Catalytic micro combustor 

As part of a atmospheric water extraction program supported by DARPA, I am currently working on a portable (<2.5 kg; <1.5 L) atmospheric water extractor capable of harvesting >5.5 L of water per day in low humidity environments. More specifically, I am developing a high-temperature (650 °C) catalytic micro combustor that will provide the necessary heat (500-2000 W) for the device operation in a light and compact setup using high energy density fuels such as propane or butane. 

Hybrid evaporative and radiative cooling

By combining evaporative and radiative cooling in a hybrid architecture, we can achieve much higher cooling heat flux than standalone radiative cooling while also saving significantly on water consumption over standalone evaporative cooling, thus combining the best of both technologies. In this project, we have been developing models and prototypes of this hybrid cooling architecture using polyethylene aerogel, hydrogel and solar reflecting layers. We are currently looking into the commercial potential of this cooling architecture to help decrease space cooling energy use in buildings such as data centers and supermarkets. 

Related publications:

  1. A. Leroy*, Z. Lu*, et al., Hybrid evaporative-radiative cooling architecture for large energy savingsin buildings. (Submitted)


Polyethylene aerogels for radiative cooling

Radiative cooling can passively cool terrestrial objects to sub-ambient temperatures by radiating heat to the cold outer space through the infrared (IR) transparent window of the atmosphere (8-13 µm)While past work has mostly focused on developing spectrally selective surfaces that minimize solar absorption and maximize IR emission, significant parasitic heating of radiative coolers due to the higher-temperature ambient severely limits the overall cooling performance. Over the last few years, I have developed polyethylene aerogels (PEAs) – an optically selective and thermally insulating cover that can significantly reduce parasitic heat gain at the emitter while strongly reflecting sunlight and still allowing for radiative exchange with outer space. By optimizing the porous structure of the PEA, I was able to maximize scattering and reflectance in the solar spectrum (92% solar-weighted reflectance at 6 mm thickwhile achieving high transmittance in IR wavelengths (80% transmittance between 8-13 µm at 6 mm thick) and low thermal conductivity (kPEA = 28mW/mK). Using PEA, I experimentally demonstrated a daytime cooling power of 96 W/m² at ambient temperature and cooling up to 13 °C below ambient under direct sunlight. In addition, I developed a radiative transfer equation based framework to model thermal transport within the PEA and evaluate the resulting radiative cooling performance – which is compared with experiments. Overall, the work demonstrates that using optically selective and thermally insulating covercan provide access to a wide range of previously inaccessible sub-ambient temperatures and cooling powers for both daytime and nighttime operation which could enable application of radiative cooling in emission-free air-conditioning and food storage.   

Related publications:

  1. A. Leroy, et al. (2019), High-performance subambient radiative cooling enabled by optically selective and thermally insulating polyethylene aerogel. Science Advances.
  2. B. Bhatia, A. Leroy, et al. (2018), Passive directional sub-ambient daytime radiative cooling. Nature Communications.

High optical selectivity polyethylene aerogels