Thermal conductivity data of carbon-carbon composite materials (3)

The thermal conductivity k of a material is related to its thermal diffusivity data by the following equation:

K=ραcp

Where ρ is the density; α is the thermal diffusivity; and cp is the heat capacity (specific heat). Bulk density measurements at room temperature were obtained from mass and volume measurements. Although the density of carbon-carbon material does change slightly with temperature, this change was neglected because only minimal error is introduced. Carbon-carbon composites made with T300 fibers have an in-plane coefficient of thermal expansion of 0.56-10-6/K and through-the-thickness CTE of 2.04-10-6/K values from 811 K to 1366 K. With the use of these CTE values, the volume of the material would increase a maximum of about 1.5 percent from room temperature to 1922K. This volume change was considered to be sufficiently small so that density could be taken as a constant for the thermal conductivity calculations reported in this paper.

Figures 2 and 3 summarize the thermal conductivity results. Figure 2 shows the range of in-plane thermal conductivity data for materials evaluated in this report, and figure 3 shows the range of through-the-thickness thermal conductivity data. The temperatures and corresponding thermophysical property data for the individual materials are shown in tables 2 through 29. Thermal diffusivity as a function of temperature is plotted for all materials (figs. 4 through 31). Values are given in both square centimeters per second and square feet per hour. Temperatures are shown in both Kelvin (K) and degrees Fahrenheit (F). For uncoated materials, both in-plane and through-the-thickness values are plotted. For coated materials, only through-the-thickness values are shown because that was the only direction in which measurements were made. For both in-plane and through-the-thickness directions, thermal diffusivity values are maximum at room temperature and decrease with increasing temperature. Values are fairly flat from 1200 to 1900K.

Carbon-carbon composite materials are candidates for use in advanced thermal protection systems. Because a need was recognized for in-plane and through-the-thickness thermal conductivity data for carbon-carbon composite materials over a wide temperature range. This report documents the thermal conductivity data generated for these materials. In-plane thermal conductivity values range from 10 to 233 W/m-K, whereas through-the-thickness values range from 2 to 21 W/m-K.

range of in-plane thermal conductivity values for materials reported in paper

fig2-range of in-plane thermal conductivity values for materials reported in paper

range of through-the-thickness thermal conductivity values for materials reported in paper

fig3-range of through-the-thickness thermal conductivity values for materials reported in paper

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