Liquid Metal Loop and Heat Pipe Radiator
for Space Reactor Power Systems
Jean-Michel P. Tournier
*
and Mohamed S. El-Genk
†
Institute for Space and Nuclear Power Studies, University of New Mexico,
Albuquerque, New Mexico 87131
DOI: 10.2514/1.20031
This paper presents four radiator configurations that could be stowed in the launch bay of the DELTA-IV Heavy
vehicle and have effective areas of 69.1 to 350 m
2
. The radiator for a space reactor power system with a lithium-
cooled sectored compact reactor and thermoelectric converters has an effective area of 203 m
2
and lowest specific
mass. The sectored compact reactor and thermoelectric converters system generates 114 kWe for 7–10 years. The
radiator consists of six panels, each having a forward, fixed segment and two rear, deployable segments, and rejects
heat into space using rubidium heat pipes with carbon–carbon armor and fins. The D-shaped heat pipes operate
below 50% of the prevailing sonic or capillary limit. The radiator operates at a constant pressure drop of 12 kPa and
inlet and exit temperatures of 780 and 755 K. Investigated are the effects on the radiator’s specific mass and lithium
inventory of 1) tapering and changing width of coolant channels, 2) thermal-hydraulically coupling the panel
segments in parallel, and 3) using perforated dividers between inlet- and exit-channels. The radiator with perforated
dividers has a wet specific mass of 6:82 kg=m
2
, a liquid-lithium inventory of 179.3 liters, and a stowed height of 8 m.
Nomenclature
A = surface area, or flow cross section area, m
2
C
p
= coolant specific heat capacity, J=kg K
D = equivalent diameter of flow channel, m
D
V
= diameter of heat pipe vapor space, m
d
orif
= circular orifices diameter, m
F = local radiation view factor
f = Darcy friction coefficient, f a=Re
b
H = height, height of flow channel, m
H
V
= height of D-shaped, heat pipe vapor space,
m
h
fg
= latent heat of vaporization, J=kg
h
fin
= fin average heat transfer coefficient,
W=m
2
K
h
= dimensionless, fin heat transfer coefficient
K = dimensionless pressure loss coefficient
k
fin
= fin average thermal conductivity, W=m K
L = length of radiator panel segment, m
L
cd
= heat pipe condenser length, m
L
ev
= heat pipe evaporator length, m
L
i
= section length for computing P,m
_
M
i
= crossflow rate through orifices, kg=s
M
L
= figure-of-merit, W=m
2
_ m
i
= axial mass flow rate along channel, kg=s
N = number of axial sections along radiator
segment
N
00
= orifices number density, # per m
2
n
HP
= number of heat pipes in radiator segment
Q = radiative heat rejection to space, W
th
R = radius, m
Re = flow Reynolds number, Re
L
VD=
T = temperature, K
T
fin
= average carbon–carbon fin temperature, K
T
sink
= space sink temperature, K
V = average flow velocity, m=s
W = width of coolant channel, m
W
fin
= width of carbon–carbon fin, m
= aspect ratio of D-shaped heat pipe,
H
V
=D
V
= orifices area ratio, A
orif
=HZ
= thickness, m
P = pressure drop, Pa
T = coolant temperature drop through radiator,
K
Z = length of each axial section,
Z L=N; m
" = wick volume porosity, radiative emissivity
"
o
= orifices pressure loss correction factor
fin
= thermal efficiency of carbon–carbon fin
= liquid dynamic viscosity, kg=m s
= density, kg=m
3
= Stefan–Boltzmann constant,
5:67 10
8
, W=m
2
K
4
L
= liquid surface tension, N=m
vis
= coolant viscous dissipation, W
Subscripts/Superscripts
b = coolant bulk temperature
base = base of carbon–carbon fin
C = coolant exit-channel
cd = heat pipe condenser
dis = orifices discharge
ev = heat pipe evaporator
ex = coolant at exit of radiator segment channel
fin = carbon–carbon fin
gap = liquid-return annulus in heat pipe
H = coolant inlet-channel
HP = heat pipe
in = coolant at inlet of radiator segment channel
L = liquid phase of heat pipe working fluid
liner = metallic liner/wall of heat pipe, Ti
orif = orifices in divider wall
rad = radiator panel
turb = turbulent flow
Received 12 September 2005; revision received 24 January 2006; accepted
for publication 28 January 2006. Copyright © 2006 by Copyright 2006 by M.
S. El-Genk. Published by the American Institute of Aeronautics and
Astronautics, Inc., with permission. Copies of this paper may be made for
personal or internal use, on condition that the copier pay the $10.00 per-copy
fee to the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers,
MA 01923; include the code $10.00 in correspondence with the CCC.
*
Research Assistant Professor, Chemical and Nuclear Engineering
Department, Institute for Space and Nuclear Power Studies.
†
Regents’ Professor of Chemical and Nuclear Engineering and Director,
Institute for Space and Nuclear Power Studies; (505) 277-5442; Fax: (505)
277-2814; mgenk@unm.edu.
JOURNAL OF PROPULSION AND POWER
Vol. 22, No. 5, September–October 2006
1117