Abstract
Fuel elements in a high-temperature gas-cooled reactor (HTGR) core may be stacked with a hexagonal close-packed (HCP) structure; therefore, analyzing the temperature distribution and heat transfer efficiency in the HCP pebble bed is of great significance to the design and safety of HTGR cores. In this study, the heat transfer characteristics of an HCP pebble bed are studied using CFD. The thermal fields and convective heat transfer coefficients under different coolant inlet velocities are obtained, and the velocity fields in the gap areas are also analyzed in different planes. It is found that the strongest heat transfer is shown near the right vertices of the top and bottom spheres, while the weakest heat transfer takes place in areas near the contact points where no fluid flows over; in addition, the correlation of the overall heat transfer coefficient with the Reynolds number is proposed as havg = 0.1545(k/L)Re0.8 (Pr = 0.712, 1.6 × 104 ≤ Re ≤ 4 × 104). It is also found that the heat transfer intensity of the HCP structure is weaker than that of the face-centered-cubic structure. These findings provide a reference for reactor designers and will contribute to the development of safer pebble-bed cores.
Highlights
Academic Editors: Rachid Bennacer, The spherical fuel elements in a high-temperature gas-cooled reactor (HTGR) core are randomly packed [1], resulting in uneven heat transfer on the surface of the pebbles and hotspots being formed [2], which will affect the integrity of the fuel spheres and may cause serious accidents [3,4]
The results showed that placing pebbles of different diameters (D = 0, 0.03, 0.04, and 0.05 m) in the voids of the pebble layer with a diameter of 12 cm could maximally increase the average heat transfer coefficient (HTC) by 28.8%
For the diagonal plane (Figure 9b), the local HTC at the upper pebble firstly increased from positions 1 to 6 and decreased until position 10; while it firstly decreased from positions 11 to 15 and increased thereafter till position 18, and decreased again
Summary
Academic Editors: Rachid Bennacer, The spherical fuel elements in a high-temperature gas-cooled reactor (HTGR) core are randomly packed [1], resulting in uneven heat transfer on the surface of the pebbles and hotspots being formed [2], which will affect the integrity of the fuel spheres and may cause serious accidents [3,4]. Shams et al [22] conducted a quasi-direct numerical simulation (q-DNS) and large-eddy simulation (LES) on the flow field in a single FCC pebble bed Those results were used to assess the predictions of the detachededdy simulation (DES) and unsteady Reynolds-averaged Navier–Stokes (RANS) model computations. The results showed that placing pebbles of different diameters (D = 0, 0.03, 0.04, and 0.05 m) in the voids of the pebble layer with a diameter of 12 cm could maximally increase the average heat transfer coefficient (HTC) by 28.8% As stated above, these studies mainly focus on the analysis of heat transfer characteristics of SC, FCC, and BCC stacking structures, while research on a hexagonal-close-packed (HCP) pebble bed are scarcely conducted.
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