Kick the tires, light the fires...

If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

Moderators: tonybarry, MSimon

David_Jay
Posts: 57
Joined: Sat Jan 19, 2008 2:49 pm
Location: Grand Rapids, Michigan

Post by David_Jay »

I especially like the molecular vacuum sleeve on the flywheel shaft that provides better than 5 mT vacuum without a discrete vacuum pump.
not tall, not raving (yet...)

ravingdave
Posts: 650
Joined: Wed Jun 27, 2007 2:41 am

Post by ravingdave »

David_Jay wrote:These guys look even better - vacuum chamber with magnetic levitation bearings - 20 year maintenance free.

http://www.pentadyne.com/site/our-produ ... ology.html

Wasn't it larry niven that wrote a story in which they used superflywheels to power cars in the future ? I wonder what the energy storage density is for current designs that might fit in a car ?
The biggest problem with electric vehicles currently is the battery storage system.

David

hanelyp
Posts: 2257
Joined: Fri Oct 26, 2007 8:50 pm

Post by hanelyp »

ravingdave wrote: superflywheels to power cars in the future ?
Both batteries and flywheels are limited by the strength of molecular bonds. Not sure which can make better use within that limit.

MSimon
Posts: 14332
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

For our purposes it is not the energy density that matters but the ability to deliver high pulse powers.

I think ultimate flywheels have about 5X the energy density of the best batteries. There is the problem of gimbals. And the fact that the flywheel is going to rotate with time.

The other thing is that for real utility type storage the losses of the best flywheels have to be reduced 10X from what they are now. Better yet 100X.
Engineering is the art of making what you want from what you can get at a profit.

David_Jay
Posts: 57
Joined: Sat Jan 19, 2008 2:49 pm
Location: Grand Rapids, Michigan

Post by David_Jay »

Simon:

What efficiencies are you thinking about? The conversion efficiencies? I am not following.

The Pentadyne specs claim a 1000Wh thermal load (for the HVAC system) when idling a 225kW storage system. Since essientially all losses (electrcial and mechanical) will take the form of heat, this looks pretty good. The implied efficiency (again, this is only in standby) is over 99.55 / hr.
not tall, not raving (yet...)

MSimon
Posts: 14332
Joined: Mon Jul 16, 2007 7:37 pm
Location: Rockford, Illinois
Contact:

Post by MSimon »

The flywheel can store 1 MJ (100 KW for 10 seconds).

It has a standby load of 300 W. That is 300 J/ second or 1 MJ in 1 hour.

Thus: high losses.
Engineering is the art of making what you want from what you can get at a profit.

Mike Holmes
Posts: 308
Joined: Thu Jun 05, 2008 1:15 pm

Post by Mike Holmes »

Isn't the real problem with flywheels for cars, no matter how efficient, that a collision involving a car with one could be catastrophic? If a full-spin wheel comes into contact with anything, the damage could be collossal. No?

I recall this, because I believe Niven himself cited the problem. His engineering ideas are usually eventually found to be flawed, and really are in the fiction to discuss the implications of such engineering feats in the abstract, rather than proposing them as effective. That is, he's smart enough to know that he can't predict what technology will actually be implemented, so he simply posits one that gets us thinking.

I recall that at one sci-fi convention (long ago) a group of students from MIT or someplace stormed in moblike, chanting "The Ringworld is Unstable" after one of their number had proved that even with unobtanium that the thing could not exist.

The question of elecrical transportation is a solvable one. In fact, we forget that at one time we had efficient electric transportation in the US in every major city. Streetcars (do I have to put in a link for the youngsters?) They were killed by the automakers working with legislators to see that they went away.

Electric transportation is merely a case of having the will to have it occur. Note that you could even do this with cars, with existing safe technology, if you're willing to put electromagnets in every street... we could even all have maglev cars. The cost would be astronomical. But from a technical POV, it's an easy feat. You just can't take such a vehicle "offroad".

Not that I ever go offroad, I don't know about you. Of course it could have a backup ICE. I can't wait for the day when "Hybrid" means, "mostly runs on electric, but on ICE when electricity isn't available." The plug-in Hybrids due out in the next two years are the first step there. With current battery technology, I can make my daily commute with no gas used at all.

Mike

Betruger
Posts: 2311
Joined: Tue May 06, 2008 11:54 am

Feasibility

Post by Betruger »

Mike Holmes wrote:Isn't the real problem with flywheels for cars, no matter how efficient, that a collision involving a car with one could be catastrophic? If a full-spin wheel comes into contact with anything, the damage could be collossal. No?
Isn't that just a matter of isolating the flywheel mechanism from everything else? Would such an assembly be unfeasible?
You just can't take such a vehicle "offroad".
Would it be so unfeasible to have the wheels retract while on maglev, and come back out like any aircraft's landing gear once on its own, "off-road"?

Mike Holmes
Posts: 308
Joined: Thu Jun 05, 2008 1:15 pm

Post by Mike Holmes »

Like I said, sure, "Hybrid" meaning "On-grid/Off-grid."

You can "isolate" the flywheel in the vehicle from it's other components, sure. But when your can impacts mine at a relative 70 MPH (both going 35 in the opposite direction), it's going to be an amazing engineering trick to keep that flywheel isolated. Oh, it won't tip at all... the gyrostabilization energy will see to that. But the casing and internal gimbals would have to withstand the impact somehow, and that's a tremendous amount of energy. Those would be some impressive "crumple zones."

Oh, sure, you're probably thinking "well I'll probably be dead in such a head-on collision anyhow." But it's not the vehicle occupants I'm worried about. The flywheel is going to rapidly convert it's angular momentum to linear momentum and become a giant bullet that's going to crush whatever it hits like a railgun. If it stays in one piece. More likely it fragments into a thousand bits of shrapnel killing everyone within 100 yards, even inside nearby buildings.

The amount of energy being stored in a flywheel like that... well consider what happens when the energy in a gas tank is released all at once... now, instead of wasting most of the energy on heat, convert that almost all to kinetic energy flinging stuff around.

I dunno... sounds dangerous to me...

Mike

Betruger
Posts: 2311
Joined: Tue May 06, 2008 11:54 am

Post by Betruger »

Thanks, I had to ask to be sure.. I thought it was feasible to have the flywheel precisely made so that it'd grind itself evenly to a stop on the casing after collapsing the rolling mechanism. But if it can cause certain damage within 100 yards even inside buildings, it'd take a really dense shielding to contain and do it with the usual safety margins. I've seen people on the road eye and keep safe distance from gas-powered SUVs already :)

Roger
Posts: 788
Joined: Fri Jul 06, 2007 2:03 am
Location: Metro NY

Post by Roger »

Mike Holmes wrote: The plug-in Hybrids due out in the next two years are the first step there.
Mike


calcar.org

They have had the Prius plugin kit for a while.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

Mike Holmes
Posts: 308
Joined: Thu Jun 05, 2008 1:15 pm

Post by Mike Holmes »

Note that my comments about the energies involved with the flywheel are completely spurious. In fact, somebody above quoted that they had a one Megajoule capacity? If so that's only equal to about .2 KG of TNT. Sounds like too little to get around with, however...

The point is that batteries are safer, assuming they're made from something that's not terribly toxic if they end up in a collision (or are well housed). Hydrogen fuel cells are becoming safe by containing the hydrogen in other substances, and having it converted for use by catalysts. But I'm a little skeptical of those complexities.

Batteries - supercapacitors even better - seem like a very simple option for various reasons. Like the fact that you can plug some of these into your wall at home and charge them overnight with no new technology required (like the hybrid conversions that Roger mentions*).

Cheap electricity from BFRs, and electric vehicles to use it, is a very pretty picture to me.

Mike

*"Available" and "Marketable" are different. Heck, they had production electric vehicles ten years ago. It's a matter of the technology pipeline being ready to mass-market these things to make a difference.

Aero
Posts: 1200
Joined: Mon Jun 30, 2008 4:36 am
Location: 92111

We'll need more than one power type

Post by Aero »

Electric cars will satisfy most people, but I suspect that, for example, long haul trucking, aircraft, particularly small agile military aircraft, as well as farm equipment will use diesel or kerosene into the foreseeable future. Just my opinion. The real problem will be political, not technological, (Once it works). Unless we are very careful and very lucky, the BFR will be relegated to the nuclear category with most of the rules and regulations that entails. But that has been recognized here already. And they will still have a huge positive impact as stationary power plants and ship engines.
Aero

Post Reply