V. G. Sviridov

Liquid Metal Heat Transfer Investigations Applied to Tokamak Reactor

The liquid metal (LM) investigations of hydrodynamics and heat transfer affected by longitudinal and transverse magnetic field (MF) were carried out. The current experiments program deals with temperature and velocity fields, local and average heat transfer intensities, temperature fluctuation intensities in a horizontal heated tube. The strong influence of thermo gravitational convection (TGC) in all regimes was observed in experiments applied to blanket and divertor of tokamak. Two unexpected troubles were discovered: zones of extremely low local heat transfer intensities in some regimes of MF and TGC joint influence; dangerous temperature low-frequent fluctuations with high amplitude near the tube wall in some MHD configurations with TGC affect. Numerical simulation of magneto hydrodynamic (MHD) heat transfer is working out simultaneously with experiments.Copyright

Laboratory simulation of heat exchange for liquids with Pr > 1: Heat transfer

Liquid metals are promising heat transfer agents in new-generation nuclear power plants, such as fast-neutron reactors and hybrid tokamaks—fusion neutron sources (FNSs). We have been investigating hydrodynamics and heat exchange of liquid metals for many years, trying to reproduce the conditions close to those in fast reactors and fusion neutron sources. In the latter case, the liquid metal flow takes place in a strong magnetic field and strong thermal loads resulting in development of thermogravitational convection in the flow. In this case, quite dangerous regimes of magnetohydrodynamic (MHD) heat exchange not known earlier may occur that, in combination with other long-known regimes, for example, the growth of hydraulic drag in a strong magnetic field, make the possibility of creating a reliable FNS cooling system with a liquid metal heat carrier problematic. There exists a reasonable alternative to liquid metals in FNS, molten salts, namely, the melt of lithium and beryllium fluorides (Flibe) and the melt of fluorides of alkali metals (Flinak). Molten salts, however, are poorly studied media, and their application requires detailed scientific substantiation. We analyze the modern state of the art of studies in this field. Our contribution is to answer the following question: whether above-mentioned extremely dangerous regimes of MHD heat exchange detected in liquid metals can exist in molten salts. Experiments and numerical simulation were performed in order to answer this question. The experimental test facility represents a water circuit, since water (or water with additions for increasing its electrical conduction) is a convenient medium for laboratory simulation of salt heat exchange in FNS conditions. Local heat transfer coefficients along the heated tube, three-dimensional (along the length and in the cross section, including the viscous sublayer) fields of averaged temperature and temperature pulsations are studied. The probe method for measurements in a flow is described in detail. Experimental data are designated for verification of codes simulating heat exchange of molten salts.

Instabilities in Extreme Magnetoconvection

Thermal convection in an electrically conducting fluid (for example, a liquid metal) in the presence of a static magnetic field is considered in this chapter. The focus is on the extreme states of the flow, in which both buoyancy and Lorentz forces are very strong. It is argued that the instabilities occurring in such flows are often of unique and counter-intuitive nature due to the action of the magnetic field, which suppresses conventional turbulence and gives preference to two-dimensional instability modes not appearing in more conventional convection systems. Tools of numerical analysis suitable for such flows are discussed.

Laboratory simulation of heat transfer in liquids with Pr > 1. Temperature field

Combined measurements of heat transfer coefficients, average temperature profiles, and statistical characteristics of temperature fluctuations were performed for a water flow in a round heated pipe on a laboratory test installation. The studies were carried out with reference to physical simulation of heat transfer in molten salts, which are promising heat tranport media in nuclear and thermonuclear power engineering. The use of original probes with microthermocouples allowed one to perform measurements in many cross-sections along the length of the heated pipe with a small step in radial direction from the axis to the touch point between the probe and the wall in each cross-section. Detailed temperature measurements were performed in near wall region witin the viscous sublayer. This information is especially important for liquids with Prandtl numbers Pr > 1, such as water and molten salts. The tendencies in stabilization of the local heat transfer coefficients, average temperature fields, and temperature fluctuation intensity were investigated. The data presented here are useful for optimization and verification of numerical simulation codes for heat transfer of liquids with large Prandtl numbers.

Experimental investigations of heat transfer and temperature fields in models simulating fuel assemblies used in the core of a nuclear reactor with a liquid heavy-metal coolant

The aim of this experimental investigation is to obtain information on the temperature fields and heat transfer coefficients during flow of liquid-metal coolant in models simulating an elementary cell in the core of a liquid heavy metal cooled fast-neutron reactor. Two design versions for spacing fuel rods in the reactor core were considered. In the first version, the fuel rods were spaced apart from one another using helical wire wound on the fuel rod external surface, and in the second version spacer grids were used for the same purpose. The experiments were carried out on the mercury loop available at the Moscow Power Engineering Institute National Research University’s Chair of Engineering Thermal Physics. Two experimental sections simulating an elementary cell for each of the fuel rod spacing versions were fabricated. The temperature fields were investigated using a dedicated hinged probe that allows temperature to be measured at any point of the studied channel cross section. The heat-transfer coefficients were determined using the wall temperature values obtained at the moment when the probe thermocouple tail end touched the channel wall. Such method of determining the wall temperature makes it possible to alleviate errors that are unavoidable in case of measuring the wall temperature using thermocouples placed in slots milled in the wall. In carrying out the experiments, an automated system of scientific research was applied, which allows a large body of data to be obtained within a short period of time. The experimental investigations in the first test section were carried out at Re = 8700, and in the second one, at five values of Reynolds number. Information about temperature fields was obtained by statistically processing the array of sampled probe thermocouple indications at 300 points in the experimental channel cross section. Reach material has been obtained for verifying the codes used for calculating velocity and temperature fields in channels with an intricately shaped cross section simulating the flow pass sections for liquid-metal coolants cooling the core of nuclear reactors.

HEAT TRANSFER INVESTIGATION AT LIQUID METAL FLOWING IN FUSION REACTOR CONDITIONS

Акционерное общество «Ордена Ленина Научно-исследовательский и конструкторский институт энерготехники им. Н.А. Доллежаля» (АО «НИКИЭТ»), Москва, Россия Объединённый институт высоких температур Российской академии наук (ОИВТ РАН), Москва, Россия Национальный исследовательский университет «МЭИ», Москва, Россия Акционерное общество «Научно-исследовательский институт электрофизической аппаратуры им. Д.В. Ефремова» (АО «НИИЭФА им. Д.В. Ефремова»), Санкт-Петербург, Россия