Fix Volume tank problem, temperature Vs Pressure 2

[WJW]

When you have a fixed volume steel vessel totally filled with water (no air), and the tank temperature is raised by say 30deg C from ambient. As the water tries to expand due to volumetric expansion but can't as it’s a fixed volume, it will raise the pressure within the tank.

How is this pressure calculated as a function of temperature rise??

 

[gladkenn]

Check your thermodynamics book and look for the nonflow process of fluids. Im sure this is elementary.

 

[JStephen]

It's not so elementary and probably not in the thermodynamics book, either.

When the temperature of the water is raised, it expands slightly. But the temperature of the vessel also increases, and the vessel volume increases slightly, too. Assuming the water volume increases faster than the vessel volume (and I'm not sure if it does), you build up pressure in the vessel. The pressure further expands the vessel and shrinks the water (relative to what it would be if unpressurized).

So given a set temperature increase, calculate the increase in the volume of water and the increase in the volume of the vessel. Then start checking the volume changes from different pressures until you find the pressure that makes the two final volumes equal again.

 

[WJW]

to be honest the fluid isn't water its rubber in a very thick wall tube (30mm wall)
the volumetric expantion for rubber is = 0.000271/deg C

FROM 80Deg to 150 Deg is 70 Deg change
so: taking a unit volume of '1' =

0.000271 * 70 * 1 = 0.01897m^3

or 1.89% increase in volume
would this be a 1.89% increase in pressure ????????

please read this i found on the net about fule oil in a tank.:-

"All liquids have a coefficient of cubical expansion. Simply put, this is the amount the liquid will expand as its temperature increases. As an example, fuel oil has a Mean Coefficient of 0.00045 per unit volume, per degree Fahrenheit. What that translates to is: a trapped volume of fuel oil will increase its pressure by 75 psi with a 1°F rise in temperature. If the pump were deadheaded with an inlet pressure of 100 psi, it now “sees” a discharge pressure of 175 psi. If you have a 2°F rise in temperature, you're looking at 250 psi discharge pressure. It would not be unusual to see system pressure rise to over 400 psi, as it would only require a temperature rise of 5°F. "


=======================================================

So if i apply the above:- it's around half my volume coefficient so say 37.5psi per 1Deg F
And i have 70 Deg C = 158 Deg F

SO 158 * 37.5 = 5925 PSI !!!!!!!!!

==================

Thank you all for your input

 

[quark]

Past threads in these forums echo the same data of 75psi with 1[sup]0[/sup]F rise in temperature(this seems to be common for most of the liquids). I never came across any formulae to calculate the liquid pressure rise due to temperature increase. You can't directly apply the supposed percentage volume increase to pressure like you do for gases in a similar case.

Your calculation makes sense to me.

Regards,

 

[JStephen]

A 1.89% increase in volume would NOT be a 1.89% increase in pressure; it would typically be much more if restrained.

 

[StoneCold]

WJW
This thread may be of use to you.


Thread124_83163


Good Luck

StoneCold

 

[WJW]

Thank you all for your input. Its all helped
Cheers
WJW (UK)

 

[mgp]

These threads might also be of use

thread378-981

thread391-15161

regards
Mogens

 

[GenB]

My guess is that the rubber will compact when water will not, so the vessel may enlarge by coeficient of temperature and a little the increased pressure. but not relative to the rubber changes.
ER

 

[TD2K]

Your pressure rise is not unrealistic for a 30C rise in temperature. This is why small thermal relief valves are provided just for this case.

The rule of thumb is that the rise in pressure increases from 40 to 100 psi per deg F temperature rise.

 

[112101ma]

To whom it correspond:

I need help with the following doubt: How can interprete the following especification for a tank (vessel for buffer prep); MAWP=Pressure=FV/60psi at temperature=350F AND MDMT=FV/60 psi at -20F? Both specifications applying a vessel and jacket.

I appreciate HELP AS SOON AS POSSIBLE!

Ana Carmen Vázquez

 

[quark]

MAWP is maximum allowable working pressure. The range FV/60 indicates full vacuum to 60 psi pressure at 350F. MDMT is minimum design metal temperature.

The spec. indicates your vessel should withstand full vacuum and upto 60psi at 350F and same for MDMT and pressure. Do you really need -20F for buffer preparation?

PS: It is a good practice to start a new thread always.

 

[quark]

To add further, you are not supposed to pressurize your vessel at MDMT to avoid brittle failure. When your area is conditioned all the time then I don't see any problem why you have to strictly adhere to it.

Perhaps, ASME wizards in here can help you out.

 

[chicopee]

Under the condition stated, specific volume remains constant for any temp/pressure. Using the Mollier diagram or thermodynnmics tables you can determine the pressure or temperature as long as one of these variables is available under this constant specific volume.