H
Huw Groucutt
Guest
this is true. At least he wont have a light on to cause a fire hazard!
Let's go for 1 dafter than Cap'n'Chris. Haven't tried this but...
You want air in your dig. You have lots of moving air nearby. So, why not nab it? I give this about a 5% chance of working but : big polythene sheet, hosepipe, roll of gaffer tape/similar. Block the adit with the poly sheeting (hold it onto the walls with gaffer tape - see 'repairing gear' thread for other uses of gaffer tape - thanks Brendan....), poke a pipe through it and down into your dig. Then swear profusely at the fool who insists they want to get past your blockage into Carno.
Some modification on this may, just may, work :no:
Another line I'm thinking on for more remote places is this : Spent carbide is calcium hydroxide. Calcium hydroxide solution (limewater) reacts with CO2 to form calcium carbonate then hydrogencarbonate - so absorbs CO2 from the air. Rates could be rather slow - haven't done any hard research - but this may get rid of CO2 - I think diving rebreathers must use a simlar system?
Trouble is you then have no warning when the air is going, so a candle or similar would be essential, or better, a source of oxygen or - better yet - both. Easy source of oxygen is hydrogen peroxide if you can get it - drip a solution of this onto a piece of raw liver and it fizzes oxygen like there's no tomorrow.
I have not done any 'real work' on this and don't recommend trialling it without some sort of decent air monitoring - remove the CO2 and the oxygen from air and you WILL black out without warning as you need CO2 to trigger the breathing reflex, lack of oxygen doesn't do it. However if someone has the spare time to develop it, it could be a useful/useable system.
Any thoughts on either of these rather silly and untried ideas welcome - but IMHO you're better digging where there's air
You want air in your dig. You have lots of moving air nearby. So, why not nab it? I give this about a 5% chance of working but : big polythene sheet, hosepipe, roll of gaffer tape/similar. Block the adit with the poly sheeting (hold it onto the walls with gaffer tape - see 'repairing gear' thread for other uses of gaffer tape - thanks Brendan....), poke a pipe through it and down into your dig. Then swear profusely at the fool who insists they want to get past your blockage into Carno.
Some modification on this may, just may, work :no:
Another line I'm thinking on for more remote places is this : Spent carbide is calcium hydroxide. Calcium hydroxide solution (limewater) reacts with CO2 to form calcium carbonate then hydrogencarbonate - so absorbs CO2 from the air. Rates could be rather slow - haven't done any hard research - but this may get rid of CO2 - I think diving rebreathers must use a simlar system?
Trouble is you then have no warning when the air is going, so a candle or similar would be essential, or better, a source of oxygen or - better yet - both. Easy source of oxygen is hydrogen peroxide if you can get it - drip a solution of this onto a piece of raw liver and it fizzes oxygen like there's no tomorrow.
I have not done any 'real work' on this and don't recommend trialling it without some sort of decent air monitoring - remove the CO2 and the oxygen from air and you WILL black out without warning as you need CO2 to trigger the breathing reflex, lack of oxygen doesn't do it. However if someone has the spare time to develop it, it could be a useful/useable system.
Any thoughts on either of these rather silly and untried ideas welcome - but IMHO you're better digging where there's air
M
mudman
Guest
mudmonkey said:
I like the idea of this, it sounds like it may work. However, I don't think just dumping air into the dig will be adequate. What you have is a 'pool' of CO2 at the bottom. Imagine a pipe in a tankk of water letting out air. The air bubbles straight to the surface and doesn't hang around the surface. You really need to remove the CO2.
Now, if you block off the adit as you suggest but include a tube that will allow the draft to flow through, then this will have the effect of creating a very high speed flow of air. Then if you joint another pipe into this pipe that leads into the dig, the fast flow of air will create an area of very low pressure that will cause suction in the other pipe thus bringing up the CO2 from the dig face. Now I reckon that would work.
I would seal the adit in two places, either side of the entrance to the dig, with poly sheeting. Put a hole in both of these and connect with a plastic tube. It doesn't matter which way the draft is going as the effect is the same. Put a t-piece into the middle attach another hose and you have an airflow driven vacuum pump.
You also get the added bonus of a nice warm, draft free area to drink all of that tea.
Waddya think?
M
mudman
Guest
And don't forget, the narrower the tube connecting the two blocking sheets, the faster the airflow and the greater the suction, think Bernoulli.
Not convinced by the Bernoulli idea, must admit (flow speeds need to be pretty high to get much suck, don't they? Anyway, you must suck less air than goes through the pipe?), though it is ingenious - would work very well if there was falling water, we use those sorts of pumps in teaching labs all the time.
Good point about 'suck is better than blow', mind - maybe put the barrier down-wind of the dig, this would have the same effect (all/some of the draught directed down the dig), and would take used air out the bottom.
Good point about 'suck is better than blow', mind - maybe put the barrier down-wind of the dig, this would have the same effect (all/some of the draught directed down the dig), and would take used air out the bottom.
M
mudman
Guest
I can see how a single barrier downdraft would work. It would cause the mass of air to build up at the barrier and to continue flowing would need to move into the dig and then find the inlet to the pipe. However, you may find that it isn't sucking the pooled CO2 out of the dig, just creating a different route for the air to flow. It wouldn't be a suction effect, just a re-routing of the airflow. This would actually be the same effect as blowing air into the dig.
But I doubt if you need a high vacuum to be created, you just need to be able to keep the CO2 moving out of the dig at a constant rate.
Also, you don't need to have a huge pressure differential as it works by creating a force due to the pressure differential which then accelerates the CO2 out of dig through the suction tube. As the CO2 has only a small mass, then the pressure differential only needs to be small to achieve quite a high acceleration. (Anyone who's physics is a bit more recent able to confirm this for me?ldgit: )
The amount of CO2 exhaled in each breathe is not great and I reckon that if the suction pipe were placed so it was exhausting the pool of CO2 that would collect at the lowest point, then it may work okay.
I don't think it would make a difference if it was water or air moving. They can both be treated as a fluid and Bernoulli's principle is related to the rate of flow, the faster it is the greater the pressure differential.
The draft in the Carno Adit is one hell of a wind. Not sure if the rate of flow has ever been measured but I know how cold it can be to stand around in it.
The velocity of a fluid moving in a pipe is inversely proportional to the cross-sectional area, so, if you halve the diameter of the tube it moves in, you double the velocity.
I reckon that the Carno Adit is an eggy-shape about 2 metres high. If we assume this to give a cross-section of about half that of a circle of equal diameter (as a guess), then this is a cross sectional area of about 5 sq-metres. If this is reduced by blocking the adit down to a narrow tube of only 7cm (the size of my coffee cup). This gives a new cross-sectional area of only This means that the velocity of the air will increase by a factor of 0.35/5 or by 14 times faster. So if the air is moving down the adit at a velocity of 1 m per s, then this will become 14 ms-1, quite an increase.
I think as well that the suction would be related to the force generated by accelerating the air through the reduced pipe and if this is simply the old F=ma then it should be F = (density of air) x (volume of air) x acceleration. That would turn out quite large. Must be some equations out there somewhere, effectively it's a Venturi tube so I bet there is a few sites dealing with it.
I bet that the main problem would be attaching the sheeting securely to the walls without it being blown off by the mass of air behind it.
Anyway, I was supposed to be working, but that was more fun. Now I'm off to me evening class. :dancing:
But I doubt if you need a high vacuum to be created, you just need to be able to keep the CO2 moving out of the dig at a constant rate.
Also, you don't need to have a huge pressure differential as it works by creating a force due to the pressure differential which then accelerates the CO2 out of dig through the suction tube. As the CO2 has only a small mass, then the pressure differential only needs to be small to achieve quite a high acceleration. (Anyone who's physics is a bit more recent able to confirm this for me?
ldgit: )The amount of CO2 exhaled in each breathe is not great and I reckon that if the suction pipe were placed so it was exhausting the pool of CO2 that would collect at the lowest point, then it may work okay.
I don't think it would make a difference if it was water or air moving. They can both be treated as a fluid and Bernoulli's principle is related to the rate of flow, the faster it is the greater the pressure differential.
The draft in the Carno Adit is one hell of a wind. Not sure if the rate of flow has ever been measured but I know how cold it can be to stand around in it.
The velocity of a fluid moving in a pipe is inversely proportional to the cross-sectional area, so, if you halve the diameter of the tube it moves in, you double the velocity.
I reckon that the Carno Adit is an eggy-shape about 2 metres high. If we assume this to give a cross-section of about half that of a circle of equal diameter (as a guess), then this is a cross sectional area of about 5 sq-metres. If this is reduced by blocking the adit down to a narrow tube of only 7cm (the size of my coffee cup). This gives a new cross-sectional area of only This means that the velocity of the air will increase by a factor of 0.35/5 or by 14 times faster. So if the air is moving down the adit at a velocity of 1 m per s, then this will become 14 ms-1, quite an increase.
I think as well that the suction would be related to the force generated by accelerating the air through the reduced pipe and if this is simply the old F=ma then it should be F = (density of air) x (volume of air) x acceleration. That would turn out quite large. Must be some equations out there somewhere, effectively it's a Venturi tube so I bet there is a few sites dealing with it.
I bet that the main problem would be attaching the sheeting securely to the walls without it being blown off by the mass of air behind it.
Anyway, I was supposed to be working, but that was more fun. Now I'm off to me evening class. :dancing:
H
Huw Groucutt
Guest
hmmm might work. Trouble is the draft often changes direction during the course of an evening. When we go in its hotter outside so drafts out, as evening goes on neutral conditions mean the draft stops, then if its cold outside drafts inwards.
M
mudman
Guest
But the beauty of it is that it doesn't matter which way the draft is blowing. In or out it still has the same action. The only problem you get is if it stops completely.
I've also thought about getting a good seal. Had an idea on this.
Cos of course the problem is that you're trying to seal the poly to a rough surface. So what you do is build a rough timber frame that will fit roughly to the shape of the tunnel. Attach your poly sheeting to this and then get it set upright in the adit. Then on the outside of the frame you attach, preferably a long thin bag, sealed that is the right size to reach the walls and plug the gap. Then you make a small hole and pump in a few cans of the cavity filler that expands to fill the bag and forms exactly to the shape of the walls. I reckon that that should form a good enough seal for the purpose but if it's not good enough, run a bead of mastic along the join of bag to wall. Do it on the outside (away from the dig) so that when the draft pushes against it, the mas of air will wedge it in rather than try to blow it out from the other side.
You could make it semi-permanent for the duration of the dig by putting a long slit in the poly sheeting and seal it with duct tape when you need a seal. Remove it to allow passage of cavers.
Hey, you could even create airlocks with each barrier being a pair with it's own seal.
Then it should be warm and dry enough to put in a couple of armchairs, a coffee table, maybe a bit of lighting, would make it right homely.
I've also thought about getting a good seal. Had an idea on this.
Cos of course the problem is that you're trying to seal the poly to a rough surface. So what you do is build a rough timber frame that will fit roughly to the shape of the tunnel. Attach your poly sheeting to this and then get it set upright in the adit. Then on the outside of the frame you attach, preferably a long thin bag, sealed that is the right size to reach the walls and plug the gap. Then you make a small hole and pump in a few cans of the cavity filler that expands to fill the bag and forms exactly to the shape of the walls. I reckon that that should form a good enough seal for the purpose but if it's not good enough, run a bead of mastic along the join of bag to wall. Do it on the outside (away from the dig) so that when the draft pushes against it, the mas of air will wedge it in rather than try to blow it out from the other side.
You could make it semi-permanent for the duration of the dig by putting a long slit in the poly sheeting and seal it with duct tape when you need a seal. Remove it to allow passage of cavers.
Hey, you could even create airlocks with each barrier being a pair with it's own seal.
Then it should be warm and dry enough to put in a couple of armchairs, a coffee table, maybe a bit of lighting, would make it right homely.
D
diggerdog adam
Guest
Well ive just being reading the sugestons with intrest so heres mine
What you need is 2 12v electric fans (the type you use on the dash board of your car) i think there about a fiver
Dig a small sump (hole) at the face of the dig so all the co2 falls into it and then using plastic drain pipe with the blades cut down to fit snunlly inside pipe to surface/clean air.
Do the same at the other end if nessercy, you will pobally find you won't need to push the fresh air in as the differance in pressure will pull fresh air in on its own.
The good thing about this system is all parts are cheap and those small fans shift loads of air with not much battery useage.
Let me know how you get on
What you need is 2 12v electric fans (the type you use on the dash board of your car) i think there about a fiver
Dig a small sump (hole) at the face of the dig so all the co2 falls into it and then using plastic drain pipe with the blades cut down to fit snunlly inside pipe to surface/clean air.
Do the same at the other end if nessercy, you will pobally find you won't need to push the fresh air in as the differance in pressure will pull fresh air in on its own.
The good thing about this system is all parts are cheap and those small fans shift loads of air with not much battery useage.
Let me know how you get on