The steady flow energy equation relates to open systems working under steady conditions i.e in which conditions do not change with time.

The boundary encloses a system through which fluid flows at a constant rate, whilst heat transfer occurs and external work is done all under steady conditions ,that is , the rates of mass flow and energy flow are constant with respect to time.

The equation for steady flow ( the steady flow energy equation ) is generally written per unit mass as

q = heat transfer across boundary per unit mass
w = external work done by system per unit mass
z = fluid height
v = fluid velocity
h = fluid enthalpy ( u (internal energy + pv (pressure.specific volume)