Optically transparent aerogel is essentially a lightweight foam made of silica, the material of beach sand, and consists mostly of air. It reduces the rate of heat loss by tenfold.
This transparent insulating material is bonded onto the top of off-the-shelf equipment for producing solar hot water. A copper plate with a heat-absorbing black coating is bonded to a set of pipes on the underside. As the sun heats the plate, water flowing through the pipes underneath picks up that heat. But with the addition of the transparent insulating layer on top, plus polished aluminum mirrors on each side of the plate to direct extra sunlight at the plate, the system can generate high-temperature steam instead of just hot water. The system uses gravity to feed water from a tank into the plate; the steam then rises to the top of the enclosure and is fed out through another pipe, which carries the pressurized steam to the autoclave. A steady supply of steam must be maintained for 30 minutes to achieve proper sterilization.
A steady supply of pressurized steam at a temperature of about 125 degrees Celsius will sterilize medical equipment in the developing world and in any off-grid situation. There are still about 700 million people in the world without electricity.
It will take a few years to scale up the production of the aerogel. One company, founded by Elise Strobach PhD ’20, who is a co-author of this paper, is already attempting to scale up the production of transparent aerogel, for use in high thermal efficiency windows. The offgrid medical autoclave would then cost about $160.
• A passive solar thermal device that can generate steam at 128°C and 250 kPa
• Efficient thermal concentration enabled by an ultra-transparent aerogel layer
• Up to 56% efficiency when generating steam at 100°C with 0.7 kW/m2 solar flux
• Effective medical sterilization demonstrated under realistic weather conditions
Context & Scale
Healthcare-associated infections cause a massive burden for the health care system and the patients. Although the standard sterilization protocol with saturated steam (over 121°C and over 205 kPa) is effective, generating high-temperature and high-pressure steam is challenging without reliable access to electricity or fuel. While abundant solar energy is readily available, utilizing sunlight to generate steam beyond 100°C requires costly and bulky optomechanical components. 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.
Saturated steam (over 121°C and over 205 kPa) is widely used in the medical sterilization process known as autoclaving. However, solar-driven steam generation at such high temperature and pressure requires expensive optical concentrators. We demonstrate a passive solar thermal device mostly built from low-cost off-the-shelf components capable of delivering saturated and pressurized steam to drive sterilization cycles even under hazy and partly cloudy weather. Enabled by an optimized ultra-transparent silica aerogel, the device utilizes an efficient thermal concentration strategy to locally increase the heat flux and temperature obviating the need for active optical concentrators. With almost 2× higher energy efficiency (47%) than those previously reported at 100°C, the device demonstrated successful sterilization in a field test performed in Mumbai, India. In addition to enabling passive sterilization, this work promises the development of solar thermal energy systems for saturated steam generation in energy conversion, storage, and transport applications.
SOURCES- MIT, Journal Cell
Written By Brian Wang, Nextbigfuture.com
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