7 replies to this topic

[salvatorespiezia]

Dear colleagues,

I would much appreciate if you could provide me an ‘average value’ for the LPG bulk modulus of elasticity.
I had a look on the Internet but I cannot find this information.
I need this data to estimate the ‘celerity of the pressure waves’
travelling through an LPG section of pipe after a sudden closing of a valve.

Best regards,

Salvatore Spiezia

[gvdlans]

As you probably know LPG is basically a mixture of propane and butane.

Bulk modulus of propane is 0.22 GPa (Giga Pascal) at temperature of 20 °C.
Bulk modulus of butane is 0.36 GPa (Giga Pascal) at temperature of 20 °C.

This is relatively low compared to bulk modulus of water (=2.2 GPa), resulting in lower surge pressures.

[SPOOK]

As you probably know LPG is basically a mixture of propane and butane.

Bulk modulus of propane is 0.22 GPa (Giga Pascal) at temperature of 20 °C.
Bulk modulus of butane is 0.36 GPa (Giga Pascal) at temperature of 20 °C.

This is relatively low compared to bulk modulus of water (=2.2 GPa), resulting in lower surge pressures.

gvlands,

Kindly can you please provide a source for this data. or any other reference where the liquid bulk modulus of elasticity could be found?

Also for LPG should we consider an aritmatic average of the above values of use the formula.
sigma xiMi

where xi is the wt fraction of the components
and Mi is the modulus of elasticity of the components making up the LPG

Help appreciated.

Regards
SPOOK

[gvdlans]

gvlands,

Kindly can you please provide a source for this data. or any other reference where the liquid bulk modulus of elasticity could be found?

Also for LPG should we consider an aritmatic average of the above values of use the formula.
sigma xiMi

where xi is the wt fraction of the components
and Mi is the modulus of elasticity of the components making up the LPG

Help appreciated.

Regards
SPOOK

Some editions of CRC Handbook of Chemistry and Physics contained tables with liquid compressibility (=1/bulk modulus). I will check my version when I am back home.

I would use a conservative value of 0.36 GPa for LPG, although probably a weighed average ("Sigma xiMi") would be a best estimate.

Anyway, I have done quite a few Pipenet calculations on LPG pipelines (several kilometers in length) in the past and found that surge/waterhammer is hardly any issue with LPG because of the low bulk modulus (= high liquid compressibility).

[Qalander (Chem)]

Dear salvatorespiezia&spook,

My observation while with my previous employeris that; on a few Kilometers long LPG pipeline no water hammer like problems throughout the operations spreaded over several years.

Hope this helps.

[SPOOK]

Some editions of CRC Handbook of Chemistry and Physics contained tables with liquid compressibility (=1/bulk modulus). I will check my version when I am back home.

I would use a conservative value of 0.36 GPa for LPG, although probably a weighed average (xiMi) would be a best estimate.

Anyway, I have done quite a few Pipenet calculations on LPG pipelines (several kilometers in length) in the past and found that surge/waterhammer is hardly any issue with LPG because of the low bulk modulus (= high liquid compressibility).

Thanks gvlands,

your help was indeed insightful.

SPOOK

[SPOOK]

[/quote]

Dear salvatorespiezia&spook,

My observation while with my previous employeris that; on a few Kilometers long LPG pipeline no water hammer like problems throughout the operations spreaded over several years.

Hope this helps.
[/quote]

Qalander,

If the pipelines are designed considering the surge scenarios obviously the water hammer issues will not result. Can you give details about your experience where in emergency situations hammers did not occur.

Appreciated

SPOOK

[gvdlans]

Some editions of CRC Handbook of Chemistry and Physics contained tables with liquid compressibility (=1/bulk modulus). I will check my version when I am back home.

The CRC Handbook of Chemistry and Physics does contain a table "Isothermal Compressibility of Liquids" (on pages F-12 - F15 in the 67th edition), but there is no data for propane or butane. The following book does contain a value for bulk compressibility (0.53 GPa at -5 degC) for butane:
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