An experimental study of dynamic flashing in a square tube using tap water

Abstract

Flashing is a pressure driven phase change phenomenon. It is widely studied due to its richness in physics and applications such as in desalination, in nuclear industry to name a few. Dynamic flashing is a situation wherein the pressure drop for flashing is initiated through the flow of liquid. A recently developed novel desalination system [1] utilizes combined dynamic flashing and vapor separation through tangential injection for producing potable water. An understanding of dynamic flashing in a tube with reference to the novel desalination system could help with its optimization. In this work, dynamic flashing of tap water occurring in a clear quartz square tube was studied. The pressure and temperature measurements along the tube were made and analyzed for different inlet flowrates and initial liquid temperatures. The pressure and temperature values showed increasing gradients along the tube indicating increased vapor production or flashing for increasing flowrates and initial liquid temperatures. The vapor production from flashing and the resulting flow regimes along the tube were tracked and identified through high-speed imaging. Visual observations showed complex flow regimes with bubbles nucleating and growing throughout the tube due to flashing. Most of the bubble formation was observed in the bulk with little nucleation on the glass tube wall. Void fraction measurements along the tube based on capacitance impedance technique were performed to supplement the visual observations which showed increasing void fraction along the tube matching the observed flow regimes from vapor production.