The procedures and computations used to identify an MHD channel for a 540 mW(I) EFT-scale plant are presented. Under the assumed constraints of maximum E(x), E(y), J(y) and Beta; results show the best plant performance is obtained for active length, L is approximately 12 M, whereas in the initial ETF studies, L is approximately 16 M. As MHD channel length is reduced from 16 M, the channel enthalpy extraction falls off, slowly. This tends to reduce the MHD power output; however, the shorter channels result in lower heat losses to the MHD channel cooling water which allows for the incorporation of more low pressure boiler feedwater heaters into the system and an increase in steam plant efficiency. The net result of these changes is a net increase in the over all MHD/steam plant efficiency. In addition to the sensitivity of various channel parameters, the trade-offs between the level of oxygen enrichment and the electrical stress on the channel are also discussed

Smith, J. M.

Staiger, P. J.

Wang, S. Y.

English

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.fir - ate
(NASA-Tti-81764) A MHE CHANNEL STUDY FOR The
ETP CCNCIPTUAL CES.' . GN (NASA)
	 13 pliC A02/!IF A01
	 CSCL 201
981-24927
U-0cla a
G3/75 42407
DOE/NASA/10769-14
NASA TM-81764
C /lyIl/!P4
An ^AHDStud^► for the ETF
Conceptual Deal"'gn
S. Y. Wang, P. J. Stalger,
	 * ►^
and J. Marlin Smitht	
National Aeronautics and Space Administration 	 ,^l1tY +^^
r f	 Lewis Research Center	 REI^EO
MAG ^
Work performed forU.S. DEPARTMENT OF ENERGY
Fossil Energy
Office of Magnetohydrodynamics
Prepared for
Nineteenth Symposium on Engineering
Aspects of Magnetohydrodynamics
p Tullahoma, Tennessee, June 15-17, 1901
6
il
ERRATA
NASA Technical Memorandum 81784
DOE/NASA /10789-14
AN MHD STUDY F011 THE ETF CONCEPTUAL DESIGN
S. Y. Wang, P. J. Staiger, and J. Marlin Smith
June 1881
Cover and title page; The title of the report should be An MHD Channel Study for the
ETF Conceptual Design.
e
b
i.
k
DOE/NASA/1 0769-14
NASA TM-81764
An MHD Study ior the ETF
Conceptual Design
S. Y. Wang, P. J. Staiger,
and J. Marlin Smith
N tional Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135
Performed for
U.S. DEPARTMENT OF ENERGY
Fossil Energy
Office of Magnetohydrodynamics
Washington, D.C. 20545
Under Interagency Agreement DE-A101-77E1°10769
Nineteenth Symposium on Engineering
Aspects of Magnetohydrodynamics
Tullahoma, Tennessee, June 15-17, 1981
ORIG11
OF P(
AN M10 CHANNEL STUDY FOR THE ETF CONCEPTUAL DESIGN
S. V. Mang, P. J. Staiger. and J. Marlin Smith
NASA Lewis Research Center
Cleveland, Ohio 44135
Abstract
In this paper, the procedures and computation:
used to identify an MHD channel for a 540 mWT
ETF-scale plant are presented. Under the assumed
constraints of maximum Ex, t , J	 and a,
our resu;ts show the best plait performance is
obtalnvi for active Leng th. l - 12 M. whereas In
the iritiel ETF studies 1 . 2 , L - 16 M. As MID
channel length is reduced from 16 M. thu channel
enthalpy extraction falls off, slowly. This tends
to reduce the MHO power output. But the shorter
channels result in lower heat losses to the WD
channel cooling water which allows for the in^or-
poration of more low pressure boiler feedwater
heaters into the system and an increase in steam
plant eff f clenc. In addition to the sensitivity
of various channel parameters (B. K. L. Me, and
PC), thN trade-offs between the level of oxygen
enrichment and the electrical stress on :he chan-
nel are also discussed.
Background
Previous studles 3-5 have considered the
optimization of channel performance in terms of
the NO power (PMHD ) or the net power
( P NET - Pn - PCPR. where PCPR denLtes
the WD cyc a compressor power consumption).
These analyses which utilized a modified chemical
equilibrium program and a quasi-one-dimensional
channel code vv . have been extended to identify
MID channels that result in the highest overall
thermodynamic cycle efficl.nw:y of the MD/steam
plant. In addition to the normal constraints con-
sidered for determing the best channel perfor-
manc	 we have found that the variation of channele
heat loss (Qno) with channel length and the
effects of this heat loss on the thermodynamic
efficiency of the steam bottoming plant (nS^ are
important in establishing the proper genere.ot
length.
The value of QMD has a direct effect on
the value of n
	
because the channel is assumed
to be ccoled with low temperature boiler feedwater
(<290' F). The channel cooling displaces re-
generative feedwater heaters (FWH) which could
otherwise be used. For example, when L - 10 m
and Q p < 20 mW, two FWH can be used; when
L . 12 5 m and QMp . 20-36 NW, one FWH can
still be used; but when QMD > 40 mil for longer
channels, no FWH can be effectively used. Con-
sequently, the net result is that nS decreases
with increasing QMD.
Constraints and Assumptions
The channel is assumed to perform under a com-
mon set of 'imiting design constraints4:
1. Axiai electric field, Ex < Ex max - 2.5 kV/m
2. Transverse electrical field. E y < E y.max -
4.0 kV/m
3. Transverse current density, Jy < Jy.max •
10 kA/m
4. Hall parameter, a < smax - 4
This choice nr limiting values 1pgroxlmately re-
presents the current technology 	 on channel
hardware based on limited endur4r:e tests, The
electrical stresses due to too high a value of
Ex, E , or J can cause interelectrode
and/oP sidewall breakdown. If a is too high,
non-uniformities and current leakage paths within
the WD channel can be amplified and degrade the
generator performance. In the analysis, the val-
ues are maintained within the design constraint
limits by varying the B-field and load parameter
axial profiles along the channel. The channel
is operated in the Foradav mode at nearly constant
Mach number.
To obtain the channel design conditions for a
prescribed channt.l length and an assumed diffuser
pressure recovery coefficient (0.46), several
iterations are required to meet the prescribed
diffuser exit pressure. The correct conditions
are reached by adjusting either the combustor
pressure and/or the minimum load parameter
( Kmin) . This gives the performance parameters
required for the overall plant calculation; i.e..
the total WD power and the total channel heat
loss (Qwp). Also calculated are the axial pro-
files of the plasma conditions and the channel
loft. By assuming a polytroplc efficiency (0.898)
and pressure drop fraction (ap - 0.1), the cycle
compressor power consumption is calculated. Using
the specific power of the air separation unit
(204 kWh/equivalent ton of pure oxygen), the ASU
compressor power is also computed for a fixed
level of oxygen enrichment. Finally, the bottom-
ing steam cycle efficiency (nS) and the overall
thermodynamic plant efficiency (nTH) err
obtained.
Inlet Condittoos
The conditions used in these calculations are
consistent with those designated for the ETF.3
The plant is sited in Montana (elevation .
3300 ft, ambient pressure - 0.89 atm. and ambient
temperature . 42^ F). The designated fuel is
Montana Rosebud coal dried to 5 percent moisture
and the oxidant is oxygen-enriched air preheated
to 1100 * F. Ii. this study two levels of oxygen
enrichment, 30 and 35 percent by volume. were con-
sidered. The combustion gas conditions are com-
puted for an oxygen sto+chiometric ratio of 0.9,
with a combustor-nozzle heat loss of 5 percent of
the total thermal input. The seed is injected as
K2CO3 with the potassium being 1 percent of
the total mass flow rate.
Results
Using the abovementioned constraints, the pri-
mary operating parameters Bmpx, Ma, L. 0j
percent, Pc, and Kmin, as well as the axial
OF POOR Qt!iWllY
profiles of 8 and K that y ield the highest
overall performance are determined. hundreds of
calculations were performed to cover the wide
variation of these parameters in order to identify
the che^:*ls that will result in the best nTM.
Two sees of calculations were oerformed. In the
first set. the axial profile of the magnetic field
and load parameter were adjusted to keep the elec-
trical fiold. current, and hall parameter con-
straints within limit. From these calculations an
optimum B-field p•-ofile we5 selected and a pre-
liminary magnet design approximating this profile
was obtained 9. This designed B-field profile
was then flxeu for a second set of calculations.
the results are summarited in two sets of date:
thirteen "desiyynod-B" cases and eighteen 	 ixed-B"
cases, rospecfivoly.
"Designed-B" Cases (CR.guter Generated-B) :
Tioles Ito 3
To illustrate the sensitivity of the results
about the channels that yield the highest n h
(case 1-1 . four other sub-ctsr • (1-2 to 1-5) are
also tabulated for common L - .0 m and 02 . 30
percent. Both the ?c and Kmin have been
varied and the optimum conditions meeting the pre-
scribed exit pressure are shown in Fig. 1. The
highest n H (41.23 percent) occurs at Pc .
4.2 atm. For the 10 M channel, Pc cannot be
increased beyond 4.2 atm without causinq a lower-
ing of Kmin below 0.611 and this in turn will
cause Ex.max to be exceeced. Typical axial
profiles of B, Ex, E	 Jy, K. e, and
2 HD(L are 
1 plotted in A gs. 2-A (L - 10 m) and
Compering cases 1 to 3 for L - !0, 12, and
15 
in
	 30 percent-02. the 12 in channel is
found to have the highest nTM (41.37 percent),
while for 35 percent-02 (cases 4 to 6) the high-
est n
	
(41.44 percent) is found for the 10 m
channel. The variations of nTM. WIIS• and
nEN with channel length are presented in Fig. 3
for the two levels of oxygen enrichment. For
shorter channels (L < 15 m). nEN is dropping
slowly while nj
	
is increasing. The effect of
less channel heat loss results in the best nTM
at L - 12 m.
The dependence of nTM on Bmax and Ma
is shown in Fig. 4. At Bmax - 6 Tesla. the
highest performance is obtained at a Mach number
of 0.9. Lowering Bmax lowers the overall
plant efficiency and shifts the optimum Mach num-
ber to supersonic values. These results, as also
illustrated in Tables 2 and 3. indicate that the
final selection of the final configurations may
depend upon a tradeoff study between magnet cost
and system efficiency. Other factors which might
result in better performance for low B-fields are
variations in the gas stream velocity in the chan-
nel and the channel length which were not included
in this study.
The magnet sizes (b8 2 , m3T 2 ) are estimated
to be 636. 764. and 968 for L - 10. 12, and 15 in
re!pectively (02 - 30 percent); and be 508. 644.
and 782, respectively (02 . 3a percent). The
savings due to the reduction in length are thus
significant.
"Fixed-On Cases (National Magnet Laborator -0):
TWO, 4
The previous cases provided simple magnetic
field profiles designed from the channel perfor-
mance point of view. Together with the channel
loft they provided the basic requirements for a
detailed magnet design. These detaileddetiigns
wan* supplied by the National Magnet Leb 90 and
their 8-field profiles are shown in Fig. S. for
active lengths of 10. 12, and 15 in. The channel
performance was then recalculated, in terms of
nTM , using these fixed-8 profiles and oxygen
enrichment levels of 30 percent (cases 14 to 22)
and 35 percent (cases 23 to 31) by volume. The
results are given in Table 4.
The cecrease in nTM as compared to the
previous designed-B cases is within 0.32-0.85 of a
point. the small change in nTM
 is a result of
the local optimization process which is capable of
maximizing power by shifting load.
The effect cf variations in Ex.max on
WITH was also investigated and the results are
shown in Figs. 6 and 7 for 02 - 30 and 35 per-
cent, respectively. From the design point of
view, the 35 percent-02 channel is preferred
over the 30 percent-02 channel because the best
performance is obtained at lower values of
E x max . Furthermore, the Hall electrical field
doe• not reach the critical value until much later
to the channel for the higher enrichment case, as
shown in Fig. 8. This means reduced stress level
for the channel. however, a larger ASU is re-
quired for the higher level 02 caw.
Concluding Remarks
The initial design parameters (B-field, Com-
bustor Pressure, Length, Load Parameter, Mach Num-
ber, and Oxygen Enrichment) of the 540 MWT ETF
channel have been identified with respe:t to the
overall plant efficiency. The results are:
1. The basic design conditions ( Bm0x .
6 Tesla, Mp - 0.9. L - 12 m. 02 - 30-35 per-
cent by volume) yield an overall plant efficiency.
nTM - 41 percent.
2. Recalculation using the fixed-B profiles
has shown little change in nTM
 from the orig-
inal desi5ned-B channels.
3. Lower Bmax results in higher Ma for
the best performance. but results in lower nTM
for the same channel length.
4. Higher oxygen enrichment results in a
shorter channel and lower Ex.max. but requires
a larger air separation plant. Consequently, the
selection of Oz level still depends upon further
study of the air separation plant. especially on
the economy of size.
S. Results have shown that when the effect of
channel heat loss on bottom cycle efficiency is
taken into account, the best performance is ob-
tained at significantly shorter channel lengths
than were previously thought necessary. This is
primarily due to the recovery of the MHO generator
heat loss as low grade heat by the steam plant
which is an important feature considered in this
paper.
OF POOR V,fa-i Y
Nomenclatural
   
8 Magnetic field, testa (or T)
E Electric field, kVlm
J Electrical current density, kA/m2
K Faraday load parameter or factor
L Active channel length, m
Ma Mach number
02 Oxygen enrichment, percent by volume
P Electrical power, W
P Pressu ►a. stm
AP
Q
(PCP' - PC;/ tamheat toss	 n the channel, m^
p Magnet warm bore volume, m
U Velocity. km/s
a Hall parameter
n Efficiency, percent
Subscript:
ASU Air sopira.1on unit
C Combustor
CPR MHO cycle compressor
EN Enthalpy attraction
IS 1 sentropic
MAX Maximum; critical
MIN Minimum
NET Net
S Steam thereadynamic bottoming cycle
Tn Overall cycle of WO/steam dlant
X Axial
y Transverse
References
1. Avco Everett ResearcP Lob., Inc., "Einearing
Toct fat±lity Conceptual Design," Final
Report WEIFE/2814-3, February 1980.
P. 6enerel Electric Company, "IND-ETF Program Final
Reeppoort," ODE/FE/281J-4, Vol$. 1 thru 4E,
February 1981.
J. Bon w, A. Y. and 6. A. Seikel, "Engineering
Test Facility Design Pd inlQion," NASA
TM41499. DOEINASA/2674-11, 1980.
4. Pion C. C. P., Seikel, G. A., and
Smith,, J. M.. *Performance optimisation of an
Ml1D 6enerstrr with Physica i Constraints."
NASA 1!/.79112, DOE/NASA1204-7916. 1919.
S. Pion, C. C. ► .. Staiger, P. J., and
Seikel. 6. C. 4WD Performance Calculations
with G.	 Enrichment " NASA Tii-79140.
DOE/NMA12674-7914, 19;9.
6. McBride. B. J. and Gordon, S., "Computer Pro-gram for Calculation of Complex Chemical
Equilibrium Compositions. Rocket Performance.
Incident and Reflected Shocks, and
Chapman-Jouquet oetowitions." NASA SP-273.
1976, Nov.
7, Kessler. A., "open-Cycle WO Generator Channel
Development." Energy to the 21st Century;
15th Intersociety Energy Conversion
Engineering Conference, American Institute of
Aeronautics and Astronautics. Inc.. New York,
1980, Vol. 1. pp 170-176.
8. 7th International Conference WO Electrical
Power Generation Symposium, Cambridge. MA,
June 16-20, 1980, Vol. 1, Sessions 0 and E.
9. Private communication with National Magnet Lab.
MIT. Cambridge, Massachusetts, 1980.
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A MHD channel study for the ETF conceptual design

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