Onset of nucleate boiling — ONB — and critical heat flux — CHF — on subcooled flow boiling under oscillatory flow and vibration conditions, focusing on liquid velocity, amplitude and frequency of oscillation and 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. Frequency of oscillatory flow was 2, 4 and 6 Hz, respectively; amplitude of oscillatory flow was 25 and 50% in a ratio of main flow rate, respectively. For the vibration condition, 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 present experimental results showed that temperature at ONB and critical heat flux for oscillatory flow were lower than those for steady flow. The decreasing of liquid velocity by oscillatory caused the ONB and the CHF to decrease. Critical heat fluxes under the vibration conditions 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, the effects of oscillation and vibration on velocity profile in a channel were estimated to discuss behaviors of a coalesced bubble on a heater.
MODEL OF CRITICAL HEAT FLUX IN SUBCOOLED FLOW BOILING
