The Mechanical Engineering Handbook



Pressure and Density (Isentropic Relationships)

Pressure and Density Equation



$$ \frac{p_2}{p_1} = \left( \frac{\rho_2}{\rho_1} \right)^\gamma $$ where:

p1   =   Pressure at point 1   (Pa)

p2   =   Pressure at point 2   (Pa)

ρ1   =   Density at point 1   (kg/m³)

ρ2   =   Density at point 2   (kg/m³)

γ   =   Ratio of Specific Heats   (Dimensionless)


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Equation Assumptions



  • The process is isentropic.
  • Specific heat ratio remains constant.
  • The system is in steady-flow.
  • The fluid behaves as an ideal gas.
  • Fluid is homogeneous.