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SUPERFLUID HELIUM (He II, Superfluidity)
The vapor pressure (in torr) of Superfluid (He II) can be approximated by the following equation,
Log P = -3.018 (1/T) + 2.484 Log T - 0.00297 T4 + 2.197
The two fluid model postulates that the density of liquid helium is composed of the density of the superfluid and that of the normal fluid.
r = rs + rn
The density of the normal fluid is given by the following equation.
rn = r (T/Tl)5.6
The entropy of the superfluid can be represented by
S = 1.5838 (T/Tl)5.6
The specific heat of He II is
Cv = (dQ/dT)v = T(dS/dT)v = 5.6 (T/Tl)5.6
Knowing the vapor pressure, one can calculate the latent heat of vaporization of Superfluid
l = RT2(dP/dT)/P
The viscosity of He II is represented by
hn = 8.7 x 10-3 (eD/KT) T-1/2 + 11 + (2(2.2-T))-1
The first term on the right hand side of the above equation is based on Landaus collision theory with D being the energy gap between the phonon and the roton state. Landau suggested that D/K has a value between 8 and 9 K. In the present equation, a value of D/K = 8.0802 K is assumed.
The surface tension of liquid helium can be written as
s = 0.37 - 0.0079 T7/3
Material on this page is taken from an extension course the author taught at UCLA.
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About the author- Dr. Sidney Yuan is a consultant in the field of Low Temperature Physics and Cryogenics, and has written a Book on Cryogenics and published extensively in the field. E-Mail.
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