Why No Consideration of Pykrete?
January 27, 2009 at 11:07 pm #796
Browsing through the forums, and watching the videos, I’m noticing that there’s no mention of a previous design that seems to fit a large percent of the engineering requirements you guys are looking for.
In world war 2, pykrete ( http://en.wikipedia.org/wiki/Pykrete ) was considered as a building material for what would have been a huge carrier, basically an entire city at sea ( http://en.wikipedia.org/wiki/Project_Habakkuk ). Some of the interesting features of the material and the project are that since pykrete is so cheap to manufacture, the scale of the carrier was going to be immense, with 10 foot thick walls making it virtually indestructible. Pykrete’s main advantages, besides price, are that it is immensely strong, and it is buoyant. The disadvantage is that it would require active cooling to the freezing point, but when you begin to think about a model where you apply some insulation or cladding, this really becomes less of an issue, and is outweighed by the amount of space you could have.January 28, 2009 at 12:47 am #4744
Are you familiar with any actual floating structures built with Pykrete?January 28, 2009 at 1:12 am #4745
I could imagine pykrete breakwaters. But energy is expensive, and making huge amounts of ice sounds really expensive. Concrete is pretty cheap.
And I’d like to be in warm waters, which would be a problem for pykrete.January 28, 2009 at 1:33 am #4748
I doubt it would be expensive to freeze as long as you were willing for it to take a little while and let mother nature do it. Also, I looked into project Habbakkuk a while ago and I remember that the idea was that it could travel in warmer waters. Pykrete melts more slowly than ice does, and the idea was that a series of bilge pumps and refrigeration units would keep it cold. The main problem is that Pykrete is malleable. one of the major things that killed the carrier idea was that it would still need steel reinforcement to support the structures. I don’t know. If one could build a large tank in northern alaska and fill it with the water and pykrete, then I see no reason why it would not freeze by itself. Heck, build small chunks of it and sink some to stack blocks. The problem remains, though, that you would want to keep it somewhere cool most of the time. Doesn’t have to be freezing as long as you got it wrapped in insulation, but still pretty cold.January 28, 2009 at 2:42 am #4749
There was at least one structure built out of pykrete, it was the proof of concept for Habakkuk. The interesting thing about it was that they found that the wood embedded in the ice insulated the ice, and so they had no trouble (with WW2 technology!) keeping their prototype cool and functioning throughout the summer.January 28, 2009 at 5:13 am #4752
Okay… consider if you will… a breakwater made primarily of insulated pykrete. Electricity sent to the structure (via electrc lines and a centralized power supply – nuclear, wind, wave, whatever- or a simple series of PV solar collectors on top of it) travels through a thermoelectric cooler (made of bismuth telluride or whatever). The TEC should be able to keep the structure cool enough. With TECs, when you cool one side, you heat the other, so the “heat sink” can be fresh water piped directly back the main seastead structure to provide hot water. Whether that water is purified and reused, or some other technique is used to send water back into the loop, it doesn’t matter, but such a system should be able to work, and be cheaper than huge steel structures, while providing additional benefits at the cost of only electricity (which should be relatively inexpensive).
Once we have a system in place, we can start producing more breakwaters to form new sister communities. Instead of wood pulp, which would be costly to transport to our location, we could use hydroponically grown kenaf (which should provide considerably more pulp than wood per acre anyway). We use the same TEC technology to freeze water to form the pykrete… rinse, and repeat.
There will obviously be SOME need for additional materials… like the piping and insulation and such, but I see the formations here of an idea that could have promise.
What are your thoughts?January 28, 2009 at 6:39 am #4753
Actually, I think the prototype was made of just ice. Not that they didn’t have the ability to make it, as it was the ever increasing pile of demands all branches of the military asked that doomed its timeline until it was of no interest.
As for the pykrete being cooled by thermoelectric coolers, I think efficiency is a problem. Plus, http://www.marlow.com/TechnicalInfo/frequently_asked_questions_faqs.htm#th06 mentions that they really work best when they are small. I really think that pykrete with another form of cooler may be viable, though. Anyone have access to sawdust?
Actually, an amusing thought. Why not try replacing the wood pulp with seaweed? Its long, stringy, and abundant. Seems to fit the bill for an alternate source of strength.January 28, 2009 at 12:30 pm #4754
Even if you manage to insulate the pykrete well I am guessing you will still need lots of energy to cool it. Consider a household fridge. It is well insulated, yet still requires like a couple of hundred watts at least probably to maintain a temperature that is not even below freezing. Scale this up to seastead size and you are probably looking at a big energy bill, even considering the benefits you get with bigger volume.
There is also the issue of relying on a structure that needs active monitoring and control. If I was to live on it I´d rather have my seastead be inert and somewhat resistant to operator errors and machinery breakdowns..
And compared to ferrocement, pykrete is by no means free. You still need rebar. And sawdust. And then there is the cooling apparatus and ducting and insulation.
Perhaps if you were planning an arctic seastead this would make more sense. Maybe for a Dr. Evil style secret lair, that doesn´t benefit from proximity to civilized areas. Or whatever business you can come up with near the poles. Research, oil exploration, etc.January 28, 2009 at 6:47 pm #4755
That’s a really novel idea: use some sort of seaweed pulp instead of sawdust to make the pykrete. Come up with a mold you can just follow for some sort of large lego-style brick, and just keep expanding the structure as long as you have piping.
I really don’t think, with good insulation, that cooling would be much of an issue. Pykrete melts considerably slower than regular ice, and you really only need to keep the exterior cool, as the interior of the pykrete will be whatever temperature the outside of the block is at. I would suggest that the easiest way to maintain a good temperature is either going to be some sort of cladding that you cool, or else to lay pipes near the surface edges of the pykrete that you run a cooled fluid through – which points out another advantage of the pykrete idea. Generally, large cooling systems use some sort of cooling circulation system that you run a chilled fluid through. Since we’re only aiming for the freezing point of fresh water, we can simply run chilled saltwater through our pipes.
Another interesting idea is that if you chilled both sides of the cladding and expected some ice build up along the outer sides of the seastead, you might avoid the buildup of barnacles and other sea debris that normally slows down and corrodes ships and such, especially if you had a method to shake loose the exterior ice occasionally – a self cleaning ship!January 29, 2009 at 11:55 pm #4759
Yes, it could be very expensive. But I don’t think it would be. I would think that the energy needed to cool it would not be too terribly high. You would only need to worry about the surface of the ice because the rest will be cooled by itself. Insulation could take care of most of the cooling, with the rest being done via saltwater, which freezes at -21.1 degrees Celcius. As you don’t have to worry about freezing, the tunnels can be melted out of the pykrete itself for the saltwater to be piped through.
I am also unsure about the additional active structure risks. Yes, it needs cooling, but even given the case of complete cooling system failure, you are still sitting on a very large block of ice wrapped in insulation. That will take quite a while to melt.
As far as cost goes, rebar would be completely unnecessary if it is just a giant block. Alternatively, in the Habbakkuk design, supposedly if the block was kept at at -15 degrees celcius it would not deform much either, after some initial sag period.. As cooling to that temperature could be quite expensive, I think it would be better to make the structure a giant block. Also, sawdust is not the only possible solution. I proposed seaweed as an option. I bet pumice or other porous rocks could work too, probably being able to absorb heat better than seaweed. Or a combination between many materials mixed in. One to absorb heat and one to add structure. Either way, only 7% needs to be made up of something other than water, supposedly.
Yes, this woud definitely be more feasable in colder environments. However, I see no reason why that environment must be freezing. Even reducing the average temperature to 50 degrees fahrenheit would work wonders, and that is a quite enjoyable temperature for me. Plus, if you can migrate, just dodge the freezing winter.
Oh, and two resourses for you guys: Pykrete being shot with a rifle and shotgun http://video.google.com/videoplay?docid=-8151564007161180301
And some notes about Habbakkuk that are applicable to the discussion. A little light, but… http://www.goodeveca.net/CFGoodeve/bergship.html
*edit I just found out that normal ocean water, at least according to one source, freezes at -1.94 Celcius. The other figure was for maximum salinity. Oops. However, I don’t think that dooms the idea. If you are desalinating ocean water, then you are getting salt. Mix that in with the cooling water, and it reaches will drop the freezing temp.January 30, 2009 at 6:09 am #4770
I like the concept of the concept of a barnacle resistant structure. We wouldn’t need to worry about oxidation, as well. Replacing older pykrete structures looks like it would be simpler than having to mess with the weight of ferrocement AND a floatation device.
The key, obviously, would be to keep the breakwater… or entire seastead, cold… like, really cold. If we make an entire seastead out of pykrete, I think a thick layer of insulation between the habitable areas and the pykrete is a must.
Even if the costs of cooling the structures might seem prohibitive, the reduced cost of construction and maintenance may be worth a look.
Points to ponder, I suppose.February 10, 2009 at 1:33 am #4907
It is very inefficient, and costs more than conventional refrigeration systems, which is why it is not used in any conventional cooling application.
Anyway, I await your DIY pykrete experiments to show me that a pykrete structure can be kept cooled in the ocean, before I am willing to give it more serious consideration. Until then, concrete and steel for me.February 10, 2009 at 6:14 am #4913
If I didn’t have a tiny condo I would totally do some experiments of my own. That still might be possible, but I’ll have to think about how to pull it off a bit before I make the attempt, as I don’t exactly have a workspace I can leave things around to tinker with.
Anyone else able to play with this concept? While Pykrete’s structural strength is pretty well known, there are a couple of cooling concepts worth testing. One probably involves some aquarium tubing and a pump, and one probably involves peltier plates or something. A couple of relatively simple concept tests on the viability of keeping a block of pykrete (or even ice for the concept test, but preferably pykrete) chilled and frozen in a warmer water environment.February 12, 2009 at 9:09 pm #4926
The prototype Habbakuk was 60 feet long and 30 feet wide, weighing in at 1,000 tons, and was kept frozen by a one-horsepower motor. It took over two years to melt completely.
True, this was in water that is substantially cooler than the oceans nearer the equator, but one may think that a cooling system shouldn’t be prohibitively expensive, compared to the inital added costs of making concrete float.
But, I guess, that’s where the models come in.
To the testing arena it is!April 18, 2009 at 3:07 pm #5592
Hi. I’m no expert at much of anything, so thanks for putting up with me. As I understand it, the more pressurized a gas is, the colder it is. Hence, pressurized nitrogen is really, really cold- dry ice. It occured to me, if you put some dry ice bubbles in the pykete hull towards the outside, the pykrete would be strong enough to keep the gas pressurized and the gas would be cold enough to keep the stuff frozen. Thus you get a low-cost, low maintenance, easy to expand hull. Any thoughts? Thanks.
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