Bulk Modulus and Fluid Elasticity

Introduction and definition of Bulk Modulus Elasticity - commonly used to characterize compressibility of fluids

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

bulk modulus elasticity

The Bulk Modulus Elasticity can be expressed as

E = - dp / (dV / V)         (1)


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 alternatively be expressed as

E = dp / (dρ / ρ)         (2)


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 lbf/in2 (psi)
  • 1 lbf/in2 (psi) = 6.894 103 N/m2 (Pa)

A large Bulk Modulus indicates a relative incompressible fluid.

Bulk Modulus for some common fluids:

Bulk Modulus - E Imperial Units - BG
(psi, lbf/in2)
SI Units
(Pa, N/m2)
Acetone 1.34 0.92
Benzene 1.5 1.05
Carbon Tetrachloride 1.91 1.32
Ethyl Alcohol 1.54 1.06
Gasoline 1.9 1.3
Glycerin 6.31 4.35
ISO 32 mineral oil 2.6 1.8
Kerosene 1.9 1.3
Mercury 41.4 28.5
Paraffin Oil 2.41 1.66
Petrol 1.55 - 2.16 1.07 - 1.49
Phosphate ester 4.4 3
SAE 30 Oil 2.2 1.5
Seawater 3.39 2.34
Sulfuric Acid 4.3 3.0
Water 3.12 2.15
Water - glycol 5 3.4
Water in oil emulsion 3.3 2.3

Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves velocity, pressure, density and temperature as functions of space and time
  • Material Properties - Material properties for gases, fluids and solids - densities, specific heats, viscosities and more

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