The hydroxyl radical yield prediction of cavitation bubble clouds during the hydrodynamic cavitation process for chitosan degradation

Abstract

In order to measure the influence of chemical effects in the process of hydrodynamic cavitation (HC) degradation of chitosan, a prediction model for the hydroxyl radical (˙OH) yields of cavitation bubble clouds (CBCs) was developed based on a single-hole orifice plate cavitator. The choking cavitation number (C_cv) was introduced to define whether choking cavitation occurs. The ˙OH yield calculation model for single cavitation bubbles was first developed. Furthermore, the range of gas nucleus radii in chitosan solution (R ∼ (R + dR)) was divided equally into N intervals of 10 μm. The ˙OH yields of the cavitation bubble formed by the largest gas nucleus in each interval was calculated, respectively, and then the relationship between the radius of the cavitation bubbles and the ˙OH yields was fitted to obtain the equation π(R₀). Moreover, the ˙OH yields of CBCs were calculated by coupling π(R₀) with the gas nucleus steady-state cavitation number equation (J) and the gas nucleus steady-state size distribution equation (N(R₀)). The results showed that the ˙OH yields were positively correlated with the upstream inlet pressure (P₁), the throat diameter of the orifice plate (d₀), and solution concentration (C) and negatively correlated with downstream recovery pressure (P₂) as well as the pipe diameter of the orifice plate (d_p). The maximum ˙OH yield was obtained as 0.4772 mol m⁻³ S⁻¹ at C = 0.7 g L⁻¹, T₀ = 303 K, P₁ = 0.55 MPa, P₂ = 0.1 MPa, d₀ = 6 mm and d_p = 20 mm. The present work provides a theoretical basis for measuring the chemical effects in the HC process for chitosan degradation.