Time-Averaged Analysis and Numerical Modelling of the Behavior of the Multiphase Flow and Liquid Lamella Thickness Inside an Internal-Mixing ACLR Nozzle

Abstract

The Air-Core-Liquid-Ring (ACLR) atomizer is an innovative internal-mixing pneumatic atomization technique, suitable for energy-efficient spray drying of 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 needs to be properly studied and comprehended. With that in mind, a computational fluid dynamic (CFD) model was implemented and tested with experimental data collected for different air pressures and liquid feed viscosities. The model used can predict average lamella thickness with a relative error of less than 10%, when compared to experimental results, although some degree of artificial dampening of the flow instabilities occurs at high viscosities and low pressures. These instabilities have to be investigated in more detail from both the numerical side, by further refining the CFD model to capture the moment-to-moment behavior of the flow, as well as on the experimental side, by studying the instability development at higher recording speeds.

Modelling the Flow Conditions and Primary Atomization of an Air-Core-Liquid-Ring (ACLR) Atomizer Using a Coupled Eulerian–Lagrangian Approach

“…The experimental data used for this work was collected in a spray test rig which is described in detail in our previous study (Ballesteros Martínez and Gaukel 2023). In summary, all trials were performed at room temperature, which was assumed to average 25 • C for all calculations and simulations.…”

“…The numerical model was implemented on STAR-CCM+ v.2206 (Siemens AG, Munich, Germany). The CFD model presented in this study was built up in our previous work (Ballesteros Martínez and Gaukel 2023), which used the Volume Of Fluid (VOF) method to represent the Eulerian multiphase flow as an immiscible mixture of two phases: an incompressible Newtonian liquid, and an ideal gas phase. The details of the governing equations, mesh specifications and numerical schemes of the original model can be found there.…”

“…The boundary and initial conditions were setup following the same procedure from our previous work (Ballesteros Martínez and Gaukel 2023). The way the boundaries were defined can be seen in Fig.…”

“…1. A more detailed schematic of the initialization is shown in Ballesteros Martínez and Gaukel (2023). Compared to the previous work, however, a half of the nozzle was simulated, instead of just a quarter.…”

“…For the simulations of only internal volume, the simulations were run for 8 ms, of which the last 4 ms were used for data analysis. These times were based on our previous calculations in Ballesteros Martínez and Gaukel (2023). The simulations with the large airbox were run for 12 ms, to allow extra time for the external flow to develop.…”