Discussion about Flask with Tea found in treasury sump.

[Chocolate fireguard]

Adding hot water will cause the air to expand, as already described. You don't actually need to think about the addition of water vapour by evaporation (although this will add to the partial pressures I think); just heating the air will cause expansion. This will take a bit of time; adding hot water and then immediately closing the lid means the trapped cold air will attempt to expand as it heats, but can't, so the pressure goes up. But if you let the air heat and then _then_ closed the lid then you would get no further expansion but would get a partial vacuum/pressure drop as the water and air slowly cooled.

The expansion of the air due to the increase in temperature will contribute of course, but for the temperature changes here the presence of the water vapour will be the dominant factor.

This is because thermal expansion of air (at constant pressure, ie before the flask is closed) is determined by the increase in the Absolute (Kelvin) temperature, which is obtained by adding 273 to the Celsius temperature.
If the flask contains only air an increase from 20C (293K) to 90C (363K) expands the air by a factor of 363/293 or 1.24 so about a fifth of the air is pushed out of the flask.
When the flask is closed and cooled back to 20C the 80% of the original air left in the flask will suffer a reduction in pressure (now at constant volume) to 0.8 atmospheres.

Now with some hot water in the open flask: the increase in the partial pressure of water vapour is (almost) exponential in the 0 to 100C range and goes from about zero up to 1 atmosphere in that range ? reasonable considering what happens to liquid water at 1 atmosphere at each end of the range.
At 20C the partial pressure of water vapour is about 0.025 atmospheres and rises to just under 0.7 atmospheres at 90C. This means that at the higher temperature the very large amount of water vapour that has been produced has ejected nearly 70% of that 80% of air that remained after thermal expansion.

So when the flask is closed only about 25% of the original air is still in there and when the water vapour has condensed after cooling the pressure will have fallen to 0.25 atmospheres, perhaps a third of what would have happened with air alone.
Of course because the pressure is now below 1 atmosphere not all of the water vapour will have condensed, but I have been unable to find any figures to use there.

If a lower temperature is chosen, say 70C, the thermal expansion of the air alone would produce a pressure drop to 0.85 atmospheres after sealing and cooling, and with water in the flask a drop to 0.6 atmospheres.

 

[Chocolate fireguard]

Schools buy cylindrical cans made from quite heavy gauge steel to use in a classic demonstration where a small amount of water is boiled in the can, until a lot of water vapour can be seen coming out.
Then the heat is removed, the screwtop fitted and the can is left in a stream of cold air to cool it down so the water vapour condenses.
Usually after a couple of minutes it goes like that Sigg bottle, with a bang.

But sometimes it doesn't. It just sits there, amid hoots of derision from the class. Because you've picked the only one without any small dents in it!

It is considered (by some) to be highly unprofessional to ask the class toerag to put on a pair of gloves and bring the can over to you so you can see what has gone wrong, because as soon as (s)he grips it it deforms slightly and the bang scares the **** out of the poor child.

Fifty years ago school physics lessons used screw top oil cans for this experiment. I must admit I have never heard of special cans being purchased for this once-off destructive demo. More than twenty years ago most of us switched to simply using empty soft drink cans which are free, quicker and usually more spectacular. A little water, about one cm, is boiled in the can on a tripod and gauze above a Bunsen burner. When copious steam is observed the can is gently picked up using thick gloves and inverted into a container of cold water. The can collapses within a second as the pressure inside falls to well below atmospheric as water vapour condenses.

.

Yes my old physics teacher (now long gone to his rest, bless him) used an empty Castrol can, and in my day I also used  drinks cans, but at my last school we had those posh bought-in ones which were very strong and went with a fine bang. They came in boxes of 20, were about 200mm high, 50mm in diameter with a screw top incorporating a polythene (I think) seal. The wall thickness was, from memory, at least 1mm.
I retired over 12 years ago now, and from what I hear about funding I suspect ecomomies will have been necessary.

 

[IanWalker]

Railway tank wagons do a similar thing if not vented properly

https://www.youtube.com/watch?v=Zz95_VvTxZM

 

[ZombieCake]

What would happen if the tea was replaced with coffee?  Not the instant stuff but proper espresso coffee that makes distilled RedBull look like Evian water.

 

[alastairgott]

Then we would probably be having the discussion as to whether it was Taylors of Harrogate ground coffee, or Aldi own brand "French Press".
I'm not sure I could taste the difference, but I think I'd get it between Instant and real coffee.

 

[pwhole]

So getting back to the actual route the flask may have undergone - given that the depth of Treasury Sump is only a few metres at most, are we in agreement that the flask could have made that small journey (upwards from Speedwell) relatively unscathed? So it could at least have made it from The Bung, the first likely spot that it could have been lost but still made it down the streamway intact?

 

[alastairgott]

Yes I think so. I think it would be a 75:25 split as to whether it went down the bung or carried on down speedwell, I think the odds may have won on this.

Downstream, would it have got past the section of streamway that dry cavers bypass by using the short bypass or (irregularly) the long bypass?

Upstream, I think if a flood was pulsing over the boulder piles, It would be highly probable that the flask passed over the top.

Is there any easy way of measuring how buoyant an item is?

I guess I could strap weights to it and see when it sinks.

 

[alastairgott]

I guess I could strap weights to it and see when it sinks.

I think it will have to be measured in Mailions.

 

[Benfool]

The Lower Bung Streamway doesn't  end at Treasury Sump, Treasury Sump is a static passageway off the streamway. If Speedwell was in enough of a flood to carry the flask down the Lower Bung Streamway then it is very very unlikely that it went into a static side passage to emerge at he far side of Treasury Sump, rather than traveling downstream into the main downstream sump (and eventually coming out at Russet Well).

Why dont we do an experiment and put several objects into the lower bung streamway at Egnaro Aven and see how many make it into treasury passage. My vote would be toasters.....

Pretty sure that flask came from the Peak side of the system!

B

 

[alastairgott]

True, Treasury sump is a static passage 99% of the time.

However let's assume we are in the 1%, ie flood conditions.

If Speedwell was in enough of a flood to carry the flask down the Lower Bung Streamway...

I've never been in under these conditions and I'm sure very few have and I certainly don't want to just yet. but Treasury sump becomes a rising for the speedwell streamway up into Treasury chamber and along the upper gallery towards the mucky ducks/wallows. Scum lines on the walls at the first section of water are a clear indication of this, as is the rope being thrown out of the climb down into Treasury sump.

I'd hasten to say that for this to happen the lower bung must back up a considerable way. and therefore any object passing through under these 1% conditions would be both constrained by its buoyancy and by the flow it was experiencing.
It would be difficult to work the example, as we do not have any information about the input velocity into the section containing treasury sump and do not have any information about the output velocity either further into the lower bung or coming out of Treasury sump.

I would guess that Treasury may have pulsed in this instance, whether it would be enough to push a flask through despite it's buoyancy etc, I don't know.

 

[pwhole]

If Speedwell was in enough of a flood to carry the flask down the Lower Bung Streamway then it is very very unlikely that it went into a static side passage to emerge at he far side of Treasury Sump, rather than traveling downstream into the main downstream sump (and eventually coming out at Russet Well).
B

That was my reason for asking about the bottom end of the sump passage - I've never seen it, so unable to visualise the scenarios down there under low or high water. My guess is that it's from the Peak side too, as it seems more likely that the flask would just continue down into the phreatic section to Russet Well in high water - but then water flow is a very random thing, and a lucky 'bump' could send it round a corner into a passage, I guess.

I've got a big box of hi-vis ping-pong balls here for flow speed checking, but I doubt many would want those bouncing around the system for the next ten years. That said, if anyone does have a use for them, they're free to a good home...?

 

[maxf]

This has a trial of attempting to trace a water route using fancy ping pong balls.

https://youtu.be/SS2yMD9MgYg?t=2785

(after 46mins if time link doesn't work)

 

[mikem]

Floating items are great in vadose, but not much good in phreatic systems..

Mike

 

[Pitlamp]

I doubt that a completely filled flask would be very buoyant.

To understand why the Speedwell stream overflows via Treasury Sump into Peak Cavern it helps to know a little about how the Speedwell streamway has developed. As you go downstream in Speedwell there are many distributaries. Some are relict, such as Colostomy Crawl. Some are intermittently active, such as Overspill Passage. Some are very occasionally active, such as the route up to Peak Cavern's Speedwell Pot. And the final two are permanently active (the two, as yet unexplored sections which feed Russet Well and Slop Moll).

The net effect of the Speedwell streamway shedding many distributaries is that it gets generally smaller as you go downstream. By the time the conduit approaches the two risings referred to above it is either tiny (Russet Well), or badly restricted by chokes (Slop Moll). So, as the flow increases, the level of Speedwell's downstream sump surface soon rises up the steeply sloping stream passage. As the water level reaches and then rises above the level of Sand Passage (the original name of the canal leading to Treasury Sump) the Peak Cavern end of Treasury Sump the also rises.

However, the overspill point in Peak Cavern is (from memory) some 12 m above the normal level of Treasury Sump. So for water to flow from Speedwell via Treasury Sump into Peak Cavern, it must rise more than 12 m further in height up the Speedwell streamway. In such conditions the downstream sump in Speedwell Cavern will have backed up over a vertical range of probably approaching 30 m.

A lot of the massive flow in such conditions can't get through to the Peak Cavern gorge via Russet Well and Slop Moll. The least restricted of several other outlets for the excess water is Treasury Sump. This is why such a great volume of water gets from Speedwell into Peak in extreme flood.

So what's the significance of all of this to our celebrated flask of cold tea?

1. There is no hydrological reason it couldn't have come through Treasury Sump from Speedwell.

2. Its buoyancy would not have been great enough to prevent this.

3. However, as it would have been subjected to at least 2.2 bars pressure in the process (travelling underwater via a minimum depth of 12 m) and have been battered mercilessly against the many jagged flakes in Speedwell in the very high flow, the visible damage on the flask seen in those pictures suggests it may not actually have passed through from Speedwell to Peak.

But "flask tracing" is very much a new science, so maybe the jury should remain out on the source of that flask until the original experimenter comes forward? 

. . .  and with that, I think I need to put the kettle on. 

 

[pwhole]

Fantastic stuff - just what I needed to know, and very useful for all sorts of reasons. I was going to eat now, but may have to celebrate with another cuppa first!