Enhancement Of Mass Transfer Performance Research Articles

CFD–PBM coupled modeling of liquid–liquid interphase mass transfer behaviors inside the Kenics static mixer

Kenics static mixers (KSM) are commonly used in various industries for its excellent mass transfer performance. It is essential to systematically analyze the relationship between fluid parameters and mass transfer parameters to better understand the mass transfer behaviors between liquid–liquid phases and optimize the mass transfer efficiency of the KSM. In this work, a computational fluid dynamic–population balance model coupled method is utilized and three mass transfer models are compared and analyzed. Further simulations investigate the mass transfer behaviors inside the KSM under different superficial velocities, dispersed phase volume fractions, and aspect ratios. The results show that the increase of superficial velocity leads to the 2.23–14.15–fold increase of volumetric mass transfer coefficient and the 1.71–4.56–fold increase of mass transfer rate. What's more, increasing the dispersed phase volume fraction leads to the significant increase of 15.51 times in volumetric mass transfer coefficient and 34.92 times in mass transfer rate. Moreover, the increase of aspect ratio could result in the reduction of 4.19–1.72 times in volumetric mass transfer coefficient and 1.81–1.17 times in mass transfer rate. This work provides valuable theoretical insights for the optimal design of the KSM and the enhancement of mass transfer performance.

Enhancement of mass transfer performance by nanoparticles during the CO2 absorption with MDEA solution in a randomly packed tower

AbstractIn this study, the mass transfer enhancement by nanoparticles during CO2 absorption process with MDEA solution in a randomly packed tower was investigated. The mass transfer performance of MDEA solution with and without nanoparticles were quantified and analyzed in terms of the volumetric overall mass transfer coefficient (KGav). An enhancement factor (E), defined as the ratio of KGav with and without nanoparticles, was further introduced to evaluate the enhancement effect of the addition of nanoparticles. The effects of TiO2 nanoparticle concentration, MDEA concentration, liquid flow rate, liquid temperature, inert gas flow rate, and CO2 loading on KGav and E were systematically studied in the packed tower. It is found that the maximum value of E can reach 1.37, when the nanoparticle concentration is 0.09wt%, the liquid flow rate is 21.22 m3/m2·h, the liquid temperature is 27°C, the MDEA concentration is 30%, the gas flow rate is 7.58 kmol/m2·h and the CO2 loading is 0.2 mol CO2/mol MDEA. Usually, the KGav of the MDEA nanofluids can be increased by 10–37% in a randomly packed tower compared to that of the MDEA solution, which is consistent with the results from the bubbling reactors. However, when the CO2 loading of absorption exceeds 50%, E becomes less than 1.0, which means that high CO2 loading inhibits the enhancement effect of nanoparticles. In order to predict the mass transfer performance of MDEA nanofluid, a formula correlating E and various dimensionless operating parameters (i.e. , , and ) is proposed and fitted with an average absolute deviation of 14%. © 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.

Combined heat and mass transfer performance enhancement by nanoemulsion absorbents during the CO2 absorption and regeneration processes

Nanoemulsion absorbents are manufactured using methanol and undecane for CO2 absorption and regeneration performance enhancement. The most representative physical CO2 absorbent, methanol, is mixed with undecane and dispersed by the ultrasonication method. Span 60 and Tween 60 are used to obtain a high dispersion stability. To determine the effect of undecane concentration on the combined heat and mass transfer performance during the absorption and regeneration processes, various concentrations of nanoemulsion absorbents are prepared. The thermal conductivity of the nanoemulsion is also measured to estimate the effect of nanodroplets on the heat transfer performance. It is concluded that the average absorption rate increases by 13.04% at 0.05 vol% of undecane and the average regeneration rate does by 22.03% at 0.05 vol% compared to the base absorbent. Various mechanisms for combined heat and mass transfer performance enhancement by nanoemulsion absorbents are discussed. It is concluded that the mechanism of regeneration performance enhancement by the thermal effect in the nanoemulsion absorbents is less effective compared to that in the nanofluid absorbents.

Mass transfer performance enhancement by nanoabsorbents during CO2 absorption process

A fluid in which nano-sized particles are dispersed is called nanofluids. It has been actively studied in the field of heat and mass transfer because of its attractive thermophysical properties. Since methanol is mainly used as a physical CO2 absorbent, methanol-based nanofluids (nanoabsorbents) are tested for mass transfer performance enhancement. Al2O3 and SiO2 nanopowders are used, and the nanoabsorbents are manufactured by the ultrasonication method. Thermal conductivity (0.005–1.0 vol%, 24–40 °C), viscosity (0.005–1.0 vol%, 20 °C), surface tension (0.005–0.1 vol%, 20 °C) and average cluster size (0.005–1.0 vol%, 20 °C) are measured to analyze the combined heat and mass transfer and the dispersion characteristics of the nanofluids. Also, the mass transfer characteristics between CO2 and nanoabsorbents is evaluated using the Schlieren visualization experiment. It is found that the thermal conductivity and viscosity of the nanoabsorbents increase with increasing the volume concentration of nanoparticles. At 1.0 vol%, the thermal conductivities of Al2O3/methanol and SiO2/methanol nanoabsorbents are 4.6% and 5.5% higher than that of pure methanol, respectively, while the viscosities are also increased by 21% and 11%, respectively. The average cluster sizes of Al2O3 and SiO2 nanoabsorbents are not vary depending on the volume concentration, and they range 267–288 nm and 496–507 nm, respectively. It is concluded that the mass diffusivities of nanoabsorbents are significantly higher than that of pure methanol, and the enhancement mechanism of mass transfer is newly proposed.

Development of nanoemulsion CO2 absorbents for mass transfer performance enhancement

Nanofluids as CO2 absorbents have problems involving precipitation or flocculation of the seeding particles. Nanoemulsion CO2 absorbents are expected to solve these problems. In this study, nanoemulsion (Dodecane/Methanol) absorbents were proposed and their thermophysical properties and dispersion characteristics were evaluated for mass transfer performance enhancement during CO2 absorption process. Both Span 60 and Tween 60 were selected due to their nonionic surfactant feature and hydrocarbon chemical types of dodecane. The nanoemulsion absorbents were ultrasonically manufactured after adding Span 60 and Tween 60 in a ratio of 4:6 to match the required hydrophile-lipophile balance (HLB = 11). Thermal conductivity and viscosity of nanoemulsion absorbents were measured for various surfactant ratios. Tyndall effects and turbidity measurements were executed to find out the best dispersion stability condition. An optimal ultrasonication time was proposed based on the smallest mean size of nanoemulsion droplets and their uniformity. Both mechanisms of thermophysical properties and dispersion stability of nanoemulsion absorbents were proposed based on cryo transmission electron microscope (TEM) results.

Mass transfer performance enhancement by nanoemulsion absorbents during CO2 absorption process

In this study, nanoemulsion absorbents (silicone oil/methanol) were manufactured by adding nano-size oil to absorbents for CO2 absorption performance enhancement. To evaluate the dispersion stability of the nanoemulsion, oil droplet size measurement, turbidity measurement, and Tyndall effect visualization experiments were conducted. The effect of the ratio and concentration of oil and surfactants on the mass transfer enhancement was evaluated through thermal conductivity measurement using the transient hot wire method and the visualization analysis of CO2 bubble absorption. The oil (silicone) and surfactant ratio of 2:1 was found to be the optimum condition through the results of dispersion stability analysis. In the CO2 bubble absorption results obtained through the visualization analysis, the nanoemulsion with 0.01vol% oil concentration showed the most significant absorption performance improvement. It was found that nano-size oil dispersion contributed to mass transfer enhancement, which was caused by the convective motion of nano-size oil droplets, not by enhanced thermal conductivity. Finally, the mechanisms of mass transfer enhancement by nanoemulsions are proposed, and it is concluded that the CO2 absorption performance is enhanced by the shuttle effect and the hydrodynamic effect by the nanoemulsion absorbents.

On the mass transfer performance enhancement of membraneless redox flow cells with mixing promoters

Membraneless flow cells for electrochemical energy conversion exploit the laminarity of microscale flows to avoid undesirable mixing of reactants. To increase the performance of microfluidic redox flow cells we employ herringbone-inspired flow promoters, thereby increasing convection of each individual species to the electrodes, while minimizing reactant mixing. Polarization curves from electrochemical discharge measurements with a dilute anthraquinone/iron redox system reveal that the presence of flow promoters substantially boosts device performance. Mass transfer enhancement for devices with flow promoters is demonstrated through both higher limiting currents and increased power density; the former is more than double compared to a plain reference microchannel for Reynolds numbers of Re >155. The chaotic mixing effect induced by the flow promoters also becomes apparent in the scaling regimes, the limiting currents are proportional to Re0.58 instead of Re1/3 (as for purely laminar flow). Further, we quantify the area specific resistance (ASR) of the electrolyte in our membraneless devices finding a reduction of more than one order of magnitude compared to the ASR of conventional membranes employed in redox flow cells. Overcoming mass transfer limitations, this work highlights the necessity of passive mixers in significantly raising the performance of microfluidic flow cells.

Enhancement of mass transfer performance of liquid–liquid system by droplet flow in microchannels

Abstract Two multiphase flow microfluidic devices based on the use of droplet flow to enhance the mass transfer performance have been specially developed. Mass transfer performance data has been obtained by monitoring the extraction of succinic acid from n-butanol to aqueous drops containing NaOH. Monodisperse aqueous droplets with average diameters of 130–550 μm were generated, and the mass transfer time was 0.4–4.0 s accordingly. The mass transfer rate was 10–1000 times higher comparing to the traditional liquid–liquid systems. Vortex flow patterns within the droplet were generated during droplet forming stage that enhanced mass transfer rate greatly. The mass transfer during droplet formation stage contributed at least 30% of the total mass transfer quantities from the theoretical analyzing. And the mass transfer coefficients were 10–100 times higher than that of droplet moving stage. These results were very different to the mass transfer in conventional extraction processes. The mass transfer mechanism during droplet forming stage in microscale should be investigated fundamentally in the further work. The mass transfer results from this study indicate that droplet flow within a microscale environment offers a viable alternative for two-phase reaction or separation systems.

Numerical design of ammonia bubble absorber applying binary nanofluids and surfactants

The objectives of this paper are to analyze the combined heat and mass transfer characteristics for the ammonia bubble absorption process and to study the effects of binary nanofluids and surfactants on the absorber size. The ammonia bubble absorbers applying binary nanofluids and surfactants are designed and parametric analyses are performed. In order to express the effects of binary nanofluids and/or surfactants on the absorption performance, the effective absorption ratios for each case are applied in the numerical model. The values of the effective absorption ratio are decided from the previous experimental correlations. The kinds and the concentrations of nano-particles and surfactants are considered as the key parameters. The considered surfactants are 2-ethyl-1-hexanol (2E1H), n-octanol, and 2-octanol and nano-particles are copper (Cu), copper oxide (CuO), and alumina (Al 2O 3). The results show that the application of binary nanofluids and surfactants can reduce the size of absorber significantly. In order to reach 16.5% ammonia solution under the considered conditions, for example, the addition of surfactants (2E1H, 700 ppm) can reduce the size of absorber up to 63.0%, while the application of binary nanofluids (Cu, 1000 ppm) can reduce it up to 54.4%. In addition, it is found that the effect of mass transfer resistance is more dominant than that of heat transfer resistance. That is, the enhancement of mass transfer performance is more effective than that of heat transfer performance.