|
| |
|
|
ELECTROCHEMICAL DETECTOR WITH ELECTRODES ARRAY AND ROTATING DISK
SAJDLOVÁ, Zuzana
The thesis deals with the testing and optimization of hydrodynamic conditions of the electrochemical detector, which consists of a flow cell containing the electrochemical sensor with an array of electrodes. The flow cell includes a rotating disc-shaped component, which allows radial flow of analytes along the sensor electrodes. This principle imitates the rotating disk electrode, with the difference that here the electrodes are immobile. Hydrodynamic phenomena in this case are similar to RDE. Therefore, the theoretical part of my work deals with hydrodynamics and mass transfer for the well-described case of rotating disk electrode. It was found that in the current set-up under certain conditions, an analyte flowed back from the output cell channel to the sensor, even at the laminar flow. This causes a nonlinear response of the electrodes and their low reproducibility. The solution is to reduce the distance between the rotation component and the electrodes surface and reduce flow speed of analyzed liquid towards the sensor. A novel type of sensor with annular electrodes was designed and tested. It showed four times higher conversion rate of the analyte compared with the originally used AC9 electrochemical sensor having electrodes in the form of full circles lying on a circumference of a common circle. Based on calculations, conversion of the analyte on the plane electrode can be increased up to 100% when using this annular sensor, adjusting flow cell and reducing of the input flow rate. The detector was connected to the liquid chromatograph and its function was tested on two substances - ascorbic acid and dopamine. For the current detector these parameters were set: dynamic range, linearity, noise, detection limit, time constant and the temperature range at which the detector can be operated.
|
|
| |
|
|
Gas Hold-up and Volumetric Mass Transfer Coefficient of Various Impeller Types in Gas-Liquid Dispersion with Higher Viscosity
Zedníková, Mária ; Linek, V. ; Moucha, T.
In a vessel with inner diameter 0.29 m supplied by one, two or three impellers on a common shaft, there were measured transport characteristics (gas hold-up and volumetric mass transfer coefficient) in dependence on power consumption. As an impeller there was used the pitched blade impeller pumping the liquid either upwards or downwards. Air was used as a gas phase and 3% solution of Sokrat 44 as a liquid phase. The solution behaves as a newton liquid with viscosity 12.9mPa.s. Volumetric mass transfer coefficient was measured by dynamic pressure method. Gas hold-up and kLa were presented in dependence on power consumption and on gas superficial velocity. Results are compared with the data of given impeller types obtained in low viscous solutions and with the data of other impeller types.
|
|
| |
|
|
Experimentální mechanika tekutin a sdílení tepla a hmoty: strategie výzkumu
Trávníček, Zdeněk
The so-called “Research Strategy” seems to be a typical and quite effective tool for dealing with various problems in Experimental Thermal Fluid Sciences. The working hypothesis is proposed first and then a specific plan is derived from the hypothesis. The problem is divided into manageable parts (step-by-step approach). The purpose of the experiments is to confirm or to reject the hypothesis. The presentation introduces several examples of the recent original results: the influence of the flow structure on heat transfer, passive/active flow control of impinging jets, convective heat transfer enhancement of (steady or pulsatile) impinging jets, synthetic jets, hybrid synthetic jets, stability and bistability of jets, and thermal flow control of wakes. The examples emphasize the role of the discussed methodology, namely the roles of the task motivation, working hypothesis, and interpretation and publication of the results.
|
|
|
Heat/mass transfer of axi-symmetric, actively controlled impinging jet
Trávníček, Zdeněk ; Peszynski, K.
Annular nozzle has been equipped by a fluidic control of a jet flow state. The jet flow can be either focused along the nozzle axis or spread out of nozzle axis. Nozzle geometry aimed an enhancement of head and mass transfer on exposed wall by means of active flow control. A visualization of the jet flow was performed, mass transfer was measured by naphthalene sublimation method, and heat/ mass transfer analogy was used.
|
|
|
Určení transportních charakteristik z protiproudé difuze plynů
Soukup, Karel ; Šolcová, Olga ; Schneider, Petr
Two types of a diffusion cell commonly used for studying of isobaric counter-current diffusion in porous solids are compared. Both cells enable determination of diffusion coefficients and transport characteristics of porous materials. Transport parameters are material constants of the porous solids and can be evaluated through application of a suitable model of porous solids to results of measurements of transport processes withing the porous structure
|
|
| |
|
|
Distribuce porů z permporometrických měření
Šolcová, Olga ; Schneider, Petr
Two measurement modes for obtaining wet-curves were suggested and verified. In the figure the obtained wet and dry curves for two catalysts are shown. It was verified that LEPP gives consistent pore size distribution of flow-through pores and, thus, should be tried as the standard texture characteristic suitable for prediction and/or simulation of gas flow in porous media
|
guest ::
