We discuss and comment on the role agriculture will play in the containment of the CO2 problem and address protocols for terraforming the planet Earth.
A model farm template is imagined as the central methodology. A broad range of timely science news and other topics of interest are commented on.
Monday, October 1, 2012
Thermoelectric energy conversion has been a sweet spot forever since
we still depend on heat engines hugely. The caveat has been the
weight penalty for the best known technology which is the reverse
Rankin cycle which is able to convert the heat in boiling water to
seventy five percent brake horsepower. A creditable addon for a
thermal power plant but useless for mobile devices. Thus stripping
energy out of exhaust gases is attractive.
It still does nothing for jacket heat, but it sounds like this
technology may be able to ultimately work at lower heat levels. It
is a good beginning wrre progress has been invisible.
I do expect heat machines to become obsolete however, and I do not
think we will be left waiting much longer. Thus this is a solution
in which the market is preparing to disappear.
material is world's best at converting heat waste to electricity
September 19, 2012
University scientists have developed a thermoelectric material that
is the best in the world at converting waste heat to electricity.
This is very good news once you realize nearly two-thirds of energy
input is lost as waste heat.
The material could
signify a paradigm shift. The inefficiency of current thermoelectric
materials has limited their commercial use. Now, with a very
environmentally stable material that is expected to convert 15 to 20
percent of waste heat to useful electricity, thermoelectrics could
see more widespread adoption by industry. Possible areas of
application include the automobile industry (much of gasoline's
potential energy goes out a vehicle's tailpipe), heavy manufacturing
industries (such as glass and brick making, refineries, coal- and
gas-fired power plants) and places were large combustion engines
operate continuously (such as in large ships and tankers).
temperatures in these areas can range from 400 to 600 degrees Celsius
(750 to 1,100 degrees Fahrenheit), the sweet spot for thermoelectrics
use. The new material, based on the common semiconductor lead
telluride, is the most efficient thermoelectric material known. It
exhibits a thermoelectric figure of merit (so-called "ZT")
of 2.2, the highest reported to date. Chemists, physicists, material
scientists and mechanical engineers at Northwestern and Michigan
State University collaborated to develop the material. The study will
be published Sept. 20 by the journal Nature.
"Our system is
the top-performing thermoelectric system at any temperature,"
said Mercouri G. Kanatzidis, who led the research and is a senior
author of the paper. "The material can convert heat to
electricity at the highest possible efficiency. At this level, there
are realistic prospects for recovering high-temperature waste heat
and turning it into useful energy."
Charles E. and Emma H. Morrison Professor of Chemistry in
Northwestern's Weinberg College of Arts and Sciences. He also holds a
joint appointment at Argonne National Laboratory.
ask, what is the energy solution?" said Vinayak P. Dravid, one
of Kanatzidis' close collaborators. "But there is no unique
solution—it's going to be a distributed solution. Thermoelectrics
is not the answer to all our energy problems, but it is an important
part of the equation."
Dravid is the Abraham
Harris Professor of Materials Science and Engineering at the
McCormick School of Engineering and Applied Science and a senior
author of the paper. Other members of the team and authors of the
Nature paper include Kanishka Biswas, a postdoctoral fellow in
Kanatzidis' group; Jiaqing He, a postdoctoral member in Dravid's
group; David N. Seidman, Walter P. Murphy Professor of Materials
Science and Engineering at Northwestern; and Timothy P. Hogan,
professor of electrical and computer engineering, at Michigan State
Even before the
Northwestern record-setting material, thermoelectric materials were
starting to get better and being tested in more applications. The
Mars rover Curiosity is powered by lead telluride thermoelectrics
(although it's system has a ZT of only 1, making it half as efficient
as Northwestern's system), and BMW is testing thermoelectrics in its
cars by harvesting heat from the exhaust system.
"Now, having a
material with a ZT greater than two, we are allowed to really think
big, to think outside the box," Dravid said. "This is an
"Improving the ZT
never stops—the higher the ZT, the better," Kanatzidis said.
"We would like to design even better materials and reach 2.5 or
3. We continue to have new ideas and are working to better understand
the material we have."
The efficiency of
waste heat conversion in thermoelectrics is governed by its figure of
merit, or ZT. This number represents a ratio of electrical
conductivity and thermoelectric power in the numerator (which need to
be high) and thermal conductivity in the denominator (which needs to
be low). "It is hard to increase one without compromising the
other," Dravid said. These contradictory requirements stalled
the progress towards a higher ZT for many years, where it was
stagnant at a nominal value of 1.
Kanatzidis and Dravid
have pushed the ZT higher and higher in recent years by introducing
nanostructures in bulk thermoelectrics. In January 2011, they
published a report in Nature Chemistry of a thermoelectric material
with a ZT of 1.7 at 800 degrees Kelvin.
This was the first
example of using nanostructures (nanocrystals of rock-salt structured
strontium telluride) in lead telluride to reduce electron scattering
and increase the energy conversion efficiency of the material.
The performance of the
new material reported now in Nature is nearly 30 percent more
efficient than its predecessor. The researchers achieved this by
scattering a wider spectrum of phonons, across all wavelengths, which
is important in reducing thermal conductivity. "Every time a
phonon is scattered the thermal conductivity gets lower, which is
what we want for increased efficiency," Kanatzidis said. A
phonon is a quantum of vibrational energy, and each has a different
wavelength. When heat flows through a material, a spectrum of phonons
needs to be scattered at different wavelengths (short, intermediate
and long). In this work, the researchers show that all length scales
can be optimized for maximum phonon scattering with minor change in
three techniques to scatter short, medium and long wavelengths all
together in one material, and they all work simultaneously,"
"We are the first
to scatter all three at once and at the widest spectrum known. We
call this a panoscopic approach that goes beyond nanostructuring."
"It's a very
elegant design," Dravid said. In particular, the researchers
improved the long-wavelength scattering of phonons by controlling and
tailoring the mesoscale architecture of the nanostructured
thermoelectric materials. This resulted in the world record of a ZT
of 2.2. The successful approach of integrated all-length-scale
scattering of phonons is applicable to all bulk thermoelectric
materials, the researchers said.
More information: The
paper is titled "High-Performance Bulk Thermoelectrics With