Pipe Flov with Viscosity Gradient and Frictional Resistance : 1st Report, Flow of a High Viscosity Fluid in a Heated or Cooled Pipe

概要

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The flow of a highly viscous fluid in a pipe, of which the wall is heated or cooled at a constant temperature, is studied theoretically and experimentally in order to determine the frictional resistance of the flow with a viscosity gradient. Measurements are performed for the Reynolds number 20<Re<850, the Prandtl numbers 500<Pr<2400 and the temperature difference between the fluid and the wall -40°<ΔT<40°. The results show that the theoretical analysis, assuming an axisymmetric flow and taking into account the local viscosity gradient, agrees well with the measurements when the buoyancy effect is not large. Even though the buoyancy effect is large, the pressure drop in the flow direction is little influenced by buoyancy and is well predictable by the theory. The pressure drop increases almost linearly in the measured range and the frictional coefficient is expressed by a simple empirical equation. The velocity measurements by Pitot probes in the low Reynolds number range are carefully examined, and the influence of temperature upon the performance of Pitot tubes is also determined.
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