Science > Physics > PHYSICS NEWS UPDATE -- Number 727 April 14, 2005 by Phillip F. Schewe,Ben Stein
| Topic: |
Science > Physics |
| User: |
"Sam Wormley" |
| Date: |
14 Apr 2005 01:33:05 PM |
| Object: |
PHYSICS NEWS UPDATE -- Number 727 April 14, 2005 by Phillip F. Schewe,Ben Stein |
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 727 April 14, 2005 by Phillip F. Schewe, Ben Stein
A NEW KIND OF EQUILIBRIUM. Normally heat will flow from a hot place
to a neighboring cold place. In a new form of thermoelectric
refrigerator, proposed by Tammy Humphrey (University of Wollongong,
Australia) and Heiner Linke (University of Oregon), temperature
imbalances can be held at bay by electrochemical imbalances. The
implications? Possibly much more efficient forms of no-moving-parts
electric refrigerators.
Heat and electricity are two forms of energy, and in a special
circuit, made from thermoelectric materials, a temperature
difference can generate electricity and, conversely, a voltage
difference can bring about a temperature difference. A
thermoelectric circuit usually consists of two semiconductors joined
at two junctions. One of the semiconductors is of the p type with a
surplus of holes, the other of the n type with a surplus of
electrons. Here's how you can generate heat or electricity in
contrary phenomena. In the Peltier effect, a voltage imbalance will
pull electrons and holes out of one of the junctions, thus cooling
that junction and warming the other junction. In the Seebeck
effect, things work in reverse: a temperature imbalance between the
junctions will set electrons and holes in motion, thus constituting
an electric current. The Peltier effect is at work, for example, in
on-chip cooling of critical microcircuitry. The Seebeck effect is
used in powering spacecraft (too far from the sun for photocells to
be of use), where the heat from a radioactive source is used to make
electricity. What keeps thermoelectric devices from greater
applicability is the poor efficiency, typically 10%. One of the
main problems is that some of the heat (applied at one junction)
used to drive a current through the circuit is carried by electrons
to the other junction, reducing the thermal gradient and therefore
sapping the process of generating electricity. What one needs is a
circuit good for electric conduction but poor for thermal conduction
by electrons. And this is what Humphrey (tammy.humphrey@unsw.edu.au
) and Linke's proposed circuit would do (see figure at
http://www.aip.org/png ). The p-leg and n-leg parts of the circuits would
consist not of bulk matter but of quantum dots, nanoscopic pieces of
matter in which only select electron energies are allowed. Engineer
the dots to discourage the higher-energy electrons carrying thermal
energy, heat leakage will drop, and the overall efficiency will go
up. The best thermoelectric efficiencies are about 10%. If
efficiencies could be pushed to 50%, the thermoelectric approach
(silent, less bulky, no refrigerant, long lived) would compete to
take over even bulk household refrigeration, Humphrey says.
(Physical Review Letters, 11 March 2005; lab website
http://www.humphrey.id.au,
http://darkwing.uoregon.edu/~linke/ )
COOLING OF BULK MATERIAL has been achieved with a solid-state
refrigerator. At the heart of the NIST-Boulder device is a tiny
sandwich-shaped diode whose layers are successively a normal metal,
an insulator, and a superconductor. The stack has the effect of
pulling the hottest electrons out of the normal-metal layer. This
no-moving-parts refrigerator is not the first to achieve 100 mK
temperatures but it is the first to do so with technologically
useful cooling powers. The NIST micro-fridge chilled a cube of
germanium about 250 microns on a side and with a mass of 80
micrograms. This sounds like a small speck of matter, but it was
enormous compared to the size of the refrigerating junctions (see
figure at http://www.aip.org/png ). Indeed, the ratio of the volume of the
cube to the volume of the junctions is 11,000. This is equivalent
to a refrigerator the size of a person chilling something the size
of the Statue of Liberty. In preliminary tests, the cube was cooled
from 320 mK down to 240 mK. Future improvements should lower the
base temperature to near 100 mK. According to NIST physicist Joel
Ullom (ullom@boulder.nist.gov), their refrigerator works best at
temperatures below 1 K, so it won't be used to cool foods. But it
will be very useful for chilling circuitry on chips and maybe
samples as large as the centimeter size. (Clark et al., Applied
Physics Letters, upcoming article)
***********
PHYSICS NEWS UPDATE is a digest of physics news items arising
from physics meetings, physics journals, newspapers and
magazines, and other news sources. It is provided free of charge
as a way of broadly disseminating information about physics and
physicists. For that reason, you are free to post it, if you like,
where others can read it, providing only that you credit AIP.
Physics News Update appears approximately once a week.
.
|
|
| User: "Uncle Al" |
|
| Title: Re: PHYSICS NEWS UPDATE -- Number 727 April 14, 2005 by Phillip F.Schewe,Ben Stein |
14 Apr 2005 03:21:11 PM |
|
|
Sam Wormley wrote:
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 727 April 14, 2005 by Phillip F. Schewe, Ben Stein
A NEW KIND OF EQUILIBRIUM. Normally heat will flow from a hot place
to a neighboring cold place. In a new form of thermoelectric
refrigerator, proposed by Tammy Humphrey (University of Wollongong,
Australia) and Heiner Linke (University of Oregon), temperature
imbalances can be held at bay by electrochemical imbalances. The
implications? Possibly much more efficient forms of no-moving-parts
electric refrigerators.
[snip]
What one needs is a
circuit good for electric conduction but poor for thermal conduction
by electrons.
An electronic crystal simultaneously being a photonic glass. It's not
news.
And this is what Humphrey (tammy.humphrey@unsw.edu.au
) and Linke's proposed circuit would do (see figure at
http://www.aip.org/png ). The p-leg and n-leg parts of the circuits would
consist not of bulk matter but of quantum dots, nanoscopic pieces of
matter in which only select electron energies are allowed.
Uncle Al had grown tired of seeing cancer cures needing more studies
everywhere. As nanoscopic materials have been implicated in vigorous
carcincogenesis, the new someday cure-all for the world's problems
forges a nice symbiotic relationship for future grantsmanship
developments re the old someday cure-alls.
Engineer
the dots to discourage the higher-energy electrons carrying thermal
energy, heat leakage will drop, and the overall efficiency will go
up. The best thermoelectric efficiencies are about 10%. If
efficiencies could be pushed to 50%, the thermoelectric approach
(silent, less bulky, no refrigerant, long lived) would compete to
take over even bulk household refrigeration, Humphrey says.
Damn the thermodynamics, more studies are needed!
COOLING OF BULK MATERIAL has been achieved with a solid-state
refrigerator. At the heart of the NIST-Boulder device is a tiny
sandwich-shaped diode whose layers are successively a normal metal,
an insulator, and a superconductor. The stack has the effect of
pulling the hottest electrons out of the normal-metal layer. This
no-moving-parts refrigerator is not the first to achieve 100 mK
temperatures but it is the first to do so with technologically
useful cooling powers. The NIST micro-fridge chilled a cube of
germanium about 250 microns on a side and with a mass of 80
micrograms.
[snip]
In preliminary tests, the cube was cooled
from 320 mK down to 240 mK. Future improvements should lower the
base temperature to near 100 mK.
[snip]
More studies are needed! Cooling a 1/4 millimeter cube by 0.08 degees
deserves performance bonuses for all the many layers of management
that did the hard work. Fire a few researchers for not making it
better faster.
According to NIST physicist Joel
Ullom (ullom@boulder.nist.gov), their refrigerator works best at
temperatures below 1 K, so it won't be used to cool foods.
Fire the insubordinate sonofabitch. New food cooler! New food
cooler!
But it
will be very useful for chilling circuitry on chips and maybe
samples as large as the centimeter size.
Yeah, that 0.08 degree triumph will sure make a difference when my AMD
Athlon 64 55-FX goes 99% and heats to 50 C. I'm gonna toss my forced
100 cfm muffin fan that brings it down to 40 C and wait for NIST to
reach more benchmarks. (Pentium-4s don't need good cooling. They
automatically slow down to stay within temp specs. Hello to all you
underclockers out there!)
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
.
|
|
|
|
|
Related Articles |
PHYSICS NEWS UPDATE -- Number 818 April 5, 2007 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 821 April 23, 2007 by Phillip F.Schewe, Ben Stein
Physics News Update -- Number 682, April 21, 2004
PHYSICS NEWS UPDATE -- Number 772 April 5, 2006 by Phillip F. Schewe,Ben Stein, and Davide Castelvecchi
Physics News Update -- Number 679, April 1, 2004
PHYSICS NEWS UPDATE -- Number 774 April 19, 2006 by Phillip F.Schewe, Ben Stein, and Davide Castelvecchi
Physics News Update Number 680, April 8, 2004
PHYSICS NEWS UPDATE -- Number 729 April 27, 2005 by Phillip F. Schewe,Ben Stein
| PHYSICS NEWS UPDATE -- Number 725 April 1, 2005 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 820 April 18, 2007 by Phillip F.Schewe, Ben Stein
Physics News Update -- Number 683, April 29, 2004
Physics News Update -- Number 681, April 13, 2004
PHYSICS NEWS UPDATE -- Number 775 April 26, 2006 by Phillip F.Schewe, Ben Stein, and Davide Castelvecchi
PHYSICS NEWS UPDATE -- Number 726 April 7, 2005 by Phillip F. Schewe,Ben Stein
PHYSICS NEWS UPDATE -- Number 728 April 20, 2005 by Phillip F. Schewe,Ben Stein
|
|
|
