Measurement of intrinsic thermal conductivity of carbon fiber using direct electrical heating method

It is usually very difficult to measure the intrinsic thermal conductivity of fibers using direct electrical heating method, due to the presence of lateral heat loss. In this study, we demonstrate that the intrinsic thermal conductivity and lateral heat transfer coefficient of fibers can be extracted simultaneously via multiple measurements on the same fiber. In our experiments, three samples of various lengths were prepared from an individual polyacrylonitrile-based carbon fiber of 5.6 µm in diameter and measured with the direct electrical heating method. From each sample, we can get a curve of thermal conductivity vs lateral heat transfer coefficient. We showed that the intrinsic thermal conductivity and lateral heat transfer coefficient can be extracted from the intersection of these curves. Our results also showed that ignoring the lateral heat loss can result in an overestimation in thermal conductivity of carbon fibers by more than 3 times.