# Thermodynamics-Entropy Question

1. Dec 12, 2008

I am just confused as to how to evaluate the term sa=specific entropy of air

I have reduced an entropy balance to the following:

$$\sigma=\dot{m_{a3}}(s_{a3}+\omega_3s_{v3})-\dot{m_{a2}}(s_{a2}+\omega_2s_{v2})-\dot{m_{a1}}(s_{a1}+\omega_1s_{v1})$$

I know how to evaluate sv and how to evaluate entropy differences but the air has three terms, so how can evaluate it?

Here's a schematic.

2. Dec 13, 2008