Water Vapor Concentration In Air Research Articles

Atmospheric water harvesting in semi-arid regions by membranes: A techno-economic assessment

The availability of a reliable and sufficient amount of water constitutes one of the Sustainable Development Goals set by the United Nations. The provision of water is still challenging in many regions of the world, especially in arid and semi-arid regions, where the precipitations are rare and there is no access to water bodies. We propose to use a water harvesting device based on high-performance membranes to produce water from air in a decentralized way. The device presents a single membrane stage to increase the purity of water vapor in air and a condenser to produce liquid water. We optimize the operating conditions to bring down the water cost to 3.2 cent/L when the water fraction in air is 3% and 5.0 cent/L when the water fraction is 2%. We also found that the increase of water vapor permeance up to 5 × 104 gas pemeation units is beneficial to cost reduction (between 2.2 and 3.0 cent/L) and that the losses due to concentration polarization can be reduced by designing properly the channel geometry. Finally, we simulated the yearly operation of a device located in a semi-arid region, by taking into account the variation of water vapor concentration in air, and we found attractive values of water cost, below 10 cent/L for most of the year. Thus, the proposed process can give an important contribution to the alleviation of water shortage issue in semi-arid regions. Importantly, it makes membrane-based process attractive for atmospheric water harvesting.

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.

Effects of humidity on SrTi0.05Co0.95O3-δ cathode properties and durability of solid oxide fuel cells

Degradation suffering from ambient water vapor in air is harmful for cathodes of solid oxide fuel cells (SOFCs), it is necessary and important to research its attenuation mechanism and related preventive methods. Here, effects of humidity on SrTi0.05Co0.95O3-δ (STC) cathode have been discussed in detailed. X-ray diffraction analysis reveals that STC is relatively stable in wet air with a little crystal contraction, but without obvious impurities. Because active sites of STC for oxygen reduction reaction (ORR) are covered by water vapor, the electrical conductivity decreases while the polarization resistance (Rp) increases with the increasing of the water vapor concentration in air. Compared with Rp measured in dry air, the enhanced Rp value is 0.0347 Ω cm2 and 0.0493 Ω cm2 in containing 3% and 5% H2O air after a continuous testing for 96 h at 800 °C, respectively. Furthermore, a maxium power densities of 832 mW cm−2 and 814 mW cm−2 can be obtained for STC/LSGM/STC in dry air and containing 5% H2O air after 96 h operating at 800 °C, respecctively. Interestingly, the degradation coming from humidity can be recovered partially by switching the feedgas back to dry air again. The Rp of STC becomes ~0.0402 Ω cm2 again after switching the operating atmosphere from 5% H2O air to dry air for 5 h.

Effect of humidity on gas temperature in the afterglow of pulsed positive corona discharge

The effects of humidity on gas temperature in the afterglow of a pulsed positive corona discharge are studied. The gas temperature is measured using the laser-induced fluorescence (LIF) of NO molecules. The discharge occurs in a 13 mm point-to-plane gap under atmospheric pressure. When the water vapor concentration in air is increased from 0.5% to 2.4%, the temperature increases from 550 to 850 K near the anode tip, and from 350 to 650 K at a position 2.5 mm from the anode tip. The gas heating in the humid environment is due to the fast vibration-to-vibration processes of the O2–H2O and N2–H2O systems and the extremely rapid vibration-to-translation process of the H2O–H2O system. These processes accelerate the transfer of energy from O2(v) and N2(v) to translational energy. Measurements of the LIF of O2(v = 6) show that the decay rate of O2(v) density is increased by humidification.

Implications of persistent ice supersaturation in cold cirrus for stratospheric water vapor

Recent measurements made near the tropical tropopause during the NASA Cirrus Regional Study of Tropical Anvils and Cirrus Layers ‐ Florida Area Cirrus Experiment (CRYSTAL‐FACE) indicate persistent ice saturation ratios (si) of about 1.2–1.3 in cold ice clouds (T < 200 K) even when the ice surface area is substantial [Gao et al., 2004]. These observations challenge the conventional thinking that any water vapor in excess of ice saturation should be depleted by crystal growth given sufficient time. Here we use model simulations to evaluate the impact of this steady‐state ice supersaturation on cirrus formed in situ within the tropical tropopause layer and water vapor fluxes across the tropical tropopause. We show that cirrus occurrence frequencies are unexpectedly increased, and we estimate an increase of about 0.5–1 ppmv in the water vapor concentration in air entering the stratosphere. Inclusion of the enhanced in‐cloud supersaturation in our simulations improves agreement with satellite measurements of water vapor.