J Ther Eng, Vol. 7, No. 5, pp. 1090–1099, July, 2021 ABSTRACT Flow behaviour and thermal separation mechanism on vortex tubes have been studied numer- ically. Rapid expansion indicated by high-pressure gradient near the inlet and the exit ports contributes to energy separation on the parallel and the counter fow vortex tubes. It creates a cooling process at the core region and drives an internal and rotational energy transfer to the peripheral region, then increases the gas temperature at the periphery along with friction due to the presence of the confned wall. Static temperature is related to static pressure in such a way that low pressure leads to the low static temperature at the same region inside the vortex tube. On the other hand, the high total temperature is found in the region with the low dynamic velocity. For both vortex tubes, the fow felds are mainly governed by the tangential velocity at the periphery and by the axial velocity at the core region. Te maximum Mach number values based on the maximum tangential velocities in the inlet area for the counter and the parallel fow vortex tubes are 0.689 and 0.726, respectively, so both are compressible and subsonic fows. For the same size of geometry and boundary conditions, the parallel fow vortex tube has higher COP than the counter flow vortex tube i.e. 0.26 and 0.25, respectively. Cite this article as: Noor DZ, Mirmanto H, Sarsetiyanto J, Soedjono DME. Flow behavior and thermal separation mechanism on vortex tube. J Ther Eng 2021;7(5):1090–1099. Journal of Termal Engineering Web page info: https://jten.yildiz.edu.tr DOI: 10.14744/jten.2021.0005 Research Article Flow behavior and thermal separation mechanism on vortex tube Dedy zulhidayat NOOR 1 * , Heru MIRMANTO 1 , Joko SARSETIYANTO 1 , Denny M.E.SOEDJONO 1 1 Department of Industrial Mechanical Engineering, Sepuluh Nopember Institute of Technology, Surabaya, Indonesia ARTICLE INFO Article history Received: 02 July 2019 Accepted: 08 October 2019 Key words: Vortex tube; Flow feld; Termal separation; Numerical study INTRODUCTION A vortex tube is a thermal-mechanical device that splits an inlet compressed gas into two streams at the outlet with higher and lower temperatures than the inlet one. It has no moving parts, electrical and chemical processes involved which make its maintenance is free, simple operation and durable, furthermore allowed the use of vortex tube in many engineering applications. Te thermal separation phenomena in the vortex tube werefrstly introduced by Ranque [1]. More detailed experimental work then carried out by Hilsch [2] to confrm this phenomenon and then it is well-known as Ranque-Hilsch Vortex Tube (RHVT). *Corresponding author. *E-mail address: zulnoor@me.its.ac.id This paper was recommended for publication in revised form by Regional Editor Jovana Radulovic Published by Yıldız Technical University Press, İstanbul, Turkey Copyright 2021, Yıldız Technical University. Tis is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).