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Real Gases: Compression and expansion of real gases (Strategy of real gas…
Real Gases: Compression and
expansion of real gases
Lee-Kesler correlation method
for turbine calculations
Adiabatic and reversible expansion of water vapour from 940°C, 200MPa to 7 Mpa
Use Lee-Kesler correction method to find out:
How much work is produced?
(assume you don’t have table B1)
What is Tout?
Turbine calc. using Lee-Kesler -relations
Problem 1: we can calculate T2 if we have ΔSd
, but we need T2 to determine ΔSd!
Problem 2: if we don’t know T2
, we can’t calculate Cp,avg
Solution: iterate!
Strategy of real gas turbine calculation
1) Guess Tout. It does not have to be accurate
2) Calculate Cp,avg
3) Assume for now that ΔSd=0
4) Use polytropic relationship to calculate Tout
5) Now you have a reasonable estimate of Tout. Use it
to calculate Δ(Sd) and Cp,avg
6) Cpln(T2/T1) =ΔSd+Rln(P2/P1)
7) Now you have a reasonably accurate estimate of T2
, calculate Δh (Δh= Δhig- Δhd)
