Research Projects

Harnessing Heat Beyond 200°C with Natural Sunlight

Heat at intermediate temperatures (120−220 °C) is in significant demand in both industrial and domestic sectors for applications such as water and space heating, steam generation, sterilization, and other industrial processes. Harnessing heat from solar energy at these temperatures, however, requires costly optical and mechanical components to concentrate the dilute solar flux and suppress heat losses.

In this work, we demonstrate a solar receiver capable of reaching over 265 °C under ambient conditions without optical concentration. The high temperatures are achieved by leveraging an artificial greenhouse effect within an optimized monolithic silica aerogel to reduce heat losses while maintaining high solar transparency. This study demonstrates a viable path to promote cost-effective solar thermal energy at intermediate temperatures.


Aerogel solar thermal
Aerogel solar thermal

Light propagating in aerogel (Honourable mention 2019 OPN Photo Contest)

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Aerogel solar thermal
Aerogel solar thermal

Solar thermal conversion with transparent aerogels

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Aerogel solar thermal
Aerogel solar thermal

Transparent aerogel (higher transparency than glass)

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Aerogel solar thermal
Aerogel solar thermal

Light propagating in aerogel (Honourable mention 2019 OPN Photo Contest)

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Featured News:


MIT News

Radiative Transport in Random Media

Light propagation in random scattering media is a common phenomenon in many scientific and engineering fields. Because of multiple light-matter interactions, the transport of light intensity within a random medium is complex. Detailed understanding of the process is critical to enable rational material designs and system optimizations.

In this work, we built a radiative transfer model to accurately capture the photon transport phenomena in a general random medium characterized by its scattering and absorption properties. We successfully used the model to study the light transport in aerogels and other media. The insights gained from the model also led to a discovery of using absorption to regulate haze in a random medium.


Radiative Transport
Radiative Transport

Photon transport in a scattering aerogel medium

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Radiative Transport
Radiative Transport

Validation of radiative transfer model on aerogels

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Radiative Transport
Radiative Transport

Haze suppression with plasmonic absorption (gold nanoparticle)

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Radiative Transport
Radiative Transport

Photon transport in a scattering aerogel medium

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Stefan Flow in High-Flux Evaporators

High-flux evaporators are important for various fundamental research and industrial applications. Understanding the heat loss mechanisms, especially the contribution of natural convection during evaporation is thus a ubiquitous process to predict and optimize the performance of evaporators.

In this work, we developed a theoretical framework to elucidate the effect of Stefan flow on natural convection during evaporation. This theory incorporates the vertical Stefan flow into the conventional boundary layer theory. We found that a significant suppression of natural convection can be induced by a weak Stefan flow owing to the increase of boundary layer thickness. This work improves the fundamental understanding of the natural convection during evaporation and can help guide future high-performance evaporator designs.


Stefan Flow
Stefan Flow

Schematic

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Stefan Flow
Stefan Flow

Simulated flow and temperature field

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Stefan Flow
Stefan Flow

Schematic

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Journal Publication:


Stefan flow induced natural convection suppression on high-flux evaporators (International Communications in Heat and Mass Transfer)

Solar Steam Generator for Medical Sterilization

Health care-associated infections cause a massive burden for the health care system and the patients. Although the standard sterilization protocol with saturated steam (>121 °C and >205 kPa) is very effective, generating high-temperature and high-pressure steam is challenging without reliable access to electricity or fuel.

In this work, we developed a stationary solar thermal device capable of providing the required saturated steam. Enabled by an optimized transparent aerogel layer, the device can efficiently convert solar energy into heat to drive the steam generation process. Successful sterilization cycles were demonstrated in a field test conducted in Mumbai, India. As a general approach, this work also promises further development of solar thermal technology in energy conversion, storage, and transport applications.


Aerogel sterilization
Aerogel sterilization

Aerogel solar sterilization

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Aerogel sterilization
Aerogel sterilization

Steam outlet 100 °C

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Aerogel sterilization
Aerogel sterilization

Aerogel on solar absorber

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Aerogel sterilization
Aerogel sterilization

Aerogel solar sterilization

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Understanding Haze in Transparent Aerogels

Haze in optically transparent aerogels severely degrades the visual experience, which has prevented their adoption in windows despite their outstanding thermal insulation property. Previous studies have primarily relied on experiments to characterize haze in aerogels, however, a theoretical framework to systematically investigate haze in porous media is lacking.

In this work, we present a radiative transfer model that can predict haze in aerogels based on their physical properties. The model is validated using optical characterization of custom-fabricated, highly-transparent monolithic silica aerogels. The fundamental relationships between the aerogel structure and haze highlighted in this study could lead to a better understanding of light-matter interaction in a wide range of transparent porous materials and assist in the development of low-haze silica aerogels for high-performance glazing units to reduce building energy consumption.


Aerogel haze
Aerogel haze

Radiative transport in aerogel

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Aerogel haze
Aerogel haze

Relationship between haze and aerogel structural properties

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Aerogel haze
Aerogel haze

Correlation of haze and total transmittance in aerogels

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Aerogel haze
Aerogel haze

Radiative transport in aerogel

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Ultrahigh-efficiency Multistage Solar Desalination

Passive vapor generation systems with interfacial solar heat localization enable high-efficiency low-cost desalination. In particular, recent progress combining interfacial solar heating and vaporization enthalpy recycling through a capillary-fed multistage architecture, known as the thermally-localized multistage solar still (TMSS), significantly improves the performance of passive solar desalination.

In this work, using a low-cost and free- of-salt accumulation TMSS architecture, we experimentally demonstrated a record-high solar-to-vapor conversion efficiency of 385%. Our device can provide more than 1.5 gallons of fresh drinking water per hour for every square meter of solar collecting area - a significant advancement in passive solar desalination devices.


Multistage Solar Desalination
Multistage Solar Desalination

Multistage solar still

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Multistage Solar Desalination
Multistage Solar Desalination

Solar still prototype

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Multistage Solar Desalination
Multistage Solar Desalination

Outdoor demonstration at MIT

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Multistage Solar Desalination
Multistage Solar Desalination

Multistage solar still

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