LAMINAR COOLING OF PSEUDOPLASTIC FLUIDS FLOWING THROUGH CYLINDRICAL HORIZONTAL PIPES

We present results concerning heat transfer for pseudoplastic fluids f lowing inside cylindrical tubes. The fluids are cooled by an external turbulent counterflow of water. A method is developed to evaluate the values of the local heat exchange coefficients. The variations of the associated Nusselt numbers can be approached using the dimensionless a xial abscissa X(+) = (2z/D)/Pe. Experimentation shows that the Nusselt numbers remain slightly dependent on the difference between the inlet temperature of the pseudoplastic fluid T-e and the wall temperatures T-W(z). This last phenomenum, attributed to the variations of consiste ncy K and rheological index n with temperature, can be linked to the e volutions of the axial velocity profiles, experimentally determined by laser Doppler anemometry. A very simple correlation Nu(z) = 1.15{(3n + 1)/(4n)}(1/3){1 - 0.008[T-e - T-W(z)]} X(+)(-0.36) Seem to be accept able in our experimental range. Comparisons with numerical predictions are also proposed.