Report on the Closed cycle MHD specialist meeting : working group of the joint ENEA/IAEA international MHD liaison group : Eindhoven, September 1971

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group of the joint ENEA/IAEA international MHD liaison group

: Eindhoven, September 1971

Citation for published version (APA):

Rietjens, L. H. T. (1972). Report on the Closed cycle MHD specialist meeting : working group of the joint ENEA/IAEA international MHD liaison group : Eindhoven, September 1971. (EUT report. E, Fac. of Electrical Engineering; Vol. 72-E-29). Technische Hogeschool Eindhoven.

Document status and date: Published: 01/01/1972

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REPORT on the

CLOSED CVCLE MHD SPECIALIST MEETING

...

Working group of the joint ENEA/IAEA international

MHD liaison group

at

Eindhoven, The Netherlands, September 20, 21 and 22, 1971

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GROEP DIREKTE ENERGIE OMZETTING

REPORT on the

GROUP DIRECT ENERGY CONVERSION

CLOSED CYCLE MHD"SPECIALIST MEETING

Working group of the joint ENEA/IAEA international MHD liaison group

at

Eindhoven, The Netherlands, September 20, 21 and 22, 1971

Editor: L.H.Th. Rietjens

TH-Report 72-E-29 ISBN 90 6144 029 7

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Program of the meeting

List of participants

Abstracts of papers delivered during the meeting

I Reports on the status and results of closed cycle

experiments

II Plasma properties - Instabilities and stabilization in nonequilibrium plasmas

III Loss mechanisms - Current distributions - Electrode effects - Boundary layers - Gas dynamic effects

3

6

9

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PROGRAM

Sunday 19,

Monday 20,

Tuesday 21,

OF THE MEETING

9:00 p.m., Informal gathering at the Cocagne Hotel

9:00 a.m. - 12:30, Session I

Reports on the status and results of closed cycle

experiments

2:00 p.m. - 4:00, Session II

Plasma properties - Instabilities and stabilization in nonequilibrium plasmas

4:00 p.m., Visit to the laboratory of the group

Direct Energy Conversion

9:00 a.m. - 12:30, Session III

Loss mechanisms - Current distributions - Electrode effects - Boundary layers - Gas dynamic effects

2:00 p.m. - 4:00, Session IV

Design concepts of large MHD generators - Nuclear MHO power plants

4:00 p.m., Visit to the permanent scientific exhibition of Philips Gloeilampenfabrieken N.V.,

the "Evoluon"

7:00 p.m., Dinner at Rotisserie "De Kempen"

Wednesday 22, 9: 15 a.m. - 12:00, Session V

State of the art in closed cycle MHD - General

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ORGANISING COMMITTEE:

Prof.Dr. L.H.Th. Rietjens (chairman) Ir. J.H. Blom

IF.· J.W.M.A. Houben

The organisation of this meeting was possible by the sponsorship of the Eindhovens Hogeschoolfonds.

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LIS T

OF

PARTICIPANTS

INTERNATIONAL ATOMIC ENERGY AGENCY (IAEA)

KOLBASOV, B., Dr., Division of Nuclear Power and Reactors,

Karntner Ring II, P.O. Box 590, A-lOll Vienna

GERMANY

BOHN, Thomas, Dr., Projekt Argas, Institut fur Technische Physik, KFA Julich, Postfach 365

BREDERLOW, Gunther, Dr., Max-Planck-Institut fur Plasmaphysik, 8046 Garching bei Munchen

HAHN, Gerard, Max-Planck-Institut fur Plasmaphysik, 8046 Garching bei Munchen

HOLZAPFEL, Christian, Dr., Projekt Argas, Institut fur Technische Physik, KFA Julich, Postfach 365

KOMAREK, Peter, Dr., Projekt Argas, Institut fur Technische Physik, KFA Julich, Postfach 365

KUPSCHUS, Peter, Dr., Projekt Argas, Institut fur Technische Physik, KFA Julich, Postfach 365

LANG, Hermann, Projekt Argas, Institut fur Technische Physik,

KFA Julich, Postfach 365

MEITZNER, Gisela, Projekt Argas, Institut fur Technische Physik, KFA Julich, Postfach 365

NAKAMURA, Takashi, Dr., Max-Planck-Institut fur Plasmaphysik, 8046 Garching bei Munchen

NOACK, Georg, Projekt Argas, Institut fur Technische Physik,

KFA Julich, Postfach 365

SCHABEL, Peter, Dr., Projekt Argas, Institut fur Technische Physik, KFA Julich, Postfach 365

WITTE, Klaus-Jurgen, Dr., Max-Planck-Institut fur Plasmaphysik, 8046 Garching bei Munchen

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ITALY

BERTOLINI, Enzo, Dr., Laboratorio Conversione Diretta, Comitato

Nazionale per l'Energia Nucleare, Via Enrico Fermi,

Frascati (Roma) 00044

GASPAROTTO, Maurizio, Laboratorio Conversione Diretta, Comitato

GAY, Paolo, Laboratorio Conversione Diretta, Comitato Nazionale

per l'Energia Nucleare, Via Enrico Fermi, Frascati (Roma) 00040

NIGRINI, Francesco, Dr., Instituto Elettrotecnica, Viale

Risorgimento 2, 40136 Bologna

SOBRERO, Henrico, Dr., Instituto Imenti Meccanici, Viale

Risorgimento 2, 40136 Bologna

TAMBURANO, Aido, Laboratorio Conversione Diretta, Comitato

NETHERLANDS

BENACH, Robert,

University

Department of Electrical Engineering, Eindhoven

of Technology, Insulindelaan 2, Eindhoven

BLOM, Jan, Department of Electrical Engineering, Eindhoven University of Technology, Insulindelaan 2, Eindhoven

HOUBEN, Jan, Department of Electrical Engineering, Eindhoven

University of Technology, Insulindelaan 2, Eindhoven

JANSSEN, Jos, Department of Applied Mathematics, Eindhoven

University of Technology, Insulindelaan 2, Eindhoven MAS SEE , Peter, Department of Electrical Engineering, Eindhoven

University of Technology, Insulindelaan 2, Eindhoven

MERCK, Wim, Department of Electrical Engineering, Eindhoven

University of Technology, Insulindelaan 2, Eindhoven RIETJENS, Leo, Prof.Dr., Department of Electrical Engineering,

Eindhoven University of Technology, Insulindelaan 2, Eindhoven

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VEEFKIND, Bram, Dr., Department of Electrical Engineering, Eindhoven University of Technology, Insulindelaan 2, Eindhoven

VELTKAMP, Gerhard, Prof.Dr., Department of Applied Mathematics, Eindhoven University of Technology, Insulindelaan 2,

Eindhoven

WIJKER, Wim, KEMA N.V., Utrechtseweg 310, Arnhem

SWEDEN

BRAUN, Joseph, Prof.Dr., AB Atomenergi, Studsvik, Fack S-611 01,

Nykoping 1

PALMGREN, Soren, AB Atomenergi, Studsvik, Fack S-611 01,

Nykoping 1

ZINKO, Heimo, Dr., AB Atomenergi, Studsvik, Fack S-611 01,

Nykoping 1

UNITED KINGDOM

HAINES, Malcolm, Dr., Department of Physics, Imperial College of Science and Technology, Prince Consort Road, London sw7

USSR

OVCHARENKO, Valery, Dr., Institute for High Temperatures, the USSR

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ABSTRACTS OF PAPERS DELIVERED DURING

THE MEETING

SESSION I Reports on the status and results of closed cycle experiments

EXPERIMENTAL INVESTIGATION OF A RECOMBINING PLASMA

presented by Gerard Hahn

The decay of the electrical conductivity of a preionized, pure helium plasma is investigated under the conditions that will probably be present in an MHD generator working in the afterglow mode, that is:

- during a plasma recombination time of 1 to 2 msec,

- at a gas pressure of about 10 atm,

- at a gas temperature of about 1500 K,

- at electron temperatures - at electron densities of between 1500 and 19 -3 about 10 m . 3000 K, and

The experimental results show that for an initial electron density

n

=

5'1019 m-3 and for a gas pressure of I atm, between t

=

0 and

eo

I. I msec, the electrical conductivity is somewhat greater than Z ~-l

-I -I

For a gas pressure of 4 atm, the values of a are about 0.5 ~ m

-I m

With the correspondent n values one can define a global recombination

e

coefficient with a formula of the type dne/dt

= -

azn;,

in which

a

Z

is a

function of n , T , n , and T . The investigation of the a

Z

dependence on

e e g g

these parameters yielded the following results:

- a

2 is nearly independent of the electron temperature, - a

Z 1S also nearly independent of the electron density, and

- a

Z

increases with the gas density.

A consistent theoretical model for the description of this recombination process in not yet available.

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RECENT RESULTS FROM THE CNEN BLOW-DOWN FACILITY IN FRASCATI

presented by Paolo Gay

In March 1971 we made a new series of eight helium seeded experiments the following characteristics: helium mass flow from 0.55 to 0.152 kg

with

-I

sec

duct cross section from

3

x 5 cm2 to 3.4 x 5 cm2 in a length of 4b cm; seed

fraction from 0.27 to 0.31

%

At.; stagnation temperature from 1670 K to

1800

K;

stagnation pressure from 1.1 to 3.3 atm; inlet Mach number from 0.3

to 0.73; magnetic field from 0 to 4 Wb m-2 during a time of 10 sec; Hall

parameter in different experiments from 3.4 to 12 at the maximum magnetic field.

The open circuit voltage is very close (95 %) to the ideal open circuit for a Hall parameter up to 10. The maximum Hall voltage measured, on the

duct with 23 electrode pairs and a length of 25.2 em, was 1150 V,

over-coming the maximum Hall voltage of 600 V measured previously.

The trend of the current and of the conductivity along the duct with a

load greater than 22.4 Q shows a saturation (at the same value with and

without preionization) of the current after a transient which is longer without the pre ionization; in the short circuit mode a sharp increase of

the current is seen from 6 to 13 A in the last electrodes. The ratio of

the outlet and inlet conductivity is 7 at k

y

=

0.12 and 4.8 at k Y

=

0.38

with the preionization, and 30 at k 0.15 and 12 at k

y Y

=

0.36 without

preionization; the maximum measured conductivity (short circuited) was

15

n-

I m-I .

In these experiments we have obtained a good reproducubility of the

ex-tracted power with values from I kW to 5.7 kW with and without

pre-ionization.

The maximum power extracted on the external load for one pair of electrodes has been 340 W at electrode number 30 with a load factor of 0.44, and a

d ' t . h 1 of 36 MW m-3 .

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CLOSED CYCLE MHD IN THE USSR presented by Valery Ovcharenko

A technical proposal has been completed for a relatively large scale closed cycle MHD installation with seeded noble gas nonequilibrium plasmas. In a case of a helium seeded with cesium

given: T <

0 - 2300 K; P 0 -< 9 atm; G -<

plasma the following parameters can be -1

kg sec ; and M

=

0.5-2.0. The moment

of starting the construction of the facility will depend on the success in the UHTR or on the success of some other method of the high temperature gas production.

An economical analysis of a large closed cycle MHD generator has been com-pleted. The major advantage has the MHD plant with a steam turbine driven compressor. Argon and helium like working fluids give approximately equal

efficiency in a range of 50 %. Argon has some advantage at the low

tempe-ratures, but it contaminates the cycle.

The economical analysis was based on the design investigation of the plant. In the case analysed the argon pressure was 30 atm and the temperature 1500 C, including a reactor for 1200 MW MHD plant and a superconducting magnet. The calculations show that capital investments are 117 rubl/kW

and the electricity costs 0.609 kop/kWh, the fuel cost is 0.132 kop/kWh.

An increase of the temperature up to 2000 C gives us 53 % efficiency and

a decrease in the capital investments and electricity cost down to 90 rubl/kW and 0.446 kop/kWh respectively.

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SESSION II

Plasma properties - Instabilities and stabilization in

nonequilibrium plasmas

SWEDISH CONTRIBUTION TO THE CLOSED CYCLE MHD SPECIALIST MEETING presented by Heimo Zinko

Results presented at the Fifth Symposium on MHD Power Generation have demonstrated that

density of 5.1019

the

-3 m

lifetime of a decaying helium plasma with a starting is long enough to operate an MHD generator with a stagnation pressure of 10 atm in a region with satisfying power density (other

B

=

10

parameters are T

=

2000 K, np

=

0.6, n

=

0.2, x

=

5 m,

o stag c

T). Furthermore, the experiments have shown that by means of Penning ionization the admixture of argon can double the effective

recom-bination time.

As the Penning ionization cross section for He-Xe is much larger than for He-Ar we have recently investigated the performance of He-Xe mixtures. In the pressure region between 0.5 and 1.5 atm and at temperatures between 900

-3

and 1200 K it has been shown that at a xenon seeding rate of 10 the

effective lifetime of the plasma can be increased by a factor of 5 compared to pure helium. This results in a considerable increase in power density and a simple calculation shows that this can be reflected in a possible

in-crease of the input stagnation pressure by about 50 %.

As the ionization potential for xenon is appreciable lower than that of helium the possibly use of a helium-xenon mixture as the working fluid for a nonequilibrium generator was investigated. The principle idea was to use the afterglow generator as a first stage and to operate the generator in the conventional nonequilibrium mode in an adjacent second stage where pressure has dropped and the electron temperature is high. However, results

have shown that even at atmospheric pressure and B = 10 T the Mach number

becomes unrealisticly high before useful power densities can be obtained.

It was recognized that the NOGAG (Noble gas afterglow generator) concept is one member of a family of generators where st,.bility is achieved by

decoupling the conductivity from the electron tetIlperature, ;nother member

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THE INVESTIGATION OF THE NONEQUILIBRIUM MHD PLASMA IN THE REGIME OF FULLY IONIZED SEED

presented by Takashi Nakamura

We have reported at the last meeting at Munich that the nonequilibrium MHD plasma has the regime of fully ionized seed where the plasma is stable with respect to the ionization instability and that the stable regime can be achieved in an actual MHD generator. We report some results from the

continued experiment with improved experimental conditions. We have

focused our efforts on the following items.

1) The electrode segmentation ratio (HiS, where H is the distance between

the anode and the cathode, and S is the distance between the adjacent electrodes) was increased up to 10 in order to make more accurate measurements of a

eff and Seff by limiting the turning of the current

direction.

2) The measurement of the electron temperature and the electron density was made by means of the cesium recombination continuum at the wave lengths of 4228 Rand 4857 R. The above mentioned wave lengths were

chosen in order to avoid the radiation from the excited argon atoms.

3) The used concentration was changed to demonstrate the influence of the seed fraction.

The experimental results show that the value of the conductivity (and the corresponding current density) at the fully ionized seed increases

proportionally to the seed fraction and that it is indeed the ionization of the noble gas (argon) which limits the regime of the stable plasma. In the stable regime the Hall parameter as high as 6.5 was measured at the magnetic field strength of 2.2 T while the conductivity remained virtually constant. These results justify the effort to investigate the stability of the helium-cesium mixture and to investigate the overall efficiency of the Faraday generator in stable mode and the possibility of the nonequilibrium Hall generator.

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DISPERSION RELATION OF IONIZATION INSTABILITIES presented by Peter Massee

The purpose of an experiment, which is set up at the Eindhoven University of Technology, is a verification of the dispersion relation of ionization instabilities. To do this, perturbations will be launched artificially in a plasma in a subcritical state (Hall parameter below its critical value). This requires homogeneous plasma conditions and has led to the construc-tion of a discharge chamber, the walls of which will be heated to the heavy particle temperature.

Theoretical work, performed by Bram Veefkind, aims to investigate whether the critical Hall parameter can be increased by means of grids that short circuit the AC component of the electric field without effecting its DC component. The grid wires are parallel to the magnetic field and are connected externally by suitable passive LCR circuits. The planes of the grids are oriented along the direction of maximum growth. The analysis is similar to that of Nelson and shows that only the wavelength component

parallel to the grid planes

A

is of importance for the value of the

x

critical Hall parameter. When the distance between the grid planes is d

the final conclusion is that only waves with the ratio A /d > ] will be

x

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THE INFLUENCE OF ELECTROTHERMAL INSTABILITIES ON THE CURRENT VOLTAGE CHARACTERISTIC

presented by Christian Holzapfel

Due to the finite time to establish the equilibrium electron density we have relaxation phenomena in the MHD generator. At lower gas temperature we have no rise of electron density above that corresponding to the gas

temperature

if

we do not use any preionization. That means we have no

rise of the plasma conductivity also if the electron temperature is higher than the gas temperature. Even we have a reduction of the plasma conductivity due to instabilities. Defining the apparent conductivity

o

app

=~

E*

Y

which we get from the current-voltage characteristic, we have the relation

between 0 and the plasma conductivity

app

0(1 +

a·a

)

=

0 (1 +

a

2)

app app

with the apparent Hall parameter,

E

x

E*

Y

From that we see, that it is possible that 0 increases if

a

drops. This

app

is seen in the nonlinearity of t~e current-voltage characteristic where we

only see 0 and not the plasma conductivity o. In current-voltage

app

characteristics, as they were measured both in Frascati and in Julieh, we

see a break due to this rise of the apparent conductivity. The electron density and electron temperature depend on the current; the electron density does not rise in spite of the increasing temperature. Electro-thermal instabilities are seen. The different Hall parameters S, Sapp'

and

a

_cralso depend on the current. Due to the drop in S the apparent

conductivity increases whereas the plasma conductivity- 0 goes down. This

increasing of the apparent conductivity leads to the break in the

characteristic. That means the nonlinearity of the characteristic comes from the fact that the current in the Faraday generator is changed from

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the x-direction more into the y-direction due to the reduction of the Hall parameter. Therefore, the nonlinear characteristic is not in any case a significant prove of nonequilibrium ionization, that means of higher electron density. It only shows the influence of the electro-thermal instabilities at increasing electron temperature.

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SESSION III

Loss mechanisms

Current distributions Electrode effects

-Boundcrt>y layers

Gas dynamic effects

CONTRIBUTION ON EXTERNAL LEAKAGE RESISTANCES IN AN MHD GENERATOR presented by Maurizio Gasparotto

A simplified analytical model in which are taken into account i) resistances between opposite electrodes, ii) resistances between each electrode to

ground, and iii) resistances between adjacent electrodes on one side of the

generator, has been considered. Theoretical results for the open circuit

Faraday voltage relative to the ideal value versus

S,

and for the Hall

voltage in short circuit Faraday generator along the duct, using different values of leakage resistances, are compared with FRASCATI experiments made

in 1967,1969 and 1971.

It is shown that in the 1967 and 1969 experiments there were leakages

between adjacent electrodes and to ground. Furthermore, breakdowns did not occur in the plasma but outside the duct and Were strictly related to the channel technology.

The main results obtained in 1971 experiments are the following.

I) A ratio between the open circuit Faraday voltage and the ideal value

uBd equals to one for S from 1 to 12.

2) No breakdown is observed and the maximum value

Hall field and gas density equals to 1.4.105 V

of 2 m the ratio -I kg between

3) No difference on the results is observed with and without preionization. 4) A constant Hall field along the duct is found.

5) A high value ('V 10 kll) is found for the leakage resistance loading the

Hall generator.

6) A substantial improvement in generator performances is observed.

These results support the conclusion that in 1971 FRASCATI channel external

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ON ELECTRICAL LOSSES IN THE MHD GENERATOR presented by Christian Holzapfel

In the last year it has been pointed out, that we have to consider several loss mechanisms in the MHD generator. One of the most important losses is the loss of electrical power due to poor insulation, short circuits and the current distribution in the plasma.

Briefly repeating the possibilities of current leaks in the channel we

firstly have a reduction of the Faraday voltage due to back flowing current at the insulator walls as a result of the velocity profile in the gasflow,

secondly have a reduction of the Faraday voltage due to the cold boundary layer on the electrodes, and

thirdly have a reduction of the Hall voltage due to finite segmentation and due to current leaks through the hot plasma in the diffusor to ground or back to the channel entrance. This also leads to a reduction of the Faraday voltage.

If we now separate the bulk flow from the boundary layer all these effects

can be described by resistances and we can describe the influence of theSe

effects on the bulk flow of the system. Doing this we can set up a simple model of the electrical conditions of the bulk flow.

R ay R ax R ay

The resistances R describe the electrical performances of the layers on

ay

the insulator walls and on the electrodes in connection with the normal loading resistance and with poor insulation. The resistance

the reduction due to finite segmentation and the resistance

R describes

ax

of the plasma

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In order to calculate the electric field two parameters are introduced des-cribing the components of the field

E = - L8vB

x and E Y = KvB ( 1 )

The parameter L describes the x-field and the ordinary loading factor K

describes the y-field. 8 is the Hall parameter, v is the velocity and B the

magnetic field.

In the ideal Faraday generator, where R

ax = m

,

in the Hall generator we have

K

=

O.

Generally

lated by L = r( 1 - K)· R ax R ax + R. 1X we have L

=

1 - K, whereas

the two parameters are

re-(2)

with the reduction factor r due to finite segmentation and with the internal resistance of the generator in the x-direction.

If we now calculate these parameters K and L, then we have a complete

electrical description of the bulk flow. From the field we get the current density and thus also a power density

JE

=

0(vB)2 • [K(K - I) + 82L(L - I)] 1 + 82

(3)

with the electrical conductivity

°

of the plasma. From this power density

only a fraction appears in the external load resistances R of the channel.

ay 2 = o(vB) 2 I + 8 2 • [K(K - I - S L)

J

whereas the rest

. E

~x = .:.0-,-( V:.;B:.<.)."..2 _J ₊

82

appears in the resistance R •

ax

(4)

(5)

We see from equation (4) that if L is going down then also the electrical power jyEy from the generator used in Faraday mode goes down.

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But not only due to this effect the power density is reduced, also due to the electron heating by the term

(6 )

which also is reduced with L, the conductivity is reduced.

Calculating the parameters K and L we have to consider the variation of the electrical and gas dynamic parameters along the channel due to energy ex-traction. That means also the parameters K(x) and L(x) vary along the channel. In this case the relation (2) is replaced by

1

f

LSvBdx

=

o R 1 ;:-R-7'ax=7--

f

r( I - K) SvBdx + R. ax ~x 0 (7)

Using this and the other gas dynamic relations we can calculate the para-meters K(x) and L(x) along the channel.

In a slide these parameters along the channel were shown at a high value of the resistance R ,that

ax means for an ideal Faraday generator. The

calcu-lations were made on the IBM for

3 Torr cesium with a velocity of

an Ar-Cs plasma at 1500 K, 3 bar argon,

-I

500 m sec and a magnetic field of 2 T.

The external load resistance R is 333

n.

ay

For a lower value of the resistance R ,both Land K are smaller. The

ax

influence of the resistance R is not homogeneous; the influence is

ax stronger at the channel end.

At a very low resistance R at the channel end the value of L becomes

ax

negative. That means that the Hall field E has opposite direction or that

x

the total Hall voltage is reduced after this point. This is the same effect which was pointed out by Celinsky who calculated this critical length of the Hall generator. Also this was verified experimentally by the group in Tullahoma. From (5) we see that the power density gained from the Hall

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ON THE INFLUENCE OF THE ELECTRODE CONFIGURATION ON THE DISCHARGE STRUCTURE IN A NONEQUILIBRIUM MHD PLASMA AT HIGH MAGNETIC FIELD STRENGTHS

presented by Gunther Brederlow and Klaus-Jurgen Witte

In noble gas MHD generators discharge structures have been detected re-ferred to as streamers. By means of probe measurements and image converter pictures it could be shown [I] that these streamers are current layers in-side which ionization instabilities may develop. Similar current distribu-tions were also theoretically found under equivalent condidistribu-tions [2]. According to this analysis the striated structure of the discharge is due to the finite segmentation of the electrodes; it is a consequence of the inhomogeneous boundary conditions. In the paper presented some experimental observations are reported confirming the theoretically deduced conclusions. The analysis given in [2] starts from a steady-state loss-free

non-equilibrium plasma in which all convection and relaxation effects are

neglected. An axial discharge fits these conditions better than a

trans-verse discharge because in the latter relaxation and convection effects are more pronounced thereby rendering more difficult the comparison between

theory and experiment. Using an axial discharge the image converter pic-tures taken clearly show the one to one correspondence between the streamers and the electrode pairs as predicted by the theory.

[1] G. Brederlow, H. Zinko, K.J. Witte, Performance of the IPP Noble-Gas

Alkali MHD Generator and Investigation of the "Streamers" in the Generator Duct, Fifth Int. Conf. on MHD Electrical Power Generation, Munich, Vol. II, p. 387, 1971.

[2] L.L. Lengyel, On Current and Potential Distribution on Nonequilibrium

MHD Plasmas at High Magnetic Field Strengths, Fifth Int. Conf. on MHD Electrical Power Generation, Munich, Vol. II, p. 207, 1971.

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STATUS OF THE COLLABORATIVE PROGRAMME IN U.K. BETWEEN IMPERIAL COLLEGE, LONDON, AND INTERNATIONAL RESEARCH AND DEVELOPMENT CO., NEWCASTLE-UPON-TYNE presented by Malcolm Haines

Experimental Results

The first and second stage of the programma sponsored by the Science Re-search Council involved the design, construction and testing of a new 80 kW third stage heater and MHO duct section. This was completed by the end of

1970, and in May 1971 a 100 hour run was successfully made.

The third stage heater is constructed of tantalum mesh, allowing for the injection of cesium upstream to obtain good mixing. The duct section is carefully constructed to minimise leakage currents, and the closed loop is divided into several sections, each of which is electrically isolated.

In the experimental run, the leakage resistances were in the range

10 - 30 kn, but unfortunately the interelectrode plasma resistance corres-ponded to about 10 kn reducting to 1 kn with preionization. It is thought

that incomplete vapourisation and ionization of the injected cesium

con-tributed to the high plasma resistance. Also, in such a small duct, the electrode voltage drop represented a large fraction of the total potential drops. No significant difference was recorded when the seed was injected, after, rather than before the third stage heater. The experimental condi-tions were a helium outlet temperature of 2000 K at a mass flow rate of

-1

12 g sec Three preionization methods were employed, namely a discharge

upstream of the MHO section, a discharge from upstream to the first

electrode pair, or applied voltages to the first six pairs of electrodes.

Theoretical Work

This is now mainly devoted to computational models of the nonequilibrium plasma behaviour. Whilst the two-dimensional code can be used to describe leakage currents, growth of electrothermal instabilities, relaxation

effects, and segmentation effects in an MHD duct, we have concentrated on

a study of a simpler geometrical configuration in order to understand fully the numerical and physical problems present.

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Two simple configurations are the continuous electrode configurations bounded by periodic boundary conditions or continuous insulator bounded by periodic boundary conditions. In this latter case, there is an equilibrium current flow parallel to the planes of the insulators and orthogonal to

the magnetic field. The equilibrium is perturbed at time t

=

0 and the

physical system is followed as an initial value problem. Results obtained include the tabulation of the critical Hall parameter for stability as a function of geometry, together with linear growth rates as a function of the Hall parameter. The evolution of the effective conductivity, Hall parameter, and fluctuation level, can also be found.

The enclosed example is for continuous insulators. In fig. I(a) the initial electron density perturbation and I(b) the corresponding perturbed current

stream function ~'

(1'

= curl(~'~)) is shown. In fig. 2(a) and 2(b), the

corresponding functions are shown 2.94 x 10-4 sec later. The initial Hall

parameter is 3 and thermal conductivity and radiation transfer are both neglected. We have clearly shown the growth of striations which seem to be independent of the form of the initial perturbation.

(25)

I I 1 1 I 1 I

1

1 1

1

l'

I

1

I

1

I I 1 1 1 1 i ( I ( NGt.P= C

NE

i I I I I I I I _I /

,

1 1 1 1 1 1 1 1

ii

1111111 1111111 111

nu,

1 11122222~222222222222222222221t[ I 1123~333333333333333333J333332tl 1 11233333333333333333333333333211 " 11233333333333333333333333333211

1

11233333333333333333333333333211 I 11233333333333333333333J33333211 1 11233333333333333J~3333333333~11 1'1123333j333333333333333333333211 I ' i1233333333333333333333333333211 I 11233333333333333333333333333211

1

llZ33333333333333333333333J332!1 1 11233333333333333333333333333211 1 1123333333333333333333333333321J 1 ,11233333333333333333333]33333211 I 11233333333333333313333333333211

r.

/ _I ~;Ji':X=':'1;-9;15E;';6~;"'-TiiJ.i';)(=-"--'/25··

/"

';,r-'7---:;,-' ----:---"--;---:----;'

Fig. I(a). Perturbed electron density at t

=

O.

1_.-4.-_ I I I i

I

i

I

_i

I

(26)

NGAP=

0 PERTUf!BED PSI

T1I-1(= O.E+Ol'

I33333333333333333J3333333Jj333j33333J3333333333~3333333333333333313 133313333]3333333333J333331333333333333333333313333J33313333331333~3 I33333]3333333333333J3]333331333333333333333333333333311333333333331 13333333333333333313J3333313333333333333331333]333333333333333~J33;1 13333J33113313333331J3~3331"l333333333J3333131J33J31J133133'JJJ1JJ3~c r3333J333333J33j33J3~333J33J33333J33333333333333333;333~3J3313~3133J 13333:133333333333333~3J3J33J3333J3333J3333333333JJ3J33333:i3333133313 13333J333333333333~3~3J333333333333333333333333333333333333333333333 13333333333333333333J333333J333333333333333333~3J33~3333333333333333 I3333333333333333333J333333J33333333333333333333J33J33333333333333l~ 1333333333333333333333333313333333331333333333331333333~33l313111J3~ 13333J33333333333333~333333333333333333333333333~33333333333333333)3 13333J33333333333333~3333333333333333333333333333 3333333313 13333333333333333333J3J3333333333333333333333333 333333333 133333333333333333333333333333333333333333333 3133311 133333333333333 333333333333333333 33331' 1333333333333 333333333333333 33333 13333333333 3333333333333 33333 133333333 3333333333 l3]' . j3333333 333333333 3333 1333333 444444 33333333 331 133333 4444444~4444 333333 2222 331 133333 444444444~444444 333333 222222222222 331 13333 4444444 444444 3333 2222222~222222 33 13333 44444 4444 3333 222222 222222 33 13333 44444 5S5~55 4444 3333 222 72272 11 1313 4444 5555~5S55 444 3333 ~2 11111 22772 l~ 13:'3 444 555r;5:,5c,5'5 ,+44 33J 222· 11111111 2??"'~-" :-;:\ ! 333 4444 55555:;'5555 4'+'+ 333 22 1111111 i 1 22" " _l:l !333 4444 55SS5:,5t_;S'5 ₄₄₄ ₃₃ ₂₂₂ _{111111li 11} _{,:;';, )} _"!l 1333 444 55555:'5555 444 333 22 1111111111 ~?22 31 13333 444 55555~SS55 444 333 22 1111111111 2227 ~! 13~33 4444 55555555 444 333 22 111111111 ??2?

:1

13~33 444 5555:'555 ~44 3333 222 111111111 2Z?22 J:I 133333 444 444 3333 221111111 ?2222 33 1333333 4444 444 33333 222 22222 1] 1~333]33 444444444444 333333 2:2 22222 lj 13333333333 33333333 22222222222 3~" 1333313333333333 3333J333333333 3331~ 133333333333333333333333333 3 3333333]333333333333333333333333J33333JJ

(27)

NGAP= 27

tiE

12223333333333332222222221iil11 111ll11111122222?2~2?2 12?2222222222222221l1111111111 Illllllllll111????22?22??222?2 12222222?11111111111 11111111l11l122~2222222222222222222 I2222.111ill 11111111222222222221.2222333222222222 1111111 11111111222?2222222!22~222222?222?22211 I i

i

11l122222,~222222?222' 2?:???;:22211111111 I lliI22222222222222~2?222~2?22??1111111 1 11.112222222233322222222222?22111111 1 111222222333333222222222211111111 1 111122223333333333222222211111 1 l1122223~33333333322222221111 1 iil122223..l3:!3J33332222211111 I lil222233333333333z2222111 1 111222333333333J3:1332?22111 1 111)22223333333333222221111 11222;:?333333333332221111 III !233~333~3333332222111 111222 1333333333332222111 111122223 1333333222221111 1111222222333 13333~?2211i 1112222233333333 132222111 1112222333333333333 12111; 11112222233333333322222 II 11J??2?2333333333332?22111 I 111???3]3]33J3}33333?22?lll 1 1111?22233333333322?2221111 I 1111222233~33J~3.IJ1;'22?ll1l I 111222'23J33333333333nt!2 I I I 1 111222233333333333222211!1 , 1111i22222333J33331?22??111 1 111122222Z33333333333322?1111 1 11111~22222?3333333332222?111 I 11)11112222222222333222222221111 I 1111122?2222?22~23332?22222222111 11111:222222;2222i~222222222222221111 II J22~?222222222222222222222111111 12222~~2222222222222222211ill11 &3332??2??2222222222111111Ii 1 111111 1111111:'222(:,,' 111111 2 22222222223 1111111111122?~2222222222? 1111111:11111222~2222~22?22222~222?~?? 1111122222222J3JJlj:lJj3J13J22222~2?2?2 04 12?22222~??2~2111111111111i 12722;:;'211111111111111 I 2,: 1 1 ' 1 1 I 1 ) 1 ! 1 ,. J i, X

=

'1.:11 4 E - C' 1

(28)

NG!',P= Z7 F'UnURBED rSI

(29)

LOSS MECHANISMS IN FARADAY-TYPE MHD GENERATORS presented by Jan Houben

Results of recent calculations concerning the influence of electrode and end losses on the performance of an MHD generator have been presented. Numerical two-dimensional calculations including the electron energy equation, the electron continuity equation, Ohm's law and the Maxwell equations are used to investigate the mentioned loss mechanisms. In the calculations, the current density is low and consequently the total heat flux vector can be neglected in comparison with the elastic losses. The method of solution is similar to Lengyel.

To compare the performance of rod electrodes in the flow with flat elec-trodes in the wall, we have started calculations for those geometries using the plasma conditions of the Eindhoven shocktube experiment. The

conclusions of these calculations are:

- Rod electrodes have a rather homogeneous current distribution along the electrodes. Whereas, flat electrodes have current concentrations near the electrode edges.

- For the flat electrode geometry, there exist along the electrode walls

layers with higher conductivity than the electrical conductivity of

the bulk region. Depending of the velocity profile near the electrode these layers disappear for rod electrodes.

- Rod type electrodes have small, shape induced, voltage drops.

By studying the end effects we have separated the effects of gradients in the magnetic induction from the influence of the absolute value of

the magnetic induction on the conductivity. Three different magnetic induction configurations near the end of the generator have been

cal-culated. An increasing, a decreasing and a constant one. The conclusions of these calculations are:

- A magnetic induction extended with constant value over a length equal to the height of the MHD generator yield the best results concerning undisturbed current pattern and end leakages.

The effects of inhomogeneou.:i rnugnet.:_c inducti)1I ilre dominant over the

(30)

TURBULENT FLOW IN AN MHD DUCT presented by Wim Merck

This contribution deals with the investigation of friction and heat losses in MHD ducts.

Considerations of the Reynolds and Hartman numbers in MHD generators show that the ratio Re/Ha always exceeds the critical value 225, which means

that the flow will be turbulent due to the high Reynolds number (> IDS).

From the available solution methods, the wellknown Prandtl mixing length theory appears to be the most promising to solve the problem of the fully developed turbulent compressible flow between the insulator walls of an

MHD duct. The main problem is the solution of the momentum equation [I]

dU

pu dX =

- 2R

(~ ~)

+

~

(T ) - a(u - u e)B

2

dX dy dy t s

and the energy equation

- u

( I )

(2)

where T

t is the turbulent shear stress, qt is the turbulent heat flux and

the last term of (2) stands for the magnetic damping of the turbulent energy.

These equations can be transformed by non-dimenzionalization, linear~zation

and discretization into finite difference equations. The matrices of the

latters can be solved by standard numerical methods after calculation of

the velocity and temperature dependent coefficients with estimated profiles, whereafter the end solutions are found iteratively.

Experiments have been performed at the 200 kW test rig of the "Max-Planck-2 Institut fur Plasmaphysik" in Garching (F.R.G.) in a duct of 2 x 3 cm cross-section under the following test

with potassium; gas temperature 1900 K;

conditions: working fluid argon

5 2

(31)

velocity, 250 - 450

m/s.

The diagnostics, developed at the Eindhoven University of Technology, exist of a tantalum pi tot tube of 1.5 mm outer-diameter and 0.5 mm inner-outer-diameter (fig. 1) and a W-Re thermocouple of 0.1 mm wirediameter and 3 mm length in a 1.8 mm thick alumina holder (fig. 2). These diagnostics enable us to obtain high spatial resolution and accurate relative measurements, necessary to determine the small differences between the profiles of aerodynamical (AO) and MHO flow.

The comparison of experiments with theory shows a good agreement for the velocity profiles, both AD (fig. 3) and MHO (fig. 4), and the

AD-temperature profiles (fig. 5). The case of MHO AD-temperature profiles shows a great discrepancy caused by the short entrance length of the MHO duct itself, which affects stronger the temperature profile. The latter cannot be regarded fully developed.

Conclusions

The theory developed enables us to calculate the velocity and temperature profiles on the fully developed MHO flow, including the friction and heat losses at the insulator walls. From these calculations it appears that the turbulent character of the flow is dominant and the increase of

friction and heat losses for the MHO case is limited to some ten percents, compared with the AD flow. Further investigation into turbulent entrance flow in MHO ducts is necessary for the near future, especially in regard with the heat losses.

Reference

[1] Merck, W.F.H., On the Fully Developed Turbulent Compressible Flow in an MHD Generator, Thesis, Eindhoven University of Technology, Eindhoven, (1971).

(32)

15

_{t.ntd ....} l°!d-copper .older suinleu ",ul j)

J-1~--.n~----~-~-. -~-~E-~

1.8

~=:==~_junction

•

E => 3 N _alumina cement

0.5

covered thermocouple

Fig. Construction detail of tantalum pitot tube.

"'1"f'I,'D!I-.~four hole alumina tube 1.4 1.2 1.0 .8 .6 A .2 0

Fig. 2 Construction detail

of thermocouple tip. ,

,

1.4 1.4 1.2 1.2 o , 0 0 0 a 0 1.0 _.'~ 1.0 Co Co 0 .8 0 0 · 0 o Ra" 0

.r::

0 ₀ )ter~\r. ,R .. _2.SxI04 ~ilm[.d.e. Rf! _ 1.1 K 106 0 .6 .6 t:. Ka .. 42.8 _ thaory 0 .1 Y/l • • -• 1te_2.lx104 theory ,Re_2.SxI04 .2 .3 Fig. 3 .4

•

::> 3 .5 .4 .2 o .1 Y/l _ thaory h" 21.'" 103 M .. ().~4 .2 .3 Fig. 4 .4 .4 .5 o .1 Yll .2 .3 Fig. 5

Fig. 3 Velocity profiles for turbulent flow.

Comparison of Nikuradse's measurements for incompressible flow with

the author's experimental results and theory for gasdynamic flow.

Fig. 4 Velocity profiles measured during one rune with Ha • 0 resp. 43.5,

compared with the calculated profile at Ha ~ 43.5.

Fig. 5 Temperature profiles measured during one run with Ha c 0 resp. 42.8,

compared with the calculated profiles at a: Ha ~ 0 and b: Ha = 42.8.

Co Co

(33)

INFORMATION ON THE CANADIAN PROGRAM ON MHD CARRIED OUT AT THE UNIVERSITY

OF TORONTO

Information obtained from Dr. S.J. Townsend

The major facility for studies in nonequilibrium MHD is a large blowdown experiment having a thermal input of up to 10 MW

th at 2200 K and 8 atm

stagnation conditions. Under contract to the University, IRD-Newcastle

is designing a 5 MW

th duct incorporating the Hall voltage insulation

techniques used with such success by the IRD and Frascati groups. A

collaboration has been established with IRS and the University of Sydney, as well as with the CNEN group at Frascati in order to exchange progresS reports and duct blueprints.

In the area of open-cycle MHD, a Canadian industrial program is being laid out by SJT Consultants Limited, directed toward the development of

a small test-bed facility rated at 60 MW h/IO MW MHD/IO MW hot-air

t e e turbine over an eight-year period.

Phase one involves the design, construction and operation of a

20 MW

th/2 MWe basic test-bed facility capable of operating with a

variety of clean fuels burned with gaseous oxygen at pressures up to 10 atm. The seed will be pollucite powder, and the carbonates, nitrades and sulphates of cesium and potassium. The facility will initially have

a 4.0 T conventional magnet to be sized interchangeable with a later

SC magent. The function of this Phase-One test bed will be primarily that of materials testing for duct and metallic air preheater component

development, and secondarily, for high enthalpy extraction and studies directed toward increasing the turbine efficiency of the duct.

The phases to follow in the program are still in the conceptual stage.

Phase 2 will involve the addition of a 4.5 T SC magnet and

high-temperature metal heat exchanger(s) to supply hot air to a small turbo-alternator and with the possibility of oxygen-enriched air

3MW

e

to the combustor. The combustor would be developed initially using air from a

ceramic pebble bed; it would operate first on a clean fuel ~ut would

(34)

Phase 3 would involve the development of a 60 MW

th combustor to operate

on a clean fuel, as well as 15 and 60 MW

th gasifying combustors to

operate on coal and preheater air.

Phase 4 would see the units combined to produce a 60 MW

th/20

bed for material development as a peaking plant. Such a unit MW

e

has test been indicated by Canadian utilities to be attractive in situations where cooling water is not adequately available at the site of large reserves of low cost coal. The conceptual design and scale of the MHD/air turbine

unit are being evolved in concert with a group of utilities. Negotiations

are proceeding for utility and Federal Government funding for the first

phase of the research program. Favorable indications have been received from a number of utilities.

(35)

Reports:

I) Dijk, J., Jeuken, M. and Maanders, E.J.

AN ANTENNA FOR A SATELLITE COMMUNICATION GROUNDSTATION (Provisional Electrical Design)

TH-Report 68-E-01, March 1968. ISBN 90 6144 001 7.

2) Veefkind, A., Blom, J.H. and Rietjens, L.H.Th.

THEORETICAL AND EXPERIMENTAL INVESTIGATION OF A NON-EQUILIBRIUM PLASMA IN AN MHD CHANNEL

TH-Report 68-E-02, March 1968. Submitted to the Symposium on a

Magnetohydro-dynamic Electrical Power Generation, Warsaw, Poland, 24-30 July, 1968. ISBN 90 6144 002 5.

3) Boom, A.J.W. van den and Melis, J.H.A.M.

A COMPARISON OF SOME·PROCESS PARAMETER ESTIMATING SCHEMES

TH-Report 68-E-03, September 1968. ISBN 90 6144 003 3.

4) Eykhoff, P., Ophey, P.J.M., Severs, J. and Oome, J.O.M.

AN ELECTROLYTIC TANK FOR INSTRUCTIONAL PURPOSES REPRESENTING THE COMPLEX-FREQUENCY PLANE

TH-Report 68-E-04, September 1968. ISBN 906144 004 I.

5) Vermij, L. and Daalder, J.E.

ENERGY BALANCE OF FUSING SILVER WIRES SURROUNDED BY AIR

TH-Report 68-E-05, November 1968. ISBN 90 6144 005 X.

6) Houben. J.W.M.A. and Massee. P.

MHD POWER CONVERSION EMPLOYING LIQUID METALS

TH-Report 69-E-06, February 1969. ISBN 90 6144 006 8.

7) Heuvel, W.M.C. van den and Kersten, W.F.J.

VOLTAGE MEASUREMENT IN CURRENT ZERO INVESTIGATIONS

8) Vermij, L.

SELECTED BIBLIOGRAPHY OF FUSES

9) Westenberg, J.Z.

SOME IDENTIFICATION SCHEMES FOR NON-LINEAR NOISY PROCESSES

TH-Report 69-E-09, December 1969. ISBN 90 6144 009 2.

10) Koop, H.E.M., Dijk, J. and Maanders, E.J. ON CONICAL HORN ANTENNAS

TH-Report 70-E-IO, February 1970. ISBN 90 6144 010 6.

II) Veefkind, A.

NON EQUILIBRIUM PHENOMENA IN A DISC-SHAPED MAGNETOHYDRODYNAMIC GENERATOR

TH-Report 70-E-II, March 1970. ISBN 90 6144 OIl 4.

12) Jansen, J.K.M., Jeuken, M.E.J. and Lambrechtse, C.W. THE SCALAR FEED

(36)

Reports:

13) Teuling, D.J.A.

ELECTRONIC IMAGE MOTION COMPENSATION IN A PORTABLE TELEVISION CAMERA TH-Report 70-E-13, 1970. ISBN 90 6144 013 O.

14) Lorencin, M.

AUTOMATIC METEOR REFLECTIONS RECORDING EQUIPMENT

TH-Report 70-E-14, November 1970. ISBN 90 6144 014 9. 15) Smets, A.J.

THE INSTRUMENTAL VARIABLE METHOD AND RELATED IDENTIFICATION SCHEMES TH-Report 70-E-15, November 1970. ISBN 90 6144 015 7.

16) White Jr., R.C.

A SURVEY OF RANDOM METHODS FOR PARAMETER OPTlMALtZATION TH-Report 70-E-16, February 1971. ISBN 90 6144 016 5. 17) Talmon, J.L.

APPROXIMATED GAUSS-MARKOV ESTIMATORS AND RELATED SCHEMES TH-Report 71-E-17, February 1971. ISBN 90 6144 017 3. 18) Kalasek, V.

MEASUREMENT OF TIME CONSTANTS ON CASCADE D.C. ARC IN NITROGEN TH-Report 71-E-18, February 1971. ISBN 90 6144 018 1.

19) Hosselet, L.M.L.F.

OZONBILDUNG MITTELS ELEKTRISCHER ENTLADUNGEN

TH-Report 71-E-19, March 1971. ISBN 90 6144 019 X. ·20) Arts, M.G.J.

ON THE INSTANTANEOUS MEASUREMENT OF BLOODFLOW BY ULTRASONIC MEANS TH-Report 71-E-20, May 1971. ISBN 90 6144 020 3.

21) Roer, Th.G. van de

NON-ISOTHERMAL ANALYSIS OF CARRIER WAVES IN A SEMICONDUCTOR TH-Report 71-E-21, August 1971. ISBN 90 6144 021 I.

22) Jeuken, P.J., Huber, C. and Mulders, C.E. SENSING INERTIAL ROTATION WITH TUNING FORKS

TH-Report 71-E-22, September 1971. ISBN 90 6144 022 X. 23) Dijk, J. and Maanders, E.J.

APERTURE BLOCKING IN CASSEGRAIN ANTENNA SYSTEMS. A REVIEW TH-Report 71-E-23, September 1971. ISBN 90 6144 023 8. 24) Kregting, J. and White Jr., R.C.

ADAPTIVE RANDOM SEARCH

TH-Report 71-E-24, October 1971. ISBN 90 6144 024 6. 25) Darnen, A.A.H. and Piceni, H.A.L.

THE MULTIPLE DIPOLE MODEL OF THE VENTRICULAR DEPOLARISATION TH-Report 71-E-25, October 1971. ISBN 90 6144 025 4.

(37)

Reports: 26)

~~~~~CAL

THEORY CONNECTING SCATTERING AND DIFFRACTION PHENOMENA, INCLUDING BRAGG-TYPE INTERFERENCES

TH-Report 71-E-26, December 1971. ISBN 90 6144 026 2. 27) Bokhoven, W.M.G. van

METHODS AND ASPECTS OF ACTIVE-RC FILTERS SYNTHESIS

TH-Report 71-E-27, 10 December 1971. ISBN 90 6144 027 O. 28) Boeschoten, F.

TWO FLUIDS MODEL REEXAMINED