An American university has made progress in Atmospheric Water Harvesting (AWH) technology, which can more effectively collect water from the air and potentially help alleviate water scarcity issues.
Although AWH technology holds promise as one of the solutions to global water resource shortages, traditional AWH equipment has often been limited in water production capacity due to their large size, the material of adsorbents used, and the efficiency of the system cycle.
The water collection capacity of this technology is mostly positively correlated with the adsorbents used, making the water adsorption and desorption capabilities of the adsorbents a key focus of research. Scientists have utilized the large absorbance and easy regeneration characteristics of metal-organic frameworks (MOFs) to produce the main adsorbents for Atmospheric Water Harvesting technology.
In order for AWH machines to continuously absorb and release water, external energy is required to drive the reactions. In the past, scientists have considered using electric grids or solar photovoltaic (PV) panels as the energy source for equipment heating, but these methods rely on electrochemical storage to operate at night and continuously.
Recently, researchers at the University of Utah in the United States introduced the first combustion-driven Atmospheric Collecting Water machine (CRCF). It is compact in size and can quickly cycle and collect water from the air through combustion heating. The research results were published on July 22 in the journal “Cell Reports Physical Science.”
The CRCF consists of an adsorbent heat exchanger (AHX), a heat transport system, steam transmission, and a condensation system. Its circulation process is divided into two stages: “water absorption” and “water release.”
The AHX on this type of CRCF has a cube-shaped exterior measuring close to 20 cm, with multiple porous copper foam fins arranged in parallel inside. The fins are filled with an adsorbent called “aluminium fumarate,” a common MOF material that can capture a large amount of water vapor within a relative humidity range of 20% to 30%, achieving the water absorption effect.
These fins are connected through several copper tubes, with the tubes linked to a small copper base for heating. When heated, the base conducts heat to the fins, releasing the water vapor inside the fins. The vapor is then transported by a small fan to a compact condensation device below, forming drinking water stored in a small water tank for human use.
To test the performance of this CRCF prototype, scientists conducted experiments near Salt Lake City, Utah, where humidity fluctuates significantly (20% to 80%) and temperatures are unstable (3°C to 20°C). The experiments lasted for 25 hours and experienced 5 consecutive water absorption and release cycles, successfully collecting 431.2 grams of water vapor and producing 266.12 grams of drinking water.
The researchers mentioned that each cycle used 120 grams of kerosene fuel and lasted approximately 1.5 hours, with an average of 64.3% of captured water vapor condensed into drinking water.
Although the efficiency of the water condensation process in this experiment was not ideal, it provided the research team with insights into the prototype’s issues. They optimized the design of the AHX in the CRCF prototype by increasing fin thickness and density, conducting tests at different temperatures and humidity levels. The results showed that at a temperature of 25°C and humidity of 40%, each kilogram of MOF material could produce 3.19 kilograms of condensed water.
The research team stated that this study allowed the scaling up of the CRCF system to be relatively simple, with the ability to adjust fin thickness and density inside the AHX based on actual needs in order to produce more drinking water for human use. However, this is still influenced by environmental temperature and humidity.
The experimenters mentioned that the current prototype machine has achieved the goal of producing 5 liters of water per day per kilogram of adsorbent material, and the device can be used for water absorption by heating it with a camping stove.
The team is considering providing enough water for a household’s daily consumption of 15 to 20 liters, as the researchers discovered during the system design process that the water resource issue is not only a matter of national defense but also significantly impacts civilian life.
The senior author of this research, Assistant Professor of Mechanical Engineering at the University of Utah, Sameer Rao, explained, “This prototype machine relies on adsorbent materials that absorb water molecules from non-humid air and then apply heat to release these molecules in liquid form.”
He further stated, “We have used specific MOFs to turn them into materials specialized in absorbing water vapor in the air, and this absorption process is reversible, so the water vapor does not dissolve into the material. In addition, these absorbent materials have a huge internal surface area, allowing them to temporarily trap a large amount of water from the air.”
Funding for this research came from DEVCOM Soldier Center, operated by the U.S. Department of Defense, aimed at supporting the modernization of U.S. Army equipment so that the Army can obtain water sources in water-scarce remote areas through small and compact water-making devices without the need to carry water-filled canteens.
The primary author of this research, graduate student Nathan Ortiz, mentioned that choosing fuel as the heating source was because “solar panels can only operate during the day, and batteries are both bulky and take up space.” The experimenters believe that their equipment is the first device to produce water using fuels like gasoline.
The research team has filed an initial patent application based on this technology and believes it can also meet non-military needs in the future.