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THERMODYNAMICS - CASE STUDY

    Introduction


A Seller's Call
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A spot cooler is a device which can produce hot and cold streams of air from a single stream of air at an intermediate temperature without any work or heat transfer. This product can be used for emergency cooling or short-term cooling. A seller called Kay and said his spot cooler can work at normal atmospheric pressure and cost nothing to cool the air. Can Kay trust the salesperson?

What is known:

  • The ambient air enters the spot cooler at a temperature of 36oC and a pressure of 1 atm.
  • 25% of the air exits as cooled air at 24oC and a pressure of 1 atm.
  • 75% of the air exits as hot air at 40oC and a pressure of 1 atm.
     
    Question


 

Is the salesperson telling the truth?

     
    Approach



  If the product satisfies both the first and the second law of thermodynamics, it can work. To verify if it satisfies the first law, check the energy balance of the system. To verify if it satisfies the second law, check the entropy change of the entire process.