Thermal Conductivity of Plastic Foams from -423° to 75°F

Abstract

Plastic foams are being used extensively in certain missile and space-vehicle designs as low-temperature insulation. Information on plastic foams has previously been reported at this conference using both guarded hot plate and cal-orimetric techniques [1–3]. This paper presents a. method for measuring the thermal conductivity of certain plastic foams over the temperature range from room temperature to -423°F. Results are given for polystyrene foam, poly-urethane foam, composite plastic structure, and Teflon sheet. The essential requirements for a measurement of this type are described in ASTM C-177. The hot plate was constructed to meet particular requirements but in general is similar to one used by Gilbo [4], Work previously reported by Gray and Gelder [2] used a similar technique without a guard ring heater. The measurements did not go below liquid-nitrogen temperature. Housing the insulation panels satisfactorily at liquid-hydrogen temperature presents a number of interesting problems which are described in the text. The thickness of all materials was ½ in. and the test panel was an 8-in. square. The details of the liquid-hydrogen cryostat and the facility for handling hydrogen are not discussed. The method was kept as simple as possible using only standard laboratory equipment. Procedures such as automatic regulation of the guard heater were not attempted.