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Title: Convection induced by radiative cooling of a layer of participating medium

Simulations and experiments have been conducted to study the effect of radiative cooling on natural convection in a horizontal layer of a participating medium enclosed between isothermal opaque wall and radiatively transparent wall and exposed to a cold background. The study is of relevance to a nocturnal boundary layer under clear and calm conditions. The focus of the study is to capture the onset of convection caused by radiative cooling. The experiments have been designed to mimic the atmospheric radiative boundary conditions, and hence decoupling convection and radiation boundary conditions. Planck number Pl and optical thickness of the layer τ{sub H} are the two important parameters that govern the interaction between radiation and convection. The radiation-convection coupling is a strong function of length scale. Convection sets up within first few seconds for all the experiments. Strong plume like convection is observed for the experimental conditions used in the present study. Both simulations and experiments confirm that radiative cooling increases substantially with decrease in emissivity of the bottom wall. Radiative cooling is strongly influenced by the nongray nature of the participating medium, especially when strong emission from the medium escapes to space, in the window region of the atmosphere. Accurate representationmore » of radiative properties is critical. Linear stability analysis of onset of convection indicates that radiation stabilizes convection as Pl decreases. The observations are similar to the case of Rayleigh Bénard convection in a radiating gas. However, for both experimental and numerical conditions, the observed Rayleigh numbers are much greater than the critical Rayleigh number. To conclude, the role of radiation is to drive and sustain convection in the unstable layer.« less
Authors:
 [1] ;  [2]
  1. Laboratoire EM2C, CNRS UPR 288 92295, Chatenay-Malabry, France and Ecole Centrale Paris, Grande Voie des Vignes 92295, Chatenay-Malabry (France)
  2. HTTP Laboratory, Department of Mechanical Engineering IIT Madras, Chennai (India)
Publication Date:
OSTI Identifier:
22256999
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Fluids (1994); Journal Volume: 26; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BOUNDARY CONDITIONS; BOUNDARY LAYERS; COUPLING; DECOUPLING; DESIGN; EMISSIVITY; NATURAL CONVECTION; PLUMES; RADIATIVE COOLING; RAYLEIGH NUMBER; SIMULATION; THICKNESS