# CFD Investigations of Cyclone Separators with Different Cone Heights and Shapes
## 1 Introduction
Compared to the widely used tangential inlet, a scroll-type inlet design attaching several subsidiary cyclones to the exterior of the cyclone body increased collection efficiency and significantly lowered the pressure drop [26]. The circular rod inserted at the centre of cyclones was reported to enhance cyclone performance [27]. The dipleg shape also affected the pressure drop and collection efficiency [28]--the pressure drop was highest observed in cylindrical dipleg, whereas the lowest pressure drop occurs in the cyclone without a dipleg. A cyclone separator with fin diameter ratios of 2/5 or porosity equal to 0.2 was recommended for lower pressure drops [29]. [PERSON] et al. [30] considered optimizing the performance of two-stage cyclones in series using response surface methodology and reported enhancement in the overall performance. A dynamic cyclonic classifier was employed to classify particles according to their sizes by [PERSON] et al. [31], wherein a rotating impeller was employed to improve the efficiency of the cyclone. Another classifier was proposed by [PERSON] et al. [32], in which three characteristic regions were used to capture solid particles based on the particle size. The novel slotted vortex finder was reported to enhance the cyclone performance by [PERSON] et al. [33]. [PERSON] et al. [34] designed a cyclone for indoor use to separate the pollens that may lead to severe allergies in humans. [PERSON] et al. [35] made use of cyclone separators for sampling black carbon. The cone tip diameter was found to have a mild effect on the cyclone performance [17; 36]. [PERSON] et al. [37] experimented on a lab-scale cyclone model with a diameter of 0.031 m to determine the pressure drop and collection efficiency. They reported a mild pressure drop as well as collection efficiency with a decrease in the cone tip diameter. However, [PERSON] et al. [38] (mentioned in [37]) stated that the cone was merely a carrier of separated solid particles, and that it does not have any influence on the cyclone performance. In a different study by [PERSON] and [PERSON] [39] and [PERSON] et al. [40], the cone was revealed to be an important entity in cyclones. With an increase in the cone length (thus the overall height of the cyclone is the same), the collection efficiency was found to increase, and vice versa--the cyclone model without the cone was reported to have the lowest collection efficiency. [PERSON] et al. (2016) reported that an increase in the length of the conical section significantly increases the collection efficiency than an increase in the length of the cylindrical section. Considering the studies performed so far on the conical section, it becomes apparent that the cone is one of the most important parts of the cyclone. However, it has also been observed that the impact of different shapes of the conical walls on cyclone performance has not been taken into account so far. Therefore, in this study, we consider studying the impact of the curved wall profile of the conical section rather than the straighter one (as in the conventional design) for analysis. Here, two different shapes viz. the cone with concave wall and the convex wall profiles are accounted for. The definition of convexity and concavity of the walls is in context to the observer exterior to the cyclone. A part of the convex profile and concave profile has been earlier analyzed by ([PERSON] and [PERSON], 2011) in hydrocyclone, and no such study has been undertaken in the context of the gas cyclones. Hence, the present study undertakes different shapes of the cone section. Apart from the different shapes of the cone section, the length of the cylindrical section is also included in this study to evaluate its impact on the different shapes of cone sections. In short, we consider three different lengths of the cylindrical section while three different shapes of the conical section viz. a conventional (straight) profile, concave profile, and convex profile for analysis.