COLLEGE PARK, Md. - Engineers at the University of Maryland's A. James Clark School of Engineering say they've found a solution to the rising global challenge of water scarcity: solar steam generation devices. Easily accessible, the engineers say the devices are efficient, environmentally friendly, biodegradable, and extremely low-cost. 
 
Inspired by the process by which water is carried through trees from roots to small pores on the underside of leaves, the UMD research team created several new ways in which water can be transported through wood, purifying it for safe use. Energy from the sun and a block of wood smaller than an adult’s hand are the only components needed to heat water to its steaming point in these devices.
 
The global crisis of water scarcity is a pressing global challenge, and the situation is far worse in developing countries, where safe water is difficult to secure for 1 billion people, says UMD.
 

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Filtering water: a new use for wood?

Engineers at the University of Maryland have developed a new use for wood: filtering water.


“Cost and manufacturing are key challenges in using the solar-steam technology for seawater desalination and for the first time, wood-based structures can potentially provide solutions,” said Liangbing Hu, UMD associate professor of materials science and engineering and the leader of the projects. Hu is interested in scaling up these devices for commercial use, which includes designing ways to easily manufacture the devices and bring down their cost. 

One way works like this: imagine a bowl of unpurified water sitting in a sunny spot. On top of it floats a small block of wood about two inches by two inches. The side of the block facing up is darkened, to catch the sun's rays. As the sun heats the wood, the water below is drawn up through the wood’s natural channels. The hot dark surface evaporates the water, which can be condensed and distilled off. The salt or other contaminants are too heavy to evaporate, so they stay below.
 
Another design uses carbon nanotubes -- tiny, naturally dark structures grown in a lab -- to coat one side of the wood and heat the water inside.  Another, described in the journal Advanced Energy Materials, uses metal nanoparticles to achieve the same results. Both of these designs are very efficient, but come with a higher cost to produce.
 
Another innovative design involves carbonizing -- essentially, burning -- the top layer of wood to create a dark surface. The team tried this with the natural wood’s channels oriented up-and-down, just as they would be inside the tree.
 
By the same measure used to test solar cells’ efficiency, the team measured how efficient the solar steam generation devices are. The most efficient device was the burned-top wood, with 87% efficiency at ten suns of light. It was also the least expensive to produce, coming in at only $1 per square meter.
 
Source: University of Maryland
 
 

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