Hydroxyl Radical (OH) Gas Detector

NASA’s Carbon Capture Filter was designed to trap solid carbon dust through a variety of mechanisms. These include inertial separation, flow recirculation, flow tortuosity, media filtration, and quenching of hot particles or of precursor particles from pyrolysis. The filter uses a custom-designed housing to produce a strong and large recirculating pattern to remove dust through inertial forces and confine it into a large collection cup, which is enshrouded in a cold trap (using a thermoelectric cooler) to thermally induce precipitation of the solid carbon. The flow then passes through a single stage baffle and tube filters before exiting through the outlet at the top of the housing. During operations, gaseous carbon-containing streams enter the filter via an inlet tube at the top of the housing. The inlet tube extends down towards the bottom of the collection cup, where the high-speed stream meets a sudden perpendicular bottom wall, inducing a stagnation flow. Large particles inertially separate from the flow and impinge onto the bottom wall. The partial enclosure of the collection cup (aside from a small slit connecting it to the upper chamber) causes a recirculation bubble to form, increasing the residence time of the stream. The vortical motion of the recirculation bubble causes the large particles to spin outwards towards the walls of the collection cup. The collection cup is cooled to quench the carbon particles, causing them to precipitate out and collect on the walls of the cup. The extended residence time caused by the recirculating flow further quenches the stream. Only small particles that are entrained sufficiently by the flow make it through the slit between the collection cup and upper chamber. On the top wall of the upper chamber, an array of tubular filters collects the remaining particles before the gaseous stream exits the system. NASA’s Carbon Capture Filter has been prototyped and undergone initial testing with simulant dust, yielding promising results. The invention is available for licensing to industry.

This technique takes advantage of Ozone's strong absorption at specific wavelengths in the UltraViolet (UV). To take measurements, UV light is projected through a cell bounded by highly reflective mirrors. These mirrors increase the path length of the cell by inducing the light to bounce back and forth within the cell, increasing the likelihood of Ozone absorption within the cell. Finally, an absorption measurement is taken via a detector outside the cell and opposite of the UV source. This innovation produces an ozone detection precision of 0.12 parts per billion (ppb) in 0.1 second integration. This corresponds to 0.012 ppb in ten seconds integration.

Conventional ambient-temperature oxygen sensors are limited in various ways: optically based sensors can be expensive and challenging to manufacture; electrochemical cells with liquid electrolytes can have limited lifetimes and become leak sources; and both types of sensors are difficult to miniaturize. These problems are addressed with Glenn's novel ambient temperature oxygen microsensor, which is based on a Nafiontm polymer electrolyte, microfabricated using thin-film technologies. In the past, one drawback of Nafiontm film has been that it can lose conductivity when the moisture content in the film is too low, potentially affecting sensor operation. Glenn researchers devised a method to use certain salts to hold water molecules in the Nafiontm film structure at room temperature. The presence of these salts provides extra sites in the film to promote proton (H+) mobility, thus improving film conductivity and overall sensor performance, particularly in arid and high-temperature environments. The innovative use of metal/metal oxide as the reference electrode enables miniaturization by eliminating the reference gas and sealing the reference electrode. The combination of interdigitized electrodes with the unique metal/metal oxide reference electrode permits sensor operation in either potentiometric or amperometric mode, as appropriate. In potentiometric mode, which measures voltage differences between working and reference electrodes in different gases, the voltage differences can be monitored with a voltmeter; however, the sensor itself does not need a power source. In room-temperature testing, the sensor achieved repeatable responses to 21 percent oxygen in nitrogen (using nitrogen as a baseline gas), and also detected oxygen from 7 to 21 percent, making Glenn's breakthrough technology usable for personal health monitoring as well as fire detection, fuel-leak detection, and environmental monitoring.

In conjunction with academia and industry, NASA's Glenn Research Center has developed a range of microelectromechanical systems (MEMS)-based and Silicon Carbide (SiC)-based microsensor technologies that are well-suited for many applications. The suite of technologies includes hydrogen and hydrocarbon leak detection sensors; emissions sensor arrays; and high-temperature contact pads for wire bond connections. Currently used to protect astronauts on the International Space Station, the hydrogen and leak detection sensors have many Earth-based applications as well. They can function as a single-sensor unit or as part of a complete smart sensor system that includes multiple sensors, signal conditioning, power, and telemetry. The system can comprise sensors for hydrogen, hydrocarbons, oxygen, temperature, and pressure. The emissions sensor array features a gas-sensing structure that detects various combustion emission species (carbon monoxide, carbon dioxide, oxygen, hydrocarbons, and nitrogen oxides) over a wide range of concentrations. In addition, the emissions sensor array remains highly sensitive and stable while providing gas detection at temperatures ranging from 450 to 600°C. These new sensors provide a combination of responsiveness and durability that offers great value for a wide range of applications and industries.

The technology is a solid state, Carbon Dioxide (CO2) sensor configured for sensitive detection of CO2 having a concentration within the range of about 100 Parts per Million (ppm) and 10,000 ppm in both dry conditions and high humidity conditions (e.g., > 80% relative humidity). The solid state CO2 sensor achieves detection of high concentrations of CO2 without saturation and in both dynamic flow mode and static diffusion mode conditions. The composite sensing material comprises Oxidized Multi-Walled Carbon Nanotubes (O-MWCNT) and a metal oxide, for example O-MWCNT and iron oxide (Fe2O3) nanoparticles. The composite sensing material has an inherent resistance and corresponding conductivity that is chemically modulated as the level of CO2 increases. The CO2 gas molecules absorbed into the carbon nanotube composites cause charge-transfer and changes in the conductive pathway such that the conductivity of the composite sensing material is changed. This change in conductivity provides a sensor response for the CO2 detection. The solid state CO2 sensor is well suited for automated manufacturing using robotics and software controlled operations. The solid state CO2 sensor does not utilize consumable components or materials and does not require calibration as often as conventional CO2 sensors. Since the technology can be easily integrated into existing programmable electronic systems or hardware systems, the calibration of the CO2 sensor can be automated.