Investigation of the Film Thickness of the Wall Flow created by the impingement of a free-surface liquid Jet*

Liquid jet impingement is used in industry when surfaces must be cooled or cleaned, because it’s high heat or mass efficiency, respectively. The film thickness and velocity distribution as well as the flow regime in the zone surrounding the impingement point and confined by the hydraulic jump are of high interest, since they govern the heat and mass transport and thereby determine the jet impingement performance.

In the present work, the horizontal impingement of a free-surface liquid jet onto a vertical substrate is investigated at jet Reynolds numbers of 20,000 to 50,000, with nozzle sizes of 3 and 4 mm different nozzle types (pipe or convergent), and various nozzle to plate distances. The impinging jets show surface disturbances, that origin in turbulence flow inside the nozzle as well as in Kelvin-Helmholtz instability. These surface disturbances and the internal flow have a strong influence on the local film thickness distribution in the wall flow, which is measured along the radial axis from the impingement point using Chromatic Confocal Spectroscopy.