BT-25 Falling Film Flow Distribution Methods

H. U. Zettler and J. W. Palen

HTRI has developed initial recommendations for the design of distributors to be used in falling film evaporators. These recommendations are based on current open literature publications and patents.

Selection of a distribution design depends on operating conditions and fluid characteristics in two process categories: uncritical and critical service.

  • In uncritical service the liquid is not heat sensitive; thus, the exchanger can be small, and overdesign is permissible. Using the simplest and least expensive distributor system—such as simple cross flow—makes both economic and design sense.
  • In critical service with heat-sensitive liquid, dry wall conditions can result in fouling and/or product deterioration. When the exchanger is large or the liquid is highly viscous, a more complex and expensive distribution system such as direct placement is needed.

Previous experience with similar services remains the best guide. Lacking that, manufacturers of falling film evaporator equipment should be consulted.