Experimental Validation of Falling Liquid Film Models: Velocity Assumption and Velocity Field Comparison.

Ruiqi Wang,Riqiang Duan,Haijun Jia

doi:10.3390/polym13081205

Ruiqi Wang, Riqiang Duan + Show 1 more

Open Access

https://doi.org/10.3390/polym13081205

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Journal: Polymers	Publication Date: Apr 8, 2021
Citations: 2	License type: CC BY 4.0

Affiliation: Tsinghua University

Abstract

This publication focuses on the experimental validation of film models by comparing constructed and experimental velocity fields based on model and elementary experimental data. The film experiment covers Kapitza numbers Ka = 278.8 and Ka = 4538.6, a Reynolds number range of 1.6–52, and disturbance frequencies of 0, 2, 5, and 7 Hz. Compared to previous publications, the applied methodology has boundary identification procedures that are more refined and provide additional adaptive particle image velocimetry (PIV) method access to synthetic particle images. The experimental method was validated with a comparison with experimental particle image velocimetry and planar laser induced fluorescence (PIV/PLIF) results, Nusselt’s theoretical prediction, and experimental particle tracking velocimetry (PTV) results of flat steady cases, and a good continuity equation reproduction of transient cases proves the method’s fidelity. The velocity fields are reconstructed based on different film flow model velocity profile assumptions such as experimental film thickness, flow rates, and their derivatives, providing a validation method of film model by comparison between reconstructed velocity experimental data and experimental velocity data. The comparison results show that the first-order weighted residual model (WRM) and regularized model (RM) are very similar, although they may fail to predict the velocity field in rapidly changing zones such as the front of the main hump and the first capillary wave troughs.

Highlights

Falling liquid films are examples of open-flow systems that bring a laminar steady state to a disordered state in both time and space as the film develops [1,2]
These features enable modelling of the flow with reduced equations from the Navier–Stokes equations; the models need solid experimental data to be validated and verified [1,3,4]. To validate these different models, knowledge of the velocity field with the correlating film topology under various surface waves would be of great value [5]
To validate the film models, modelpredicted velocity fields were calculated based on the experimental flow rate, film thickness and their derivatives; the validated models included Nusselt’s theory, Kapitza’s theory, and the 1st weighted residual model (WRM) and regularized model (RM) models

Summary

Introduction

Falling liquid films are examples of open-flow systems that bring a laminar steady state to a disordered state in both time and space as the film develops [1,2]. Film flows have a long wave nature, the typical length of which is much larger than the thickness of the film These features enable modelling of the flow with reduced equations from the Navier–Stokes equations; the models need solid experimental data to be validated and verified [1,3,4]. To validate these different models, knowledge of the velocity field with the correlating film topology under various surface waves would be of great value [5].

Methods

Results

Conclusion