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It's common knowledge that sand behaves like water when in small grains. So can you make a pipe that carries sand in the same way pipes carry water? If not, is there another way you could?

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closed as off-topic by AccidentalFourierTransform, stafusa, ZeroTheHero, user191954, Sebastian Riese Oct 4 '18 at 3:21

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  • $\begingroup$ A sandblaster would do exactly this, but it is using air as the transport and the sand/abrasive is carried along for the ride. $\endgroup$ – Criggie Sep 30 '18 at 18:50
  • $\begingroup$ A pneumatic delivery tube could carry sand, but again its air driven, and the sand would be inside capsules, so different to a pumped pipe of sand. $\endgroup$ – Criggie Sep 30 '18 at 18:51
  • $\begingroup$ 'Fluidized bed' combustion systems might come close. Or, have you visited your local grain elevator? $\endgroup$ – Jon Custer Oct 1 '18 at 13:27
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Tricky for sand, most grains of sand are 'sharp' they will lock into each other and form jams in the pipe unless you have some fluid (eg. air or water) carrying them along. There are types of sand with smooth polished grains which flow more freely (eg desert sand) but these aren't used in construction so there isn't much effort into moving it around.

Smoother particles like grain are routinely moved around in pipes.

The other problem is how to pump them. Pumping requires a fluid that you can compress in the pump so there is a pressure difference that transfers force to other particles. Although it's easy to lift particles to the top of a pipe and have them flow down, it's less clear how you can pump solid sand particles up without using some carrier fluid like air or water.

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    $\begingroup$ Also, coal slurry pipelines: en.wikipedia.org/wiki/Coal_pipeline en.wikipedia.org/wiki/Mohave_Power_Station $\endgroup$ – Keith McClary Sep 29 '18 at 18:19
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    $\begingroup$ The process also tends to sandblast the pipes. Fracking considers pipes to be consumables because this is exactly what the process involves. $\endgroup$ – chrylis Sep 29 '18 at 18:38
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    $\begingroup$ But both these use a powder/water slurry, it's much harder to pump a dry powder $\endgroup$ – Martin Beckett Sep 30 '18 at 1:33
  • $\begingroup$ Not to be rude- but it seems as though you have merely assessed rather than answered the question... $\endgroup$ – yolo Sep 30 '18 at 19:24
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To pump the grains up, the Archimedes Screw is used in agriculture. This should also work for sand.

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  • $\begingroup$ Not just in agriculture; the Archimedean screw is the principle of the familiar cement mixer/truck. $\endgroup$ – Whit3rd Sep 29 '18 at 17:17
  • $\begingroup$ I think drill bit flutes(they carry chip) work on the same principle as Archimedis screw. $\endgroup$ – Mohan Sep 29 '18 at 17:28
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    $\begingroup$ But you have to be careful. Sand is enormously abrasive (see @chrylis comment above), typically harder than a steel file. So without careful design and construction the bearings bite the big one pretty quickly. $\endgroup$ – WhatRoughBeast Sep 30 '18 at 0:47
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Yes! If you go back to see how the old steam locomotives were built, one of the domes on the steam engine held sand that flowed down through a pipe were it ended near the tracks in front of the front drive wheel. The sand was added to provide traction between the steel wheel and the steel track. There was also a washer that washed the sand from the tracks just after of the rear drive wheel. For the sand to flow, it needed to be completely dry. The railroads had a house, not surprisingly called the sandhouse, where the sand was dried by heating it using a coal stove.

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  • $\begingroup$ What if you wanted the sand to go up, or left, or right/ $\endgroup$ – yolo Sep 29 '18 at 18:23
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    $\begingroup$ It's not just steam -- modern rail vehicles usually have sanding systems to help with adhesion too. They often use compressed air to make the sand flow reliably, though. $\endgroup$ – Henning Makholm Sep 30 '18 at 13:03
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Yes. Dense-phase pneumatic conveying does exactly this. A powder is fluidized with air and then flows under gravity. It is widely used in process industries. For example, it is widely used in aluminium smelting to convey alumina (aluminium oxide) with particle sizes similar to sand. The solids flow like water when fluidized. A quick search found this recent paper Pneumatic conveying of alumina - comparison of technologies by Garbe, Hilck and Wolf. This is a well-studied area, but much of the literature is behind paywalls.

There are a number of forms of pneumatic conveying:

  • lean phase, where the pipe is mainly air with particles "blowing in the breeze"
  • dense phase, where the pipe is full of particles with just enough air injected along the length to allow flow
  • other intermediate cases

This is a special case. The alumina is dry and has been precipitated from solution in the alumina refinery. The grain size and shape are controlled. Factors that influence the "conveyability" are part of the specification.

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  • $\begingroup$ +1 for showing that it's already done. Shotcrete and concrete pumps would be additional examples. $\endgroup$ – Pere Sep 30 '18 at 20:26

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