Topic Options
#20866 - 09/19/08 02:58 AM Full Vacuum Design????????
Shabeer Offline
Member

Registered: 12/26/07
Posts: 266
Loc: india
Hi all,

When designing a vessel for Full Vacuum condition, what should be the External pressure value to be entered.

I prefer 1.01325 bar as when there exists a vacuum inside a vessel then the pressure outside it(Atmospheric pressure) thrusts the vessel to crash inside.

Kindly, correct me if im wrong!!!!

Top
#20893 - 09/19/08 11:07 AM Re: Full Vacuum Design???????? [Re: Shabeer]
corne Offline
Member

Registered: 07/09/07
Posts: 401
Loc: The Netherlands
You're correct saying that full vacuum is 1.01325 bar, if the outside of the vessel is in contact with an unpressurized enviroment. If you have a vessel with double-walls (sorry, can't remember the correct term), then there is a change the pressure in the outer hull is 5 bar, and the pressure inside the inner is FV, so the calculating pressure is 6 bar external.

Personally I would use 1 bar as FV for single shelled vessels. 1.01325 is very accurate, except when the weather is bad and the ambient pressure is approx. 0.998 bar. :-)

Top
#21085 - 09/27/08 01:30 AM Re: Full Vacuum Design???????? [Re: corne]
Shabeer Offline
Member

Registered: 12/26/07
Posts: 266
Loc: india
Hi corne,

Thanks for ur reply.

In ur reply u have mentioned "Except when the weather is bad", can u explain me clearly....Do our External pressure go beyond 1 bar?

Top
#21089 - 09/27/08 07:06 AM Re: Full Vacuum Design???????? [Re: Shabeer]
corne Offline
Member

Registered: 07/09/07
Posts: 401
Loc: The Netherlands
Shabeer,
it was more of a little joke. You said FV for you is 1.01325 bar. This is a very specific value and imo you can just use 1 bar.
When you have to calculate a vessel for FV you have to apply an external pressure that is the equivalent of the external pressure - the internal pressure (0 bar(a)).
A vessel that is placed in a non-conditioned space, or just outside, will have varying pressures due to weather changes, check the barometer in your office. In such a condition however 1 bar external pressure is applied to the vessel for a FV calculation.

You have to be careful when doing a FV calculation for heat exchanger tubesheets or for jacketed vessels. The most inner part can have a FV, but the part next to it (heat exchanger internal for example) can have 10 bar(g).
In such a case you have to apply 11 bar as external pressure.

Personally I think it's best to think in terms of internal and external pressures. That makes is more clear what you're trying to do.

Top
#21259 - 10/04/08 11:39 PM Re: Full Vacuum Design???????? [Re: corne]
Shabeer Offline
Member

Registered: 12/26/07
Posts: 266
Loc: india
Corne,
Thanks for ur suggestions.

Top



Who's Online
0 registered (), 124 Guests and 0 Spiders online.
Key: Admin, Global Mod, Mod
May
Su M Tu W Th F Sa
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
Forum Stats
12065 Members
14 Forums
16973 Topics
75151 Posts

Max Online: 303 @ 01/28/20 11:58 PM
Top Posters (30 Days)