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THERMODYNAMICS - CASE STUDY

    Introduction



Pressure Cooker

 

Jack's mom bought a new pressure cooker. Jack is interested in the petcock, which is a small piece of mass, sits on top of the only opening in the middle of the lid and prevents steam from escaping until the pressure force overcomes the weight of the petcock. He just wonders the weight of the petcock which can maintain a high pressure inside the cooker.

What is known:

  • The operation pressure is 100 kPa gage
  • The opening cross-sectional area is 4 mm2
  • Atmospheric pressure is 101 kPa

 

    Questions


Pressure Cooker
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  • What is the mass of the petcock?
  Approach

 
  • Solve the problem using the basic steps in engineering problem solving: 1) read 2) draw diagrams 3) write equations 4) solve and 5) check solution.
  • For step 3, use the force balance in the base of the petcock:
    F - ( Fa+ G ) = 0