Wet or Dry rope SRTing ???
- Thread starter Geoff R
- Start date
Peter Burgess
New member
or a rope powered dynamo to generate a bit of electricity, to use as you choose. You could top up your rechargeable lamp cells, or charge a rope-climbing device for the return trip.
Peter Burgess
New member
A friction descender with an internal water-cooled circuit could be used to heat up a small reservoir of water sufficiently to make a nice cup of coffee to drink when you reach the bottom. 
Roger W
Well-known member
You could need a lot of hose for peristaltic pumping... With just a single length, any peristaltic action when descending would tend to force the fluid in the hose downwards. That might be OK for pumping water from Fell Beck down to the bottom of GG... :-\
To pump water upwards you'd need a long length of hose reaching from your sump up to the top of the pitch, then back down again to get the peristaltic pumping, then back up again unless you would be happy to leave the water at the bottom of the pitch.
You'd do better descending on a long length of rope over a pulley, with the descending caver on one side of the rope and a bucketful of boulders (or water) on the other to counterbalance.
Hmm... Think that has been done before somewhere on a building site.
A descender with the bobbin connected to a siren would provide braking by converting kinetic energy into sound energy.
You'd start off at the top with a low plaintive moan as you started to slide gently down the rope...
Which would turn into a piercing scream warning people to get out of the way as you plummeted to the bottom.
Sorry, Geoff - your original query seems to have been the trigger for a whole bucketful of misplaced ingenuity!
To pump water upwards you'd need a long length of hose reaching from your sump up to the top of the pitch, then back down again to get the peristaltic pumping, then back up again unless you would be happy to leave the water at the bottom of the pitch.
You'd do better descending on a long length of rope over a pulley, with the descending caver on one side of the rope and a bucketful of boulders (or water) on the other to counterbalance.
Hmm... Think that has been done before somewhere on a building site.
A descender with the bobbin connected to a siren would provide braking by converting kinetic energy into sound energy.
You'd start off at the top with a low plaintive moan as you started to slide gently down the rope...
Which would turn into a piercing scream warning people to get out of the way as you plummeted to the bottom.
Sorry, Geoff - your original query seems to have been the trigger for a whole bucketful of misplaced ingenuity!
ttxela
New member
Roger W said:
That's why you'd need a loop of hose
Although thinking on you'd probably need a rigid bend at the top, you'd probably want a good jubilee clip on that :read:Mind you the amount of water you could pump would be limited to the volume in the hose going up then down again :-\
The siren idea is quite good.
Also I remember at the heights of Abraham there is a rescue device for riding out to stranded cablecars that uses a sort of windmill as a brake, that idea must have some merit too.
Roger W
Well-known member
The energy lost as heat when descending a pitch is crying out to be put to some useful purpose instead of just making your descender to hot to hold and glazing the surface of your rope.
The problem is that any likely energy conversion system - dynamo, siren, windmill or whatever - looks like being too big and heavy for anyone to want to lug around a cave or prussik back up the shaft with.
I don't know if a workable generator/motor unit could be built that would lower you down gently and then motor you back up the shaft on your way out. You could leave the charged unit at the bottom of the pitch ready for your return. The trouble there is that inevitable energy losses would mean your battery would run out somewhere short of the top of the pitch...
The problem is that any likely energy conversion system - dynamo, siren, windmill or whatever - looks like being too big and heavy for anyone to want to lug around a cave or prussik back up the shaft with.
I don't know if a workable generator/motor unit could be built that would lower you down gently and then motor you back up the shaft on your way out. You could leave the charged unit at the bottom of the pitch ready for your return. The trouble there is that inevitable energy losses would mean your battery would run out somewhere short of the top of the pitch...
Well, it's a long time since I did A-level physics? but according to my calculations (which I'd be happy to see checked and corrected) then a 70 kg caver descending 50 m converts 34,335 joules of potential energy into some other form of energy ? heat in the descender / kinetic energy of descent?
If he takes 1 minute, that's a rate of just over half a kilowatt ? or, to put it another way, the energy is equivalent to that from a 1-kw fire in34 secs.
If he takes 1 minute, that's a rate of just over half a kilowatt ? or, to put it another way, the energy is equivalent to that from a 1-kw fire in34 secs.
SamT
Moderator
ChrisJC said:Indeed, and if you assume 50% of the energy goes into a 326g aluminium Stop, you can calculate quite a spectacular rise in temperature. I wonder what the melting point of rope is........
Chris.
Made from nylon so according to Wikipedia - 190 to 350 deg C
We know a stop gets hot enough to melt the rope!!
Chocolate fireguard
Active member
I have been preoccupied lately with cataloguing and rearranging our extensive collection of Royal Wedding memorabilia to make way for the exciting new items my lady wife and I have just obtained, but now turning to this forum I am impressed by the quality of some of the stuff on this thread.
The estimates offered by Fulk and ChrisJC are good and I shall try to do them justice.
Just to clear up this kinetic energy thing, a 70kg caver arriving at the bottom at 10m/s (like stepping out of a first floor window!) would have 3500J of KE. More sensible figures are about 1m/s and 35J. Compare with the total energy change involved with a 50m pitch (35000J for the same caver) and it`s obvious that KE can be ignored unless something has gone seriously wrong.
Using the figures from ChrisJC and Fulk, 900J/kg degree Celsius for the specific heat capacity of aluminium and assuming the heat is distributed uniformly in the Stop, gives over 50C for the temperature rise.
Aluminium is a far better conductor of heat than nylon so it is likely that more than half the energy goes into the descender. Also, the mass of 5 rack bars is 150g and perhaps only the top few generate a lot of the heat so things could be worse than with a Stop.
Moving on to ttxela`s idea for converting the energy into sound.
Using Fulk`s estimate of half a kilowatt, if all this was released as sound, uniformly in all directions, then at the caver`s ear (30cm away?) the sound intensity would be about 500W/square metre. The threshold of hearing (0dB) is about 10^-12W/m^2, so using Sound Pressure Level = 10log to base 10(intensity/reference intensity) gives around 145dB (I do not have a calculator handy). If all the sound energy was in the 500Hz to a few kHz region this would correspond to a sound level of 145dB(A). The threshold of pain is usually taken a 140dB(A).
Some of us remember Marlow yachting rope from the 80s.
What great times for those of us who know how things should be done (thoroughly and at great length) and do so with no fear of wrath from moderators, republicans and those who think scientific rigour is nerdy.
Street party anyone?
The estimates offered by Fulk and ChrisJC are good and I shall try to do them justice.
Just to clear up this kinetic energy thing, a 70kg caver arriving at the bottom at 10m/s (like stepping out of a first floor window!) would have 3500J of KE. More sensible figures are about 1m/s and 35J. Compare with the total energy change involved with a 50m pitch (35000J for the same caver) and it`s obvious that KE can be ignored unless something has gone seriously wrong.
Using the figures from ChrisJC and Fulk, 900J/kg degree Celsius for the specific heat capacity of aluminium and assuming the heat is distributed uniformly in the Stop, gives over 50C for the temperature rise.
Aluminium is a far better conductor of heat than nylon so it is likely that more than half the energy goes into the descender. Also, the mass of 5 rack bars is 150g and perhaps only the top few generate a lot of the heat so things could be worse than with a Stop.
Moving on to ttxela`s idea for converting the energy into sound.
Using Fulk`s estimate of half a kilowatt, if all this was released as sound, uniformly in all directions, then at the caver`s ear (30cm away?) the sound intensity would be about 500W/square metre. The threshold of hearing (0dB) is about 10^-12W/m^2, so using Sound Pressure Level = 10log to base 10(intensity/reference intensity) gives around 145dB (I do not have a calculator handy). If all the sound energy was in the 500Hz to a few kHz region this would correspond to a sound level of 145dB(A). The threshold of pain is usually taken a 140dB(A).
Some of us remember Marlow yachting rope from the 80s.
What great times for those of us who know how things should be done (thoroughly and at great length) and do so with no fear of wrath from moderators, republicans and those who think scientific rigour is nerdy.
Street party anyone?
JasonC
Well-known member
When a caver descends a rope, there are only two significant forces acting - gravity, and resistance from the descender in the form of friction. The more resistance, the slower the descent.
To me, this implies that a slow descent generates more heat overall than a quick one - simply because more resistance is required (in the extreme case of the quickest possible descent where the caver has forgotten to attach descender to rope, then no heat at all is generated!)
Countering that, a swift descent gives less time for the heat to dissipate, so the descender gets hotter, but the overall heat absorbed by the rope should be less.
Of course, none of this bears on the original question of whether it's best to wet the rope first.....
To me, this implies that a slow descent generates more heat overall than a quick one - simply because more resistance is required (in the extreme case of the quickest possible descent where the caver has forgotten to attach descender to rope, then no heat at all is generated!)
Countering that, a swift descent gives less time for the heat to dissipate, so the descender gets hotter, but the overall heat absorbed by the rope should be less.
Of course, none of this bears on the original question of whether it's best to wet the rope first.....
Sorry, Jason ,but you're wrong ? Laws of Thermodynamics as expounded by Newton many years ago!!If you carry out a process in whatsoever fashion, but start at the same place and end at the same place, then the energy change is the same. It does not matte how quickly or slowly you descend a pitch, you convert X amounts of gravitational potential energy (PE) intt some other form of heat / energy (which are, of course ( ), equivalent).
If you run round the Three Peaks in 2.5 hours or stagger round in 12, you use the same amount of energy.
When abseiling, of course, the more quickly the energy is released, the hotter the descender gets. As for the 'descent without a descender' ? well, wrong again; some heat will be generated because the PE has to go somewhere . . . but the thought of sticking a thermometer into the crumpled bloody mass at the foot of the pitch to detect a tiny (fraction of a degree) increase in temperature doesn't appeal!
), equivalent).If you run round the Three Peaks in 2.5 hours or stagger round in 12, you use the same amount of energy.
When abseiling, of course, the more quickly the energy is released, the hotter the descender gets. As for the 'descent without a descender' ? well, wrong again; some heat will be generated because the PE has to go somewhere . . . but the thought of sticking a thermometer into the crumpled bloody mass at the foot of the pitch to detect a tiny (fraction of a degree) increase in temperature doesn't appeal!
