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Radiator Materials Appendix

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.

2 Structural Materials

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.

| |Solid Density |Specific Heat |Thermal Conductivity |Melting Point |Emissivity |

| |(kg/m3) |(J/g K) |(W/m K) |(K) | |

|Graphite |2250 |0.69 |24 |3800 |0.9 |

|Carbon-Carbon Composite |1000 |0.3 |66 |3650 |0.9 |

|Zirconium Carbide |6730 |0.37 |21 |3805 |0.4 |

|Silicon Carbide |3200 |0.84 |50 |2200 | |

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 Density |Specific Heat |Thermal Conductivity |Melting Point |Emissivity |

| |(kg/m3) |(J/g K) |(W/m K) |(K) | |

|Aluminum 6061-T6 |2700 |0.896 |167 |855-925 |0.1 |

|Carbon Steel |7872 |0.481 |51.9 |1813 |0.9 |

|Stainless Steel |7850 |0.5145 |12.22 |1643 | |

|Titanium |4500 |0.528 |17 |1923 |0.63 |

|Niobium |8570 |0.265 |54 |2750 | |

3 Working Fluids

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 Density (kg/m3) |Gas Density (kg/m3) |Specific Heat (J/g K) |Thermal Conductivity (W/m K) |Melting Point (K) |Boiling Point (K) | |Ammonia |682 |0.86 |1.673 |0.0221 |195 |239.5 | |CO2 |1032 |2.814 |0.657 |0.0146 |194.5 |194.5 | |Freon-12 |1486 |6.25 |0.54 |0.0094 |115 |243 | |Freon-13 |1526 |6.94 |0.494 |0.0123 |84 |192 | |Freon-22 |1413 |4.706 |0.561 | |116 |232 | |Freon-23 |1431 |4.57 | | |117.9 |191 | |Helium |124.96 |16.9 |5.193 |0.1426 |0.8 |4 | |Nitrogen |808.6 |4.614 |0.742 |0.024 |63 |77.1 | |

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) |Liquid Density (kg/m3) |Gas Density (kg/m3) |Specific Heat (J/g K) |Thermal Conductivity (W/m K) |Melting Point (K) |Boiling Point (K) |Heat of Vaporization (kJ/kg) | |Lead-Bismuth Eutectic |10500 | | |0.15 |12 |397 |1943 | | |Lithium |530 |512 |457 |3.305 |71.2 |453 |1615 |22730 | |Potassium |860 |680 |600 |0.757 |99.2 |337 |1032 |1985 | |Sodium |970 |927 |711 |1.225 |135 |371 |1156 |3874 | |

References

1] Air Liquide. (2004). “Gas Data,” Air Liquide (Online).

2] Air Liquide. (2004). “Material Safety Data Sheets,” Air Liquide (Online).

3] Bauccio, Michael. (1994). ASM Engineered Materials Reference Book, 2nd ed. ASM International, Materials Park, OH.

4] Boyer, H.E. and Gall, T.L. (Eds.). (1985). Metals Handbook. American Society for Metals, Materials Park, OH.

5] Giancoli, Douglas C. (1989). Physics for Scientists and Engineers with Modern Physics, 2nd ed. Prentice Hall Publishers, Englewood Cliffs, NJ.

6] Handbook of Chemistry and Physics, 84th ed. CRC Press LLC, 2004.

7] Ho, C.Y. and Holt, J.M. (Eds.). (1996). Structural Alloys Handbook, 1996 ed. CINDAS / Purdue University, West Lafayette, IN.

8] Indium Corporation of America. (2004). “Table of Specialty Alloys and Solders,” Indium Corporation of America (Online).

9] Metal Handbook Volume 2- Properties and Selection: Nonferrous Alloys and Special Purpose Materials, 10th ed. ASM International, 1990.

10] Metals Handbook Desk Edition, (1998) Second Edition, ASM International. ASM Handbooks Online. (Online).

11] Morita, K., Maschek W., Flad M., Tobita Y., Yamano H. (2004). “Thermophysical Properties of Lead-Bismuth Eutectic Alloy for Use in Reactor Safety Analysis,” Meeting of NEA Nuclear Science Committee Working Group on LBE Technology of the WPFC. NEA Headquarters, Issy-les-Moulineaux, France.

12] N. Mukherjee, N., Sinha, I.K. (1996). “Thermal Shocks in Composite Plates: a Coupled Thermoelastic Finite Element Analysis,” Composite Structures 34.

13] Nayer, Alok. (1997). The Metals Databook. McGraw-Hill, New York.

14] Physical Constants of Inorganic Compounds. (2004). Handbook of Chemistry and Physics, 84th ed. CRC Press LLC.

15] Ross, Robert R. (1992). Metallic Materials Specification Handbook, 4th ed. Chapman and Hall, London.

16] SAE Ferrous Materials Standards Manual, 1999 ed. HS-30, Society of Automotive Engineers, Inc., Warrendale, PA, 1999.

17] Suzuki, T., Chen X., Rineiski, A., Maschek, W. (2003). “Analyses of Unprotected Transients in the Lead/Bismuth-Cooled Accelerator Driven System PDS-XADS,” Proceedings of Global 2003: 2003 ANS/ENS International Winter Meeting. New Orleans, LA.

18] Thermal and Physical Properties of Pure Metals. (2004). Handbook of Chemistry and Physics, 84th ed. CRC Press LLC.

19] Winkler, E.M. (1975). Stone: Properties, Durability in Man’s Environment, 2nd ed. Springer-Verlay, New York.

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