Stationary System and Operating Point

The operating region of a system is an area in which the state of the system can be varied diuing the operation. This area is determined dttring the design of the system. If all system inputs are corrstant (disturbances and controls of the system), every stable system will eventually move towards a stationary condition (steady state). By changing the controls of the system, the location of the stationary point can be influenced. In many cases, the system never reaches a steady state as a result of the presence of disturbances. 

The point where the system should be maintained or operated is called the operating point. Characteristics of the operating point are  

A system is in equilibrium if all balances are in equilibrium, i.e. if the variables that describe the system, such as temperature, pressure and flow, do not change. This means that the sum of the flows of mass, energy and momenmm that are produced by the system or are supplied to the system is equal to the sum of the flows that are dissipated by the system or discharged from the system. If these flows are constant, the system remains in a stationary condition. 

The flows that are produced (the rate of production) or dissipated (rate of consumption) are usually dependent on the state of the system  

For a closed system, an operating point can be graphically depicted by plotting the rate of production and the rate of consumption against the state of the system. The lines that describe the flows are called characteristics. This is shown in Fig. 7.1 the operating point is the intersection of both lines. It holds that the produced mass, energy or momentum is equal to the consumed mass, energy or momentum. 

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