1 Radiator Materials Appendix1.1 Summary1.2 Structural Materials1.2.1 Non-metals1.2.2 Metals1.3 Working Fluids1.3.1 Non-metals1.3.2 MetalsMSR - Chapter Title1 Radiator Materials Appendix1.1 SummaryIn the course of the radiator design, the design team considered a variety of materials forthe supports, panels and heat pipes. The team compiled the important thermo-physicalproperties of materials commonly used for these purposes below.1.2 Structural Materials 1.2.1 Non-metalsThe benefits of non-metal structural materials are higher melting points and smallerdensities when compared to metal alloys. Carbon-carbon fiber materials are a new butexpanding category of materials that offer tensile strengths similar to metals with verylow density, in combination with flexibility and chemical resistance. The very highmelting points of these materials also add structural integrity and a greater margin ofsafety with respect to overheating transients.Table Structural Materials -1: Thermo-physical properties of non-metallic elementsand compounds that are candidates for use in a Martian or Lunar radiator as structuralmaterials.SolidDensity(kg/m3)SpecificHeat(J/g K)ThermalConductivity(W/m K)MeltingPoint(K)EmissivityGraphite 2250 0.69 24 3800 0.9Carbon-Carbon Composite1000 0.3 66 3650 0.9Zirconium Carbide 6730 0.37 21 3805 0.4Silicon Carbide 3200 0.84 50 2200- 1 -MSR - Chapter Title1.2.2 MetalsThe benefits of metallic structural materials include high thermal conductivities andtensile strength; however, the low melting points pose the problem of long-termdeformation. In addition, oxidation effects at high temperatures may alter the thermal ormechanical properties.Table Structural Materials -2: Thermo-physical properties of metals and metalliccompounds that are candidates for use in a Martian or Lunar radiator as structuralmaterials.SolidDensity(kg/m3)SpecificHeat(J/g K)ThermalConductivity(W/m K)MeltingPoint(K)EmissivityAluminum 6061-T62700 0.896 167 855-925 0.1Carbon Steel 7872 0.481 51.9 1813 0.9Stainless Steel 7850 0.5145 12.22 1643Titanium 4500 0.528 17 1923 0.63Niobium 8570 0.265 54 2750 - 2 -MSR - Chapter Title1.3 Working Fluids 1.3.1 Non-metalsThe non-metallic fluids are generally less reactive, less dense, and have lower meltingpoints 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 startupand decrease the chance of solid blockages occurring. Because of the low boiling pointsof non-metallic fluids, radiator piping may require extremely high pressures to forcefluids to remain liquid as they enter an evaporator section. High pressures necessitateticker 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 heatcapacities. However, the low density would require high pressures and high flow rates. Asystem of pumps would be required to maintain high flow rates, which introduces a majorsource of failures and significant power consumption. The Freon derivatives listed heremake up only a partial list of the possible chlorofluorocarbon radiator fluids; however,environmental regulations may make most of these alternatives impractical.Table Working Fluids -3: Thermo-physical properties of non-metallic elements andcompounds that are candidates for use as the working fluid in a Martian or Lunarradiator.LiquidDensity(kg/m3)GasDensity(kg/m3)SpecificHeat(J/g K)ThermalConductivity(W/m K)MeltingPoint(K)BoilingPoint(K)Ammonia 682 0.86 1.673 0.0221 195 239.5CO2 1032 2.814 0.657 0.0146 194.5 194.5Freon-12 1486 6.25 0.54 0.0094 115 243Freon-13 1526 6.94 0.494 0.0123 84 192Freon-22 1413 4.706 0.561 116 232Freon-23 1431 4.57 117.9 191Helium 124.96 16.9 5.193 0.1426 0.8 4Nitrogen 808.6 4.614 0.742 0.024 63 77.1- 3 -MSR - Chapter Title1.3.2 MetalsThe 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 alsomuch denser, thus heavier, and more chemically reactive than other substances underconsideration. Increased densities may offer an advantage, however, when consideringstructural failures since the fissure needed to leak material is much greater than for a lightgas such as helium.Researchers have done a large amount of research and development with these materialsgeared towards high-temperature heat transfer and space radiators. For instance, lithiumis a common working fluid in terrestrial and space heat pipes because it offers a lowdensity and high specific heat, although its melting point may be too high to ensure fullmelting in the current application.Table Working Fluids -4: Thermo-physical properties of metals and metalliccompounds that are candidates for use as the working fluid in a Martian or Lunarradiator.SolidDensity(kg/m3)LiquidDensity(kg/m3)GasDensity(kg/m3)SpecificHeat(J/g K)ThermalConductivity(W/m K)MeltingPoint(K)BoilingPoint(K)Heat ofVaporization(kJ/kg)Lead-Bismuth Eutectic10500 0.15 12 397 1943Lithium 530 512 457 3.305 71.2 453 1615 22730Potassium 860 680 600 0.757 99.2 337 1032 1985Sodium 970 927 711 1.225 135 371 1156 3874- 4 -MSR - Chapter TitleReferences[1] Air Liquide. (2004). “Gas Data,” Air Liquide (Online). http://www.airliquide.com/en/business/products/gases/gasdata/index.asp[2] Air Liquide. 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