Research – WATER-ENERGY RESEARCH LAB (WERL)

Ongoing Projects

Thermal Energy Storage for Decarbonizing Buildings

The buildings sector accounts for a third of the total energy consumption in the United States, of which 60% is utilized in space heating/cooling and water heating. Thermal energy storage (TES) is one of the “five thermal energy grand challenges for decarbonization” as it has the potential to be store energy across different time scales (hourly to seasonal) to match supply with demand, while also being low cost and scalable. Thermochemical materials (TCMs) in the form of salt hydrates undergo an endothermic dehydration reaction (charging) and an exothermic hydration reaction (discharging), making them suitable for a thermal battery using reversible solid-gas chemical reactions. TCM-based storage is still in the early stages of development – our research is focused on addressing challenges spanning the range from materials to the system. We synthesize and characterize composite TCMs to improve their hygrothermal and structural stability during thermal cycling. We also develop coupled heat and mass transfer models across different length- and time scales to determine the performance (storage capacity and thermal power output) of packed bed TCM reactors. Finally, we develop system designs to integrate TES with HVAC to decarbonize thermal loads in buildings. These projects are funded by the U.S. Department of Energy and the National Science Foundation.

Related publications: Journal of Energy Storage (2024), MRS Communications (2022).

Thermal Energy Storage for Decarbonizing Industry and the Grid

Electrification can lead to decarbonization of buildings, transportation, and industrial processes, but it must be accompanied by expanded adoption of clean electricity. High temperature thermal storage is critical to a decarbonized electric grid, allowing for storage of excess energy from renewable sources such as solar and wind. High temperature thermal storage is also critical to decarbonize industrial process heat (e.g., steel and cement manufacturing). As part of the DEGREES Energy Earthshot Research Center, we are characterizing low-cost thermochemical materials with sufficient energy density and reaction temperatures, and we are developing a fundamental understanding of the degradation mechanisms that occur during thermal cycling. We are also designing a novel rapid thermal cycling capability that will enable long duration studies (over hundreds of cycles and across a large range of temperatures). This work is supported by the U.S. Department of Energy.

Thermal Brine Concentration and Zero Liquid Discharge Desalination

Desalination technologies hold great promise to sustainably provide reliable and climate-independent freshwater on a global scale, especially by treating nontraditional water sources that are inland. However, the challenge with existing desalination technologies is the large volume of brine (hypersaline byproduct) generated during the process that has an adverse environmental and economic cost. Further concentration of the brine not only addresses this, but also achieves higher water recoveries >90% towards zero liquid discharge (ZLD). We have developed a thermal brine concentrator based on Air Gap Diffusion Distillation (AGDD) that operates at ambient pressure and uses engineered plastic heat transfer surfaces to manage salt precipitation at high salinities. At a fundamental level, we study the surface wettability and salt adhesion behavior of different polymers at elevated temperatures and concentrations. At an applied level, we model the combined heat and mass transport in the AGDD system at different operating parameters, with latent heat recovery integration to achieve a high thermal efficiency. Overall, this AGDD-based brine concentrator can desalinate concentrated streams and lower the levelized cost of water (LCOW) to enable beneficial reuse. This work is supported by the American Chemical Society.

Related publications: Desalination (2024), MRS Communications (2022)

Solar Desalination using Thermally Responsive Materials

Beyond traditional membrane-based and thermally-driven desalination technologies, there are hybrid processes that combine the benefits of both approaches. Forward osmosis (FO) desalination is one such process, that uses a draw solution to drive water flux across a membrane. Separation of the draw from the permeate water conventionally requires significant amounts of energy (evaporation of water), which has limited the applicability of FO thus far. To address this, we select and characterize thermally responsive draw solutes based on ionic liquids (IL) that exhibit a liquid-liquid phase separation with water upon heating. These IL-water mixtures separate into a water rich phase (WR) and an ionic liquid rich phase (ILR) when heated above the lower critical solution temperature (LCST). We also develop IL mixtures of two ILs (IL1+IL2) with synergistic phase behavior and thermal regeneration pathways with fast kinetics. This in turn enables the use of low-grade heat (e.g., solar collectors) to yield fresh water at a low levelized cost as our technoeconomic models show.

Energy Modeling for Decarbonizing the Aluminum Industry

Aluminum is a widely used material for applications ranging from automobiles and beverage cans, to heat exchangers. Novelis is the leading producer of flat-rolled aluminum products and the world’s largest recycler of aluminum. To support their sustainability goals, we are developing thermofluidic models of heat exchangers to investigate the use of novel, higher recycled content aluminum alloys in fin stock. We are also working to provide feasible technology solutions that improve the energy efficiency of the secondary aluminum manufacturing process and reduce carbon emissions associated with this high temperature process. These projects are part of The Novelis Innovation Hub at Georgia Tech.

Thermally-Driven Dehumidification and Refrigeration

Air conditioning systems account for approximately 4% of global greenhouse gas emissions, due to the refrigerants and electricity needed to provide dehumidification and cooling. These emissions are projected to increase significantly as countries begin to adopt air conditioning more heavily. To address this, we have conceptualized a new thermodynamic cycle that uses phase separation in lower critical solution temperature (LCST) mixtures to provide both dehumidification and cooling. The cycle is powered by low-grade heat, operates without any greenhouse gas refrigerants, and recycles water in a closed loop. Our work on this “LCST cycle” spans all the way from fundamental thermodynamic analyses to experimental demonstrations of prototype systems. This work is supported by the U.S. Department of Energy.

Related publications: Energy Conversion and Management (2022)

Natural Fibers for Low Carbon Thermal Insulation

The building sector contributes to approximately 40% of global carbon dioxide (CO₂) emissions annually. As buildings lower their operational carbon footprint, embodied carbon contributes over 50% to the emissions of high-efficiency buildings. Most embodied carbon is emitted during raw material extraction, transport, and product manufacturing. Thermal insulation is the second largest contributor of embodied emissions in residential buildings after concrete, and this is attributed to the manufacturing of common insulation materials (e.g., expanded polystyrene or EPS and fiberglass). Although many studies have investigated bio-based alternatives, further development is required to achieve carbon-negative insulation. We are using plant fibers that sequester CO₂ as they grow, as their inherently porous and amorphous structure makes them a promising feedstock for sustainable thermal insulation. We have developed insulation comprising hemp and kenaf natural fibers with polylactic acid (PLA) and cellulose acetate (CA) binding fibers, and we are characterizing the thermal conductivity of these composites. This project is supported by the Renewable Bioproducts Institute at Georgia Tech.

Previous Projects

Photo-Thermal Converters for Enhanced Evaporation

The water-energy nexus necessitates the use of renewable energy sources for wastewater treatment, such as evaporation ponds that rely on solar energy to passively evaporate water from waste streams to achieve zero liquid discharge. However, efficient utilization of solar energy for evaporation is limited by the transparency of water in the visible and near-infrared. To address this, we convert sunlight into mid-infrared radiation where water is strongly absorbing using a photo-thermal converter. This results in radiative heat localization at the water surface, which in turn enhances the evaporation rate by over 100%. Furthermore, the non-contact nature of the device eliminates issues such as fouling and scaling with high salinity streams, thus making it suitable for brine management.

Related publications: Nature Sustainability (2020)

Thermoelectric energy conversion

Over 60% of energy rejected to the environment is at temperatures below 250 °C. Thermoelectric generators based on polymers can be used to economically capture this heat and convert it into electricity at a low cost and on a large scale. Their inherently low thermal conductivity and solution processability enables new device architectures: for waste heat recovery from pipes, I developed a radial design based on characteristic thermal length scales for polymers ~1 cm. This design enables a 10x improvement in power density compared to flat plate TEGs. By spreading the heat outward, the need for active cooling is eliminated. I have also developed a close-packed printing layout for high fill factor TE devices. Fractal space-filling curves are used as interconnect patterns, enabling tessellation of the device into sub-modules for load matching to a variety of applications, and eliminating the need for power convertors. I have also developed textiled-integrated polymer TE devices. These developments enable new applications of TEs in self-powered sensors, internet-of-things, and wearable electronics.

Polymer and Hybrid Organic-Inorganic Materials

A practical thermoelectric device requires both a p-type and an n-type material with reasonably large power factors. Although p-type organic materials with high performance have been reported and are commercially available, their n-type counterparts have not benefited from the same level of development due to their propensity to react in air. To address this, I have synthesized and characterized metal-organic polymers as electrically conducting and air stable materials, and studied their structure-property relationship. I have also developed a probe station to measure temperature-dependent thermoelectric properties of thin films.

Renewable Hydrogen Production

Hydrogen serves as an attractive alternative to fossil fuels for the production of steam, power, and some major chemical commodities with zero or near to zero emissions. However, hydrogen production is currently via the steam reforming of methane, which has a large carbon footprint. To address this, solar-thermal cracking of natural gas has been investigated which yields high-grade carbon as the by-product. Concentrated solar energy is used to maintain reactor temperatures over 1000 °C using a variable aperture mechanism. I have performed optical ray tracing and Monte-Carlo simulations to simulate the reactor temperature and heat loss mechanisms under different operating conditions.