Answer to Question #133333 in Mechanical Engineering for lucky mojeremane

Question #133333
B. The pressure in a steam main is 12 bar. A sample of steam is drawn off and passed through a throttling calorimeter, the pressure and temperature at exit from the calometer being 1 bar and 140 degree C respectively. Calculate the dryness fraction of the steam in the main, stating any assumptions made in the throttling process.
Expert's answer

Let the initial pressure and temperature of steam be P1 and T1 respectively.

Given as P1=12 bar=12x105 N/m2

From steam table : At P1=12 bar=12x105 N/m2

hf=798.33 kJ/kg, hg=2783.7kJ/kg, hfg=1985.4 kJ/kg

Steam is throttled to final state having pressure and temperature as P2=1bar=1x105 N/m2 and T2 =140oC.

During throttling process the enthalpy of steam remains constant.

Therefore, h1=h2

From steam table : At P2=1bar=1x105 N/m2 and T2 =140oC.(Steam is super heated)

h2= 2756.7 KJ/kg

If X=dryness fraction of steam in main

h1=hf+X. hfg=h2


Solving for X => X=0.986

Ans: Dryness fraction of steam in main(X)=0.986

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