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Thread: Torr = Barg
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27-10-2011, 08:28 PM #1
Torr = Barg
I'll try to explain this the best i can,
Basically when a system is under vacuum say at 2 torr for instance, the atmospheric pressure exerted on the said system is then increased (theoretically),
My question is, is there a calculation to work this out?
ie if the system is at 2 torr then what is the pressure exerted on the system by atmosphere?
I ask this as i recently repaired a tube in an evap (flooded) the unit held its pressure test for 48hrs then when vacced down a tube collapsed under vaccum.
For anyone suggesting "GOOGLE" jog on!!!!
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27-10-2011, 09:02 PM #2
Re: Torr = Barg
James I'm guessing at approx 14.7 pounds per square inch at sea level .
If it collapsed it must have been faulty anyway!
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27-10-2011, 09:13 PM #3
Re: Torr = Barg
Have a look at this James....as they say - a picture is worth a thousand words
http://www.youtube.com/watch?gl=GB&v=vGulvutZJpg
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27-10-2011, 09:16 PM #4
Re: Torr = Barg
Hi James
as you know atmosphere is 1bar or 14.7 psi
1 torr is 1 atmosphere(1bar/14.7psi) devided by 760
2 torr = 0.0386 psi / 0.0026 bar atmosphere
at 2 torr you then have atmospheric pressure being exerted of 14.6974 psi / 0.9974 bar
this added to your water pressure is the external force on the tubework
R's chillermanIf the World did not Suck, We would all fall off !
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27-10-2011, 09:24 PM #5
Re: Torr = Barg
Yes it would if the system was at a positive or equal pressure to atmosphere,
eg if your at 1barg atmosphere both inside and outside the tube then the pressure equals it's self out meaning there is no outward or inward force exerted on the tube, or
you have 2barg on the outside of the tube (water pressure) and 4 barg on the inside you would have pushing outward of 2 barg.
reverse this to 4barg outside and 2barg inside you have 2 barg pushing in on the tube a crushing effect if you like.
So in my theory
you have 1barg (atmospheric pressure) outside the tube, and for ease say -5barg inside the tube then your crushing effect would the increase to 6barg.
or is my theory way wrong????
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27-10-2011, 09:35 PM #6
Re: Torr = Barg
Hi James,
According to Andylogic, if atmospheric pressure is 14.7psi then each square inch has 14.7 lbs of force on it.
If the inside of the pipe is at 2 torr then convert this to psi (0.038673549 psi) take atmospheric pressure from vaccuum pressure then that is the force per square inch on the tube.
In this case this results in 14.66psi.
Now need to find the surface area of the evaporator tube, use the formula Pi x diameter x length.
Out of interest imagine a coil in a commercial fridge, 3/8" pipe say 14" long, 10 rows along and 2 rows deep, not including the passes exactly but add 2 lengths (yeah we should include them but then it's another equation - not sure which one right now but would it not be easier to estimate how long the passes would be if straightened out?)
So...
10 rows x 2 deep = 20 rows. Add 2 for the passes = 22 x 14" = 308" long
3/8 x 3.14 x 308 = 362.67 square inches.
Total force is total surface area x psi
362.67 x 14.66 = 5317lbs
Thats 380 stone - over 2 1/4 tons!!Health and safety first..........unless I'm in a hurry.
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27-10-2011, 09:40 PM #7
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27-10-2011, 09:41 PM #8
Re: Torr = Barg
Ha ha, no relies when I started mine, 4 replies in the 30 mins it took me to construct it. Guess my maths is still too slow.
Health and safety first..........unless I'm in a hurry.
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27-10-2011, 09:44 PM #9
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27-10-2011, 09:47 PM #10
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27-10-2011, 09:49 PM #11
Re: Torr = Barg
Also am i right in thinking that a cylinder is weaker pushing inside out rather than vice versa
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27-10-2011, 10:06 PM #12
Re: Torr = Barg
Hi James,
Oo, I get a different answer.
For your tube surface area is 1/2 x 3.14 x 10 = 15.7 square inches.
If it's the same pressures invovled then 15.7 x 14.66 = 230 lbs = Over 16 stone.
In my example the pressure on the tube is 14.66psi or 1.01 bar. These are absolute values because we are referencing from a perfect vaccuum.
Where did you get 4.98 bar from?
Cheers,
Andy.Health and safety first..........unless I'm in a hurry.
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27-10-2011, 10:13 PM #13
Re: Torr = Barg
Hi James
may be I wrong, but I think that is all it is mate
as there is virtually no air/mass inside the tube, there is nothing to support the structure
nothing to be comressed and pushed back from inside
so any weakness in the tube and it collapses
lets look at it another way miles of water pipes serving your home
if we add up all the weight over its entire length, thats ??? huge
but it still only has the same ??? pressure per square inch
R's chillermanIf the World did not Suck, We would all fall off !
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27-10-2011, 10:22 PM #14
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27-10-2011, 10:27 PM #15
Re: Torr = Barg
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28-10-2011, 12:17 AM #16
Re: Torr = Barg
Hi James
been trying to find the answer to your question, all I can say is ''my brain hurts''
maybe the answer is here somewhere, try a google of
Implosion/viktor schauberger/etheric energies
R's chillermanIf the World did not Suck, We would all fall off !
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28-10-2011, 12:39 AM #17
Re: Torr = Barg
I've already said google suggesters can jog on
I've done all that mate till the cows come home where's NNM when you need him
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28-10-2011, 06:37 AM #18
Re: Torr = Barg
When we pressurize something it always wants to go to a spherical volume because the force is then everywhere equally applied on the surface. Reason why a tube is round, a gas cylinder is round.
But also reason why a PET bottle of cola is round and can withstand at least 7 to 10 bar - I tried this once -but can't withstand any vacuum at all. It crushes immediately.
So you must have had a weak place in your tube. Some Italian brands I know - ie ECO - uses 0.3 mm thick copper. Th smallest failure makes it collapse.
Read once the article Geoff Alder from SA and I wrote on http://www.alder.co.za/raca61.pdfIt's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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29-10-2011, 01:19 AM #19
Re: Torr = Barg
Hi Peter & (me new physical trainer) James
I do another couple of laps if I missed something ???
the conclusion is possible damage by partially freezing vessel at some point and/or
manufacturer defect, weak point callapses
Thanx for your time on this Peter
R's chillermanIf the World did not Suck, We would all fall off !
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29-10-2011, 12:57 PM #20
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29-10-2011, 01:04 PM #21
Re: Torr = Barg
CM, there is no doubt in my mind that the tube was weak, i agree a freeze issue could cause this but in my situation it was not a contributing factor.
the thing that gets me is it held 1500Kpa over 48hrs and not 1Kpa drop then a vacuum goes and pops the thing, which turned out to be quite embarrasing as i had to go back to the customer and ask for the ends to be taken back off which in this case was not an easy task,
My main objective from this is to carry out further pressure testing.
When i can establish the pressure equivilent i plan to test the outside of the tubes after testing the inners, bit of a pain but if a jobs worth doing!!!!!
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30-10-2011, 12:02 AM #22
Re: Torr = Barg
Hi James
maybe I missing yours & Peters points here
understand you did not have a freezing vessel at the time you tested
was wondering if in the past there had been partial freezing of the vessel
damaging the tube only slightly, that would need a close inspection to see
'IF' this is possible then it would tie in with Peters post of once a tube has damage (how ever small)
it will collapse under vacuum.... this link also gives good credit to what you said previously
http://www.youtube.com/watch?v=Zz95_VvTxZM
Be sure to post any conclusion you find mate & any suggestions for checking external pressure, as have asked a number of tech's about this now & no-one has shed more light than Peter and although I have not been unlucky enough yet, for this to happen to me, have heard of it several times
R's ChillermanIf the World did not Suck, We would all fall off !
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30-10-2011, 02:10 AM #23
Re: Torr = Barg
B”H
Peter is right. In general tube shape does not withstand well to the external pressure or internal vacuum both creating collapsing forces. Tube shape will withstand well to the compression force parallel to tube walls.