A 30-tesla magnet design is studied which calls for forced convection liquid neon heat transfer in small coolant channels. The design also requires suppressing boiling by subjecting the fluid to high pressures through use of magnet coils enclosed in a pressure vessel which is maintained at the critical pressure of liquid neon. This high pressure reduces the possibility of the system flow instabilities which may occur at low pressures. The forced convection heat transfer data presented were obtained by using a blowdown technique to force the fluid to flow vertically through a resistance heated, instrumented tube

Hendricks, R. C.

Papell, S. S.

English

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NASA TECHNICAL
	
NASA TM X-71712
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LIQUID NEON HEAT TRANSFER AS APPLIED
TO A 30 TESLA CRYOMAGNET
1411-76'! ^by S. S. Papell and R. C. Hendricks 	
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Cleveland, Ohio 44135
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ogenic Engineering Conference	 ^FCZ
Kingston, Ontario, July 22-25, 1975
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LIQUID NEON HEAT TRANSFER AS APPLIED
TO A 30 TESLA CRXOMAGNET
by S. S.. Papell and R. C Hendricks
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio
INTRODUCTION
Superconducting magnets cooled by liquid helium are limited to
magnetic fields of about 18 teslas. When higher fields are required for
research into solid-state physics, other types of magnets must be used.
The Lewis Research Center now has a liquid neon cooled 20 tesla nlag-
net system, Refs. 1 and 2, that is being upgraded to reach steady-state
fields of 30 teslas. This advance in magnet technology requires a new
i:oil design and a change in the technique used for the cooling.
The 20 tesla magnet, cooled by natural convection pool boiling,
had relatively large coolant passages (width = 0 762 cm, depth = 0. 15 cm)
to permit the vapor to escape through the coil windings. The magnetic
field was heat transfer limited by the maximum heat flux that could be
removed by pool boiling. The large size of the coolant channels also
limited the total current density that could be achieved in the coil
windings,
The 30 tesla magnet design calls for forced convection liquid neon
heat transfer in small coolant channels (width = 0 445 cm, depth =
0. 038 cm). Since these channels are too small to handle the vapor flow
if the coolant were to boil, the design philosophy calls for suppressing
boiling by subjecting the fluid to high pressures. The magnet coils
will, therefore, be enclosed in a pressure vessel (fig. 1) maintained
at about 27 barn which is the critical pressure of liquid neon. The high
pressure on the liquid will also reduce the possibility of the occurrence
of system flow instabilities that are more prevalent at low pressures.
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2The experimental program reported herein was initiated to support
the design study for the 30 tesla magnet because liquid neon forced con-
vection heat transfer data are not available In fact, very little neon
heat transfer data have been obtained and they are for the boiling re-
gime
The forced convection peat transfer data presented herein were ob-
tained by using a blowdown technique to force the fluid to flow vertically
through a resistance heated, instrumented tube
Apparatus and Operations
The joule heated inconel test section shown in Fig. 2 is 12.7 cm
long by 0. 198 cm I D. and 0. 256 cm O. D. , with a resistance of approx-
imately 0. C63 ohms. An a, c power supply provided up to 3 volts
across the test section, for a, maximum heat flux of 16 5 watt/cm2.
The 40 gage Chromel-Constantan thermocouples located at 2. 54 0 4.88,
7. 23, and 10 8 cm from the lower heater flange (with lead wires
wrapped around the test section) were referenced to the fluid tempera-
ture in the inlet mixing chamber. Platinum resistance thermometers
measured the inlet and outlet temperatures, and mixing chamber pres-
sure taps provided for pressure measurements
The flow rate was determined by using an orifice in conjunction with
measurements of local temperature and pressure near the bottom of the
liquid neon dewar.
Before using any of the liquid cryogens shown in Fig. 2, we took
gaseous heat transfer data and compared it with heat transfer predic-
tions frum the Dittus-Boelter equation. When these results were within
t10 percent of the Dittus-Boelter equation, the system was considered
operational. Prior to the initial transfer of liquid neon, the system,
including the radiation shield, was precooled to approximately 25 K
using liquid helium This minimized the neon boiloff losses during the
initial transfer The pressurizing gas, either helium or neon, was
precooled to approximately 80 K to reduce fluid heating.
`y
.,' 19
3The flow rates and desired pressure level were set using a com-
bination of the flow control valve and the pressure control valve,
Fig 2. These two valves in close proximity to the test section provide
stable operation of the flow system.
Although the system vacuum often rose to 300 millitorr, the tem-
perature difference between the test section and the radiation shield
was always less than ±10 K, thus assuring minimal heat gain from ex-
ternal sources. Extraneous heat leaks make the attainment of good
heat transfer data at low temperatures and small temperature differences
difficult to achieve
Data and Results
Liquid neon forced convection heat transfer data were obtained at
inlet temperatures between 28 to 34 W and system pressures between
28 to 29 bars. Fluid velocity was varied between 250 to 800 cm/sec
and heat fluxes varied from 7. 5 to 16. 5 w/cm2
The data are shown on Fig. 3 in the conventional manner, i.e. ,
Nusselt/(Prandtl)0 4 as a function of Reynolds number. The experi-
mental data show reasonably good agreement with the Dittus-Boelter
equation represented by the solid line. *
The amount of data scatter is modest considering the small (OT)
existing between the tube wall and the bulk fluid. It should be em-
phasized that the data correlation is limited to a very narrow range of
test conditions because these tests were designed to simulate the heat
transfer characteristics in the coolant channels of the proposed
30 tesla cryomagnet. These results , can, therefore, be applied directly
to the design of the magnet system. Pool boiling heat transfer data
already in the literature (ref. 3) will be used to design the heat ex-
changers (fig, 1) required to transfer the heat from the coolant loop to
the liquid neon reservoir.
*The small differences between the data obtained by pressurizing
with helium or neon gas have not been resolved.
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4
References
1. G. V. Brown and W. D Coles, 'High-Field Liquid-Neon-Cooled
Electromagnets, " in Advances in Cryogenic Engineering, Vol. II,
Plenum Press, New York (1966), p. 6W8.
2. J. C Laurence; "High-Field Electromagnets at NASA Lewis Research
Center," NASA Tech, Note TN D-4910 (November 1968).
3. J. M. Astruc and P. Perroud, "Etude des 4changes thermiques dans
lesfluides cryogeniques," Centre d'Etudes de/'Energie Nucleaire,
Grenoble, France, No 132 (December 1968).
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-NEON INUT
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—NEON TO HEAT EXCHANGER
Figure 1. - Conceptual design of 30 tesla liquid neon cooled magnet. (Entire syst• m Immersed in cryos'at. )
ORIGINAL YAtIVi IIS
OF NUt)l.t QUALM
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0POIIT-
TQI I T --
OUTLET MIXING
CHAM"'
FORCED CONVECTION
COOLED COPPER
RADIATION SHIELD
PRESSURt
CONTROL
VALVE7
110 A, C a	 +
P
IN—
INLET TIN_
	
VENT	 MIXING
	
1
CHAMBER —
INSTRUMENTED
TEST SECTION
VA(-"IJM PUMPS
VENT
-T4RMOCOl1PlE
REFERENCE
1 UNCTION
THREE-WAY	 LHe^—
	 /-THREE
UVLNI	 HftlVUl^
el	 GNe
G He
—	 . Ne	 GN2	 GHe
LNe	 =
(4 LITERS)
r	 `1300 LITERS I150 LITERS) LIQUID	 '(150 LITERS) LN	 0 LITERS)	 LIQUID HEL IUM\
	
NEON TRANSFER DEWAR ,
 HEATEXCHANG?	
120
R,' LIQUID NITROGEN-'
GAS PRECOOLER^	 RADIATIOONNSHIELDAND SYSTEM
PRECOOL
Figure 2. - Schematic - liquid neon heat transfer facility. 	 CD-IIBW34
FLOW 1
CONTROL
VALVE
P TANK—
T TANK —
I	 FLOW ORIFICE
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PRESSURE
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Figure 3. - Liquid neon= 29 bars.
NASA-Lewl,


Liquid neon heat transfer as applied to a 30 tesla cryomagnet

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