Low-pressure-vaporization of free water – Characterization of the boiling regimes

• Detailed characterization of the low-pressure-vaporization process.
• Identification of two vaporization stages on of low-pressure-vaporization process.
• Identification of two boiling regimes in the 2nd stage of low-pressure-vaporization.
• The vaporization rate increases with the initial temperature and volume of the water.
• Superheating degree and specific vaporization rate are defined as process parameters.

This paper reports an experimental study for the detailed characterization of the low-pressure-vaporization (LPV) process of free water. For that purpose, an integrated analysis of the influences of the initial temperature Tw,0 and volume Vw,0 of the liquid water on the LPV process is made. The time evolutions of the water temperature and of the total pressure within the LPV chamber, for different initial conditions, were experimentally measured. The two stages of the LPV process and the respective regimes were identified and characterized, enhancing the current knowledge of the phenomena.The experimental set-up comprises two main components: the vaporization chamber (VC) and the depressurization system (DS). Part of the VC volume is occupied by an open container for the water, which is insulated from the VC walls. Two different containers were used having different surface areas and heights, both with a negligible heat capacity.The results obtained show that the process parameters studied, Tw,0 and Vw,0, have great influence on the superheating degree, and consequently on the LPV evolution, as well as on the total mass of the water vaporized. The identification and characterization of distinct boiling regimes in the second LPV stage allow a physically based optimization of the processes, such as enhanced heat removal or water vaporization existing in several industrial areas.