A comprehensive study on the effects of annular protrusion for cavitation intensification in Venturi tubes

Hydrodynamic cavitation, a novel advanced oxidation technique that is notable for its high performance on energy efficiency and environmentally friendly, has incited broad interest. Enhancement of cavitation forms an emerging field in this context. A semi-circular annular protrusion has been introduced into Venturi tubes for cavitation intensification. Initially, improved multiphase flow-cavitation chemical effect simulations are constructed, enabling accurate estimations of the cavitation process on multiscale. Based on this model, an in-depth analysis is carried out to reveal the influential mechanisms of protrusion. Subsequently, optimization of protrusion structure is conducted through a comprehensive analysis of cavitation flow characteristics. The interaction between pressure and protrusion structure are further explored utilizing multi-factor optimization methods. Results indicate a significant performance improvement on the cavitating Venturi tube with a semicircular annular protrusion. This is attributed to an extended low-pressure area, prolonged high-speed duration, and the increase in both collapse pressure and temperature, yielding higher amounts of free radicals. The semi-circular protrusion is superior to the triangle and rectangle shape. Its position and height significantly impact cavitation intensity in accordance with the generated cavitation patterns, pressure distribution, velocity magnitude and streamlines. Interactive factors analysis reveals strong linear relationships between optimal protrusion height, position and inlet pressure (R-2 = 0.999 and 0.992). In comparison to smooth Venturi tubes, recommended designs have shown the vapor volume fraction enhanced by 212 %, 230 %, 255 %, and 117 % at 3, 4, 5, and 6 bar. Accordingly, the (OH)-O-center dot prediction multiplies to 23 times, 33 times, 107 times and 3 times. This study provides theoretical backing for engineering applications of the semi-circular annular protrusion in Venturi tubes and contributes towards improved cavitation efficiency and reduced experimental and time costs.