Thermal decomposition behavior of tobacco stem Part I: TGA–FTIR–MS analysis

In the present study, the thermal degradation behavior of tobacco stem was examined by means of a thermogravimetric analyzer (TGA) under nitrogen atmosphere at temperature range of 25–1,000°C. The TG curve indicated that the pyrolysis process of tobacco included three zones, and main pyrolysis occurred in the second zone by means of the decomposition of hemicellulose, cellulose, and lignin in a temperature range of 180–540°C. Furthermore, the gases evolved during the degradation were analyzed simultaneously via TGA coupled with a Fourier transform infrared spectrometer (FTIR) and mass spectrometer (MS). Carbon dioxide, methane, water, formaldehyde, and propanal were the main volatiles detected via MS and confirmed by FTIR.     

Numerical Method for Calculation of Complete Casting Processes—Part I: Theory

This article presents a method for calculation of the complete casting process, including the pouring of the liquid metal into the mold, its solidification, the deformation of the solidified cast, the formation of airgaps between the cast and the mold and their influence on the heat transfer, and the residual stresses. An original phase-change procedure is developed, valid for an arbitrary number of pure metals and/or alloys. A collocated version of a segregated finite-volume method is used to calculate both the liquid metal flow and the deformations and stresses in solids.     

Modelling of hybrid energy system—Part I: Problem formulation and model development

A well designed hybrid energy system can be cost effective, has a high reliability and can improve the quality of life in remote rural areas. The economic constraints can be met, if these systems are fundamentally well designed, use appropriate technology and make use effective dispatch control techniques. The first paper of this tri-series paper, presents the analysis and design of a mixed integer linear mathematical programming model (time series) to determine the optimal operation and cost optimization for a hybrid energy generation system consisting of a photovoltaic array, biomass (fuelwood), biogas, small/micro-hydro, a battery bank and a fossil fuel generator. The optimization is aimed at minimizing the cost function based on demand and potential constraints. Further, mathematical models of all other components of hybrid energy system are also developed. This is the generation mix of the remote rural of India; it may be applied to other rural areas also.     

Implementation of boundary conditions in the finite-volume pressure-based method—Part I: Segregated solvers

ABSTRACT

The paper deals with the formulation of a variety of boundary conditions for incompressible and compressible flows in the context of the segregated pressure-based unstructured finite volume method. The focus is on the derivation and the implementation of these boundary conditions and their relation to the various physical boundaries and geometric constraints. While a variety of boundary conditions apply at any of the physical boundaries (inlets, outlets, and walls), geometric constraints define the type of boundary condition to be used. The emphasis is on relating the mathematical derivation of the boundary conditions to the algebraic equations defined at each centroid of the boundary elements and their coefficients. All derived boundary conditions are validated through a set of test cases with comparison of computed results to available numerical and/or experimental data.     

Investigation Methods for Thermal Shock Crack Problems of Functionally Graded Materials–Part I: Analytical Method

In most published papers, in order to obtain the analytical solution of the crack problems in functionally graded materials (FGMs), the thermomechanical properties of FGMs are usually assumed to be very particular functions and, hence, may not be physically realizable for many actual material combinations. Very few analytical methods can be used to solve the thermal shock crack problem of an FGM cylindrical shell or plate with general thermomechanical properties. In this article, a set of analytical methods is proposed for the thermal shock crack problem of an FGM plate or cylindrical shell with general thermomechanical properties. The crack problem of a cylindrical shell is modeled by a plate on an elastic foundation. Greatly different from previous studies, a set of analytical methods using both the perturbation method and a piecewise model are developed to obtain the transient temperature field and thermal stress intensity factor (TSIF). The perturbation method is applied to deal with the general thermal properties and the piecewise model is used to deal with the general mechanical properties. In the analytical procedure, integral transform, the residue theorem, and the theory of singular integral equation are used. Several representative examples are considered to check the capability of the present method. The transient thermal shock behavior of a ZrO₂/Ti-6Al-4 V FGM plate with a surface crack and a Rene 41-Zirconia FGM cylindrical shell with a circumferential crack are analyzed.     

Constructal design of T–Y assembly of fins for an optimized heat removal

Constructal design has been applied to a large variety of problems in nature and engineering to optimize the architecture of animate and inanimate flow systems. This numerical work uses this method to seek for the best geometry of a T–Y assembly of fins, i.e., an assembly where there is a cavity between the two branches of the assembly of fins. The global thermal resistance of the assembly is minimized by geometric optimization subject to the following constraints: the total volume, the volume of fin-material, and the volume of the cavity. Parametric study was performed to show the behavior of the twice minimized global thermal resistance. The results show that smaller cavity volume and larger fins volume improve the performance of the assembly of fins. The twice minimized global thermal resistance of the assembly and its corresponding optimal configurations calculated for the studied parameters were correlated by power laws.     

Policy and institutional dimensions of the water–energy nexus

Energy and water are interlinked. The development, use, and waste generated by demand for both resources drive global change. Managing them in tandem offers potential for global-change adaptation but presents institutional challenges. This paper advances understanding of the water–energy nexus by demonstrating how these resources are coupled at multiple scales, and by uncovering institutional opportunities and impediments to joint decision-making. Three water–energy nexus cases in the United States are examined: (1) water and energy development in the water-scarce Southwest; (2) conflicts between coal development, environmental quality, and social impacts in the East; and (3) tensions between environmental quality and economic development of shale natural gas in the Northeast and Central U.S. These cases are related to Eastern, Central, and Western regional stakeholder priorities collected in a national effort to assess energy–water scenarios. We find that localized challenges are diminished when considered from broader perspectives, while regionally important challenges are not prioritized locally. The transportability of electricity, and to some extent raw coal and gas, makes energy more suitable than water to regionalized global-change adaptation, because many of the impacts to water availability and quality remain localized. We conclude by highlighting the need for improved coordination between water and energy policy.     

Final Shape of Precision Molded Optics: Part I—Computational Approach,Material Definitions and the Effect of Lens Shape

Coupled thermomechanical finite element models were developed in ABAQUS to simulate the precision glass lens molding process, including the stages of heating, soaking, pressing, cooling and release. The aim of the models was the prediction of the deviation of the final lens profile from that of the mold, which was accomplished to within one-half of a micron. The molding glass was modeled as viscoelastic in shear and volume using an n-term, prony series; temperature dependence of the material behavior was taken into account using the assumption of thermal rheological simplicity (TRS); structural relaxation as described by the Tool-Narayanaswamy-Moynihan (TNM)-model was used to account for temperature history dependent expansion and contraction, and the molds were modeled as elastic taking into account both mechanical and thermal strain. In Part I of this two-part series, the computational approach and material definitions are presented. Furthermore, in preparation for the sensitivity analysis presented in Part II, this study includes both a bi-convex lens and a steep meniscus lens, which reveals a fundamental difference in how the deviation evolves for these different lens geometries. This study, therefore, motivates the inclusion of both lens types in the validations and sensitivity analysis of Part II. It is shown that the deviation of the steep meniscus lens is more sensitive to the mechanical behavior of the glass, due to the strain response of the newly formed lens that occurs when the pressing force is removed.     

Crack-opening-area analyses for circumferential through-wall cracks in pipes—Part I: analytical models

Leak-before-break (LBB) analyses for circumferentially cracked pipes are currently being conducted in the nuclear industry to justify elimination of pipe whip restraints and jet impingement shields which are present because of the expected dynamic effects from pipe rupture. The application of the LBB methodology requires calculation of leak rates. The leak rates depend on the crack-opening area of the through-wall crack in the pipe. In addition to LBB analyses which assume a hypothetical flaw size, there is also interest in the integrity of actual leaking cracks corresponding to current leakage detection requirements in NRC Regulatory Guide 1.45, or for assessing temporary repair of Class 2 and 3 pipes that have leaks, as are being evaluated in ASME Section XI. The objectives of this study were to review, evaluate, and refine current predictive models for performing crack-opening-area analyses of circumferentially cracked pipes. A three-phase effort was undertaken to accomplish this goal. It is described here in a series of three papers generated from this study. In this first paper (Part I — Analytical models), a comprehensive review is performed to determine the current state-of-the-art in predicting crack-opening displacements for circumferentially cracked pipes under pure bending, pure tension, and combined bending and tension loads. Henceforth, new and improved analytical models and some preliminary results are presented for cases where current methods are inadequate or there are no available methods. Also, based on this review, a number of appropriate predictive models are identified for a systematic evaluation of their accuracy. The results of their evaluations will be presented and examined in the forthcoming companion papers (Part II — Model validations [1] and Part III — Off-center cracks, restraint of bending, thickness transition, and weld residual stresses) [2].     

Totally analytical closure of space filtered Navier–Stokes for arbitrary Reynolds number: Part I. Theory,resolutions

ABSTRACT

Rigorously space filtering the thermal, multispecies Navier–Stokes (NS) conservation principle partial differential equation (PDE) system embeds a priori undefined tensor and vector quadruples. Large eddy simulation (LES) computational fluid dynamics algorithm resolutions replace the tensor quadruple with a single tensor then secures closure through “physics-based” modeling, assuming the velocity field is turbulent, i.e., the Reynolds number (Re) is large. In complete distinction, a totally analytical closure is derived for the rigorously generated tensor/vector quadruples, achieved totally absent any modeling component or Re assumption. For Gaussian filter of uniform measure δ, derived analytical filtered Navier–Stokes (aFNS) theory PDE system state variable is significance scaled O(1; δ²; δ³) through classic fluid mechanics perturbation theory. That uniform measure δ filter penetrates domain boundaries requires O(1) resolved scale PDE system inclusion of boundary commutation error (BCE) integrals, (unfiltered) NS state variable extension in the sense of distributions, and domain enlargement to encompass all surfaces with Dirichlet boundary condition (DBC) specification. Theory-derived O(δ²) resolved–unresolved scale interaction PDE system, also the O(1) system, is rendered bounded domain, well posed through a priori identification of O(1; δ²) state variable nonhomogeneous DBCs. BCE and DBC resolution algorithm derivations use O(δ⁴) approximate deconvolution (AD) differential definition Galerkin weak forms. Theory analytically derived unresolved scale O(δ³) state variable annihilates discretization-induced O(h²) dispersion error at unresolved scale threshold δ, h the mesh measure. Net is an analytical theory closing rigorously space-filtered NS exhibiting potential for first principles prediction of viscous laminar–turbulent transition, separation, and relaminarization.     

Nonlinear control of fuel cell hybrid power sources: Part I – Voltage control

In this paper is proposed a nonlinear control for fuel cell/battery/ultracapacitor hybrid power sources (HPS) that improves the performance and durability of fuel cell. The nonlinear voltage control is analyzed and designed using a systematic approach. The design goal is to stabilize the HPS output voltage at a low voltage ripple that is also spread in a large frequencies band. All the results have been validated in several simulations. The simulation results successfully show that nonlinear voltage control performs good performances in the frequency-domain (a high spreading level of power spectrum) and in the time domain (a low level of output voltage ripple factor), too.     

Sustainability of hydrogen supply chain. Part I: Identification of critical criteria and cause–effect analysis for enhancing the sustainability using DEMATEL

The enhancement of sustainability of hydrogen supply chain is of vital importance for the stakeholders/decision-makers to design a sustainable hydrogen supply chain. The objective of this paper is to develop a method for prioritizing the influential factors, identifying the key driving factors that influence the sustainability of hydrogen supply chain and mapping the cause–effect relationships to improve the sustainability of hydrogen supply chain. In this paper, thirty seven criteria in four aspects including economic, technological, environmental and societal aspects are considered for enhancing the sustainability of hydrogen supply chain, and decision making trial and evaluation laboratory has been used to analyze the relationships among these criteria. The status of hydrogen supply chain in China has been studied by the proposed method, and the results are consistent with the actual conditions. It could be concluded that the proposed method is feasible and could be popularized to some other cases.     

Suppression of hydrogen–oxygen–nitrogen explosions by fine water mist: Part 2. Mitigation of vented deflagrations

The simultaneous use of water mist and dilution by nitrogen has not been previously considered for the mitigation of hydrogen containing gas explosions and there is little guidance currently available to plant and safety engineers in the nuclear industry. This gap in knowledge is addressed and data reported for the reduction of rates of pressure rise experienced in a vented apparatus. Such information will also be of use in subsequent, separate modelling studies.     

Generalized Thermoelastic Models for Linear Elastic Materials with Micro-Structure Part I: Enhanced Green–Lindsay Model

In this article, we derive constitutive thermoelastic models for linear elastic materials with micro-structure. The elastic behavior is assumed to be consistent with Mindlins’ Form II gradient elasticity theory, whereas for the thermal behavior the generalization of Clausius-Duhem inequality, proposed by Green and Laws, is adopted. The resulting model is actually a generalization of the thermoelastic theory of Green and Lindsay for linear elastic materials with micro-structure, taking into account micro-inertia effects, as well. It is demonstrated that classical thermoelasticity models are retrieved from the present general formulation, when some of the model constants are set to zero. Finally, the uniqueness of solution for the general case of anisotropic materials is proved.     

Influence of annealing treatment on Laves phase compound containing a V-based BCC solid solution phase—Part I: Crystal structures

Two multi-component Laves phase hydrogen storage alloys containing a body centered cubic (BCC) solid solution phase were prepared and the effects of annealing treatment on their crystal structures have been studied in this part. It is found by X-ray powder diffraction and energy dispersive X-ray spectrometer analysis that the as-cast alloys mainly consist of two phases: the C14 Laves phase matrix with hexagonal structure and the dendritic V-based solid solution phase with BCC structure. In addition, a small amount of TiNi-based third phase is also found precipitated within both the C14 Laves phase and the V-based solid solution phase. However, the content of the TiNi-based phase is decreased greatly by an appropriate annealing treatment owing to the compositional homogenization. Furthermore, the lattice parameters and unit cell volumes of both the C14 Laves phase and the V-based solid solution phase have all increased after the annealing treatment.     

Modeling of the transport phenomena in GMAW using argon–helium mixtures. Part I – The arc

This article presents a numerical investigation on the transient transport phenomena in the arc which include the arc plasma generation and interactions with moving droplets and workpiece for pure argon and three argon–helium mixtures (75% Ar + 25% He, 50% Ar + 50% He, and 25% Ar + 75% He) during the gas metal arc welding (GMAW) process. The results indicate that the arcs in various shielding gases behave very differently due to the significant differences in thermophysical properties, including the ionization potential and the electrical conductivity, thermal conductivity, specific heat, and viscosity at high temperatures. For the same welding power input, it was found the increase of helium content in the mixtures results in (1) the change of plasma arc shape from bell-like to cone-like and (2) the change of arc pressure distribution along the workpiece surface from Gaussian-like to flat-top with decreasing peak value. Detailed explanations to the physics of the very complex but interesting transport phenomena are given.