Measurement of thermal conductivity
Microtherm obtains thermal conductivity measurements by two different test procedures:
1. Guarded Hot Plate equipment complying with ISO 8302 and ASTM C 177 standards is used for all of our published data.
This produces precise data over a wide temperature range (up to a mean value of 800°C / 1472 °F). Two flat panels are tested and when steady state conditions are reached heat flow is measured between a heated test square and water cooled outer plates. This method is recognized as the most accurate for the measurement of thermal conductivity of high temperature insulation materials. Although we have our own guarded hot plate equipment, all Microtherm® published TC data are produced for us by the National Physical Laboratory in the UK using this measurement technique.
2. Microtherm also uses in-house testing facilities of their own specialized design.
This testing equipment is based on a cylindrical geometry with a central heat source. It is used for routine quality control and product development. The cylindrical test cells also make this equipment particularly suitable for measurements of thermal conductivity at pressures greater than atmospheric, and in gases other than air.
Another measurement technique that is sometimes used for thermal conductivity measurement is the "Hot Wire Method" (ASTM C1113). This method is more suitable for measuring powder, fibrous materials, and liquids.
When comparing the thermal conductivities of different insulation materials it is important to compare only data generated by the same measurement technique. This is why all responsible manufacturers of high temperature insulations always quote the guarded hot plate method.