Effect of the number of vortices on the torque scaling in Taylor-Couette flow

Torque measurements in Taylor-Couette flow, with large radius ratio and large aspect ratio, over a range of velocities up to a Reynolds number of 24 000 are presented. Following a specific procedure, nine states with distinct number of vortices along the axis were found and the aspect ratio of the vortices were measured. The relationship between the speed and the torque for a given number of vortices is reported. In the turbulent Taylor vortex flow regime, at relatively high Reynolds number, a change in behaviour is observed corresponding to intersections of the torque-speed curves for different states. Before each intersection, the torque for a state with larger number of vortices is higher. After each intersection, the torque for a state with larger number of vortices is lower. The exponent, from the scaling laws of the torque, always depends on the aspect ratio of the vortices. When the Reynolds number is rescaled using the mean aspect ratio of the vortices, only a partial collapse of the exponent data is found.Comment: 11 pages, 6 figure

Inertio-elastic focusing of bioparticles in microchannels at high throughput

Controlled manipulation of particles from very large volumes of fluid at high throughput is critical for many biomedical, environmental and industrial applications. One promising approach is to use microfluidic technologies that rely on fluid inertia or elasticity to drive lateral migration of particles to stable equilibrium positions in a microchannel. Here, we report on a hydrodynamic approach that enables deterministic focusing of beads, mammalian cells and anisotropic hydrogel particles in a microchannel at extremely high flow rates. We show that on addition of micromolar concentrations of hyaluronic acid, the resulting fluid viscoelasticity can be used to control the focal position of particles at Reynolds numbers up to Re≈10,000 with corresponding flow rates and particle velocities up to 50 ml min[superscript −1] and 130 m s[superscript −1]. This study explores a previously unattained regime of inertio-elastic fluid flow and demonstrates bioparticle focusing at flow rates that are the highest yet achieved.National Institute for Biomedical Imaging and Bioengineering (U.S.) (P41 BioMicroElectroMechanical Systems Resource Center)National Institute for Biomedical Imaging and Bioengineering (U.S.) (P41 EB002503)National Science Foundation (U.S.). Graduate Research FellowshipUnited States. Army Research Office (Institute for Collaborative Biotechnologies Grant W911NF-09-0001

Phenomenology of ultrafine particle concentrations and size distribution across urban Europe

The 2017-2019 hourly particle number size distributions (PNSD) from 26 sites in Europe and 1 in the US were evaluated focusing on 16 urban background (UB) and 6 traffic (TR) sites in the framework of Research Infrastructures services reinforcing air quality monitoring capacities in European URBAN & industrial areaS (RI-URBANS) project. The main objective was to describe the phenomenology of urban ultrafine particles (UFP) in Europe with a significant air quality focus. The varying lower size detection limits made it difficult to compare PN concentrations (PNC), particularly PN10-25, from different cities. PNCs follow a TR > UB > Suburban (SUB) order. PNC and Black Carbon (BC) progressively increase from Northern Europe to Southern Europe and from Western to Eastern Europe. At the UB sites, typical traffic rush hour PNC peaks are evident, many also showing midday-morning PNC peaks anti-correlated with BC. These peaks result from increased PN10-25, suggesting significant PNC contributions from nucleation, fumigation and shipping. Site types to be identified by daily and seasonal PNC and BC patterns are: (i) PNC mainly driven by traffic emissions, with marked correlations with BC on different time scales; (ii) marked midday/morning PNC peaks and a seasonal anti-correlation with PNC/BC; (iii) both traffic peaks and midday peaks without marked seasonal patterns. Groups (ii) and (iii) included cities with high insolation. PNC, especially PN25-800, was positively correlated with BC, NO2, CO and PM for several sites. The variable correlation of PNSD with different urban pollutants demonstrates that these do not reflect the variability of UFP in urban environments. Specific monitoring of PNSD is needed if nanoparticles and their associated health impacts are to be assessed. Implementation of the CEN-ACTRIS recommendations for PNSD measurements would provide comparable measurements, and measurements of <10 nm PNC are needed for full evaluation of the health effects of this size fraction

Velocity field of the spiral vortex flow in the Couette-Taylor system

International audienceSpiral vortex flow in the counter-rotating Couette-Taylor system with a large aspect ratio and an intermediate gap has been investigated using Particle Image Velocimetry (PIV). From data of velocity components, we have determined nonlinear properties (anharmonicity, mirror symmetry, axial and radial flow rates) of spiral vortices and compared them to those of Taylor vortices. The velocity field around a spatio-temporal defect has been measured. There is a good agreement between these experimental results with available results from numerical simulations

Parabolic flight experiment "Convection in a Cylinder" – Convection patterns in varying buoyancy forces

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Destabilization of the Couette–Taylor flow by modulation of the inner cylinder rotation

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Hygro-thermal behavior of raw earth concrete

International audienceRaw earth materials represent an alternative to the traditional building materials since a lot of time. It is a material available in large quantities, ecological, economic and environmental. This material can be compacted or stabilized by small quantities of binders to improve its mechanical behavior. For its hygro-thermal behavior, several studies have shown that the raw earth is characterized by a very interesting and encouraging temperature-humidity regulating power for comfort and well-being. In this study, we are interested in the hygrothermal characterization of raw earth concrete. Different complementary techniques were used on the one hand for the thermal properties and on the other hand for the water vapor permeability. For the measurement of thermal conductivity, the device KD2 Pro was used to determine. For the measurement of water vapor permeability, the cup method was used (Ferroukhi, 2016; Hibouche, 2013). The results were analyzed and compared with those of traditional building materials which highlighted the interesting hygrothermal behavior of the studied raw earth concrete

Hygro-thermal behavior of raw earth concrete

Raw earth materials represent an alternative to the traditional building materials since a lot of time. It is a material available in large quantities, ecological, economic and environmental. This material can be compacted or stabilized by small quantities of binders to improve its mechanical behavior. For its hygro-thermal behavior, several studies have shown that the raw earth is characterized by a very interesting and encouraging temperature-humidity regulating power for comfort and well-being. In this study, we are interested in the hygrothermal characterization of raw earth concrete. Different complementary techniques were used on the one hand for the thermal properties and on the other hand for the water vapor permeability. For the measurement of thermal conductivity, the device KD2 Pro was used to determine. For the measurement of water vapor permeability, the cup method was used (Ferroukhi, 2016; Hibouche, 2013). The results were analyzed and compared with those of traditional building materials which highlighted the interesting hygrothermal behavior of the studied raw earth concrete