First Law of Thermodynamics for a Control
Volume
Mass simultaneously entering and leaving the system is a very
common phenomenon in most of the engineering applications. Control volume concept is applied to these
devices by assuming suitable control surfaces.
To analyze these control volume problems, conservation of mass and
energy concepts are to be simultaneously considered.
Energy may cross the control surface not only in the form of heat
and work but also by total energy associated with the mass crossing the
boundaries. Hence apart from kinetic,
potential and internal energies, flow energy should also be taken into account.
The Steady-state Flow Process
When a flow process is satisfying the following conditions, it is
known as a steady flow process.
1. The mass and energy content of the control
volume remains constant with time.
2. The state and energy of the fluid at inlet, at
the exit and at every point within the control volume are time independent.
3. The rate of energy transfer in the form of
work and heat across the control surface is constant with time.
Therefore for a steady flow process
This equation is commonly known as steady flow energy equation
(SFEE).
