Tunable diode laser absorption TDLAS

Tunable diode laser absorption spectroscopy (TDLAS) has been used to measure oxides of nitrogen during flight (71). By tuning the laser to specific infrared absorption bands, the technique can selectively measure each compound. Detection limits are higher (25-100 pptrv for a 3-min response time) than the best chemiluminescent methods, and the instrumentation is less amenable to aircraft operations than the chemiluminescence techniques because of weight and size. 

In-situ measurement technique of water vapor concentration in gas flow channels in PEMFCs using tunable diode laser absorption spectroscopy (TDLAS)31-36 is also shown with fundamental descriptions on its measuring principle and validity of a practical system. Localized current density and through-plane water-back transport index are obtained with variation of vapor concentration along the gas channel taken into account. Demonstrative results showing that effect of the micro porous layer (MPL) on variation of through-plane water-back transport index is shown in an operating PEMFC. 

TUNABLE DIODE LASER ABSORPTION SPECTROSCOPY (TDLAS) AS A DIAGNOSTIC TOOL FOR IN-SITU DETECTION OF WATER VAPOR CONCENTRATION IN PEMFCs... 

Localized remote sensing for chemical compositions in operating PEMFC can be performed by tunable diode laser absorption spectroscopy (TDLAS). Measurement of water vapor and carbon dioxide has been reported by using TDLAS.31-36 In TDLAS measurement, the absorption of the laser beam passing through the gas sample is expressed with the partial pressure of the absorbing species, Pa (atm), by Beer s law,... 

Chapters 4-6 address specific diagnostic methods in PEFCs. Martin et al. provide a detailed review of methods for distributed diagnostics of species, temperature, and current in PEFCs in Chapter 4. In Chapter 5, Hussey and Jacobson describe the operational principles of neutron radiography for in-situ visualization of liquid water distribution, and also outline issues related to temporal and spatial resolution. Tsushima and Hirai describe both magnetic resonance imaging (MRI) technique for visualization of water in PEFCs and tunable diode laser absorption spectroscopy (TDLAS) for measurement of water vapor concentration in Chapter 6. 

The advantages of Tunable Diode Laser Absorption Spectrometry (TDLAS) for measuring trace atmospheric gases are universality positive identification good sensitivity and rapid response time. An instrument is described which can measure two gases simultaneously under automatic computer control with detection limits better than 100 parts per trillion and with response times better than 5 minutes. Procedures have been established for the measurement of NO N0a, HNOa NH3 HbQb and HCHO. These species have been measured under a variety of conditions in smog chambers and in ambient air from mobile laboratories and from aircraft. 

Gas phase component concentrations A number of standard gas analysers are routinely available for determination of gaseous mixing ratio of CH4, CO, O3, NO, NO2 and SO2 at moderate atmospheric concentrations. GC determination of a limited number of NMHC species is also available for appropriate experiments. An Aerodyne Quantum Cascade Tunable Diode Laser Absorption Spectrometer (QC-TDLAS) is periodically available for NH3 measurements using tiie line at 967 cm and for NO2 measurement at 1606 cm . There are several potential experiments which may benefit from measurement of other trace species. The Differential Optical Absorption Spectrometer (DOAS) described below may be used for determination of lO, OIO, BrO, NO3, HCHO, SO2 and other trace species. 

Recently, very sensitive and selective measurements became possible by tunable diode laser absorption spectroscopy (TDLAS). Diode lasers that lase in the mid-infrared region give extremely high resolution (3 x 10 " cm ) and can tune the emission line to one of many vibration-rotation bands by changing the laser temperature and current (10-100K, 0.1-2.0 A). The TDLAS measurement is usually carried out at reduced pressure to avoid band broadening due to molecular collision. Practically interference-free measurements are possible with a typical detection limit of sub-ppbv levels (100 m path, at 25 Torr), although the TDLAS system is still expensive and under development. 

Various methods have been developed for remote gas sensing. These include differential optical-absorption spectroscopy (DOAS), differential absorption lidar (DIAL), and a number of methods that use spectroscopic methods with an atmospheric path in place of a laboratory long-path cell, for example tunable diode laser absorption spectroscopy (TDLAS) and Fourier transform infrared (FTIR) spectroscopy. 

The tunable diode laser absorption spectroscopy (TDLAS) sensor is a real-time, non-invasive device that is used to measure water vapor concentration and gas flow velocity in the duct connecting the freeze-drying chamber and the condenser using... 

Kuu, W. Y, Nad, S. L Sacha, G 2009. Rapid determination of vial heat transfer parameters using tunable diode laser absorption spectroscopy (TDLAS) in response to step-changes in pressure set-point during freeze-drying./. Pharm. Sci. 98 1136-1154. 

Schneid, S., Gieseler, H., Kessler, W., Pikal, M. J., 2007. Tunable Diode Laser Absorption Spectroscopy (TDLAS) as a residual moisture monitor for the secondary drying stage of freeze-drying. Proceedings of AAPS Annual Meeting and Exposition, San Diego (CA), USA. 

Experimental methods - applications of tunable diode laser absorption spectroscopy (TDLAS)... 

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