Carbon fiber reinforced plastic (CFRP) is widely used in electric vehicles, aircraft, satellites, rockets, and other applications where accurate knowledge of thermal conductivity is crucial.

For example, in electric vehicles, understanding thermal conductivity is essential for heating performance and battery thermal management. Since heating performance and thermal management impact electricity consumption, they play a significant role in determining driving range. Similarly, for satellites and rockets used in space, thermal conductivity must be understood to ensure heat resistance in the harsh conditions of outer space.

As you may know, CFRP is made by impregnating resin into woven carbon fibers, which results in significant differences in thermal conductivity between the thickness and in-plane directions of the material. Such materials are difficult to measure using standard thermal conductivity measurement devices. However, the Thermowave Analyzer from Bethel Co., Ltd. is designed to measure anisotropic materials, allowing for easy and accurate measurements. Here, we present an actual measurement example.

The sample used is a sheet-like CFRP material.

*Figure 1. Sheet-like CFRP*

While the Thermowave Analyzer can accommodate samples up to 100 mm square, this time we measured a 50 mm square sample. For reference, this device does not require samples to be cut into a specific shape, and samples over 10 mm in diameter can be measured. The thickness of the CFRP measured here is 1 mm.

*Figure 2. CFRP for measurement*

Sample placement is also very straightforward. Simply placing the sample on the stage enables measurement.

*Figure 3. Sample installation state*

Measurement and analysis were conducted using the Thermowave Analyzer. The following images show the measurement and analysis screens.

*Figure 4. Measurement screen*

*Figure 5. Analysis screen*

Here are the measurement results. For samples like this one, which have relatively high thermal conductivity and are thin, a transient method such as that used in this device is employed. In the transient method, thermal diffusivity is measured directly.

Thermal diffusivity in the thickness direction: 2.25 × 10^-7 [m²/s]  

Thermal diffusivity in the in-plane direction: 5.06 × 10^-6 [m²/s]

When thermal conductivity is required, it can be calculated from the specific heat and density. In this case, we used reference values from literature to calculate thermal conductivity. (Source: *New Handbook of Thermal Properties*, p. 354)

Thermal conductivity in the thickness direction: 0.34 [W/m·K]  

Thermal conductivity in the in-plane direction: 7.6 [W/m·K]

We measured the thermal conductivity of CFRP, which is of increasing industrial importance, using the Thermowave Analyzer.

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