Accurate thermal performance information, including effective thermal conductivity data, are needed as a result of advances in polymers and composites, along with growing industrial needs in below ambient temperature applications.
NASA Kennedy developed a method for measuring thermal performance of materials at below ambient temperatures or those subjected to a large temperature difference. The technology uses liquid nitrogen as a direct heat energy meter and is applicable to testing at a wide range of temperatures from 373 K down to 77 K and under an ambient pressure environment.
The Macroflash follows the guidelines of technical standard ASTM C1774 (Annex A4) and provides a cost-effective, field-representative methodology to test any material for below ambient temperature applications. From engineered systems to research testing to quality control in manufacturing, the technology provides utility for the fields of energy, transportation, construction, and environment.
The Macroflash can test solids, foams, or powders that are homogeneous or layered in composition. Test specimens are typically 75 mm in diameter and 6 mm in thickness. The cold side is maintained by liquid nitrogen at 77 K while a heater disk maintains a steady warm-side temperature from ambient up to 373 K. The steady boiloff of the liquid nitrogen provides a direct measure of the heat energy transferred through the thickness of the test specimen.
Nitrogen or other gas is supplied to the instrument to establish a stable, moisture-free, ambient pressure environment. Different compression loading levels can also be conveniently applied to the test specimen as needed for accurate, field-representative thermal performance data. The Macroflash is calibrated from approximately 10 mW/m-K to 800 mW/m-K using well-characterized materials.