Boiling Heat Transfer Under Oscillatory Flow Condition

Abstract

Onset of nucleate boiling (ONB), point of net vapor generation (NVG) and critical heat flux (CHF) on subcooled flow boiling under oscillatory flow, focusing on liquid velocity, amplitude and frequency of oscillations were investigated experimentally and analytically. 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. 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. The effects of liquid oscillatory flow on the incipient boiling temperature were examined through a classical stability theory of preexisting nuclei. Heat flux at NVG reduced by superimposed oscillatory flow; the increase of liquid velocity by the oscillatory flow caused the NVG to decrease. The CHF under the oscillatory flow condition was examined analytically by using a liquid sub-layer model and a lumped-heat-capacity model in the heater.