Thermal expansion for trapped liquid in pipe
Thermal expansion for trapped liquid in pipe
(OP)
Dear all,
I would like to ask for some advise regarding thermal expansion of liquid in a pipe. There are 2 cases:
1) For liquid trapped in a pipe without external heat source except from the surrounding, I want to know how can I calculate the increase in the pipe pressure if I know the expansion in liquid volume. If I can calculate this, then I will know if the pipe can withstand the delta increase and if a RV is required.
2) Heated liquid is pumped to a header through an insulated pipe. Is it true to say - thermal expansion is not a problem in this case if the liquid is trapped? Because the insulation is to maintain the temperature. Tendency would be for the pipe to cool down rather than to be heated up and expand.
Thanks.
Raingal
I would like to ask for some advise regarding thermal expansion of liquid in a pipe. There are 2 cases:
1) For liquid trapped in a pipe without external heat source except from the surrounding, I want to know how can I calculate the increase in the pipe pressure if I know the expansion in liquid volume. If I can calculate this, then I will know if the pipe can withstand the delta increase and if a RV is required.
2) Heated liquid is pumped to a header through an insulated pipe. Is it true to say - thermal expansion is not a problem in this case if the liquid is trapped? Because the insulation is to maintain the temperature. Tendency would be for the pipe to cool down rather than to be heated up and expand.
Thanks.
Raingal





RE: Thermal expansion for trapped liquid in pipe
above 100 C at 1 bar you know water boils. Or is teh system below 100 C all the time.
RE: Thermal expansion for trapped liquid in pipe
I'm not referring to water. I'm just taking a general term "liquid" as a whole. Surrounding tempt varies from 28 - 38 degC..
Raingal
RE: Thermal expansion for trapped liquid in pipe
I'm not referring to water. I'm just using a general term "liquid". Surrounding tempt is around 28 - 38 degC.
Raingal
RE: Thermal expansion for trapped liquid in pipe
RE: Thermal expansion for trapped liquid in pipe
I assume you've already used the liquid's expansion coefficient to calculate the volume change associated with the temperature change at constant pressure.
Similarly, you use the liquid's bulk modulus to calculate the pressure required to shrink it back down to the original volume at constant temperature. The number may surprise you; in general, you want some trapped gas or other elastance in a closed system.
2)
Maybe true, but beware of buckling if the pipe is relatively thin walled.
Mike Halloran
Pembroke Pines, FL, USA
RE: Thermal expansion for trapped liquid in pipe
raingal79 (Chemical)How did you determine the expansion in liquid volume?
RE: Thermal expansion for trapped liquid in pipe
Steel pipe can probably yield before bursting, which would act to relieve some of the pressure as well.
RE: Thermal expansion for trapped liquid in pipe
thread798-96681, thread391-38740, thread391-15161, thread378-82763, thread378-55232, thread378-55160, thread378-981, thread124-102722, thread124-16098.
RE: Thermal expansion for trapped liquid in pipe
H_tot=m_gas*h_gas+m_liq*h_liq
If the closed (static) volume is subject to some heat source or-sink the enthalpy will drop or rise with a known quantity resulting in a new "state" for the mixture.
Use a handbook for enthalpies and phase diagrams.
Bugs are thermal expansion of the liquid/gas mixture and the mechanical deformation of the tube interfering in calculations. You got to decide yourself if approxiamtions can be made giving you more or less exact results.
RE: Thermal expansion for trapped liquid in pipe