The characteristics of the sea water flow in multi-stage flash (MSF) desalination devices were simulated via numerical method. Two applications were presented and compared with each other: one with four block-boards installed in each flash chamber

and the other without. The simulation showed that the large-scale circulations and vortices in the water flow would cause the exchange of fluid between upper and lower layers

which was favorable to flash efficiency. On the other hand

turbulence can enhance the exchange in the vicinity of free surface. The rationally-arranged block boards in the flash chamber would improve the structure of the circulations and vortices

so as to promote the exchange between upper and lower layers

but they would cause loss and reduce turbulence. A discussion about the optimal design of flash chamber was presented.