Micro-salt channels help turn seawater into potable water, using solar energy for emergencies.
Imagine yourself alone with a wild tiger on a small boat in the open ocean to start the journey of fighting for survival for 277 days before you are rescued.
This scenario was the focus of the story of the movie “Hayat Bay”, which was produced in 2012, and won 11 Oscar nominations and won four of them. It revolves around the Indian boy (B Patel), the son of a zookeeper, whose family decides to move to Canada, while traveling across the ocean. Heidi, the ship is sinking.
On this journey, the hero of the film adopted the idea of a floating solar still to survive. The idea is to use the sun's heat to desalinate water by distillation by raising the temperature of salt water to a boiling point and forming water vapor, which is then condensed into water.
The scenes of this film were a source of inspiration and motivation for a scientist at King Abdullah University of Science and Technology (KAUST), to develop this process by using a number of nanomaterials and thermal insulation processes to increase the evaporation of salt water and convert it into pure steam.
The solar distillation device developed by a research team led by Professor Xiaoxiong Gan, Professor of Materials Science and Engineering at KAUST, was able to purify salt water from reverse osmosis plants, whose salinity exceeds 10%, and it also succeeded in purifying water derived from the Red Sea. directly; This means that it doubles the rate of fresh water production from the currently used anti-salt solar distillers.
Reverse osmosis technology is one of the modern and important methods in the non-potable water treatment industry because it contains a very high percentage of pollutants such as salt, minerals and bacteria.
In 2016, Gan founded a startup called Sunny Clean Water, which makes low-cost, inflatable distillers that produce ten to twenty liters of fresh water per day.
Despite this, he says that when it comes to purifying sea water, his personal tools are limited, and he adds: “We always notice the deposition of salt on materials that absorb solar energy over time, so the deposited salt reflects sunlight and disrupts the workflow of the distiller.”
In 2021, Gan joined KAUST and teamed up with fellow Professor Yu Han, Professor of Chemistry, and Dr. Caiji Yang, whose research interests include generating solar steam and harvesting water from the atmosphere to improve the efficiency of salt deposition, a strategy that employs technologies like Such as: waterproof surfaces, or liquid convection in order to reduce mineral build-up.
The secret of the plastic cube
The team's new evaporator consists of a one-centimetre plastic cube that contains a number of fiberglass membranes, a thin material commonly used in distillation. The horizontally aligned film, covered with carbon nanotubes, acts as a light-absorbing layer on the cube's top surface. Below it, a series of vertically mounted membranes, or mass transfer bridges, separate the solar absorber from the brine accumulator.
Yang, who developed the design, explains that the bridges have micro-channels that absorb water, so naturally, they absorb seawater and deliver it to the upper solar layer to distill it into steam, and when the accumulated salt reaches the edge, the same micro-channels transfer the brine back into the water the sea; Due to the presence of capillary concentration gradients.
These advanced bridges clear the way for the conductive heat that flows through the reverse salt flow to the solar distiller, improving evaporation efficiency. “Other evaporators can remove salt from the water effectively but with a short backflow process, huge amounts of heat energy is lost and water generation rates are affected,” Yang points out. Our system is distinguished by its ability to balance salt expulsion with water generation.”
The tests carried out inside the factory and at the external stations revealed that the solar distillers could meet the need of two people of water per day, and the cost of the raw materials used was estimated at $50 per square meter.
Han adds, "We can improve the structure and double its size by assembling the cubes together, and since this device works for long times without the need for any maintenance, we are preparing for the next stage, which is putting it into commercial use."
quotes:
“Solar stills can meet the need of two people per day.”
First: desalination by distillation methods
Second: Desalination using membrane methods
Third: desalination of water by crystallization or freezing.
Okaz (Jeddah) @okaz_online