Nucleate boiling heat transfer coefficients of flammable refrigerants

Nucleate boiling heat transfer coefficients (HTCs) of propylene (R 1270), propane (R290), isobutane (R600a), butane (R600), and dimethylether (RE170) on a horizontal smooth tube of 19.0 turn outside diameter have been measured. The experimental apparatus was specially designed to accommodate high vapor pressure refrigerants such as propylene and propane with a sight glass. A cartridge beater was used to generate uniform heat flux on the tube. Data were taken in the order of decreasing heat flux from 80 kW m(-2) to 10 kW m(-2) with an interval of 10 kW m(-2) in the pool temperature of 7 degreesC. Test results exhibited a typical trend that HTCs of flammable refrigerants increase with increasing vapor pressure. Existing nucleate boiling heat transfer correlations showed up to 80% deviation as compared to the present data. Hence a new correlation was developed through a regression analysis taking into account dimensionless variables affecting nucleate boiling heat transfer. The new correlation showed a good agreement with data for flammable refrigerants as well as halogenated refrigerants with a deviation of 5.3%. (C) 2003 Elsevier Ltd and IIR. All rights reserved.