Heat Transfer and Superfluidity of Helium II

P. L. KAPism between the alkali earth metals cannot be as close as superficially appears, because at atmospheric pressure calcium and strontium are facecentered cubic, whereas barium is body-centered. It is surprising that these simple cubic structures permit so many other forms. Selenium is probably a mixture of amorphous and crystalline material. On the initial application of pressure it experiences some permanent change, but a single application apparently forces it into a more or less well-defined condition. The results obtained now agreed well in the common range with the former measurements to a pressure maximum of 50, 000 kg/cm'. The very sharp drop

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of compressibility of selenium in the neighborhood of 25, 000 is to be noted. The curve of compression of selenium against pressure is quite different in character from that of all the other elements, dropping off with pressure at a much more rapid rate. The amorphous material doubtless functions more like a liquid than a crystalline solid. As in all this work, I am indebted to the Carboloy Company for the Carboloy. I have received financia assistance from the Milton Fund of Harvard University, and the skillful assistance of my mechanic Mr. Charles Chase was essential.

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sT 15, 1941

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Heat Transfer and SuperfluidityP. L.KAPITZA

of Helium

II

Institute for Physical Problems, Academy of Sciences USSR, Moscow, USSR (Received June 23, 1941)

our recent researches, when studying the heat transfer of helium I I in capillaries, we established the existence of a counter current in the liquid. ' An analysis of the experimental results indicated that the transfer of heat into the kinetic energy of the current might take place in a thermodynamically reversible way. From these experiments it was suggested that the helium II flowing in thin films could be in a different energy state. In the present experiments wc studied the flow of helium through a narrow slit, about 10 ' cm, obtained by means of two optically polished quartz disks in the same way as in the viscosimeter by the aid of which we originally established the superfluiditv of helium II.' Bv making the helium flow through this slit under the influence of a temperature gradient in a container with a good heat insulation it was possible to show that the flowing helium has zero entropy. The difference of the heat content Q(cal./g of free helium and helium fiowing through the slit~

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obtained at a number of temperatures is plotted by crosses in Fig. 1. From a simple thermodynamic analysis of this phenomenon it follows that if the helium II is forced through a narrow channel under a pressure p; then in the case of thermohydrodynamically reversible phenomena a temperature difference hT will be caused which can bc determined from the following expression.P=A pQ(67'/T),where p is the density of thc helium and A the mechanical heat equivalent. By means of the same apparatus the existence of th

e temperature difference hT was established and measured. In such a way we have an independent means of determining the value of Q from expression (1). On the curve in Fig. 1 these values of Q are plotted by circles. The coincidence of Q determined by two diferent methods shows processes of that the thermohydrodynamic reversible. helium II are The reversibility of the thermohydrodynamical processes in helium II must evidently be attributed to the lack of the sources of energy

J. Phys.2

Kapitza, J. Exp. Theor. Phys. 11, 1 (1941); USSR 4, 177 (1941). P. L. Kapitza, Rec. Acad. Sci. USSR$18j 28 (1938); Nature 74, 141 (1937).

' P. L.

SUPF. RFLUI

D

ITY OF HELIUM

355

dissipation. This shows once more that helium II is a superfluid and a poor heat conductor. The former experiments made to study the viscosity of helium II when flowing through narrow channels did not take into account the inHuence of a possible temperature difference which, according to Eq. (1) would cause an additional pressure. Therefore, all the data obtained when studying the possibility of a viscous flow of helium II through a slit or through capillaries must be revised. By taking into account this extra pressure, we found that the limit of a possible viscosity for helium II is less than 10 poise. This is about 100 times less than the limit found with the same viscosimeter in our original experiments' and also much smaller than that established by other research workers. ' The reversibility of the thermohydrodynamic phenomena in helium I I gives the research worker the possibility of establishing a method for attaining very low temperatures. As there are, at present, no experimental or theoretical reasons for supposing that helium II changes its thermohydrodynamical properties on approaching zero, this method for obtaining low temperatures as distinguished from the magnetic method will a priori permit us to approach as near to absolute zero as our technical means will permit. This method is now being worked out by us, and in the preliminary experiments temperature drops of 0.4'K have alreadv been easily obtained. A possibility of helium. II flowing with zero entropy has already been put forward in the theoretical views of London' and Tisza. ' The

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FIG. 1. Heat content of helium.

recently proposed theory of Landau' establishes a quantum basis for the phenomena of superfluidity and also permits us to make a qualitative calculation of the heat content of helium I I at low temperatures. According to these theories

——

Q=ST,where

4 W. F. Giauque, J. W. Stout and R. E. Barieau, Phys. Rev. 54, 147 (1938); J. Am. Chem. Soc. 61, 654 (1939); H. London, Proc. Roy. Soc. 171, 484 …… 此处隐藏：4428字，全部文档内容请下载后查看。喜欢就下载吧 ……