Jump to content

Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Gas Turbine Re-Ratings- posted in Ankur's blog


Api 521 Isothermal Compressibility Coefficient

1 reply to this topic
Share this topic:
| More

#1 ykkim


    Brand New Member

  • Members
  • 1 posts

Posted 12 November 2017 - 02:36 AM

Dear experts,

As I calculated isothermal compressibility coefficient of thermal expansion in pipe, the result seems negative (minus) number. As API 521, isothermal compressibility coefficient is


X = 1/v1 (v1-v2)/(p2-p1)


X = the isothermal compressibility coefficient, expressed in 1/kPa (1/psi)

v1 = the specific volume of liquid at the first pressure, expressed in m3/kg (ft3/lb)

v2 = the specific volume of liquid at the second pressure, expressed in m3/kg (ft3/lb)

p1 = the first absolute pressure, expressed in kPa (psi)

p2 = the second absolute pressure, expressed in kPa (psi)


The conditions I've calculated are showen below.


roh at T1 = 1046.8 kg/m3

roh at T2 = 1045.5 kg/m3


DeltaT = 1 degC (assume)


v1 at T1 =0.00095530 m3/kg

v2 at T2 =0.00095649 m3/kg


p1 = 70 kPa (Actual)

p2 = 653 kPa (Actual)


x = -0.000021


It means T2 is lower than T1. But P2 is higher than P1. What am I wrong? I am still struggling to understand. Please correct me where I am wrong. Thank you!




#2 sukanta87


    Gold Member

  • Members
  • 88 posts

Posted 13 November 2017 - 11:34 PM

It's isothermal. Why your temperature changed? v2 should have the lower value than the v1, as an  increase in fluid pressure (p2>p1) causes the fluid volume to decrease (v1>v2). Always x > 0.

Similar Topics