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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Enhancement of Heat Transfer at Transition and Film Boiling of Nitrogen on Spheres with Dimples and Low Conductivity Coating

Get access (open in a dialog) DOI: 10.1615/IHTC15.pbl.009224
pages 6253-6259

Resumo

Among the efficient and recently widely applied methods to enhance the heat transfer in the channels of heat exchange equipment is technique of applying spherical dimples and low conductivity coating. Influence of dimples and low conductivity coating put on copper spheres at film and transition boiling of liquid nitrogen under the conditions of free convection and natural circulation was investigated. Experiments on immersing of copper spheres with diameter 20 mm warmed up above Leidenfrost temperature into the liquid nitrogen which is at saturation temperature under atmospheric pressure were carried out. The distribution density of dimples (d=3 mm and h/d=0,17) on a surface of spheres is up to 45 %. Testing out there are has been measured the dependences of heat transfer coefficient on temperature differences at boiling of nitrogen on spheres under free convection and natural circulation at atmospheric pressure. It was discovered that the most increase in intensity of heat removal is observed while using dimples with low conductivity coating under the conditions of natural circulation. The reflooding time of spheres with dimples and low conductivity coating is up to 2.5 times less than for sphere without dimples and coating.