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A Simplified Calculation of a Continuous Flow Packed Contactor with Help of Characteristic Times
Sovová, Helena
The proposed approach is illustrated on several examples of supercritical fluid extraction kinetics. Simple expressions for the calculation of characteristic times of both extraction and individual extraction steps are derived from mass balance equations and applied on experimental data from typical extractions from plants with supercritical CO2, as the extraction of oils from seeds or the extraction of essential oils from aromatic plants.
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A New Look on the Nernst Model in Electrochemistry
Wein, Ondřej
The present paper is inspired by the electrodiffusion (ED) flow measurement, utilizing the limiting-diffusion regime (LDR) in two-electrode ED cells. The electrochemical testing and calibrations of the ED cells is based on two standard electrochemical techniques - quasi-steady voltammetry and voltage-step transient. Recently published theory of the voltage-step transient under simultaneous effect of Faradaic and Ohmic resistances is based on a suitably extended Nernst model. An analogous theory of the voltammetric experiment is presented here.
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AWS Viscosimetry of Microdispersions - Detection of Apparent Wall Slip
Pěnkavová, Věra ; Večeř, M. ; Wein, Ondřej
The rheometric data measured using three various sensor geometries (PP60, ZZ40DIN and KK-sensor) are compared in this contribution at the case of water solution of polymer welan. The KK-sensor, constructed at our department, combines advantages of geometry both plate-plate and concentric cylinder geometry. It is shown that KK-sensor is comparable to commercial sensors. It is presented for water kaolin dispersions that apparent wall slip does not disappeared neither for low consistent dispersions. The values of slip coefficients are even higher in the case of less consistent samples.
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Oscillations of a Bubble Attached to a Capillary Tip
Vejražka, Jiří ; Vobecká, Lucie
The contribution provides a procedure for computing the eigenmode frequencies, shapes and dampings for the case of oscillations of a bubble or drop attached to a capillary tip. The procedure is based on the analysis of Bostwick and Steen, but its results are recast to a more convenient and more compact form. Analytical results are in a good agreement with experiments, if the bubble size is sufficiently smaller than the size at detachment due to Archimedes forces.
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Oscillation of Interfacial Meniscus during the Formation of Bubbles
Stanovský, Petr ; Růžička, Marek
A closer look at the interphase meniscus in the model system with a transparent plate using a high-speed camera has showed that after detachment of the bubble the meniscus moves to the lower orifice rim. On that rim the meniscus oscillate dumped by increasing pressure in the space below the plate. In the description of the bubble growth at the orifice during so called waiting period accrue the equations describing the oscillatory behavior of the meniscus. Together with the nonlinear Rayleigh-Plesset equation it results in a bifurcation behavior - the volume of bubbles differ by up to 50% from the mean at certain values of the gas flow. This phenomenon has not been previously identified as the time-averaged values of bubble sizes conceal this effect.
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