Torr = Barg

[james10]

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!!!! ;):p

[RANGER1]

James I'm guessing at approx 14.7 pounds per square inch at sea level .

If it collapsed it must have been faulty anyway!

[frank]

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

[chillerman2006]

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 chillerman

[james10]

James I'm guessing at approx 14.7 pounds per square inch at sea level .

!
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????

[Tayters]

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!!

[james10]

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
Very interesting Frank, in his demo removing the pressure from outside the balloon sort of confirms my theory pressuming that the same applyies when the priciple ir reversed

[Tayters]

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.

[james10]

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 chillerman
Thanks CM but im still scrathcing my brain on that one it would take more than 1 bar of force to crush a tube in the centre with a pair of grips, so im still thinking that the pressure equivilant is greater

[james10]

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!!
Tayters, thats more like my way of thinking it was in fact a 1/2" tube 10' long so in your maths the pressure crushing the tube would be 4.986394557823129 Barg

[james10]

Also am i right in thinking that a cylinder is weaker pushing inside out rather than vice versa

[Tayters]

Hi James,


Tayters, thats more like my way of thinking it was in fact a 1/2" tube 10' long so in your maths the pressure crushing the tube would be 4.986394557823129 Barg

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.

[chillerman2006]

Thanks CM but im still scrathcing my brain on that one it would take more than 1 bar of force to crush a tube in the centre with a pair of grips, so im still thinking that the pressure equivilant is greater

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 chillerman

[james10]

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.
You are indeed correct i missed out the pi part of the equation, shame i ddidnt do the same at lunch time and i wouldnt look thre months pregnant ;)

[james10]

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 chillerman
Totally agree in principle but there has to be more to it if a tube can take 15barg pushing out on it then surley it can take the same pushing inward, in that i may have answered my own question provided that a cylindrical shape is stronger pushing out than in

[chillerman2006]

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 chillerman

[james10]

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

[Peter_1]

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.pdf

[chillerman2006]

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 chillerman

[james10]

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.pdf
Thanks Peter i have started to read your paper and will finish it on monday (maintenance) think its going to be an interesting read

[james10]

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 chillerman
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!!!!!

[chillerman2006]

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



i may have answered my own question provided that a cylindrical shape is stronger pushing out than in

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 Chillerman

[michaelm]

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.