A Continuous Helium II Refrigerator
At the present time, experiments with superfluid helium are still being carried out in relatively small cryostats. Reduction of the helium temperature down to the λ-point and below is accomplished with the help of a vacuum pump which pumps on the helium and reduces its vapor pressure, The evaporating helium is warmed up in the intervening piping to the pump to nearly room temperature; the enthalpy difference between the boiling temperature of the helium and room temperature is essentially wasted. In small experimental arrangements and if the duration of tests is relatively shorty such loss of enthalpy difference can be neglected, With the efficient helium liquefiers now available, sufficient helium can be produced continuously and test operations with superfluid helium are possible-by these means, even if it becomes necessary to evaporate quantities of up to 50 liters/hr and more for short durations of time.
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