Yuichi Hamada

Effect of carbon-fiber brushes on conductive heat transfer in phase change materials

Brushes made of carbon fibers are used to improve the thermal conductivities of phase change materials packed around heat transfer tubes. The transient thermal responses measured in brush/n-octadecane composites essentially improve as the volume fraction of the fibers and the brush diameter increase. However, there is a critical diameter above which further improvement is not expected due to thermal resistance between the fibers and the tube surface. A two-dimensional heat transfer model describing anisotropic heat flow in the composite is numerically solved. The calculated transient temperatures agree well with the experimental. A simple model is also developed to predict the heat exchange rate between the composite and the heat transfer fluid. The values of the correction factors are identified on the basis of the results for the anisotropic model.

Improvement of thermal characteristics of latent heat thermal energy storage units using carbon-fiber brushes: experiments and modeling

Brushes made of carbon fibers with a high thermal conductivity are inserted on the shell side of a heat exchanger to enhance the conductive heat transfer rates in phase change materials. The experimental results show that the brushes essentially improve the heat exchange rate during the charge and discharge processes even when the volume fractions of the fibers are about one percent. A three-dimensional model describing the heat transfer in the heat exchanger is numerically solved. The model predicts well the experimental outlet fluid temperatures and the local temperatures in the composite.