Changes of enthalpy slope in subcooled flow boiling
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Void fraction data in subcooled flow boiling of water at low pressure measured by General Electric in the 1960s are analyzed following the classical model of Griffith et al. (in Proceedings of ASME-AIChE heat transfer conference, #58-HT-19, 1958). In addition, a new proposal for analyzing one-dimensional steady flow boiling is used. This is based on the physical fact that if the two phases have different velocities, they cannot cover the same distance—the control volume length—in the same time. So a slight modification of the heat balance is suggested, i.e., the explicit inclusion of the vapor–liquid velocity ratio or slip ratio as scaling time factor between the phases, which is successfully checked against the data. Finally, the prediction of void fraction using correlations of the net rate of change of vapor enthalpy in the fully developed regime of subcooled flow boiling is explored.
KeywordsHeat Flux Mass Flow Rate Void Fraction Vapor Bubble Slip Ratio
The authors thank to the Spanish Minister of Education and Science (MEC) the funding of this research through the special action ENE2004-0279-E and the research project DPI 2005-08654-CO4-04.
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