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Abstract

Heat transfer and pressure-drop measurements were made with non-Newtonian aqueous thorium oxide suspensions. A comparison of the results of the two different kinds of measurement allowed the general features of non-Newtonian thorium oxide suspension heat transfer to be readily identified, thus leading to a clear understanding of anomalies observed in previous suspension heat transfer studies.

Data were obtained at suspension concentrations up to 0.10 volume fraction solids, (1,000 g. of thorium/kg. of water) in systems having tube diameters of 0.318 and 1.030 in. In addition laminar-flow data were taken with a capillary-tube viscometer with a tube diameter of 1/8 in. and an L/D of 1,000. It was shown that laminar flow physical properties determined with the 1/8 in. diameter tube were satisfactory for correlating data taken with tubes up to 1.030 in. in diameter.

Until the present study information was not available which would permit a choice between two different viscosities for use in correlating non-Newtonian turbulent heat transfer and flow data. The limiting viscosity at very high shear rates is shown to give a unique correlation of turbulent data for tube diameters from 0.124 to 1.030 in., whereas the use of the effective viscosity (that is the viscosity evaluated at the point value of the wall shear stress corresponding to each given flow condition) gives a pronounced diameter effect in turbulent-flow correlations.

The data show that the onset of turbulence for both the pressure-drop and heat transfer measurements occurs at the same Reynolds number and is approximated by the value predicted by the Hedstrom criterion (II). The heat transfer transition region extends to Reynolds numbers a factor of four times greater than the critical, as is also the case with Newtonian materials. Heat transfer to thorium oxide slurries in fully developed turbulent flow is the same as that predicted by the usual correlations for Newtonian fluids to within the precision of the experimental data, provided that the Reynolds and Prandtl numbers are calculated with the limiting viscosity at high rates of shear, η, for this viscosity. An approximate form of Martinelli's momentum heat transfer analogy correlates the experimental results within +17 and −36%.