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由溶解的CO2引发的Rayleigh对流,对咸水层中CO2的捕获与封存至关重要。为了更加直观地了解该过程的混合规律和盐浓度变化带来的影响,本文采用格子Boltzmann方法(LBM)对该过程进行了模拟。通过建立包含密度和浓度分布函数的双分布模型,同时引入静电力和体积力等外力项,对293.15K、101kPa下有多个离散的CO2扩散源时的浓度分布进行了模拟。结果表明,模拟得到的Rayleigh对流结构、对流发生时间、流场速度和瞬时传质通量的数量级与前人研究结果一致;在咸水吸收CO2过程中,Rayleigh对流结构可有效强化传质;瞬时传质通量随着时间增长先减小后增大再减小,对应了Rayleigh对流结构产生、发展、稳定的变化过程。同时模拟CO2在纯水和不同盐浓度咸水中的溶解过程结果表明,盐浓度的增加会延迟Rayleigh对流的开始时间、降低传质效率,这与前人的实验结果一致,模拟结果可为不同盐浓度咸水层中CO2的封存提供指导。 相似文献
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针对乙醇吸收CO2过程中,由CO2通过界面向液体乙醇传递所导致的Rayleigh对流现象的模拟,建立了二维格子Boltzmann方法(LBM)。采用浓度分布函数和流体质点密度函数的双分布模型格子Boltzmann方法,同时引入由浓度差导致的重度差作为外加力,实现了流体中浓度场与速度场的模拟。应用所建立的LBM方法,对界面具有多个离散CO2扩散源的二维区域液相Rayleigh对流现象进行了模拟,结果显示,模拟得到的浓度分布结构与文献中实验结果相一致。通过考察Rayleigh对流和浓度分布结构,分析了Rayleigh对流存在条件下的传递规律。通过采用LBM方法对浓度场模拟可以定量给出液相界面瞬时传质通量。计算结果表明,瞬时传质通量随时间的增长先增加后减小,这种变化与相似文献
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通过纹影光路观察了特定气液传质装置中乙醇吸收CO2过程所引发的Rayleigh对流在垂直界面方向上的发展过程。随着溶质吸收的进行,液层的流体稳定性变弱,扰动加剧气液界面失稳并发生湍动,进而发展为羽状流并逐步向液相主体发展,在此过程中伴随着对流胞的融合与增长。液层的浓度分布可通过对相应液层纹影图像进行定量分析获得。液层浓度分布和瞬时传质系数变化表征了Rayleigh对流的引发与发展及其对传质过程的强化效果,界面浓度分布及临界Rayleigh数解释了非均匀传质对湍动的引发机理。羽状流将高浓度液体快速带入主体,加速了近界面液层与主体液层的混合,增强了气液传质。 相似文献
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采用激光诱导荧光(LIF)观测方法考察了在气相中分别添加乙醇和二氯甲烷分别对CO2在水中溶解过程界面对流的影响,得到了液相中CO2浓度分布及其演化的观测结果,通过物料衡算得到了相应条件下的液相传质系数。CO2溶解过程会出现由密度梯度引起的Rayleigh对流。实验结果表明,当添加的乙醇含量小于8.47 mg·L-1时,Rayleigh对流会被增强,进而促进了CO2的溶解;随着气相中乙醇含量的增大,Rayleigh对流反而被抑制;气相添加二氯甲烷会显著增强Rayleigh对流,提高了CO2的传质速率,随着气相二氯甲烷含量的增大,CO2在水中溶解过程的液相传质系数呈现先加强后恒定的趋势。 相似文献
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建立了用于观测水溶解CO2过程界面Rayleigh对流现象的粒子成像测速(PIV)和激光诱导荧光(LIF)技术联用方法,同时获得了该对流传质过程的液相速度场及浓度分布,定量观测了Rayleigh对流的发展过程。经界面对流发生条件下传质过程的分析,指出Rayleigh对流过程的涡量是影响传质过程的主要因素,给出了传质系数随涡量的变化关系和相应的关联式,进而为通过液相速度场的测量预测Rayleigh对流条件下的液相传质系数提供了一种有效的方法。 相似文献
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《化工学报》2016,(11)
通过纹影光路观察了特定气液传质装置中乙醇吸收CO2过程所引发的Rayleigh对流在垂直界面方向上的发展过程。随着溶质吸收的进行,液层的流体稳定性变弱,扰动加剧气液界面失稳并发生湍动,进而发展为羽状流并逐步向液相主体发展,在此过程中伴随着对流胞的融合与增长。液层的浓度分布可通过对相应液层纹影图像进行定量分析获得。液层浓度分布和瞬时传质系数变化表征了Rayleigh对流的引发与发展及其对传质过程的强化效果,界面浓度分布及临界Rayleigh数解释了非均匀传质对湍动的引发机理。羽状流将高浓度液体快速带入主体,加速了近界面液层与主体液层的混合,增强了气液传质。 相似文献
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CO2 absorption into absorbents is a widely used method to reduce carbon emissions, in which the concentration gradient near the gas-liquid interface may induce Rayleigh convection (RC). Once RC occurs, the mass transfer rate will be significantly enhanced. Therefore, it is necessary to explore the mass transfer enhancement mechanism further and develop a penetration/surface divergence hybrid mass transfer model. In this study, we conduct research on the process of CO2 absorption into ethanol with RC. Firstly, we use a multi-relaxation time lattice Boltzmann method to simulate the absorption process and obtain the flow and concentration fields. And we also verify the reliability of the numerical simulation results by comparing with the experimental results. Then, we analyze the characteristics of non-uniform flow and concentration fields in RC. Moreover, we divide the near-interface region into diffusion-dominated and convection-dominated mass transfer zones by checking whether the horizontal average velocity is greater than 1.0×10-4 m·s-1. Furthermore, based on the differences in mass transfer mechanisms of the aforementioned two zones, we propose a penetration/surface divergence hybrid model to predict the instantaneous mass transfer coefficient. The prediction results demonstrate that the hybrid model can precisely predict the instantaneous mass transfer coefficient of the entire CO2 absorption process. Our proposed hybrid model provides a promising way to deal with the complex mass transfer problems with non-uniform flow and concentration fields. 相似文献
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An exploration of the gas CO2 absorbed into liquid ethanol accompanied with Rayleigh convection is performed by analyzing the mass entransy dissipation; this new statistical quantity is introduced to describe the irreversibility of mass transfer potential capacity. Based on the general advection–diffusion differential equation for an unsteady mass transfer process, the variation of the included angle between the velocity vector and concentration gradient fields is investigated to reveal the underlying mechanism of interfacial convection enhancing mass transfer. Results show some identical characteristics with the qualitative analyses of the synergy effects generated by the concentration and velocity fields after interfacial convection occurring for a boundary condition of fixed surface concentration. And the equivalent mass resistance for convective mass transfer process presents the similar variation with the reciprocal of instantaneous mass transfer coefficient. Accordingly, it is reasonable to be seen that mass transfer dissipation rate could be provided to assess the convection strength and explain fundamentally how Rayleigh convection improves mass transfer performance through establishing a close relationship between the mass transfer capacity and field synergy principle from the view of mass transfer theory. 相似文献
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A multiphase flow 3D numerical simulation method employing the coupled volume of fluid (VOF) and level set model is established to study the reactive absorption of CO2 by the monoethanolamine (MEA) aqueous solution in a falling film microchannel. Based on the flow-reaction-mass transfer model of the MEA-CO2 system in the falling film microchannel, the enhancement effect of the Marangoni convection in this reactive absorption process is analyzed. The enhancement factor of the Marangoni convection obtained in this work is in good agreement with experimental results in the literature. With consideration of the absorption ratio as well as the enhancement effect of the Marangoni convection, the influence of different MEA concentrations on absorption of CO2 is investigated. Furthermore, the appropriate MEA concentration for absorption enhanced by the Marangoni convection is acquired. 相似文献
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Saline aquifers are chosen for geological storage of greenhouse gas CO2 because of their storage potential. In almost all cases of practical interest, CO2 is present on top of the liquid and CO2 dissolution leads to a small increase in the density of the aqueous phase. This situation results in the creation of negative buoyancy force for downward density-driven natural convection and consequently enhances CO2 sequestration. In order to study CO2 injection at pore-level, an isothermal Lattice Boltzmann Model (LBM)with two distribution functions is adopted to simulate density-driven natural convection in porous media with irregular geometry obtained by image treatment. The present analysis showed that after the onset of natural convection instability, the brine with a high CO2 concentration infringed into the underlying unaffected brine, in favor of the migration of CO2 into the pore structure. With low Rayleigh numbers, the instantaneous mass flux and total dissolved CO2 mass are very close to that derived from penetration theory (diffusion only), but the fluxes are significantly enhanced with high Ra number. The simulated results show that as the time increases, some chaotic and recirculation zones in the flow appear obviously, which promotes the renewal of interfacial liquid, and hence enhances dissolution of CO2 into brine. This study is focused on the scale of a few pores, but shows implications in enhanced oil/gas recovery with CO2 sequestration in aquifers. 相似文献
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中空纤维膜吸收烟气中CO2是一种清洁、高效、最具潜力的脱碳技术方法之一。本文建立了一个二维的中空纤维膜接触器平行逆流吸收混合气中CO2的非润湿模型。考虑轴向和径向扩散,模拟了EEA、EDA和PZ 3种吸收剂在不同操作条件下对CO2的脱除效果和传质性能。结果表明:脱碳性能从大到小为PZ>EDA>EEA;气相参数对脱碳和传质的影响比液相参数更显著;提高气体流速、CO2浓度和气温,脱碳率均会下降;提高液速、吸收剂浓度和液温,脱碳率均增大,而传质速率只有在提高气温时会下降,其他参数的升高均会使其增大;应采用适当的液相参数,防止操作参数过高带来的不利影响。 相似文献