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Fundamentals of a liquid (soap) film tunnel

Beizaie, M. and Gharib, M. (1997) Fundamentals of a liquid (soap) film tunnel. Experiments in Fluids, 23 (2). pp. 130-140. ISSN 0723-4864. doi:10.1007/s003480050094.

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The continuously running liquid film tunnel (LFT) is a novel device suitable for the study of two-dimensional flows. In this innovation, the films start from a reservoir, run over a horizontal or non-horizontal wire frame and get pulled/washed by a water sheet or by gravity of liquid film. How-ever, despite the simple design and widespread application of LFT, its working mechanisms are not well understood. In the present work, an experimental effort for explaining these mechanisms is reported. The results show that both film velocities and film flow rates increase with water sheet velocity up to a saturation level. This behavior is described via a force balance between the shear force produced by the water sheet and the opposing pulling force of reservoir and boundary layer frictions. The results also show that the average film thickness depends on the surfactant concentration. This is as predicted by a model based on Langmuir’s adsorption theory, in which the liquid film contains two external monolayers of surfactant and a slab of surfactant solution in between. When a film is drawn from the reservoir to the water sheet, the surfactant molecules start migrating from the former to the latter. To restore the thermodynamic equilibrium, the dragged film pulls more surfactant due to Marangoni elasticity, and thus a flow is established. The film flow soon reaches an equilibrium rate as required by the force balance mentioned above.

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Additional Information:© 1997 Springer-Verlag. Received: 15 August 1996; Accepted: 12 November 1996. This work was supported by a grant from the National Science Foundation (NSF Contract MSM 88-20182). Both authors would like to thank Professor Mysels for his enthusiastic support of soap-film efforts in our group.
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NSFMSM 88-20182
Issue or Number:2
Record Number:CaltechAUTHORS:20130912-093505922
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:41277
Deposited By: Tony Diaz
Deposited On:12 Sep 2013 23:07
Last Modified:10 Nov 2021 04:28

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