Bulk Modulus and Fluid Elasticity
Introduction and definition of Bulk Modulus Elasticity - commonly used to characterize compressibility of fluids
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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 lbf/in2 (psi)
- 1 lbf/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:
| Bulk Modulus - E | Imperial Units - BG (105 psi, lbf/in2) |
SI Units (109 Pa, N/m2) |
| Acetone | 1.34 | 0.92 |
| Carbon Tetrachloride | 1.91 | 1.32 |
| Ethyl Alcohol | 1.54 | 1.06 |
| Gasoline | 1.9 | 1.3 |
| Glycerin | 6.31 | 4.35 |
| Mercury | 41.4 | 28.5 |
| Paraffin Oil | 2.41 | 1.66 |
| Petrol | 1.55 - 2.16 | 1.07 - 1.49 |
| SAE 30 Oil | 2.2 | 1.5 |
| Seawater | 3.39 | 2.34 |
| Water | 3.12 | 2.15 |
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