Abstract
The present paper described the onset cavitation conditions, acoustic noise characteristics and void behaviors of flowing liquid sodium in the venturi made of 316 SS with an inner diameter of 6.5 mm and a length of 20 mm. An experiment was conducted in the range of sodium stagnant pressure in the expansion tank of 0.061-0.181 MPa-a and in the temperature range of 200°-400°C. As a result, it was found that the noise intensity increased greatly when the cavitation coefficient approached unity (onset of cavitation), and it became saturated in lower cavitation coefficient (developed cavitation). The cavitation coefficient at the onset of cavitation was nearly equal to unity. However, an increase in temperature shifted the cavitation coefficient to a value a little higher than unity. The results also showed that velocity in the venturi at the onset of cavitation also increased by increasing the stagnant pressure. Cavitation occurrence produced a noise in the range of 600-20,480 Hz. In developed cavitation condition, the noise intensity was nearly constant at around -50 dB which might be caused by the choking of the fluid. At 400°C, instabilities or fluctuations of the noise spectrums were observed. Simulated results by using CFD showed that voids were formed at the throat of the venturi and the void fraction increased as the static pressure decreased by the flow. The voids were conveyed and collapsed in the downstream of the venturi outlet because of an increase in the static pressure. These voids could cause choking and noise as well as erosion.
