Degree-of-Freedom Analysis Revisited

As defined in Section 4.3d, the degrees of freedom of a system, is the number of system variables whose values must be specified before the remaining variables can be calculated. If a system is described by independent equations in variables, then = nv e  

The remainder of this section illustrates degree-of-freedom analyses for increasingly complex systems first a single nonreactive process unit, then a single reactive unit, and finally a system of several interconnected units. 

The number of unknown variables for a single unit is the sum of the unknown component amounts or flow rates for ail inlet and outlet streams, plus all unknown stream temperatures and pressures, plus the rates of energy transfer as heat and work. The equations available to determine these unknowns include material balances for each independent species, an energy balance, phase and chemical equilibrium relations, and additional specified relationships among the process variables. 

Let us first consider a heated mixer in which a stream of oxygen and nitrogen at 25 C is blended with a stream of pure oxygen at 40°C. and the combined stream is heated to SO C. 

A degree-of-freedom analysis on this simple process would proceed as follows  

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