Some experimental observations on the single and multi-phase flow patternsin a model flash evaporation chamber

Flow characteristics inside a model flash evaporation chamber for Multi-sta ge Flash (MSF) desalination have been investigated using Particle Image Vel ocimetry (PIV). The back flow region near the inlet gate, the free water su rface shape, and the overall velocity distribution were measured so as to i dentify the characteristics of the now pattern at different water levels in the chamber. The results show that a large recirculation region with sever al vortices embedded would be generated at a higher water level (approximat ely twice the inlet gate height). The water level remained uniform in spite of the presence of the vortices. Three flash evaporation modes at differen t superheats of the water in the flash chamber were also studied using a hi gh speed CCD camera. The bubble behaviors such as the size, velocity, and g rowth rate were estimated and analyzed. It was found that the multi-phase f low pattern during the flash evaporation was mainly determined by the liqui d superheat and the nuclei distribution. (C) 1999 Elsevier Science Ltd.