Experimental Parametric Study of Droplet Rapid Boiling in Immiscible Liquid

The process of rapid boiling of a two phase droplet rising in an immiscible liquid environment has been experimentally considered within a new range of superheats (normalized Jacob number, 0.2< $Ja˜$ <0.5). In the course of the research numerous water-column boiling experiments were conducted for liquid propane droplets in a water environment. Boiling was generally calm and very rapid, concluding within several milliseconds, due to high heat fluxes across the interface. This work deals with the effect of various initial conditions on this distinctive boiling process. The parameters considered, are: the host liquid temperature, background pressure, initial droplet size and the size of the vapor nucleus inside the droplet. Their separate and combined effects have been recognized, and a correction factor based on initial droplet and bubble size is proposed. Through the parametric study the limits of rapid boiling have been approximately defined — between explosive and slow “conduction” boiling. In all experiments considered mass boiling rate is given by a function of the normalized Jacob number $Ja˜$ and the correction factor, to good agreement. Furthermore, due to the special nature of this boiling process, by use of the proposed factor the rapid boiling curve may be predicted for a wide range of initial conditions, for liquid propane or similar hydrocarbons. This allows design of a rapid boiling curve for a required application. Suggested applications range from alternative marine propulsion, to rapid direct-contact heat exchange.