Good practice guide to ensure complete conversion from para to normal hydrogen of vaporized liquified hydrogen

This report examines how the two spin isomers of hydrogen, namely para and ortho hydrogen, can influence the measurement of its flow which is of particular interest for vaporized liquid hydrogen. Based on differences in physical properties, flow measurement methods which are affected by the para to ortho ratio are identified. The widely used ortho para catalyst hydrous ferric oxide is introduced and its applicability for the conversion from para to equilibrium hydrogen is discussed. A practical example including the calculation of the required amount of catalyst is given. Alternative approaches to the use of a catalyst as well as measurement methods for the determination of the para to ortho ratio are provided as well.PTB-Bericht M-