Vaporization-induced overpressures

Elsworth D., B Voight, J Simmons, S Young and B Winkler, Vaporization-induced overpressures as a trigger for the hazardous collapse of lava domes, this volume, 2004. 

VAPORIZATION-INDUCED OVERPRESSURES AS A TRIGGER FOR THE HAZARDOUS COLLAPSE OF LAVA DOMES... 

On the basis of Fig. 5 from [9], Lc was defined as the location in the channel where the flow stops and the slug expands and then purges all the fluid out of the minichannel. Uq is the injection liquid velocity at the bottom of the minichannel and U the average two-phase flow evacuation velocity. Two terms were quantified the overpressure induced by the expansion of the vapor slug and the injection pressure minus the minichannel outlet pressure. 

While the unit operation evaporation, that is, the mass transfer from the liquid phase to the vapor phase, still possesses a direct connection with vacuum techniques, the connection of today s single mass crystallization from solution with vacuum techniques is only indirect. The techniques of vacuum cooling and vacuum evaporation are only the mostly used means for inducing the crystallization process. The reason for the dominant position of vacuum crystallization over classical surface cooling crystallization is the considerably reduced inclination to form incrustations. Vacuum crystallization is used in the low vacuum field down to 1 mbar. There are also applications in the overpressure field, although with increasing pressure the number of applications is reduced. In vacuum crystallization, one can find all the classical process control options used in the more familiar vacuum evaporation processes. However, an important difference to evaporation is the fact that the separation process is not concluded with the crystallization step. The suspension formed still has to be separated into crystal mass and mother liquor. Crystallization is therefore always associated with a mechanical separation process. The better this separation, the greater the purity of the crystallized masses. 

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