Photographic study of bubble behavior in subcooled flow boiling using R-134a at low pressure range

摘要

This paper reports an experimental study and photographic investigation of the subcooled flow boiling on plain and augmented (hypervapotron) surfaces. The test sections are single-side heated and have a projected heating surface of 12.25 × 100 mm. Subcooled flow boiling heat transfer results were obtained from onset of nucleate boiling to critical heat flux and film boiling under conditions of inlet subcooling range from 10 ℃ to 30 ℃, outlet pressure range from 0.4 to 0.8 MPa and mass flow rate range from 124 to 372 kg/m~2 s. The data of bubble growth, bubble departure size, nucleation distribution are measured. Nucleation distribution has an exponential relationship with uniform heat flux under moderate and high heat flux in subcooled flow boiling. The high nucleation density results in liquid supply shortage for nucleation and local dry out, which possibly initiates CHF. The visualization data did not show significant difference in hypervapotron structure with respect to bubble growth, departure and nucleation distribution, although hypervapotron delivers 40-50% higher CHF under same thermohydraulic conditions.