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Salt solution cools computers, boosts performance

Posted on November 3, 2023 by dishanth

Researchers at the City University of Hong Kong found the secret to a more efficient, less expensive approach to keeping massive computer systems cool: Just add salt.

A growing concern in computing is the enormous amount of heat generated in ever-increasing global computer arrays churning out more than 2 zettabytes per week.

Such gigantic processing capacity leaves an enormous carbon footprint. Commercial cloud providers utilize cooling systems requiring billions of gallons a year to maintain optimal temperatures.

According to the MIT Press Reader, cooling processes account for more than 40% of electricity usage. A single data center can consume the same amount of electricity as 50,000 homes.

“As a result, the cloud now has a greater carbon footprint than the airline industry,” anthropologist Steven Gonzalez Monserrate wrote in an MIT Press article last year.

Wei Wu, a professor in the School of Energy and Environment at the Hong Kong university, devised a system with several colleagues that improves upon current heat dissipation technology.

In a paper published Oct. 31 in the journal Device, Wu described a process in which water containing the salt lithium bromide relies on evaporation and reabsorption to keep temperatures low.

The process is “a passive thermal management strategy that relies on moisture desorption from hygroscopic salt solutions through a protective membrane that only allows water vapor to pass through,” Wu said.

The porous membrane is set in a structure that prevents any salty solution from contact with computer components. A heat sink directs accumulated heat away from sensitive electronics.

Wu, in his paper, “Membrane-encapsulated, moisture-desorptive passive cooling for high-performance, ultra-low-cost, and long-duration electronics thermal management,” said the device “can spontaneously and quickly recover its cooling capacity by absorbing water vapor from the air during off hours.” He compared the process to nature, where mammals regulate body temperature by sweating and rehydrating.

The high moisture absorption capacity and low cost of the lithium bromide-treated water offers a clear advantage over competing cooling strategies using hydrogels and metal-organic frameworks. Those systems require time-consuming regeneration rates and require active replenishment of water supplies.

“In contrast, hygroscopic inorganic salts, such as LiCl and LiBr, show promise in addressing these issues due to their extremely high moisture absorption capacity and low cost,” Wu said.

Applying the process to a single computer, the researchers measured an improvement of more than 32% in performance. They also said the process was completed “with a record-high cost effectiveness.”

“Poor thermal management can cause tremendous heat accumulation within electronic devices, resulting in the loss of functionality and, eventually, device failure,” Wu said. “We demonstrate that the proposed strategy is capable of offering a long-duration stable cooling capacity without solution leakage and corrosion, which can suppress the temperature rise of an emulated heater with a record-high cost effectiveness compared with state-of-the-art passive cooling strategies.”

The cooling strategy, Wu said, is cost effective and highly scalable, and “can be useful for various cooling applications with few technological barriers.”

Source Tech Xplore

Desalination system could produce freshwater that is cheaper than tap water

Posted on October 2, 2023 by dishanth

Engineers at MIT and in China are aiming to turn seawater into drinking water with a completely passive device that is inspired by the ocean, and powered by the sun.

In a paper appearing in the journal Joule, the team outlines the design for a new solar desalination system that takes in saltwater and heats it with natural sunlight.

The configuration of the device allows water to circulate in swirling eddies, in a manner similar to the much larger “thermohaline” circulation of the ocean. This circulation, combined with the sun’s heat, drives water to evaporate, leaving salt behind. The resulting water vapor can then be condensed and collected as pure, drinkable water. In the meantime, the leftover salt continues to circulate through and out of the device, rather than accumulating and clogging the system.

The new system has a higher water-production rate and a higher salt-rejection rate than all other passive solar desalination concepts currently being tested.

The researchers estimate that if the system is scaled up to the size of a small suitcase, it could produce about 4–6 liters of drinking water per hour and last several years before requiring replacement parts. At this scale and performance, the system could produce drinking water at a rate and price that is cheaper than tap water.

“For the first time, it is possible for water, produced by sunlight, to be even cheaper than tap water,” says Lenan Zhang, a research scientist in MIT’s Device Research Laboratory.

The team envisions a scaled-up device could passively produce enough drinking water to meet the daily requirements of a small family. The system could also supply off-grid, coastal communities where seawater is easily accessible.

Zhang’s study co-authors include MIT graduate student Yang Zhong, and Evelyn Wang, the Ford Professor of Engineering, along with Jintong Gao, Jinfang You, Zhanyu Ye, Ruzhu Wang, and Zhenyuan Xu of Shanghai Jiao Tong University in China.

A powerful convection

The team’s new system improves on their previous design—a similar concept of multiple layers, called stages. Each stage contained an evaporator and a condenser that used heat from the sun to passively separate salt from incoming water.

That design, which the team tested on the roof of an MIT building, efficiently converted the sun’s energy to evaporate water, which was then condensed into drinkable water. But the salt that was left over quickly accumulated as crystals that clogged the system after a few days. In a real-world setting, a user would have to place stages on a frequent basis, which would significantly increase the system’s overall cost.

In a follow-up effort, they devised a solution with a similar layered configuration, this time with an added feature that helped to circulate the incoming water as well as any leftover salt. While this design prevented salt from settling and accumulating on the device, it desalinated water at a relatively low rate.

In the latest iteration, the team believes it has landed on a design that achieves both a high water-production rate, and high salt rejection, meaning that the system can quickly and reliably produce drinking water for an extended period.

The key to their new design is a combination of their two previous concepts: a multistage system of evaporators and condensers, that is also configured to boost the circulation of water—and salt—within each stage.

“We introduce now an even more powerful convection, that is similar to what we typically see in the ocean, at kilometer-long scales,” Xu says.

The small circulations generated in the team’s new system is similar to the “thermohaline” convection in the ocean—a phenomenon that drives the movement of water around the world, based on differences in sea temperature (“thermo”) and salinity (“haline”).

“When seawater is exposed to air, sunlight drives water to evaporate. Once water leaves the surface, salt remains. And the higher the salt concentration, the denser the liquid, and this heavier water wants to flow downward,” Zhang explains. “By mimicking this kilometer-wide phenomena in small box, we can take advantage of this feature to reject salt.”

Tapping out

The heart of the team’s new design is a single stage that resembles a thin box, topped with a dark material that efficiently absorbs the heat of the sun. Inside, the box is separated into a top and bottom section. Water can flow through the top half, where the ceiling is lined with an evaporator layer that uses the sun’s heat to warm up and evaporate any water in direct contact.

The water vapor is then funneled to the bottom half of the box, where a condensing layer air-cools the vapor into salt-free, drinkable liquid. The researchers set the entire box at a tilt within a larger, empty vessel, then attached a tube from the top half of the box down through the bottom of the vessel, and floated the vessel in saltwater.

In this configuration, water can naturally push up through the tube and into the box, where the tilt of the box, combined with the thermal energy from the sun, induces the water to swirl as it flows through. The small eddies help to bring water in contact with the upper evaporating layer while keeping salt circulating, rather than settling and clogging.

The team built several prototypes, with one, three, and 10 stages, and tested their performance in water of varying salinity, including natural seawater and water that was seven times saltier.

From these tests, the researchers calculated that if each stage were scaled up to a square meter, it would produce up to 5 liters of drinking water per hour, and that the system could desalinate water without accumulating salt for several years. Given this extended lifetime, and the fact that the system is entirely passive, requiring no electricity to run, the team estimates that the overall cost of running the system would be cheaper than what it costs to produce tap water in the United States.

“We show that this device is capable of achieving a long lifetime,” Zhong says. “That means that, for the first time, it is possible for drinking water produced by sunlight to be cheaper than tap water. This opens up the possibility for solar desalination to address real-world problems.”

Source Tech Xplore

MIT engineers have discovered a completely new way of generating electricity

Posted on June 8, 2021 by dishanth

Tiny Particles Power Chemical Reactions

A new material made from carbon nanotubes can generate electricity by scavenging energy from its environment.

MIT engineers have discovered a new way of generating electricity using tiny carbon particles that can create a current simply by interacting with liquid surrounding them.

The liquid, an organic solvent, draws electrons out of the particles, generating a current that could be used to drive chemical reactions or to power micro- or nanoscale robots, the researchers say.

“This mechanism is new, and this way of generating energy is completely new,” says Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT. “This technology is intriguing because all you have to do is flow a solvent through a bed of these particles. This allows you to do electrochemistry, but with no wires.”

MIT engineers have discovered a way to generate electricity using tiny carbon particles that can create an electric current simply by interacting with an organic solvent in which they’re floating. The particles are made from crushed carbon nanotubes (blue) coated with a Teflon-like polymer (green). Credit: Jose-Luis Olivares, MIT. Based on a figure courtesy of the researchers.

In a new study describing this phenomenon, the researchers showed that they could use this electric current to drive a reaction known as alcohol oxidation — an organic chemical reaction that is important in the chemical industry.

Strano is the senior author of the paper, which appears today (June 7, 2021) in Nature Communications. The lead authors of the study are MIT graduate student Albert Tianxiang Liu and former MIT researcher Yuichiro Kunai. Other authors include former graduate student Anton Cottrill, postdocs Amir Kaplan and Hyunah Kim, graduate student Ge Zhang, and recent MIT graduates Rafid Mollah and Yannick Eatmon.

Unique properties

The new discovery grew out of Strano’s research on carbon nanotubes — hollow tubes made of a lattice of carbon atoms, which have unique electrical properties. In 2010, Strano demonstrated, for the first time, that carbon nanotubes can generate “thermopower waves.” When a carbon nanotube is coated with layer of fuel, moving pulses of heat, or thermopower waves, travel along the tube, creating an electrical current.

That work led Strano and his students to uncover a related feature of carbon nanotubes. They found that when part of a nanotube is coated with a Teflon-like polymer, it creates an asymmetry that makes it possible for electrons to flow from the coated to the uncoated part of the tube, generating an electrical current. Those electrons can be drawn out by submerging the particles in a solvent that is hungry for electrons.

To harness this special capability, the researchers created electricity-generating particles by grinding up carbon nanotubes and forming them into a sheet of paper-like material. One side of each sheet was coated with a Teflon-like polymer, and the researchers then cut out small particles, which can be any shape or size. For this study, they made particles that were 250 microns by 250 microns.

When these particles are submerged in an organic solvent such as acetonitrile, the solvent adheres to the uncoated surface of the particles and begins pulling electrons out of them.

“The solvent takes electrons away, and the system tries to equilibrate by moving electrons,” Strano says. “There’s no sophisticated battery chemistry inside. It’s just a particle and you put it into solvent and it starts generating an electric field.”

“This research cleverly shows how to extract the ubiquitous (and often unnoticed) electric energy stored in an electronic material for on-site electrochemical synthesis,” says Jun Yao, an assistant professor of electrical and computer engineering at the University of Massachusetts at Amherst, who was not involved in the study. “The beauty is that it points to a generic methodology that can be readily expanded to the use of different materials and applications in different synthetic systems.”

Particle power

The current version of the particles can generate about 0.7 volts of electricity per particle. In this study, the researchers also showed that they can form arrays of hundreds of particles in a small test tube. This “packed bed” reactor generates enough energy to power a chemical reaction called an alcohol oxidation, in which an alcohol is converted to an aldehyde or a ketone. Usually, this reaction is not performed using electrochemistry because it would require too much external current.

“Because the packed bed reactor is compact, it has more flexibility in terms of applications than a large electrochemical reactor,” Zhang says. “The particles can be made very small, and they don’t require any external wires in order to drive the electrochemical reaction.”

In future work, Strano hopes to use this kind of energy generation to build polymers using only carbon dioxide as a starting material. In a related project, he has already created polymers that can regenerate themselves using carbon dioxide as a building material, in a process powered by solar energy. This work is inspired by carbon fixation, the set of chemical reactions that plants use to build sugars from carbon dioxide, using energy from the sun.

In the longer term, this approach could also be used to power micro- or nanoscale robots. Strano’s lab has already begun building robots at that scale, which could one day be used as diagnostic or environmental sensors. The idea of being able to scavenge energy from the environment to power these kinds of robots is appealing, he says.

“It means you don’t have to put the energy storage on board,” he says. “What we like about this mechanism is that you can take the energy, at least in part, from the environment.”

Reference: “Solvent-induced electrochemistry at an electrically asymmetric carbon Janus particle” by Albert Tianxiang Liu, Yuichiro Kunai, Anton L. Cottrill, Amir Kaplan, Ge Zhang, Hyunah Kim, Rafid S. Mollah, Yannick L. Eatmon and Michael S. Strano, 7 June 2021, Nature Communications.
DOI: 10.1038/s41467-021-23038-7

The research was funded by the U.S. Department of Energy and a seed grant from the MIT Energy Initiative.

By Anne Trafton, Massachusetts Institute of Technology

Source SciTech Daily