Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur Influence of the dipleg shape on the performance of gas cyclones Farzad Parvaz a , Seyyed Hossein Hosseini b, ⁎ , Khairy Elsayed c,d , Goodarz Ahmadi e a Department of Mechanical Engineering, Semnan University, P.O. Box 35131-191, Semnan, Iran b Department of Chemical Engineering, Ilam University, Ilam 69315–516, Iran c Mechanical Power Engineering Department, Faculty of Engineering at El-Mattaria, Helwan Uinversity, Masaken El-Helmia P.O., Cairo 11718, Egypt d Mechanical Engineering Department, College of Engineering and Technology-Smart Village Campus, Arab Academy for Science, Technology and Maritime Transport (AASTMT), P.O. Box 12676, Giza, Egypt e Department of Mechanical and Aeronautical Engineering, Clarkson University, Potsdam, NY 13699-5725, USA ARTICLE INFO Keywords: CFD Gas cyclone Dipleg shape Pressure drop Performance ABSTRACT The influence of dipleg shape on the flow pattern and performance of gas-solid cyclone was investigated. Different diplegs including cylindrical, inverted cone, conical, and diamond were studied. Due to the turbulent nature of the flow in the cyclone, the RSM turbulence model was used in the simulations. It was found that the mean tangential velocity in the cyclone for different dipleg geometries were about 1–1.2 times the inlet velocity, while the maximum tangential velocity was 1.7 times the inlet velocity. In addition, the tangential velocity in the cylindrical dipleg was greater than those of the other dipleg models. Changes in the dipleg shape significantly affect the axial velocity in the dustbin. The maximum axial velocity was observed in the vortex finder region and the entrance region of the dipleg for different models. It was also found that the dipleg geometry significantly affected the cyclone pressure drop. The cylindrical dipleg generated the highest pressure drop, whereas the lowest pressure drop was seen for the cyclone without dipleg. Among the studied geometries, the highest effi- ciency was found for the cyclone with conical dipleg and the diamond dipleg led to the lowest efficiency. Finally, the influence of constant parameter of the eddy lifetime model on the turbulent dispersion of particles and the corresponding cyclone performance was studied. 1. Introduction The physical nature of air contaminants typically consists of two groups, namely, particles and gaseous pollutants. It is well-known that the air quality plays an important role in human health, as well as, performance. In particular, exposure to particulate contaminant leads to serious respiratory and cardiovascular diseases and thereby in- creasing mortality [1–3]. Most industries generate particulate pollu- tants in their processes that need to be removed from the gas before exhausting into the atmosphere. Gas cyclones separator are used ex- tensively in many industries to separate the particles from the gas flow using the centrifugal force. In addition to being economical, gas cy- clones have simple design and are compatible with different industrial applications. The gas flows inside cyclones, however, are quite com- plex, highly three dimensional with strong rotational patterns [4], the nature of which are not as yet fully understood. The larger and denser particles tend to move toward the cyclone wall due to the action of the centrifugal force and are eventually removed from the airflow. The smaller and lighter particles remain suspended in the spinning airflow. Therefore, the airflow field is an important parameter affecting the cyclone efficiency [5]. Numerous investigations that have been carried out on gas-particle flows in cyclones can be classified into four categories: experimental, analytical, statistical and numerical. Advanced experimental tools used for measurement of airflow parameters through cyclones include Laser Doppler Anemometry (LDA) [6,7] and Particle Image Velocimetry (PIV) [8–10]. Analytical and semi-analytical models for airflow and particle transport in cyclones using simplifying assumptions were reported in [11–18]. These models are associated with low computing cost but lead to outcomes with low accuracy. The statistical regression-based models that cover a wide range of experimental data for examining the effects of geometrical parameters of a cyclone was reported in [19] among others. Along with progresses in the measurement tools for analyzing fluid flow in different applications, the numerical methods have been sig- nificantly improved in both solution algorithm and computer hardware in the recent years. Many researchers have studied the effects of changes in design and dimensions of cyclone geometry on their internal https://doi.org/10.1016/j.seppur.2019.116000 Received 8 May 2019; Received in revised form 24 July 2019; Accepted 28 August 2019 ⁎ Corresponding author. E-mail address: s.h.hosseini@ilam.ac.ir (S.H. Hosseini). Separation and Purification Technology 233 (2020) 116000 Available online 29 August 2019 1383-5866/ © 2019 Elsevier B.V. All rights reserved. T