Fig. 1. Experimental observation of bubble structure in injected helium phosphoric acid solution.

Fig. 2. Acoustic cavitation characteristics of four kinds of bubble groups composed of same size and same gas bubbles: (a) Change of bubbles radius; (b) change of bubbles radial velocity; (c) magnified figure of bubbles radius at the stage of collapse and rebound; (d) change of bubble group radius; (e) change of bubble groups radial velocity; (f) change of temperature in bubbles; (g) change of pressure in bubble groups.

Fig. 3. Acoustic cavitation characteristics of two kinds of mixed bubble groups composed of same size and different gas bubbles: (a) Change of bubbles radius; (b) change of bubbles radial velocity; (c) magnified figure of bubbles radius at the stage of collapse and rebound; (d) change of bubble group radius; (e) change of bubble groups radial velocity; (f) change of temperature in bubbles; (g) change of pressure in bubble groups.

Fig. 4. Acoustic cavitation characteristics of two kinds of mixed bubble groups composed of different size and same gas bubbles: (a) The change of the maximum temperature in the large bubble with the number of large bubbles; (b) the change of the maximum temperature in the small bubble with the number of large bubbles; (c) the change of the peak of pressure pulse with the number of large bubbles in a bubble groups.

Fig. 5. Radius change of large (red solid line) and small (black dotted line) bubbles in helium bubble group and corresponding pressure pulse change in the group: (a1), (a2) ; (b1), (b2) ; (c1), (c2) ; (d1), (d2) ; (e1), (e2)

Fig. 6. Acoustic cavitation characteristics of two kinds of mixed bubble groups composed of different size and different gas bubbles: (a) The change of the maximum temperature in the large bubble with the number of large bubbles; (b) the change of the maximum temperature in the small bubble with the number of large bubbles; (c) the change of the peak of pressure pulse with the number of large bubbles in a bubble groups.

Table 1. Physical parameters of 75% phosphoric acid^[22].