Pressure due to Temp Change in Liquid Full System
Pressure due to Temp Change in Liquid Full System
(OP)
My Friends,
I am asked to build a spreadsheet (or equivalent tool) for our mechanical engineering manager which can calculate the pressure in a liquid full system as a function of temperature, given an initial condition of temperature and pressure. For his needs it must be as rigorous as possible. Typical engineering assumptions (incompressible liquid, fixed volume, etc) cannot be used. Such a correlation would need to include:
1) Rho calculations for water as f(T,P)- i.e. the pressure dependency is an issue as it will require more rigorous solution of a water EOS rather than a simplified coefficient of expansion as per thermal relief sizing.
2) Volume changes of vessel as f(T,P)- i.e. thermal expansion and modulous of elasticity.
As this has probably been done many times before (I think even I have for incident investigations, etc), I am asking if anyone knows of a either a tool, example, or partial calculation such as Excel addin for water Rho(T,P), vessel volume change as f(T,P), etc. Anything that saves me a completely from scratch development is appreciated.
best wishes,
Sean
I am asked to build a spreadsheet (or equivalent tool) for our mechanical engineering manager which can calculate the pressure in a liquid full system as a function of temperature, given an initial condition of temperature and pressure. For his needs it must be as rigorous as possible. Typical engineering assumptions (incompressible liquid, fixed volume, etc) cannot be used. Such a correlation would need to include:
1) Rho calculations for water as f(T,P)- i.e. the pressure dependency is an issue as it will require more rigorous solution of a water EOS rather than a simplified coefficient of expansion as per thermal relief sizing.
2) Volume changes of vessel as f(T,P)- i.e. thermal expansion and modulous of elasticity.
As this has probably been done many times before (I think even I have for incident investigations, etc), I am asking if anyone knows of a either a tool, example, or partial calculation such as Excel addin for water Rho(T,P), vessel volume change as f(T,P), etc. Anything that saves me a completely from scratch development is appreciated.
best wishes,
Sean





RE: Pressure due to Temp Change in Liquid Full System
Good luck,
Latexman
RE: Pressure due to Temp Change in Liquid Full System
I am concerned that there will be problems with making a general tool. With my simple model (fixed volume), even small temperature drops (the usual situation) lead to results that don't match well- i.e a few degC temp drop and you are in a vacuum. This does not seem to be the case from plant observations. I will add volume changes for the cylindrical vessel (T and P) and see if it helps.
Thanks,
sshep
RE: Pressure due to Temp Change in Liquid Full System
You want a rigorous EOS-based GENERAL tool for this? Not in this lifetime. For vessel that is liquid full and blocked in, the 100 psi/°F number is safe and reasonably representative. You can apply more precision than that for a very carefully defined system, but you are not going to successfully make it a general-purpose calculator that works everywhere.
David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
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