Study on Subcooled Flow Boiling Heat Transfer Under Vibration Conditions of Sinusoids and Seismic Shock Waves

Onset of nucleate boiling — ONB — and critical heat flux — CHF — on subcooled flow boiling under vibration condition, focusing on liquid velocity, amplitude and frequency of vibration, were investigated experimentally. Experiments were conducted using a copper thin-film and subcooled water in a range of the liquid velocity from 0.27 to 4.07 m/s at 0.10MPa. The liquid subcooling was 20K. The test section was set on a vibration table. The acceleration was 1.3 and 4.2 m/s², respectively; the frequency was 2, 4 and 20 Hz, respectively. The test section was arranged for horizontal position facing upward and for vertical position, respectively: the vibration directions were horizontal and vertical to orientation of the heater. The present experimental results showed that critical heat fluxes under the vibration conditions of both vibration directions, i.e., horizontal and vertical vibrations to the heater, were higher than those for steady flow. The CHF under the vibration condition was increased with an increasing of acceleration of vibration. According to present observations, coalesced bubble on the heater was frequently released by vibration of the test heater. This behavior causes the CHF to become higher under the vibration condition. Furthermore, some experiments were demonstrated under vibration condition of seismic shock wave at the South Hyogo prefecture Earthquake in 1995. It was confirmed from the present experimental results that thermal limit of heater was a conservative evaluation during earthquake.