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International Heat Transfer Conference 12

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

Influence of the immiscibility of refrigerant-oil mixtures on pool boiling heat transfer

Klaus Mohrlok
Institut für Thermodynamik und Wärmetechnik, Universität Stuttgart, Germany Pfaffenwaldring 6, D-70550 Stuttgart

Klaus Spindler
Institut fur Thermodynamik und Warmetechnik Universitat Stuttgart Pfaffenwaldring 6, D-70550 Stuttgart Germany

Erich Hahne
Institut fur Thermodynamik und Warmetechnik, Universitat Stuttgart, 70550 Stuttgart, Germany

Hans Muller-Steinhagen
Institute for Technical Thermodynamics, German Aerospace Research Centre (DLR), Stuttgart; Institute for Thermodynamics and Thermal Engineering, University of Stuttgart, Germany Pfaffenwaldring 38-40, D-70569 Stuttgart, Germany

DOI: 10.1615/IHTC12.2800
6 pages

Abstract

Pool boiling heat transfer of refrigerant mixtures with oil is influenced by the ranges of immiscibility of the mixture components with the oil, because each component of the refrigerant mixture has its own range of immiscibility with the oil. However, usually only the range of immiscibility of the refrigerant mixture with the oil is known. The ranges of immiscibility for the components of the refrigerant mixtures are also relevant, especially for the understanding of the heat transfer enhancement or deterioration of the refrigerant-oil mixtures in some cases.
The influence of a polyolester based lubricating oil on pool boiling heat transfer to different refrigerants is discussed in this paper. The single component refrigerant R134a and the refrigerant mixtures R410A, R507 and R404A have been investigated for oil mass fractions up to 10%.
For R134a the oil reduces the heat transfer. However, at 3% oil mass fraction and a reduced pressure of 0.1 an improvement in heat transfer is observed. The immiscibility of R410A (R125/R32) and R507 (R125/R143a) with the POE-oil effects a reduction in heat transfer. However, in the ranges of immiscibility of the components R32 and R143a the oil improves heat transfer by up to 70% e.g. for R507 at a reduced pressure of 0.06 and 3% oil mass fraction. The heat transfer coefficient of R404A (R125/R143a/R134a) is not influenced as significantly by the addition of oil as that of R507. The ratio of the heat transfer coefficient of the refrigerant-oil mixture to that of the pure refrigerant αmix/α/ref decreases for all refrigerants with increasing reduced pressure p* for p* ≥ 0.1. The improvement in heat transfer by addition of oil seems to be much greater for the component R125 than the reduction in heat transfer for the components R32 and R143a. The lower improvement in the heat transfer coefficient of R404A-oil mixtures may be caused by the lower molar fraction of the component R125 in R404A (35.8%) than in R507 (41.2%).

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