Numerical modeling of dimethyl ether (DME) bubble growth and breakup

Abstract

A numerical program is written to simulate the process of vapor bubble growth with spherical symmetry from the thermodynamic critical radius in an initially uniformly superheated liquid. The program is validated by the experimental data of superheated water. The calculated results agree with those of experiments well. The program takes into account the variations of properties with temperature precisely to simulate the DME bubble growth under flash boiling conditions. Considering the influences of pressure, surface tension and viscous stress, the linear stability analysis method is adopted to deduce the dispersion equation to represent the disturbance development during the bubble growth, and a new criterion for bubble breakup is established. The results show the bubble becomes more unstable with the increase of bubble Weber number and void fraction, and that with the increase of bubble growth rate or the decrease of initial radius ration of droplet to bubble, the breakup time of bubble becomes shorter.dimethyl ether, flash boiling, bubble growth, instability, bubble breakupThe flash boiling spray has potential in improving engine performance since it can be used to promote the atomization of fuels with a larger spray cone angle and a smaller droplet Sauter Mean Diameter (SMD) and so on [1,2] . As a clean fuel with potential long-lasting resources, DME has been considered as a promising alternative fuel for compression-ignition engines in recent years. The low boiling point and high saturated vapor pressure nature make the DME spray undergo flash boiling at lower ambient pressure [3,4] . Therefore, the research on DME spray under flash boiling conditions is of great significance.As two stages of flash boiling spray, bubble growth and breakup [5] , are becoming more central to the deep understanding of the spray atomization under flash boiling conditions. So, a single bubble in the infinite liquid field is chosen as the investigated subject in this paper and a computational program is presented for the solution of DME bubble growth based on the one-dimensional mathematic model. In addition, the linear stability theory is applied to solve the instable problem during the DME bubble growth, and a more complete dispersion equation is obtained, which is helpful to improve the study on the atomization mechanism of flash boiling spray.

Effects of surface tension on bubble growth in an extensive uniformly superheated liquid

“…Strictly speaking, in uniformly superheated liquids, bubble growth can be divided into three stages [4]: the inertiacontrolled stage, the heat-controlled stage, and a transitional stage simultaneously controlled by both inertia and heat. The more general intermediate stage is fairly complex to analyze and there are few reports on it apart from that by Mikic et al [5].…”