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Boiling 2000 Phenomena and Emerging Applications Volume 2

ISSN:
1-56700-148-3 (Print)

INFLUENCE OF MICROSCALE CONCENTRATION GRADIENTS IN NUCLEATE BOILING HEAT TRANSFER OF BINARY MIXTURES

Jurgen Kern
Darmstadt University of Technology, Chair of Technical Thermodynamics, Petersenstr. 30, 64287 Darmstadt, Germany

Peter Stephan
Darmstadt University of Technology, Institute for Technical Thermodynamics, Petersenstr. 30, 64287 Darmstadt, Germany

Abstract

Nucleate boiling heat transfer coefficients of binary mixtures can be calculated using a micro region model. The model is described and assessed by comparing calculated heat transfer coefficients with experimental values. The model includes the governing physical phenomena, such as the meniscus curvature, the adhesion pressure, and the interfacial thermal resistance as well as the local variation of composition and liquid-vapor equilibrium and the Marangoni effect. Due to the preferential evaporation of the more volatile component of the mixture, strong concentration gradients occur close to the heated wall. The influence of these microscale concentration gradients is investigated. By means of various calculations the physical phenomena are quantified and their relevance in the nucleate boiling process is evaluated.