Water water everywhere and plenty of drops to drink. Researchers from MIT have found a way to passively convert seawater into drinking water using a setup so simple it seems too good to be true. Their device basically uses heat from the sun rays and a siphon. The apparatus produces more water and rejects more salt than other passive setups, it can generate five litres of water if the device is one square meter in size. All of this with no external energy. They have even tested the device in open water – and it works! Imagine hundreds of these devices floating on the ocean bringing drinking water to cities.
The heart of the team’s new design is a single stage that resembles a thin box, topped with a dark material that efficiently absorbs the heat of the sun. Inside, the box is separated into a top and bottom section. Water can flow through the top half, where the ceiling is lined with an evaporator layer that uses the sun’s heat to warm up and evaporate any water in direct contact. The water vapor is then funneled to the bottom half of the box, where a condensing layer air-cools the vapor into salt-free, drinkable liquid. The researchers set the entire box at a tilt within a larger, empty vessel, then attached a tube from the top half of the box down through the bottom of the vessel, and floated the vessel in saltwater.
In this configuration, water can naturally push up through the tube and into the box, where the tilt of the box, combined with the thermal energy from the sun, induces the water to swirl as it flows through. The small eddies help to bring water in contact with the upper evaporating layer while keeping salt circulating, rather than settling and clogging.
