57779 20200221144319.0 doi 10.1103/PhysRevApplied.6.024017 sideral 97028 ART-2016-97028 eng (orcid)0000-0002-5022-5094 Gabal, M. Hydrogen-Free Liquid-Helium Recovery Plants: The Solution for Low-Temperature Flow Impedance Blocking 2016 Access copy available to the general public Unrestricted 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. info:eu-repo/grantAgreement/ES/MINECO/IPT-2012-0442-420000 info:eu-repo/grantAgreement/ES/MINECO/MAT2015-64083-R info:eu-repo/semantics/openAccess by http://creativecommons.org/licenses/by/3.0/es/ 4.808 2016 PHYSICS, APPLIED 21 / 147 = 0.143 2016 Q1 T1 2.448 2016 Physics and Astronomy (miscellaneous) 2016 Q1 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion (orcid)0000-0002-5999-341X Arauzo, A. Universidad de Zaragoza (orcid)0000-0001-7289-5649 Camón, A. Universidad de Zaragoza Castrillo, M. Guerrero, E. Lozano, M.P. (orcid)0000-0001-9897-6527 Pina, M.P. Universidad de Zaragoza (orcid)0000-0002-7742-9329 Sesé, J. Universidad de Zaragoza Spagna, S. Diederichs, J. Rayner, G. Sloan, J. Galli, F. Van, Der Geest Haberstroh, C. Dittmar, N. Oca, A. Grau, F. Fernandes, A. (orcid)0000-0002-5710-5562 Rillo, C. Universidad de Zaragoza 5005 555 Universidad de Zaragoza Dpto. Ing.Quím.Tecnol.Med.Amb. Área Ingeniería Química 0 X Universidad de Zaragoza Serv.Gral. Apoyo Investigación Servicios. Div.Caract.Físi.Quí 2003 395 Universidad de Zaragoza Dpto. Física Materia Condensa. Área Física Materia Condensada 6, 2 (2016), 024017 [11 pp] Phys. rev. appl. Physical review applied 2331-7019 2558119 http://zaguan.unizar.es/record/57779/files/texto_completo.pdf Versión publicada 110771 http://zaguan.unizar.es/record/57779/files/texto_completo.jpg?subformat=icon icon Versión publicada oai:zaguan.unizar.es:57779 articulos driver 2020-02-21-13:40:31 ARTICLE