Search results for "THERMODYNAMICS"
showing 10 items of 2774 documents
Evaluation of building heating loads with dimensional analysis: Application of the Buckingham π theorem
2017
Abstract A detailed assessment of building energy performance requires a large amount of input data concerning building typology, environmental conditions, envelope thermophysical properties, geometry, control strategies, and several other parameters. Notwithstanding, the use of specialized software tools poses many challenges in regards to the retrieval of reliable and detailed information, setting a steep learning curve for engineers and energy managers. To speed up the preliminary assessment phase, it might be more convenient to resort to a simplified model that allows the evaluation of heating energy demand with a good level of accuracy and without excessive computational cost or user e…
SIMULATION OF THE HEAT TRANSPORT PROBLEMS WITH RADIATION IN PLATE
2001
In the literature [1 -5 ] simple and effective algorithms for mathematical modelling processes of distribution of heat in multilayered spaces are created. In the given work the way of improvement o f accuracy of algorithms is considered at approximation of integrals derivatives more the supreme orders are used.
Theorems of restricted dynamic shakedown
1993
Abstract Dynamic shakedown for a rate-independent material with internal variables is addressed in the hypothesis that the load values are restricted to those of a specified load history of finite or even infinite duration, thus ruling out the possibility—typical of classical shakedown theory—of indefinite load repetitions. Instead of the usual approach to dynamic shakedown, based on the bounded plastic work criterion, another approach is adopted here, based on the adaptation time criterion. Static, kinematic and mixed-form theorems are presented, which characterize the minimum adaptation time (MAT), a feature of the structure-load system, but which are also able to assess whether plastic w…
The shakedown load boundary of an elastic-perfectly plastic structure
1995
In the hypothesis of small displacements and combined time-variable/steady loads, the geometrical-mechanical properties of the shakedown load boundary are investigated. It is shown that, in the load space, the shakedown load boundary plays the role of yield surface, and that a certain plastic strain accumulation vector—characterizing some impending inadaptation collapse mechanism—obeys the normality rule, whereas a specific form of the maximum plastic work theorem constitutes an effective tool for the evaluation of the shakedown limit load corresponding to a specified inadaptation collapse mode. The equations governing the state of the structure at the shakedown limit are provided and the r…
Microwave-based gas sensor with phthalocyanine film at room temperature
2013
Abstract This work presents the development of a microwave gas sensor at room temperature. The design of the sensor includes a coplanar grounded wave guide where is deposited a molecular gas sensing material. In this study, the sensitive material is a thin layer of cobalt phthalocyanine (CoPc), sensitive to ammonia and toluene. Submitted to an electromagnetic incident wave in the microwave range, the sensor response is a reflected wave. In the presence of pollutant, the reflected wave shape is specific to the species concentrations. The results interpretation is led at each frequency by the evaluation of the reflected coefficient, which traduces the ratio between the reflected wave over the…
Phase Stability of Natural Ni0.75Mg0.22Ca0.03CO3 Gaspeite Mineral at High Pressure and Temperature
2020
[EN] Divalent metal carbonates play an important role in Earth's carbon cycle, but the effect of chemical substitution is still poorly known. In this work, we have studied the structural and vibrational properties of natural mineral gaspeite (Ni0.75Mg0.22Ca0.03CO3) under high pressure and temperature using in situ synchrotron X-ray diffraction and Raman spectroscopy in diamond-anvil cells. These experiments have been complemented by ab initio simulations. Synchrotron high-pressure XRD measurements at room temperature using He as the pressure transmitting medium have shown that the calcite-type structure is stable up to 23.3 GPa. A bulk modulus at zero pressure of B-0 = 105(2) GPa with B-0' …
Viscoelasticity: an electrical point of view
2014
Time dependent hereditary properties of complex materials are well described by power-laws with real order exponent. This experimental observation and analogous electrical experiments, yield a description of these properties by using fractional-order operators. In this paper, elasto-viscous and visco-elastic behaviors of fractional order hereditary materials are firstly described by using fractional mathematical operators, based on recent work of some of the authors. Then, electrical analogous models are introduced. Viscoelastic models have elastic and viscous components which can be obtained by combining springs and dashpots: these models can be equivalently viewed as electrical circuits, …
Chain Connectivity and Conformational Variability of Polymers: Clues to an Adequate Thermodynamic Description of Their Solutions, 1
2003
This is the first of two parts investigating the Flory-Huggins interaction parameter, χ, as a function of composition and chain length. Part 1 encompasses experimental and theorical work. The former comprise the synthesis of poly(dimethylsiloxane)s with different molar mass and the measurements of their second second osmotic virial coefficients, A 2 , in solvents of diverse quality as a function of M via light scattering and osmotic pressures. The theorical analysis is performed by subdividing the dilution process into two clearly separable steps. It yields the following expression for χ ο , the χ value in range of pair interaction : χ ο = α - ζ λ. The parameter α measures the effect of con…
Comparison of 2D versus 3D diffusion analysis at Nanowire Electrodes: Finite element analysis and experimental study
2021
In electroanalysis, finite element simulations of electrochemical processes occurring at electrodes are used to provide key insight into experimental design in relation to diffusion profiles and expected currents. The diffusion domain approach (DDA) offers a means of reducing a three dimensional design to two dimensions to ease computational demands. However, the DDA approach can be limited when basic assumptions, for example that all electrodes in an array are equivalent, are incorrect. Consequently, to get a more realistic view of molecular diffusion to nanoelectrodes, it is necessary to undertake simulations in 3D. In this work, two and three dimensional models of electrodes comprising o…
Kramers potential study of the Rouse-like dynamics of short alkane chains.
1999
In this work we present a Kramers potential study of the orientational dynamics and shear viscosity of short chain alkanes. In this approach the determination of the orientational relaxation time is reduced to the calculation of static moments of single chain conformations. We study a chemically realistic alkane model that asymptotically produces Gaussian chain conformations by means of a Monte Carlo simulation. Our results are applicable to single chain descriptions of polymer melt dynamics and to the intrinsic viscosity of molecules in a Theta solvent. When we map the unknown time unit of our relaxation time result for one particular chain length and temperature to the value obtained for …