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THERMODYNAMICS - CASE STUDY

    Introduction


Problem Description
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Pat is taking a thermodynamics course this semester and in the class, his professor states that person increase entropy every time they do anything in daily life. Pat's mom cook eggs for his breakfast. He wonders how much entropy is generated when eggs are cooked.

What is known:

  • 6-cm-diameter spherical egg at 10oC is dropped into boiling water.
  • The boiling water temperature is 100oC.
  • Egg has a density of 1000 kg/m3 and a specific heat of 3.4 kJ/(kg-K).
     
    Question


 

How much entropy is generated by boiling one egg to 100oC?

     
    Approach



 
  • Method A: Take the egg as a system. It is a closed system due to no mass transfer involved. The entropy transfer is only due to the heat transfer. Model the egg as incompressible, and the entropy change in the system is

    ΔS = mCaveln(T2/T1)

    where 1 denotes the initial state and 2 denotes the final state.
  • Method B: take the egg as a closed system. Consider the entropy change of the isolated system formed by the egg and the surrounding water.