Calculation of coil type economizers / waste heat recovery units

Program features

The WAK program designs coil type economizers with multiple helical tube bundles. Hot water or thermal oil heaters can be calculated. The standard medium is hot oil on the tube side and flue gas on the shell side. The composition of the flue gas can be entered or standard compositions for typical gas, fuel oil or solid fuel combustion can be selected.

Calculation of horizontal or vertical exchanger arrangement is possible. The flow pattern is either countercurrent or co-current. The program suggests parallel flow in coils and annulus.


  • 2 to 14 concentric tube baskets
  • if the most inner or most outer basket touches the shell or displacement body or can be constructed with a gap
  • Gap widths at the displacement cylinder and at the shell independent of each other
  • the tube geometry and number of tubes in the coils may be freely specified.

Compared to the standard approach, an improved calculation of the heat transfer on the flue gas side now permits longitudinal pitch ratios from 1.0, i.e. the tubes are “tightly” wound and welded. The radiation portion from the flue gas around the tubes is also taken into account in the calculation.

The maximum film temperature is calculated for the coil with the lowest inner heat transfer coefficient and for the area with the highest temperature level.

Coil type economizer
Coil type economizer

Physical properties

  Module Standard
Water and steam H2O X  
Air (dry) LUFT X  
Flue gas RGAS X  
typical machine oils OEL X  
more than 120 thermal oils T-OIL X  
Heavy fuel oils HFO X  
Free input of physical properties (only for media in the coils) S-DAT X  
Refrigerants FRIG    X
Properties of pure substances and mixtures (only for media in the coils)
(requires program PROPER)
User-supplied properties tables S-TAB   X

Price: on request


  • VDI Heat Atlas
  • F. Brandt, Wärmeübertragung in Dampferzeugern und Wärmetauschern, Vulkan Verlag 1995
  • H. Hausen, Wärmeübertragung im Gegenstrom, Gleichstrom und Kreuzstrom, Springer 1976

see also:

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