Tunable diode-laser absorption-based sensors for the detection of water vapor concentration, film thickness and temperature
Year: 2012
Type: article
Abstract: Temperature and species concentration are fundamental parameters in combustion-related systems. For optimizing the operation and minimizing the pollutant emissions of combustion devices and to provide validation data for simulations, quantitative measurement techniques of these parameters are required. Laser-based diagnostic techniques are an advantageous tool for in-situ non-intrusive measurement in combustion related systems, e.g. flame reactors, combustors, and shock tubes. Fiber-based multiplexed tunable diode laser absorption spectroscopy (TDLAS) is attractive and employed in this thesis because of compact, rugged packaging, low cost, reliability and relative ease of use. In the present work, water (H2O) is chosen as the target species for the technique, since it has a rich absorption spectrum in the vapor-phase and a broad-band absorption spectrum for the liquid-phase in the near infrared region (NIR). TDLAS two-line thermometry is used to determine the temperature in gas-phase systems with homogenous temperature distribution. However, in many practical environments, temperature varies along the beam path. For this case the temperature-binning technique is used for retrieving non-uniform temperature distributions from line-of-sight (LOS) absorption data with multiplexed five-color absorbance areas. In this thesis, TDLAS was applied to determine the spatially-resolved temperature information inside a low-pressure nanoparticle flame synthesis reactor. The temperature distribution was obtained by assuming the temperature to be constant in variable lengths along the LOS. The length fractions for the temperature values along the LOS are determined using postulated temperature bins. Quantitative knowledge of liquid film thickness is important in many industrial applications. One example is Diesel engine exhaust gas aftertreatment, where NOx reduction via selective catalytic reduction (SCR) is accomplished in the exhaust using sprays of water/urea solutions. In this thesis a novel TDLAS sensor was developed to simultaneously measure the water film thickness, film temperature and vapor-phase temperature above the film. For this sensor four individual NIR wavelengths were selected for optimized sensitivity of the technique. The sensor was first validated using a calibration tool providing known film thicknesses and temperature, and then applied to open liquid water films deposited on a transparent quartz plate. In a collaborative project the technique was also compared with imaging measurements based on laser-induced fluorescence and Raman scattering, respectively. Furthermore, the TDLAS sensor was applied to determine time series data of liquid water film thickness resulting from impinging water jets and subsequent film evaporation on the wall of a gas flow channel.
Author: Huinan Yang
Language: English
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Funder: Universität Duisburg-Essen
OpenAlex ID: W1606755381