The Mechanical Engineering Handbook



Steady Flow Energy Equation

Steady Flow Energy Equation



$$ \dot{Q} + \dot{W} = \dot{m} \left(h_1 + \frac{v_1^2}{2} + gz_1\right) - \dot{m} \left(h_2 + \frac{v_2^2}{2} + gz_2\right) $$
where:

Q   =   Heat added to the system   (W)

W   =   Work done by the system   (W)

m   =   Mass flow rate (kg/s)

h1   =   Enthalpy at state 1 (J/kg)

h2   =   Enthalpy at state 2 (J/kg)

v1   =   Flow velocity at state 1 (m/s)

v2   =   Flow velocity at state 2 (m/s)

g =   Gravitational acceleration (m/s²)

z1   =   Height at state 1 (m)

z2   =   Height at state 2 (m)


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Equation Assumptions



  • The system is in steady state.
  • Flow is uniform at inlets and outlets.
  • The flow is steady and isentropic.
  • Flow is single phase.