Summary: Flash Separations 
  1. The exiting streams are in vapor-liquid equilibrium.
  2. The same calculations (mass balances, phase equilibrium) are used for systems with more than two components. 
  3. Usually an energy balance is also necessary to determine the outlet temperature.
  4. When pressure is lowered on a hot liquid, some of the liquid evaporates, and when this is done adiabatically the temperature decreases; the heat of vaporization comes from cooling down the liquid.
  5. The operating line relates the compositions of the two exiting streams.