Physics question

[Goldfreak]

I know to suck water and other liquids up a pipe you need a stronger pump the higher it is and then past a certain point some where around 10 meters its impossible to do, but what about loose dry material being vacuumed up a tube ? Is this limited in the same way by height or is length of the tube to the vacuum the only issue ?

 

[user 4386]

I know to suck water and other liquids up a pipe you need a stronger pump the higher it is and then past a certain point some where around 10 meters its impossible to do, but what about loose dry material being vacuumed up a tube ? Is this limited in the same way by height or is length of the tube to the vacuum the only issue ?

I am trying to reason this from first principles. We talk about "sucking" water up a pipe but what we are really doing is creating a vacuum in the pipe so that atmospheric pressure pushing down on the water at depth will push the water up the pipe (i.e. there is no pressure pushing down on the liquid in the pipe because we have created a near-vacuum). How far water will rise in the pipe is limited by atmospheric pressure, and is about 10 metres..

The limitation on this (other than atmospheric pressure and frictional losses in the pipe) is the density (specific gravity) of the fluid being pumped on. Water has a density of 1.0. Anything else will have a greater density so will not be pushed as far up the pipe by atmospheric pressure - I imagine the same should apply to dry solids.

Pumps that "push" liquids, partly-solid slurries and (I imagine) particulate dry material up a pipe for higher than this limitation involve "pushing" from below with a pressure greater than atmospheric, or staged lifts between "dams" at different elevations (as when pumping mine water from great depths via dams on different levels).

I imagine someone else here will correct me if I am wrong.

 

[Dihusky]

For vacuuming dry material I think there will be 3 elements involved: 1. The size of the particles you are wanting to move, 2. The velocity of the air. 3. The volume of air being moved in relation to time.

Once you have the material at the end of the 'lift', you'll need a 'cyclone chamber to centrifugally separate the dry material and allow it to drop to the bottom of the cyclone cone so it doesn't damage the fan.

No idea how to calculate all of this, but the ones I have seen working have massive fan systems. I think the only height limitation is $$$ and practicality. Systems like this used to be are/used to be used in opal mining.

 

[Goldfreak]

Interesting.

For vacuuming dry material I think there will be 3 elements involved: 1. The size of the particles you are wanting to move, 2. The velocity of the air. 3. The volume of air being moved in relation to time.

Once you have the material at the end of the 'lift', you'll need a 'cyclone chamber to centrifugally separate the dry material and allow it to drop to the bottom of the cyclone cone so it doesn't damage the fan.

No idea how to calculate all of this, but the ones I have seen working have massive fan systems. I think the only height limitation is $$$ and practicality. Systems like this used to be are/used to be used in opal mining.
View attachment 6855

Thanks Dhusky and Goldielocks. Answers my question.

 

[aurville]

I am trying to reason this from first principles. We talk about "sucking" water up a pipe but what we are really doing is creating a vacuum in the pipe so that atmospheric pressure pushing down on the water at depth will push the water up the pipe (i.e. there is no pressure pushing down on the liquid in the pipe because we have created a near-vacuum). How far water will rise in the pipe is limited by atmospheric pressure, and is about 10 metres..

The limitation on this (other than atmospheric pressure and frictional losses in the pipe) is the density (specific gravity) of the fluid being pumped on. Water has a density of 1.0. Anything else will have a greater density so will not be pushed as far up the pipe by atmospheric pressure - I imagine the same should apply to dry solids.

Pumps that "push" liquids, partly-solid slurries and (I imagine) particulate dry material up a pipe for higher than this limitation involve "pushing" from below with a pressure greater than atmospheric, or staged lifts between "dams" at different elevations (as when pumping mine water from great depths via dams on different levels).

I imagine someone else here will correct me if I am wrong.

Goldierocks, just a tiny nitpick: "Water has a density of 1.0. Anything else will have a greater density". Not true - many hydrocarbon liquids have a density less than 1 eg petrol, oil, kerosene, ethanol, propanol, acetone etc.

 

[user 22230]

Going by a few adds on telly and what is claimed the vacuum units are capable of, there are a few that should do the job On a serious note I think Dihusky has pretty well nailed it

 

[user 4386]

Goldierocks, just a tiny nitpick: "Water has a density of 1.0. Anything else will have a greater density". Not true - many hydrocarbon liquids have a density less than 1 eg petrol, oil, kerosene, ethanol, propanol, acetone etc.

True, and of course I knew that - I had solid-liquid suspensions or solids in my mind, but did not say that. Petrol is about 0.7 from memory.

 

[user 12139]

Hydrostatics;

density (ppg) x height (ft) x 0.052 (hydrostatic constant) = lbs of force per foot (psi)
so if your slurry was for example 9.5 ppg and the fluid column height was 100ft then the equation is..
9.5 x 100 x 0.052 = 49.5 psi of force for every 100 ft in height
you need to determine the density of the slurry before you can work out what vacuum or pump force is required before movement occurs, allow about 5% more for pipe friction

Fresh Water = 8.34 ppg
Sea Water = 8.6 ppg
Diesel = ~6 ppg
ppg = pounds per US gallon

any solid within the liquid increases the overall density per gallon, and therefore increase the overall hydrostatic pressure per foot, as exerted by the column of fluid. Its this pressure in the column you need to overcome before movement occurs. To determine the slurry density, a simple mud cup balance test is needed, or you can calculate it using the block calc method if the bulk density and concentration is known for all matter within the liquid. Alternately, measure out exactly 1 US gallon of the slurry and weight it in lbs

Once you've determined the slurries density AND more importantly its Hydrostatic pressure rating then decide what your going to do to move it... ie push or pull (pump or vacuum). Either way, you need to understand the Hydrostatics first prior to purchasing any equipment

If it were me, I'd pump it, why.... way cheaper to setup initially and also maintain

Lastly... your opening statement "moving liquid past 10m is near impossible to do". Lets see how impossible that is when the liquid is fresh water..
10m = 10 x 3.2808 ft/m = 32.808ft
32ft x 8.6 ppg x 0.052 = 14.6 psi
You only need a pump that can output 14.6 psi head pressure plus ~5% for friction and you'll move the water past 10m in height mark!

I've a Triplex pump outside rated to 12,000 psi MCWP @ 8 bpm (336 gpm)