Exergy loss_Throttling Process

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An airflow of 5 g/s is throttled adiabatically to ambient pressure (pa=1bar). The air enters the throttling at the pressure p1. The flowing of exergy loss due to the throttling is 160 W. Determine the pressure p1 before the throttling.

The ambient temperature is Ta=298K. The changes of kinetic und potential energies can also be neglected. Air is assumed to be perfect gas.

The specific gas constant for air is Rair=0.287 J/g∙K and the specific heat capacity at constant pressure cp=1 J/g∙K

Solution:

In order to calculate the exergy loss, we also need to determine the production of entropy during this process: th1

The general expression for the exergy loss is: th2

Considering the throttling process, we can reduce the conservation of energy equation to:

h1 = h2

That means, enthalpy values at the inlet and outlet are the same.

h1 = h2 → cp∙T1=cp∙T2 → T1 = T2

Therefore the equation of exergy loss is reduced to: th3th4

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