An Apparatus for Thermal Conductivity at Cryogenic Temperatures Using a Heat Flow Meter

This paper describes a heat-flow-meter apparatus capable of rapidly measuring thermal conductivity of flat insulation specimens under cryogenic temperatures. It has been used successfully with various types of insulations, including rigid and flexible fibrous glass or mineral fiber materials, rigid and flexible foamed insulations, loose-fill granular or powder specimens, and the super insulations. A single 12 by 12-in. test specimen is sandwiched between a copper plate cooled by liquid nitrogen and a heat flow meter maintained near the 80 F ambient. The apparatus is built into a standard vacuum bell jar to allow for testing in controlled atmospheres or under high vacuum. Calibration of the heat flow meter is accomplished using specimens whose conductivities at elevated mean temperatures are accurately known from guarded-hot-plate measurements. The validity of the calibration assumption is borne out by apparent good agreement between data from this apparatus and published data on similar materials from other types of equipment. The simplicity of its construction and rapidity of operation recommend this type of apparatus to anyone contemplating such measurements.