Explosive Boiling of a Depressurized Volatile Liquid

Summary

The explosive boiling that occurs when a pressure-liquefied gas is suddenly vented to the atmosphere has been investigated experimentally at small scale. The test liquid (refrigerant-22), initially in equilibrium with its vapor, is suddenly depressurized by bursting a foil diaphragm. The competition between the rates of vaporization and venting can lead to substantial repressurization within the vessel. The influence of vent area, liquid fill volume, and initial pressure on the amount of repressurization has been studied in a small (260 ml) steel vessel as well as in a 75 ml glass tube. The time for repressurization is typically more than an order of magnitude larger than the time for the initial pressure drop. The amount of repressurization is found to be proportional to the pressure drop which determines the degree of superheat attained by the liquid. Repressurization within both vessels reaches a maximum value over a range of initial pressures that is independent of the initial liquid fill volume and vessel geometry. High-speed photography shows that the mode of nucleation is dependent on the surface condition of the vessel walls and the initial vapor pressure. With the steel vessel, heterogeneous boiling from the side walls dominates. With the glass tube, for initial pressures less that 1 MPa, an evaporation wave propagates (at a speed ∼0.15 m/s) from the free surface whereas for higher initial pressures heterogeneous boiling from the tube walls also occurs.