mollier chart

[harsh789]

hiiii..

i want to know how to find enthalpy when only tempreture is given in isentropic process

example-(1) p4= 0.07375 bar ; dryness fraction x4= 0.85; so h4=2220
(2)isentropic process T3=400 degree celsius ;find p2 and find h3



usually 2 value are enough to calculate enthapy or entropy but how to h or s when only one value is given?

 

[IRstuff]

Student homework problems are not allowed

TTFN
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[Pederator]

However this seems to be - like IRStuff said - a homework problem, I will answer you. The given values allow to conclude that the medium is steam. You should write it. Secondly, the process seems to be expansion in steam turbine. I will show you one of the ways how you can find if using electronic steam tables (like XSteam).

The enthalpy of steam at 0.07375 bara and quality of 0.85 is 2213 kJ/kg (instead of 2200). Next you must find the entropy:
s(0.07375 bara, 2213 kJ/kg) = 7.105 kJ/(kg*K)

Now you can find the enthalpy of the inlet steam. Using equation for temperature T(h,s), by trial-and-error you find that the enthalpy is 3247 kJ/kg. It took me a few seconds to find the value.

Using equation p(h,s) you find pressue. It is 21 bara.

Good luck in your thermodynamic calculations and next time find another board, eng-tips is for professionals, not students.

 

[chicopee]

When only one value is given, then it will either be at the saturated liquid line or at the saturated vapor line. Use tables or the Mollier's diagram, to find T or P or H or S.

 

[IRstuff]

I'm guessing the OP doesn't know, or missed the lecture on, how to use the chart.

TTFN
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Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[Pederator]

Chicopee, i think you misuderstood him when he asked "usually 2 value are enough to calculate enthapy or entropy but how to h or s when only one value is given?" - from my understanding he wanted to find p, h and s for the given temperature (400C). If I am wright, he does not know what is isentropic process, as he ask how to find s. Maybe I am wrong.

 

[GHartmann]

Pederator:

Well maybe its a trick exam question

 

[rkvbobby123]

May be we could also give equivalent units in PSIA and BTU/lb.
Old Charts do not have BARS or KJ/kg.
Thanks.

 

[chicopee]

Pederator, based on this statement"...but how to h or s when only one value is given?", I don't think that I misunderstood his OP

 

[chicopee]

Pederator, based in his statement "... but how to h or s when only one value is given?", I don't think that I misunderstood his OP.