Search results for "Heat Transfer"
showing 10 items of 442 documents
Structure and dynamics of CaO films: A computational study of an effect of external static electric field
2017
Oxide films play a significant role in a wide range of industrial fields, mostly due to the thickness-dependent variation of their properties. Recently, it has been proposed based on the experimental study that carrier transport in CaO films proceeds via strong phonon excitations with a variable signal depending on the film thickness. In this paper, we report a detailed investigation in the frame of the density functional theory of structural and electronic properties of freestanding and Mo(100)-supported CaO films, as well as phonons therein, as functions of the film thickness and intensity of the external static electric field. Our calculations demonstrate that phonon frequencies negligib…
Physical modelling of Czochralski crystal growth in horizontal magnetic field
2017
Abstract This study addresses experimentally the heat transfer, the temperature azimuthal non-uniformity and the onset of oscillations in a low temperature physical model of a medium-sized Czochralski crystal growth process with a strong horizontal magnetic field (HMF). It is observed that under certain conditions the integral heat flux may decrease with increasing magnetic field strength at the same time as the flow velocity increases. The azimuthal non-uniformity of the temperature field in the melt near the crystal model rim is only little influenced by its rotation rate outside of a narrow range where the centrifugal force balances the buoyant one. The flow oscillation onset has been ob…
Thermomechanical effects in the flow of a fluid in porous media
2002
This paper deals with analysis, by methods of extended thermodynamics, of the thermomechanical effects which arise in the flow of a weakly viscous fluid in a porous medium. Under the hypothesis that the fluid fills all the interstices among the powder and that the size of the powder grains and of the interstices is much lower than a suitable characteristic length, linearized field equations are written, which include, in a natural way, terms which take into account the Dufour, Soret, and virtual mass effects. As a limiting case when the evolution time of the heat flux goes to infinite and no entropy flux is carried, the flow of liquid helium II in a porous medium is obtained.
Transport coefficients of n-butane into and through the surface of silicalite-1 from non-equilibrium molecular dynamics study
2009
We have studied coupled heat and mass transfer of n-butane through a membrane of silicalite-1. A description of the surface was given using non-equilibrium thermodynamics, and transport coefficients were determined. Three independent coefficients were found for the whole surface: the resistance to heat transfer, the coupling coefficient and the resistance to mass transfer. These coefficients were defined in stationary state. All resistances are significant, and show that the surface acts as a barrier to transport. A new scheme was devised to find the enthalpy of adsorption, from two particular coupling coefficients, namely the measurable heats of transfer. The method yields the enthalpy of …
Numerical study of the ZnO growth by MOCVD
2004
Abstract In order to analyze the growth of zinc oxide by metalorganic chemical vapor deposition, a numerical model has been developed to simulate the gas flow in a horizontal reactor. A two-inlet system, one for the Zn precursor and the other for the oxygen one, has been studied in the framework of this numerical simulation. This model takes into account the momentum conservation equation coupled with the heat transfer and mass transport of chemical species. Different Zn precursors, DiethylZinc (DEZn), DimethylZinc (DMZn) and DimethylZinc-TriethylAmine (DMZn-TEA) and oxygen precursors, ( tert -butanol, iso -propanol and acetone) as well as carrier gases (H 2 and N 2 ) have been considered. …
Transfer coefficients for the liquid–vapor interface of a two-component mixture
2011
Abstract We present the excess entropy production for heat and mass transport across an interface of a non-ideal two-component mixture, using as interface variables the excess densities proposed by Gibbs. With the help of these variables we define the interface as an autonomous system in local equilibrium and study its transport properties. The entropy production determines the conjugate fluxes and forces, and equivalent forms are given. The forms contain finite differences of intensive variables into and across the surface as driving forces. These expressions for the fluxes serve as boundary conditions for integration across heterogeneous systems that are far from global equilibrium. The r…
Influence of Micromixing on Microorganisms and Products
2001
The influence of mixing intensity as well as physical and chemical parameters on the cells of different microorganisms and the biosynthesis process is examined in this paper. Some reactions of cells effecting mixing intensity are described, such as retarded biomass growth, changes in aggregation and mutual arrangement of cells, morphological changes of cells and decreasing of biological activity, caused by an increased intensity of turbulence (turbohypobiosis). Several methods for investigating the local energy in reactors are compared. It is concluded that conventional methods of hydrodynamic analysis do not always allow valid results for the optimization of the mixing regime to be obtaine…
Simulation of photovoltaic installation connected to the grid with storage system
2017
Abstract In the present paper, a new approach for the management of energy resources in a research laboratory is proposed and evaluated. A simulation study for the photovoltaic (PV) installation was conducted under the Tunisian-Italian cooperation project DE.DU.ENER.T, using renewable energy and economic criteria. The aim of the study is to improve the energy efficiency in order to minimize the electricity cost consumed in the laboratory. A Hybrid Renewable Energy System consisting of a photovoltaic field of 12KWc was installed to reduce the exorbitant bills, due to intensive energy equipment such as drying ovens and workstations, using sustainable, green and clean sources. In addition, a s…
Preliminary design of EU DEMO helium-cooled breeding blanket primary heat transfer system
2018
Abstract The European DEMO conceptual design foresees four Breeding Blanket (BB) concepts that rely on different cooling and breeding technologies. As DEMO has been conceived to deliver net electricity to the grid, the choice of the blanket coolant plays a pivotal role in the reactor design having a strong influence on plant operation, safety and maintenance. Moreover, the machine pulsed operation makes the BB Primary Heat Transfer System (PHTS) the main hub of the DEMO Balance of Plant (BoP). Within this framework, a study has been carried out to design the Ex-Vessel PHTS of the Helium-Cooled Pebble Bed (HCPB) BB concept. The paper describes criteria and rationale followed with the aim to …
Improved locally adaptive least-squares detection of differences in images
2007
We introduce a method for change detection under nonuniform changes of intensity using an improved least-squares method. A locally adaptive normalizing window is correlated with the two images, and a morphological postprocessing is then applied to isolate objects that have been added or removed from the scene. We use a modification of the least-squares solution to get rid of clutter caused by intensity changes that do not satisfy the model assumed for the least-squares solution.