###### Abstract
[PERSON] et al. [17] verified two mechanisms of vapor shedding (re-entrant jet and condensation shock) and offered more information on vapor shedding using the computational fluid dynamics (CFDs) method. [PERSON] et al. [18] investigated the primary features and physical signals of two vapor-shedding mechanisms in Venturi tubes using a self-developed compressible cavitation phase change solver. [PERSON] et al. [19] evaluated the global cavitation behavior in a Venturi tube and found that the inlet pressures had no effect on the cavity length, which was only a function of the pressure ratio or the cavitation number. [PERSON] et al. [20] optimized the structural characteristics of various types of Venturi tubes (such as slit, circular, and elliptical), and they came to the conclusion that the optimal geometry for cavitational activity has a throat height/diameter to length ratio of 1:1 and a divergence angle of 6.5\({}^{\circ}\). [PERSON] et al. [21] carried out two-dimensional (2D) CFD simulations using a two-phase mixture model to investigate the impact of the convergent angle on the cavitation performance in the Venturi tube; the numerical findings revealed that a larger convergent angle enhances the cavitation yield but requires more power. In addition, they developed a semi-empirical model for predicting cavitation in the Venturi tubes. In a study by [PERSON] et al. [22], experiments were conducted to identify the role of the Venturi divergent angle in bubble breakup and showed that the divergent angle had a significant influence on the deceleration process. The larger the divergent angle, the shorter the distance and time, which is required for bubble deceleration. While much research has been conducted on the inception, evolution, and structural parameters of Venturi-induced cavitation, there remains a lack of discussion on the influence of converging and diverging section lengths of a Venturi on cavitation characteristics under varying operating pressure. Furthermore, in this study, the convergence and divergence angles of the Venturi tube, which are significant factors influencing cavitations, were not altered. This provided a favorable starting point for conducting such research. Additionally, the Venturi cavitation reactors are often subject to different pressure conditions in various application scenarios, such as wastewater treatment, organic compound synthesis, and biodiesel production [23; 24; 25]. Therefore, we focus our attention on an investigation of the effect of diverging and converging section lengths on cavitation characteristics at different pressure conditions. In this study, several Venturi devices with varying converging and diverging section lengths were simulated with a two-phase mixture model and the standard k-\(\epsilon\) turbulence model, and the simulated results were validated using an actual pressure drop and flow rate data. Additionally, changes in the cavitation flow field within the Venturi under different pressure conditions were also investigated. Other flow field characteristics in the Venturi, such as the maximum throat velocity, mass flow rate, and vapor volume, were also measured and analyzed. The findings and conclusions from this study can provide insights for the design and application of Venturi cavitation devices.