This paper studies the liquid-to-vapor phase transition in a cone-shaped nozzle. Using the geometric method presented in [P. Szmolyan and M. Wechselberger, we further develop results on subsonic and supersonic evaporation waves in [H. Fan and X.-B. Lin, SIAM J. Math. Anal., 44 (2012), pp. 405-436] to transonic waves. It is known that transonic waves do not exist if restricted solely to the slow system on the slow manifolds [H. Fan and X.-B. Lin, SIAM J. Math. Anal., 44 (2012), pp. 405-436]. Thus we consider the existence of transonic waves that include layer solutions of the fast system that cross or connect to the sonic surface. In particular, we are able to show the existence and uniqueness of evaporation waves that cross from supersonic to subsonic regions and evaporation waves that connect from the subsonic region to the sonic surface and then continue onto the supersonic branch via the slow flow.
Introduction.In this paper, we investigate the liquid-to-vapor phase transition in a spherically symmetric cone-shaped nozzle. Subsonic evaporation processes, such as fuel injection into a combustion engine, show up in many important engineering problems and are studied in many research laboratories around the world. The ring formation observed in a shock tube experiment [33] is an example of a supersonic process, as argued by Fan in [11]. Our focus is on transonic evaporation waves. While we are not aware of any experiments where transonic evaporation waves have been observed, we expect that our theoretical results might be useful in some physical and engineering process when the speed of the fluid in a nozzle approaches sonic speed.The study of nozzle flows was pioneered by Courant and Friedrichs [6] and Liu [26]. Transonic flow without liquid-gas phase transition has been studied by many authors; see the recent articles [3,5,4,23,35,36]. Among them [35] dealt with subsonic and subsonic-to-sonic flows through infinitely long nozzles. For transonic flows modeled by reaction-diffusion equations, Liu and coworkers [17,18,27] considered one-dimensional standing waves for a simplified model of gas flows in a nozzle with general variable cross-sectional area a(x). To the best of our knowledge, transonic flows that include a reaction-diffusion equation describing evaporation or condensation have not been rigorously analyzed mathematically.Liquid-vapor phase transitions have been much studied using a van der Waals pressure function [15]. The van der Waals model requires detailed modeling of the evaporation of individual droplets [8,30] or of the nucleation process by which vapor condenses. Figure 1(a) shows the graph of pressure p as a function of specific volume v