We are in the process of building a lab and setting up new experiments to develop energy efficient desalination technologies and thermal energy storage concepts. Here’s a summary of some of the prior work.
Photo-Thermal Converters for Enhanced Evaporation (Water)
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)
An emerging desalination technology is based on forward osmosis (FO), which uses a draw solution to drive water flux across a membrane. However, separation of the draw from the permeate water requires significant amounts of energy, and this has limited the applicability of FO thus far. To address this, we are developing a thermally-responsive draw solutes and photo-thermal converters to efficiently harness the solar spectrum. This in turn enables the use of solar heat for the water-draw separation process via direct radiative heating to yield fresh water.
Related publications: Environmental Science & Technology (2021)
Thermoelectric energy conversion (Energy)
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 (Energy)
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.
Related publications: Journal of Applied Physics (2019); Advanced Energy Materials (2019); Advanced Electronic Materials (2019) – 1; Advanced Electronic Materials 2029) – 2; Advanced Energy Materials (2018); Advanced Functional Materials (2018) – 1; Advanced Functional Materials (2018) – 2
Renewable Hydrogen Production (Energy)
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.