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Resumen: The blocking of fine-capillary tubes used as flow impedances in He4 evaporation cryostats to achieve temperatures below 4.2 K is generally attributed to nitrogen or air impurities entering these tubes from the main bath. The failure of even the most rigorous low-temperature laboratory best practices aimed at eliminating the problem by maintaining the cleanliness of the helium bath and preventing impurities from entering the capillary tubes suggests that a different cause is responsible for the inexplicable reduction of impedance flow. Many low-temperature research laboratories around the world have suffered this nuisance at a considerable financial cost due to the fact that the affected systems have to be warmed to room temperature in order to recover their normal low-temperature operation performance. Here, we propose an underlying physical mechanism responsible for the blockages based upon the freezing of molecular H2 traces present in the liquid-helium bath. Solid H2 accumulates at the impedance low-pressure side, and, after some time, it produces a total impedance blockage. The presence of H2 traces is unavoidable due its occurrence in the natural gas wells where helium is harvested, forcing gas suppliers to specify a lower bound for impurity levels at about 100 ppb even in high-grade helium. In this paper, we present a simple apparatus to detect hydrogen traces present in liquid helium and easily check the quality of the liquid. Finally, we propose a solution to eliminate the hydrogen impurities in small- and large-scale helium recovery plants. The solution has been implemented in several laboratories that previously experienced a chronic occurrence of blocking, eliminating similar occurrences for more than one year.
Idioma: Inglés
DOI: http://dx.doi.org/10.1103/PhysRevApplied.6.024017
Año: 2016
Publicado en: Physical review applied 6, 024017 [11p.] (2016)
ISSN: 2331-7019
Financiación: info:eu-repo/grantAgreement/ES/MINECO/IPT-2012-0442-420000
Financiación: info:eu-repo/grantAgreement/ES/MINECO/MAT2015-64083-R
Tipo y forma: Article (Published version)
Área (Departamento): Física de la Materia Condensada (Departamento de Física de la Materia Condensada)
Área (Departamento): Ingeniería Química (Departamento de Ingeniería Química y Tecnologías del Medio Ambiente)

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Este artículo se encuentra en las siguientes colecciones:
Articles > Artículos por área > Física de la Materia Condensada
Articles > Artículos por área > Ingeniería Química