Help needed on THERMODYNAMICS Question

• Mariner

  17 Sep 05, 18:14

  Pls help me with this question
  
  
  
  A piston cylinder device contains steam initially at 1MPa, 350 degrees celcius and 1.5 metre cube. The steam is allowed to cool at constant pressure intil it first starts condensing. Determine,
  
  1.) the mass of the steam
  
  this is my problem...since it is cooled till it starts condensing, the quality of it is x=0.5. So, how to use it to find the mass?
• fudgester

  17 Sep 05, 18:20

  Originally posted by Mariner:

  Pls help me with this question
  
  
  
  A piston cylinder device contains steam initially at 1MPa, 350 degrees celcius and 1.5 metre cube. The steam is allowed to cool at constant pressure intil it first starts condensing. Determine,
  
  1.) the mass of the steam
  
  this is my problem...since it is cooled till it starts condensing, the quality of it is x=0.5. So, how to use it to find the mass?

  I don't think you need to make use of the quality....
  
  You need thermodynamics tables to solve this. At 1MPa and 350 degrees, water exists as superheated steam. According to the thermodynamics tables, the specific volume of water in those conditions would be 0.2825 m3/kg.
  
  So to find the mass, divide the volume of the steam by the specific volume...
  
  So the mass is 1.5 /0.2825 = 5.31kg.
  
  Erm... any mistakes?
• fudgester

  17 Sep 05, 18:23

  Another thing.... how did you get quality x =0.5? If memory serves me right, quality refers to the proportion of steam in the system. Since it is cooled until JUST BEFORE IT CONDENSES (just to emphasize things), quality ought to be 1.
• hisoka

  17 Sep 05, 18:26

  PV = nRT?
  
  get n then use the nolecular weight?
• Mariner

  17 Sep 05, 18:27

  ok thanks..will try on that
• valentinoo

  17 Sep 05, 18:28

  wow i studied all this b4..but i cant remember shytes now...no point studying coz u aint makin use of wht u study most of the time