Flow exergy equation

Second law analysis results are shown in Figure 23.13. The flow exergy (vj/) of each point is calculated using Equation 23.52 where potential and kinetic energy are ignored. 

Flow exergies of each real point are calculated using Equation 23.52. 

Eq. (2.22) may be interpreted in terms of exergy flows, work output and work potential (Fig. 2.5). The equation may be rewritten as... 

The analysis requires the calculation of three exergy flow rates, at 0°C, 50°C, and 100°C. As no heat or work is transferred between the considered system and its environment, the first law, Equation 6.1, yields that the overall enthalpy change is zero ... 

Introducing this relation into Equation 6.22 gives us the temperature T3 of the flow leaving the mixer T3 = 323.15 K. The exergy flow rates can now be calculated from... 

Equation 13.15 uses the exergy flows of the resources because these values express the minimum amount of work required to produce these resources from compounds that are thermodynamically in equilibrium with the natural environment. As, ultimately, only exergy is scarce, the exergy flows of resources are better indicators of relative importance than their mass or volume flows. 

Equation 13.17 explicitly mentions the useful exergy flows coming out of the process because exergy can be lost in two different ways. First, exergy is lost in any real process as a result of irreversibility in the process itself, and such losses are called internal exergy losses. Second, exergy can be lost via waste streams that are not yet at equilibrium with the natural environment. 

Michaelis-Menten equation shows that the enzyme reactions in certain regions can be approximated by linear kinetics. Stucki (1984) demonstrated that variation of the phosphate potential at constant oxidation potential yields linear flow-force relationships in the mitochondria. Through linear flow-force relationships, cells may optimize their free energy production and utilization by lowering their entropy production and hence exergy losses at stationary states. 

Typically, hii (the vent flow rate for noncondensable gases) is small, so that the energy and exergy contributions in the vent stream are small and may be neglected in the analysis. Excluding the vent stream under steady-state conditions, the exergy balance from Equation 23.58 yields. 

Heat and exergy balances are calculated in a similar manner to the previous example, except that all quantities are normalized on a per unit boiler flow basis. For example, the work and irreversibility of the low-pressure turbine are from Equations 23.77 and 23.79, modified for the flow rates are... 

Exergoeconomic analysis of dual purpose plant is presented. The thermodynamic properties and cost flow of various streams in the hybrid pipeline gas station and desalination systems are determined in Table 4 and 5 (Fig. 1). Exergy destruction for the hybrid components are determined based on the derived equations. Fig. 2. As can be observed the highest amount of exergy destruction is related to the combustion chamber. 

The last term in Equation (8.3) is not applied for most of the evaluated streams, as the concentration potential is not usable. However, the concentration exergy represents the minimal necessary reversible separation energy for the concentrated oxygen (in gasifying agents) and nitrogen flows (e.g., for dry feeding from the air separation unit. Therefore, it is included in these streams. 

Equation (8.7) is also used to determine the exergy of all boiler feed water or steam flows. 

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