# CFD Investigations of Cyclone Separators with Different Cone Heights and Shapes
## 4 Conclusions  
In the present study, unsteady simulations were performed using RSM as a closure model to RANS. The airflow was simulated over the stationary grids, whereas the solid particles were tracked using the Lagrangian approach. Hence, we made use of the Eulerian-Lagrangian approach to model the cyclonic flow field. Nine cyclone models were simulated at three different inlet velocities viz. \(U_{in}\) = 10 m/s, 15 m/s, and 20 m/s--thus, a total of twenty-seven cases were simulated. We considered three cyclone variants viz. a straight wall of the conical section as in the conventional cyclone design (referred to as ST variant), a curved wall with convex profile (referred to as CV variant), and a curved wall with concave profile (referred to as CC variant)--the convex and concave terminology was adopted with reference to an observer outside the cyclone structure. Furthermore, three different lengths of the cylindrical section were considered in all the three cyclone variants keeping the total cyclone length a constant.  
Based on the analysis of the obtained results, the following conclusions were defined:  
* With the increase in inlet velocity:
* Pressure drop increased significantly in all cyclone variants.
* Cut-off particle size reduced tremendously.
* Collection efficiency increased by a large amount.
* With an increase in the length of the cylindrical section:
* Pressure drop was reduced in all the cyclone variants.
* Cut-off particle size increased mildly.
* Collection efficiency reduced by a marginal amount.
* With wall profile:
* Pressure drop was the lowest in models 1 and 2 of the CV, particularly at \(U_{in}\) = 10 m/s, and 15 m/s. At \(U_{in}\) = 20 m/s, pressure drop was the largest in CV variants, and at \(U_{in}\) = 10 m/s, and 15 m/s, as compared with the ST variant, the variations were moderate.
* Cut-off particle size showed a mild variation at a given \(U_{in}\). The cut-off size was largest in CV variants, whereas this size was comparable in ST and CC variants.
* Collection efficiency increased by a marginal amount in the CC variant and was minimum in the CV variant.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \begin{tabular}{c} **Cyclone** \\ **Variants** \\ \end{tabular} & \
\begin{tabular}{c} **Cyclone** \\ **Models** \\ \end{tabular} &
\begin{tabular}{c} **\% Change in Overall Separation Efficiency * \\ \end{tabular} & \multicolumn{3}{c}{**\% Change in Cut-Off Diameter * ** \\ \hline \multirow{4}{*}{ST} & ST1 & 0.73 & 2.36 & 2.45 & \(-\)2.16 & \(-\)2.95 & \(-\)2.14 \\  & ST2 & – & – & – & – & – & – \\  & ST3 & \(-\)2.37 & \(-\)2.17 & \(-\)2.66 & 3.30 & 1.91 & 1.77 \\  & CV1 & \(-\)0.31 & 5.19 & \(-\)1.78 & 0.36 & \(-\)2.31 & 3.35 \\  & CV2 & \(-\)1.69 & 3.16 & \(-\)1.74 & 1.26 & 4.55 & 8.93 \\  & CV3 & 1.55 & 6.77 & \(-\)0.24 & 1.98 & 6.54 & 13.67 \\  & CC1 & 0.89 & 5.98 & 4.13 & \(-\)7.02 & \(-\)4.47 & 1.30 \\ CC & CC2 & \(-\)1.25 & 3.40 & 1.10 & \(-\)1.74 & 0.56 & 5.21 \\  & CC3 & \(-\)0.52 & 3.60 & \(-\)3.55 & 1.92 & 6.38 & 10.88 \\ \hline \hline \end{tabular}  
* \(\%\) Change w.r.t. the standard cyclone model ST2.  
\end{table}
Table 3: Percent change in overall separation efficiency and cut-off diameter at different \(U_{in}\).  
**Author Contributions:** Conceptualization, L.S.B.; methodology, L.S.B. and M.W.; software, S.P., I.S., O.P., T.M., L.S.B. and M.W.; validation, S.P. and M.W.; formal analysis, M.W.; investigation, S.P., L.S.B. and M.W.; resources, S.P., I.S., O.P. and T.M.; data curation, S.P., L.S.B., M.W., J.I. and A.K.R.; writing--original draft preparation, S.P., L.S.B. and M.W.; writing--review and editing, S.P., L.S.B., M.W., L.S.B., J.I. and A.K.R.; visualization, S.P., L.S.B. and M.W.; supervision, L.S.B., and M.W.; project administration, L.S.B. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.