Thin Film Flow of a Liquid down Smooth and Rough Surfaces

Advancing the chemical engineering fundamentals

Interfacial & Colloidal Phenomena (T2-6P)

Prof Lubomira Broniarz-Press
Poznan University of Technology
Dpt. of Chemical Engineering and Equipment
pl. M. Sklodowskiej-Curie 2
PL 60-965 Poznan
Poland

Dr Szymon Woziwodzki
Poznan University of Technology
Dpt. of Chemical Engineering and Equipment
pl. M.Sklodowskiej-Curie 2
PL 60-965 Poznan
Poland

Dr Daniela Dulska
Poznan University of Technology
Dpt. of Chemical Engineering and Equipment
pl. M. Sklodowskiej-Curie 2
PL 60-965 Poznan
Poland

Keywords: falling film, film thickness, rough plate

The flow of viscous liquids in thin films down a vertical or inclined to horizontal plates under the influence of gravity and surface tension is of both fundamental and practical importance in a wide variety of separation and heat/mass transfer processes. The occurrence of waves on the film surface as well as the solid wall roughness are known to enhance greatly the rates of mass and heat transfer. The small thickness of a film compared to the characteristic sizes is usually encountered in nature and patterns of liquid flows. In the present work the results of the studies on the effect of plate roughness on a mean film thickness s of a Newtonian liquids, have been presented.
The experiments were performed using two types of plates of 241 mm width and 1165 mm length: smooth constructed from organic glass and rough (coated with grains of abrasive material of various size distributions). The plates studied were inclined to horizontal of the angles  equal to 16o and 24o. The grain-size distributions ranged as follows: dr  (125,300) μm, dr  (300,710) μm and dr  (1.00,2.36) mm. All experimental data were elaborated using the dimensionless relationship of the reduced mean thickness of a film taking into consideration their non-Newtonian properties on equivalent Reynolds number. It has been shown that in the laminar region of the falling liquid flow the small artificial roughness (dr  710 μm) does not effect on the mean thickness of the thin layer. The effect of the wall roughness was found as the evident one in turbulent film flow down the surfaces studied. The film thickness values increased with increase of the grain size values. The effect observed can be explained by the adsorption effect on the surface material used.

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Presented Thursday 20, 13:30 to 15:00, in session Interfacial & Colloidal Phenomena (T2-6P).