A novel filtration device has the potential to filter wastewater much more efficiently and in an environmentally-safe manner, using 3D printing to manufacture structures based on fish gills.��

Their device is chemical-free and uses a 3D printing-on-membrane approach to develop a single device that mimics the shape and high surface area of fish gills at the microscale.

Prof. TieJun Zhang, Professor of Mechanical Engineering; Dr. Hongxia Li, Postdoctoral Research Fellow; Dr. Aikifa Raza, Research Scientist; and Dr. Faisal AlMarzooqi, Assistant Professor of Chemical Engineering; with Shaojun Yuan, Sichuan University; and Nicholas Fang, MIT, published their results in.

Membrane filtration is a widely used technique with applications from the biomedical industry to environmental sciences. At its simplest, the water-filtration process sees purified water permeate through the membrane, while contaminants such as microplastics, oil droplets, and other soluble pollutants are stopped by the membrane. Some contaminants would accumulate on membrane surface, or get trapped in membrane. This trapping is the major bottleneck in effective water filtration, as, over time, the membrane becomes clogged with the separated particles.

Most solutions to overcome membrane clogging focus on developing novel materials or modifying the surface of the membrane, using metal oxides and photocatalytic materials to repel contaminants and prevent the membrane from degrading. However, such chemical approaches may be easy to implement and effective, but environmental concerns have been raised around their use in nature.

Many fish species feed by filtering food particles from huge volumes of water without clogging their oral filters. Their mouths contain structures called gill rakers, which work much in the same way that a spaghetti strainer or coffee filter functions: Water is forced through the pores of the filter, trapping the desired particles.

“Surface patterning and creating topological structures on membrane surfaces can manipulate the local hydrodynamics and prevent clogging on the membrane,” Prof. Zhang said. “With properly designed surface structures, the flow of water near the membrane surface can be controlled to inhibit the deposition of particles that would clog the membrane. For this, surface geometry is the key.”

Different surface structures like grooves and pyramids have demonstrated anti-fouling properties. Fish gills present these structures but they are remarkably complex, and replicating them is made possible only with emerging 3D printing techniques. Recent advances in micro-stereolithography 3D printing have made it possible to fabricate complex structures at the microscale, but it is still challenging to fabricate these surface architectures and membranes with nanometer pores at one-step, and usually, the nanoporous membrane has to be manufactured separately. With the new direct-printing on membrane technique used by the research team, the filtration membrane and complex surface structures can be integrated as an all-in-one device, making it the first of its kind for filtration purposes. A patent has been filed for this technique, towards its commercialization.

Gill raker-shaped structures were printed directly onto the membrane surface, with the final device integrating all the functional components of a filter.

“We developed a microfluidic filtration device,” Dr. Li said. “When we tested it against oily water and wastewater with microplastics, we found that the extraordinary anti-fouling performance of a fish gill-structured membrane originates from the unique flow behavior of the oil droplet and plastic microparticle during the filtration process. As the water containing the droplet/particle approaches one of the gill structures, the forces acting on the water cause the droplet/particle to ‘ricochet’ away, and thus avoid oil droplets or microplastics contaminating the membrane surface. In this way, even though the droplet/particle size is much smaller than the gap between two neighboring gill structures, it cannot pass through the gap and remains in the main flow of water. This means that only clean water passes through the membrane and the filtration device does not become clogged with contaminates.”

The potential application fields of printing on membrane are myriad and diverse, with membranes in microfluidics one of the most important. Integrated with the enormous variety of materials, morphologies, and design options, the ”print-and-play” microfluidic membrane devices can be readily tailored to other emerging energy, chemistry, bioengineering, and medical applications.��

Jade Sterling
Science Writer
19 July 2022

The post How Fish Gills Inspired Clog-Free Filters to Tackle Ocean Pollution appeared first on Khalifa University.

Researchers at Khalifa University’s Center for Catalysis and Separations (CeCaS) have been granted two patents for their work on the effect of magnetic fields on separating mixtures and detecting gases.��

Gas separation is a process used across myriad disciplines and industries, with use cases ranging from purifying natural gas and removing carbon dioxide to producing oxygen for medical use and nitrogen for chemical feedstocks. There are various ways of separating gases in a mixture, including absorption, distillation, and membrane separation.��

The research was initiated in collaboration with the Abu Dhabi National Oil Company (ADNOC) and continues under the umbrella of the CaCaS center of KU in collaboration with the Demokritos National Research Center in Greece.��

“Sorption and desorption are typically controlled by swings in temperature or pressure, or both in combination,” Dr. Karanikolos said. “In our technology, a magnetic field swing is introduced. By switching the magnetic field on and off, gas is absorbed and desorbed without externally changing temperature or pressure, which is a great novelty in this area.”

Examples of application of gas separation are the removal of carbon dioxide from steam methane reforming gas mixtures and as the final step in the large-scale commercial production of hydrogen, which is important for the production of ammonia. Air separation is carried out to produce pure oxygen, while oil refineries and gas processing plants apply separation technologies in hydrocarbon fractionation and in the removal of hydrogen sulfide, a toxic byproduct of certain refinery processes.��

However, gas separation processes typically require generating high temperatures for heat-assisted absorbent regeneration, pumping liquid absorbents between absorption towers and regeneration towers, processing and handling of byproducts, repairing absorbent leakage problems, and replenishing the lost absorbent. In addition to being energy intensive, these processes contribute significantly to the operational cost of a gas separation process, according to Dr. Karanikolos. Gas separation processes with lower energy requirements and lower operational costs would be a substantial advancement in this area.��

“Conventional gas separation processes have high energy requirements,” Dr. Karanikolos said. “Magnetic swing absorption can be far less energy consuming, particularly if the magnetic field used in these cycles is generated by permanent magnetic assemblies. In order to turn the field on or off, these permanent magnets can either be mechanically added to or removed from the absorption cell, or simply switched on and off if they have a permanent magnet switch.”

In this method, a gas mixture is introduced to a magnetic field – responsive liquid and a magnetic field is applied. One of the gases is absorbed into the liquid, effectively separating the gas mixture. Once the non-absorbed gas is purged from the system, the magnetic field is removed or switched off, and the absorbed gas releases.��

Dr. Karanikolos was also awarded a patent for his work on a smart gas sensor to detect impurities and analyze gas mixtures. His technology provides an easy way of measuring gas sorption selectivity: the ratio of adsorbed amounts of two gases being simultaneously adsorbed to the same sample, and can also operate as a gas sensor under certain conditions.��

“Gravimetric microbalance is commonly used to measure the amount of adsorbed gas on sorbent materials,” Dr. Karanikolos said. “Our invention offers a low-cost gas sensing and measuring device, using a modified gravimetric microbalance, in which the hanging sample holder is located in a space where a magnetic field can be turned on and off. This allows us to measure the ratio of adsorbed gases that are simultaneously adsorbed to the same sorbent surface so we can calculate the real adsorbent selectivity.”

This new device and sensor is low-cost and rapid, replacing conventional chromatographic techniques for fast and easy continuous monitoring of gas concentration. It offers a single-step solution to gas analysis and can also measure magnetic susceptibility of the gases in a mixture.

Jade Sterling
Science Writer
1 June 2022

The post Research on Use of Magnetic Fields for Gas Separation and Gas Mixture Analysis Yields Two Patents appeared first on Khalifa University.

Carbon capture technology can be further improved for efficiency by simply irradiating one of the components, according to research from a Khalifa University team of chemical engineers

Reducing greenhouse gas emissions, particularly carbon dioxide (CO2), is paramount in combating climate change. Along with a paradigm shift from fossil fuels to renewable energy sources, deployment of carbon capture and storage technologies is a key strategy to actively limit the global average rise in temperature to less than 1.5 ⁰C relative to pre-industrial levels.

Carbon capture, utilization and storage (CCUS) is the most widely accepted and promising strategy for mitigating point source CO2 emissions, with technologies being increasingly demonstrated across a number of industries globally. These technologies typically include capturing CO2 from emission sources such as power plants, followed by compression prior to transportation to long-term storage sites. These approaches can be further improved for increased efficiency and reduced energy consumption and cost.

The team found that activating the graphene oxide using ultraviolet light improves the surface, structural, and morphological properties for enhanced selective carbon dioxide affinity.

Team members included Eng. Anish Mathai Varghese, Research Associate, Dr. K. Suresh Kumar Reddy, Research Scientist, and Dr. Georgios Karanikolos, Associate Professor of Chemical Engineering. Their results were published in

Successful carbon capture needs a sorbent material that will selectively grab CO₂ in a stream of mixed gases and then readily release it when desired so that the material can be reused, while the captured CO₂ can be utilized or sent for long-term storage.

In adsorption, CO₂ collects in the pores in the material that serve as active capture sites. When, for instance, temperature is lowered, CO₂ adheres to the surface, and when temperature is raised, CO₂ is released. Changes in pressure can also bring about these capture and release cycles.

Currently, aqueous amine solutions, which are solutions containing water and organic compounds called amines that contain nitrogen atoms attached to hydrogen and carbon atoms, are used to capture CO₂ in industrial applications. Amine solutions are excellent at capturing the CO₂, making them the most popular and developed carbon capture technology. However, their disadvantage is that in order to recover the trapped CO₂ from the amine solution, the solution has to be heated, requiring large amounts of thermal energy and resulting in some amines being lost to the environment in this high-energy process.

To overcome the shortcomings of amine solutions, solid sorbent materials are a viable alternative. Solid sorbents can selectively adsorb CO₂, however some solid sorbent materials perform better than others.

“Adsorption is gaining increased attention due to advantages that include low energy consumption, ease of implementation, cost-effectiveness, and generation of harmless byproducts,” Eng. Varghese explained. “To be suitable for large scale carbon capture, however, the adsorbent materials need to offer certain features and properties, including low energy consumption, chemical and thermal stability, low manufacturing cost, and mechanical robustness. As such, a large variety of materials are being investigated globally, like metal-organic frameworks, zeolites, covalent organic materials, and porous polymers, among many others. We developed a hybrid metal-organic framework adsorbent using copper ions, and UV-activated graphene oxide.”

Metal-organic frameworks offer superior textural properties, high structural flexibility, and can be combined with various functional groups for different applications. However, MOFs typically possess low thermal and chemical stability, restricting their use in harsh environments. To overcome this, the research team used a MOF-based hybrid known as HKUST-1 or MOF-199. This MOF is particularly promising for CO2 capture thanks to its extended porous structure with large surface area and pore volume, along with good chemical stability, ease of synthesis and commercial viability. It is a 3D porous framework combining copper ions with oxygen atoms.

The team went a step further too: they used UV-irradiated graphene oxide to increase the hybrid MOF’s CO2 adsorption capacity by 45 percent.

UV irradiation of the graphene oxide affected the distribution of the copper ions on the surface of the resulting MOF, which enhanced the pore shape and structure to allow for better CO2 selectivity and adsorption.

“These results show that UV treatment is a simple and scalable technique that can enhance the characteristics and performance of MOF/GO hybrid adsorbents for CO2 capture,” Eng. Varghese said. “Our hybrid material is an excellent adsorbent in humid conditions, which is beneficial since water vapor is often present in CO2-containing mixtures, such as in post-combustion of fuels.”

This material now has the potential to be further developed and scaled-up, with UV activation of graphene before capture application serving as an easy and low-cost pre-treatment technology.

Jade Sterling
Science Writer
12 April 2022

The post UV Radiation of Graphene Oxide Improves Carbon Capture Efficiency in Metal-Organic Frameworks appeared first on Khalifa University.

The American Institute of Chemical Engineers (AIChE) is a leading organization of chemical engineering professionals with more than 60,000 members from more than 110 countries.

Dr. Lourdes F. Vega, Professor of Chemical Engineering and Director of Khalifa University’s Research and Innovation Center on CO2 and Hydrogen (RICH), has been elected as a new fellow of the American Institute of Chemical Engineers (AIChE), the highest grade of membership of the institute. AIChE Fellows, nominated by peers and elected by the board of Directors, are prominent members recognized for their significant service to the profession and contributions to the industry.��

Dr. Vega is an internationally recognized leading authority in the field of molecular thermodynamics, clean energy, and sustainability. She has also integrated molecular modeling and simulations with process modeling and optimization—developing a holistic approach for process design, with recent applications in CO2 capture, hydrogen production, water treatment, and sustainable cooling systems.��

This is a new recognition of her work in the area of clean energy and sustainable products, for which she received the Mohammed Bin Rashid Medal of Scientific Distinguishment in 2020.��

Aside from her accomplishments in research, Dr. Vega is a member of the Mohammed Bin Rashid Academy of Sciences (MBRAS) and the Emirates Scientists Council where she leads the Engineering and Technology Advisory Board.��

“I am very honored with this election. Being recognized by peers is very rewarding. Thanks to all my colleagues and collaborators who led to this achievement, without you it would have been impossible!”��

Ara Maj Cruz
Creative Writer
29 March 2022

The post AIChE Elects Dr. Lourdes Vega as New Fellow appeared first on Khalifa University.

Khalifa University Graduate Teaching Assistant and PhD candidate, Jawaher AlYammahi, has been awarded an Excellence in Research award from the Second Forum for Women in Research hosted by University of Sharjah.��

Quwa: Empowering Women in Research and Innovation categories address the most important issues, topics and priority research challenges in different fields, including health sciences, medicine, engineering, and computing and informatics. Coinciding with Emirati Women’s Day, the Quwa forum was held on 26 August with the 7th International Conference on Arab Women in Computing event.

AlYammahi won the award for engineering for her paper on water-based extraction of sugar from dates. With Rambabu Krishnamoorthy, Post-doctoral Fellow, and Dr. Fawzi Banat, Professor of Chemical Engineering, AlYammahi used a novel technique to extract sugars and micronutrients from dates for use in sugar-alternative products.

“Recently, consumers have been preferring natural fruit sugar products, rather than commercial refined sugar, thanks to growing awareness of the various health risks and diseases related to white sugar,” AlYammahi said. “Date palm fruit is an excellent – and green – source for the glucose and fructose sugars that are a great alternative to the sucrose of refined sugar. However, dates have a gummy consistency, tough skin and rigid cell membrane, hindering the extraction of these alternative sugars, and current techniques just aren’t good enough. We used sub-critical water extraction to get 81 percent of the sugar from the dates, compared to the very low amounts seen using standard techniques.”

Sub-critical water extraction is a new and powerful technique that uses hot water and high pressure to extract different compounds from natural sources, like sugars from dates. It is recognized as a safe, cost-effective and more environmentally-friendly method as it uses water rather than other solvents in the process.

AlYammahi and her team were joined in the competition by other female researchers and students from Khalifa University.

Dr. Ameena Al Sumaiti, Associate Professor of Electrical Engineering, designed a multi-strategy planning support tool for electricity supply management.

With Dr. Mahmoud Meribout, Professor of Electrical Engineering, MSc students Asma Baobaid developed an artificial intelligence platform for face recognition and Budoor Alblooshi developed an autopilot system for autonomous vehicles.

PhD candidate Lamees Al Qassem created a framework for managing cloud workloads with Dr. Ibrahim Elfadel, Professor of Electrical Engineering and Computer Science, Dr. Ernesto Damiani, Professor and Senior Director of the Robotics and Intelligent Systems Institute, and Dr. Thanos Stouraitis, Professor and Department Chair of Electrical Engineering and Computer Science.

Dr. Maisam Wahbah, Post-doctoral Fellow, developed an algorithm to capture ECG signals from babies still in the womb in the early stages of pregnancy with Dr. Ahsan Khandoker, Associate Professor of Biomedical Engineering, and Dr. Mohammad Zitouni, Post-doctoral Fellow.

Maryam Alhasmi and Dr. Balasubramanian Vaithilingam, Principal Research Scientist, created a porous material from carbon to capture carbon dioxide from the atmosphere.

PhD candidate Fahmi Anwar and Dr. Georgios Karanikolos, Associate Professor of Chemical Engineering, developed a novel material for separating ethylene from ethane in the petrochemical industry.

Dr. Saeed Alkhazraji, Associate Professor of Chemical Engineering and Senior Director of Petroleum Institute, and Anjali Goyal, Research Assistant, collaborated with researchers from Higher ��ݮ��Ƶ of Technology in Abu Dhabi to develop natural particles to remove oil from water after an oil spill.

PhD candidate Amani Alhammadi and Dr. Daniel Choi, Professor of Mechanical Engineering, analyzed the performance of lithium ion batteries in low-temperature space applications.

Jade Sterling
Science Writer
28 October 2021

The post KU Student Awarded for Excellence in Engineering Research at Quwa Forum appeared first on Khalifa University.

Seramic Materials applies patented technology to upcycle industrial solid waste to sustainable and high-value ceramic products, driving the industry towards a near-zero waste goal

Started by Dr. Nicolas Calvet, Khalifa University Assistant Professor of Mechanical Engineering and CEO of Seramic Materials, and Dr. Khalid Al Ali, Khalifa University Assistant Professor of Chemical Engineering and Director of Operations at Seramic Materials, Seramic Materials Ltd. was established in 2019 to manufacture 100 percent recycled ceramic products from heavy industry waste, such as incinerator ash and byproducts from the steel industry.

“Seramic Materials is a UAE-based company born out of the unique and innovative environment of the Masdar Institute at Khalifa University,” Dr. Calvet said. “We developed a unique circular economy solution to recycling solid industrial waste into sustainable value-added products in the technical ceramics and construction materials markets.”

Replacing a precious natural resource with waste products for ceramic production has myriad advantages beyond keeping the conventional raw materials in the ground. Using waste products can be significantly cheaper, meaning a final product can be 10 to 50 percent cheaper depending on its application.

By avoiding the extraction of natural resources and their transport, carbon emissions are significantly reduced and manufacturing energy consumption is also lowered. Dr. Calvet says this represents at least a 20 percent reduction in carbon dioxide emissions compared with conventional ceramic manufacturing methods. Plus, all the waste that would have headed to landfill can now be diverted to a second life and purpose.

. Seramic Materials can combine the UAE’s steel slag, municipal solid waste incinerator ashes, bauxite residue, waste sludge, broken glass and more with non-depleting natural resources, such as desert sand, to develop their ceramic products.

“We tune the properties of the final ceramic product depending on its expected use by mixing different waste products together,” Dr. Calvet said. “Our ceramic materials can be shaped in any form and dimension depending on their intended applications, such as bricks, floor and wall tiles, 3D claddings, pavers, and much more.

Seramic Materials is now expanding into technical ceramics, manufacturing advanced thermal energy storage materials, which can operate in temperatures as high as 1250°C, and which are, to date, the most cost-efficient ceramics on the market.

Thermal energy storage involves storing heat, generated for instance by solar energy, until it is needed to be turned into electricity or reused directly as process heat. It is the release of the heat that is used to generate the power.

“Our solution is called ReThink Seramic – Flora and it is a game changer in high-temperature applications – anything over 700°C,” Dr. Calvet said. “Until now, the bottleneck in this industry was the high cost of the ceramic material itself. By operating at a higher temperature, the heat-to-electricity conversion efficiency is improved, and since Flora is durable up to 1250°C, it can be thermally cycled over decades without damage.”

“We have developed the first state-of-the-art laboratory in the GCC dedicated to industrial solid waste valorization” said Dr. Khalid Al Ali.�� Thanks to this one-of-its-kind laboratory, the team at Seramic Materials have developed formulations that are patented in Europe, USA, India, China and the GCC and are constantly working on new applications to support products across the ceramics value chain.�� Seramic Materials recently signed an intellectual property (IP) agreement with Khalifa University to commercialize 5 patents related to steel slags upcycling.

“Our vision is a more sustainable present achieved by developing a circular economy,” Dr. Calvet said. “We have an innovative approach that we hope will continuously enhance our ceramic formulations and offer countless new value-added applications for our commercial products.”

Jade Sterling
Science Writer
18 October 2021

The post KU Start-Up Pioneers in Upcycling Waste for Circular-Economy Ceramics appeared first on Khalifa University.

The Undergraduate Research Competition (URC) is one of the largest competitions in the GCC that promotes scientific research among undergraduate students and supports the UAE government’s initiative of fostering innovation and empowering the youth to prepare them for the future. This is the eighth year of the competition and the research event has attracted creative minds not only from the GCC but in other countries as well such as Indonesia, Malaysia, Malta, and Morocco.

Around 315 original research papers were presented from 87 major universities in different disciplines, including engineering, natural and health sciences, business administration, education and law, and arts and social sciences.

The Chemical Engineering senior project of Khalifa University students Muna Al Jasmi, Anfal Abloushi, Shamma Thani, Reem Saeed Salem, and Ali Ahmed Algallaf, supervised by Prof. Lourdes Vega and Dr. Daniel Bahamon, won second place in the Chemical and Petroleum Engineering Category of the competition, with the project titled “Design of an Adsorption Air-Conditioning System Using Low Global Warming Potential (GWP) Refrigerants.”

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“This system is the first of its kind in the region and considered as one of the most promising technologies because of its advanced features as it does not depend on the electric energy generated from fossil fuels. It can work using electricity from renewable sources and a great alternative from an economical as well as environmental point of view,” Muna said. She explained that the system uses water as the refrigerant that provides powerful cooling while at the same time offers a sleek design that incorporates simple construction, easy control, quiet operation with no vibration, and low maintenance.

Cooling systems are an essential technology in our life, especially in arid and semi-arid regions, like the UAE.

“Current air-conditioning and refrigeration systems are energy-intensive, consuming around 17 percent of the global electricity production and more than 60 percent in the Emirates, representing a major impact on global warming and climate change. Moreover, the primary refrigerants used today have a high global warming potential (GWP), being thousands of times more potent greenhouse gases than carbon dioxide. Hence, active work is needed to replace them with low GWP refrigerants and to find more efficient cooling equipment. In their research project, our group of students proposed and designed an adsorption refrigeration system as an alternative to the compression system using water as the refrigerant, a silica-gel as the adsorbent, and a solar collector to provide the heat source to operate the system, a creative system with much lower impact into the environment than the ones currently used, representing a step forward on solving this very important environmental issue,” Dr. Vega said.��

“Obtaining second place in such a strong competition is a well-deserved recognition of their hard and innovative work and we are so proud of them!” she added.

The design the team came up with can be used here in the UAE and in other countries with similar weather conditions.��

“This project gave us an opportunity to apply the chemical engineering knowledge we gained during our academic journey to find and implement a solution to a major climate dilemma. We expect that in the near future, these novel technologies will change the whole scenario of sustainability, and will position the UAE to become a pioneer in the field of the new green economy globally,” Muna added.

Dr. Fawzi Banat, Professor and Chair of the Chemical Engineering Department, commented, “In the Shanghai Global Ranking of Academic Subjects 2021, which is dedicated to academic institutions for teaching and research, the Department of Chemical Engineering is ranked among the top 76-100. To achieve this ranking, the department achieved high scores on all of the analyzed indicators, which include articles indexed in Web of Science, the total number of citations, citations per article, articles published in the top 25% of scientific journals, and international interaction developed through collaborations with foreign institutions.”

“The department is dedicated to research and teaching excellence and currently offers doctoral, master’s, and bachelor’s degrees,” Dr. Banat added.��

The UAE actively supports a knowledge-based economy transformation, and events such as the URC encourages students to be more involved in accelerating the research needed to drive innovation in the country.

Ara Maj Cruz
Creative Writer
5 August 2021

The post Research on Sustainable Refrigeration System Nabs 2nd Place Win at the 8th Undergraduate Research Competition appeared first on Khalifa University.

As global energy demand from air conditioners continues to rise, finding a way to replace energy-intensive systems is paramount.

Read Arabic story .

As the mercury rises in the UAE, Dr. Lourdes Vega, Director of the Khalifa University Research and Innovation Center on CO2 and hydrogen (RICH), and KU Research Scientists Dr. Edder Garcia and Dr. Daniel Bahamon are turning their attention to finding efficient and environmentally-friendly forms of air conditioning systems.

“Due to global warming and a boost of wealth in tropical regions, the demand for refrigeration and air-conditioning is likely to increase in the coming years,” explained Dr. Vega. “This process already accounts for around 10 percent of the global electricity consumption, so finding green alternatives is of utmost importance.”

Global energy demand from air conditioners is expected to triple by 2050, and supplying power to these AC units comes with large costs and environmental implications.

Dr. Vega and her team are investigating a cleaner cooling process known as ‘absorption refrigeration,’ which could replace conventional energy-intensive vapor compression refrigeration, and could even be used as a way to store solar energy.

Conventional AC systems rely on vapor-compression cycles and a mechanical compressor. This is how it works: Refrigerant flows through a compressor, where it gets pressurized. Then the refrigerant flows through a condenser, where it condenses from vapor form to liquid form, giving off heat in the process. From the condenser, the refrigerant goes through an expansion valve and its pressure drops. Finally, the refrigerant travels to the evaporator, where it draws heat from the air around it (the air that needs to be cooled), which causes the refrigerant to vaporize. The vaporized refrigerant then goes back to the compressor to restart the cycle. In addition to the electricity consumption associated with air conditioning, in current vapor-compression cycles the refrigerant is usually a fluorinated gas (F-gas) with high global warming potential, making the phase out of such gases an urgent environmental need.

An adsorption-based refrigeration system is much simpler. It has two main components: a tank, where the liquid refrigerant is stored, and a bed filled with a solid material known as an ‘adsorbent.’ The refrigerant molecules ‘adsorb’, or attach, onto the surface of this material instead of dissolving into a liquid, creating a film on the surface where refrigerant vapor accumulates.

The adsorbent is a highly porous material with a large internal surface, full of holes that collect the refrigerant vapor. These systems transform energy into cooling power without any moving parts, making them low maintenance and more durable than conventional vapor-compression refrigeration systems.

Importantly, adsorption refrigeration can be powered by renewable energy sources, like the sun.

During energy production peaks, such as during the middle of the day for solar power supplies, heat is transferred to the adsorbent, causing the refrigerant to vaporize and desorb from the solid adsorbent. It detaches from the pores in the adsorbent and is condensed into a liquid for storage in the tank.

When it is time to cool down the air outside the unit, the liquid refrigerant is released to the evaporator, removing a heat from the surrounding area.

“When the refrigerant adsorbs onto the solid surface adsorbent, energy is released,” explained Dr. Vega. “Therefore, the adsorbent can be used as a thermal energy storage unit. Energy is stored during the removal of the refrigerant from the adsorbent material. The stored energy is recovered during the adsorption step and can be used as a low-temperature energy source. In this way, we can make a unit that both cools the air and stores energy.”

Developing such a unit however requires finding the perfect adsorbent-refrigerant pair. Currently, the most common refrigerants for domestic and automobile air conditioning and for vapor-compression cycles are hydrofluorocarbons, but these have tremendous global warming potential and are being phased out globally.

Using computational simulations, Dr. Vega and her team are trying to find the best adsorbent-refrigerant pair, and they are specifically looking for the ideal pairing with compounds known as metal-organic frameworks, or MOFs, combined with low global warming potential refrigerants including hydrofluoroolefins (HFO). They published their results in

“Several criteria can be used to select an adsorbent-refrigerant working pair,” said Dr. Vega. “The energy density that can be stored by adsorbent per unit of volume is an important indicator of performance. The difference in the adsorbed amount of refrigerant between adsorption and desorption—the working capacity—can also be considered. However, given the large number of potential materials that could be utilized, experimental evaluation is an expensive, time-consuming and tedious endeavor.”

Rather than individually test each pairing, the research team conducted simulations to guide selection of MOFs for thermal-storage applications. A total of 40 MOFs were studied using three refrigerants based on HFO, which has much lower global warming potential than the traditional hydrofluorocarbons.

The research team established a relationship between the adsorptive capacity and the properties of the materials, finding that MOFs with open metal sites interact strongly with the refrigerants, making them more suitable for thermal energy storage applications.

For cold thermal energy storage, MOFs with larger pore sizes showed a considerably higher energy density than the materials currently used commercially.

Jade Sterling
Science Writer
30 March 2021

The post Searching for Suitable Materials and Refrigerants for AC Units That Also Store Heat for Energy appeared first on Khalifa University.