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CO2 absorption performance enhancement by dodecane nanoemulsion absorbents
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Research article
Model study of CO 2 absorption in aqueous amine solution enhanced by nanoparticles .
International Journal of Greenhouse Gas Control, Volume 60, 2017, pp. 51-58
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An investigation for the enhancement of nanoparticles (TiO 2 , MgO, SiO 2 ) on the mass transfer for CO 2 absorption was presented through both the experiment method and a 3-D unsteady model. The effects of nanoparticle loadings, nanoparticle diameters, nanoparticle species, solution species, experimental temperature and the CO 2 initial volume fraction on the CO 2 absorption were investigated in this paper. Considering the chemical reaction between gas and solution, a 3-D unsteady model was developed to study the mass transfer for CO 2 absorption enhanced by nanoparticles in monoethanolamine (MEA) solution. Based on the analysis of zwitterion mechanism in the process of chemical reaction between MEA and CO 2 , it was shown that the rate of chemical reaction is proportional to the concentration of CO 2 due to the large MEA concentration and the zero-order reaction in the liquid membrane. Further, the differential equation of mass transfer in three dimensions was set up, which is related to the rate of chemical reaction and the random distribution of nanoparticles. The random distribution of nanoparticles in a fluid element was determined by Monte Carlo method. In addition, the absorption experiments of CO 2 in MEA solution using the bubbling reactor were carried out, which could also verify the correctness of the developed model.
Research article
Supercritical CO 2 encapsulation of bioactive molecules in carboxylate based MOFs .
Journal of CO2 Utilization, Volume 30, 2019, pp. 38-47
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Caffeine and carvacrol were encapsulated using supercritical CO 2 (sc-CO 2 ) impregnation in MOFs, MIL-53(Al) and Mg-MOF-74, at different contact times. High additive loadings were achieved, 32.1 and 34.3% for caffeine, and for carvacrol 34.4 and 30.1%, respectively. The sc-CO 2 encapsulation was more effective compared to the typical liquid phase encapsulation in ethanol. In fact, the encapsulation in Mg-MOF-74 was only possible in sc-CO 2 , null loading was observed in the liquid ethanol phase process. The products required no purification and the excess of additives could be reused. In all the studied cases, the materials maintained their crystalline structure and MIL-53(Al) displayed its characteristic flexibility adapting its structure to the additives. The total release of caffeine and carvacrol from Mg-MOF-74 was produced after 5?h in distilled water, while in the case of MIL-53(Al) no release was observed for 10 days.
Research article
CO 2 regeneration performance enhancement by nanoabsorbents for energy conversion application .
Applied Thermal Engineering, Volume 103, 2016, pp. 980-988
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Due to the recent increase in the consumption of energy and the use of fossil fuels, global warming has become a serious issue. To address this problem, CO 2 gas, which is the major element of the greenhouse gases, should be captured, regenerated and converted to useful fuels. The Integrated Gasification Combined Cycle (IGCC) and cement process generate large amount of CO 2 , which are controlled through pre-combustion capture. However, this method has a disadvantage because the system temperature should be decreased to ?20 ? °C or lower. Therefore, the development of new absorbent is required to reduce the energy consumed for refrigeration. There is a study that improved the CO 2 absorption performance by adding Al 2 O 3 nanoparticles to methanol. However, studies on the regeneration of CO 2 in nanofluid absorbents (nanoabsorbents) are insufficient. Therefore, in this study, the CO 2 regeneration performance in Al 2 O 3 nanoabsorbents is evaluated. It is found that the regeneration performance of CO 2 is improved by 16% by using nanoabsorbents compared to methanol. Furthermore, the CO 2 regeneration characteristics of nanoabsorbents are analyzed by considering the detachment time of CO 2 bubbles from the surface, the cross-sectional area of CO 2 bubble, and the number of regeneration sites through the CO 2 regeneration and bubble visualization experiments. It is concluded that the mechanism of surface effect is the most plausible to explain the CO 2 regeneration performance enhancement by nanoabsorbents.
Research article
Bubble behaviors and CO 2 absorption characteristics in nanoabsorbents .
Journal of CO2 Utilization, Volume 33, 2019, pp. 488-499
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The objectives of this study are to present a comprehensive analysis of the CO 2 bubble population dynamics and to investigate their effects on the CO 2 absorption characteristics in nanoabsorbents (methanol with various concentrations of Al 2 O 3 nanoparticles) with a rectangular bubble column. The population balance model (PBM) as a well-established method based on the Euler-Euler model is employed to compute the size distribution of bubbles and to account for the bubbles coalescence and breakage in multiphase flow. The coupled volume-of-fluid (VOF) method is selected to clearly capture the coalescence and breakup processes of successively rising bubbles. The results show that there is a significant influence of the leading bubble on the following one, including the increment of the velocity, the deformation of the bubble shape and the flow instability. It is also found that the critical distance at which the influences can be exerted is related to the bubble wake trailed by the leading bubble. Accordingly, five types of bubble wakes and their effects on the bubble behaviors such as the coalescence and breakup are categorized. Finally, by further analyzing the bubble behaviors in methanol with different volume fraction of Al 2 O 3 , it is found that the coalescence and breakup of bubbles are dominated by the bubble wake and enhanced by the eddy in local liquid. It is concluded that the higher concentration of nanoparticles is favorable to the bubble coalescence and breakup, which enhance the mass transfer performance by increasing the interfacial area.
Research article
Mass transfer characteristics for CO 2 absorption in nanoabsorbents .
International Journal of Heat and Mass Transfer, Volume 129, 2019, pp. 650-659
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In this work, an improved VOF-PLIC model is developed to simulate 3D bubble behavior and to analyze the mass transfer characteristics for CO 2 absorption in pure methanol and methanol with Al 2 O 3 nanoparticles. The lower bound boundary value of CO 2 volume fraction( α g ) is redefined according to the influence of α g on bubble shape and diameter as well as the interfacial area between gas and liquid. In addition, a reasonable drag force is added into the momentum equation using UDF code based on the assumption that the drag force only exists in liquid phase. It is found that the level lines of bubbles with the α g value of 0.05 agree well with the real case, and the drag force has significant influence on the bubble behavior and mass transfer characteristics. The velocity contours and pressure gradients around the bubble are proposed to analyze the influence of drag force on the mass transfer characteristics. Also, the influence of the Al 2 O 3 nanoparticles on the mass transfer enhancement is studied, and the results show that the dispersed particles can significantly enhance the mass transfer by increasing the gas–liquid interfacial surface renewal frequency.
Research article
Characteristics on condensation heat transfer and pressure drop for a low GWP refrigerant in brazed plate heat exchanger .
International Journal of Heat and Mass Transfer, Volume 122, 2018, pp. 1272-1282
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Refrigerants have been continuously developed to improve their thermal performances and to deal with relevant environmental issues. Recently, regulations on refrigerants are being intensified due to the global warming. To meet the enhanced environmental standards, low global warming potential (GWP) refrigerants have been developed. In this study, experimental studies are conducted to investigate the characteristics of condensation heat transfer and frictional pressure drop for R-1233zd(E). The experiments are carried out under partial condensation conditions in a plate heat exchanger to measure temperature, pressure and mass flow rate. Heat transfer coefficients and frictional pressure drops with respect to mean vapor qualities are yielded. During the partial condensation process, the heat transfer coefficients increases as the mass and heat fluxes increase. However, no significant change in frictional pressure drop is observed when the heat flux changes. It is concluded that other correlations for Nusselt number and pressure drop from the literature cannot be applied for the low GWP refrigerant, R-1233zd(E), and the present experimental correlations agree well with the experimental results with the error bands of ±20%. .
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