After leaving the first stage condenser, the seawater flows through the brine heater, where the heat input to the plant (steam or engine jacket water) causes a further temperature increase.
The seawater leaves the brine heater and enters the first flash chamber, reaching a brine top temperature of approx. 80°C. At this point the pressure of the incoming seawater is suddenly reduced, by means of an orifice, below its equilibrium vapour pressure resulting in explosive boiling or evaporation (flashing).
The pure vapour produced is then condensed giving up its latent heat to preheat the incoming seawater. If this process is repeated over a large number of effects, at successively lower pressures and temperatures, large distillate production rates at reasonable performance ratios can be achieved.