SUPERFLUID FLOW OF LIQUID HELIUM THROUGH NARROW CHANNELS AND THIN FILM
The flow property of liquid helium through extremely narrow channels and of the saturated helium film was investigated. Two mediums were used to provide narrow channels, porous vycor glass and Millipore filters. The interest in the porous vycor glass was the smallness of its pores. Though the geometry of the pores is complex the average pore diameter is fairly uniform and is of the order of 5 x 10/sup -7/ cm, which is order of magnitude small than the thickness of the saturated helium film. The physical characteristics of the Millipore filter are known to a relatively high degree of accuracy. The pores are essentially direct channels through the filter and are very evenly distributed over the filter area. The filters are available in various porosity grades ranging from 10/sup -6/ cm to 5 x 10/sup -4/ cm. With regard to the saturated helium film the anomalous behavior first reported by Eselson and Lasarew and the flow property of the film at very low pressure heads were the main object of investigation. A difference thermometer which could detect temperature difference down to about 10/sup -6/ deg K was developed and used in the present work. This difference thermometer made possible a steady state method of measuring the pressure head dependence of pure superflow. The flow measurements through porous vycor and 0.01 Millipore filter showed the existence of an onset temperature lower than the bulk lambda point below which superflow becomes possible. The onset temperature is similar to that which is observed in unsaturated films in that it decreases with the pore size. Millipore flow measurements showed a limiting flow velocity where the velocity becarne independent of the pressure head. At low temperatures this limiting velocity increased as the pore size decreased and indicated a maximum of about 23 cm/sec between 10/sup -6/ cm and 5 x 10/sup -6/ cm pore size. The anomalous behavior of the film flow reported by Eselson and Lasarew was confirmed and further information such as the influence of time, rim height, and contamination was obtained. Steady-state measurements applied to the film flow indicated a noticeable pressure head dependence below 0.005 cm of liquid helium pressure. The flow rate dropped from the normally observed rate of about 8 x 10/ sup -5/ cc/sec cm to 5 x 10/sup -5/ cc/sec-cm as the pressure head decreased. Within experimental accuracy which was less than 0.002 cm of liquid helium pressure, no pressure head was observed for flow rates less than this lower value. It is believed that this is the true critical flow rate below which there are no frictional forces. Measurements were also made on the film oscillation and on the product of the vaporization coefficient with the effective area of evaporation. (Dissertation Abstr., 23: No. 3, 1962)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-17-002135
- OSTI ID:
- 4761959
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 31-DEC-63
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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