In-nozzle flow characteristics of superheated ethanol mixture

Abstract

Structural failure of storage tanks can result in the accidental release of superheated hazardous chemicals, causing catastrophic consequences. This study utilized a 20 L storage tank and a transparent nozzle to simulate the release process using pure water mixed with ethanol as the medium. The morphological characteristics of the two-phase flow of the flash jet, both inside and downstream of the nozzle, were analyzed using a capacitance sensor and high-speed imaging under storage temperatures (T_st = 110-150°C), storage pressures (P_st = 6-16 bar), and nozzle sizes (D= 1-6 mm). The results indicate that as the ethanol volume fraction increases, the physical properties of the superheated liquid-such as density and surface tension-decline, and the viscosity increases slightly. This reduces the energy required for gas nuclei within the nozzle to overcome surface tension forces. Consequently, smaller, denser bubbles are formed, leading to more intense jet fragmentation and atomization. Moreover, increasing superheat, storage pressure or nozzle size further amplifies bubble nucleation rates, jet radial expansion rates and break-up atomization, while significantly reducing droplet diameter. Finally, this study revises the void fraction criterion for the flash vaporization mechanism: external flashing (α = 0), internal flashing (0 < α < 23) and full flashing (α > 23).