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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experiments in fluids 11 (1991), S. 186-190 
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A cylindrical electrodiffusion probe for the measurement of liquid velocity vectors in the plane perpendicular to its axis was developed as an analogue to the triple-split film thermoanemometer. The geometry of the probe enables high directional resolution in the whole range of 360°. The total mass transfer of the probe was well correlated by the relation Sh = 0.76 Sc 0.33 Re 0.47.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The influence of eddy shedding on the instantaneous readings of a three-segment cylindrical electrodiffusion velocity probe was investigated in an immersed jet with a very low turbulence intensity, σ = 1.2%. The velocity fluctuations measured by the three-segment probe were smaller than 2.6%, and the maximum error in the flow angle estimation was 2∘. Vortices with the Strouhal frequency were detected by a simple electrodiffusion probe placed downstream of the three-segment probe, but no peaks with this frequency were found on the frequency spectra of the three-segment probe. From the probe response to a stepwise change of the polarization voltage the characteristic times of the transient process were estimated.
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  • 3
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Three-segment electrodiffusion probes embedded in a wall allow to determine simultaneously the three kinematic parameters of flow close to the probe surface: the flow directionθ, the wall shear rateq, and the normal velocity coefficientA,v z = −A z 2. A well-controlled three-dimensional flow, generated by a rotating disk, was used to demonstrate the capabilities of this new kind of electrodiffusion probes by comparing experimental results with the prediction based on the well-known hydrodynamical theory.
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  • 4
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Three-dimensional flow close to the stagnation point of an impinging jet cell was studied by means of three-segment electrodiffusion probes. The total current and the directional characteristics providing the wall velocity gradient and the flow direction respectively were measured at different distances from the stagnation point. The linear dependence of the wall velocity gradient on this distance was confirmed in the stagnation zone. The normal velocity component was evaluated from the flatness of the directional characteristics. The values of the normal velocity component were rather higher than those corresponding to the linear change of the velocity gradient and the dimensionless ratio of the probe radius to distance. The deviation appearing on the normal velocity component was explained by geometrical imperfections of the probes due to the technology of fabrication.
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  • 5
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  In a fully developed turbulent channel flow, the instantaneous wall shear gradient was measured simultaneously by an electrodiffusion (ED) probe and by laser-Doppler anemometry (LDA). The LDA measurements were done in the viscous sublayer and the linear velocity profile was used to calculate the instantaneous shear gradient at the wall. The electrodiffusion probe requires presence of a suitable electrolyte (e.g. an iodine and potassium-iodine aqueous solution) for reduction of the species on the working electrode (cathode). This results in a concentration gradient of the ions due to the convective diffusion of the [I3]- to the cathode. Due to the limited molecular diffusion rate and due to the dimension of the electrodiffusion probe its frequency resolution is limited. It is shown in which limits the correction of the signal on the concentration boundary layer inertia is not necessary and the probe can be used for measuring instantaneous wall shear gradients in turbulent flows. The results are compared with those obtained by LDA and elucidate the capability of the ED probe for measuring instantaneous shear rates at low Reynolds numbers.
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  • 6
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Calculation is presented of the influence of the normal velocity component on the directional characteristics of a three-segment electrochemical probe in the vicinity of a stagnation or a separation point. The results obtained here for a 2D flow corresponding to an axisymmetric flow having a stagnation point show quantitative differences, especially in the stagnation region, with respect to an earlier calculation performed on a 2D flow corresponding to a planar flow having a stagnation line. An experimental study with such a probe is then reported which demonstrates the possibility of this arrangement in the stagnation region of an immersed jet.
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  • 7
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract The axial and azimuthal components of the shear rate on the wall of the outer fixed cylinder of a pair of concentric cylinders with the inner cylinder rotating was measured using a three-segment electrodiffusion probe. The axial distribution of the components was found by sweeping vortices past the probe by means of a small axial flow. A nonzero axial shear rate component indicated the onset of Taylor vortices. Azimuthal waves on the vortices caused fluctuations of both components. The instabilities were measured in two geometries characterized by R 1/R 2 = 0.84 and 0.7. The probe was calibrated in the same apparatus with R 1/R 2 = 0.94. The Stuart theory for the growth of vortex velocity with angular velocity agrees well with the amplitude of the fundamental mode measured with R 1/R 2 = 0.84. Qualitative agreement was found with the numerical results of Fasel and Booz, especially between the axial shear rate component measured with R 1/R 2 = 0.7 and the vorticity calculated for R 1/R 2 = 0.5.
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  • 8
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract A three-segment direction specific probe based on the electrodiffusion measuring technique was used to measure local liquid velocities in gas-liquid flow. Dissolved oxygen was employed as depolarizer instead of the usually applied redox system ferro-ferricyanide in water. The concentration of the auxiliary electrolyte K2SO4 was so low that coalescence behaviour of the gas-liquid system was not influenced. It was possible to measure liquid velocities up to ca 100cm s−1. The probe showed satisfying sensitivity to flow direction. Furthermore, unequivocal discrimination between signals from the liquid and gas phases was achieved.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Mass transfer on a circular cylinder with a diameter of 0.52 mm was studied in polymer solutions by measuring the directional characteristics of a three-segment electrodiffusion velocity probe. The free stream velocity was varied in the range 0.01–0.31 m s−1 and the polyacrylamide concentration in the range 0.001–1% (by mass). A small amount of polymer produced large changes in mass transfer distribution on the cylinder in comparison to the distribution in Newtonian liquid. In particular it has been shown that the transfer rate in the aft portion of the cylinder is greater than in the front part if the Weissenberg number exceeds some critical value. The situation was identified where the local mass transfer was constant around the cylinder, i.e. the surface was uniformly accessible to diffusion.
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  • 10
    ISSN: 1572-8838
    Keywords: friction probes ; electrodiffusion ; shear rates ; calibration ; transients
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract Voltage-step transient experiments are used to calibrate electrodiffusion (ED) friction probes. The approach is demonstrated on the probes in high-speed rotating impellers. This calibration has shown that shear rates as high as 106s-1 can be measured reliably using 0.5mm Pt working electrodes in ferro/ferricyanide aqueous solutions. The complete transient calibration experiment provides sufficient information about the dynamics of ED friction probes.
    Type of Medium: Electronic Resource
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