There is limited studies, nonetheless, on the modelling, quantifica- tion of particle shape and its effects on hydrocyclone performance (Table 2). Endoh et al. employed all types of particle shape, including spherical, irregular, and plate, with aspect ratio. He found that, compared with bulky particles, the dynamic properties of flaky particles in hydrocyclones depended significantly on the particle shape, suggesting that the shape separation of fine particles by hydrocyclones is possible. Kashiwaya et al. evaluated the classification behavior of spherical particles (glass sphere), plate-like particles (PTFE and glass flake) and block-shaped particles (quartz) by using hydrocyclones and a cyclosizer, that is, a particle size distribution analyzer with five hy- drocyclones. He found that, with the ratio of particle diameter to thickness increasing, the drag coefficient increased. Zhu and Liow estimated irregular and spherical particles with the approximate value of the degree of true sphericity, φ, (Eq. (2)) by using scan- ning electron microscope (SEM). Results demonstrated that non-sphe- rical particles were separated less efficiently than spherical particles. Abdollahzadeh et al. have investigated the effects of Wadell shape factor, that is, the degree of true sphericity, ψ, on the separation performance of mini-hydrocyclone by adopting SEM and BET (specific surface area testing instrument) together with MIP software. Results indicated that the increase of Wadell shape factor increased the se- paration efficiency of hydrocyclones considerably, which ex- hibited good agreement with the results reported by Zhu and Liow.Traditionally, the particle shape is expressed by 1–2 shape factors. However, in fact, there are many shape factors and hence which shape factors were the most appropriate for depicting particle shape should be a key problem. Bouwman et al. compared nine shape factors including the aspect ratio, circularity, new projection shape factor, shape factor eR, radial shape factor, one-plane-critical-stability, stokes’ shape factor, new mass shape factor, and new roughness factor. They found that, among the aforementioned factors, both the new projection shape factor and circularity worked extremely well for their particles. Zhang et al. proposed an approach to utilize principal component analysis (PCA) to derive latent shape factors from microscope images of particles. Their method, PCA, could be employed to analyze 2-D and 3- D images.In summary, to obtain effects of feed particle shape on separation performance of hydrocyclones, it is required to describe or express the arbitrary shape of particles as accurately as possible. Thereby, as the development of novel technologies, more effective shape factors or shape-factor combinations should be developed, optimized, and se- lected to explore the above-mentioned effects of feed particle shape as accurately and comprehensively as possible.