Condensation Of Water In Pores Research Articles

Discussion on Water Condensation in Membrane Pores during CO2 Absorption at High Temperature.

Water condensation is a possible cause of membrane wetting in the operation of membrane contactors, especially under high-temperature conditions. In this study, water condensation in pores of polytetrafluoroethylene (PTFE) hollow fiber membranes was investigated during high-pressure CO2 absorption around 70 °C. It was found that the liquid accumulation rate in the treated gas knock-out drum was constant during continuous operation for 24 h when all experimental conditions were fixed, indicating a stable degree of membrane wetting. However, as the operating parameters were changed, the equilibrium vapor pressure of water within membrane pores could change, which may result in a condensation-conducive environment. Water condensation in membrane pores was detected and proven indirectly through the increase in liquid accumulation rate in the treated gas knock-out drum. The Hagen–Poiseuille equation was used to correlate the liquid accumulation rate with the degree of membrane wetting. The degree of membrane wetting increased significantly from 1.8 × 10−15 m3 to 3.9 × 10−15 m3 when the feed gas flow rate was reduced from 1.45 kg/h to 0.40 kg/h in this study due to water condensation in membrane pores. The results of this study provide insights into potential operational limitations of membrane contactor for CO2 absorption under high-temperature conditions.

Kinetic analysis on water adsorption of thermally upgraded lignite

An in-situ water adsorption analyzer was designed and set up for obtaining water dynamic adsorption process of thermally upgraded lignite under relative humidity (RH) of 55%–85% at 20 °C and 30 °C. Four upgraded samples with different pore structures and oxygen functional groups were prepared at 120, 160, 240 and 320 °C. Grey correlation degree analysis method was used to study the correlation between water adsorption capacity and its influencing factors. The results showed that upgrading temperature was the dominant factor influencing water adsorption of upgraded coals compared to RH and environmental temperature. The dynamic adsorption process of water on coal could be well described by Intra-particle diffusion model, and it could be divided into surface adsorption stage, pore diffusion stage, and dynamic equilibrium stage. The rate-controlling factors of surface adsorption stage were oxygen functional groups and specific surface area, while those of pore diffusion stage were pore volume and pore size. During adsorption under RH 55%, water was firstly adsorbed on coal surface through oxygen functional groups with a relatively fast rate, which was orderly followed by formation of water clusters and capillary condensation of water in pores with a relatively slow rate.

Pore condensation and freezing is responsible for ice formation below water saturation for porous particles

Ice nucleation in the atmosphere influences cloud properties, altering precipitation and the radiative balance, ultimately regulating Earth's climate. An accepted ice nucleation pathway, known as deposition nucleation, assumes a direct transition of water from the vapor to the ice phase, without an intermediate liquid phase. However, studies have shown that nucleation occurs through a liquid phase in porous particles with narrow cracks or surface imperfections where the condensation of liquid below water saturation can occur, questioning the validity of deposition nucleation. We show that deposition nucleation cannot explain the strongly enhanced ice nucleation efficiency of porous compared with nonporous particles at temperatures below -40 °C and the absence of ice nucleation below water saturation at -35 °C. Using classical nucleation theory (CNT) and molecular dynamics simulations (MDS), we show that a network of closely spaced pores is necessary to overcome the barrier for macroscopic ice-crystal growth from narrow cylindrical pores. In the absence of pores, CNT predicts that the nucleation barrier is insurmountable, consistent with the absence of ice formation in MDS. Our results confirm that pore condensation and freezing (PCF), i.e., a mechanism of ice formation that proceeds via liquid water condensation in pores, is a dominant pathway for atmospheric ice nucleation below water saturation. We conclude that the ice nucleation activity of particles in the cirrus regime is determined by the porosity and wettability of pores. PCF represents a mechanism by which porous particles like dust could impact cloud radiative forcing and, thus, the climate via ice cloud formation.