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COMPILATION OF THERMOPHYSICAL PROPERTIES OF LIQUID LITHIUM
by Harry W. Dauison Lewis Research Center Cleveland, Ohio
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N A T I O N A L AERONAUTICS A N D SPACE A D M I N I S T R A T I O N W A S H I N G T O N , D. C. JULY 1968 /6
TECH LIBRARY KAFB, NM- aI11111111111llllllllll1ll11IIIII1111111111111
COMPILATION OF THERMOPHYSICAL PROPERTIES
OF LIQUID LITHIUM
By Harry W. Davison
Lewis Research Center Cleveland, Ohio
NATIONAL AERONAUT ICs AND SPACE ADM INISTRATION
For sale by the Clearinghouse for Federal Scientific and Technic01 Information Springfield, Virginia 22151 - CFSTI price $3.00
A compilation of properties including density, electrical resist ivity, enthalpy, heat capacity, surface tension, thermal conductivity, vapor pressure, viscosity, Prandtl number, and thermal diffusivity is presented for temperatures between the melting point and normal boiling point of lithium. Empirical correlations were obtained by statist ically fitting a polynomial to experimental data obtained from the l i terature.
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COMPILATION OF THERMOPHYSICAL PROPERTIES OF LIQUID LITHIUM
by H a r r y W. Davison
Lewis Research Cen te r
Liquid lithium is a potential coolant candidate for use in high-temperature nuclear space power systems. It is desirable, based on thermodynamic considerations, to raise the lithium temperature as close to the normal boiling point as possible. Thermophysical property data for liquid lithium at temperatures approaching the normal boiling point are scarce , and some of the data a r e in disagreement. Empirical correlations relating density, electrical resistivity, enthalpy, heat capacity, surface tension, thermal conductivity, vapor pressure, viscosity, Prandtl number, and thermal diffusivity with temperature have been developed. These correlations, developed from experimental data obtained from the technical literature, were extrapolated to about 1600 K.
The normal boiling point, calculated from the vapor pressure correlation is 1608rt6 K. The thermal conductivity predicted from a modified Ewing, et al., correlation suggests a maximum thermal conductivity of about 65 watts per meter-K at 1500 K. The latent heat of fusion calculated from the enthalpy correlations is 4. 55x105 joules per kilogram.
Reactor designers are considering liquid lithium as a possible coolant for space power systems (ref. 1). Such systems require high operating temperatures to minimize the system size and weight and to ensure best operating efficiencies. Lithium has several desirable features for high-temperature applications such as low vapor pressure, low density, high heat capacity, and low pumping power requirements. If space power systems utilizing liquid lithium as a coolant are to be designed to obtain maximum performance, it is necessary to compile the physical properties of liquid lithium which will be required by the designer. A considerable amount of experimental data for lithium is available in the l i terature for temperatures between the melting point and about 1000 K.
For space power system application, it is desirable to obtain data up to the normal boiling point (about 1600 K) to increase the flexibility of system designs. Therefore, it is necessary to either perform experiments or extrapolate present data. Some of the present results, however, are conflicting, such as those for heat capacity and thermal conductivity.
The purpose of this report is to correlate the thermophysical properties of saturated liquid lithium as a function of temperature, using both experimental data and theoretical analyses; and based upon these correlations extrapolate the properties to about 1600 K.
The general method of correlating the data with temperature is described first. This is followed by a discussion of the experimental method, correlating equation, and standard and maximum deviation between the correlation and the data for each property. A list of references and a bibliography a r e included. All of the sources of the experimental data used to develop the empirical correlations are presented in the references. Other sources of work of interest are presented in the bibliography.
heat capacity, J/(kg)(K)
enthalpy at 273 K, J/kg
latent heat of fusiv-+ J/kg
thermal conductivity, W/(m)(K)
molecular weight, g
vapor pressure, N/m 2
electrical resistivity, (pQ)(cm)
absolute temperature, K
thermal diffusivity, m2/sec
viscosity, (N)(sec)/m 2
density, kg/m 3
surface tension, N/m
CORRELATION OF LITHIUM PROPERTY DATA
M e thod of C o r r e I ation
The experimental data on the properties of liquid lithium were obtained from a literature review. These data were empirically correlated as a function of temperature. Generally, the properties were correlated using the following relation:
where p is either the property of interest or the logarithm of the property, T is the temperature, and Ai a r e the constant coefficients. The degree of the polynomial was selected (by trial and e r ro r ) to yield the best correlation. The best correlation is the one which yields a coefficient of correlation closest to 1.0. In cases where there is little difference between correlating equations, the polynomial of lowest degree is selected. To facilitate calculations only polynomials of fourth degree and lower were investigated.
DISCUSSION OF PROPERTIES
The properties of liquid lithium at the melting point and boiling point a r e summarized in table I. These properties were obtained from the empirical correlations derived herein. The properties of the saturated liquid a r e plotted in figures l to l l as a function of temperature. Al l of the empirical correlations, shown as solid curves, a r e derived from experimental measurement. The heat capacity data and the thermal conductivity data exhibited considerable scatter. Therefore, heat capacity was calculated using the enthalpy correlation, and thermal conductivity was calculated using a modified version of the correlation proposed by Ewing e t al. (ref. 2). Prandtl number and thermal diffusivity a r e defined functions of the liquid lithium properties. The viscosity data of Novikov et al. (ref. 3), were obtained from a technical translation of work done in the U. S. S. R. There are no tabulations of the experimental data, only graphs. These data were obtained by interpolation from the graphs.
TABLE I. - THERMOPHYSICAL
PROPERTIES OF LITHIUM
De11sity, kg/m 3
Electrical resistivity, (pQ)(cm)
Latent heat of fusion, J/kg
Heat capacity, J/(kg)(K)
Surface tension, N/m
Thermal conductivity, W/(m)(K)
Vapor pressure, N/m 2
point of 453.7 K
5 16 25. 0
At boiling point of 1608 K
40 1 57. 6
5. 952X106 4 . 5 5 ~ 1 0 ~
4169 4169 0 .396 0 .240
44.0 64 .7 1. 771X10-8 1 . 0 1 3 ~ 1 0 ~
viscosity, (N) (sec)/m 2 ) . 6 4 5 x 1 0 - ~ D. 1 4 0 ~ 1 0 - ~ Prandtl number 6. 12X10-2 8 . 6 5 ~ 1 0 - ~ Thermal diffusivity, m2/sec 2 . 0 3 x 1 0 - ~ 3. 86X10-5
aAll properties obtained from empirical correlations presented herein. . .bBoiling point at 1atm (1.013x10 5 N/m 2).
The most often used method of experimentally measuring the density of liquid lithium is the maximum bubble pressure technique. This experiment is based upon the measurement of pressures required to bubble an iner t gas from a capillary tube immersed to various known depths in the liquid metal. This technique can be used for determining both the liquid surface tension and density. The experimental data determined by Been e t al. (ref. 4), and Cooke (unpublished data obtained by J. W. Cooke of Oak Ridge National Laboratory) are presented in figure 1as a function of the temperature of liquid lithium. Also shown a r e the data of Tepper e t al. (ref. 5), which were measured with a dilatometer apparatus. This apparatus allows the measurement of the change in volume of liquid with temperature for a known mass of liquid. Tepper's data agree with those of Been and Cooke. These data were correlated using the following linear relation:
p = 562 - 0. 100 T ( 1)
Using equation (1), the data a r e correlated with a standard deviation of SO. 7 percent. The maximum difference between the correlation and data is 2.4 percent.
I I I I I I Author Reference
0 Cmke Unpublished B I400 6M1 800 1000 1200 1400 1600
Temperature, T, K Temperature, T, K
Figure 1. - L i th ium density (p = 562 - 0.100 TI. Figure 2. - L i th ium electrical resist ivi ty (R = 2.256 + 0.06665 T - 4 . 2 5 5 ~ 1 0 - ~ T31.T2 + 1.398~10-~
Although this correlation could be improved slightly using a cubic polynomial, the resulting correlation exhibits a minimum at about 1600 K. Because there is no apparent way to justify an increase in density of a monatomic liquid at its boiling point, the Linear form of the polynomial was selected to represent the density.
Kapelner (ref. 6), Tepper (ref. 5), and Freedman and Rober