Exergy diagram

Fig. 11.17. Exergy diagram for a direct synthesis of methanol showing the theoretical minimum exergy consumption [Ref. 16.].

Heat engines use a thermal energy source that is transferred to a working fluid in a combustion chamber, boiler, or reactor. Energy and exergy diagrams for this process are shown in Figure 23.6. The rejected heat represents stack losses in a fossil fuel boiler. 

We next consider the application of the exergy flux equation to a closed cycle plant based on the Joule-Brayton (JB) cycle (see Fig. 1.4), but with irreversible compression and expansion processes—an irreversible Joule-Brayton (IJB) cycle. The T,.s diagram is as shown in Fig. 2.6. 

The thermal efficiency, the work output as a fraction of the fuel exergy (the maximum reversible work), is shown as no. 1 in the figure and is 0.368. The internal irreversibility terms, are shown as nos. 2, 3, and 4 in the diagram, for the combustion... 

Grassmann diagram for the Linde liquefaction process of methane. One thousand exergy units of compression energy result in 53 exergy units of liquid methane. The thermodynamic efficiency of this process is 5.3%. The arrowed curves, bent to the right, show the losses in the various process steps. 

The diagram clearly shows the "value" of each flow in terms of its ability, or potential, to perform work. The diagram also shows that a considerable amount of the exergy flowing into the system is dissipated as a result of the... 

Exergy flow diagram or Grassmann diagram for the example of Figure 6.5. 

The results of the exergy analysis of the gas-phase process are given below as a Grassmann diagram (see Figure 11.8). The efficiency of the gas-phase process is 91%. The main losses can be identified and are shown in the pie chart... 

Grassmann diagram of the gas-phase process. Exergy and lost work streams are shown as a percentage of the total input. 

Fig. 11.3. Schematic band diagram of exergy balance for a simple process from a raw material and heat to a product and waste.

Figure 11.3 shows in a schematic way the exergy balance in an irreversible process in the form of a band diagram, where the bandwidth is proportional to the exergy value. For complex physicochemical processes operating in industrial manufacturing plants, the exergy... 

Fig. 11.5. Regimes for exothermic, endothermic, spontaneous, and non-spontaneous processes in exergy-enthalpy diagrams.

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