Numerical simulation of two-dimensional kettle reboiler shell side thermal–hydraulics with swell level and liquid mass inventory prediction Blazenka Maslovaric a , Vladimir D. Stevanovic a,⇑ , Sanja Milivojevic b a Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11120 Belgrade, Serbia b Innovation Center of the Faculty of Mechanical Engineering, University of Belgrade, Kraljice Marije 16, 11120 Belgrade, Serbia article info Article history: Received 28 November 2013 Received in revised form 20 March 2014 Accepted 20 March 2014 Available online 18 April 2014 Keywords: Two-fluid model Kettle reboiler Swell level abstract Simulation and analyses of two-phase flows across tube bundles is important for design and safety anal- yses of various types of steam generators and kettle reboilers. The information about the shell side ther- mal–hydraulics in this thermal equipment should include the liquid and vapour two-phase flow velocity fields, the void fraction distribution, as well as the swell level position and the liquid mass inventory. The two-fluid model of boiling two-phase flow around tubes in the bundle is applied for the simulation of the kettle reboiler shell side thermal–hydraulics. The tube bundle is modelled as a porous medium. Transfer processes at the vapour–liquid interfaces and on the tube walls are predicted with closure laws. The model is numerically solved by the ‘‘in-house’’ CFD code. The applied modelling method is validated against measured data of pressure drops in refrigerant R113 and n-pentane two-phase flows across tube rows in the bundle of a thin slice kettle reboiler, which are available in the open literature. The swell level position on the shell side is calculated solely by solving of the two-phase flow governing equations and with the application of an appropriate closure law for the vapour–liquid drag force, which enables the prediction of the liquid separation due to gravity from the upward flowing two-phase mixture. This is an improvement on the thermal–hydraulic modelling and numerical simulation of the kettle reboiler since the previous numerical simulations from the open literature have been performed with a priori specified swell level position and arbitrary boundary conditions for the velocity (or pressure) and void fraction boundary conditions at the swell level. The prediction of the swell level position also enables the calculation of the liquid mass inventory on the shell side, which gives insight into the kettle reboiler operating conditions and is crucial for the reliable prediction of the tube bundle dry-out during incidents of liquid feeding stoppage. There is a one-to-one correspondence between the liquid mass inventory and the swell level position. The presented simulation method enables iterative prediction of the liquid mass inventory for the specified swell level position and vice versa. In addition, the correlations for the liquid– vapour interfacial drag coefficient, which have shown previously fairly good predictions in cases of water–steam and water–air two-phase flows, are extended for the general application to other fluids. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The vapour–liquid two-phase flow on the shell side of the kettle reboiler has been a topic of research for decades with the aim of providing reliable design methods for this type of shell-and-tube heat exchangers with vapour generation [1]. In addition, results obtained at the scaled experimental facilities of the kettle reboilers improve the knowledge about the boiling two-phase flows across tube bundles, which is important for the design and safety of other vapour generators with boiling on the heated tubes in a bundle submerged in a liquid pool, such as horizontal steam generators in nuclear power plants [2,3] or fire-tube shell boilers [4]. The pre- diction of vapour void fraction distribution and the two-phase flow mass flux in the tube bundle and in the pool around the bundle is a crucial step in design and analysis of the kettle reboiler, the steam generator or the shell boiler operation. The void fraction distribu- tion, for instance, determines the boiling heat transfer, the liquid inventory on the shell side and the swell level position [5]. Namely, high values of the void fraction can lead to the dry-out of the heated tubes and a reduction of the heat transfer area. The http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.03.064 0017-9310/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +381 11 3370561; fax: +381 11 3370364. E-mail addresses: bmaslovaric@mas.bg.ac.rs (B. Maslovaric), vstevanovic@ mas.bg.ac.rs (V.D. Stevanovic), smilivojevic@mas.bg.ac.rs (S. Milivojevic). International Journal of Heat and Mass Transfer 75 (2014) 109–121 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt