Investigation on the role of atomization air mixing on the spray characteristics of air assisted atomizer

Abstract

[EN] Air assisted atomizers are widely used for various purposes, for example coating processes, medical processes, and sprinkler. However, the spray development processes, especially the breakup phenomena are not fully understood yet. Generally, the main breakup of the air assisted atomizer depends on whether the mixing is internal or external. The border between these processes is not clear. In order to study changes in the spray configuration due to the way of mixing, the spray was investigated for the transition from internal to external mixing. Therefore, an air assisted atomizer which allows adjusting the distance between injector to cover was used. The atomizer consists of two components, which are a liquid injector and an injector cover with orifice. The atomization air flows through the gap between the injector and the cover. The position of cover orifice is able to be traversed from the position fully attached to the injector to several millimetre distances from the injector nozzle. In this study, the water spray characteristics depending on the air and liquid mixture position were investigated experimentally by two optical measurement techniques. Imaging techniques were used for taking the spray structure as well as liquid core in near nozzle field. The water mass flow, atomization air mass flow, and the cover position were changed and their effects on the spray were investigated. Phase Doppler Anemometer (PDA) was applied for measurement of velocity and size of droplets in water spray which injected into the atmosphere. The measurement positions were set at planes which located on 20 and 40mm downstream from the nozzle orifice. For each downstream position, radial profiles of the spray pattern were measured on one air to water flow rate condition. The cover positions were changed and the differences on the droplet velocity and diameter as a function of radial distance on each nozzle cover positions were discussed. Also, high resolution direct imaging technique has been developed and applied for measurement of size of droplets. The results from these measurement techniques were compared and they correspond well at the high air to water flow rate conditions. At the low air to water flow rate condition, the agreement of the results of these measurements became lower. It might be caused by the bouncing unspherical droplets.