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Experimental MHD facility

1. Overview

Schematic diagram of experimental MHD facility is shown in Fig.1, and the side view is shown in Fig.2 (a, b). The MHD facility consists of a magnet system, a vacuum system composed by a vacuum chamber and vacuum pumps for pressure reduction, a system of gas supply with argon storage, electrical power supply, a cooling system, control, measurement & recording system, a loading unit, a source of the working gas (plasmatron), a seed supply system, and a subject of research (linear or disc MHD channel).

            Fig. 1. Experimental disc MHD facility

The experimental MHD facility operates in the following way. Argon is supplied from a gas cylinder to the plasmatron where it is heated by DC electric arc. The heated and electrically conductive gas is supplied from the plasmatron nozzle to the MHD channel, which is hermetically connected with a vacuum chamber. Then argon is exhausted through the system of vacuum pumps into atmosphere. The transverse magnetic field in the MHD channel is created by the magnet system. General performances of the experimental MHD facility are given in Table 1.

                   Fig.2a. Left-hand side view of MHD facility                                                     Fig.3b. Right-hand side view

                       1 – magnet system; 2 – main vacuum chamber; 3 – disc vacuum chamber; 4 – measuring portholes

Table 1. General Performances of Experimental MHD Facility

The vacuum system of the experimental MHD facility consists of main cylindrical vacuum chamber of 2 m³ capacity (item 2, Fig 2a,b), and additional disc vacuum chamber (item 3, Fig 2a,b) installed on the main chamber and designed for investigations of the disc MHD channel (the linear MHD channel is installed directly on the cylindrical vacuum chamber). The reduced pressure of 10 Pa is provided by two vacuum pumps (Fig.3 a, b) with the evacuation rate of 500 l/s. When the plasmatron operates, the chamber pressure is 100 Pa. The vacuum chambers are equipped by portholes and sealed outputs for connection of different sensors. The side surface of the chambers is two-layered with pumping of the cooling water between the walls.

                                              a)                                                                                      b)

Fig.3. Vacuum pump

The hydraulic system provides the water cooling of heat-beat areas of the plasmatron, MHD channels, and the vacuum chamber. It consists of a water pump (Fig.4) providing the water flow rate of 8 m³/h at the pressure of 9 atm, pipelines with flow meters and valves installed.

                             Fig.4. Water pump                                                               Fig.5 Control panel of the gas supply system

The working gas flows from the plasmatron to the accelerating disc nozzle in the axial horizontal direction with the following flow turn in the intermediate chamber of the accelerating nozzle. The low temperature argon plasma is created by DC electric arc plasmatron. The argon flow is heated in the plasmatron by two-stage DC arc. The discharge stabilization is provided by solid walls of diaphragms restricted the arc diameter, and by flow swirl. Pressure in the plasmatron channel is less than atmospheric pressure for reducing the heat flux to the high-heat components of the plasmatron design and increasing its operating life. In this case the plasma jet pressure at the nozzle outlet is 3·10⁴ Pa. The plasmatron has the following operating parameters: electric current up to 1300 A, voltage of 100 V, diameter of stabilizing channel of 20 mm, the channel length of 200 mm, argon flow rate up to 5 g/s. Testing of the plasmatron at the power level up to 150 kW performed in the MHD facility proved its reliable and long operation without notable erosion of electrodes.

The gas supply system is designed for feeding the working gas (argon) into the plasmatron. It consists of a manifold of standard cylinders with commercial purity argon at pressure of 150 atm, pipelines, pressure gauges, and argon flow sensor. The control panel of the gas supply system is shown in Fig.5.

The PC based control, measuring and recording system of the MHD facility consists of a set of sensors and instruments for the measurement of parameters of MHD channel and various components and systems of the MHD facility. It performs an automatic recording of the parameters measured, as well as a control of the facility run. The view of the system display is shown in Fig.6.

Fig.6. Typical display of control, measuring and recording system.

The power-supply system is designed for electrical power supply of the plasmatron, the magnet system, the plasmatron triggers, and process equipment of the MHD facility. Separate components of the power-supply system are shown in Figs. 7 – 8.

                Fig.7. AC/DC converter                                              Fig.8. Control panel of the power-supply system

The seed injection system (Fig.9) is designed for injection of the ionized seed into the MHD channel, if an increasing of the electrical conductivity of working gas is required.

Fig.9. Components of the ionized seed injection system

The loading unit is designed for a loading of the MHD channel within the load factors specified.

The different components of the experimental MHD facility are shown in Figs.10 – 13. The pictures are taken in the Moscow State Aviation University, where this facility was installed for educational and scientific purposes.

         Fig.10. Wall assembly of the disc MHD channel                        Fig. 11. Components of disc MHD generator

                  Fig.12. Linear MHD channel (front view)                                      Fig.13. Linear MHD channel (side view)

2. Research capabilities of the experimental MHD facility.

For a purpose of determination of a possibility of application of the experimental data obtained at the experimental MHD facility for the full-scale MHD generators a comparison of ranges of variation of simulation criteria in the small-scale experimental MHD facility and full-scale MHD generators of output power of 10-50 MW fired by combustion products of liquid chemical fuels. Table 2 shows results of this comparison

Table 2. Comparison of simulation criteria for the small-scale and full-scale MHD generators

The table shows that the experimental MHD facility provides coincide of four groups of criteria among five ones (excluding the second group defining the dynamics of development of the boundary layers and near-electrode phenomena).

In so doing a conclusion may be made that the experimental MHD facility allows to perform the following kinds of experimental research useful for development of the full-scale MHD generators:

•  
• a study of non-viscous volume effects in the MHD channels at the considerable parameter of MHD interaction, Hall effect, various electric field strengths, and supersonic flows;
•  
• a study of output parameters of MHD generators with different cross-section areas and different design of electrode and insulation walls;
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• a comparison of relative efficiency of the process of energy conversion in various MHD channels under conditions of considerable non-uniformities of the flow in the MHD channel;
•  
• a calibrating of quasione-dimensional (engineering) techniques of calculations based on experimental study of MHD channels of various configurations.

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