Exergy flux

22) may be interpreted in terms of exergy flows, work output and work potential (Fig. 2.5). The equation may be rewritten as 

the exergy Ex of the entering flow (its capacity for producing work) is translated into 

If the heat transferred from the control volume is not used externally to create work, but is simply lost to the atmosphere in which further entropy is created, then Equj can be said to be equal to /quj, a lost work term, due to external irreversibility. Another form of Eq. (2.23) is thus 

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Application of the exergy flux equation to a closed cycle... 

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. 

Chapter 2. Reversibility and availability An exergy flux statement for the Carnot plant is... 

Fig. 2.8. Exergy fluxes in actual CBT ga.s turbine plant with combustion.

Global exergy flux, reservoirs, and destruction. (Global Climate and Energy project at Stanford University, http //gcep.stanford.edu)... 

This brief calculation is not meant to judge the viability of solar energy, but simply to provide discussion about what the appropriate methods should be to harvest the energy, which is incident on the earth. If one uses the larger estimate for exergy flux, which makes up the solar surface incident component (86,000 TW), or can obtain larger efficiencies in solar cells and use more of the earth s land for solar cells, the picture becomes much more optimistic. 

Equation (A.36) shows that the exergy destruction rate increases with changes in the gradients as well as the fluxes. There are interesting control implications from this relationship. We outline two of them here. Others are mentioned in the main text in connection with the control strategies for specific unit operations. 

The calculation of entropy fluxes for each unit leads to quantitative evaluation of the potential working performance of a system. For this purpose in technical thermodynamics a variable known as exergy is introduced. 

In solar energy applications, the ratio of the exergy of solar radiation to the total energy flux at the highest layer of the earth s atmosphere is 0.933 (Szargut, Morris, and Steward, 1988). 

A proper optimisation of a steam reformer must always be based on a furnace model, since the delivered heat flux profile is bounded by the furnace configuration and the flexibility of the burners. Seen from an exeigy point of view outer tube-wall temperature and heat flux profiles may decrease the exergy losses [335], but it should be checked if they can be provided by a furnace. 

Thus, the exergy losses due to water vapor flux in the dried layer by... 

For the secondary flux c, we obtain on eliminating enthalpy between entrance and exit, the exergy to be ... 

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