Vapor Concentration Measurements Research Articles

Estimation of errors of the spectral method for measuring the concentration of water vapor and moisture reserves in the surface layer of the Earth’s atmosphere

A method for passive measurements of water vapor concentration in the atmosphere in the presence of solar radiation has been proposed and tested. The location of the measurements is the northeast of the Moscow region. When processing the results of measurements carried out on a single water absorption line, a coincidence of experimental data and data obtained from direct meteorological measurements with an error of no more than ~7.5 % was revealed. It was also found that on the water absorption line in the region of 1653 nm, the interfering factor is the nearby methane absorption line, which introduces a systematic error in the measurement results, and the results turn out to be underestimated. A possible reason is that the absorption cross section of methane molecules is ~4 orders of magnitude larger than that of water vapor molecules and light radiation is absorbed to a greater extent by methane, reducing the fraction of absorption of water vapor at a wavelength close to the methane absorption line. Compensatory corrections have been introduced to determine the concentration and moisture content in the atmospheric column with an accuracy of several percent at this wavelength. The proposed technique allows both long-term monitoring of concentration and moisture content in the atmosphere and obtaining operational information in real time. The results of the measurements performed are, on average, consistent with the results of measurements obtained using radiometers operating in the ultrahigh frequency range.

Droplet Growth or Evaporation Does Not Buffer the Variability in Supersaturation in Clean Clouds

Abstract Water vapor supersaturation in clouds is a random variable that drives activation and growth of cloud droplets. The Pi Convection–Cloud Chamber generates a turbulent cloud with a microphysical steady state that can be varied from clean to polluted by adjusting the aerosol injection rate. The supersaturation distribution and its moments, e.g., mean and variance, are investigated for varying cloud microphysical conditions. High-speed and collocated Eulerian measurements of temperature and water vapor concentration are combined to obtain the temporally resolved supersaturation distribution. This allows quantification of the contributions of variances and covariances between water vapor and temperature. Results are consistent with expectations for a convection chamber, with strong correlation between water vapor and temperature; departures from ideal behavior can be explained as resulting from dry regions on the warm boundary, analogous to entrainment. The saturation ratio distribution is measured under conditions that show monotonic increase of liquid water content and decrease of mean droplet diameter with increasing aerosol injection rate. The change in liquid water content is proportional to the change in water vapor concentration between no-cloud and cloudy conditions. Variability in the supersaturation remains even after cloud droplets are formed, and no significant buffering is observed. Results are interpreted in terms of a cloud microphysical Damköhler number (Da), under conditions corresponding to , i.e., the slow-microphysics regime. This implies that clouds with very clean regions, such that is satisfied, will experience supersaturation fluctuations without them being buffered by cloud droplet growth. Significance Statement The saturation ratio (humidity) in clouds controls the growth rate and formation of cloud droplets. When air in a turbulent cloud mixes, the humidity varies in space and time throughout the cloud. This is important because it means cloud droplets experience different growth histories, thereby resulting in broader size distributions. It is often assumed that growth and evaporation of cloud droplets buffers out some of the humidity variations. Measuring these variations has been difficult, especially in the field. The purpose of this study is to measure the saturation ratio distribution in clouds with a range of conditions. We measure the in-cloud saturation ratio using a convection cloud chamber with clean to polluted cloud properties. We found in clouds with low concentrations of droplets that the variations in the saturation ratio are not suppressed.

Dual-Pump Vibrational Coherent Anti-Stokes Raman Scattering System Developed for Simultaneous Temperature and Relative Nitrogen–Water Vapor Concentration Measurements

Simultaneous gas phase temperature and water vapor concentration measurement are important to understand reacting flows such as combustion or gas reforming processes. Here, coherent anti-Stokes Raman scattering (CARS) offers the possibility for non-intrusive measurements with a high temporal and spatial resolution. Therefore, this work demonstrates the simultaneous measurement of temperature and relative water vapor–nitrogen concentrations by using dual-pump vibrational coherent anti-Stokes Raman scattering (DPVCARS). A calibration procedure is developed for a temperature range of 473 K to 673 K and a water vapor concentration of 24% to 46% at ambient pressure. This setup is tested with 500 CARS single pulse spectra taken in a gas cell at a known temperature and concentration. Based on these results, information about precision and accuracy can be delivered.

Full-field vapor concentration and temperature field measurement of an evaporating ethanol–water binary sessile drop by tomographic laser absorption spectroscopy

Quantitative measurement of full-field, spatially resolved temperature and concentration field of pure water and ethanol–water binary evaporating drop is realized, in which the gas-phase and interfacial temperature and concentration are accurately captured. By studying the vapor field of evaporating drop under different heating temperatures, it is demonstrated that the method can achieve a spatial resolution below 100 μm and a time resolution of <10 s. Simultaneous gas-phase temperature and concentration field measurements reveal the occurrence of buoyancy convection in the gas phase. Through the analysis of interfacial temperature and concentration distribution, it is observed that in the process of pure water drop evaporation, both buoyancy-driven convection and thermal Marangoni convection exist, while in the ethanol–water binary drop evaporation, the solutal Marangoni flow convection and thermal Marangoni convection are coupled, and the buoyancy convection is suppressed. The interfacial temperature and gas-phase water vapor concentration can be obtained from the water vapor measurement, and combined with the activity coefficient models. The liquid-phase mole fraction of water at the interface and its distribution are also obtained, such that the liquid-phase mole fraction distribution of ethanol at the interface can be obtained, and finally, the concentration of ethanol vapor near the interface is obtained. The full-field, high-resolution measurement of evaporated drops is of substantial significance for in-depth understanding of the evaporation process. The measurement of ethanol–water binary drop evaporation provides a new research perception and method exploiting the spectral dimension, providing both quantitative and qualitative observations for the study of multi-component drop evaporation.

Water vapor concentration measurements in high purity gases by means of comb assisted cavity ring down spectroscopy

In manufacturing processes of semiconductor industry accurate detection and monitoring of water vapor concentration in trace amount is of great importance. The ability to perform reliable measurements in ultra-pure gases, with a wide dynamic range and low uncertainty, can have a substantial impact on product quality and process performances. Here, we report on the development of a second-generation comb-assisted cavity ring-down spectrometer and present H2O mole fraction measurements in high-purity N2 gas. Based on the use of a pair of phase-locked lasers and referenced to an optical frequency comb synthesizer, the spectrometer allowed to record high-quality absorption spectra in coincidence with the 32,2→22,1 H2O transition at 1.3946μm. Retrieval of water mole fractions, at levels as low as 380 part per billion, was accomplished through a careful spectra analysis procedure based on the use of refined line shape models which include speed-dependent effects. Measurements were performed with a statistical reproducibility of 5 parts per billion, for an integration time of about 0.2 s. The noise equivalent and minimum detectable absorption coefficients were found to be 3.1 × 10−11 cm−1/Hz and 6.5 × 10−12 cm−1, respectively. This latter allowed for a minimum detectable water mole fraction (limit of detection) of 160 parts per trillion. Finally, the main sources of systematic uncertainty have been discussed and quantified.

A fast sensor for non-intrusive measurement of concentration and temperature in turbine exhaust

Accurate and rapid measurement of water vapor concentration and temperature in the exhaust of gas turbine engines is critical for monitoring their health and operational performance. To monitor the two parameters simultaneously, a non-intrusive sensor based on tunable diode laser absorption spectroscopy is developed using 8 laser beams targeting 3 transitions of water vapor. The sensor has in situ validated on a commercial auxiliary power unit. Seven parallel laser beams at 5000.2 cm−1 are 6.3 mm spaced at the plume boundary to characterize the edge effect between hot exhaust plume and cold surrounding flow. One beam, operating at the dual wavenumbers of 7185.6 cm−1 and 7444.4 cm−1 penetrates the plume through centerline to measure temperature via ratio thermometry. Then, this temperature information is used to obtain the concentration of water vapor. A temporal resolution of 4 ms is achieved for the 8-beam measurement, enabling high-speed and simultaneous quantification of the edge effects and the plume parameters. Results indicate water vapor concentration and temperature in the exhaust measured by the developed sensor are highly consistent with the traditional benchmarks, e.g., extractive sampling and thermocouples, with a difference of 0.02% and 3 °C, respectively. Enabled by its continuous millisecond-level measurements, the sensor, for the first time, reveals hidden engine behaviors and combustion dynamics that are unable to be observed by the traditional methods, thus facilitating next-generation real-time gas turbine engine control towards low emissions.

Utilizing Machine Learning for Rapid Discrimination and Quantification of Volatile Organic Compounds in an Electronic Nose Sensor Array

Volatile organic compounds (VOCs) are ubiquitous in the surroundings, originating from both industrial and natural sources. VOCs directly impact the quality of both indoor and outdoor air and play a significant role in processes such as fruit ripening and the body’s metabolism. VOC monitoring has seen significant growth recently, with an emphasis on developing low-cost, portable sensors capable of both vapor discrimination and concentration measurements. VOC sensing remains challenging, mainly because these compounds are nonreactive, appear in low concentrations and share similar chemical structures that results in poor sensor selectivity. Therefore, individual gas sensors struggle to selectively detect target VOCs in the presence of interferences. Electronic noses overcome these limitations by employing machine learning for pattern recognition from arrays of gas sensors. Here, an electronic nose fabricated with four types of functionalized gold nanoparticles demonstrates rapid detection and quantification of eight types of VOCs at four concentration levels. A robust two-step machine learning pipeline is implemented for classification followed by regression analysis for concentration prediction. Random Forest and support vector machine classifiers show excellent results of 100% accuracy for VOC discrimination, independent of measured concentration levels. Each Random Forest regression analysis exhibits high R2 and low RMSE with an average of 0.999 and 0.002, respectively. These results demonstrate the ability of gold nanoparticle gas sensor arrays for rapid detection and quantification.

On the measurement of local vapor concentration around sessile water droplet with high spatiotemporal resolution

Droplet evaporation is a seemingly simple heat and mass transfer process, while of which high-fidelity characterization of the vapor field remains a long-standing challenge. In this brief communication, we report the first experimental observation of the local vapor concentration of the sessile water droplet with unprecedently high spatiotemporal resolution. The experimental measurement was enabled by a tailored quartz-enhanced photoacoustic spectroscopy (QPEAS) system. In this system, a near-infrared, continuous-wave, distributed feedback laser at 1392 nm was utilized to excite the photoacoustic signal of water vapor above the sessile droplet. The photoacoustic signal between the prongs of a tiny quartz tuning fork (QTF) was detected and further interpreted as the vapor concentration information. The feasibility of QEPAS for droplet evaporation characterization was carefully verified. As a demonstration, we measured the time histories of water vapor concentration above the evaporating droplet in both open and closed chambers at the spatial resolution of ∼30 micrometers and temporal resolution of 0.1 ms. Interestingly, we found the vapor concentration above the evaporating droplet in open ambient featured distinct fluctuations indiscernible to the conventional photography method. Such fluctuation has never been reported before and further corroborated the insufficiency of quasi-steady approximation for droplet evaporation. This work not only extends the application of QEPAS to more complicated physical processes, but also advances the state of the art in the experimental characterization of sessile water droplet evaporation, which opens up a new possibility to unravel the intricate mechanism of the vapor-mediated droplet motions.

Experimental evaluation of the effect of benzene and toluene on measurement of mercury vapor concentration with an analyzer based on the transverse Zeeman effect

Experimental evaluation of the effect of benzene and toluene on measurement of mercury vapor concentration with an analyzer based on the transverse Zeeman effect

Vapor concentration and temperature field measurement of an evaporating sessile drop by tomographic laser absorption spectroscopy

Drop evaporation is a ubiquitous phenomenon that has been studied for over a century. However, the surrounding gas-phase field including the temperature and vapor concentration distribution is not sufficiently studied experimentally. In this paper, a sensor based on tunable laser absorption spectroscopy is designed to study the vapor-phase temperature and concentration distribution of evaporating sessile drops, and data processing method involving data pre-processing and tomographic reconstruction is proposed to realize high-precision, spatially resolved measurement, which was realized by scanning the mechanical galvanometer in the horizontal direction. With free-knot splines smoothing and “denucleated” onion-peeling algorithm, temperature and H2O concentration distributions surrounding the evaporated drop at three different substrate plate temperatures are observed. The concentration and temperature in close vicinity to the gas–liquid interface are reconstructed accurately despite the high-gradient changes. A spatial resolution of under 100 μm with a temporal resolution of 10 s has been realized. Quantitative depiction of the temperature and concentration fields shows evidence of convection and indicates that while the concentration level sharply peaks at the interface, temperature in the close vicinity to the drop shows flattening or even dipping trends. The in situ laser measurement results are validated against contact measurement, theoretical prediction with saturated vapor pressure, and model simulation of COMSOL. Uncertainties have been evaluated based on both repeated measurements and model prediction of input uncertainty propagation. Temperature and concentration measurement uncertainties are estimated to be <1.5% and <3.5%, respectively, even though all experiments were performed in open air with non-negligible buoyancy-induced convection.

Methanol cookstove a potential alternative to LPG cookstove: Usability, safety and sustainability studies

In the present study, the performance of methanol cookstove as a possible substitute for Liquefied Petroleum Gas (LPG) cookstoves in terms of usability (fuel convenience, cooking performance, operability, maintenance and comfort) and safety (temperature of touchable parts and mechanical stability) are presented. To introduce methanol as an alternative cooking fuel, thermal and emission performances of methanol cookstoves are evaluated. It was found that methanol cookstove yielded a maximum thermal efficiency of 63.2 % at firepower of 1.5 kW and a lesser CO/CO2 ratio of 0.0047 as compared to the prescribed limit (0.02) of IS 11760:1986. The measurement of methanol vapour concentration with burn cycle of 4 h was revealed that the methanol vapour in the confined space was less than 5 ppm which is 97.5 % lesser than the prescribed exposure limit. Also, the methanol cookstove secures a similar score of LPG in terms of maintenance, comfort and mechanical stability. Further, the fuel sustainability analysis revealed that with a 10 % methanol penetration rate in India, 3.69 MMT of LPG import could be reduced by 2030. Safety instructions are also prepared for methanol cookstove which assists in formulating a policy and planned actions that encourages the use of methanol as a safer and cleaner alternative to the LPG.

Measurements of Atmospheric Water Vapor by a 1.316 μm Optical Fiber Laser Heterodyne Radiometer

A passive optical fiber laser heterodyne radiometer prototype with a semiconductor laser near 1.316 μm as the local oscillator was built, parameters of the prototype have been optimized. Using the prototype, the water vapor concentration in the atmospheric column was measured with a spectral resolution of 0.009 cm−1 in late October and early November of 2020, the collection time was approximately 3 min, and the signal-to-noise ratio was better than 120. The water vapor column concentration and profiles were inversed based on the optimal estimation method. Compared with the measurement of the Fourier transform spectrometer (EM27/SUN) which was performed simultaneously, the inversion results deviated by less than 14%, and the variation trend of the water vapor concentration showed good consistency. It is demonstrated that the 1.316 μm optical fiber laser heterodyne radiometer possesses good stability and accuracy in the field measurement of atmospheric water vapor concentration.

Simultaneous measurement of H2O concentration and effective absorption optical path length under unknown optical path length condition based on a single spectral line

Quantitative gas measurement under the condition of unknown optical path length is a challenge in laser absorption spectroscopy technology field. In this paper, we proposed a tunable diode laser absorption spectroscopy line shape analysis (TDLAS-LSA) method for simultaneous measurement of water vapor concentration and effective optical path length (EOPL) under unknown optical path conditions. A single H2O absorption line near 1383.9 nm (7226.02 cm−1) was selected, and its line strength, self-broadening coefficient and temperature-dependence coefficient were measured experimentally to improve the HITRAN databases. The Lorentz broadening and line area were accurately extracted by Hartmann-Tran profile (HTP) fitting, and the gas concentration and EOPL were calculated based on the spectral line shape analysis method. Eight concentrations of water vapor in the range of 146 ppm ∼ 4.39% were measured experimentally, and the maximum average deviation between the TDLAS-LSA method and the commercial sensor was less than 7.1%. Comparing the EOPL with mechanical measurement, the maximum deviation of multiple measurements is less than 5.7%. The results showed that the TDLAS-LSA method can effectively perform gas sensing under unknown optical path conditions, and has great application potential in low-cost, in-situ and multi-parameter simultaneous measurement.

Supercontinuum lidar for industrial process analysis

Real-time monitoring of flue gas parameters in combustion processes is central to the optimization of the process efficiency and reduction of pollutants emission. We report simultaneous measurement of the average water vapor temperature and concentration over a 9 m distance in a full-scale industrial boiler by broadband lidar employing a custom supercontinuum source covering the wavelengths of ro-vibrational absorption of water molecules at 1.2 – 1.55 µm. The measured average temperature and concentration are in excellent agreement with reference measurements. We also take advantage of the backscattering from the aerosol particles present in the boiler to map the water vapor concentration profile in the boiler up to a distance of 2.7 m with a spatial resolution of 30 cm. Our results open novel perspectives for 3D profiling of temperature and gas concentration in industrial environments.

Linear calibration‐free wavelength modulation spectroscopy

AbstractThis article presents a new linear calibration‐free wavelength modulation spectroscopy (LCF‐WMS) technique for gas sensing. By combining the natural logarithms of the transmitted intensity and background signals, this technique eliminates the effects of the intensity, intensity modulation, and the modulation phase to obtain integrable harmonic signals along the line‐of‐sight and thus realize calibration‐free measurements. To illustrate the validity of the LCF‐WMS technique, it was applied to measurement of the water vapor concentration in air at ambient temperature. Because of its specific features of line‐of‐sight integrability and baseline independence, this method will be advantageous in absorption tomography and high‐pressure applications.

TDLAS measurements of temperature and water vapor concentration in a flameless MILD combustor

We performed non-intrusive tunable diode laser absorption spectroscopy measurements of the temperature (T) and water vapor concentration (X H2O) on a moderate or intense low-oxygen dilution combustion chamber. The combustor was operating in flameless mode by axially injecting fuel and air at high speeds through separate nozzles, thereby creating a recirculating flow of combusted gas. A pair of water vapor absorption lines near 7185.6 and 7444.36 cm−1 was used to acquire axial absorbance profiles along the height of the combustor. The axial profiles of T and X H2O were first derived using two-line thermometry measurements. Then the T profiles were estimated from each of the single absorption line measurements by assuming spatial uniformity of X H2O. Compared to a thermocouple temperature measured at the combustor outlet, the temperatures given by the two-line thermometry were under-estimated whereas the thermocouple temperature was in between the T range given by the single-line thermometry. Importantly, the measurement successfully revealed that the axial profiles of T and X H2O were mostly flat certainly due to the strong recirculation of the hot combustion gas; however, the different temperature values at a given height implied the existence of a radial temperature gradient in the combustor.

A method to measure vapor concentration of droplet evaporation based on background oriented Schlieren

The direct visualization of vapor distribution and quantitative measurement of vapor concentration plays an important role in studying droplet evaporation. In this study, we propose a method to measure the vapor concentration field based on the modified background oriented Schlieren, inverse Radon transform, high-speed imaging, and image processing. The method is demonstrated for the measurement of the transient concentration field during the impact of volatile droplets on solid surfaces. The results show that the vapor distribution is remarkably different from the diffusion-limited model because of the strong convection. The complex structure of the vapor cloud is the result of the interplay among fluid inertia, fluid evaporation, vapor diffusion, vapor convection, and droplet shape evolution.

Концентрация паров кадмия и время жизни верхнего рабочего уровня He-Cd-лазера с ядерной накачкой на переходе 5s-=SUP=-2-=/SUP=- -=SUP=-2-=/SUP=-D-=SUB=-5/2-=/SUB=--5p-=SUP=-2-=/SUP=-P-=SUB=-3/2-=/SUB=- Cd II

Experimental method is described and results of measurement of the cadmium vapor concentration in a nuclear pumped He-Cd laser on the cadmium ion transition with wave length 0.441 μm are presented . It is shown that observed concentration is about ten times less then saturated one for given temperature of laser cuvette. On the base of obtained data the conclusion is made that life time of the upper level for CdII 5s2 2D5/2 -5p2P3/2 transition in a optimum condition of He-Cd laser operation equals about 0.5 μs.

Temperature and concentration measurements in a high-pressure gasifier enabled by cepstral analysis of dual frequency comb spectroscopy

High-pressure gasification processes are important for conversion of solid materials into gaseous fuels and other chemicals. Laser absorption diagnostics are an important means to study these processes, but are challenging to implement due to the extreme temperatures and pressures present in the system. Here, we combine broadband high-resolution dual-comb spectroscopy with an advanced spectral absorption database and a new means for baseline-free absorption spectroscopy analysis to enable measurements of temperature and water vapor concentration in the core of an entrained flow gasifier operating at up to 1700 K and 15 bar. The dual-comb spectrometer measures the absorption of water vapor from 6800 to 7150 cm−1 with a point spacing of 0.0067 cm−1. The bandwidth is helpful for resolving the complex, congested absorption fingerprint of water vapor that is used to determine the species concentrations and temperature. We interpret the spectrum with absorption models based on a database measured under carefully controlled high-temperature conditions with the dual-comb spectrometer. The database includes the pressure broadening, shift, and temperature dependence of these parameters for water vapor in argon, which is the gasifier bath gas. Finally, fitting the absorption model to the data is enabled by modified free induction decay analysis, which is an approach for quantitatively obtaining species and temperature information without determining the baseline intensity of the spectrometer. The baseline-free approach is crucial to success in this environment, where there are no non-absorbing regions of the spectrum to anchor the normalization of the laser intensity as in traditional direct absorption spectroscopy. We demonstrate good agreement with temperatures measured on the reactor core via optical pyrometry, and show that water vapor concentrations in the reactor core did not reach the expected system set points during some experiments.

Research on laser water vapor concentration detection technology in the air-sea flux observation

In the observation of water vapor flux at air-sea interface, the collection frequency of water vapor concentration is more than 10 Hz. High-speed and high-precision measurement of water vapor concentration is an urgent problem to be solved in the observation of water vapor flux at air-sea interface. The ratio of the peak-peak value of second harmonic to the average value of first harmonic is used to measure water vapor concentration based on tunable diode laser absorption spectroscopy. The sensitivity of laser water vapor concentration detection equipment caused by marine salt fog and dust is reduced through precise optical design, and the water vapor concentration at the air-sea interface is calculated using a binary polynomial fitting algorithm. The response frequency of the laser water vapor concentration analyzer is 40 Hz. The water vapor concentration values from the laser water vapor concentration analyzer and LI-7500 CO2/H2O gas analyzer are collected synchronously in real time using LabVIEW software. The comparison results show that they have good consistency in the trend and response speed of water vapor concentration, and the measurement deviation of water vapor concentration is within ±1%. The experimental results show that it can meet the needs of high-speed, high-precision measurement of water vapor concentration in the air-sea interface water vapor flux observation.