Steady Flow Energy Equation (SFEE)

Consider an open system through which the working substance flows in a steady rate as shown in Figure 1.63.

STEADY FLOW ENERGY EQUATION (SFEE)

Consider an open system through which the working substance flows in a steady rate as shown in Figure 1.63. The working substance entering the system at (1) and leaves the system at (2).

Let

p1 = Pressure of the working substance entering the system in N/m2

v1 = Specific volume of the working substance entering the system in m3/kg

C1 = Velocity of the working substance entering the system in m/s

u1 = Specific internal energy of the working substance entering the system in J/kg

z1 = Height above the datum level for entry in m

p2, v2, C2, u2 and z2 are corresponding values for the working substance leaving the system.

Q = Heat supplied to the system in J/kg

W = Work delivered by the system in J/kg

The above equation is known as Steady Flow Energy Equation (SFEE). The above equation represents the energy flow per unit of mass of the working substance (J/kg). When the equation is multiplied by mass flow rate (m) of the working substance throughout, then all terms will represent the energy flow per unit time. (i.e. in J/s)

Then the above equation becomes

If the values of Q and W in kJ/kg and h1 and h2 are substituted in kJ/kg, then the above equation becomes,

If Q and W are already in kW and h1 and h2 are substituted in kJ/kg, then the above equation becomes

Note: In a steady flow system, the mass flow rate of the working substance is given by

where

The mass flow rate (m) is represented in kg/s

A1 and A2 are areas of cross section at entry and exit in m2.