RUS

 

Physical-Chemical Hydrodynamics Lab

Department of Physics and Chemistry of Non-equilibrium Media


Head of the Laboratory
Krivosheev Pavel, PhD
Phone. +375 17 2842203
e-mail: pavlik@dnp.itmo.by


History


Main Research Lines

Development and introduction of modern methods of optical diagnostics in fluid mechanics;
Solid-state physics, biophysics and biomedicine, digital dynamic speckle photography and speckle interferometry;
Shadow methods;
Methods of statistical imaging;
Investigation of heat and mass transfer processes in biotissues

Low-frequency ferromagnetic local hyperthermia;
Magnetophoretic cell sorting;
Viscosimetry of fluid microvolumes;
Dissipative self-organization processes

Thermal-physical and elementary processes in homogeneous media, including chemically reacting media:

Kinetics, energy transfer, and combustion regimes in gaseous, liquid fuel and heterogeneous systems at high temperatures and pressures;
Kinetics of nucleation and particle growth at high-temperature pyrolysis and oxidation of hydrocarbons;
Vibrational and relaxation rotation processes;

Thermal-physical and elementary processes in inhomogeneous chemically reacting media:

Initiation, combustion limits and regimes in non-one-dimensional boundary conditions;
Initiation, limits, structure and mechanisms of detonation and deflagration in gases and heterogeneous systems;
Pulsating and high-frequency detonation and supersonic combustion chambers


Elementary and collisional processes in gases and plasma:

Thermal and non-equilibrium ionization in supersonic flows;
Development of methods of forming and modeling wall plasma layers for flow control and surface modification;
Energy exchange at thermolization of plasma counter flows and development of quasi-stationary plasma formations

Hydrodynamics:

Physics of shock waves;
Jet flows;
Cavitation phenomena

Optical and contact diagnostics of liquid, gas and plasma flows:

Interferometry and speckle interferometry of gas flows and plasma;
Talbot interferometry;
Shadow, track and PIV visualization of flows;
Photoemission spectroscopy;
Spectroscopy of fast processes;
LIF, PLIF  
Laser diagnostics
High-speed photography methods

Primary Experimental Equipment

- Shock and detonation tubes
25, 28, 50, 76 mm in diameter
50 ' 50; 45 ' 90; 30 ' 120 мм

- Adiabatic machines with fast compression time
76, 50 mm dia     within 10 to 100 ms;

- Vacuum chambers with a volume up to 1m3;

- Mach-Zehnder interferometer, 30 cm field of vision;

- Holographic interferometer, 0.8 m field of vision;

- Shadow devices ИАБ-457, 2\5 сm field of vision;

- Test bench equipped with a gasoline internal combustion engine with a volume of 1.6 liter;

- Cavitation installations;

- Workshop supplied with new lathe, milling and drilling machines

- High-frequency pulsating detonation combustion chamber

 

 


Main Research Directions


- fire-proof coatings for cables and metal constructions (identification, study of characteristics, execution of fire-proof works);
- friction spark formation (development of methods and procedures of estimating fire-explosion hazard of different materials and ignition thresholds of gas mixtures and aerosol media);
- fires in the Metro (modeling of processes of heat and mass transfer in underground tunnel ventilation systems in fire conditions; development of optimal emergency regimes of underground tunnel ventilation systems);
- fire-technical examination (program complex for calculation of thermophyiscal characteristics in the fire-technical examination problems);
energy safety of Heat and Power Engineering Complex (HPEC) (development of new effective methods and means of increasing the safety of HPEC objects using modern sealing and fire-proof materials and technologies;
- liquiefied hydrocarbon gas (LHG), natural gas (NG) (accounting rules; use of NG energy for executing technological operations to move LHG; development of rates of loss; methods for re-calculation of gas amount to be taken into account by household gas meters; corrosion prevention of underground gas pipelines and LHG storage reservoirs);
- laser crystals (control technology of the process of growing crystals by modeling heat and mass transfer in the melt and furnace-crystallizer).

 


Experimental equipment

General view of the experimental setup for digital dynamic speckle photography

Micro-PIV investigation of the flow structure in microchannels of fuel elements

Research plant of low-frequency ferromagnetic local hyperthermia research plant;

Cell magnetic succeptibility research plant;

Research plant of viscosity kinetics of liquid microvolumes;

Plant for producing anisotropically conducting polymer clays

Our achievements

During the period 2011-2016 years our team successfully finished three projects in fields of plasma generation, plasma diagnostics and ballistic.
We designed and created experimental facilities for this projects and performed research work.
The main results of our activities are described in this presentation.



Colliding counter-flows of compressed erosion plasma

Experimental setup for colliding erosion plasma counter-flows investigation

Power supply voltage: 3.5 kV
Capacitor battery: 600 µF
Residual air pressure: 3·10-3 Torr

The purpose of this work is property investigation of quasi-stationary plasma formations with high energy content for practical applications in high thermal physics and diagnostic of materials under extreme conditions.

Investigated plasma formations are the result of two plasma counter-flows interaction process which is based on high-current discharges of plasma accelerators of erosion type in vacuum.

Optical scheme of the experimental facility (for shadowgraph diagnostics)


IAB-451 shadow device:
Focal length: 1917 mm
Observed field: 20 cm
Entrance slit width: 0.2 mm


PCO Dicam Pro camera
Exposure time: 5 µs

Shadowgraphs of colliding plasma flows were made using knife and slit method. As a light source a specially made argon flash lamp was used.

Averaged electron concentration in the interaction area was calculated from intensity distribution of shadowgraphs. In order to perform a correct shadow display a light filter system with transmission peak at 547 nm was mounted in front of the CCD-camera. At this wavelength the relative intensity in plasma spectrum was low while in argon lamp spectrum it was near maximum.

Emission spectra of flash lamp(light source for shadowgraph) and investigated plasma


Transmission band of optical filters set


Power supply voltage: 20 kV
Capacitor battery: 3 µF
Argon pressure: 2 atm

Flash lamp:

Plasma (in collision region):

Results of shadow visualization of colliding
erosion plasma flows

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Erosion plasma flows collision dynamics

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Results of digital proceeding of shadow pictures of two counter-directed compressed erosion plasma flows

The obtained data indicate that if a suitable choice of pulse light source is made, quantitative shadow method can be successfully used for the diagnostics of high-temperature compression plasma. The results of digital proceeding of shadow pictures of two counter-directed compressed erosion plasma flows collision area allowed to restore the field of free electrons concentration distribution with a relative error equals no more than 18%. In most cases, the distribution of the free electrons concentration has one distinct peak, located in the central region of the collision area. However, in some cases a double peak in the concentration distribution can be observed due to instability of plasma formation. These experimental results confirm the data previously obtained by spectral method.


Magneto-plasma compressor (Qausi-stationary plasma accelerator)MPC

General view of MPC


Qausi-stationary plasma accelerator is a magneto-plasma compressor (MPC) working on the ion current transport base. The plasma acceleration in an axially symmetric system of two electrodes is accompanied by its compression due to the interaction of the longitudinal current component with its own azimuthal magnetic field. As a result, behind the inner electrode cut forms compression plasma flow with parameters significantly higher than in the electrode gap. MPC is a system of two coaxial copper electrodes separated by a caprolone insulator. Impulse gas feeding system supplies the accelerator with the plasma forming substance. An outer copper electrode (anode) is sectioned and is a set of cupper rods uniformly distributed circumferentially. The inner electrode (cathode) has a divertor.

Results of integral photography of plasma flow in two modes

Results of integral photography of plasma glow in two oppositely directly MPCs operating in the residual gas mode

Results of integral photography of plasma glow during the operation of two MPCs in the mode with gas bleeding

The plasma flow to be generated in this mode is characterized by the compression region developing behind the end face of the accelerator, followed by a further plasma jet expansion. The process of colliding compression plasma flows was studied in MPC operating in the residual gas and gas injection modes. The distance between the ends of the oppositely directed MPCs was 200 mm. In these experiments, the diameter of the confining cylindrical glass pipe was 143 mm. Two MPCs were placed on the opposite flanges of the 250 liter vacuum chamber equipped with special optical windows for visualization, high-speed photography, and spectral studies of plasma. Helium was used as a working gas in MPC. The amount of helium injected via the valve during one discharge was 16 mmol. In experiments on plasma generation due to the gas injection, the initial pressure in the vacuum chamber was 1.5 Torr. In MPC operating in the residual gas mode, the helium pressure in the vacuum chamber was 10 Torr.

Compression plasma flows generation and diagnostics

Qausi-stationary plasma accelerator is a magneto-plasma compressor (MPC) working on the ion current transport base. Vacuum chamber volume - 250 liters, capacitor bank capacity – up to 1000 µF, discharge is commutated by a thyratron, initial voltage of the capacitor bank up to 8 kV, charged from a high-voltage power supply. The electromagnetic quick acting valve supplies gas feeding. It starts to operate when the capacitor of 240 µF and 4 kV discharges through the coil and generates magnetic field. To prevent gas spreading in vacuum chamber we put limiting glass tube around electrodes and nuzzles.

The plasma forming substance was mixture of gases He + H2. The residual pressure was 2.1 Torr. The emission spectrum for the time period 20.7–20.9 μsec from MPC start. The emission intensity of the plasma jet was captured from area with diameter of 2 mm at a distance of 30 mm from the inner electrode. Electron temperature in the compression zone of the plasma flow was ~ 150 ± 50 kK. Electron concentration determined from the Stark broadening of the He1 line 501.6 nm. At the maximum value of the discharge current of 240 kA electron concentration was 2.5–4 1016 cm−3.

The emission spectrum

Integral photo of plasma jet

Application

-Compression plasma flow treatment of composite ceramic coatings

Compression plasma flow treatment of model shielding elements with a dual layer composite coating surface (viscous metal sub-layer and the of hard ceramic oxide top layer) was performed firstly in order to cause the surface layer of ceramic oxide unsteady melting and recrystallization, resulting in formation of hard polycrystalline layer. Secondly, as a result of thermal impact, to improve the viscous adhesion characteristics of the metal and ceramic layers. The thickness of the oxide ceramics was 400 μm. The plasma forming gas was nitrogen.

The REM image of coating cross section after compression plasma flows treatment. Results showed the formation of the remelted layer with a thickness of about 6–7 μm, in which there are metal particles undissolved in the melt oxide

The elements surface image before the compression plasma flow treatment.

The elements surface after the compression plasma flow treatment.


Two-stage light-gas magnetoplasma launcher for material ballistic tests

under vacuum condition and modelled planet atmospheres

Design and operational principle of the two-stage light-gas magnetoplasma launcher

A ballistic range consists of a two-stage light-gas gun, vacuum chamber with windows, vacuum pump, capacitor bank, high-voltage power supply, pulse generator, start unit, and optical velocimeter for the projectile speed measurements. The launcher (a two-stage construction consisting of a magneto plasma compressor and a high-pressure channel filled with light gas) is placed inside the vacuum chamber. In the path of the projectile flight, at a certain distance from the barrel tip, a target under study is installed The erosion magnetoplasma compressor (MPC) consists of two coaxial electrodes.

A plasma forming substance is placed between the electrodes. During the discharge of the capacitor bank, electrical breakdown in the interelectrode space turns into a plasma flow. Acceleration of the flow is accompanied with its axial compression due to the interaction of the current longitudinal component with intrinsic azimuthal magnetic field. The resulting compression flow downstream of the inner electrode tip, featuring the high density and temperature, ruptures the diaphragms and generates a shock wave in the high-pressure channel filled with light gas. Due to the energy of light gas heated and compressed by a shock wave, the projectile accelerates in the barrel.

Methods of projectile speed measurement

Optical detector setup for projectile velocity measurement

Typical oscillograms of photodetectors signals

The projectile trajectory was intersected at an angle of 90° by two laser beams propagating at a distance 30 mm from each other. The beams are reflected by a beam-splitter and 100% mirror, located in the path of a semiconductor laser radiation. On exit from the vacuum chamber, they were directed by optical fibers onto the photodetectors. When the projectile moves, it shades the laser beams and signals on optical sensors interrupting sequentially. The projectile speed can be calculated from the time interval between the interrupt signals and known distance between two laser beams. Projectile velocity measurements were made in range 0.8 - 4.25 km/s

The scheme of projectile speed measurement

The projectile speed measuring method by barrel nozzle and opto-coupler was developed. A thin wire and a thin strip of copper foil are fixed by use of a special barrel nozzle at a distance from each other behind the edge of the barrel and are connected to electrical circuits. Opto-couplers consisting of a semiconductor laser and a photodetector are used to protect against electrical noise. A projectile breaks the wire and the foil after a shot. It causes the sequentially interruption of the signals from the optical sensors. The projectile speed can be calculated from the time interval between the interrupt signals and known distance between the wire and the foil.

Typical oscillograms of photodetectors signals

Ballistic tests results

Parameters of experimentvalue
Capacitance of the bank1200 mkF
Initial voltage4 kV
The maximum value of the discharge current280 kA
The volume of the working chamber of the erosion plasma accelerator3,9 cm3
Typical rise time of the discharge current to a maximum value24 mks
The length of the barrel140 mm
The helium pressure in the high pressure channel15 MPa
The residual pressure in vacuum chamber 10 Pa

Photos of the crater formed on the target surface of the duralumin plate 8 mm thick.
Projectile of 4 mm in diameter made of roller-bearing stee l was accelerated to a
speed of 4.25 km/s.


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High-speed video of projectile motion
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High-speed video of projectile impact on target (1- aluminum plate and 2 -Teflon plate)
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All described methods and facilities are available for replication and conjugation with other equipment and facilities. Besides this, other diagnostics

methods and experimental set-ups, described in our book and papers, can be duplicated and modified to meet specific demands of scientific or technological problem.

 

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