Chilled water system -Maximum Design pressure Vs Operating pressure

[Timothi]

Hi experts,

In expansion tank sizing software the following inputs required.
1. Maximum design pressure
2. Operating pressure

How to calculate these parameters?


Thank You
Timothi Albani

 

[LittleInch]

You get these figures from the process design calculations / process engineer for whatever pressure is required to meet your particular requirements.

BTW the word "maximum" is irrelevant. Your design pressure is your maximum pressure so you can't have a "minimum" design pressure...

Very vague question so very vague answer I'm afraid.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Timothi]

Dear LittleInch,

Thank you very much for your attention. Sorry for the vague question. This is what exactly I meant.

Is there any formula to find P1 & P2

For closed expansion tank
Vt = {((v2-v1)-1)-3αΔt)/((Pa/P1)-(Pa/P2))}*Vs

Vt= Expansion tank volume
P1 = Pressure at lower temperature
P2 Pressure at higher temperature

 

[BigInch]

P1 will be equal to P2, if the fluid is allowed to change its volume by the amount that thermal expansion would imply. If you restrict the change of volume of a fluid to a certain differential volume, multiply that by the fluid's bulk modulus and you can find the corresponding change in pressure.

you must get smarter than the software you're using.

 

[LittleInch]

No I don't think you can work this work as you have two variables but only one equation.

In your OP you say that you need P1 and DP. I think you also need to know expansion volume...

Normally to work out an expansion tank volume you start with your initial P1, work out the volume it expands due to increased temperature (hence you need to know the total volume of liquid you are dealing with), have your design pressure known and then you can figure out how much air volume is required to go from P1 to design pressure. You need to assume then how much volume you start with at P1 then add the air volume so that when the expansion volume fills the tank you end up with no more than design pressure. This is the relatively simple method - of course as pressure increases the density of the fluid changes a little bit and the volume of the pipes etc changes a little bit, but these are usually fairly small compared tot he expansion of the fluid. For expansion tanks it is better to be a little cautious.

If you know three of air volume, liquid expansion volume, P1 or P2 you can work out the fourth , but I don't think you can do this by reverse unless you assume a number for P1 or P2 or the volumes.

Sorry, but without guessing I don't think this will work.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[LittleInch]

I couldn't figure out your equation, but if you're using simple gas law remember to use absolute temperatures (degrees K) and absolute pressures (psia/bara)...

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

Thought "expansion tank" implied liquid, but I guess it wouldn't have to be so... maybe.

you must get smarter than the software you're using.

 

[LittleInch]

Who knows? maybe it does.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way