Physical Modeling of Hydrodynamics and Heat Transfer in Liquid-Metal Cooled Fast Reactors
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PHYSICAL MODELING OF HYDRODYNAMICS AND HEAT TRANSFER IN LIQUID-METAL COOLED FAST REACTORS A. P. Sorokin and Yu. A. Kuzina
UDC 536.24+621.039.553.34
The results of the application of the similarity theory of thermophysical processes to the modeling of hydrodynamics and heat transfer in liquid metals in intricately shaped channels and rod systems (reactor cores) as well as the temperature and velocity fields in the top chamber of a fast reactor in different operating regimes are reported. Direct modeling can be used without restrictions only for processes in which the characteristic similarity numbers are functions of only the geometric simplexes of the system and one determining criterion. The presence of two determining criteria, such as, for example, the Reynolds and Prandtl numbers, in the case of heat transfer appreciably complicates the modeling. In the case of three determining criteria, direct modeling is usually unfeasible. In such cases, systematic multivariate experiments must be performed. The task of such experiments is to determine the effects that are allowed by the general mathematical model but are not reproducible, at the current level of mathematical technologies, either analytically or in numerical studies.
In the preparation and performance of thermophysical experiments, it is important to meet the conditions of mechanical, thermal, and thermodynamic similarity, which establishes the dependence of the physical properties of moving heat-conducting media on the parameters of state and the most general relations for describing heat transfer in different liquids under diverse conditions of hydrodynamics and heat transfer in the objects under study. The liquid (fused) metals lithium (Li), sodium (Na), potassium (K), cesium (Cs), lead (Pb), bismuth (Bi), mercury (Hg), gallium, and indium (In) as well as their alloys Na–K (22% Na + + 78% K), Pb–Bi (44.5% Pb + 55.5% Bi), and Pb–Li ( 99.32% Pb + 0.68% Li) form, from the standpoint of heat transfer, a special class of coolants possessing significant volumetric heat capacity and high thermal conductivity. Their kinematic viscosity is much smaller than their thermal diffusivity or, which is the same thing, the Prandtl number is much less than 1 (Pr 105 is a small 278
Fig. 1. The experimental dependence of the hydraulic resistance coefficient ξ calculated using the Poiseuille formula (1), [5] (2) and the experimental dependence of the coefficient on the regime of motion of water (⏊ [7]): water in a clean tube (c), in an oil-covered tube (C), mercury (a, ◑, ◒ [6], A [7], ⏉ [8], +), and mercury–magnesium amalgam (* [6]).
residual roughness of the tube. Because of the high thermal conductivity, the weak temperature dependence of the thermophysical characteristics, and the profile of the temperature the thermal flow weakly affects the hydraulic resistance of liquid metals. Data on the flow of liquid metals in rough tubes also had no salient features [9]. It was established theoretically and experimentally that slipping is observed during the motion of mercu
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