RESUMO
Luminescence and chemiluminescence have been experimentally investigated in hydrodynamic cavitating flows. By using dedicated microdevices inserted inside a light tight box, photons counting has been made possible. Luminescence has been investigated with deionized water as the working fluid; chemiluminescence has resulted from cavitating alkaline luminol solutions, and has been correlated to hydroxyl radicals formation. For the first time, luminescent and chemiluminescent phenomena have been considered together on the same devices submitted to similar cavitating flow regimes. Degassed solutions enhance the luminescence and also the hydroxyl radical yield. Due to the small sizes of the channels, the lifetimes of the collapsing bubbles correspond to pseudo frequencies matching the range of optimal frequencies used in sonochemistry. New perspectives for the study of hydrodynamic cavitation as an advanced oxidation process are suggested.
RESUMO
We have performed hydrodynamic cavitation experiments with an aqueous luminol solution as the working fluid. Light emission, together with the high frequency noise which characterizes cavitation, was emitted by the two-phase flow, whereas no light emission from luminol was recorded in the single phase liquid flow. Light emission occurs downstream transparent microdiaphragms. The maximum level of the recorded signal was around 180 photons per second with flow rates of 380⯵l/s, that corresponds to a real order of magnitude of the chemiluminescence of 75,000 photons per second. The yield of emitted photons increases linearly with the pressure drop, which is proportional to the square of the total flow rate. Chemiluminescence of luminol is a direct and a quantitative demonstration of the presence of OH hydroxyl radicals created by hydrodynamic cavitation. The presented method could be a key to optimize channel geometry for processes where radical production is essential.