V. Sobolík - Academia.edu (original) (raw)

Papers by V. Sobolík

Mass transfer on a circular cylinder with a diameter of 0.52 mm was studied in polymer solutions ... more 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.

Journal of Applied Electrochemistry, 2003

The liquid film flow down an oscillating plate was used as a suitable flow configuration to study... more The liquid film flow down an oscillating plate was used as a suitable flow configuration to study the dynamic behaviour of electrodiffusion friction probes at large fluctuations. The two-segment probe was flush mounted into the plate wall to measure the fluctuating wall shear rate. The hydrodynamics of the experiment made it possible to adjust both the steady and oscillatory component of the wall shear rate through the operation parameters (flow rate, plate inclination, amplitude and frequency of wall oscillations). The approximate model of the probe dynamic response based on the similarity of concentration profiles at the probe surface was verified. This simple model proved to be able to calculate the instantaneous wall shear rate from the measured current signal even at large flow fluctuations. The analysis of the probe dynamic behaviour under reversing flow conditions provided a new method of the detection of short-time flow reversal. Finally, this method was successfully applied to confirm the existence of a small backflow region located in front of the large solitary waves, which were excited on the surface of a liquid film flowing down an inclined stationary plate.

Physics of Fluids, 2005

The effect of an external excitation on circular impinging jet flow is studied experimentally. Ve... more The effect of an external excitation on circular impinging jet flow is studied experimentally. Velocity fields in moderate air flows ͑Re= 10 000͒ are investigated by hot-wire anemometry. The basic flow is excited by a small sinusoidal modulation of the nozzle exit velocity. The phase-averaging technique is used to study the behavior of vortex structures in the jet, specifically rolling-up, pairing, and interaction with the wall. The jet is found to be sensitive to excitation in the frequency range characterized by a Strouhal number, St e = f e D / U, from 0.3 to 3. Different flow regimes are identified in the excited impinging jet: a periodic flow regime with the same frequency as the excitation, a regime with a frequency corresponding to a subharmonic of the excitation frequency, a regime alternating between these two frequencies, and two border regimes with more complicated behavior. The low-frequency excitation leads to the formation of vortices, which are larger than those occurring in an unexcited jet. Consequently, the near-wall velocity fluctuations are enhanced and the unsteady flow separation induced by vortex impingement is more pronounced. By contrast, excitation at higher frequencies, characterized by value 0.017 of a Strouhal number based on the shear layer thickness ,S t = f e / U, leads to the roll-up of small vortices and hence to the attenuation of the near-wall velocity fluctuations. In this case, the flow separation is suppressed because the small vortices are unable to induce it. Finally, the vortex merging process is sensitive to the double-frequency excitation with subharmonic components. For example, a combined excitation at St e = 1.60 and 0.53 leads to the merging of three vortices.

Measurement Science and Technology, 2007

A calibration theory for segmented probes flush mounted in a sphere exposed to uniform fluid flow... more A calibration theory for segmented probes flush mounted in a sphere exposed to uniform fluid flow was developed. The theory was checked experimentally by towing the sphere of diameter 2R = 22.2 mm with a three-segment circular electrodiffusion probe of diameter 2RE = 0.526 mm through a pool of aqueous solution of potassium ferro/ferricyanide. Oriented wall shear rates were detected and analysed at Reynolds number 660. Hydrodynamic models of the wall shear rate distribution along the sphere surface in a uniform stream are reviewed. The principles of the direction specific flow measurements using three-segment electrodiffusion friction probes are explained.

International Journal of Heat and Mass Transfer, 1991

ABSTRACT

Experiments in Fluids, 1990

ABSTRACT

Chemical Engineering Science, 1997

The stability of periodic two-dimensional waves on a liquid film falling down a vertical oscillat... more The stability of periodic two-dimensional waves on a liquid film falling down a vertical oscillating plate was studied experimentally using the aqueous solutions of carboxymethylcellulose. A set of capacitance probes was used to measure the instantaneous film thickness. Artificial flow fluctuations induced by the plate oscillations caused distinct intensification of the wavy flow. We use the methods of phase space reconstruction and deterministic chaos analysis to show that the dynamics can be understood within the framework of deterministic chaos. We find that regions of relatively ordered and more complex chaotic dynamics alternate as the frequency of oscillations is varied. There are particular oscillating frequencies at which the system is close to a three-frequency quasiperiodic motion with the spectrum of Lyapunov exponents of type (0, 0, 0, -.... ), elsewhere the system is either in a simple chaotic mode with the spectrum of type ( +, 0, 0, -.... ) or in a hyperchaotic mode with spectrum of type ( +, +, 0, -.... ). ~(, 1997 Elsevier Science Ltd. All rights reserved

The Journal of Supercritical Fluids, 2008

Internal structure of soybeans was modified by the instantaneous controlled pressure drop process... more Internal structure of soybeans was modified by the instantaneous controlled pressure drop process (DIC) when the material is heated by saturated steam for a short period of time and then rapidly evacuated. The bursting evaporation of moisture from all the mass of material caused by the pressure drop blows cavities in the material, breaks their walls and thus enhances subsequent extraction of oil from soybeans. Both the whole beans and milled beans and both the DIC-treated and non-treated beans were extracted with supercritical CO 2 at 280 bar and 40 • C. The extraction yield was measured and simulated by three mathematical models and equilibrium and mass transfer parameters were evaluated. The pore size distribution was measured as well. The results show formation of micropores in the beans by the DIC treatment and a substantial increase in the rate of extraction controlled by intraparticle diffusion.

Mass transfer on a circular cylinder with a diameter of 0.52 mm was studied in polymer solutions ... more 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.

Journal of Applied Electrochemistry, 2003

The liquid film flow down an oscillating plate was used as a suitable flow configuration to study... more The liquid film flow down an oscillating plate was used as a suitable flow configuration to study the dynamic behaviour of electrodiffusion friction probes at large fluctuations. The two-segment probe was flush mounted into the plate wall to measure the fluctuating wall shear rate. The hydrodynamics of the experiment made it possible to adjust both the steady and oscillatory component of the wall shear rate through the operation parameters (flow rate, plate inclination, amplitude and frequency of wall oscillations). The approximate model of the probe dynamic response based on the similarity of concentration profiles at the probe surface was verified. This simple model proved to be able to calculate the instantaneous wall shear rate from the measured current signal even at large flow fluctuations. The analysis of the probe dynamic behaviour under reversing flow conditions provided a new method of the detection of short-time flow reversal. Finally, this method was successfully applied to confirm the existence of a small backflow region located in front of the large solitary waves, which were excited on the surface of a liquid film flowing down an inclined stationary plate.

Physics of Fluids, 2005

The effect of an external excitation on circular impinging jet flow is studied experimentally. Ve... more The effect of an external excitation on circular impinging jet flow is studied experimentally. Velocity fields in moderate air flows ͑Re= 10 000͒ are investigated by hot-wire anemometry. The basic flow is excited by a small sinusoidal modulation of the nozzle exit velocity. The phase-averaging technique is used to study the behavior of vortex structures in the jet, specifically rolling-up, pairing, and interaction with the wall. The jet is found to be sensitive to excitation in the frequency range characterized by a Strouhal number, St e = f e D / U, from 0.3 to 3. Different flow regimes are identified in the excited impinging jet: a periodic flow regime with the same frequency as the excitation, a regime with a frequency corresponding to a subharmonic of the excitation frequency, a regime alternating between these two frequencies, and two border regimes with more complicated behavior. The low-frequency excitation leads to the formation of vortices, which are larger than those occurring in an unexcited jet. Consequently, the near-wall velocity fluctuations are enhanced and the unsteady flow separation induced by vortex impingement is more pronounced. By contrast, excitation at higher frequencies, characterized by value 0.017 of a Strouhal number based on the shear layer thickness ,S t = f e / U, leads to the roll-up of small vortices and hence to the attenuation of the near-wall velocity fluctuations. In this case, the flow separation is suppressed because the small vortices are unable to induce it. Finally, the vortex merging process is sensitive to the double-frequency excitation with subharmonic components. For example, a combined excitation at St e = 1.60 and 0.53 leads to the merging of three vortices.

Measurement Science and Technology, 2007

A calibration theory for segmented probes flush mounted in a sphere exposed to uniform fluid flow... more A calibration theory for segmented probes flush mounted in a sphere exposed to uniform fluid flow was developed. The theory was checked experimentally by towing the sphere of diameter 2R = 22.2 mm with a three-segment circular electrodiffusion probe of diameter 2RE = 0.526 mm through a pool of aqueous solution of potassium ferro/ferricyanide. Oriented wall shear rates were detected and analysed at Reynolds number 660. Hydrodynamic models of the wall shear rate distribution along the sphere surface in a uniform stream are reviewed. The principles of the direction specific flow measurements using three-segment electrodiffusion friction probes are explained.

International Journal of Heat and Mass Transfer, 1991

ABSTRACT

Experiments in Fluids, 1990

ABSTRACT

Chemical Engineering Science, 1997

The stability of periodic two-dimensional waves on a liquid film falling down a vertical oscillat... more The stability of periodic two-dimensional waves on a liquid film falling down a vertical oscillating plate was studied experimentally using the aqueous solutions of carboxymethylcellulose. A set of capacitance probes was used to measure the instantaneous film thickness. Artificial flow fluctuations induced by the plate oscillations caused distinct intensification of the wavy flow. We use the methods of phase space reconstruction and deterministic chaos analysis to show that the dynamics can be understood within the framework of deterministic chaos. We find that regions of relatively ordered and more complex chaotic dynamics alternate as the frequency of oscillations is varied. There are particular oscillating frequencies at which the system is close to a three-frequency quasiperiodic motion with the spectrum of Lyapunov exponents of type (0, 0, 0, -.... ), elsewhere the system is either in a simple chaotic mode with the spectrum of type ( +, 0, 0, -.... ) or in a hyperchaotic mode with spectrum of type ( +, +, 0, -.... ). ~(, 1997 Elsevier Science Ltd. All rights reserved

The Journal of Supercritical Fluids, 2008

Internal structure of soybeans was modified by the instantaneous controlled pressure drop process... more Internal structure of soybeans was modified by the instantaneous controlled pressure drop process (DIC) when the material is heated by saturated steam for a short period of time and then rapidly evacuated. The bursting evaporation of moisture from all the mass of material caused by the pressure drop blows cavities in the material, breaks their walls and thus enhances subsequent extraction of oil from soybeans. Both the whole beans and milled beans and both the DIC-treated and non-treated beans were extracted with supercritical CO 2 at 280 bar and 40 • C. The extraction yield was measured and simulated by three mathematical models and equilibrium and mass transfer parameters were evaluated. The pore size distribution was measured as well. The results show formation of micropores in the beans by the DIC treatment and a substantial increase in the rate of extraction controlled by intraparticle diffusion.