# CFD Investigations of Cyclone Separators with Different Cone Heights and Shapes
## 3 Results and Discussion
### Pressure Drop  
In the present study, the pressure drop is taken as the difference in the mean total pressure values at the inlet surface and outlet surface. This factor is proportional to the energy that a cyclone would require to operate. Higher pressure drop signifies large irreversible losses, and so, higher energy is required to make the fluid flow through the cyclone volume, and vice-versa. Since these devices operate continuously for a longer time in several applications, the proposed design must ensure low-pressure losses.  
Figure 7 presents the pressure drop values in the cyclone variants at different inlet velocities, categorized as variants. With an increase in the inlet velocity, pressure drop increases significantly. For a given cylinder length, in comparison with the ST variant, the pressure drop is lowest in models 1 and 2 of the CV variant, whereas in the CC variant all the models elucidate an increased pressure drop. At \(U_{in}\) = 10 m/s and 15 m/s, models 1 and 2 in the CV variant shows lower pressure losses than in the ST variant. Interestingly, for all \(U_{in}\), the pressure drop value in model 3 of the CV variant is greater than in the ST variant (as an exception, a similar observation also holds for the CV1 model at \(U_{in}\) = 20 m/s). This could be due to the larger cross-sectional area just above the downcomer tube in the CV  
Figure 6: From left to right: the radial profiles at z/D = 1.0, 2.0, and 3.0 of mean static pressure, mean axial velocity and mean tangential velocity (top to bottom), respectively, in different cyclone models.  
variant than in ST and CC variants--the area is the largest in model 3. Due to this, the flow experiences significant contraction over a small height (above the top connecting surface of the downcomer tube) that complicates the flow, particularly at higher inlet velocities. In contrast to the CV variant, the results are more consistent in the CC variant when compared with the ST variant. Here, at a given \(U_{in}\) and cylinder length, the pressure drop is larger in all the models in the CV variant than in the CC variant. Another important observation is that the pressure drop also reduces with an increase in the length of the cylindrical section at a given \(U_{in}\). A similar trend was found by [PERSON] et al. (2018) in their studies on effects of cylindrical and conical heights on pressure and velocity fields. Table 2 elucidates complete information on (percent change in) pressure drop with respect to the base variant model ST2, at different \(U_{in}\), in all models.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Cyclone Variants**} & \multirow{2}{*}{**Cyclone Models**} & \multicolumn{4}{c}{**\% Change in Pressure Drop \({}^{*}\)**} \\ \cline{3-5}  & & \(\mathbf{U_{in}}\) = 10 m/s & \(\mathbf{U_{in}}\) = 15 m/s & \(\mathbf{U_{in}}\) = 20 m/s \\ \hline \multirow{4}{*}{ST} & ST1 & 5.53 & 4.27 & 2.86 \\  & ST2 & – & – & – \\  & ST3 & \(-2.77\) & \(-2.63\) & \(-1.38\) \\ \cline{1-1}  & CV1 & \(-0.425\) & \(-1.00\) & \(18.55\) \\ \cline{1-1}  & CV2 & \(-2.55\) & \(-3.91\) & \(16.51\) \\ \cline{1-1}  & CV3 & \(15.11\) & \(14.35\) & \(22.12\) \\ \cline{1-1}  & CC1 & \(14.04\) & \(8.08\) & \(7.82\) \\ \cline{1-1}  & CC2 & \(3.83\) & \(1.91\) & \(1.94\) \\ \cline{1-1}  & CC3 & \(-0.85\) & \(-1.45\) & \(-0.87\) \\ \hline \hline \end{tabular} \({}^{*}\) % Change w.r.t. the standard cyclone model ST2.  
\end{table}
Table 2: Pressure drop at different inlet velocities.  
Figure 7: Pressure drop values in all the cyclone models of ST variant, CV variant and CC variant at inlet velocities, \(U_{in}\) = 10, 15 and 20 m/s.