- #1
kaminho
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Homework Statement
I place the question first:
Superheated steam at an absolute pressure of 10 bar and temperature of 340C expands in a nozzle reversibly and adiabatically until the pressure is 0.1 bar. the mass flow rate is 4.2kg/s.
The questions asking for:
1) Drawing the appropriate diagram for the process.
2) Dryness fraction of the steam ?
3)Dryness fraction if the process is not isentropic and isentropic efficiency is 88% ?
and my particular problem:
I know how to workout dryness fraction when this process is reversible and adiabatic because being isentropic i can use: S1=Sf + XSfg and find the appropriate values off the steam table (found S1 using interpulation between temperatures of 300C and 350C and it was S1= 7.266 kJ/kgK) to eventually find X (dryness fraction which i calculated as 88%). From there i can use X to calculate ideal h2 as well.
However my problem is, when this process is not isentropic, how to we find dryness fraction? i guess i wouldn't be able to use that same equation (used above to find X) as i end up with the same values as before. My second thought is I use the value of isentropic efficiency to find the real value of h2 and then use this real value in equation h2=hf + X hfg (obviously with same hf and hfg that i used in the first part of question) to find X in this case? am i right? any help please?
and One more thing; how do we workout the rate of entropy generation of the steam during expansion?