An experimental investigation was conducted on the convective heat transfer, friction, and rheological properties of various types of non-newtonian fluids in circular tube flows.
If an apparent Reynolds number is used and if the temperature and degradation effects are properly taken into account, the reduced turbulent friction and heat transfer results, respectively, are then shown to be well correlated by the same expressions for different fluids, regardless of the nature of the fluids and whether they are shear-thinning or shear-thickening. This representation can also separate the reductions in turbulent heat transfer and friction that are induced by viscoelasticity from those induced by pseudoplasticity.
Polyacrylamide solutions inducing asymptotic and intermediate drag reduction regimes were investigated over a broad range of Reynolds numbers. The minimum heat transfer asymptote was determined for fully-developed conditions and for the very long (up to x/D = 600) entrance region observed. Solutions subjected to various degrees of intentional pre-degradation were studied to separate this effect from that of the degradation induced in the test tube itself.
A kerosene-based antimisting polymer solution was also studied. It was found to exhibit a complex viscous behavior involving time-dependency, shear-thickening beyond a critical shear rate, high susceptibility to degradation, and large sensitivity to temperature variations. The unusual friction and heat transfer results obtained with this fluid were, however, reduced to simple correlations for asymptotic drag reduction if an appropriate computational model is used.
Suspensions of bentonite of various concentrations were investigated in laminar and turbulent regimes, and the results for fully-developed and entrance flows were well correlated by newtonian relationships when an adequate wall viscosity concept was used. A combination of bentonite and polymer was found to be unusually susceptible to mechanical degradation, which affected significantly the viscosity and the level of drag and heat transfer reductions obtained.
A suspension of organic pulp based on tomato puree was shown to exhibit up to 40% of viscoelastic-type reduction in heat transfer and friction coefficients with respect to newtonian fluids in the turbulent regime. For laminar flow, however, these coefficients were larger than expected. Combinations of pulp and polymer were investigated as well.
A method was developed to predict the "diameter effect" for viscoelastic fluids.
