Lorenz ratio

J.G. Hust, L.L. Sparks Lorenz Ratios of Technically Important Metals and Alloys, NBS Tech. Note 634, US Dept, of Commerce, Washington, DC (1973)... 

Weight - That force which, when applied to a body, would give it an acceleration equal to the local acceleration of gravity. [1] Wiedeman-Franz law - The law stating that the thermal conductivity k and electrical conductivity a of a pure metal are related hyk = LaT, where T is the temperature and L (called the Lorenz ratio) has the approximate value 2.45 x 10 W/K . Wien displacement law - The relation, which can be derived from the Planck formula for black body radiation, that... 

The effects of thermal treatment and trace impurities on magnetothermal conductivity of good conductors cannot be predicted with confidence. The available experimental data indicate the thermal conductivity can vary by at least a factor of 2 due to differences in composition and thermal treatment. A factor-of-2 decrease in thermal conductivity was also observed when a 6366-kA/m field was applied to the copper and aluminum specimens. A possible solution to this problem is to assume that the Lorenz ratio can be used when the electrical and thermal conductivities involved are actually the magnetoresistivity and magnetothermal resistivity, i.e.,... 

In solid materials that are not significantly electrically conductive, molecular vibrations known as phonons are the means of heat conduction. In metals that have free electrons available to conduct electric current, these same electrons provide another means of heat conduction. The electrical conductivity and electronic component of thermal conductivity are related by the Wiedemann-Franz-Lorenz ratio L, as shown in Eq. (1.10) ... 

This correlation is possible because both thermal and electrical conductivity of metals are due to the transport of electrons. The heat flux carried by the phonons is very small because of the collision of the phonons with the electrons. As a result, the mean free path of the electrons is approximately the same for both the thermal and electrical conductivity. Assuming them to be the same and dividing the thermal conductivity by the electrical conductivity a and simplifying yields the Lorenz ratio, L... 

Calculate the Lorenz ratio for silver at temperatures of 20, 50, 100, and 300 K. Electrical resistivities are given below, in terms of the resistivity ratio, p/p273 where P273 is the resistivity at 273 K, with a value of 1.47 x 10 n cm. 

As described above, quantum restrictions limit tire contribution of tire free electrons in metals to the heat capacity to a vety small effect. These same electrons dominate the thermal conduction of metals acting as efficient energy transfer media in metallic materials. The contribution of free electrons to thermal transport is very closely related to their role in the transport of electric current tlrrough a metal, and this major effect is described through the Wiedemann-Franz ratio which, in the Lorenz modification, states that... 

Figure 7. The Wiedemann-Franz ratio for solutions of lithium in ammonia at —33° C. The Lorenz number is 2.45 X 10 8 watt it/deg.2...

The fact that the thermal conductivity in a pure metal is dominated by the free electron contribution was Ulustrated in 1853 by Gustav Wiedemann (1826-1899) and Rudolf Franz (1827-1902), who showed that Xei and the electrical conductivity, (Tei, are proportionally related (Wiedemann and Franz, 1853). A few years later Danish physicist Ludvig Lorenz (1829-1891) realized that this ratio scaled hnearly with the... 

In a series of papers by Lorenz and collaborators dealing with molecular volumes, the approach (like Traube s) was from the angle of ions in solution. If the true volume of the ion is 0 and F , is the molar volume at 0°K., the ratio 0jV=y) is called the space-filling number. The values of ip at the critical temperature (y>c), boiling-point (ipt), melting-point and absolute zero... 

As implied by the discussion above craze fibril extension ratio or its inverse the fibril volume fraction of the craze is an important parameter of the microstructure. Fibril volume fractions can be measured by several different methods. The refractive index n of the craze can be measured by measuring the critical angle for total reflection of light by the craze surface. Using the Lorentz-Lorenz equation Vf then can be computed from The method is difficult because small variations... 

As Peierls obtains a law for the electrical resistance in the limiting case, he concludes that the ratio of the electrical and thermal resistances does not decrease proportionally to T, but to 7, or in other words at low temperatures the Wiedemann-Franz-Lorenz quantity pjTw should not be constant, but should decrease proportionally to 7. 

For this type of isotherm, represents the maximum loading, which correlates with pore volnme among different adsorbents. The other isotherm parameters, and Po [no relation to the terms in Eqnations (14.4) or (14.5)], represent the characteristic parameter of the adsorbent and an affinity coefficient of the compound of interest, respectively. The characteristic parameter, A, defines the shape of the n versns e cnrve. The affinity coefficient, po, adapts the compound of interest to the characteristic cnrve. It is a fndge factoT that has been correlated to the ratio of molar volumes, parachors, or polarizabilities (via the Lorentz-Lorenz equation) of the componnd of interest to that of a reference component (e.g., benzene or n-heptane). These three methods are ronghly eqnivalent in accuracy. The molar volume version is = The only controversy is whether to nse the... 

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