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THERMODYNAMICS - CASE STUDY

    Introduction


How a Solar Pond Traps Solar Energy
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The bottom zone of a pond can be used as a heat source since that zone has a concentrated salt solution with a higher temperature from absorbing solar radiation. This type of pond is called a solar pond. Solar ponds have been used to produce hot water and have good efficiency. A company wants to use this concept to generate power. Hence, a model pond is built to test its performance.

What is known:

  • The size of the pond is 10m x 10m x 3m.
  • The ambient air temperature is 35 oC.
  • The temperature at the bottom of the pond is 85 oC.
  • The salt water in the bottom layer absorbs solar radiation at the rate of 0.3 kW/m2.
     
    Question

   
  • Determine the maximum thermal efficiency that this power plant can have.
  • Determine the maximum power generated by each m2 of the bottom of the pond.
     
    Approach


Heat Engine Works between the Solar Pond and the Ambient Air

 
  • The power plant is a heat engine since it generates power at the expense of heat input. Carnot heat engine has the highest thermal efficiency.

    ηth,rev = 1- TL/TH

  • The thermal efficiency of a heat engine, regardless reversible or irreversible, is given by

    ηth = 1- QL/QH