Identification of unifying heat transfer mechanisms along the entire boiling curve

Autor: Hein Auracher, Torsten Lüttich, Wolfgang Marquardt, Martin Buchholz
Rok vydání: 2006
Předmět:
Zdroj: International Journal of Thermal Sciences. 45:284-298
ISSN: 1290-0729
DOI: 10.1016/j.ijthermalsci.2004.04.017
Popis: The interfacial geometry and the associated heat transfer mechanisms close to and at the boiling surface are identified rigorously along the entire boiling curve from wall temperature and two-phase flow sensor probe data taken during boiling of isopropanol. It is conjectured, that the liquid–vapor interface of the wetting structure provides the key mechanism for heat removal due to evaporation along the entire boiling curve. Local fluctuations of surface temperature superheat and heat flux are inferred by the solution of a two-dimensional inverse heat conduction problem employing wall temperature data. Peak heat fluxes of several MW⋅m −2 are estimated. In a next step, the interfacial geometry close to the surface is identified. It is shown that the size of the dry spots and the nucleation site density are well connected to the vapor fraction and the interfacial area density as well as to the contact angle of the wetting fluid. Further, we show that a suitably designed single four-sensor optical probe could provide the necessary data required to exactly identify the wetting structure using the wetting structure geometry model proposed here. We further find that interfacial area density accounts for the contact angle of the fluid and correlates well with the boiling heat flux. In conclusion, the results show that essential mechanisms of heat removal along the entire boiling curve can be attributed to interfacial presence and evolution. A single measure, namely the interfacial area density, is suspected to provide the essential mechanism of the heat removal in the boiling process. Finally, the results are discussed with respect to the candidate models for the interfacial geometry and heat transfer mechanisms proposed in the literature. Only, specifically designed and refined boiling experiments as well as identification methods along the line presented in this paper are needed to further verify this postulate.
Databáze: OpenAIRE
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