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EXPERIMENTAL INVESTIGATION OF FLOW BOILING CHARACTERISTICS OF SILOXANES AND SILOXANE MIXTURES IN A HORIZONTAL TUBE

DOI: 10.1615/ICHMT.2014.IntSympConvHeatMassTransf.720
pages 965-978

Theresa Weith
University of Bayreuth Zentrum fur Energietechnik / Lehrstuhl fur Technische Thermodynamik und Transportprozesse 95447 Bayreuth, Germany

Florian Heberle
University of Bayreuth Zentrum fur Energietechnik / Lehrstuhl fur Technische Thermodynamik und Transportprozesse 95447 Bayreuth, Germany

Dieter Brüggemann
Lehrstuhl für Technische Thermodynamik und Transportprozesse (LTTT), Zentrum für Energietechnik (ZET), Universität Bayreuth, 95440 Bayreuth, Germany

Аннотация

The present work shows results of an experimental investigation of heat transfer coefficients during flow boiling of siloxanes and siloxane mixtures. The main part of the test rig consists in a horizontal, plain tube out of stainless steel (inner diameter: 10 mm, wall thickness: 1 mm, length: 5.04 m), which is electrically heated by the Joule effect. The fluids hexamethyldisiloxane (MM) and octamethyltrisiloxane (MDM) are investigated. Mixtures in steps of 20 weight-percent of these two components are considered. The effect of pressure (pr = 0.4, Ts = 198 °C/220 °C), heat flux density (q = 9.5 −15.5 kW/m2) and mass flux density (G = 100 − 300 kg/m2s) on heat transfer is analysed. Regarding MM, the heat transfer coefficient decreases as the vapour quality increases. The variation of mass flux density shows higher heat transfer coefficients when raising the mass flux. An increase in heat flux density as well as pressure leads to no explicit influence on heat transfer coefficients in the investigated range. The measured heat transfer coefficients of MDM are on average higher than those of MM due to differences in transport properties and flow regimes. For siloxane mixtures, the average heat transfer coefficients are below the ones of pure components. The correlation by Kandlikar for pure fluids as well as for fluid mixtures predicts the general trend of heat transfer coefficient with respect to vapour quality and mass flux density. However, the values are overestimated by the correlation.

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