Page 188 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

160 Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

Fig. 4.3 Turbulent Prandtl number as predicted by Aoki and Cheng and Tak correlations
(Pr¼0.02).
Nu¼7.0+0.025 Pe 0.8 (Lyon, constant heat flux)
Nu¼5.0+0.025 Pe 0.8 (Seban and Shimazaki, constant wall temperature)
In a fast reactor core, the liquid metal flows inside a complex array of fuel pins; there-
fore, one of the most important issues is the determination of the dependence of con-
vective heat transfer coefficient from the Peclet number, the lattice geometry, the
pitch-to-diameter (p/D) ratio, and the presence of spacer grids or wires. Many corre-
lations are reported in literature, for example, the one developed by Ushakov et al.
(1977) for the flow of liquid metal in a triangular lattice of heated rods and that of
Zhukov et al. (2002) finalized to BREST lead-cooled reactor. An accurate review
of the convective heat transfer correlations for liquid metals flowing in a bundle of
cylindrical heated rods was performed by Mikityuk (2009); in this work, he proposed
a new correlation valid for rod bundles without spacer grids and for both triangular and
square lattice. More recently, El-Genk and Schriener (2017) performed a review of
available experimental data and convective heat transfer correlations for parallel flow
of alkali liquid metals and LBE eutectic in bundles, stating that the proposed convec-
tive heat transfer correlation found for alkali liquid metals may also be used for the
LBE within an uncertainty of 20%.
An important correlation developed for rod bundles is that of Kazimi and Carelli
(1976), recently implemented in the RELAP5/3D code (2009). This correlation was
derived using several sets of experiments performed using sodium, mercury, and
sodium-potassium as working fluid.
All the mentioned correlations are reported in Table 4.1 together with the condi-
tions for their applicability. In Fig. 4.4, instead, the Nusselt number is reported, as a