The Experts below are selected from a list of 1665 Experts worldwide ranked by ideXlab platform
Stan Chiriţă - One of the best experts on this subject based on the ideXlab platform.
-
on the thermomechanical consistency of the time differential dual phase lag models of Heat conduction
International Journal of Heat and Mass Transfer, 2017Co-Authors: Stan Chiriţă, Michele Ciarletta, Vincenzo TibulloAbstract:Abstract This paper deals with the time differential dual-phase-lag Heat transfer models aiming, at first, to identify the eventually restrictions that make them thermodynamically consistent. At a first glance it can be observed that the capability of a time differential dual-phase-lag model of Heat conduction to describe real phenomena depends on the properties of the differential operators involved in the related constitutive equation. In fact, the constitutive equation is viewed as an ordinary differential equation in terms of the Heat Flux components (or in terms of the temperature gradient) and it results that, for approximation orders greater than or equal to five, the corresponding characteristic equation has at least a complex root having a positive real part. That leads to a Heat Flux component (or temperature gradient) that grows to infinity when the time tends to infinity and so there occur some instabilities. Instead, when the approximation orders are lower than or equal to four, this is not the case and there is the need to study the compatibility with the Second Law of Thermodynamics. To this aim the related constitutive equation is reformulated within the system of the fading memory theory, and thus the Heat Flux Vector is written in terms of the history of the temperature gradient and on this basis the compatibility of the model with the thermodynamical principles is analyzed.
-
On the time differential dual-phase-lag thermoelastic model
Meccanica, 2017Co-Authors: Stan ChiriţăAbstract:This paper studies the time differential dual-phase-lag model of a thermoelastic material, where the elastic deformation is accompanied by thermal effects governed by a time differential equation for the Heat Flux with dual phase lags. This coupling gives rise to a complex differential system requiring a special treatment. Uniqueness and continuous dependence results are established for the solutions of the mixed initial boundary value problems associated with the model of the linear theory of thermoelasticity with dual-phase-lag for an anisotropic and inhomogeneous material. Two methods are developed in this paper, both being based on an identity of Lagrange type and of a conservation law applied to appropriate initial boundary value problems associated with the model in concern. The uniqueness results are established under mild constitutive hypotheses (right like those in the classical linear thermoelasticity), without any restrictions upon the delay times (excepting the class of thermoelastic materials for which the delay time of phase lag of the conductive temperature gradient is vanishing and the delay time in the phase lag of Heat Flux Vector is strictly positive, when an ill-posed model should be expected). The continuous dependence results are established by using a conservation law and a Gronwall inequality, under certain constitutive restrictions upon the thermoelastic coefficients and the delay times.
-
the time differential three phase lag Heat conduction model thermodynamic compatibility and continuous dependence
International Journal of Heat and Mass Transfer, 2016Co-Authors: Stan Chiriţă, Ciro Dapice, Vittorio ZampoliAbstract:Abstract This paper deals with the time differential three-phase-lag Heat transfer model aiming, at first, to identify the restrictions that make it thermodynamically consistent. The model is thus reformulated by means of the fading memory theory, in which the Heat Flux Vector depends on the history of the thermal displacement gradient: the thermodynamic principles are then applied to obtain suitable restrictions involving the delay times. Consistently with the thermodynamic restrictions just obtained, a first result about the continuous dependence of the solutions with respect to the given initial data and to the supply term is established for the related initial boundary value problems. Subsequently, to provide a more comprehensive review of the problem, a further continuous dependence estimate is proved, this time conveniently relaxing the hypotheses about the above-said thermodynamic restrictions. This last estimate allows the solutions to grow exponentially in time and so to have asymptotic instability.
Joachim Bluhm - One of the best experts on this subject based on the ideXlab platform.
-
modeling fluid saturated porous media under frost attack
Gamm-mitteilungen, 2010Co-Authors: Tim Ricken, Joachim BluhmAbstract:Freezing and thawing are important processes in civil engineering. On the one hand frost damage of porous building materials like road pavements and concrete in regions with periodical freezing is well known. On the other hand, artificial freezing techniques are widely used, e.g. for tunneling in non-cohesive soils and other underground constructions as well as for the protection of excavation and compartmentalization of contaminated tracts. Ice formation in porous media results from a coupled Heat and mass transport and is accompanied by the ice expansion. The volume increase in space and time is assigned to the moving freezing front inside the porous solid. In this paper, a macroscopic ternary model is presented within the framework of the Theory of Porous Media (TPM) in view of the description of phase transition. For the mass exchange between ice and water an evolution equation based on the local balance of the Heat Flux Vector is used. Examples illustrate the application of the model for saturated porous solids under thermal loading (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
-
modeling fluid saturated porous media under frost attack
Gamm-mitteilungen, 2010Co-Authors: Tim Ricken, Joachim BluhmAbstract:Freezing and thawing are important processes in civil engineering. On the one hand frost damage of porous building materials like road pavements and concrete in regions with periodical freezing is well known. On the other hand, artificial freezing techniques are widely used, e.g. for tunneling in non-cohesive soils and other underground constructions as well as for the protection of excavation and compartmentalization of contaminated tracts. Ice formation in porous media results from a coupled Heat and mass transport and is accompanied by the ice expansion. The volume increase in space and time is assigned to the moving freezing front inside the porous solid. In this paper, a macroscopic ternary model is presented within the framework of the Theory of Porous Media (TPM) in view of the description of phase transition. For the mass exchange between ice and water an evolution equation based on the local balance of the Heat Flux Vector is used. Examples illustrate the application of the model for saturated porous solids under thermal loading (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Tim Ricken - One of the best experts on this subject based on the ideXlab platform.
-
modeling fluid saturated porous media under frost attack
Gamm-mitteilungen, 2010Co-Authors: Tim Ricken, Joachim BluhmAbstract:Freezing and thawing are important processes in civil engineering. On the one hand frost damage of porous building materials like road pavements and concrete in regions with periodical freezing is well known. On the other hand, artificial freezing techniques are widely used, e.g. for tunneling in non-cohesive soils and other underground constructions as well as for the protection of excavation and compartmentalization of contaminated tracts. Ice formation in porous media results from a coupled Heat and mass transport and is accompanied by the ice expansion. The volume increase in space and time is assigned to the moving freezing front inside the porous solid. In this paper, a macroscopic ternary model is presented within the framework of the Theory of Porous Media (TPM) in view of the description of phase transition. For the mass exchange between ice and water an evolution equation based on the local balance of the Heat Flux Vector is used. Examples illustrate the application of the model for saturated porous solids under thermal loading (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
-
modeling fluid saturated porous media under frost attack
Gamm-mitteilungen, 2010Co-Authors: Tim Ricken, Joachim BluhmAbstract:Freezing and thawing are important processes in civil engineering. On the one hand frost damage of porous building materials like road pavements and concrete in regions with periodical freezing is well known. On the other hand, artificial freezing techniques are widely used, e.g. for tunneling in non-cohesive soils and other underground constructions as well as for the protection of excavation and compartmentalization of contaminated tracts. Ice formation in porous media results from a coupled Heat and mass transport and is accompanied by the ice expansion. The volume increase in space and time is assigned to the moving freezing front inside the porous solid. In this paper, a macroscopic ternary model is presented within the framework of the Theory of Porous Media (TPM) in view of the description of phase transition. For the mass exchange between ice and water an evolution equation based on the local balance of the Heat Flux Vector is used. Examples illustrate the application of the model for saturated porous solids under thermal loading (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Arne V. Johansson - One of the best experts on this subject based on the ideXlab platform.
-
Explicit Algebraic Reynolds-stress Modelling of a Convective Atmospheric Boundary Layer Including Counter-Gradient Fluxes
Boundary-Layer Meteorology, 2020Co-Authors: Velibor Želi, Geert Brethouwer, Stefan Wallin, Arne V. JohanssonAbstract:In a recent study (Želi et al. in Bound Layer Meteorol 176:229–249, 2020), we have shown that the explicit algebraic Reynolds-stress (EARS) model, implemented in a single-column context, is able to capture the main features of a stable atmospheric boundary layer (ABL) for a range of stratification levels. We here extend the previous study and show that the same formulation and calibration of the EARS model also can be applied to a dry convective ABL. Five different simulations with moderate convective intensities are studied by prescribing surface Heat Flux and geostrophic forcing. The results of the EARS model are compared to large-eddy simulations of Salesky and Anderson (J Fluid Mech 856:135–168, 2018). It is shown that the EARS model performs well and is able to capture the counter-gradient Heat Flux in the upper part of the ABL due to the presence of the non-gradient term in the relation for vertical turbulent Heat Flux. The model predicts the full Reynolds-stress tensor and Heat-Flux Vector and allows us to compare other important aspects of a convective ABL such as the profiles of vertical momentum variance. Together with the previous studies, we show that the EARS model is able to predict the essential features of the ABL. It also shows that the EARS model with the same model formulation and coefficients is applicable over a wide range of stable and moderately unstable stratifications.
Joan Ponsnin - One of the best experts on this subject based on the ideXlab platform.
-
a miniaturized 3d Heat Flux sensor to characterize Heat transfer in regolith of planets and small bodies
Sensors, 2020Co-Authors: Manuel Dominguezpumar, J A Rodriguezmanfredi, V Jimenez, Sandra Bermejo, Joan PonsninAbstract:The objective of this work is to present the first analytical and experimental results obtained with a 3D Heat Flux sensor for planetary regolith. The proposed structure, a sphere divided in four sectors, is sensible to Heat flow magnitude and angle. Each sector includes a platinum resistor that is used both to sense its temperature and provide Heating power. By operating the sectors at constant temperature, the sensor gives a response that is proportional to the Heat Flux Vector in the regolith. The response of the sensor is therefore independent of the thermal conductivity of the regolith. A complete analytical solution of the response of the sensor is presented. The sensor may be used to provide information on the instantaneous local thermal environment surrounding a lander in planetary exploration or in small bodies like asteroids. To the best knowledge of the authors, this is the first sensor capable of measuring local 3D Heat Flux.
