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ISSN Online: 2377-424X

ISBN Print: 0-89116-299-2

International Heat Transfer Conference 7
September, 6-10, 1982, Munich, Germany

HEAT TRANSFER IN NATURAL CONVECTIVE BOILING OF REFRIGERANT-OIL MIXTURES

Get access (open in a dialog) DOI: 10.1615/IHTC7.3810
pages 73-87

Résumé

In spite of many experiments, it is still an open question how the heat transfer in boiling of refrigerants is affected by mixing with oil. In a few of the experiments , the oil caused a decrease of heat transfer, but it has also been noted that over a certain range of the governing experimental variables, the mixing of oil caused an increase in heat transfer. The complex boiling characteristics of refrigerant-oil mixtures are probably due to the complicated interactions between the components of the mixtures, the mass transfer through the liquid-vapor interface as well as the geometry of the heating surface.
In this study, the mechanism of heat transfer in boiling at finned surfaces is first briefly explained, followed by a review of the state of research on boiling of refrigerant-oil mixtures. Experiments on heat transfer in pool boiling with horizontally placed tubes with T-shaned fins are then reported.
The boiling liquids used in the experiments were different mixtures of refrigerant R12 and Shell Clavus G68 oil. The experiments were made at 0°C and −10°C, and the mass fraction of the oil used in the mixture was increased up to o.1o. As the experiments indicate, the heat transfer coefficients in the boiling refrigerant-oil mixtures depend on the heat flux density and on the mass fraction of oil. For low heat fluxes a decrease of heat transfer was observed with increasing oil mass fraction. For higher heat fluxes the heat transfer coefficient increased slightly in a small range of the mass fraction of oil. This boiling characteristic may be explained by interfacial turbulence, an increase in surface tension, and a selective adsorption of the components of the refrigerant-oil mixtures at the heating surface.