Conference Proceedings Paper
Void Fraction Evolution in Subcooled Flow Boiling Under Low-Pressure and Low-Flowrate Condition
NURETH-14 - 2011 September 25-30
Tomio Okawa (Osaka University)
Yosuke Yamagoe (Osaka University)
Rouhollah Ahmadi (Osaka University)
Visualization of bubble behavior in water subcooled flow boiling was carried out to investigate
the triggering mechanism of the net vapor generation under a low-pressure and low-flowrate
condition. Flow direction was vertical upward and a hydrophilic surface was used as the heated
surface. In the experiments under high liquid subcooling, bubbles were lifted off the heated
surface immediately after the nucleation and collapsed in the subcooled bulk liquid. Since the
condensation rate was nearly equal to the vaporization rate, the vapor void fraction did not
increase significantly. When the liquid subcooling was low enough, bubble coalescence took
place to produce large bubbles sliding up the vertical heated surface. It was considered that the
large sliding bubbles mitigated the condensation to contribute to a rapid increase in the vapor
void fraction with an increase in the thermal-equilibrium quality.
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