MSR - Chapter Title
1 Radiator Materials Appendix
1.1 Summary
In the course of the radiator design, the design team considered a variety of materials for
the supports, panels and heat pipes. The team compiled the important thermo-physical
properties of materials commonly used for these purposes below.
1.2 Structural Materials
1.2.1 Non-metals
The benefits of non-metal structural materials are higher melting points and smaller
densities when compared to metal alloys. Carbon-carbon fiber materials are a new but
expanding category of materials that offer tensile strengths similar to metals with very
low density, in combination with flexibility and chemical resistance. The very high
melting points of these materials also add structural integrity and a greater margin of
safety with respect to overheating transients.
Table 1.2-1: Thermo-physical properties of non-metallic elements and compounds
that are candidates for use in a Martian or Lunar radiator as structural materials.
Graphite
Carbon-Carbon
Composite
Zirconium Carbide
Silicon Carbide
Solid Specific
Thermal
Melting
Density
Heat
Conductivity Point Emissivity
(kg/m3) (J/g K)
(W/m K)
(K)
2250
0.69
24
3800
0.9
1000
0.3
66
3650
0.9
6730
3200
0.37
0.84
21
50
3805
2200
0.4
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MSR - Chapter Title
1.2.2 Metals
The benefits of metallic structural materials include high thermal conductivities and
tensile strength; however, the low melting points pose the problem of long-term
deformation. In addition, oxidation effects at high temperatures may alter the thermal or
mechanical properties.
Table 1.2-2: Thermo-physical properties of metals and metallic compounds that are
candidates for use in a Martian or Lunar radiator as structural materials.
Solid Specific
Thermal
Melting
Density
Heat
Conductivity Point Emissivity
(kg/m3) (J/g K)
(W/m K)
(K)
Aluminum
6061-T6
Carbon Steel
Stainless Steel
Titanium
Niobium
2700
0.896
167
855-925
0.1
7872
7850
4500
8570
0.481
0.5145
0.528
0.265
51.9
12.22
17
54
1813
1643
1923
2750
0.9
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0.63
MSR - Chapter Title
1.3 Working Fluids
1.3.1 Non-metals
The non-metallic fluids are generally less reactive, less dense, and have lower melting
points than the metals; however, their thermal conductivities are also significantly lower.
The low melting points will make it easier to thaw out the radiator components at startup
and decrease the chance of solid blockages occurring. Because of the low boiling points
of non-metallic fluids, radiator piping may require extremely high pressures to force
fluids to remain liquid as they enter an evaporator section. High pressures necessitate
ticker walls on radiator piping and increase the chance of major leakage from the system.
The gases listed are attractive because of their very low masses and reasonable heat
capacities. However, the low density would require high pressures and high flow rates. A
system of pumps would be required to maintain high flow rates, which introduces a major
source of failures and significant power consumption. The Freon derivatives listed here
make up only a partial list of the possible chlorofluorocarbon radiator fluids; however,
environmental regulations may make most of these alternatives impractical.
Table 1.3-1: Thermo-physical properties of non-metallic elements and compounds
that are candidates for use as the working fluid in a Martian or Lunar radiator.
Liquid
Gas
Specific
Thermal
Melting Boiling
Density Density
Heat
Conductivity Point
Point
(kg/m3) (kg/m3) (J/g K)
(W/m K)
(K)
(K)
682
0.86
1.673
0.0221
195
239.5
Ammonia
1032
2.814
0.657
0.0146
194.5
194.5
CO2
1486
6.25
0.54
0.0094
115
243
Freon-12
1526
6.94
0.494
0.0123
84
192
Freon-13
1413
4.706
0.561
116
232
Freon-22
1431
4.57
117.9
191
Freon-23
124.96
16.9
5.193
0.1426
0.8
4
Helium
808.6
4.614
0.742
0.024
63
77.1
Nitrogen
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MSR - Chapter Title
1.3.2 Metals
The metallic fluids’ main benefits are high thermal conductivities and boiling points,
which make them ideal for a low pressure natural flow system. However they are also
much denser, thus heavier, and more chemically reactive than other substances under
consideration. Increased densities may offer an advantage, however, when considering
structural failures since the fissure needed to leak material is much greater than for a light
gas such as helium.
Researchers have done a large amount of research and development with these materials
geared towards high-temperature heat transfer and space radiators. For instance, lithium
is a common working fluid in terrestrial and space heat pipes because it offers a low
density and high specific heat, although its melting point may be too high to ensure full
melting in the current application.
Table 1.3-2: Thermo-physical properties of metals and metallic compounds that are
candidates for use as the working fluid in a Martian or Lunar radiator.
Solid
Density
(kg/m3)
LeadBismuth
Eutectic
Lithium
Potassium
Sodium
Liquid
Density
(kg/m3)
Gas
Density
(kg/m3)
10500
530
860
970
512
680
927
457
600
711
Specific
Heat
(J/g K)
Thermal
Conduct
ivity
(W/m K)
Melting
Point
(K)
Boiling
Point
(K)
0.15
12
397
1943
3.305
0.757
1.225
71.2
99.2
135
453
337
371
1615
1032
1156
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Heat of
Vaporizat
ion
(kJ/kg)
22730
1985
3874
MSR - Chapter Title
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