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

Abstract

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 millimeter 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.

Phase Doppler Anemometer (PDA) has been applied for measurement of velocity and size of droplets in water spray which injected into the atmosphere. 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. Imaging techniques were used also for taking the spray angle as well as the liquid core in the near field.

The measurement positions were set at planes which are located on various positions downstream from the nozzle orifice. For each downstream position, radial profiles of the spray pattern were measured. The water mass flow, atomization air volume flow, and the cover position are changed and their effects on the spray are characterized. The atomization mass flow and the cover position can be set in a way to design the radial profile of the spray according to the requirement of the process.