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Heat Pipe Science and Technology, An International Journal

ISSN Print: 2151-7975
ISSN Online: 2151-7991

Archives: Volume 1, 2010 to Volume 8, 2017

Heat Pipe Science and Technology, An International Journal

DOI: 10.1615/HeatPipeScieTech.v5.i1-4.410
pages 369-376

EVALUATION OF THE VAPOR THERMODYNAMIC STATE IN PHP

P. Gully
CEA-INAC/SBT, UMR_E 9004 CEA-UJF Grenoble, 38054 Cedex 9, France
F. Bonnet
CEA-INAC/SBT, UMR_E 9004 CEA-UJF Grenoble, 38054 Cedex 9, France
Vadim S. Nikolayev
Service de Physique de l'Etat Condensé, CNRS UMR 3680, IRAMIS/DSM/CEA Saclay, 91191 Gif-sur-Yvette, France
N. Luchier
CEA-INAC/SBT, UMR_E 9004 CEA-UJF Grenoble, 38054 Cedex 9, France
T. Q. Tran
CEA-INAC/SBT, UMR_E 9004 CEA-UJF Grenoble, 38054 Cedex 9, France

ABSTRACT

Pulsating Heat Pipe (PHP) is a recently invented kind of thermal link of high thermal performance. The heat is transferred due to self-sustained oscillations of vapor bubbles and liquid plugs in a unique capillary tube which links the hot and cold sources in several turns or branches. Increasingly strong efforts are devoted to PHP simulation models which need to be experimentally assessed. Recent models show the importance of the thermodynamic state of the vapor bulk. Indeed it may deviate from the saturation conditions due to vapor transient compression/expansion. This study aims at measuring and calculating the vapor state in a horizontal single branch PHP which allows generating oscillations of a liquid meniscus in a capillary tube with one open end, at which the pressure is imposed. The experimental setup uses oxygen at cryogenic temperatures which reduces as much as possible the radiation losses of both sensors (microscopic thermocouple) used for the direct vapor temperature measurement and of the whole PHP. We present here the simultaneous experimental measurements of the vapor pressure and temperature. The data are compared to the theoretical modeling obtained within the film evaporation/condensation model of PHP [Das et al., 2010]. The model is extended to account for the thermal gradient along and across the tube walls formed because of the poor heat conductivity of its material. The vapor is found superheated, which demonstrates the relevance of the model. The vapor temperature oscillates around the evaporator temperature. The heat transfer between the vapor and the dry evaporator wall explains this result. The corresponding heat transfer coefficient is calculated using DNS. The comparison shows an agreement between the experiment and the model.


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