The spontaneously condensing phenomena in a steam-jet pump and its influence on the numerical simulation accuracy Wang Xiao-Dong a,⇑ , Lei Hong-Jian a , Dong Jing-Liang a,b , Tu Ji-yuan b a School of Mechanical Engineering & Automation, Northeastern University, Shenyang 110819, PR China b School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Victoria 3083, Australia article info Article history: Received 12 October 2011 Received in revised form 12 April 2012 Accepted 14 April 2012 Available online 15 May 2012 Keywords: Steam-jet pump Transonic flow Spontaneous condensation CFD modelling Numerical simulation abstract A wet steam model for transonic flow was proposed to investigate the flow behaviours in a steam-jet pump. Contrary to the general ideal gas assumption adopted by the most of the researches focusing on steam-jet pump investigation, the numerical simulation using this wet steam model that was imple- mented based on a commercial computational fluid dynamics code, and the simulation results demon- strated the existence of the spontaneous condensation as the supersonic flow passing through the nozzle. Our results also gave good agreement with the referenced experimental data, and with higher accuracy when comparing with the results generated from ideal gas modelling. The present study con- firms that the simulation accuracy can be improved by the wet steam modelling, and gives a proper pre- diction of pump operating status. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Steam-jet pump is one of the important equipments that is widely used in chemistry, petroleum, metallurgy, refrigeration, and food industry to obtain a vacuum environment for special pur- poses. As shown in Fig. 1, a typical steam-jet pump consists of a nozzle, a mixing chamber, throat and a diffuser based on the con- figuration from Ref. [1]. Its axial pressure and velocity distribution profiles are also described in this diagram. First, the primary fluid, which is steam with high pressure (0.3  1.6 MPa) is accelerated to supersonic speed through the converging-diverging nozzle. Then, a low pressure area is established at the downstream region of the nozzle outlet. The secondary fluid is entrained into the mixing chamber and accelerated up by the primary fluid. After a mixing process that is accompanied by energy and momentum exchanging between these two types of fluid, a normal shock wave occurs in the throat, and the velocity of the mixing fluid suddenly drops to a subsonic value. Finally, the mixed fluid is exhausted from the dif- fuser by a further compression. The pumping performance of a steam-jet pump can be described by entrainment ratio (E m , the ratio of mass flow rate of secondary fluid to that of primary fluid), which is affected by pressure ratio (K, the ratio of back pressure to the suction pressure) and expanding ratio (B, the ratio of primary fluid pressure to the secondary fluid pressure). One-dimension mathematical models based on constant pressure mixing theory were proposed to calculate the perfor- mance of steam-jet pump [2,3]. Though the models are simplified, the expression are complex and the thermo-properties, transporta- tion properties need to be determined experimentally, which limits their applications. The mixing flow structure is complicated in a steam-jet pump due to the transonic flow and it is difficult to be described by the classical mathematical methods mentioned above. Computational fluid dynamics (CFD) is a good choice as a research tool to investi- gate and predict the complicated flow behavior in steam-jet pump. According to the performance profile versus operating back pressure of a steam-jet pump [3], which is shown in Fig. 2, the pump operating status can be divided into three stages: critical mode, subcritical mode and malfunction. When the outlet pressure of the pump P b is below its critical value P  b , the secondary flow is choked in the mixing chamber. Therefore, the entrainment value E m , which is the mass flow rate ratio of the secondary fluid to the primary fluid, remains constant. However, if P b is raised higher than P  b , the secondary flow becomes unchoked, and the value of E m decreases rapidly. When the value of P b is greater than the revers- ing pressure P r b , the high back pressure jeopardizes the entrain- ment process of the pump, which leads to reversed flow in the mixing chamber. In order to maintain a steady pumping perfor- mance, the steam-jet pump should be operated within the range of its critical mode. As a result, predicting the performance profile of the pump for its critical value P  b with high accuracy plays a crit- ical role in its theoretical analysis and engineering applications. 0017-9310/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2012.04.028 ⇑ Corresponding author. Address: Vacuum and Fluid Research Center, Northeastern University, Shenyang 110819, PR China. Tel.: +86 24 8368 7618; fax: +86 24 8368 0459. E-mail address: xdwang@mail.neu.edu.cn (X.-D. Wang). International Journal of Heat and Mass Transfer 55 (2012) 4682–4687 Contents lists available at SciVerse ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt