Evaporator \E*vap"o*ra`tor\, n.
   1. An apparatus for condensing vegetable juices, or for
      drying fruit by heat.
      [1913 Webster]

   2. Any device designed to evaporate a fluid.
      [PJC]

   3. Specifically: The portion of a refrigeration system in
      which the refrigerant evaporates and thus absorbs heat.
      [PJC]

   rotary evaporator (Chem.) a device used in laboratories in
      which a liquid is evaporated by reducing the pressure and
      applying heat, while rotating the liquid in a vessel such
      as a round-bottomed flask. The reduced pressure speeds the
      evaporation process and allows the evaporation to be
      conducted at temperatures lower than would otgherwise be
      possible, thus reducing decomposition of unstable
      substances. The rotation also serves to increase the
      surface area from which evaporation takes place and to
      reduce the effect of "bumping", the sudden burst of
      vaporization that can scatter liquid exposed to reduced
      pressure.
      [PJC]