Search results for "Convection"

Definition and predictability of an OLR based West African monsoon onset

2008

The monsoon onset is documented in terms of latitudinal shift of deep convection areas within the ITCZ using an interpolated version of the National Oceanic and Atmospheric Administration (NOAA) Outgoing Longwave Radiation (OLR) at a 5-day time-step over West Africa for the period 1979–2004. Signals in moist convection derived from OLR values lower than 180 W/m2 allow better determination of onset dates (ODs) than the use of other thresholds or of the raw values of OLR. Such ODs are defined without any time filtering or spatial averaging along the meridional plane. They are also significantly correlated with ODs based on other datasets such as the CMAP and Global Precipitation Climatology P…

2014

Abstract. This study uses the EMAC atmospheric chemistry-climate model to simulate cloud properties and estimate cloud radiative effects induced by aerosols. We have tested two prognostic cloud droplet nucleation parameterizations, i.e., the standard STN (osmotic coefficient model) and hybrid (HYB, replacing the osmotic coefficient by the κ hygroscopicity parameter) schemes to calculate aerosol hygroscopicity and critical supersaturation, and consider aerosol–cloud feedbacks with a focus on warm clouds. Both prognostic schemes (STN and HYB) account for aerosol number, size and composition effects on droplet nucleation, and are tested in combination with two different cloud cover parameteriz…

The dynamics of tropospheric aerosols

1966

After a brief review of the present knowledge of the Stratospheric sulfate layer, several possible mechanisms of formation are discussed in detail. A direct transport of low tropospheric particles into the stratosphere by convective clouds penetrating the tropopause is not very likely because these penetrations are not high enough and because of the chemical composition of the stratospheric particles. DOI: 10.1111/j.2153-3490.1966.tb00287.x

Convective Roll Instabilities of Vertical Throughflow with Viscous Dissipation in a Horizontal Porous Layer

2009

Published version of an article from the journal: Transport in Porous Media. The original publication is available at Spingerlink. http://dx.doi.org/10.1007/s11242-009-9417-y The vertical throughflow with viscous dissipation in a horizontal porous layer is studied. The horizontal plane boundaries are assumed to be isothermal with unequal temperatures and bottom heating. A basic stationary solution of the governing equations with a uniform vertical velocity field (throughflow) is determined. The temperature field in the basic solution depends only on the vertical coordinate. Departures from the linear heat conduction profile are displayed by the temperature distribution due to the forced con…

Linear instability of mixed convection of cold water in a porous layer induced by viscous dissipation

2009

Accepted version of an article published in the journal: International Journal of Thermal Sciences, Elsevier Published version available on Science Direct: http://dx.doi.org/10.1016/j.ijthermalsci.2008.06.012 An analysis of linear stability of the stationary laminar Darcy flow in a horizontal porous layer is performed. The porous layer is saturated with cold water. The upper plane boundary is assumed to be subject to heat transfer with finite conductance to an environment at the temperature of maximum density of cold water. The lower plane boundary is adiabatic. Convective instabilities are caused by flow viscous dissipation, inducing a basic temperature distribution that decreases in the u…

Suitability of the VOF Approach to Model an Electrogenerated Bubble with Marangoni Micro-Convection Flow

2022

When a hydrogen or oxygen bubble is created on the surface of an electrode, a micro-convective vortex flow due to the Marangoni effect is generated at the bottom of the bubble in contact with the electrode. In order to study such a phenomenon numerically, it is necessary to be able to simulate the surface tension variations along with a liquid-gas interface, to integrate the mass transfer across the interface from the dissolved species present in the electrolyte to the gas phase, and to take into account the moving contact line. Eulerian methods seem to have the potential to solve this modeling. However, the use of the continuous surface force (CSF) model in the volume of fluid (VOF) framew…

Etude numérique de la convection forcée turbulente dans un dissipateur thermique composé de plusieurs rangées d'ailettes de différentes formes

2016

In this thesis, we present an numerical study of turbulent forced convection in a heat sink provided with a transverse baffle in the bypass. The first model is composed of plates fins and the second consists of adding pin fins between the plates fins. The governing equations, based on the k- SSt turbulence model, are disscredized and solved by the finite volume method and the SIMPLE algorithm. Dynamic results are presented in terms of velocity fields, profiles of the axial velocities in selected sections and pressure drop. The thermal study is presented in terms of temperature fields and the distribution of Nusselt number. A ratio between the thermal and dynamic performances is presented to…

Transport coefficients in desalting processes by electrodialysis

2011

Abstract In this work a thermodynamic analysis on the transport equations in the processes of electrodiffusion (EF) and electrodialysis (ED) has been developed. The transport equations are classified in two sets according to the information they contain: i ) fundamental and ii ) complementary. We determine that there are four fundamental transport coefficients needed to characterize these membrane systems. We also conclude that this number is not reduced to three when the Onsager reciprocal relation (ORR) is assumed. I have also obtained a new expression for the concentration rate in EF and ED processes from the mass and volume balance. This relation provides a new way for evaluating the ap…

On the a posteriori error analysis for linear Fokker-Planck models in convection-dominated diffusion problems

2018

This work is aimed at the derivation of reliable and efficient a posteriori error estimates for convection-dominated diffusion problems motivated by a linear Fokker-Planck problem appearing in computational neuroscience. We obtain computable error bounds of the functional type for the static and time-dependent case and for different boundary conditions (mixed and pure Neumann boundary conditions). Finally, we present a set of various numerical examples including discussions on mesh adaptivity and space-time discretisation. The numerical results confirm the reliability and efficiency of the error estimates derived.

Study of thermomagnetic energy conversion driven by renewable energy

2017

Magnetic heating, refrigeration and energy conversion have been defined very important challenges for promising environmentally future choices. Recent studies are focused attention on new thermomagnetic systems, devices working through thermomagnetic effect, driven by renewable energies. The aim of this work is a case study presentation of new thermomagnetic energy prototype coupled with renewable technologies or industrial waste heat. The paper is divided into four sections: the first gives a general state of art about magneto-caloric energy conversion systems, the second describes all general thermodynamics and magnetic laws governing the process, the third and fourth sections study in mo…