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Density of Fluids - Changing Pressure and Temperature

Calculating density of fluids when changing pressure and temperature

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The density of a fluid changes with temperature and pressure. The density of water versus temperature and pressure is indicated in the chart below:

water density temperature pressure

Density and change in Temperature

When temperature is changed the density of a fluid can be expressed as

ρ1 = ρ0 / (1 + β (t1 - t0))          (1)

where

ρ1 = final density (kg/m3)

ρ0 = initial density (kg/m3)

β = volumetric temperature expansion coefficient (m3/m3 oC)

t1 = final temperature (oC)

t0 = initial temperature (oC)

Volumetric Temperature Coefficients - β

  • water : 0.0002 (m3/m3 oC)
  • ethyl alcohol : 0.0011 (m3/m3 oC)

Density and change in Pressure

When pressure is changed the density of a fluid can be expressed as

ρ1 = ρ0 / (1 - (p1 - p0) / E)      (2)

where

E = bulk modulus fluid elasticity (N/m2)

ρ1 = final density (kg/m3)

ρ0 = initial density (kg/m3)

p1 = final pressure (N/m2)

p0 = initial pressure (N/m2)

Bulk Modulus Fluid Elasticity some common Fluids - E

  • water : 2.15 109 (N/m2)
  • ethyl alcohol : 1.06 109 (N/m2)
  • oil : 1.5 109 (N/m2)

Density of a fluid changing  both Temperature and Pressure

The density of a fluid when changing both temperature and pressure can be expressed by combining (1) and (2)

 ρ1 = [ ρ0 / (1 + β (t1 - t0)) ] / [1 - (p1 - p0) / E]          (3)

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Related Topics

  • Fluid Mechanics - The study of fluids - liquids and gases. Involves various properties of the fluid, such as velocity, pressure, density and temperature, as functions of space and time.
  • Thermodynamics - The effects of work, heat and energy on a system

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