Heat transfer from a layer of a carbon fiber cluster at low reynolds numbers

The heat transfer coefficient from a cluster of very fine carbon fibers was measured by a transient test method. Air was heated by a heater composed of a cluster of 8 μm diameter carbon fibers. The input to the heater was an electric pulse, and the transient gas temperature was measured and compared with the numerical result with an assumed heat transfer coefficient. The obtained heat transfer coefficient was compared with that of single fibers and packed beds for a wide range of Reynolds numbers. The heat transfer coefficient of a fiber cluster showed a much smaller value than that of a single fiber at very low Reynolds numbers. This result implies that the heat transfer coefficients of fibrous or porous media at low Reynolds numbers do not approach those of a single particle or fiber. Correlations of heat transfer were investigated on the basis of internal flow rather than external flow, and it was found that the nonuniformity of the fiber location and cohesion of fibers strongly affect the heat transfer characteristics.