Hydrogen-free liquid-helium recovery plants: the solution for low-temperature flow impedance blocking

Gabal Lanau, Miguel ; Arauzo García, Ana Belén ; Camón Lasheras, Agustin Hispanico (Universidad de Zaragoza) ; Castrillo, Marta ; Guerrero Domínguez, Enrique ; Lozano, María Pilar ; Pina Iritia, María Pilar (Universidad de Zaragoza) ; Sesé Monclús, Javier (Universidad de Zaragoza) ; Spagna, Stefano ; Diederichs, Jost ; Rayner, Grant ; Sloan, Jeff ; Galli, Federica ; van der Geest, Wilfred ; Haberstroh, Christoph ; Dittmar, Nico ; Oca, Arancha ; Grau, Fernando ; Fernandes, Adelino ; Rillo Millan, Conrado Miguel (Universidad de Zaragoza)

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: Artículo (Versión definitiva)

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)