
#1
Mar2408, 07:12 PM

P: 6

Hey, I have a problem in which there are two water tanks with different pressure. If they are connected together, how to calculate the time it takes to arrive to the steady state(same pressure)?
Thank you. 



#2
Mar2608, 10:57 AM

P: 7

Have you tried Poiseuille's law? Does this sound familiar  the total volume of liquid which flows across the entire crosssection of a cylindrical tube in time? See link http://en.wikipedia.org/wiki/Poiseuille's_law




#3
Mar2608, 03:35 PM

P: 6

Thank you for the reply.
The detail of the problem is that two tanks have pressure 87psi and 40 psi respectively. The 40psi tank connects to the water main. The 87psi tank has a expansion tank connected. When they are connected together, is it possible to know how pressure in the 87psi tank change with time? Thanks for any help. 



#4
Mar2708, 06:15 AM

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P: 2,877

Connect two tanks together
hi zax,
The flow of water is restricted by the various pipe lengths, fittings and valves you have installed between the tanks. The change in pressure is also a function of the thermodynamics of the air in the tank and heat transfer. Look through this post here to get a general idea of some of the concepts and what you might do to calculate things. In your case you might want to simplify the heat transfer and thermodynamics a bit. If you need help understanding flow restrictions, check the attached. Generally in industry, we use the Darcey Weisbach equation as indicated on the attached. 



#5
Dec1411, 12:29 PM

P: 4





#6
Dec1411, 05:49 PM

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P: 2,877

Once you get to the T in the line that connects the 2 tanks, it no longer matters how much restriction you put in the line downstream of that T. Note that this assumes the tanks are at the same elevation. If that isn't true, you may have to actively control tank level. 



#7
Dec1411, 06:26 PM

P: 4

Awsome so bascially ballancing the pressures at were the Two lines connect. Does the cross sectional venting associated with the Tank have to be at least 11/2 the cross sectional diameter of the discharge piping configeration in order to flow correctly should this be calculated as well or does it matter. One more thing if a pump is attached to this configeration does accelerated suction velocities need to be accounted for to ensure the ballanced pressure at the connection point of the lines connecting the two tanks?
Thank You for the reply it is great information 



#8
Dec1411, 07:24 PM

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#9
Dec1511, 08:27 AM

P: 4





#10
Dec1511, 08:28 AM

P: 4

Thank you for the information



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