Numerical Simulation of the Water Vapor Separation of a Moisture-Selective Hollow-Fiber Membrane for the Application in Wood Drying Processes

In this study, a simplified two-dimensional axisymmetric finite element analysis (FEA) model was developed, using COMSOL Multiphysics® software, to simulate the water vapor separation in a moisture-selective hollow-fiber membrane for the application of air dehumidification in wood drying processes. The membrane material was dense polydimethylsiloxane (PDMS). A single hollow fiber membrane was modelled. The mass and momentum transfer equations were simultaneously solved to compute the water vapor concentration profile in the single hollow fiber membrane. A water vapor removal experiment was conducted by using a lab-scale PDMS hollow fiber membrane module operated at constant temperature of 35 °C. Three operation parameters of air flow rate, vacuum pressure, and initial relative humidity (RH) were set at different levels. The final RH of dehydrated air was collected and converted to water vapor concentration to validate simulated results. The simulated results were fairly consistent with the experimental data. Both experimental and simulated results revealed that the water vapor removal efficiency of the membrane system was affected by air velocity and vacuum pressure. A high water vapor removal performance was achieved at a slow air velocity and high vacuum pressure. Subsequently, the correlation of Sherwood (Sh)–Reynolds (Re)–Schmidt (Sc) numbers of the PDMS membrane was established using the validated model, which is applicable at a constant temperature of 35 °C and vacuum pressure of 77.9 kPa. This study delivers an insight into the mass transport in the moisture-selective dense PDMS hollow fiber membrane-based air dehumidification process, with the aims of providing a useful reference to the scale-up design, process optimization and module development using hollow fiber membrane materials.

What caused the frequent and widespread occurrences of noctilucent clouds at middle latitudes in 2020?

The 2020 summer season has revealed frequent occurrences of noctilucent clouds (NLCs) around the Northern hemisphere at middle latitudes (45–55° N), with the lowest latitude at which NLCs were seen being 34.1° N. In order to investigate a reason for this NLC extraordinary summer season, we have analyzed long-term Aura/MLS satellite data for all available summer periods from 2005 to 2020. Both Aura/MLS summer temperature and water vapor in the upper mesosphere and the mesopause region, between 74 and 89 km altitude, have been considered. We have found that there has been a moderate decrease in the upper mesosphere temperature between 2016 and 2020 and no dramatic changes have been observed in temperature in the summer of 2020 at the middle latitude mesopause. At the same time, water vapor concentration has significantly increased (by about 12–15 %) in the zonal mean H2O value in the 2020 summer compared to 2017, meaning that the summer mesopause at middle latitudes has become more wet. At the same time, no increase in water vapor has been detected at the high latitude high altitude mesopause. A combination of lower mesopause temperature and water vapor concentration maximum at middle latitudes is the main reason for frequent and widespread occurrences of NLCs seen around the globe at middle latitudes in the summer of 2020. The 24th solar cycle minimum cannot explain the H2O maximum in 2020 since the correlation between Lyman-α flux and the amount of water vapor is low. The increase in volcanic activity from 2013 to 2015 (and its recent maximum occurred in 2015) explains the increased amount of water vapor in the upper mesosphere for the past years and its maximum in 2020 due to volcanic water vapor being injected into the atmosphere and transported into the upper mesosphere. The 5-year delay between volcanic activity and water vapor maximum is well explained by a general meridional-vertical atmospheric circulation.

Macro-Scale Numerical Simulation of Moisture Transmission in Zeoli-Based Moisture Conditioning Material

By random growth method, this paper constructs isotropic porous media, anisotropic-1 porous media, and anisotropic-2 porous media, which have the same porosity but different micropore morphologies, and explores how the pore morphology affects the water vapor diffusion in the pores of porous media. The results show that: the random growth method can effectively reconstruct various porous moisture conditioning materials, and control their porosity and pore morphology; the equilibrium water vapor concentration and stabilization time of water vapor diffusion can effectively demonstrate the pore connectivity of porous media and the dynamic migration features of materials in the pores; the greater the change in the equilibrium water vapor concentration, the faster the stabilization of water vapor diffusion, and the better the pore connectivity of porous media.

Catalytic hydrolysis of CFC-12 over MoO3/ZrO2 -TiO2 solid acid

The catalytic hydrolysis of Difluorodichloromethane(CFC-12) by solid acid of MoO3/ZrO2-TiO2 calcined at different temperature had been studied. The effects of catalytic hydrolysis temperature and water vapor concentration on catalytic hydrolysis of CFC-12were also studied. The results showed that catalytic hydrolysis rate of CFC-12 reached to 98.65% at 400 ℃ when the MoO3/ZrO2-TiO2 catalyst was calcined at 500 ℃ with a concentration of water vapor of 83.18%, and the main hydrolysis products were CO, CO2, HF and HCl. After 30 hours’ continuous reaction, the hydrolysis rate of CFC-12 was 65.34%. The XRD result reveals that the main phase of solid MoO3/ZrO2-TiO2 catalyst is the tetragonal Zr (MoO4)2 with doped TiO2 of anatase.

Catalytic hydrolysis of Dichlorodifluoromethane over MoO3/ZrO2 -TiO2 solid acid

The catalytic behaviors of solid acid of MoO3/ZrO2-TiO2 calcined at different temperature for the catalytic hydrolysis of Dichlorodifluoromethane have been studided. The effects of catalytic hydrolysis temperature and water vapor concentration on catalytic hydrolysis of Dichloro difluoromethane were also studied. The Results show 98.65 % of Dichlorodifluoromethane is degraded over MoO3/ZrO2-TiO2 catalyst calcined at 500 ℃ with a concentration of water vapor of 83.18% when the hydrolysis temperature is 350 ℃ and the Dichlorodifluoromethane flux rate is 1 mL/min with main degradation products were CO, CO2, HF and HCl. A maintained degradation rate of 65.34% of Difluoromethylene Chloride has been observed through 30 hours’ continuous reaction over the catalyst of MoO3/ZrO2-TiO2. The XRD result reveals the main phase of solid MoO3/ZrO2-TiO2 catalyst is the tetragonal Zr (MoO4)2 that dopedTiO2 of anatase.

Catalytic hydrolysis of Dichlorodifluoromethane over MoO3/ZrO2 -TiO2 solid acid

The catalytic hydrolysis of Difluoro dichloromethane (CFC-12) by solid acid of MoO3/ZrO2-TiO2 calcined at different temperature had been studied. The effects of catalytic hydrolysis temperature and water vapor concentration on catalytic hydrolysis of CFC-12 were also studied. The results showed that catalytic hydrolysis rate of CFC-12 reached to 98.65 % at 400℃when the MoO3/ZrO2-TiO2 catalyst was calcined at 500℃ with a concentration of water vapor of 83.18%, and the main hydrolysis products were CO, CO2, HF and HCl. After 30 hours’ continuous reaction, the hydrolysis rate of CFC-12 was 65.34%. The XRD result reveals that the main phase of solid MoO3/ZrO2-TiO2 catalyst is the tetragonal Zr (MoO4)2with doped TiO2 of anatase.

Catalytic hydrolysis of Dichlorodifluoromethane over MoO3/ZrO2 -TiO2 solid acid

The catalytic hydrolysis of Difluorodichloromethane(CFC-12) by solid acid of MoO3/ZrO2-TiO2 calcined at different temperature had been studied. The effects of catalytic hydrolysis temperature and water vapor concentration on catalytic hydrolysis of CFC-12were also studied. The results showed that catalytic hydrolysis rate of CFC-12 reached to 98.65 % at 400。C when the MoO3/ZrO2-TiO2 catalyst was calcined at 500℃ with a concentration of water vapor of 83.18% ,and the main hydrolysis products were CO, CO2, HF and HCl. After 30 hours’ continuous reaction, the hydrolysis rate of CFC-12 was 65.34%. The XRD result reveals that the main phase of solid MoO3/ZrO2-TiO2 catalyst is the tetragonal Zr(MoO4)2with dopedTiO2 of anatase.