Evaluating velocity and temperature ﬁelds for RanqueHilsch vortex tube using numerical simulation Ahmad M. Alsaghir, Mohammad O. Hamdan, Mehmet F. Orhan* Department of Mechanical Engineering, American University of Sharjah, P.O. Box: 26666, Sharjah, United Arab Emirates ARTICLE INFO Article History: Received 1 February 2021 Revised 17 February 2021 Accepted 23 February 2021 Available online 2 March 2021 ABSTRACT In this study, a three-dimensional numerical investigation is carried out to study the ﬂow ﬁeld inside a Ran- que-Hilsch vortex tube (RHVT) model. Flow parameters such as velocity, temperature, and pressure are plot- ted at various locations inside the tube. The study reports the effect of cold mass fraction on the energy separation of vortex tube . The results show that the ﬂow inside RHVT consists of a free vortex from r/R=0 to 0.9 and a force vortex from r/R=0.9 to 1 and that heat transfer occurs from the inner core to the periphery of the tube. Furthermore, it is observed that the minimum cold temperature and the maximum hot temperature are achieved at different mass fractions, 0.19 and 0.8, respectively. © 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Vortex tube ﬂow ﬁeld Flow structure inside vortex tube Energy separation Turbulence modeling of vortex tube 1. Introduction Thermal management is achieved using different tools such as heat exchanger [1], vortex tube [2], ﬁns [3], heat pipes [4] and phase change material [5]. A vortex tube (VT) is a thermo-ﬂuidic device that is capable of splitting a pressurized ﬂuid into hot and cold currents simultaneously, without any moving parts or chemical reactions. It was accidently discovered by a French scientist in 1933 [6]. In 1947, a German scientist modiﬁed the structural parameters of the tube to improve its performance [7]. VT consists of inlet nozzles where ﬂuid is admitted in a tangential manner (known as vortex generator), a strait tube, a cold oriﬁce, and a hot oriﬁce with a control valve to adjust the mass ﬂow fractions. VT has a wide range of spot cooling applications. For instance, it is used for cooling milling machining to preserve the properties of the work piece and protect the cutting tools [8,9], cooling the working suits of mines workers [10], solidli- quid separators [11], convex mirror cooling [12] or other air-condi- tioning systems [13]. Shmroukh et al. [14] have reported the feasibility of using a vortex tube in water desalination. Currently, there is no consensus on how the energy separation effect in VT takes place. Nonetheless, many theories have been pro- posed to explain this phenomenon [1517]. For instance, the viscous shear theory suggests that the angular velocity increases towards the center and tends to conserve the angular momentum of the ﬂuid, which in turn transfers the excess kinetic energy to the periphery of the tube through the shear force [15,16]. Another theory has proposed [17] that the cause of temperature difference is a phenome- non named “acoustic streaming”. This phenomenon relates the acoustics waves generated at the hot outlet to the formation of some secondary ﬂows and turbulent eddies inside the tube. Hilsh’s modiﬁcations [7] and the advantages of VT have motivated the scientiﬁc community to look for further ways to improve its oper- ating efﬁciency. Many experimental and numerical studies have been carried out to investigate the effect of the structural parameters as well as the operating conditions on the performance of the vortex tube. Hamdan et al. [2] have experimentally investigated the effect of 4 different design parameters, namely (1) inlet pressure, (2) tube length, (3) tube diameter, and (4) tube tapered angle, on the perfor- mance of the vortex tube. It was reported that the inlet pressures rise achieves a greater temperature difference until a peak value, after which the performance starts to deteriorate [2]. It was suggested that the performance deterioration occurs due to the inlet nozzles choked condition. The effect of tube’s roughness has been investigated by Parulekar [18] and it was reported that the efﬁciency of VT decreases as the tube’s roughness increases. Eiamsa-ard et al. [19] have investi- gated the effect of number of inlet nozzles on the temperature sepa- ration. The measurements showed that the energy separation increases with more nozzles and this improvement has been referred to the increase in the swirl intensity. Similar results have been reported by Dincer et al. [20] who have stated that the efﬁciency of the vortex tube with 4 and 6 inlet nozzles are better than with 2 inlet nozzles. Beside the number of nozzles, their size also has a great effect on the separation. Mohammadi et al. [21] have revealed that a smaller nozzle area results in a higher separation magnitude. Also, Celik et al. * Corresponding author. E-mail addresses: b00079096@aus.edu (A.M. Alsaghir), mhamdan@aus.edu (M.O. Hamdan), morhan@aus.edu (M.F. Orhan). https://doi.org/10.1016/j.ijft.2021.100074 2666-2027/© 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) International Journal of Thermoﬂuids 10 (2021) 100074 Contents lists available at ScienceDirect International Journal of Thermoﬂuids journal homepage: www.elsevier.com/locate/ijtf