Numerical simulation of a continuous sonoreactor for cotton cellulose residues recovery

Numerical simulations are a tool for sonoreactors design and reaction parameters choice. We modeled a sonoreactor with six lateral flat transducers along the walls and a concentric high intensity focused ultrasound (HIFU) transducer at the bottom. We examined the effects of the gap between the reflector and transducers (h), cone radii in the lower part and ultrasound frequency (f) on the cavitation activity of cellulose esters solutions. Then, we investigated the effects of the properties of cellulose solutions on the cavitation activity. The simulation accounts for the attenuation due to the cavitation bubbles and considers the propagation of sound waves from the HIFU as linear. We measured the speed of sound in a cellulose esters solutions and included it in our simulations: 1545 m s^-1 for 6.25 g L^-1. h, f, the density (ρ) and the viscosity (μ) of the cellulose solutions have the most significant effects - accounting for 34 % to 61 % of the variance - on the total acoustic pressure (p_T) and active cavitation surface area (V). p_T and V increase as f and ρ increase, and as h and μ decrease. At 78 kHz and h = 0.075 m, with μ = 5.3 × 10^-3 Pa.s and ρ = 941.8 kg m^-3, the simulation resulted in the highest p_T and largest V: 1.96 × 10⁶ Pa and 3.99 × 10^-2 m². These data provide a basis to optimize sonoreactor design and operating conditions for enhanced cavitation performance in cellulose processing.