Bulk Modulus and Fluid Elasticity

An introduction to and a definition of the Bulk Modulus Elasticity commonly used to characterize the compressibility of fluids

The Bulk Modulus Elasticity is a material property characterizing the compressibility of a fluid - how easy a unit of the fluid volume can be changed when changing the pressure working upon it.

The Bulk Modulus Elasticity can be expressed as

E = - dp / (dV / V) (1)

where

E = bulk modulus elasticity

dp = differential change in pressure on the object

dV = differential change in volume of the object

V = initial volume of the object

The Bulk Modulus Elasticity can be alternatively expressed as

E = dp / (dρ / ρ) (2)

where

dρ = differential change in density of the object

ρ = initial density of the object

An increase in the pressure will decrease the volume (1). A decrease in the volume will increase the density (2).

• The SI unit of the bulk modulus elasticity is N/m² (Pa)
• The imperial (BG) unit is lb_f/in² (psi)
• 1 lb_f/in² (psi) = 6.894 10³ N/m² (Pa)

A large Bulk Modulus indicate a relative incompressible fluid.

Bulk Modulus for some common fluids can be found in the table below:

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