Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water.

Abstract

High pressure water jets (HPWJ) are frequently used in industrial applications like cleaning, further processing of workpieces or cutting of materials. In a joint research program with the International Geothermal Centre (GZB) the HPWJ process is adapted to the field of rock drilling to develop and enhance an innovative drilling technology for geothermal applications. In this case, the HPWJ is used to cut and destroy rock in deep geothermal reservoirs to make them accessible for energy generation. This transfer requires a broad knowledge of the process and interaction between the HPWJ and the rock surface. The challenges in analysis and characterization of the process are high velocities of the water jet of several hundred meters per second based on the high pump pressure of up to 180 MPa and the very small spatial expansion of the field of interest between the nozzle outlet and the rock surface, which is within a few centimeters. The objective of the present work is the visualization of a HPWJ in diverse fluids as a first step to increase the process knowledge of waterjet cutting of rocks. Tests are performed in air, water and slurry respectively and a parametric study is carried out to examine the influence of different operating parameters on the HPWJ formation and structure. Moreover, the influence of the surrounding fluid on the HPWJ is investigated.Optical measurement techniques are applied to analyze the HPWJ and results will be presented. The high velocities, the very small spatial expansion and the dense liquid jet represent challenges to the application of these measurement techniques. High speed photography in terms of shadow experiments is used for visualization and relevant spray parameters are evaluated with common spray analysis techniques. Adopting the double frame technique, well-known with particle image velocimetry (PIV), an estimation of the fluid velocity on the boundary of the HPWJ is performed. In addition to the shadowgraph analysis, PIV in auto-correlation mode with fluorescent tracers is applied to analyze velocity fields, the dimension of the potential core as well as the interaction with the surrounding fluid.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4736