Novel Method for Measurement of the Para-Content of a Hydrogen-Stream
Hydrogen at ambient temperature is a mixture of 75% ortho- and 25% para-hydrogen whilst it is 100% para-hydrogen at boiling temperature. Hydrogen liquefaction processes use catalysts to stepwise convert normal-hydrogen to para-hydrogen during cooldown to cryogenic temperatures. This conversion at different temperature levels is necessary to avoid release of the heat of conversion in the liquid state which would result in losses due to enhanced evaporation. Therefore customers can expect to receive a liquid hydrogen quality with a para-content of almost 100% from their gas supplier.
A novel technique was developed1 to precisely measure the para content during cool-down of the hydrogen as well as of the liquid product. The measurement principle is based on the caloric differences of ortho- and para-hydrogen. A direct determination of the para-concentration is accomplished by using a simple measurement of a temperature difference and is therefore superior to previous techniques which are based on the thermal conductivity of hydrogen. The new method was experimentally verified. It has shown a very close agreement with theory.
This paper describes the novel method along with the experimental apparatus and the test results. Based on the experimental setup an industrialized instrument was developed and is now available. It features a direct readout of the para-content of the measured hydrogen stream.
KeywordsLiquid Hydrogen Hydrous Ferric Oxide Para Content Hydrogen Stream Adiabatic Reactor
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