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Will concrete conduct heat well?

See the picture for  more detail, but I basically need to know if this design of rock-steel-concrete-pipe will transfer heat to the oil in the pipe well.

Thanks in advance, I don't need big fancy explanations, I just need to know if this will be a substantial heat source.

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g-one5 years ago

Yes, concrete will conduct heat but not well. Because the environment is rock it doesn't matter because it has approx. the same thermal conductivity.
The LAMBDA value in W/(m.K) of concrete can reach 1.9.
Rock 0.5 - 7 (depending on the material)
Steal 15 - 58 (depending on the alloying level)
Oil 0.15

Well, the oil seems to be the bottleneck in your schematic but it isn't because it's circulating in the pipes and not static.

For comparision only:
Air 0.03
Water 0.6
Glass 1
Dry earth 1.5
Copper 401
Silver 429
jj.inc (author)  g-one5 years ago
THANKS!!!! I liked your good facts without flooding me, and you understood my concept well.
lemonie5 years ago

Why use concrete at all?
Heavy steel alone would conduct heat better, or lose the outer steel-pipe.

*Do consider this though, big geothermal systems use water - it comes back out as steam and gets a lot of contact with the rock.
If you suck heat out of dry/solid rock it'll cool locally, you get only a fraction of the amount of contact as compared with a steam-system.

L
jj.inc (author)  lemonie5 years ago
The steel is needed to provide extra support against the crushing rock above, the concrete, is probably the best thing you can inject that will make good contact with both the external ring and internal pipes. I really don't know how to get the heat out of the rock once I am in the area. Please help me.

What I originally thought was that I would have a large boiler that had a hot-oil radiator, and a water to steam radiator. The oil would come from multiple branches drilled out into walls spaced enough to avoid over-cooling the rock around the outside. Then, there would be a secondary heater, to increase the steam temperature, and therefore pressure, which results in exponential heating because quick pressure increase adds more heat. That is done by drilling deep holes even deeper than the original, these extreme deep holes would have two large pipes, the hole would be filled with oil because of its good conductive ability, and the ease of keeping it in a vertical hole vs horizontal. This very hot steam 150-200 degrees Celsius would drive the turbines.

I did originally look at that Wikipedia page, and others but I found this problem: the rock at these depths likes to flow, which means there will be no cracks for this to pass through. Therefore it renders all three of today's options impossible.

I am now starting to have more ideas about using a liquid that boils at very low temperatures so a good 150 degree heat-up will give it a mega-boil.

PLEASE HELP ME, I don't have any idea to capture the massive amounts of heat down there and I want to. The way we capture geothermal energy today gives us a max of only 2000 GW while the earth gives of 30 Terra-watts which we could capture.
lemonie jj.inc5 years ago

Steel deforms under load too you know, I suggested losing some of the design because it would be prohibitively-expensive to build something like that.
Water has a much better heat-transfer function - this is why vehicle cooling systems, power stations, central heating systems etc use water. Water is also cheaper, environmentally safer, and non-flammable.

With regards to "quick pressure increase adds more heat" - this sounds like non-ideal gas behaviour when it's rapidly compressed. It's the work done in compressing gas that raises temperature. Raising pressure by increasing temperature only doesn't that, it doesn't then create more heat.

I don't have any idea to capture the massive amounts of heat down there either, but if I did, I would spend a lot of time looking at current research & development with an aim to get a job in the area of geothermal energy.

L


jj.inc (author)  lemonie5 years ago
I just got a BRILLIANT IDEA. You have a good 12 inch pipe or so, and it is spaced relatively close to the others. They are filled 50% with water for maximum surface area to volume of water. As that water steams it exits out of the pipe and contributes to the turbine, then the water is pumped back in via a leveling float system.
lemonie jj.inc5 years ago

High-pressure steam is well understood and well-used, I would strongly advise you think about water - it's surely the best for the job. (extreme pressures which we can not handle)
I was looking for pictures of coal-mines with steel-reinforcements (buckled out of shape by the weigh above) but I couldn't find any good ones. Anyway, as I was thinking previously, if you get your bores to a certain depth, where rock is fractured/porous you do not need to actually run tubes any further. Inject water in one bore and take steam out of the other.

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jj.inc (author)  lemonie5 years ago
Ok, concrete is flammable or were you talking about the oil? I also chose the steel because it will hold up better that the rocks would because we all know how metals handle higher pressures, which overall is well. I know for sure that water will only be used in the steam section, or may be replaced by pentane or butane. If we use water to conduct boiling temperatures, we end up with problems of extreme pressures which we can not handle as it starts to boil so oil will be used.

With your reply to the heat pressure ratio, what I meant was that when you increase the temperature the overall pressure increases, which adds a little more pressure, and then your done, I actually saw that on the wiki page you sent me.
rickharris5 years ago
I think your biggest issue is going to be drilling a hole deep enough. Unless you live in a volcanic area and Magma is readily available close to the surface.

The deepest hole so far is around 40,230 feet this took 24 years to drill and a lot of specialised equipment.

In many parts of the world there is enough heat close to the surface to heat water to a respectable temp. In all parts of the world ground source heating at a meter or two will hate water to provide background heat for a house even in winter.
iceng5 years ago
Concrete is composed of a powder ( Portland cement ) and aggregate
mixed with water.
I believe initially the freshly poured concrete in the steel pipe will transfer
heat by moisture conduction very well.
FACT Concrete can set under water.
That fact leads me to further speculate that the mixture will loose its
water content to chemical reaction and the remaining heat conduction
will be controlled by the particulate contact points which is not as good
as solid rock.
LAST FACT in North Illinois pipes are laid in the side walk and hot water
is passed through them to melt away snow in the winter.


A
jj.inc (author)  iceng5 years ago
Thanks for your input, I am happy to know concrete doesn't need open-air to dry, which means no need for segments of pipe and concrete slid into one long steel pipe,
caarntedd5 years ago
This is similar construction to MIMS electrical cables. Mineral Insulated Metal Sheathed. Copper sheath (steel pipe) filled with mineral powder (concrete) containing copper wires (oil pipes).
They are used for maintaining an electric supply to important equipment for a specified length of time in a fire situation.
I guess if they are "fireproof" they resist heat transfer from the outer sheath to the internal conductors until the structural integrity of the sheath is compromised, and then the system fails. If your pipe works anything like this then it won't conduct heat well.
Try looking up MIMS cables, and for that matter, check up on how heating systems embedded in concrete floors work. There might be some tips on what materials would be good for your project.
If the oil is hotter than the surrounding environment, the oil will try to raise the temperature of the surroundings, the reverse is also true.
Concrete will conduct heat. I believe the RHO (thermal resistivity) value of concrete is 55.