A Rational Friction Factor Correlation for Laminar Fully-Developed Pipe Flows of Shear-Thinning Non-Newtonian Fluids

A friction factor correlation for laminar, hydrodynamically fully-developed pipe flows of shear-thinning non-Newtonian fluids is derived through analysis and asymptotic considerations. The specific non-Newtonian fluid model used is the Extended Modified Power Law (EMPL) model, which is functionally equivalent to the Cross model. The EMPL model spans the entire shear rate range from the low to the high shear rate Newtonian regions, and includes the intermediate shear rate power law region. The friction factor correlation has an explicit form and is a function of three dimensionless parameters, making it well-suited to design calculations. The overall accuracy of the correlation is 6.6%, though it is much better in most cases. Graphical results for the correlation, and deviations with respect to high-accuracy numerical calculations are presented and discussed.

Experimental Study on the Effect of Localized Blockages on the Friction Factor of a 61-Pin Wire-Wrapped Bundle

The thermal-hydraulic behavior of the flow in rod bundles has motivated numerous experimental and computational investigations. Previous studies have identified potential for accumulation of debris within the small subchannels of typical wire-wrapped assemblies with subsequent total or partial blockage of subchannel coolant flow. A test campaign was conducted to study the effects of localized blockages on the bundle averaged friction factor of a tightly packed wire-wrapped rod bundle. Blockages were installed within the bundle, and fluid pressure drop was measured across one wire pitch for a Reynolds number range of 500–17,200. The Darcy–Weisbach friction factor of the perturbed rod bundle geometry was compared with that of the unblocked bundle, as well as with the predictions of a well-established friction factor correlation. Differing effects based on blockage size and location for various flow regimes were studied. A number of conclusions can be made about the effects of the blockages on the friction factor, such as an increasing effect of the blockage on friction factor with an increase in Reynolds number, a change in flow behavior in the turbulent transition flow regime near Reynolds number 3000, differences in effect on friction factor for different types of subchannel blockage, and a nonlinear trend in friction factor variation with flow area impeded for edge subchannels. To this end, all data and quantified uncertainty produced in this study are made available for comparison and validation of advanced computational tools.

Friction Factor Correlation for Molten Metals Flow in a 3-Rod Bundle in Cylindrical Shroud, With Smooth and Scalloped Inner Wall

Thermal-hydraulic experiments to help develop and qualify new fuel designs for advanced liquid metal cooled reactors could use reduced-size triangular pitch, 3 rods within a circular shroud. In such an arrangement, scalloping the shroud wall helps achieve lateral flow uniformity and high velocity, but at the expense of increasing the pressure losses. Owing to the practical challenges of conducting experimental investigations with molten lead, Computational Fluid Dynamics (CFD) could a practical alternative to generate large enough database to develop a friction factor correlation. This work performed CFD analyses of molten lead flow in 3-rod bundle with circular shroud to investigate the effect of scalloping the shroud wall on the lateral flow uniformity and pressure. The developed friction factor correlation is very smooth, spanning the laminar, transition, and turbulent flow regions. Scalloping the shroud wall increases the pressure losses, but not the friction factor in the transition and turbulent flow regions. In the laminar flow region, however, scalloping the shroud wall only slightly increases the friction factor.

Effect of Localized Blockages on the Friction Factor of a 61-Pin Wire-Wrapped Bundle

A test campaign has been conducted to study the effects of localized blockages on the friction factor of a 61-pin wire-wrapped bundle replica. Blockages of selected sizes and locations within the bundle have been installed, and fluid pressure drop was measured across one wire pitch. The friction factor was compared with the unblocked bundle friction factor, and with the predictions of a well-established friction factor correlation. A computational fluid dynamics model of the experimental bundle was prepared, and simulations were compared with experimental results with the ultimate goal to complement the experimental activity with validated simulation data. The unique sets of experimental data, complemented with simulation results, provide a quantification of the increase of the bundle friction factor produced by the blockages, and the different expected effects based on blockage size and location for various flow regimes.