Sodium thermal conductivity

Sodium is used as a heat-transfer medium in primary and secondary cooling loops of Hquid-metal fast-breeder power reactors (5,155—157). Low neutron cross section, short half-life of the radioisotopes produced, low corrosiveness, low density, low viscosity, low melting point, high boiling point, high thermal conductivity, and low pressure make sodium systems attractive for this appHcation (40). 

Special correlations have also been developed for liquid metals, used in recent years in the nuclear industry with the aim of reducing the volume of fluid in the heat transfer circuits. Such fluids have high thermal conductivities, though in terms of heat capacity per unit volume, liquid sodium, for example, which finds relatively widespread application, has a value of Cpp of only 1275 k.l/ni1 K. 

Here, Q is the heat energy input per area p and Cp are the density and specific heat capacity, respectively and indices g, d, and s refer to the gas, metal, and liquid sample layers, respectively. With Eq. (106), the thermal conductivity of the sample liquid is obtained from the measured temperature response of the metal without knowing the thermal conductivity of the metal disk and the thickness of the sample liquid. There is no constant characteristic of the apparatus used. Thus, absolute measurement of thermal conductivity is possible, and the thermal conductivities of molten sodium and potassium nitrates have been measured. ... 

In the inter-alkali alloys, eutectic equilibria have been observed in a number of systems very low melting points have been determined for instance in the Rb-Na system (L (Rb) + (Na), at 82.5 at.% Rb and —4.5°C) and even lower melting temperatures have been observed in ternary systems. Binary sodium-potassium alloys, liquid at room temperature (at 25°C in a composition range of about 15-70 at.% Na, about 7-57 mass% Na), have a good thermal conductivity and a wide temperature range where they are liquid they may be used in heat-exchange systems. Their extremely high chemical reactivity must of course be taken into account. 

Based on the discussion of the previous section, we would also expect that structural complexity and disorder present in glasses would tend to decrease the thermal conductivity. This is true, especially when alkalis are added to sodium silicate glasses. Figure 4.32 shows the effect of replacing SiOa in Na20-Si02 glass with other oxides. 

The sp-valent metals such as sodium, magnesium and aluminium constitute the simplest form of condensed matter. They are archetypal of the textbook metallic bond in which the outer shell of electrons form a gas of free particles that are only very weakly perturbed by the underlying ionic lattice. The classical free-electron gas model of Drude accounted very well for the electrical and thermal conductivities of metals, linking their ratio in the very simple form of the Wiedemann-Franz law. However, we shall now see that a proper quantum mechanical treatment is required in order to explain not only the binding properties of a free-electron gas at zero temperature but also the observed linear temperature dependence of its heat capacity. According to classical mechanics the heat capacity should be temperature-independent, taking the constant value of kB per free particle. 

Potassium and sodium are good conductors of heat.23 If the conductivity of silver be unity, that of sodium is 0 365. J. W. Hornbeck found the temp, coeff. of the thermal conductivity of potassium or sodium falls with rise of temp. The alkali metals are also good conductors of electricity 24 for example, the conductivity of sodium for heat and electricity is exceeded only by silver, copper, and gold. According to E. F. Northrup, the metals sodium, potassium, mercury, tin, lead, and bismuth have the same value for the ratio of the coeff. of electrical resistance to the coeff. of cubical expansion at the same temp. The electrical conductivity of lithium is nearly ll-4xl04 reciprocal ohms at 20°, that is, about 20 4 per cent, of the conductivity of hard silver of sodium at 2T 70, 22 4 XlO4 reciprocal ohms, that is, about 36 5 per cent, of the value of silver. 

The soft drink is initially cooled to 4°C in a fridge. The container is then opened and an aliquot of concentrated sodium hydroxide (40%) is added to quench the carbon dioxide in the product (typically 10 ml of NaOH is added to 284 ml of product). The carbon dioxide is quenched by reaction with the sodium hydroxide to form bicarbonate and carbonate ions. An aliquot (50 /a/) of the quenched product is removed and pipetted into the corning instrument s cell. The cell is closed and the solution acidified to release the carbon dioxide, which is then detected by the change in the thermal conductance of the vapour phase. 

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An appreciation of the properties of liquid electrolytes can be gained by a comparison between molten ice (water) and molten sodium chloride (Table 5.2). Both liquids are clear and colorless. Their viscosities, thermal conductivities, and surface tensions near their melting points are not very different. 

The main advantage of UC is the high thermal conductivity. On the other hand, the low chemical resistance is a major disadvantage UC is decomposed by water below 100 °C, which is prohibitive for its use in water-cooled reactors. However, UC may be applied in gas-cooled reactors or in the form of UC/PuC mixtures in fast sodium-cooled breeder reactors. 

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