Validation of Pronghorn Pressure Drop Correlations against Pebble Bed Experiments

Abstract

The verification and validation of Pronghorn is imperative for predicting the fluid velocity, pressure, and temperature in advanced reactors, specifically high temperature gas-cooled reactors. Pronghorn is a coarse-mesh, intermediate-fidelity, multidimensional thermal-hydraulics code developed by Idaho National Laboratory. The Pronghorn compressible/incompressible Navier-Stokes equations are validated by using the pressure drop measurements and axial velocity aver-aged from the particle image velocimetry data obtained at the engineering-scale pebble bed facility at Texas A&M University. Additionally, the Pronghorn energy equations with the valid correlations for the solid-fluid convective heat transfer coefficient and effective thermal conductivities predict fluid and solid temperatures well in the SANA pebble bed region.

Pronghorn and STAR-CCM+ porous media models using the Handley, KTA, and Carman correlations comparably estimate the pressure drop better than other functions with a maximum 3.34%average relative difference compared to the experimental measurements. The precise average pebble bed porosity estimation has a large impact on the pressure drop. The implementation of the volume-averaged porosity in several sectors, with each sector’s thickness larger than the representative elementary length, has the potential to improve pressure drop modeling or provide more detailed velocity profiles in nuclear reactors with high aspect ratios. In addition, the pressure gradients and volume- or surface-averaged axial velocities from the realizable two-layer k − ε and shear stress transport k − ω models are in good agreement with the porous media simulations and particle image velocimetry data.

The bed porosity study concludes that the MATLAB and VGSTUDIO reconstruction methods provide the average bed porosities close to the reference with less than the 1.22% relative difference. The sensitivity study of the radial porosity values verifies the 1.1% average relative difference for 75% of the original reconstructed geometries’ full bed height. At a minimum, the whole bed volume within the pebble diameter length in axial direction is necessary to bring the close radial locations of local porosity oscillations. Furthermore, the new oscillatory porosity function derived based on the Martin porosity correlation or the Hunt and Tien exponential function can be utilized for approximating the radial porosity of pebble bed experiments.