The purpose of this research was to develop an improved method for measuring hydrogen concentrations in a cryogen flow stream to minimize helium waste during the purge process. Currently, this type of measurement is performed manually with a sniffer, and involves obtaining periodic measurements that are not accurate or repeatable and do not optimize the conservation of hydrogen. The goal of this project was to create an autonomous real-time method for continuously measuring hydrogen that potentially offers not only cost saving advantages by conserving expensive resources that are used for purging, but also for providing an additional safety mechanism to monitor hydrogen in a cryogenic flow stream.

For this innovation, a sensor configuration was developed that enables the sensor to measure hydrogen concentrations at extremely low temperatures during hydrogen purges using helium as a purge gas. This method balances both response time and accuracy, while simultaneously protecting the measuring instrumentation from extremely cold temperatures. A test fixture was developed to characterize the sensor and determine if the sensor could potentially obtain the necessary accuracy and response.

The sensor was incorporated into an innovative capillary standoff design with a redundant sensor installed to confirm measurement accuracy in each configuration. A capillary shunt was installed at two access points with the hydrogen sensor held at a distance from the pipe, and an isolation valve at both ends of the shunt to allow sufficient thermal protection. This design afforded the advantage of accurate hydrogen measurement in a cryogen flow stream without any invasive hardware directly in the flow stream, as well as continuous autonomous monitoring of hydrogen content. The hydrogen concentration was measured and used as an indicator of the purging effectiveness, so that helium waste could be minimized. Tests were performed to characterize the sensor’s performance over the range of temperatures and pressures specified by the manufacturer. Results demonstrated the potential of placing the sensor near the flare in a bypass configuration to obtain the required thermal protection and provide for the real-time measurement of the flow stream hydrogen concentration.

Implementation of the developed sensor configuration will enable purge time to be decreased by indicating when residual hydrogen has been cleared. This will eliminate the need for further purging and result in the conservation of helium via real-time measurement of hydrogen concentration in the purge gas. With this bypass configuration, a hydrogen sensor that normally cannot be used in cryogenic conditions can be safely utilized to measure flow streams at cryogenic temperatures through a design that combines isolation, standoff, and a capillary bypass. With future research, this type of bypass configuration could be implemented for rocket engine testing; saving time, reducing costs, and conserving dwindling helium reserves for future generations.

This work was done by Randy Buchanan of the University of Southern Mississippi and Bill West of Radiance Technologies, Inc. for Stennis Space Center. For more information, contact Randy Buchanan at 601-266-4949. Refer to SSC-00394.

NASA Tech Briefs Magazine

This article first appeared in the August, 2014 issue of NASA Tech Briefs Magazine.

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