Vibration analysis as a non-invasive method for studying hydrodynamic cavitation-Fenton coupled system based on chaos theory

FLEITE S. N.; NAPOLEONE S.; GARCÍA A. R.; AYUDE A.; CASSANELLO MIRYAN

Congreso; WCCE11 ? 11th Word congress Chemical Engineering; 2023

Hydrodynamic cavitation (HC) is an emerging technology applicable to the intensification of different processes due to the elevated temperatures and pressures reached during cavities collapse. Acoustic analysis using microphones has been conducted [1], allowing the identification of the inception point. This work aims to analyze HC by calculating the Kolmogorov entropy (KML) from vibration signal time series. The setup reported by Salierno et al. [2] was used. Two piezoelectric vibration sensors coupled with an oscilloscope were used to register vibrations time series (1 MHz sampling rate). They were located on the HC device and on the flow control valve as reference. First, operation of the HC reactor was tested at different temperatures (head loss 2.8bar), different head losses (at 40ºC), and H2O2 concentrations (0-40 mM at 16ºC, 2.8bar). Then, the vibrations were measured while the HC reactor (head loss 3.5 bar) was connected in series with a Fenton upflow fixed bed reactor (UFBR) operated in continuous mode with different flow rates. Water temperature increased during the experiment from 16ºC to 50ºC before attaining steady-state.Results showed changes in KML with temperature and head loss. An exponential increase with increasing temperature was observed, whereas it linearly increased with head loss. From 20 to 60ºC KML increased 250%, with almost no change between 10 and 20ºC. Besides, from 0.5 to 3.5 bar, KML increased 229%. No significant changes were observed with the addition of H2O2. When the UFBR-HC in-series system was in operation, a sudden increase in KML (335%) was evident after approximately 1±0.25 hours, regardless of the flow rate. The reference measurement in the valve did not exhibit any significant trend. The change was always observed at the same temperature.The influence of temperature on KML can be attributed to the reduction in water viscosity and increased water vapor pressure affecting bubbles implosion behavior. This would increase turbulence and the number of water molecules inside the cavitation bubble before the final implosion, slowing it down and increasing system complexity (compared to a vacuum bubble imploding). Nevertheless, the temperature increase cannot explain by itself the huge increase in KML. Under the extreme conditions reached during bubble implosion in HC, supercritical water can be formed. Hence, in the case of the combined system, radicals and dissolved oxygen formed by hydrogen peroxide decomposition in the UFBR may affect the system. This analysis can be useful in monitoring cavitation device performance, likely suggesting a temperature threshold between two distinctive regimes.