Experimental study of cavitation intensity using a novel hydrodynamic cavitation reactor

The cavitation intensity of a novel hydrodynamic cavitation reactor (HCR) was experimentally evaluated in terms of the amount of bubble generation and bubble collapse energy. The amount of bubble generation was analyzed by flow visualization using a high-speed camera. The bubble collapse energy was evaluated by calculating the generated thermal energy. Pressure and velocity were selected as parameters affecting cavitation intensity. Further, to evaluate the effect of pressure, cavitation intensity was evaluated according to the pressure upstream of the HCR. Because HCR is a rotating fluid machine, the velocity was divided into radial and tangential components. First, cavitation intensity was analyzed using the flow rate to evaluate the effect of the radial velocity. Then, cavitation intensity according to the rotational speed was analyzed to evaluate the effect of the tangential velocity. As a result, the cavitation intensity was inversely proportional to the pressure and directly proportional to the rotational speed. However, when the density of bubbles in the cavitation region exceeded a certain level, the bubble collapse energy did not increase owing to the decrease in the heat transfer rate required for bubble growth. Conversely, the flow rate has a slight effect on the amount of bubble generation; however, the cavitation region is expanded, and the heat transfer rate and the thermal energy are increased. Fundamental analysis of the factors affecting cavitation intensity in an HCR was conducted.