Experimental Analysis and CFD Modelling of the Flow Conditions inside an Air-Core-Liquid-Ring Atomizer

Abstract

The Air-Core-Liquid-Ring (ACLR) atomization is an innovative internal-mixing pneumatic atomization technique, suitable for energy-efficient spray drying because of its ability to handle highly viscous liquid feeds with high solid contents. However, pneumatic atomizers such as the ACLR can suffer from unstable internal flow conditions, which may lead to a wide variation in the droplet diameter obtained. Therefore, the internal flow conditions of an ACLR-atomizer prototype needed to be studied and comprehended. With that in mind, a computational fluid dynamic (CFD) model was developed, and tested with experimental data collected for different gas pressures and liquid feed viscosities. A mesh independence study, as well as some testing of Physics models were performed. A mixed polyhedralprismatic mesh was generated, and the k-ω SST model was selected as it showed a good balance between representation of the turbulence in the system and computational effort. The predicted average lamella thickness is similar with experimental results, with an average 10 % error, but the thickness variations observed in the experiments dampen quickly over time in the simulations. This is not the case in the experiments with the higher viscous maltodextrin solution. Therefore, further model refining has still to be done. Nonetheless, the flow behaves as expected in the CFD simulation with changes in pressure and liquid viscosity. This opens up the possibilities of doing more in-detail CFD studies of the effect of liquid feed properties and geometrical variations of the nozzle.