PRESSURE PULSE GENERATION BY SINGLE BUBBLES IN SUBCOOLED POOL BOILING

Noise generation in nucleate boiling systems is a widely known phenomenon. Nevertheless, the physics connecting bubble dynamics and pressure pulse generation does not seem to be fully understood. This paper reviews literature on boiling sound emission and focuses on pressure pulses generated by bubbles at a single nucleation site. Experimental results are presented for water vapor bubbles in subcooled boiling on a vertical copper surface at subatmospheric pressure. Signals of two hydrophones at different positions in the evaporator have been recorded. These signals are synchronized with high speed video recordings. Bubbles at a single nucleation site and at two simultaneously activated sites have been observed at a pressure of 40 kPa. The experimental findings confirm results from a momentum balance for potential flow which yields a direct proportionality between pressure pulse amplitude and liquid level. Also, the influence of the free surface and the dependence of pulse shape on bubble volume acceleration and deceleration is shown.