The wall temperature distributions of a boiling two-phase flow of R113 in helically coiled tubes were measured, and the effects of a coil diameter and inclined angle on the heat transfer ...characteristics were investigated. There were large differences in the temperature distributions between the vertically placed coil and the horizontally placed coil at the lower quality region. When the coil was vertically placed, the ratio of the heat transfer coefficient of a boiling two-phase flow to that of a liquid single-phase flow was not affected by coil diameter. When the coil was horizontally placed or inclined by 45 degrees, the heat transfer coefficient at the upper part of the coil was larger than that at the lower part in the lower quality region but smaller in the higher quality region. The overall average heat transfer coefficient of a horizontally placed coil was larger than that of a vertically placed coil.
High temperature horizontal platinum filaments have been dipped into subcooled water to simulate a new rapid solidification process, and forced convectional boiling heat transfer has been examined. A ...vapor film first collapsed at the edges of the filament and the collapsing sites propagated towards the center at rates ranging from 0.25∼2 m/s. The propagating rate of the collapsing site increased with increasing subcooling. A minimum heat flux point did not appear clearly in the boiling curve, and a variation of the heat flux corresponded to that of the propagating rate. Epstein and Hauser's expression of the convection film boiling of a sphere or cylinder could be applied for that of the filament during water quenching.
Influence of Oil on Refrigerant Evaporator Performance KIM, Jong-soo; NAGATA, Karsuya; KATSUTA, Masafumi ...
Transactions of the Japan Society of Refrigerating and Air Conditioning Engineers,
1988, Volume:
5, Issue:
1
Journal Article
Peer reviewed
In vapor compression refrigeration system using oil-lubricated compressors, some amount of oil is always circulated through the system. Oil circulation can have a significant influence on the ...evaporator performance of automotive air conditioner which is especially required to cool quickly the car interior after a period standing in the sun. An experimental investigation was carried out an electrically heated horizontal tube to measure local heat transfer coefficients for various flow rates and heat fluxes during forced convection boiling of pure refrigerant R12 and refrigerant-oil mixtures (0-11% oil concentration by weight) and the results were compared with oil free performance. Local heat transfer coefficients increased at the region of low vapor quality by the addition of oil. On the other hand, because the oil-rich liquid film was formed on the heat transfer surface, heat transfer coefficients gradually decreased as the vapor quality became higher. Average heat transfer coefficient reached a maximum at about 4% oil concentration and this trend agreed well with the results of Green and Furse. Previous correlations, using the properties of the refrigerant-oil mixture, could not predict satisfactorily the local heat transfer coefficients data. New correlation modified by oil concentration factor was developed for predicting the corresponding heat transfer coefficient for refrigerant-oil mixture convection boiling. The maximum percent deviation between predicted and measured heat transfer coefficient was within ±30%.
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