Page 185 - Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors

System thermal hydraulics 4

for liquid metals

¶
§
†
‡
N. Forgione*, D. Castelliti , A. Gerschenfeld , M. Polidori , A. Del Nevo ,R.Hu k
*Dipartimento di Ingegneria Civile e Industriale, Universita ` di Pisa, Pisa, Italy,
†
Commissariat a ` l’Energie Atomique et aux Energies Alternatives (CEA), Saclay, France,
‡
Advanced Nuclear Systems (ANS) Institute, Nuclear System Physics Expertise Group SCK.
§
CEN, Mol, Belgium, Agenzia nazionale per le nuove tecnologie, l’energia e lo sviluppo
¶
economico (ENEA), FPN-SICNUC-SIN, Bologna, Italy, Agenzia nazionale per le nuove
tecnologie, l’energia e lo sviluppo economico (ENEA), FSN-ING-PAN, Camugnano, Italy,
Nuclear Science and Engineering Division, Argonne National Laboratory, Lemont, IL,
k
United States
4.1 Convective heat transfer with liquid metals

One of the main differences of liquid metals with respect to nonmetallic fluids (like
water) stays in their relatively large thermal conductivity: two orders of magnitude
greater (e.g., 0.6W/(mK) for water and 80W/(mK) for sodium). This affects
the nondimensional Prandtl number (Pr), which represents the ratio of momentum
1
diffusivity to thermal diffusivity :
ν c p μ
Pr ¼ ¼
α k
For a liquid metal, the Pr value is relatively low (in the order of 0.001–0.02). This
means that the rate of momentum transfer is relatively small with respect to the rate
of heat transfer.
Generally, water has a Pr 1 in the typical thermodynamic conditions of a pressur-
ized water reactor (PWR), while for liquid metals, the value is typically ≪1 (see
Fig. 4.1). Typical Prandtl values for different liquid-metal coolants are as follows:

l Liquid lead (foreseen as coolant in ALFRED and SEALER): Pr ffi 0.0175
l Liquid sodium (to be used for ASTRID): Pr ffi 0.0022
l Lead-bismuth eutectic (adopted for MYRRHA): Pr ffi 0.02
Due to the low liquid-metal Prandtl number, momentum and temperature fields are
nonsimilar (see Fig. 4.2) so that the turbulent heat flux models based on the Reynolds
analogy cannot be applied.

1
Pr is a property of the fluid, and it is not related to any specific system or geometry.
Thermal Hydraulics Aspects of Liquid Metal Cooled Nuclear Reactors. https://doi.org/10.1016/B978-0-08-101980-1.00004-1
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