Alternative technology
37
Science Daily
Bubbly solution
to water heating
Massachusetts Institute of Technology (MIT) researchers and
others from the Masdar Institute of Science and Technology, in
the United Arab Emirates have invented a device that absorbs
natural sunlight and heats water to boiling temperatures.
The bubblewrapped, spongelike device that
soaks up natural
sunlight and heats
water to boiling
temperatures.
By Jennifer Chu – MIT News
The bubble-wrapped, sponge-like device soaks
up ambient sunlight and heats water to boiling
temperatures, generating steam through its pores.
How do you boil water? Do you usually use an electric
or stovetop kettle? Not at MIT. This design, which the
researchers call a “solar vapour generator”, does not
require expensive mirrors or lenses to concentrate the
sunlight. Instead, it relies on a combination of relatively
low technology materials to capture ambient sunlight and
concentrate it as heat. The heat is then directed towards
the sponge’s pores, which draw water up and release it
as steam.
From their experiments — including one in which they
simply placed the solar sponge on the roof of MIT’s Building
3 — the researchers discovered that the structure heated
water to its boiling temperature of 100°C even on relatively
cool, overcast days. The sponge also converted 20% of the
incoming sunlight to steam.
This low technology design may provide inexpensive
alternatives for applications ranging from desalination and
residential water heating, to wastewater treatment and
medical tool sterilisation.
www.plumbingafrica.co.za
The team published their results in the Nature Energy
journal in September. The research was led by George
Ni (an MIT graduate student) and Gang Chen (the Carl
Richard Söderberg Professor of Power Engineering and
head of the Department of Mechanical Engineering
at MIT), in collaboration with TieJun Zhang and his
group members Hongxia Li and Weilin Yang from the
Department of Mechanical and Materials Engineering at
the Masdar Institute of Science and Technology, in the
United Arab Emirates.
Looking for answers
The researchers’ current design builds on a solar-absorbing
structure they developed in 2014: a similar floating,
sponge-like material made of graphite and carbon foam,
which was able to boil water to 100°C and convert 85% of
the incoming sunlight to steam.
To generate steam at such efficient levels, the researchers
had to expose the structure to simulated sunlight that
was 10 times the intensity of sunlight in normal, ambient
conditions. “It was relatively low optical concentration,”
Chen says. “But I kept asking myself, ‘Can we basically boil
water on a rooftop, in normal conditions, without optically
concentrating the sunlight?’ That was the basic premise.”
Continued on page 38 >>
November 2016 Volume 22 I Number 9