: December 2021

The delamination resistance of filament wound glass/epoxy cylinders has been characterized for a range of winding angles and fracture mode ratios using beam fracture specimens. The results reveal that the fracture resistance increases with increasing winding angle and mode II (shear) fraction (GII/G). It was also found that interlaced fiber bundles in the filament wound cylinder wall acted as effective crack arresters in mode I loading. To examine the sensitivity of delamination damage on the implosion behavior of cylinders, external pressure tests were performed on filament-wound glass/epoxy composite cylinders with artificial defects and impact damage. The results revealed that the cylinder strength was insensitive to the presence of single delaminations but impact damage caused reductions in failure pressure. The insensitivity of the failure pressure to a single delamination is attributed to the absence of buckling of the delaminated sublaminates before the cylinder wall collapsed. The impacted cylinders contained multiple delaminations, which caused local reduction in the compressive load capability and reduction in failure pressure.
High Strain Rate Response of Resin Infusion Molded Sandwich Composites
Authors: Mahfuz Hassan , Al Mamun Wahid , Mohamed Hisham , Vaidya Uday , Haque Anwarul , Jeelani Shaik
Published: December 2021

Foam core sandwich composites have been tested under high strain rate (HSR) loading in the thickness direction. The regular Split Hopkinson Pressure Bar (SHPB) has been modified by replacing the steel transmitter bar by a polycarbonate bar. This modification resulted in stronger signals from the transmitter bar, which would otherwise be very feeble especially when testing soft materials. New sets of mathematical formulations have been derived to account for the impedance mismatch between the incidence and transmitter bars. The modified equations are first verified with a known material and then used for sandwich composites. Three types of core with various densities have been tested under compression at strain rates ranging from quasi-static to 1000 S−1. The compressive failure stress has been observed to be directly proportional to the core density, as well as to the strain rate. The strain rate sensitivity was moderate, and the sandwich composites mostly failed by the collapse of the foam-cell. Delamination did not play a major role in the failure process. Details of the mathematical derivations and the analysis of the HSR behavior are presented in this paper.