## Bulk modulus of compressibility

## Bulk modulus of compressibility

(OP)

Well that should be a basic question but for me it needs some clarification .

for the bulk modulus of compressibility : K = - dP / (dV/V)

why does K = 0 for compressible fluids ?? ,,,, I think of it like if we compress gas ie:decrease a certain masses volume (compressible fluid) its pressure will increase . So K would have a value greater than zero .

Can anyone help me figure out why it should be = 0 ??

for the bulk modulus of compressibility : K = - dP / (dV/V)

why does K = 0 for compressible fluids ?? ,,,, I think of it like if we compress gas ie:decrease a certain masses volume (compressible fluid) its pressure will increase . So K would have a value greater than zero .

Can anyone help me figure out why it should be = 0 ??

## RE: Bulk modulus of compressibility

## RE: Bulk modulus of compressibility

You are right, non-zero but low values as may be seen for air in:

http://en.wikipedia.org/wiki/Bulk_modulus

Another site:

http://www-mdp.eng.cam.ac.uk/web/library/enginfo/a...

## RE: Bulk modulus of compressibility

isothermal compressibility coefficient = -(1/V)*dV/dP

or the derivative of volume vs. pressure,

bulk modulus is not 0 for real gases, see below,

for the derivative of volume vs. temperature

volumetric expansivity coefficient = (1/V) dV/dT

for mixture you can calculate these properties for both vapors and liquids

with a EOS or equivalent procedures,

see for example the Excel macros StrGIC, StrLIC, StrGVE, StrLVE in

"http://www.prode.com/en/properties.htm"

another possibility is

"http://www.nist.gov/srd/nist23.cfm"

## RE: Bulk modulus of compressibility

you must get smarter than the software you're using.