The system builds on a proof-of-concept design initially developed three years ago. The latest design, say the researchers, brings the process closer to something that could become a practical water source for remote regions with limited access to water and electricity.
The system harnesses a temperature difference within the device to allow an adsorbent material - which collects liquid on its surface - to draw in moisture from the air at night and release it the next day. When the material is heated by sunlight, the difference in temperature between the heated top and the shaded underside makes the water release back out of the adsorbent material. The water then gets condensed on a collection plate.
The original device required the use of specialized materials - called metal organic frameworks (MOFs) - which are expensive and limited in supply, and the system’s water output was not sufficient for a practical system. Now, say the researchers, by incorporating a second stage of desorption and condensation, and by using a readily available adsorbent material, the device’s output has been significantly increased, and its scalability as a potentially widespread product is greatly improved.
Instead of using MOFs, the new design uses an adsorbent material called a zeolite, which in this case is composed of a microporous iron aluminophosphate. The material is widely available, stable, and has the right adsorbent properties to provide an efficient water production system based just on typical day-night temperature fluctuations and heating with sunlight.
The two-stage design, say the researchers, makes clever use of the heat that is generated whenever water changes phase: The sun's heat is collected by a solar absorber plate at the top of the box-like system and warms the zeolite, releasing the moisture the material has captured overnight. That vapor condenses on a collector plate - a process that releases heat as well.
The collector plate is a copper sheet directly above and in