Bulk Energy Density Research Articles

Temperature-induced hexagonal–orthorhombic phase transition in lutetium ferrite nanoparticles

The x-ray diffraction, Raman, and infrared spectroscopies and magnetic measurements were used to explore the correlated changes of the structure, lattice dynamics, and magnetic properties of the LuFeO3 nanoparticles, which appear in dependence on their sintering temperature. We revealed a gradual substitution of the hexagonal phase by the orthorhombic phase in the nanoparticles, with sintering temperature increasing from 700 to 1100 °C. The origin and stability of the hexagonal phase in the LuFeO3 nanoparticles are of the special interest, because the nanoparticles in the phase can be a room-temperature multiferroic with a weak ferromagnetic and pronounced structural and ferroelectric long-range ordering. The antiferromagnetic and nonpolar orthorhombic phase is more stable in the bulk LuFeO3. To define the ranges of the hexagonal phase stability, we determine the bulk and interface energy densities of different phases from the comparison of the Gibbs model with experimental results. Using effective parameters of the Gibbs model, we predict the influence of size effects and temperature on the structural and polar properties of the LuFeO3 nanoparticles. Analysis of the obtained results shows that the combination of the x-ray diffraction, Raman and infrared spectroscopies, magnetic measurements, and theoretical modeling of structural and polar properties allows us to establish the interplay between the phase composition, lattice dynamics, and multiferroic properties of the LuFeO3 nanoparticles prepared under different conditions.

Quasiconvex bulk and surface energies: C 1,α regularity

Abstract We establish regularity results for equilibrium configurations of vectorial multidimensional variational problems, involving bulk and surface energies. The bulk energy densities are uniformly strictly quasiconvex functions with p p -growth, p ≥ 2 p\ge 2 , without any further structure conditions. The anisotropic surface energy is defined by means of an elliptic integrand Φ \Phi not necessarily regular. For a minimal configuration ( u , E ) \left(u,E) , we prove partial Hölder continuity of the gradient ∇ u \nabla u of the deformation.

Morawetz Estimates Without Relative Degeneration and Exponential Decay on Schwarzschild–de Sitter Spacetimes

We use a novel physical space method to prove relatively non-degenerate integrated energy estimates for the wave equation on subextremal Schwarzschild–de Sitter spacetimes with parameters (M,Lambda ). These are integrated decay statements whose bulk energy density, though degenerate at highest order, is everywhere comparable to the energy density of the boundary fluxes. As a corollary, we prove that solutions of the wave equation decay exponentially on the exterior region. The main ingredients are a previous Morawetz estimate of Dafermos–Rodnianski and an additional argument based on commutation with a vector field which can be expressed in the form r1-2Mr-Λ3r2∂∂r,\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\begin{aligned} r\\sqrt{1-\\frac{2M}{r}-\\frac{\\Lambda }{3}r^2}\\frac{\\partial }{\\partial r}, \\end{aligned}$$\\end{document}where partial _r here denotes the coordinate vector field corresponding to a well-chosen system of hyperboloidal coordinates. Our argument gives exponential decay also for small first-order perturbations of the wave operator. In the limit Lambda =0, our commutation corresponds to the one introduced by Holzegel–Kauffman (A note on the wave equation on black hole spacetimes with small non-decaying first-order terms, 2020. arXiv:2005.13644).

Multifield driven bond relaxation on the dielectric constant of GaN, InN, and ZnO

From the perspective of bond relaxation under multifield perturbation, we examined the dielectric response to perturbation for GaN, InN, and ZnO. It is found that the surface local bond contraction and quantum entrapment dictate the size dependency of the dielectric constant at the nanometer scale. Reproduction of experimental observations under temperature, pressure, and tensile strain derived respective information of the Debye temperature and atomic cohesive energy, the bulk modulus and energy density, the bond length, bond energy, and force constant. The formulation of the multifield effects on the dielectric constant of semiconductors is beyond the scope of the available approaches, which not only revealed quantitative information but also provides deeper insight into the physical origin of the dielectric response to perturbations.

Periodic homogenization in the context of structured deformations

An energy for first-order structured deformations in the context of periodic homogenization is obtained. This energy, defined in principle by relaxation of an initial energy of integral-type featuring contributions of bulk and interfacial terms, is proved to possess an integral representation in terms of relaxed bulk and interfacial energy densities. These energy densities, in turn, are obtained via asymptotic cell formulae defined by suitably averaging, over larger and larger cubes, the bulk and surface contributions of the initial energy. The integral representation theorem, the main result of this paper, is obtained by mixing blow-up techniques, typical in the context of structured deformations, with the averaging process underlying the theory of homogenization.

Heavy bio‐oils as bio‐binders for rice husk densification: Parameter optimization, binding mechanisms and subsequent pyrolysis and combustion performances

AbstractDensification is widely considered as a means to improve the bulk energy density and transportation efficiency of biomass, while the durability and fuel quality of densified biomass often need to be further improved by the addition of binders. In this study, the heavy fractions of bio‐oils from slow pyrolysis (HBO‐SP) and hydrothermal treatment (HBO‐HT) of rice husk (RH) are used as bio‐binders for RH densification. Optimal parameters are determined based on Taguchi methods. They are: densification temperature 130 °C, densification pressure 200 MPa, bio‐binder content 8%, particle size 0.4–0.6 mm, and using HBO‐HT as the binder. The obtained pellets showed a high drop resistance of 99.8% and the binding mechanism is governed by solid bridges between particles. Heavy bio‐oils are deformed and re‐solidified and function as a binder for RH densification. The RH/HBO‐HT pellets showed lower activation energy for pyrolysis as well as lower ignition temperature (292.81 °C compared with 298.34 °C for RH pellets). The higher heating value of pellets was increased from 14.99 to 16.29 MJ kg−1 with 8 wt% HBO‐HT. The co‐densification of heavy bio‐oils and RH provides an approach for producing more qualified solid biofuels from agriculture wastes. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd

Monte Carlo event generator for initial conditions of conserved charges in nuclear geometry

At top collider energies where baryon stopping is negligible, the initial state of heavy-ion collisions is overall charge neutral and predominantly composed of gluons. Nevertheless, there can also be significant local fluctuations of the baryon number, strangeness, and electric charge densities about zero, perturbatively corresponding to the production of quark/antiquark pairs. These previously ignored local charge fluctuations can permit the study of charge diffusion in the quark-gluon plasma (QGP), even at top collider energies. In this paper we present a new model denoted ICCING (initial conserved charges in nuclear geometry) which can reconstruct the initial conditions of conserved charges in the QGP by sampling a ($g\ensuremath{\rightarrow}q\overline{q}$) splitting probability over the initial energy density. We find that the new charge distributions generally differ from the bulk energy density; in particular, the strangeness distribution is significantly more eccentric than standard bulk observables and appears to be associated with the geometry of hot spots in the initial state. The new information provided by these conserved charges opens the door to studying a wealth of new charge- and flavor-dependent correlations in the initial state and ultimately the charge transport parameters of the QGP.

Performance of High-Layer-Thickness Ti6Al4V Fabricated by Electron Beam Powder Bed Fusion under Different Accelerating Voltage Values.

The electron beam powder bed fusion (EB-PBF) process is typically carried out using a layer thickness between 50 and 100 μm with the accelerating voltage of 60 kV for the electron beam. This configuration ensures forming accuracy but limits building efficiency. The augmentation of the accelerating voltage enlarges the molten pool due to the rise in penetrability, suggesting that a higher layer thickness can be used. Therefore, the effects of layer thickness and accelerating voltage were investigated simultaneously in this study to explore the feasibility of efficiency improvement. Ti6Al4V was fabricated by EB-PBF using layer thicknesses of 200 and 300 μm. Two accelerating voltage values of 60 and 90 kV were used to study their effects under expanded layer thickness. The results reveal that dense parts with the ultimate tensile strength higher than 950 MPa and elongation higher than 9.5% could be fabricated even if the layer thickness reached 300 μm, resulting in a building rate of up to 30 mm3/s. The expansion of the layer thickness could decrease the minimum bulk energy density needed to fabricate dense parts and increase the α platelet thickness, which improved the energy efficiency. However, expanding layer thickness had a significant negative effect on surface roughness, but it could be improved by applying augmented accelerating voltage.

The effect of continuous electron beam scanning process on the microstructure and geometry of U-5.5 wt%Nb alloy

A continuous electron beam scanning process was used for the surface treatment on U-5.5Nb alloy, under various combinations of beam current, beam accelerating voltage, and scanning speed. The transverse cross-section characteristics of the resulting modification layers were metallographically measured to investigate the relationship between the electron beam processing parameters and the fusion zone geometry or the resolidification microstructure. Results showed that the resolidified modified layers were obtained with the bulk energy density (E0*) value exceeding 60.7 J/mm3. An “equiaxed-columnar-equiaxed” sandwich-type grain structure was formed in the resolidification fusion zone under the effects of local temperature gradient (G) and the growth rate (R). Different from that of traditional surface modified alloys, the cross-sectional microstructure of surface modified U-5.5Nb alloy consists of four characteristic areas: fusion zone (FZ), heat affected zone (HAZ), base metal (BM), and partially fusion zone (PFZ). The width (W) and depth (D) of the fusion zone had an almost linear increase with the bulk energy density (E0*). The Vickers hardness, Nb composition, and phase microstructures were also examined. The surface hardness values increased significantly following surface treatment, which was mainly attributed to phase transformation.

Study of the structure and mechanical properties of samples obtained by the selective laser alloying technology from the Inconel 738 heat-resistant alloy powder

The technology of selective laser melting of heat-resistant alloys is of great interest in the aerospace industry, because it allows you to implement a more complex geometry of parts in comparison with traditional technologies. This paper presents the results of determining the rational technological parameters of scanning a metal powder of a heat-resistant alloy Inconel 738. By statistical processing of experimental data to determine the effect of technological parameters of scanning on the tensile strength of a material, rational technological parameters of scanning are established, namely, the laser radiation power is 325 W, the scanning step is 0,12 mm, scanning speed of 677 mm/s, which corresponds to a bulk energy density of 80 J/mm3. The results of tests of cylindrical samples manufactured at angles of 0°, 30°, 45°, 60° and 90° to the uniaxial tension building platform are presented. A study of the microstructure of the samples was executed.

Combining multi-phase field simulation with neural network analysis to unravel thermomigration accelerated growth behavior of Cu6Sn5 IMC at cold side Cu–Sn interface

In Pb-free solder alloys used in solder balls of diameter of 50 µm or smaller, larger proportion of Cu6Sn5 intermetallics formation is a major reliability concern, and this is aggravated in presence of external thermal gradient. A complete understanding of the mechanism for intermetallics compound (IMC) growth under thermomigration is essential for devising solder materials resistant to degradation under thermal gradient. This work integrates neural network analysis with multi-phase field method to quantify the mechanism of thermomigration at the cold side of a solder-substrate system. At hot side temperature of 523.15 K, 1D multi-phase field model is built for a combined driving force of bulk diffusion and thermomigration, and is solved using finite element method (FEM). The free energy density function for the thermomigration driving force is introduced, and coupled with the functions for bulk and interfacial free energy density of each phase. Data of heats of transport, temperature difference and growth rate constant of IMC are obtained from multiple FEM simulations, and the FEM-generated dataset is employed in the neural network. The machine learning predicted growth rate constant is tallied with experimental value, and heat of transport of Cu in IMC phase (QCuimc) is determined from the inverse method. The obtained value of optimized QCuimc is +35.10 kJ/mol. 2D IMC grain growth simulations are performed with hot-side at 523.15 K and the cold side lowered to 523.0817 K and 522.0 K respectively, thereby revealing that the accelerated grain growth for larger temperature difference is noticed within the first 20 s of the simulations.

Computer Test of a Modified Silicene/Graphite Anode for Lithium-Ion Batteries.

Despite the considerable efforts made to use silicon anodes and composites based on them in lithium-ion batteries, it is still not possible to overcome the difficulties associated with low conductivity, a decrease in the bulk energy density, and side reactions. In the present work, a new design of an electrochemical cell, whose anode is made in the form of silicene on a graphite substrate, is presented. The whole system was subjected to transmutation neutron doping. The molecular dynamics method was used to study the intercalation and deintercalation of lithium in a phosphorus-doped silicene channel. The maximum uniform filling of the channel with lithium is achieved at 3% and 6% P-doping of silicene. The high mobility of Li atoms in the channel creates the prerequisites for the fast charging of the battery. The method of statistical geometry revealed the irregular nature of the packing of lithium atoms in the channel. Stresses in the channel walls arising during its maximum filling with lithium are significantly inferior to the tensile strength even in the presence of polyvacancies in doped silicene. The proposed design of the electrochemical cell is safe to operate.

Characterizations of Biomasses for Subsequent Thermochemical Conversion: A Comparative Study of Pine Sawdust and Acacia Tortilis

The bioenergy production potential from biomasses is dependent on their characteristics. This study characterized pine sawdust samples from Zimbabwe and acacia tortilis samples from Botswana using conventional and spectrometry techniques. The ultimate analysis results for pine were 45.76% carbon (C), 5.54% hydrogen (H), 0.039% nitrogen (N), 0% sulphur (S) and 48.66% oxygen (O) and, for acacia, were 41.47% C, 5.15% H, 1.23% N, 0% S and 52.15% O. Due to the low N and S in the biomasses, they promise to provide cleaner energy than fossil-based sources. Proximate analysis results, on a dry basis, for acacia were 3.90% ash, 15.59% fixed carbon and 76.51% volatiles matter and 0.83%, 20% and 79.16%, respectively, for pine. A calorific value of 17.57 MJ/kg was obtained for pine, compared with 17.27 MJ/kg for acacia, suggesting they are good thermochemical feedstocks. Acacia’s bulk energy density is five times that of pine, making it excellent for compressed wood applications. Though the ash content in acacia was much higher than in pine, it fell below the fouling and slagging limit of 6%. In pyrolysis, however, high ash contents lead to reduced yields or the quality of bio-oil through catalytic reactions. Fourier transform infrared spectrometry indicated the presence of multiple functional groups, as expected for a biomass and its derivatives.

The potential use of torrefied Nigerian biomass for combustion applications

Many countries are seeking to expand their use of solid biomass for electricity and heat generation. Nigeria, too, is exploring its own potential energy crops and indigenous residues. The use of this biomass for energy production is, however, limited by factors such as high moisture content, low bulk and low energy density. This study examines the torrefaction and combustion properties of four readily available Nigerian woody biomass, Gmelina arborea, Terminalia superba, Nauclea diderrichii, Lophira alata and a residue, palm kernel expeller (PKE). They are considered for their suitability for use in large scale power stations, especially as pulverized fuels.The Fuels were torrefied at 270 and 290 °C for either 30 or 60 min, and assessed for pyrolysis and combustion characteristics in comparison to their untreated counterparts. Energy densities of the woods improved from 19.2 to 21.2 MJ/kg for the raw fuels to 21.5–24.6 MJ/kg for the torrefied fuels. The milling behaviour of the torrefied fuels improved upon torrefaction, especially for Nauclea; however, torrefaction had very little effect on the grindability of PKE. The apparent first order kinetics for pyrolysis were determined by thermogravimetric analysis (TGA). After torrefaction, the fuels become less reactive; Nauclea and Gmelina were the most reactive fuels, whilst PKE was the least reactive. The combustion behavior of selected fuels was visually examined in a methane air flame. This showed that torrefaction resulted in shorter ignition delay, shorter duration of volatile combustion and longer duration of char burn out.

Interfacial energy as the driving force for diffusion bonding of ceramics

Diffusion bonding of ceramics with a metallic interlayer can give a variety of very complex joint microstructures, which are highly influenced by ceramic compositions, the material and thickness of the interlayer, bonding temperature as well as time at the peak bonding temperature. Experiments with a diffusion bonding of ZrC using a Ti interlayer clearly show that under a certain bonding condition, a seamless joint with the total dissolution of the interlayer can be obtained. They also indicate the existence of the critical interlayer thickness, below which the seamless homogeneous joint domain is obtained, and above which the joint does not homogenize. The key process leading to these outcomes is the diffusion of carbon from ZrC into Ti, which, when the critical carbon concentration is reached, initiates the phase transformation of bcc Ti to TiC, while the binary Zr/Ti diffusion is then driven by entropy and results in a seamless Zr(Ti)C joint.We first show that the dependence of ZrC/Ti interfacial energy on the carbon concentration jump across the interface is the main thermodynamic driving force of the diffusion of carbon from ZrC to the Ti interlayer. Then, we show that the characteristic length (critical thickness of the interlayer) arises as the ratio of this driving force (energy/area) and the bulk energy densities, which oppose the carbon diffusion. Finally, we develop a diffuse interface (phase-field) model to simulate the process. The novelty in the phase-field model is the introduction of a dependence of the interfacial energy on the carbon concentrations on the two sides of the interface. The critical thickness of the interlayer is estimated employing both models and good agreement with experimental findings is obtained.

Apple pruning residues: Potential for burning in boiler systems and pellet production

Residues from management activities of fruit growing can be an important source of biomass for energy generation. The aim of this study was to determine the potential use of apple pruning residues for energy generation as process steam or power energy. To this end, branches from the pruning of commercial apple orchards have been evaluated in the Santa Catarina State, Brazil. To compare with the traditional biomass used for energetic purposes, particles of Pinus sp. from the industrial timber processing have also been analysed. Homogeneous pellets of the two types of biomass were produced, and three more mixes containing the two raw materials were made. Pellets have been evaluated according to their physical and energetic properties. The results have been compared to the ISO 17,225-2 Standard. Apple pruning residues have the potential for energy generation in boilers, that is, for the production of process steam and electric power. Their potential can vary from 12,649.54 MWh y−1 to 115,442.44 MWh y−1. The physical and energetic properties varied between the analysed residues, except the gross calorific value (19.69 MJ kg−1 for pine wood particles and 20.27 MJ kg−1 for apple pruning). Comparing with the pine wood (87 kg m−3), the apple pruning (141 kg m−3) has a higher amount of biomass per unit volume processed for energy and less residence time in the burning systems (17.54% fixed carbon for apple pruning and 18.91% fixed carbon for pine wood). However, it generates more wastes (ashes) after burning (3.25% for apple pruning and 0.46% for pine wood). The pellets’ energy density increased by 3.35 times the energy density of the apple pruning particles after pelletizing. The homogeneous apple pruning pellets can only be applied to industrial use (I3), mainly because of its high ash content (2.27%). The pine wood with apple pruning mix used for pellet production reduces the ash content and increases the bulk density and energy density, which improves the quality of the pellets.

Particle temperature and flue gas emission of a burning single pellet in air and oxy-fuel combustion

Pelletization of biomass increases the bulk energy density and the uniformity in size and shape with minimized mechanical degradation from transport, storage, and handling. A pellet can be burned in industrial circulating fluidized-bed or fixed-bed furnaces. This experimental study examines the combustion behavior of single pine wood and empty fruit bunch pellets in a laboratory-scale entrained-flow reactor. Individual biomass pellets were oxidized under both N2/O2 (79%/21%) and CO2/O2 (79%/21%) to investigate the burning characteristics during oxy-fuel combustion. The gas temperature was set at 860 K, 970 K, and 1090 K to examine its effect on combustion behavior. The burning pellets were directly observed in a visualization window in the reactor throughout the sequential combustion process. Direct observation, optical pyrometry, and flue gas analysis are synchronized for each pellet to interpret the relation between phenomenological events, particle temperature, and flue gas emission. The experimental results shows an increased homogenous ignition delay and a conical, less sooty flame in the presence of CO2. The particle temperature under CO2/O2 atmosphere is slightly lower than that under N2/O2, especially for the volatile combustion. The CO emission under CO2/O2 is significantly higher and produced from incomplete combustion. These combustion characteristics are attributed to low oxygen diffusion and the high volumetric heat capacity of CO2. The pine wood displayed a fast, homogeneous ignition and a sooty flame with high NO and SO2 emissions compared to the empty fruit bunches.

Quality Properties and Pyrolysis Characteristics of Cassava Rhizome Pellets Produced by Alternating between Pelletizing and Torrefaction

This work investigated quality properties of pellets of raw cassava rhizome (P-RC), pellets of pelletized cassava rhizome followed by torrefaction (T-CP), and pellets of torrefied cassava rhizome followed by pelletizing (P-TC). Torrefaction was conducted at temperatures of 230, 250, and 280 °C for 30 min. Pyrolysis characteristics of T-CP and P-TC at torrefied temperatures of 230 and 250 °C were studied using thermogravimetric analysis. It was found that at the similar torrefied temperature, P-TC had a higher bulk density, energy density, and pellet durability than that of T-CP and P-RC while T-CP had a higher HHV and moisture absorption than P-TC and P-RC. The bulk density of P-TC was 1.13–1.19 and 1.33–1.52 times higher than that of P-RC and T-CP, respectively. The HHV of T-CP was 1.07 and 1.29 times higher than P-TC and P-RC, respectively. The energy density of P-TC was 1.24–1.56 and 1.20–1.41 times higher than that of P-RC and T-CP. In terms of Pellet Fuel Institute (PFI) standard, the durability index of P-RC, P-TC, and T-CP at torrefied temperatures of 230 and 250 °C was acceptable. However, dramatically low and unacceptable durability index was found in case of T-CP at torrefied temperature of 280 °C. The moisture absorption of P-TC was lower than that of P-RC and T-CP. Finally, T-CP had a lower pyrolysis temperature and had a much lower solid yield than that of P-TC. Variation of pyrolysis characteristics indicated the difference in chemical composition between T-CP and P-TC.

Nonlinear viscous cosmological models in f(R,T) gravity

This article presents nonlinear viscous cosmological model of the universe that arises in the modified gravity theory in which the Lagrangian of the gravitational action contains a general function [Formula: see text], where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the energy–momentum tensor, respectively, in the flat Friedmann-Robertson-Walker background metric with isotropic fluid. We obtain cosmological solutions in [Formula: see text] theory of gravity, specially for the choice [Formula: see text] with nonlinear viscosity described by nonlinear Israel Stewart theory. The physical and geometrical properties of the models in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are coupling parameters, with nonlinear Israel Stewart theory are studied in detail. The analysis of the variation of bulk viscous pressure, energy density, scale factor, Hubble parameter and deceleration parameter with cosmic evolution is done in the nonlinear Israel Stewart theory with [Formula: see text] gravity. The stability analysis of the equilibrium points of the dynamical system associated with the exponential evolution of the universe in [Formula: see text] gravity theory with nonlinear dissipative effects is also studied.

Energy Characteristics of Composite BioFuel Based on Sunflower Husk

The paper considers the prospect of using renewable energy sources in the country’s fuel balance. An important source of energy is biomass, which is characterized by renewability, accessibility, versatility, minimal impact on the environment, transportation, accumulation and storage. At the same time, biomass has a number of disadvantages: a heterogeneous structure with a broad fractional composition, with low bulk density and energy density, and high initial humidity, and often ash content. To improve the thermal characteristics and to increase the energy efficiency of using biomass, it is subjected to physical, biochemical or thermochemical conversion. An effective way to improve the thermal characteristics of the original biomass is to compress it in a mixture with other combustible materials, for example, organic waste from agriculture, oil refining, coal, paper industry, which allows, in particular, to solve environmental problems as well. An estimation of the possibility of using organic waste from livestock and poultry farming in a composition with waste biomass of vegetable origin is conducted. The results of calorimetric studies of the calorific value of samples of such composite fuel, based on husk of sunflower seeds are presented. Based on experimental research and calculations, empirical formulas were proposed to calculate the combustion heat of composite fuel, containing a mixture of sunflower husk, sludge, irrigation, chicken droppings and manure. The dependence of the heat of combustion of composite fuel, produced from the waste of the biomass from agricultural production on humidity has been researched. Since briquetted fuel from such wastes has a significant hygroscopicity, it is recommended to provide appropriate conditions for its storage. It is concluded that during the long-term storage of poultry and livestock waste there may be biochemical processes that change the heat of combustion, indicating the need to take into account the terms and conditions of storage of the source components. It is concluded that composite fuel from biomass waste from agricultural production can be a significant component of the country’s fuel balance, saving traditional fossil fuel. In addition, the disposal of these wastes contributes to the reduction of environmental pollution.