Ethylene Refrigerator

To solve this problem, we employ the law of conservation of mass and the law of conservation of energy. Since mass and energy are conserved in the refrigerator, we use mass balances and energy balances.

 Mass Balances:

{rate of accumulation}={mass flow rate in}-{mass flow rate out}


Energy Balances:

{rate of accumulation of energy}+{net rate of energy transport} = Heat flow - Work flow

In math terms: 
But often, potential and kinetic energy changes are negligible, so the equation becomes:


Mass and energy are conserved for the whole refrigerator and for the individual components. Since this is the case, we can consider several different regions to solve for our unknown variables.

 Consider the following mass/energy balances in the problem in this order:

  1. Overall
  2. Evaporator
  3. Compressor
  4. Valve
After figuring out the mass/energy balances, we can put the equations together. 

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