A GAS-DYNAMIC CHOKING PHENOMENON IN EARLY TIME INTENSE TRANSIENT CONDENSATION

Following the sudden contacting of vapor with a cold surface, transient condensation may take place with initially extremely high heat and mass fluxes. The initiation of condensation induces a flow of the vapor toward the interface and a rarefaction wave propagates into the vapor. The induced vapor velocity may be much larger than relative velocities associated with liquid jets or sprays that introduce the liquid into the vapor. The vapor reaching the surface has a reduced pressure and temperature owing to its adiabatic expansion in the rarefaction wave. In this paper we show that a previously unnoticed transient choking phenomenon may limit the early time condensation flux to levels below those predicted by the kinetic theory, particularly when the initial vapor condition is close to stagnant. In addition, we examine the relative importance of liquid phase thermal resistance and determine the time at which the condensation flux becomes dependent only upon the liquid phase resistance. These phenomena may be of importance in a number of applications such as the injection of cold liquid blanket material into the reaction vessel of inertial confinement fusion reactors or the spraying of cold water into vapor spaces (such as in PWR pressurizers).