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

[EN] High pressure water jets (HPWJ) with Reynolds numbers in the scale of 104 are visualised by high speed photography in air and water. Moreover, suitable measurement techniques are tested and verified by quantitative analysis of the emerging jet to identify the influence of the surrounding fluid on the HPWJ. The HPWJ process known from industrial applications can be adapted to the field of rock drilling. In this specific case, the HPWJ is used to cut and destroy rock in deep geothermal reservoirs. The process is known as jet drilling. Although there have been research activities in this field, the process itself is not well understood so far and practical applications are rare. Therefore, the aim of our work is the visualisation of the process to increase the knowledge of waterjet and rock interactions. High speed photography in terms of shadowgraph experiments is used for visualisation. Moreover, an estimation of the fluid velocity on the boundary of the HPWJ in air is performed. For this, the shadowgraph images are evaluated with the double-frame technique well known with particle image velocimetry (PIV). Analysis of both the structure and the velocity distribution of the HPWJ in water is done by combined PIV and laser induced fluorescence (LIF) analysis with fluorescent dye.This work is being funded through the “FH-Struktur2016” venue for universities of applied sciences by the ministry for innovation, science and research of the state of Nordrhein-Westfalen, Germany (AZ: 322-8.03.04.02).Jasper, S.; Hussong, J.; Lindken, R. (2017). Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 947-953. https://doi.org/10.4995/ILASS2017.2017.4736OCS94795

PIV investigation of high Reynolds number submerged water jets at high-pressure ambient conditions

High-pressure water jets bear a great technological potential to enhance geothermal deep drilling. Compared to existing water cutting technologies, significantly different operation conditions are encountered under deep-drilling conditions, such as high ambient pressures. The fundamental fluid mechanics are significantly affected by those operation conditions. In this work we examine the influence of increasing ambient pressure of up to 12.0 MPa on the water jet characteristics under submerged drilling conditions. PIV measurements of the jet flow field at changing cavitation numbers reveal two characteristic regimes, which are distinguished by a critical cavitation number. In the cavitating regime, the jet decays considerably faster with increasing distance to the nozzle than in the non-cavitating regime. In addition to that, an increasing cavitation intensity shortens the potential core length of the water jet and increases the jet spreading angle and with this has a similar effect on the jet as increasing turbulence intensity in single-phase flows. Related to the decreasing kinetic energy of the jet in the cavitating regime, the resulting impact force of the water jet on the specimen surface decreases with increasing cavitation intensity. Our investigations indicate that a technology transfer from water jet cutting to submerged jet drilling requires adjustments of both nozzle geometries and jet operation conditions

Optical correlation techniques for the investigation of colloidal systems

This review aims to provide a simple introduction to the application of optical correlation methods in colloidal science. In particular, I plan to show that full appraisal of the intimate relation between light scattering and microscopy allows designing novel powerful investigation techniques that combine their powers. An extended version of this paper will appear in "ColloidalFoundations of Nanoscience", edited by D. Berti and G. Palazzo, Elsevier (ISBN 978-0-444-59541-6). I am very grateful to the publisher for having granted me the permission to post this preprint on arXiv.Comment: 19 pages, 5 figure

What factors influence the rediscovery of lost tetrapod species?

We created a database of lost and rediscovered tetrapod species, identified patterns in their distribution and factors influencing rediscovery. Tetrapod species are being lost at a faster rate than they are being rediscovered, due to slowing rates of rediscovery for amphibians, birds and mammals, and rapid rates of loss for reptiles. Finding lost species and preventing future losses should therefore be a conservation priority. By comparing the taxonomic and spatial distribution of lost and rediscovered tetrapod species, we have identified regions and taxa with many lost species in comparison to those that have been rediscovered—our results may help to prioritise search effort to find them. By identifying factors that influence rediscovery, we have improved our ability to broadly distinguish the types of species that are likely to be found from those that are not (because they are likely to be extinct). Some lost species, particularly those that are small and perceived to be uncharismatic, may have been neglected in terms of conservation effort, and other lost species may be hard to find due to their intrinsic characteristics and the characteristics of the environments they occupy (e.g. nocturnal species, fossorial species and species occupying habitats that are more difficult to survey such as wetlands). These lost species may genuinely await rediscovery. However, other lost species that possess characteristics associated with rediscovery (e.g. large species) and that are also associated with factors that negatively influence rediscovery (e.g. those occupying small islands) are more likely to be extinct. Our results may foster pragmatic search protocols that prioritise lost species likely to still exist

Conformation dependence of DNA electrophoretic mobility in a converging channel

The electrophoresis of Λ-DNA is observed in a microscale converging channel where the center-of-masses trajectories of DNA molecules are tracked to measure instantaneous electrophoretic (EP) mobilities of DNA molecules of various stretch lengths and conformations. Contrary to the usual assumption that DNA mobility is a constant, independent of field and DNA length in free solution, we find DNA EP mobility varies along the axis in the contracting geometry. We correlate this mobility variation with the local stretch and conformational changes of the DNA, which are induced by the electric field gradient produced by the contraction. A “shish-kebab” model of a rigid polymer segment is developed, which consists of aligned spheres acting as charge and drag centers. The EP mobility of the shish-kebab is obtained by determining the electrohydrodynamic interactions of aligned spheres driven by the electric field. Multiple shish-kebabs are then connected end-to-end to form a freely jointed chain model for a flexible DNA chain. DNA EP mobility is finally obtained as an ensemble average over the shish-kebab orientations that are biased to match the overall stretch of the DNA chain. Using physically reasonable parameters, the model agrees well with experimental results for the dependence of EP mobility on stretch and conformation. We find that the magnitude of the EP mobility increases with DNA stretch, and that this increase is more pronounced for folded conformations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77968/1/2813_ftp.pd