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International Heat Transfer Conference 9

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

FREE CONVECTIVE HEAT TRANSFER TO A CRITICAL BINARY MIXTURE WITHOUT RETROGRADE CONDENSATION

Karl Stephan
Institut fur Technische Thermodynamik und Thermische Verfahrenstechnik, Universitat Stuttgart, Pfaffenwaldring 9, 70550 Stuttgart, Germany

H. Ettle
Institut fur Technische Thermodynamik und Thermische Verfahrenstechnik Universitat Stuttgart, 7000 Stuttgart 80, FRG

D. Jump
Institut fur Technische Thermodynamik und Thermische Verfahrenstechnik Universitat Stuttgart, 7000 Stuttgart 80, FRG

DOI: 10.1615/IHTC9.3120
pages 253-256

Abstract

Previous studies of free convective heat transfer to binary mixtures in their gas-liquid critical regions involved the effects of retrograde condensation. Enhancements of heat transfer were credited to turbulence in the boundary layer caused by the presence of heat sources and sinks due to this phenomena, as well as to thermal and transport property variations near the critical point. This study examines the enhancement of heat transfer to a mixture of ethane and propane without retrograde condensation. Experiments were carried out in a high pressure cell with a heated wire. The concentration of the mixture was chosen so that the critical point was very close to the point of maximum pressure along the two phase boundary, Fig. 2. Measurements were taken along isobars near the critical pressure. Large values of heat transfer coefficients obtained are attributed to the anomalous behavior of the mixtures thermal and transport properties in the neighborhood of the critical point. The literature indicates that the thermal expansion coefficient and the specific heat diverge near the critical point. No evidence of transport property divergences was found in the literature for the gas-liquid critical region, although for the liquid-liquid critical region the viscosity shows large values. These anomalies may provide an explanation as to why the heat transfer to the mixture in this work is enhanced. Measurements of heat transfer coefficients for temperature differences on the order of 3 Kelvin produced peak values in the range 3000-3500 W/(m2K), for pressures and temperatures close to their critical values, Fig. 4. These values are unusually large for free convection.

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