Water Vapor Transitions Research Articles

Studying the morphology of lyophilized protein solids using X-ray micro-CT: effect of post-freeze annealing and controlled nucleation.

The objective of this study was to determine how different techniques used during the freezing step of lyophilization affect morphology of the dried protein solids. Aqueous solutions containing recombinant human albumin, trehalose, and sodium phosphate buffer were dried after their freezing by shelf-ramp cooling, immersion in liquid nitrogen, or controlled ice nucleation. Some shelf-frozen solutions were heat treated (annealed) before the vacuum drying. We used three-dimensional (3D) X-ray micro-computed tomography (micro-CT) and scanning electron microscopy (SEM) to study the morphology of solids. The X-ray micro-CT images of the lyophilized microporous solids showed traces of varied size and structure ice crystals that were comparable to corresponding SEM images. A post-freeze heat treatment and a controlled nucleation both induced larger ice crystal ghosts in the solids. The variations in the structure of walls surrounding ice crystals, formed by the different freezing procedures, should affect the water vapor transition during the primary and secondary drying. Some solids also showed higher-density layer in the upper surface. Overall, the simple sample preparation procedures and the ample morphological information make the X-ray micro-CT appropriate for analyzing lyophilized pharmaceuticals.

Search for the 22 GHz water maser emission in selected comets

Following the first evidence of planetary water maser emission induced by the collision of comet Shoemaker/Levy with Jupiter and the puzzling detection of the 22GHz water emission line in Comet Hyakutake we started in the period 2002–2008 systematic observations of selected comets at 22GHz (1.35cm) with the aim of clarifying the unusual behavior of the maser line in the cometary “scenario”. Using a fast multichannel spectrometer coupled to the 32m dish of the Medicina (Bologna, Italy) Radio Telescope we investigated 6 bright or sungrazing comets down to a heliocentric distance of 0.11AU: 96P/Machholz, 153P/ Ikeya–Zhang, C/2002 V1 (NEAT), C/2002 X5 (Kudo–Fujikawa), C/2002 T7 (Linear), and 73P/Schwassmann–Wachmann 3. All of them, similarly to Comet Hyakutake, demonstrate spectral features that, if real and due to the 1.35cm water vapor transition, are strongly (up to tens of km/s) shifted relative to the radial velocity of the nucleus and, at least sometimes, seem to be present as two separate peaks. If our interpretation of these spectral peaks is correct, there must be some mechanism of acceleration of neutral water molecules up to the velocities of ions. We discuss here the results achieved and the possible explanation of the chemo-physical constraints.

High-speed diode laser measurements of temperature and water vapor concentration in the intake manifold of a diesel engine

A diode laser–based sensor system, utilizing absorption spectroscopy, has been developed to provide high-speed (5 kHz) simultaneous measurements of temperature and water vapor concentration in the intake manifold of a diesel engine. A fiber-coupled 1.38 µm diode laser was used to probe absorption transitions of water vapor for the high-speed gas temperature and water vapor concentration measurements. Water vapor readily absorbs in the near-infrared region, and distributed feedback diode lasers as well as optics for near-infrared region are readily available because of their use in telecommunications. Fresh charge and combustion products are the only sources of water vapor in an engine’s gas exchange path; therefore, water vapor concentration at various locations in the intake manifold is a useful measure of the recirculated exhaust gas distribution in the intake manifold. Measurements were performed on a six-cylinder Cummins diesel engine using compact fiber optic–coupled connectors. The chosen water vapor absorption transitions provided good absorption strength even without exhaust gas recirculation and water vapor concentration of as low as 0.7 vol.% could be measured with a signal-to-noise ratio of ∼35 leading to very good spectral fits. The sensor output was within 2% of the thermocouple readings and within 10% of the water vapor concentration derived from mean CO2 analyzer measurements for steady-state engine operation. For transient engine operation, the time response of the diode laser sensor was shown to be vastly superior to that of the installed thermocouple and the gas analyzer system.

Measurement of nonuniform temperature and concentration distributions by combining line-of-sight tunable diode laser absorption spectroscopy with regularization methods

Regularization methods were combined with line-of-sight tunable diode laser absorption spectroscopy (TDLAS) to measure nonuniform temperature and concentration distributions along the laser path when a priori information of the temperature distribution tendency is available. Relying on measurements of 12 absorption transitions of water vapor from 1300 to 1350 nm, the nonuniform temperature and concentration distributions were retrieved by making the use of nonlinear and linear regularization methods, respectively. To examine the effectiveness of regularization methods, a simulated annealing algorithm for nonlinear regularization was implemented to reconstruct the temperature distribution, while three linear regularization methods, namely truncated singular value decomposition, Tikhonov regularization, and a revised Tikhonov regularization method, were implemented to retrieve the concentration distribution. The results show that regularization methods not only can be used to retrieve temperature and concentration distributions closer to the original but also are less sensitive to measurement noise. When no sufficient optical access is available for TDLAS tomography, the methods proposed in the paper can be used to obtain more details of the combustion field with higher accuracy and robustness, which are expected to play a more important role in combustion diagnosis.

Rayleigh convective instability in the presence of phase transitions of water vapor. The formation of large-scale eddies and cloud structures

Convective motions in moist saturated air are accompanied by the release of latent heat of condensation. Taking this effect into account, we consider the problem of convective instability of a moist saturated air layer, generalizing the formulation of the classical Rayleigh problem. An analytic solution demonstrating the fundamental difference between moist convection and Rayleigh convection is obtained. Upon losing stability in the two-dimensional case, localized convective rolls or spatially periodic chains of rollers with localized areas of upward motion evolve. In the case of axial symmetry, the growth of localized convective vortices with circulation characteristic of tropical cyclones (hurricanes) is possible at the early stages of development and on the scale of tornados to tropical cyclones.

Velocity effects on the shape of pure H2O isolated lines: Complementary tests of the partially correlated speed-dependent Keilson-Storer model

Complementary tests of the partially correlated speed-dependent Keilson-Storer (pCSDKS) model for the shape of isolated transition of pure water vapor [N. H. Ngo et al., J. Chem. Phys. 136, 154310 (2012)] are made using new measurements. The latter have been recorded using a high sensitivity cavity ring down spectrometer, for seven self-broadened H(2)O lines in the 1.6 μm region at room temperature and for pressures from 0.5 to 15 Torr. Furthermore, the H(2) (18)O spectra of [M. D. De Vizia et al., Phys. Rev. A 83, 052506 (2011)] in the 1.38 μm region, measured at 273.15 K and for pressures from 0.3 to 3.75 Torr have also been used for comparison with the model. Recall that the pCSDKS model takes into account the collision-induced velocity changes, the speed dependences of the broadening and shifting coefficients as well as the partial correlation between velocity and rotational-state changes. All parameters of the model have been fixed at values previously determined, except for a scaling factor applied to the input speed-dependent line broadening. Comparisons between predictions and experiments have been made by looking at the results obtained when fitting the calculated and measured spectra by Voigt profiles. The good agreement obtained for all considered lines, at different temperature and pressure conditions, confirms the consistency and the robustness of the model. Limiting cases of the model have been then derived, showing the influence of different contributions to the line shape.

Line mixing in the water vapour transitions of the ν1 + ν2 + ν3 band perturbed by helium pressure

The line mixing effect for two pairs of transitions with rotational quantum numbers (3 1 2) ← (4 1 3), (3 2 1) ← (4 2 2), (4 3 1) ← (3 3 0) and (4 2 2) ← (3 2 1) in the ν1 + ν2 + ν3 band of H2O has been studied. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm−1 and in a wide pressure range of helium. Pressure-broadening and -shifting coefficients and mixing parameter were obtained with help of the line profile using the Rosenkranz first-order approximation.

Stability of a water-vapor phase transition interface in geothermal systems

The problem of normal stability of a phase transition interface for vertical flows in a geothermal reservoir with the water layer lying above the vapor layer is solved. The problem is formulated with account for convective energy transfer, which ensures applicability for arbitrary permeability values. Typical examples of variation of the phase transition interface stability parameters in response to changes in permeability are considered for various geothermal reservoirs.

Numerical simulation of formation of cyclone vortex flows in the intratropical zone of convergence and their early detection

Mechanisms of formation of cyclonic vortices in the tropical atmosphere of the Earth are investigated in the intratropical zone of convergence using numerical simulation made with the complete system of equations of gas dynamics taking into account transport of infrared radiation, phase transitions of water vapor into microdrops of water and ice particles, and sedimentation of these drops and ice particles in the field of gravity force. Observational data on the structure of dominant air streams, which are formed in the intratropical zone of convergence over the North Atlantic in the periods of its highest thermodynamic intensity and instability, are used in the initial and boundary conditions of the model. Formation of cyclonic vortex flows is obtained numerically at sufficiently strong bending of the intratropical zone of convergence. The results of numerical modeling are compared with the data of satellite microwave monitoring: global radio thermal fields of the Earth from the electronic collection GLOBAL-Field allowing one to study the structure of atmospheric motions in a wide range of space-time scales.

A mechanism of formation of polar cyclones and possibility of their prediction using satellite observations

Using numerical simulation, a mechanism of formation of polar cyclones in the region of location of the arctic front in the winter troposphere of the Northern Hemisphere is studied. The simulation was performed with the help of the complete system of gas dynamics equations taking into account the transport of infrared radiation, phase transitions of water vapor into micro-drops of water and ice particles, and with allowance made for sedimentation of these drops and ice particles in the gravity field. In the initial and boundary conditions of the model, observational data on the structure of dominating air flows in the region of the arctic front over Norwegian Sea in January are used. Formation of large-scale cyclonic vortex flows in 15–20 hours at the presence of a bend of the central line of the shear flow in the arctic front 500–600 km long with northward or southward deviations by 100 km and more is obtained numerically. On the basis of the simulation results, a method of short-term forecast of formation and motion of polar cyclones is suggested.

An aircraft based three channel broadband cavity enhanced absorption spectrometer for simultaneous measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub> and NO<sub>2</sub>

Abstract. A three channel broadband cavity enhanced absorption spectroscopy (BBCEAS) instrument has been developed for airborne measurements of atmospheric trace gases involved in night-time oxidation chemistry and air quality. The instrument was deployed on board the Facility for Airborne Atmospheric Measurements BAe 146-301 atmospheric research aircraft during the Role of Nighttime Chemistry in Controlling the Oxidising Capacity of the Atmosphere (RONOCO) measurement campaigns between December 2009 and January 2011. In its present configuration (i.e. specifications of the cavity optics and spectrometers) the instrument is designed to measure NO3, N2O5 (by detection of NO3 after thermal dissociation of N2O5), H2O and NO2 by characterising the wavelength dependent optical attenuation within ambient samples by molecular absorption around 662 nm (NO3 and H2O) and 445 nm (NO2). This paper reports novel advancements in BBCEAS instrumentation including a refined method for performing BBCEAS mirror reflectivity calibrations using measurements of the phase delay introduced by the optical cavities to amplitude modulated radiation. Furthermore, a new methodology is introduced for fitting the strong but unresolved transitions of water vapour, which is required for accurate retrieval of water absorption features from the 662 nm absorption band used to measure NO3 concentrations. The paper also details the first example of airborne measurements of NO3, N2O5 and NO2 over Europe from a flight over the North Sea and Thames Estuary on the night of the 20 July 2010, one of the most polluted days of the RONOCO summertime flying period. As part of this analysis, the performance of the BBCEAS instrument is assessed by comparing airborne NO2 measurements to those reported concurrently by a photolytic chemiluminescence based detector.

HERSCHEL /HIFI OBSERVATIONS OF IRC+10216: WATER VAPOR IN THE INNER ENVELOPE OF A CARBON-RICH ASYMPTOTIC GIANT BRANCH STAR

We report the results of observations of ten rotational transitions of water vapor toward the carbon-rich AGB (asymptotic giant branch) star IRC+10216 (CW Leonis), carried out with Herschel's HIFI instrument. Each transition was securely detected by means of observations using the dual beam switch mode of HIFI. The measured line ratios imply that water vapor is present in the inner outflow at small distances (few x 1.E+14 cm) from the star, confirming recent results reported by Decin et al. from observations with Herschel's PACS and SPIRE instruments. This finding definitively rules out the hypothesis that the observed water results from the vaporization of small icy objects in circular orbits. The origin of water within the dense C-rich envelope of IRC+10216 remains poorly understood. We derive upper limits on the H2-17O/H2-16O and H2-18O/H2-16O isotopic abundance ratios of ~ 5.E-3 (3 sigma), providing additional constraints on models for the origin of the water vapor in IRC+10216.

Numerical Prediction of Impact Force in Cavitating Flows

A numerical method including a macroscopic cavitation model based on the homogeneous flow theory and a microscopic cavitation model based on the bubble dynamics is proposed for the prediction of the impact force caused by cavitation bubble collapse in cavitating flows. A large eddy simulation solver, which is incorporated with a macroscopic cavitation model, is applied to simulate the unsteady cavitating flows. Based on the simulated flow field, the evolution of the cavitation bubbles is determined by a microscopic cavitation model from the resolution of a Rayleigh–Plesset equation including the effects of the surface tension, the viscosity and compressibility of fluid, the thermal conduction and radiation, the phase transition of water vapor at the interface, and the chemical reactions. The cavitation flow around a hydrofoil is simulated to validate the macroscopic cavitation model. A good quantitative agreement is obtained between the prediction and the experiment. The proposed numerical method is applied to predict the impact force at cavitation bubble collapse on a KT section in cavitating flows. It is found that the shock pressure caused by cavitation bubble collapse is very high. The impact force is predicted qualitatively compared with the experimental data.

A comparative study of the effects of different buffer gases on the line shape of water vapour rovibronic transition

The line shape parameters of water vapour rovibrational transition at 12145.444 cm −1 belonging to the (2 ν 1 + ν 2 + ν 3) overtone band in the presence of three buffer gases He, N 2 and CO 2 are studied by high resolution near infrared (NIR) diode laser spectrometer. The wavelength modulation spectroscopy (WMS) is adopted to probe buffer gas broadened first derivative (1f) signal of water vapour transition. The simulation of the experimental signals based on Voigt profile provides the collisional broadening coefficients and line strength parameters. The comparison is made between the broadening effects on water vapour transition induced by He, N 2 and CO 2.

Diode laser spectroscopy of He, N2 and air broadened water vapour transitions belonging to the (2ν1 + ν2 + ν3) overtone band

The line shape parameters of rovibrational transitions of water vapour belonging to the (2ν1 + ν2 + ν3) overtone band due to collisions between absorber molecules and noble gas helium have been measured in the spectral range between 11988.494 cm−1 and 12218.829 cm−1 using NIR diode laser spectrometer. In addition nitrogen and air broadening effects on some water vapour transitions belonging to the same band have also been studied. Wavelength modulation spectroscopy along with phase sensitive detection technique are used to record first derivative (1f) signal of buffer gas broadened water vapour transitions. Observed line shapes are fitted to standard Voigt profiles by non-linear least squares fitting program to extract the line shape parameters, like line strength and pressure broadening coefficients. The broadening effects induced by different types of buffer gases on water vapour line shapes are compared. Rotational quantum number (J) dependence of broadening coefficients of water vapour transitions is also examined.

Overtone spectroscopy of water molecules based on room temperature diode laser emitting in the NIR range

The measurement of very weak overtone spectroscopic line shape of water molecule is performed using wavelength modulation spectroscopy (WMS). In this work a high resolution near infrared diode laser spectrometer is used to record first derivative (1f) signal of buffer gas Helium and Carbon dioxide broadened water vapour transitions around 820 nm wavelength region. The effect of collision due to perturber pressure on signal to noise ratio (SNR) is discussed. The Lorentzian HWHM of observed 1f signal is calculated. The comparison is made between collisional broadening of water vapour transition broadened by inert gas Helium and high quadrupole moment active gas Carbon dioxide.

Numerical prediction of impact force in cavitating flows

An analytical method including a macroscopic cavitation model based on the homogeneous flow theory and a microscopic cavitation model based on the bubble dynamic was proposed for the prediction of the impact force caused by cavitation bubbles collapse in cavitating flows. A Large Eddy Simulation (LES) solver incorporated the macroscopic cavitation model was applied to simulate the unsteady cavitating flows. Based on the simulated flow field, the evolution of the cavitation bubbles was determined by a microscopic cavitation model from the resolution of a Rayleigh-Plesset equation including of the effects of the surface tension, the viscosity and compressibility of fluid, thermal conduction and radiation, the phase transition of water vapor at interface and chemical reactions. The cavitation flow around a hydrofoil was simulated to validate the macroscopic cavitation model. A good quantitative agreement was obtained between the prediction and the experiment. The proposed analytical method was applied to predict the impact force at cavitation bubbles collapse on a KT section in cavitating flows. It was found that the shock pressure caused by cavitation bubble collapse is very high. The impact force was predicted accurately comparing with the experimental data.

An investigation of collisional processes in a Dicke narrowed transition of water vapor in the 7.8 μm spectral region by frequency down-chirped quantum cascade laser spectroscopy

Information about intermolecular potentials is usually obtained through the analysis of the absorption line shapes recorded in the frequency domain. This approach is also adopted to study the effects of motional narrowing and speed dependence of the pressure broadening coefficients. On the other hand, time domain measurements are directly related to molecular collisions and are therefore frequently employed to study molecular relaxation rates, as well as the effects of velocity changing collisions and the speed dependence of the absorption cross sections. Intrapulse quantum cascade laser spectrometers are able to produce both saturation and molecular alignment of the gas sample. This is due to the rapid sweep of the radiation through the absorption features. In the present work the frequency down-chirped radiation emitted by an intrapulsed quantum cascade laser operating near 7.8 mum is employed to investigate the collisional relaxation processes, and the collisional narrowing, in the 15(0,15)<--16(1,16) and 15(1,15)<--16(0,16) doublet in the water vapor nu(2) band. The effects of He, Ne, Ar, N(2), and CO(2) as collisional partners are investigated. The experimental results clearly indicate the dependence of the collisional cross sections upon the chirp rate. They also demonstrate that by using different chirp rates it is possible to gain information about the intermolecular processes driving the molecular collisions and the related energy transfer.

Technique of laser calibration for wavelength-modulation spectroscopy with application to proton exchange membrane fuel cell measurements

A diode laser sensor was developed for partial pressure and temperature measurements using a single water vapor transition. The Lorentzian half-width and line intensity of the transition were calibrated for conditions relevant to proton exchange membrane (PEM) fuel cell operation. Comparison of measured and simulated harmonics from wavelength-modulation spectroscopy is shown to yield accuracy of +/-2.5% in water vapor partial pressure and +/-3 degrees C in temperature despite the use of a single transition over a narrow range of temperatures. Collisional half-widths in air or hydrogen are measured so that calibrations can be applied to both anode and cathode channels of a PEM fuel cell. An in situ calibration of the nonlinear impact of modulation on laser wavelength is presented and used to improve the accuracy of the numerical simulation of the signal.

Tunable Diode Laser Spectroscopy With Wavelength Modulation: Calibration-Free Measurement of Gas Compositions at Elevated Temperatures and Varying Pressure

The validity of two new approaches to tunable diode laser spectroscopy (TDLS) in the near-IR, namely the residual amplitude modulation approach and the phasor decomposition method, is investigated for application in industrial process monitoring where the operating temperatures and pressures are high and subject to significant change. Both techniques allow the recovery of absolute absorption profile line shapes and are completely calibration free, making them very attractive for online deployment in stand alone instrumentation in harsh environments where the calibration factors in conventional TDLS methods are subject to significant cumulative errors and drift. Currently established TDLS techniques, and indeed conventional gas composition analysis techniques, suffer from significant limitations when applied under these conditions, and there is a clear need for the development of a suitable alternative. The primary focus in this work is the analysis of water vapor in solid oxide fuel cell diagnostics where the operating temperatures range from 700degC to 950degC, the gas pressures are subject to change and the recovered signal levels are low. The 1391.7 nm overtone water vapor transition is interrogated over the above temperature range of interest at concentrations of 6%-50%, while the 1650.96 nm methane transition is also analyzed over a range of gas pressures at a fixed concentration of 1%. Excellent agreement between the experimentally recovered absorption line shapes and simulations based on parameters from the HITRAN (2004) database is observed; further evidence for the efficacy of the techniques is demonstrated through the accuracy of the gas concentration measurements which were achieved by curve-fitting absorption line shape simulations to the experimental data.