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Gas Analyzer Measures Concentrations of H2, O2, and H2O

This apparatus can help ensure safety in a system that handles liquid hydrogen.

An apparatus measures small concentrations of H2, O2, and H2O in flowing He gas. In the original application for which the apparatus was developed, the flow of He gas is used to purge a tube through which liquid hydrogen is transferred:

  •   The tube must be purged to remove water vapor and oxygen prior to the introduction of liquid hydrogen into the tube; hence, it is necessary to verify that O2 and H2O are no longer present in the purge gas before stopping this purge.
  •   Once the transfer of hydrogen through the tube is complete, the tube must be purged to remove hydrogen; hence, it is necessary to verify that H2 is no longer present in the purge gas before stopping this purge.

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The apparatus (see figure) includes H2, O2, and H2O sensors; a sampling pump; flow controllers; a pressure transducer; a thermocouple; a computer; a display panel; and a modem. The H2 and O2 sensors can measure concentrations from 0 to 10 percent with accuracies of ±1 percent of their full-scale readings and can withstand sound and vibration conditions of a space shuttle launch. The H2 sensor can operate at temperatures from –10 to +60 °C; the O2 sensor can operate at temperatures from –10 to +40 °C. The H2O sensor can measure concentrations from 125 parts per million (ppm) to 4 percent, with an accuracy of ±10 ppm at 125 ppm. The H2O sensor can operate at temperatures from –10 to +40 °C.

The computer, modem, and display panel are used to control the operation of the rest of the apparatus and to interpret the sensor readings. Control and monitoring tasks can be performed at a safe location, remote from the sensors and the gas system during hazardous operations (e.g., operations in which significant quantities of both hydrogen and oxygen could be present).

The apparatus can be isolated from, or connected to, the purged liquid-hydrogen-transfer tube by use of manual valves V1 and V6. Once these valves have been opened, the apparatus operates in the following sequence:

1.  Solenoid valves SV3 and SV4 are opened.

2.  The plumbing of the apparatus is purged with N2 to remove traces of H2O water vapor that may have leaked in.

3.  After the N2 purge, the sampling pump is started. The pump pulls a sample of gas from the liquid-hydrogen-transfer tube through SV3, then pushes through the flow-control valves, flowmeters, and gas sensors. After passing through the gas sensors, the sampled gas is returned through SV4 back into the liquid-hydrogen-transfer tube.

The apparatus continuously measures the concentrations of H2, O2, and H2O; the rates of flow in the three sensor lines; and the pressure and temperature of the sample gas. All data are logged on a host computer and displayed at a control station. The apparatus can be calibrated from either a remote control station or from a control panel on the apparatus.

The Gas Analyzer measures the concentrations of H2, O2, and H2O in the liquid-H2-transfer tube while the tube is undergoing a purge with He.

This work was done by Clyde F. Parrish, Christian J. Schwindt, Steven J. Klinko, and Timothy R. Hodge of Dynacs Engineering Co., Inc., for Kennedy Space Center.

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