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International Heat Transfer Conference 15

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

Modeling of Boiling Heat Transfer from Microstructured Surfaces

Alexander Ustinov
Moscow Power Engineering Institute

Jovan Mitrovic
Retired from University Paderborn., Institut fur Technische Thermodynamik und Thermische Verfahrenstechnik, Universitat Stuttgart, Pfaffenwaldring 9 7000 Stuttgart 80, F.R. Germany

DOI: 10.1615/IHTC15.pbl.009551
pages 6379-6393


KEY WORDS: Boiling and evaporation, Heat transfer enhancement, Thermal management, Microstructure, Micropin, Cooling of Electronics

Abstract

Boiling on microstructured surfaces with micropins was intensively investigated by authors in several recent experimental works [1-5]. It was shown that the length of the three-phase-line (TPL) is directly related to the enhancement abilities of the surface, being a universal parameter for characterization of performance. In this article, we propose a universal classification system of enhanced surfaces for boiling, based upon consideration of their ability to extend the TPL and other mechanisms of the boiling heat transfer augmentation. Due to flexibility of classification system, future enhanced surfaces can be added later easily. Based on the TPL consideration, a calculation statistical model is proposed in order to obtain a heat transfer performance during boiling upon virtually any surface. The model involves the less possible amount of coefficients and experimental data. As input, it uses the surface micro geometry in form of a distribution function of potential nucleation sites on sizes and liquid properties at a given pressure. As result, the superheat during boiling in dependency on applied heat flux is obtained. This information can be expressed in terms of heat transfer coefficient. The proposed model is applied in the article to experimental data of authors, showing very good agreement and explaining the physical grounds of several new boiling effects, discovered earlier, namely two different regions in boiling curves for surfaces with inclined micro pins. The model also delivers additional information on boiling inception and crisis, although no additional suggestions were made to take those processes into account: it shows clearly that very small or very large cavities make almost no contribution into the heat transfer during boiling and that critical heat flux depends on surface geometry greatly.

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