Measurements of internal flow regime and bubble size in effervescent atomizer

The internal flow in an effervescent atomizer was experimentally observed for a wide range of gas-liquid flow rates with various atomizer geometries. The effects of atomizer geometry, gas and liquid flow rates on the flow regime and bubble size were investigated. The results show that the internal flow is significantly affected by exit orifice geometry, aerator location, and fluids flow rates, but less affected by aerator configuration. A high velocity of the liquid, small exit orifice diameter, and large distance between the aerators and the exit orifice are beneficial for the formation of bubbly flow. In bubbly flow, the bubble size decreases with liquid flow rate and gas-to-liquid mass ratio (GLR); it follows a normal distribution, and is less related to the atomizer geometry. At a certain liquid flow rate and GLR, small bubbles are readily formed under the exit orifice with a small diameter and proper length. It is found that there are critical values of GLR and critical mean bubble diameters related to gas-liquid mixing; values above the critical GLR and below the critical mean bubble diameter are beneficial for internal gas-liquid mixing. Based on the results of comparison of internal and external flow, it is possible to improve the spray performance by optimizing the internal flow parameters.