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First Thermal and Fluids Engineering Summer Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

FLOW AND WETTING BEHAVIOUR OF FALLING LIQUID FILMS INSIDE INCLINED AND INTERNAL STRUCTURALLY-FINNED TUBES

DOI: 10.1615/TFESC1.hte.012693
pages 1309-1321

Simon Eichinger
TU Bergakademie Freiberg

Thomas Grab
TU Bergakademie Freiberg, Gustav-Zeuner-Strasse 7, 09599 Freiberg, Germany

Thomas Storch
TU Bergakademie Freiberg, Gustav-Zeuner-Strasse 7, 09599 Freiberg, Germany

A. Gotterbarm
Wieland-Werke AG, Graf-Arco-Strasse 36, 89079 Ulm, Germany

Ulrich Gross
Institute of Thermal Engineering, Technische Universitat Bergakademie Freiberg, Gustav-Zeuner-Strasse 7, D-09596 Freiberg, Germany


KEY WORDS: Structured surfaces, Falling film evaporation, Inclined tubes, Propane, Visual observation, Heat transfer coefficient

Abstract

The objective of the research project is to gain fundamental knowledge of the flow and wetting behaviour of a falling liquid film on structured surfaces during evaporation. In order to investigate the distribution and wetting behaviour of liquid films a special test rig was designed and built. This test rig allows to research the influence of inclined (0° - 20° from the vertical), internally structured tubes and the fluid properties on the stability of the liquid film. Another major research aspect is the investigation of the film stability, the film behaviour during partly film evaporation and the determination of mean heat transfer coefficients. A major advantage of the test rig is the possibility of visual observations of the falling liquid film inside of the tube without disturbing the falling film and the vapour flow. The use of a special camera enables the investigation of the liquid film along the whole length of 2 m. Propane and water are planned as working fluids covering a wide range of properties (9.55×109 < Ka < 1.47×1012; 1 < Refilm < 1000; 3 < Pr < 7). Details of the test plant and first results will be presented. Previous experiments have shown a break up of the film in vertical and slightly inclined smooth tubes at a wide range of wetting rates. Experiments with structured surfaces showed that a film break up can be avoided even at low wetting rates and 20° inclination by using a suitable structure.

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