Turning Heat Into Sound Into Electricity

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."

Comments

No efficiency ratings

[denis-The-menace]

How efficient is it?

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_effect )

Re:No efficiency ratings

[drinkypoo]

Why not convert heat into electricity DIRECTLY using a peltier device?

Because peltier junctions are themselves horribly inefficient?

Good for comps

[eebra82]

I realize this could be a great thing for computers - especially portable computers. However, I am more interested in how large portion of the heat that turns into sound and eventually into electricity. My stationary computer is fine without all that extra power. What I want is to know if this will kill the need for huge fans and actually remove some of the heat, or if it will just suck a small portion of it.

cooling computers?

[gEvil (beta)]

I'm not sure about you, but when I spec parts for computer cooling, I'm looking for something that's cool AND quiet. I don't want whatever device to be creating extra sound in it's quest to cool more efficiently.

Re:Efficiency as opposed to thermoelectric?

[LWATCDR]

I think cost is more important the efficiency. If it was cheap enough and if you could say get 10% out of it it could be very useful.
Imagine replacing a car radiator with it?

Just a little prob with the numbers....

[Ancient_Hacker]

Nothing to see here. It's just a Prof that's spent $2 million on a wild goose chase. Now with the great smell of fish! The rub is multi-fold:

• 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?

[Phisbut]

Never mind the hair splitting over "efficiency." How about the absurdity of using the word "renewable?"

Wow, you woke up in a pedantic mood this morning...

Solar energy isn't renewable... it's continually available from the sun. [...] Wind isn't renewable - it's just generally, mostly available...

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.

Taking the meaning away from words dumbs all communication down, and erodes our culture's ability to do intellectually challenging things.

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 :

Relating to or being a commodity or resource, such as solar energy or firewood, that is inexhaustible or replaceable by new growth.

Or maybe you would prefer WordNet® 3.0© 2006 Princeton University

capable of being renewed; replaceable; "renewable energy such as solar energy is theoretically inexhaustible"

Here's a last one from The American Heritage® Science Dictionary

Relating to a natural resource, such as solar energy, water, or wood, that is never used up or that can be replaced by new growth. Resources that are dependent on regrowth can sometimes be depleted beyond the point of renewability, as when the deforestation of land leads to desertification or when a commercially valuable species is harvested to extinction. Pollution can also make a renewable resource such as water unusable in a particular location.