Turning Heat Into Sound Into Electricity 257
WrongSizeGlass writes "Science Daily is reporting on work by physicists at the University of Utah who have developed small devices that turn heat into sound and then into electricity. 'We are converting waste heat to electricity in an efficient, simple way by using sound [...] It is a new source of renewable energy from waste heat.' They report that technology holds promise for changing waste heat into electricity, harnessing solar energy and cooling computers and radars."
No efficiency ratings (Score:5, Insightful)
With double conversions it couldn't be much.
Why not convert heat into electricity DIRECTLY using a peltier device?
(aka Seebeck effect http://en.wikipedia.org/wiki/Thermoelectric_effec
Good for comps (Score:4, Insightful)
cooling computers? (Score:3, Insightful)
Re:No efficiency ratings (Score:5, Insightful)
Because peltier junctions are themselves horribly inefficient?
Re:Efficiency as opposed to thermoelectric? (Score:3, Insightful)
Imagine replacing a car radiator with it?
Just a little prob with the numbers.... (Score:5, Insightful)
- Good old Carnot's law. The efficiency is limited by the temperature drop across the device compared to the absolute temperature. Now take two thermometers, stick one up your butt and fart. compute the temperature difference. Divide by 483. That's your efficiency in converting heated gas into sound. Prolly about 0.005% as a rough approx.
- For a less gross example, pucker your lips and blow. Do this for five minutes or until you pass out. You probably feel warm-- that's the heat. How much acoustic power did you generate? Well a loud whistle is about 100dbA, about a hundredth of a watt. Efficiency, 0.004% at best.
- Piezoelectic efficiency. Well, it's really high-- for an acoustic transducer. The Interwebs seem to reveal no figures for this, and in general a high level of coyness is a way of hiding embarrasing numbers. Let's assume a best-case number of say 40%.
- The impedances. Crystals are very high impedance devices, putting out LOTS of volts at vanishingly small amps, which is bad news for us, as most of our power sinks are low impedance. Getting a few milliamps at 40KV is not very compatible with powering your laptop, which is about a million times lower in impedance. It's particularly inconcvenient converting tens of kilovolts downwards with economy and efficiency.
So sorry, probably much less than nothing to see here, just another bundle of our taxpayer's money spent on a totally pointless technical exercise.Re:Efficiency as opposed to thermoelectric? (Score:2, Insightful)
Never mind the hair splitting over "efficiency." How about the absurdity of using the word "renewable?" Where is the heat coming from? Is THAT source of energy renewable (meaning, something that grows back or becomes re-available after it's been used, with less energy required to make it that way than you get out of it? It's maddening to see presumably technical discussions about something as important as energy and its practical applications... and the main modifying word put in front of the work "energy" is... wrong. Solar energy isn't renewable... it's continually available from the sun. Logs for your fireplace could reasonably be said to be renewable, if you take the trouble (and other energy) and have the time to renew them and re-harvest them. Wind isn't renewable - it's just generally, mostly available... and it requires an ongoing expense and complex infrastructure to turn it into something handy like electricity.
Oil (from the ground, anyway) will get used up (if we're talking in reasonable time windows, here) eventually. So, let's call that NOT renewable. An electricity-producing technology (as in TFA) that happens to produce some using waste heat from burning hydrocarbons like coil or oil is NOT "renewable". Honestly: people seem to think that "renewable" and "efficient" or "not wasteful" mean the same things. They do NOT. Why does this semantic fuss matter? Because we're going to raise an entire generation of science-less, witless consumers that bandy about terms like "green" and "renewable" and "hydrogen economy" without actually having the critical thinking skills to see how it all does (or does not) fit together. Taking the meaning away from words dumbs all communication down, and erodes our culture's ability to do intellectually challenging things.
Re:Efficiency as opposed to thermoelectric? (Score:4, Insightful)
Wow, you woke up in a pedantic mood this morning...
We call "renewable" energy a form of energy that we're not exhausting by using up. Harvesting solar energy today won't make less sun energy available tomorrow. The sun will not expire faster if we use its energy to produce electricity. Hydro is the same. Water will flow from the top of the mountain to the bottom whether we build a dam or not, so while we are harvesting the water's potential energy, we are not the cause of its exhaustion (gravity is, damn you gravity!).
When you do something "from scratch", do you start by creating a whole universe from a Big Bang instead of using what's already there (thus, not starting really from scratch)? People do stuff from scratch without creating universes, and the sun provides renewable energy.
Words have accepted meanings, and that is how we communicate. Agreed upon meanings are usually recorded in big books we call dictionaries. You should get one, they're really good.
May I recommend The American Heritage® Dictionary of the English Language, Fourth Edition, which defines renewable as :
Or maybe you would prefer WordNet® 3.0© 2006 Princeton University
Here's a last one from The American Heritage® Science Dictionary
Re:Efficiency as opposed to thermoelectric? (Score:1, Insightful)