Mass transfer between microbubbles

Study on the impact of active intake air fluctuation on the performance and mass transfer of PEM Fuel Cell

The internal reflux effect on dialysis through the retentate phase of a countercurrently cross-flow rectangular module is investigated. Theoretical analysis of mass transfer in cross-flow devices with or without recycling is analogous to heat transfer in cross-flow heat exchangers. In contrast to a device without reflux, considerable mass transfer is achievable if cross-flow dialyzers are operated with reflux, which provides an increase in fluid velocity, resulting in a reduction in mass-transfer resistance. It is concluded that reflux can enhance mass transfer, especially for large flow rate and feed-concentration operated under high reflux ratio.

Mass transfer in gas—liquid slurry reactors

Use of axial membrane vibrations to enhance mass transfer in a hollow tube oxygenator

The internal reflux effect on dialysis through the retentate phase of a cross-flow rectangular module is investigated. Theoretical analysis of mass transfer in cross-flow devices with or without recycling is analogous to heat transfer in cross-flow heat exchangers. In contrast to a device without reflux, considerable mass transfer is achievable if cross-flow dialyzers are operated with reflux, which provides an increase in fluid velocity, resulting in a reduction in mass-transfer resistance. It is concluded that reflux can enhance mass transfer, especially for large flow rate and feed-concentration operated under high reflux ratio.

PurposeThe purpose of the paper is to analyze the bearing capacity of hydrostatic bearing during the change of film thickness under different working conditions and to improve the processing efficiency and precision of equipment.Design/methodology/approachIn this study, Q1-205 double rectangular cavity hydrostatic thrust bearing is selected as the research object. The dynamic mesh method and ANSYS/FLUENT software are used to simulate the curves of oil film thickness and oil pressure under different operating conditions. Finally, the change of pressure in the oil cavity at different operating speeds under a certain inlet flow rate was tested through design experiments.FindingsWhen the film thickness was thick, the maximum pressure in the oil cavity at different inlet velocities showed little difference. With a larger inlet flow, the maximum pressure in the oil cavity was higher. The pressure at the edge of the oil seal was linearly distributed. The oil pressure in the downstream side was greater than that in the counter flow side. When the working pressure was low, the pressure in the oil cavity slightly decreased with the increase of working speed. Moreover, the pressure loss at high speed was considerable.Originality/valueBased on the lubrication theory, the mathematical model of the bearing oil film was set up. The bearing capacity equation of the hydrostatic cavity was derived. The double-rectangular-annular hydrostatic guides studied in this paper have not been reported in previous research literature and the method of dynamic mesh dynamic simulation of variable viscosity is seldom studied before. The bearing characteristics and the change of oil film thickness under different working conditions have been studied systematically and comprehensively. The theoretical analysis results are basically consistent with the experimental results.

This paper reports on the gas sorption and transport properties of poly(vinylidene fluoride) (PVF2) and on the effects uniaxial drawing and processing temperature have on these properties. Sorption and transport were first examined for “as‐received” commercial Kynar PVF2 film at 35°C. This film was 54% crystalline by weight. Solubility, diffusion, and permeability coefficients were measured for He, H2, Ar, O2, N2, CH4, and CO2. The solubility coefficient and the diffusion coefficient D were correlated with the Lennard–Jones potential and mean molecular diameter of the gas, respectively. Uniaxial drawing of PVF2 films was performed up to a draw ratio of 3.7 and over the temperature range 75–140°C. Transport properties were correlated with the extent of draw and drawing temperature. The permeability P and D were found to significantly decline with uniaxial drawing; the magnitude of this effect was dependent on both the drawing temperature and the molecular size of the penetrant considered. Roduetions in P and D became progressively more pronounced with increasing molecular diameter and with decreasing drawing temperature (down to a limit of about 75°C), which reflects an increase in effectiveness of drawing at low temperatures. PVF2 films annealed above 75°C showed an increase in P and D as opposed to the effect of drawing. The solubility of various gases in PVF2 was not found to be sensitive to processing treatments such as drawing and annealing, in agreement with the relatively small changes observed in free volume. PVF2 films subjected to various treatments were characterized by DSC, density, birefringence, and dynamic mechanical measurements. Gas transport measurements appear to provide a more sensitive and hence more viable measure of the effectiveness of drawing than these other techniques. Drawing PVF2 in the melt state was found to increase P and D, in contrast with the effects observed for solid‐state drawing. The results have been interpreted in terms of existing theories on morphology and microstructure in semicrystalline polymers.

Mass transfer during surfactant-enhanced DNAPL remediation: Pore-scale experiments and new correlation

Effects of net-type spacers on heat and mass transfer in direct contact membrane distillation and comparison with ultrafiltration studies

Mass transfer in a symmetric sinusoidal wavy-walled channel for oscillatory flow

Determination of mass transfer coefficient for continuous removal of cadmium by emulsion liquid membrane in a modified rotating disc contactor

Mass transfer enhancement of CO2 absorption into [Bmim][BF4] aqueous solution in microchannels by heart-shaped grooves

Study on the synergistic effect of UV/Fenton oxidation and mass transfer enhancement with addition of activated carbon in the bubble column reactor

The local mass transfer over dissolving surfaces was measured at pipe Reynolds number of 50,000, 100,000, and 200,000. Tests were run at multiple time periods for each Reynolds number using 203 mm diameter test sections that had gypsum linings dissolving to water in a closed flow loop at a Schmidt number of 1200. The local mass transfer was calculated from the decrease in thickness of the gypsum lining that was measured using X-ray-computed tomography (CT) scans. The range of Sherwood numbers for the developing roughness in the pipe was in good agreement with the previous studies. The mass transfer enhancement (Sh/Shs) was dependent on both the height (ep−v) and spacing (λstr) of the roughness scallops. For the developing roughness, two periods of mass transfer were present: (i) an initial period of rapid increase in enhancement when the density of scallops increases till the surface is spatially saturated with the scallops and (ii) a slower period of increase in enhancement beyond this point, where the streamwise spacing is approximately constant, and the roughness height grows more rapidly. The mass transfer enhancement was found to correlate well with the parameter (ep−v/λstr)0.2, with a weak dependence on Reynolds number.

Even bubble column reactors (BCR) and airlift reactors (ALR) have been developed in terms of various related aspects towards mass transfer enhancement, the effective analysis of gas diffuser types on mass transfer and gas–liquid hydrodynamic characteristics is still limited. Therefore, the present study aims to analyze the relative effect of different types of air diffusers on bubble hydrodynamics and mass transfer performance to understand their behaviors and define the best type. The experiments were conducted by varying different diffuser types, reactor types (BCR and ALR), and superficial gas velocity (Vg) (0.12 to 1.00 cm/s). Five air diffusers including commercial fine sand (F-sand) and coarse sand (C-sand) diffusers, and acrylic perforated diffusers with orifice sizes of 0.3 mm (H-0.3), 0.6 mm (H-0.6), and 1.2 mm (H-1.2), were used in this study. For every condition, it was analyzed in terms of bubble hydrodynamics and oxygen mass transfer coefficient (KLa). Lastly, the selected diffusers that provided the highest KLa coefficient were evaluated with a solid media addition case. The results of both reactor classes showed that F-sand, the smallest orifice diffuser, showed the smallest air bubbles (3.14–4.90 mm) compared to other diffusers, followed by C-sand, which larger about 22–28% on average than F-sand. ALR exhibited a better ability to maintain smaller bubbles than BCR. Moreover, F-sand and C-sand diffusers showed a slower rising velocity through their smaller bubbles and the tiny bubble recirculation in ALR. Using F-sand in ALR, the rising velocity is about 1.60–2.58 dm/s, which is slower than that in BCR about 39–54%. F-sand and C-sand were also found as the significant diffusers in terms of interfacial area and gas hold-up. Then, the KLa coefficient was estimated in every diffuser and reactor under the varying of Vg. Up to 270% higher KLa value was achieved from the use of F-sand and C-sand compared to other types due to their smaller bubbles generated/maintained and longer bubble retention time through slower rising velocity. After adding 10% ring shape plastic media into the reactors with F-sand and C-sand diffusers, a better performance was achieved in terms of KLa coefficient (up to 39%) as well as gas hold-up and liquid mixing. Lastly, ALR also had a larger portion of mixed flow pattern than BCR. This eventually promoted mass transfer by enhancing the mixed flow regime.