11th grade students and the device that turns salt water into fresh water

A group of teachers and students in Ben Tre have just succeeded in creating a device that filters salt water into fresh water by using solar cells.

Faced with the severe drought and saltwater intrusion in the Mekong Delta, many households have no water for daily use. A group of teachers and students from Nguyen Dinh Chieu High School (Ben Tre City, Ben Tre Province) have come up with the idea of ​​filtering saltwater into fresh water using solar energy. The research has been carried out since May 2015.

There are many ways to filter salt water into fresh water such as desalination, filtration using nanotechnology, but the group chose distillation by utilizing solar energy, to save natural resources, protect the environment and contribute to combating climate change.

Device that turns salt water into fresh water. Photo provided by the research team.

Mr. Truong Huu Dung said that the device consists of three parts: the saltwater boiling part is made of a vacuum glass tube that can absorb 93% of sunlight, thereby converting light energy into heat energy to boil saltwater. The transparent tube allows light rays to pass through and reflects minimally. The inner tube is coated with a layer of paint absorbing by spraying technology, so it has high solar radiation absorption. Below is a layer of stainless steel trough to help absorb more sunlight.

The second part is a T-shaped thermos bottle made of heat-resistant plastic. The team designed two high-temperature resistant plastic bottles that can be nested together, with a space in between to pour the insulation layer.

The third part is the distillation vessel made of 8mm glass, with a double layer structure. The outer layer is a transparent rectangular glass box that allows light rays to pass through; the inner layer is smaller, shaped like a house with a black painted surface that helps absorb sunlight from the stainless steel parabolic dish placed below.

Between these two layers of glass is a vacuum to retain heat. A stainless steel plate placed on the top of the "roof" contains cool salt water to cool the water vapor so that the water vapor condenses on the underside of the "roof" and flows down the pipe to the outside, this is fresh water. The salt water used for cooling has a pipe leading through a thermos tank and has a valve that is closed when needed to open to let the water flow through.

The parabolic dish frame below is conical, made of iron and painted with anti-rust paint. It is mounted on a support system that can rotate to follow the direction of the sun. The team used stainless steel with good gloss, good light reflection and no oxidation to make the parabolic dish.

The research team hopes this device can help people in the Mekong Delta have fresh water for daily use during the dry season.

With the above design, the user will pour salt water into the top of the distillation tank, then open the valve, the water will flow through the thermos, down the vacuum tube to absorb heat from the hot sunlight and convection with colder water in the thermos (the density of hot water is lighter than cold water, so hot water floats on top, cold water sinks). At this time, the water in the thermos gradually heats up (the highest is about 75 to 85 degrees Celsius), the hot water through the bottom of the distillation tank continues to absorb heat from the parabolic pan, evaporates (fresh water vapor), condenses on the underside of the stainless steel plate and flows down the plastic pipe to the outside to the fresh water tank.

Nguyen Tan Loi said the biggest difficulty is using solar energy. Because when the weather is coolHeat will be lost in two parts: the thermos and the distillation tank, so the group spent a lot of time to fix it. If put into use, the machine will costunder 2 million VND, reaching 6 liters/day. The group plans to continue creating new versions with more modern improvements.

According to VNE