Rate of strain effect on the thermal conductivity of a polymer liquid

The effective thermal conductivity of a polymer liquid was measured as a function of strain rate. The polymer liquids studied were three commercial grades of polydimethylsiloxane. The experimental results show a dependence of effective thermal conductivity on strain rate. This dependence is believed due to either the rotation of large clusters of entangled macromolecules, or the orientation of the individual macromolecules, or possibly the combination of both mechanisms simultaneously in shear flow. The effective thermal conductivity, for all three samples studied, increased with increasing strain rate. The rate of increase was found to decrease with increasing temperature. The thermal conductivity measurements were made in an annular axial flow test cell that utilizes a hot wire probe technique. Convection problems were eliminated by proper placement of the temperature measuring section of the wire in the cell. A tentative model was used through which the size of the cluster can be estimated. Once the size of the cluster is obtained, the rotational contribution to the energy transport can be estimated. Initial predictions agree well with the observed phenomena.