# Optimised Twin Fluid Atomiser Design for High-Viscosity, Shear-Thinning Fluids
## 3 Results
### Nozzle Configurations  
Figure 6 illustrates atomisation attempts of NC No. 4 at varying ALR. The corresponding data is presented in Table 4. The spray pattern of the nozzle configurations listed in Table 3 were investigated \(100\times 10^{-3}\,\mathrm{m}\) below the atomiser and high speed recordings using the shadow photography method were made, according to Section 2.3.  
NC No. 9, supporting a typical apex angle (\(30^{\circ}\)) used in atomisation processes for low-viscosity liquids, resulted in the production of fibrous droplets. A conglomerated drop of silicone oil, increasing in size, accumulated at the nozzle tip and was torn off as  
Figure 5: Failed atomiser, no nozzle insert (1); failed nozzle inserts (2)–(3); functional nozzle insert (4).  
gravitational forces became dominant. A periodic manner was noticed but not further investigated, as atomisation did not occur.  
As a result, nozzle configurations with increased apex angles were tested. Nozzle configurations No. 4 and 10, both with an apex angle of 90\({}^{\circ}\), atomised the liquid equally well when observed visually. Using high speed image recording, however, it turned out that atomisation quality was significantly better at NC No. 4 compared to NC No. 10. Nozzle configuration No. 3, No. 5, and No. 9 with apex angles of 60\({}^{\circ}\), 120\({}^{\circ}\), and 30\({}^{\circ}\), respectively, revealed the production of a larger fibrous droplet content compared to NC No. 4, as can be seen in Figure 7. The optimal apex angle was therefore found to be 90\({}^{\circ}\).  
With the apex held constant at 90\({}^{\circ}\), different hole counts were investigated. NC No. 1 was unable to atomise the liquid and resulted in the production of fibre. NC No. 2 allowed for adequate atomisation, while NC No. 4 provided better results. A small \(s/d_{C}\) ratio therefore seemed preferable at first; however, this was counterbalanced by the inability to  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Index Figure 6** & **NC** & **FPS** & \(\mathbf{\eta_{L}^{0}}\) & **ALR** & \(\mathbf{\hat{V}_{G}\times 10^{3}}\) & \(\mathbf{\hat{m}_{L}\times 10^{3}}\) \\  & & \(\mathbf{s^{-1}}\) & **Pa s** & - & **std m3/s** & **kgs\({}^{-1}\)** \\ \hline
1 & 4 & 60 & 11.1 & 3849 & 83.33 & 21.00 \\
2 & 4 & 5000 & 11.1 & 4875 & 105.56 & 21.00 \\
3 & 4 & 10,000 & 11.1 & 6143 & 52.78 & 8.33 \\ \hline \end{tabular}
\end{table}
Table 4: Operating parameters during image acquisition, corresponding to Figure 6.  
Figure 6: Fine spray (1); motion-blurred, unsharp droplets due to low frame rate and droplets out of focus (2); fibre-like structures, resulting from subsonic gas flow (3).  
Figure 7: Recordings at 75,000 FPS, taken \(1\times 10^{-1}\) m below the nozzle assembly, for different nozzle configurations. Blurred structures result from out-of-focus regions and high-velocity motion.  
resist decreasing gas velocity down to the gas jet core due to the decreasing air jet diameter as the number of gas jet holes increased. The atomisation quality therefore decreased at some critical \(s/d_{G}\)-ratios with decreasing \(s/d_{G}\). The decline in atomisation quality became evident through the formation of large fibrous structures, as demonstrated in Figure 7. This was the case for all tested configurations with \(s/d_{G}\) ratios below 3. The optimal nozzle configuration (ONC) was therefore found to be NC No. 4.