Exergy of Gaseous and Liquid Streams

The specific exergy of gaseous and liquid streams is calculated on a molar basis taking the molar flow in kmol/s into account  

Using the molar fraction of water x h20. the thermomechanical exergy is split into the dry gas exergy ei, ,tm,dry and moisture exergy e , ,tm,H20 both in kj/kmol, the latter referring to the condensed state of water. 

As shown in Equation (8.6), the dry exergy is calculated with regard to the mean specific molar heat capacity of the dry gas mix in kJ/(kmol K) for the 

The mean specific molar heat capacity of the dry gas mix Cpm.ilT l, can be easily calculated or extracted as a stream property from a process simulator, for example, Aspen Plus [2]. The moisture exergy ei,H,tni,H20 must include the complete condensation of any water vapor. Although the specific enthalpy ho = 1890.3 kJ/ kmol and entropy So = 6.616 kJ/(lcmol K) of the reference water are fixed, the enthalpy hi in kj/kmol and entropy s, in kJ/(kmol-K) are computed applying the IAPWS-IF97 formulation for the gas temperature and partial H2O pressure. 

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

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