Fractional distillation:

Fractional distillation includes the return of condensate to the distillation unit under conditions such that this condensate is continuously and counters currently in contact with the vapors. Through this method, you could achieve greater enrichment of vapors of more volatile component than that acquired through simple distillation.

Within flash distillation, there is an instantaneous and continuous vaporization of definite elements of the mixture such that the total vapor produced is in equilibrium with the remaining liquid.