Influences of confinement on subatmospheric water vaporization phenomena in a vertical rectangular channel

摘要

The influence of confinement on water vaporization phenomena occurring close to the triple point in a vertical rectangular channel of 0.2 m x 0.5 m is investigated. The influence of the driving pressure, the operating pressure and the filling ratio on flow boiling and on time-averaged overall heat transfer depending on the channel thickness is introduced and discussed. It is shown that three main different phenomena at the top of the bubbles occurred depending on the confinement number and on water vaporization production rate: dendrites, evaporation waves and curved interface. Entrainment of droplets by the vapour flow was also observed for the highest confinement number investigated (Co = 0.69). These different phenomena observed impact the heat transfer leading to higher performances for a confinement number of 0.69 compared to confinement number of 0.35 and 0.23 for rate of vapour production obtained at high driving pressures and low filling ratio but also for operating conditions obtained at low driving pressure and high filing ratio. (C) 2019 Elsevier Ltd. All rights reserved.