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Estimate Vacuum Formed In Vessel

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#1 clarenceyue


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Posted 08 August 2018 - 01:27 AM

Dear members,


I am currently sizing a rupture disk that can relieve both pressure and vacuum (Continental CAL-VAC type). The pressure setting is set as the design pressure of vessel which is 3.5 barg (50 psig). The vessel is also designed for a vacuum pressure of -0.7 barg.


The vacuum scenario could occur supposing that the vessel (normally vented to the atmosphere) and is 90% full of water, is isolated (V-1, V-3, V-6 are closed) and only the bottom outlet to a pump is open (V-2 is open). The pump is operates normally at 14 m3/hr, with TDH 50 m W.C.


My initial estimate to determine the gas space pressure is to use the ideal gas law based on isothermal conditions prevailing, i.e.:


P1 * V1 = P2 * V2 => P2 (final gas space pressure) = V1/V2 * P1 = 0.1*Vtank / 1*Vtank * (14.7 psia) = 1.47 psia


However, I was told by my senior that one could use the pump motor power / differential head to determine the maximum vacuum formed. But I have no idea how this could be carried out, or if this suggestion is correct in the first place.


I would like to see your advice on how best to approach this issue of estimating the maximum vacuum formed.


Thank you.

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#2 Technical Bard

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Posted 12 August 2018 - 10:58 PM

The volume of vapour in the vessel will expand at the rate of the pump.  Then PV=nRT with n constant.  V grows, P and T will drop, according to the thermodynamics of the fluid in question.  

#3 breizh


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Posted 15 August 2018 - 03:34 AM



Hello clarenceyue,

You may find good pointers using the link attached .

hope this is helping you .


#4 clarenceyue


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Posted 15 August 2018 - 11:53 PM

Hi Technical Bard and Breizh,


Thanks for your help and pointers. I have done the estimation based on the suggestion in the link provided by Breizh.


Currently, we await the confirmation / comments from our technical solutions colleagues to see if this is a reasonable estimate for the case in point.

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