search.jsp?r=20120003152 2019-08-24t20:08:47+00:00z · should be able to maintain the molten phase...

https://ntrs.nasa.gov/search.jsp?R=20120003152 2020-01-02T05:21:29+00:00Z

BACKGROUND

• The maturation of Molten Regolith Electrolysis (MRE) as a viable technology foroxygen and metals production on explored planets relies on the realization of theself-heating mode for the reactor.

• Joule heat generated during regolith electrolysis creates thermal energy thatshould be able to maintain the molten phase (similar to electrolytic Hall-Heroultprocess for aluminum production).

• Self-heating via Joule heating offers many advantages:• The regolith itself is the crucible material -7 protects the vessel walls• Simplifies the engineering of the reactor• Reduces power consumption (no external heating)• Extends the longevity of the reactor

• Predictive modeling is a tool chosen to perform dimensional analysis of a selfheating reactor:

• Multiphysics modeling (COMSOL) was selected for Joule heat generationand heat transfer

• Objective is to identify critical dimensions for first reactor prototype

January 12, 2012 50th Aerospace Sciences MeetingPg.2

Lab Scale Cell for Molten Regolith Electrolysis

Self-heating Hall-Heroult reactor {Aluminum}

Crust2 0 2- +C ~ CO2 + 4 e

January 12, 2012

L .J

Anode

50th Aerospace Sciences Meeting

carbon

molten fluoride+

AI20

Pg.4

Self-heating Molten Regolith ElectrolysisPMtr'Ie(Ing ToE~ the FutUfe

liquidcathode

frozenelectrolyte

~xygengast-----l bubbles

anode

currentfeed

metal pool

molten oxide electrolyte

point feeders breakcrust and introduce

metal oxide here \-::.----1

cellsidewall ---1__

collector bar

cell floor

8IIIIct

January 12, 2012 50th Aerospace Sciences MeetingPg. 5

In-Re olith Conce t for Lunar Electrowinnin

Electrowinning

eAnode


PMtrt«1ng ToE~ tM FUll,Jrr

Self-heating Molten Regolith Electrolysis

REACTOR MODEL

January 12, 2012

Vessel

Anodelead

Cathodecollector

50th Aerospace Sciences MeetingPg. 7

~--.-----.-~.y

=position vector=direction vector=variable for control angle direction= scattering phase function= adsorption coefficient=scattering coefficient= radiative intensity at r position and s direction= black body intensity= incident radiation within the participatingmedia

x

sr0'et>k.asI(r, s)IbG

p = densityCp = heat capacityk = thermal conductivityo = electrical

conductivityT = temperatureJ = current density

The radiation direction vector s isdefined in terms of two angles aand f3

This equation needs to be integrated over the spatial as well asthe angular domain. Spatial discretization is done by dividingspatial domain into discrete control volumes or cells. The angulardiscretization is done using control angles.

Radiative Intensity for gray & isotropicmedium

VI{r,s)=kalb(r)-(ka+aJI{r,s)+ as r41< I{r,s')P(s',s~'

T+~ 4nJo~--

change in emission absorption scatteringradiativeintensity

Heat Transfer Modeling

Jouleheating

~

General Energy Equation forsolids

Boundary Conditions

• Radiative heat transfer between outersurfaces and ambient.

• Radiative heat transfer between outersurfaces

• Free convective heat transfer with ambient• Constant voltage at the top of anode lead• Electrical ground at the top Of cathode

collector• Thermal insulation at the outer bottom of the

cell• All surfaces electrically insulated

pC aT -V.(kVr)=QP at

HeatSources

Q= Q1J+2'~h:~a~ ~d~a:o:i:P~~c:~in~--:media . I

IIIIIIII

: G = :2I(r,s)L__ (, )

Qr =ka\G-4oT4


Thermophysical Properties of regolith'¥tI't«ing To Eng~ the Future

I ~

r4 0 8 0 1200 f1' 1110............

I ...I ......I~ -. -- ..... ,

.........'"I

10.0~E~~

1.0'$

'n::l'tlc:0Uiii 0.1E.,.c:t:.Cl0....

0.0

• FJS·1

TemperatLl'e (el

• Synthetic Apollo 11

Thermal Conductivity

Fitting

o

10.0000

"" ,,"E~ 1.0000

~ 3 0 600 900 rnO'$

0.1000 ....'t; ,,,....:::l'tll:

0.0100 ...0uiiiu'I: 0.0010Q.,!B.

0.0001Cl0...

0.0000Temperature (e)

• Tholeiitic basalt • lunar sample 12002.85

Electrical conductivity

Fitting

--- --........... '" -......

--'-'?,,

• FJS·1 - - Fitting

TemperatLl'tl (C)

1,150

_ 1,100~

tb 1,050~

:i'1,OOO

~ 950'u! 900«lu 85016Cl 800:I:

750

700

o 300 600 900 1200 1500 1800

3000 .----.--~--.,----,---.---,

2800 +----+---+---+---+---t~£-.M

< 2600 +---+---f----+---+~~+_-___j.[~' 2400 +---+--__jf----60,,£,.-+--+_-___j-~ 2200 +---+--~~~-+---+--+_-___j

'0~ 2000 +--~~-+---+--+_--+----I

C 1800 ~--+--_+--+---+--__+-__j

1600 +---1---+---+----+----+---1300 550 800 1050 1300 1550 1800

Temperature (C)

Heat Capacity

January 12, 2012

Density

50th Aerospace Sciences MeetingPg,9

Optical Absorption

Absorption coefficient

1Dl-r---------------,

r---..

" ..........-- ............II' I

""""li"'-- I

Lunar glassy spherules obtained fromlunar dust brought to earth by Apollo 14. .mission

450 500 550 600 650 700Wavelenght(nm)

_0: ~o mlaometer-s _0: l~O mlaometer-s

Commercial glass (clear andgray) and bronze

750 800

_ 35000

.€. 30000M

:; 25000c.~ 20000u

~ 150008 10000g 5000~ 0(;)~ 400«


JOULE HEATING PERFORMANCE WITHOUT PREHEATING

Initial temperature: 25°C

Potential (Volts) Heat dissipation (W/m3) Temperature (OC)

1

.. -

"70

o.:nnJlC1O~

..2.584 _

..38.

25.,,»


JOULE HEATING PERFORMANCE WITH PREHEATING

Preheating temperature: 1,700 °C

Potential (Volts) Heat dissipation (W/m3) Temperature (OC)

.. 6 •

o"J~-'

-4xES •

7

-7xE8 '

..

126

1,1n

.. -

74

1,888 _

357 -


'MtnMng To Ent}inHr the Futl¥e

RELEVANCE OF THERMAL RADIATION WITHIN PARTICIPATING MEDIA

Temperature (OC) Molten Phase

200

50 100

50

-0Q)

13Q)

0)Q)

z

-......I

EaaT"""

II.:::£"'-'

Applied Voltage: 34 V at the anode lead that yields 15 V at the molten phase.


RADIATION HEAT SOURCE WITHIN PARTICIPATING MEDIApMUtt!f1ng ToE~ the Funxr

Absorption yields (W/m3)...

o 'If'

-u

Total yield (W/m3)

+5. E ...•-02

-0.•

-06

-01

-1

-1.2

/'0

-u

-1.5E.x

-0.2 -0.2 6 • -1_517lXIOf

-

+

Applied Voltage: 34 V at the anode lead thatyields 15 V at the molten phase.

-0.2 ":.0, o ·...

January 12, 2012

Emission yields (W/m3)

50th Aerospace Sciences MeetingPg. 14

OPTICAL ABSORPTION EFFECT ON MOLTEN PHASE FORMATION

k = 0 m-1

k = 100 m-1

k =300 m-1

Applied Voltage: 34 V at the anode lead that yields 15 V at the molten phase.


MODEL VALIDATION

1"· -; -I'

: ""'I" .

I

Temperature profile of irradiated JSC-1Amelts predicted by the model usingOrbitec experimental conditions.

Solidified half-sphereproduced by focused solarbeam (Orbitec/PSI Corp.)


Regolith Temperature profile under a flatanode at 34 V.Max. melt temperature: 1,437 °C

EFFECT OF ANODE GEOMETRY

Regolith Temperature profile undera waffle anode at 34 VMax. melt temperature: 1,437 °C


CONCLUSIONS,.~ To Ef'ttJirt«t me Fut.urf!

• The modeling of all modes of heat transfer within a self-heating MoltenRegolith Electrolysis reactor can be useful tool to investigate the parametersdriving its design..

• The heat transfer modeling performed so far confirms the feasibility of selfheating MRE reactors for electrolytic reduction of lunar oxides from their ownmelt.

• It also confirms that another technique is required to achieve the formation ofthe melt from the regolith at ambient conditions before activating theelectrolysis and the self-heat mode.

• The combination of high surface area geometries for anodes, distributedelectrical connections and adjustments of inter-electrode gaps were found tohave strong effects on the overall power efficiency performance and thermalperformance of Joule-heated MRE reactors for electrolytic reduction of lunaroxides from their own melt. Preliminary findings suggest that the minimumcritical size of such reactor may be on the order of a cubic foot in volume with apower requirement of less than 5 kW.

• The engineering of prototype reactors designed to process regolith in space atmelting temperatures will require the knowledge of these and otherfundamental properties of the various mineral resources


Acknowledgements

The authors wish to thank the ISRU Project within NASA ExplorationTechnology Development Program for funding this effort and NASAKennedy Space.Center.

QUESTIONS?


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