Improved Thermodynamic Analysis

Improved thermodynamic analysis extends the conventional thermodynamic computations to include the second law of thermodynamics quantitatively rather than qualitatively. The extended computations permit assigning fuel consumption to each process in a system. Fuel here means the input energy resource(s) often applied at one or two locations in the system boundaries. The energy resource may be fossil fuel, power, heat or any other driving resource. Thus, the way a fuel is utilized throughout a system is revealed. Processes of high fuel consumption are identified. Means of fuel saving are inspired by a structural change of the system or/and by a change in design point. New avenues of research and development are uncovered.

The extended computations may be easily understood from the well-known definition of the adiabatic efficiency of a turbine or a compressor. Ideal adiabatic work (isentropic) is obtained when the entropy remains constant. Actual adiabatic work is associated with entropy creation. The efficiency relates the actual work to the ideal.

The extended computations are simply entropy balance computations beside the conventional mass, energy and momentum balances. Entropy is conserved in an ideal process and is created in any real process. Efficiency-related variables of a process such as pressure losses, adiabatic efficiencies, heat-exchange effectiveness permit the computation of the amount of entropy creation Sc. The created entropy is the difference between the actual process change of entropy and that of its corresponding ideal process. The process inefficiency (irreversibility) is measured as a lost work potential = T„ * Sc, where Ta is an ultimate sink temperature. Ideal processes do not create entropy. They measure 100% on the efficiency scale. It is important to note that since property relations and conventional balance equations along with efficiency variables can solve an energy system problem, engineers never bothered in the past to perform entropy balances.

A more complete picture of efficiencies and inefficiencies is obtained by using a general work potential function known as exergy. For simple chemical systems it represents the maximum useful work relative to a dead state environment defined by pressure Pa, temperature T0, and composition {Xco}.

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