Measurement of Apparent Thermal Conductivity for Fire Resistive Materials, 01-R9796

Principal Investigator
J. Marshall Sharp

Inclusive Dates:  03/17/08 – 07/17/08

Background - Many standard tests currently exist for experimental determination of the thermal characteristics of materials, such as thermal conductivity. However, few of these standards are capable of measuring low conductivity materials (less than 0.1 W/m-K) and the accuracy for many of the standards can only be assured for a limited temperature range. Apparent thermal conductivity, also known as effective thermal conductivity, is a measure of the ability of a material or assembly to transfer heat by conduction. Apparent thermal conductivity is measured as a function of temperature and encompasses several phenomena including mass transfer. ASTM has released a new standard, ASTM E 2584: Standard Practice for Thermal Conductivity of Materials Using a Thermal Capacitance (Slug) Calorimeter, which will allow for measurements of apparent thermal conductivity at temperatures from 300 K to 1100 K for homogeneous materials, composites, and layered assemblies (non-homogeneous materials). This standard practice will also allow for measurements of materials with apparent thermal conductivity from 0.02 to 2.00 W/m-K making the standard especially useful for determining apparent thermal conductivity of fire-resistive materials (FRMs) with inherently low thermal transmission by conduction.

Approach - A small-scale furnace is used to heat specimens from room temperature to a preselected maximum temperature. During this heating phase, temperature measurements are recorded for post-test analysis. Based on the 2-D transient heat conduction equation, the thermal conductivity of the sample can be calculated as a function of temperature. For samples that undergo dehydration, chemical reactions, or any other form of mass loss, the pre- and post-test mass can be incorporated in the analysis to account for this change.

Accomplishments - Three specimens were tested using the thermal capacitance calorimeter. Apparent thermal conductivity of fire rated "type X" gypsum wallboard, Douglas fir wood, and rigid polyurethane foam was measured. The measurements were in agreement with estimated values and may be used in future thermal modeling. This procedure may be used in conjunction with the method developed in 01-R9595 to validate standard testing using thermal models.

Thermal Capacitance Calorimeter (without a sample) inside a small furnace heated to 1000 °C (1832 °F).  Thermocouples are inserted through the top insulation panel to record temperature of the furnace, sample, and steel slug throughout the test.

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