Relation Between Fountain Pressure and Heat Current in Helium II

Nature ◽  
1948 ◽  
Vol 162 (4106) ◽  
pp. 67-68 ◽  
Author(s):  
LOTHAR MEYER ◽  
WILLIAM BAND
Keyword(s):  
Heat Current ◽  
Helium Ii

Superflow of helium II through compressed powder

1953 ◽  
Vol 218 (1132) ◽  
pp. 18-28 ◽  
Keyword(s):  
Flow Rate ◽  
Thermal Gradient ◽  
Heat Current ◽  
Satisfactory Explanation ◽  
Intermediate Point ◽  
Helium Ii ◽  
Flow Phenomena ◽  
Similar Character ◽  
Flow Through ◽  
Temperature And Pressure

The flow of liquid helium II through a tube packed with rouge powder has been investigated under gradients of temperature and pressure. The flow rate, the heat current and the pressures at the ends of the tube as well as at an intermediate point have been determined at various temperatures. In flow under a thermal gradient a similar character to that earlier established for flow through narrow slits has been observed. Up to a certain critical velocity which depends on temperature, the flow is free of friction, while at higher velocities, dissipation sets in. The flow under gravity differed completely in its behaviour from the observations with the slit, since dissipation occurred at all velocities. This inconsistency in the flow phenomena has been discussed but no satisfactory explanation can be offered.

Mutual friction in a heat current in liquid helium II I. Experiments on steady heat currents

1957 ◽  
Vol 240 (1220) ◽  
pp. 114-127 ◽  
Keyword(s):  
Relative Velocity ◽  
Fluid Model ◽  
Rectangular Cross Section ◽  
Heat Current ◽  
Mutual Friction ◽  
Second Sound ◽  
Helium Ii ◽  
Two Fluids ◽  
Two Fluid Model ◽  
Steady Heat

Experiments have been carried out on the conduction of heat through helium II in channels of large rectangular cross-section (~ 2 × 6 mm) for small heat current densities. The observed relationship between temperature gradient and heat-current density can be interpreted phenomenologically in terms of the Gorter-Mellink (1949) mutual friction force, F sn ≈ Aρ s ρ n ( v s - v n ) 3 per unit volume, in the two-fluid model, and observed values of A have been found to agree fairly well with those deduced from earlier measurements. Evidence is presented to show that the magnitude of the mutual friction is determined entirely by the value of ( v s - v n ), independently of the boundary conditions imposed on the flow. A study of the propagation of second sound across the heat currents has shown that, while the presence of the heat current leads to no observable change in the velocity of the second sound, it does lead to an attenuation; the attenuation is linear and approximately proportional to the square of the heatcurrent density. This behaviour can be described phenomenologically in terms of the twofluid model, if it is assumed that, in the presence of both a steady heat current and a second sound wave, the Gorter-Mellink mutual friction must be generalized to the form F sn = Aρ s ρ n U 2 u, where u is the instantaneous relative velocity between the two fluids and U is the time-average of this relative velocity. This result shows that in the presence of a steady heat current one or both of the fluids must become modified in some way, and that an essentially linear mutual friction is associated with this modification. Observation of changes in the attenuation of second sound provides a more sensitive method of measuring mutual friction than does the observation of temperature gradients, and it has been shown by the former technique that in the channels used in the present work there is a critical heat current below which the mutual friction is either absent or very small.

Influence of an Axial Heat Current on Negative-Ion Trapping in Rotating Helium II

1973 ◽  
Vol 31 (7) ◽  
pp. 433-436 ◽  
Author(s):  
D. K. Cheng ◽  
M. W. Cromar ◽  
R. J. Donnelly
Keyword(s):  
Ion Trapping ◽  
Negative Ion ◽  
Heat Current ◽  
Helium Ii ◽  
Axial Heat

Mutual friction in a heat current in liquid helium II. II. Experiments on transient effects

1957 ◽  
Vol 240 (1220) ◽  
pp. 128-143 ◽  
Keyword(s):  
Relative Velocity ◽  
Experimental Studies ◽  
Heat Current ◽  
Mutual Friction ◽  
Second Sound ◽  
Transient Effects ◽  
Uniform Rotation ◽  
Helium Ii ◽  
Two Fluids ◽  
Steady Heat

It was shown in part I that, when helium II is carrying a steady heat current on which is superimposed a second-sound wave, the mutual friction acting between the two fluids (the Gorter-Mellink force) is of the form G (v s - v n ), where (v s - v n ) is the instantaneous relative velocity between the fluids, and the factor G is proportional to the square of the time average of this relative velocity. The present paper describes some experimental studies that have been made of the manner in which G changes when the heat current in a wide (~ 2 mm) channel is suddenly changed from one steady value to another; the changes in G have been observed as changes in the attenuation of second sound, and, where possible, as changes in the temperature gradient in the helium. It has been found, for example, that, when a steady supercritical heat current is suddenly switched on in initially undisturbed helium, G rises to its equilibrium value only after a delay time which is of the order of 1s, and that, when the heat current is removed, a non-zero value of G persists for at least 30s. The results indicate that the Gorter-Mellink force is probably associated with turbulence in the superfluid. It is suggested that the force may therefore be due fundamentally to the presence in the superfluid of motions for which curl v s ≠ 0, and it is recalled that experimental evidence in favour of this view has been provided by the recent discovery (Hall & Vinen 1956 a ) that a mutual friction acts in helium that is simply in a state of uniform rotation.

Superflow of helium II through narrow slits

1952 ◽  
Vol 213 (1113) ◽  
pp. 158-175 ◽  
Keyword(s):  
Flow Rate ◽  
Critical Flow ◽  
Heat Current ◽  
Normal Flow ◽  
Critical Rate ◽  
Intermediate Point ◽  
Flow Rates ◽  
Critical Flow Rate ◽  
Helium Ii ◽  
Frictional Dissipation

The flow of liquid helium II has been investigated under gradients of pressure and temperature in slits of 1 μ diameter. Besides the flow rate, the heat current and the pressure difference at the ends of the slit, the pressure at an intermediate point within the slit has been determined. It was found that for superflow the entire drop in pressure and temperature occurs at the narrowest place in the slit. In the remainder of the slit mass flow takes place under effectively zero gradient of pressure or temperature. The experiments also indicate the existence of a critical flow rate beyond which frictional dissipation makes its appearance. The critical rate was determined by four different criteria which yielded consistent results. The temperature dependence of the critical rate is similar to that observed in the helium II film. With flow under a temperature gradient and for higher flow rates the hydrostatic pressure within the slit was found to drop below that at the ends and an explanation for this effect has been suggested. Some experiments with wider slits have shown that in these even for small velocities the transport is a mixture of superflow and normal flow which renders the phenomena very complex.

GROWTH OF MUTUAL FRICTION IN LIQUID HELIUM II

1963 ◽  
Vol 41 (8) ◽  
pp. 1307-1313 ◽  
Author(s):  
S. M. Bhagat ◽  
P. R. Critchlow
Keyword(s):  
Liquid Helium ◽  
Narrow Channel ◽  
Heat Current ◽  
Mutual Friction ◽  
Helium Ii ◽  
Propagation Velocities

An explanation is offered to account for the fact that two propagation velocities of turbulence—one in either direction—may be observed when a heat current is applied to a long, narrow channel containing liquid helium II. The theory also gives qualitatively the correct dependence of the velocities on temperature and heat current.

Steady flow of helium II in the presence of a heat current

Physica B+C ◽  
1982 ◽  
Vol 113 (3) ◽  
pp. 341-366 ◽  
Author(s):  
R.P Slegtenhorst ◽  
G Marees ◽  
H van Beelen
Keyword(s):  
Steady Flow ◽  
Heat Current ◽  
Helium Ii
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