Multiple-effect distillation

[1] Additionally, between stages this steam uses some heat to preheat incoming saline water.

Then the pressure is too low or the temperature too high in the first subspace, and the water evaporates.

At the second subspace the energy flows by conduction through the tube walls to the colder next space.

For sea water desalination, even the first and warmest stage is typically operated at a temperature below 70-75 °C, to avoid scale formation.

[3] The lowest pressure stages need relatively more surface area to achieve the same energy transport across the tube walls.

Gases dissolved in the feed water may contribute to reducing the pressure differentials if they are allowed to accumulate in the stages.