MIT invents a $4 solar desalination device

Researchers from MIT and China have developed a solar-powered desalination device that can give a family of four all the drinking water it needs — and it can be made from just $4 worth of materials.

Solar water desalination: Water covers more than two-thirds of the Earth’s surface, but 97% of it is salt water. The salt concentration in this water is too high for our bodies to process – if you drink too much of it, you will become dehydrated and die.

What we need is fresh waterwhich means that the salt concentration is less than 1%, and since this water is not abundant, humans have come up with many ways to remove enough salt from salt water to make it Drinkable.

“I think the real opportunity is the developing world.”

Evelyn Wang

One of these is solar water desalination.

While specifications vary, the basic idea is that the sun’s heat is applied to the salt water. The water evaporates leaving behind the salt, then the water vapor is collected and condensed, leaving you with liquid fresh water.

get salty: Created by engineers countless Solar desalination devices, but for the devices to make a difference where they are needed most, they need to be not only cheap and efficient, but also durable and long-lasting.

“We see these performance numbers as very attractive, but they are often limited by their longevity.”

Evelyn Wang

The problem is that salt tends to build up in these devices, especially on the wick used to draw water through the device. These wicks are difficult to clean, and over time, a buildup of salt means they need to be replaced.

“The challenge was the problem of salt pollution, which people haven’t really addressed,” said researcher Evelyn Wang. Tell MIT News. “So we see these performance numbers as very attractive, but they are often limited by longevity. Over time, things are going to screw up.”

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The idea: Researchers from MIT and China’s Shanghai Jiao Tong University have now created a wick-free solar desalination device that uses gravity-driven convection to move water.

Natural convection is a type of motion that occurs when a fluid is not of one uniform density. In this case, the less dense liquid will rise, while the denser liquid will decrease. (The same goes for gases – because hot air is less dense than cold air, it rises while cold air falls.)

This animation shows how convection rapidly pulls the dense salt water down. (credit: MIT)

How it works: The new solar desalination device consists of several layers. Add salt water to the top layer. The black paint attracts the sun’s heat to that layer, causing the formation of water vapor required for collection.

Any water left in that layer is very salty and therefore very dense.

The bottom layer of the device contains more salt water. The layers between it and the top are designed to retain heat in the top layer, while allowing the super dense salt water to move down to mix with the naturally dense salt water under the force of natural convection.

Solar water desalination

Two prototypes of a solar water desalination device are being tested outdoors. Credit: MIT

I look ahead: The device worked for a week straight with no signs of salt build-up, but we still don’t know exactly how long it could work.

But the best news is that building a solar water desalination device big enough to meet the needs of only $4 will cost only $4 drinking water He needs a family of four, according to the MIT team. If it proves to be a durable, it could be a relatively cheap way to get fresh water to those who need it.

“I think the developing world presents a real opportunity,” said Wang. “I think this is where it is [the] The most likely impact in the near term, due to the simplicity of the design.”

this is Article – Commodity Supplied by sister site Freethink.