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ISSN Online: 2377-424X

ISBN Print: 0-89116-909-1

International Heat Transfer Conference 9
August, 19-24, 1990 , Jerusalem, Israel

TURBULENT TRANSPORT ACROSS STABLE THERMAL STRATIFIED LAYER IN A CIRCULAR PIPE

Get access (open in a dialog) DOI: 10.1615/IHTC9.2170
pages 341-346

要約

The turbulent transport mechanism in mixing interfacial layer of a stable thermal stratified flow has been experimentally investigated, in order to estimate the thermal stress of horizontal pipe wall caused by an emergency cooling down of a nuclear reactor system. Experiments were performed for pipe Reynolds number 7350 and overall Richardson numbers ranging up to 1.35. Two component velocities and the temperature were simultaneously measured by two set of fibre LDVs and a resistance thermometer probe.
The temperature gradient in the shear layer becomes steeper with increase in Richardson number. At a higher Richardson number, counter gradient diffusion type turbulent heat flux comes to appear in the downstream region, where the mixing layer thickness defined as the 25% value of the temperature difference become constant. This phenomenon can be explained by the reduction of turbulent mixing due to the buoyancy effect. However, this counter gradient diffusion of heat flux is not observed near the side wall. The results of conditional sampling quadrant analyses for turbulent fluctuations confirm a counter gradient diffusion process caused by motions of the quadrants (u'<0,v'>0) and (u'>0,v'<0) with increase in Richardson number.