Particle image velocimetry and modelling of horizontal coherent liquid jets impinging on and draining down a vertical wall

TL;DR

This study uses particle image velocimetry to analyze flow patterns of horizontal liquid jets impacting vertical walls, comparing experimental data with refined models that account for surface tension and dynamic contact angles.

Contribution

It introduces a novel PIV technique with opaque fluid doped with pearlescence and refines existing models to better match experimental observations of jet impingement flows.

Findings

Flow patterns depend on wall material and contact angle.

Refined models fit experimental data well, especially with adjusted boundary conditions.

Surface waves affect flow dynamics, causing deviations from steady-state model predictions.

Abstract

The flow patterns created by a coherent horizontal liquid jet impinging on a vertical wall atmoderate flow rates (jet flowrates 0.5-4.0 L min-1, jet velocities 2.6-21 m s-1) are studied withwater on glass, polypropylene and polymethylmethacrylate (acrylic, Perspex(R)) using a novelparticle image velicometry (PIV) technique employing nearly opaque fluid doped withartificial pearlescence to track surface velocity. Flow patterns similar to those reported inprevious studies are observed on each substrate: their dimensions differed owing to theinfluence of wall material on contact angle. The dimensions are compared with models for (i)the radial flow zone, reported by Wang et al. (2013b), and the part of the draining film belowthe jet impingement point where it narrows to a node. For (ii), the model presented by Mertenset al. (2005) is revised to include a simpler assumed draining film shape and an alternativeboundary condition accounting for surface tension effects acting at the film edge. This refinedmodel gives equally good or better fits to the experimental data. The effective contact anglewhich gives good agreement with the data is found to lie between the measured quasi-staticadvancing and receding contact angles, at approximately half the advancing value. The PIVmeasurements confirmed the existence of a thin fast moving film with radial flow surroundingthe point of impingement, and a wide draining film bounded by ropes of liquid below theimpingement point. While these measurements generally support the predictions of existingmodels, these models assume that the flow is steady. In contrast, surface waves were evident inboth regions and this partly explains the difference between the measured surface velocity andthe values estimated from the models.