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1.
The heat and momentum transfer in a liquid-vapor two-phase film system at high temperature and low pressure is studied by the example of the removal of highly volatile fractions from high-boiling liquids in film evaporators. The temperature and velocity distributions in the vapor phase are determined.__________Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 3, 2005, pp. 251–258.Original Russian Text Copyright © 2005 by Babak.  相似文献   

2.
Spray towers allow for controlling air pollution in which a liquid is sprayed in small droplets to produce a large interfacial area for mass transfer between a gas and a liquid phase. An experimental study of a spray tower for removing SO2 is described. The experiments were carried out under different operating conditions by varying the gas velocity, liquid flow rate, and SO2 concentration. SO2 removal efficiency, volumetric mass transfer coefficient, and liquid‐film formation as a result of the collision of droplets against the tower wall are investigated. Removal efficiency and volumetric mass transfer coefficient are analyzed as a function of gas velocity, liquid flow rate, and SO2 concentration, while liquid‐film formation is evaluated as a function of tower height. The results indicate high removal efficiency. Correlations to predict the volumetric mass transfer coefficient are also proposed.  相似文献   

3.
Unsteady-state absorption of inorganic gases by aqueous solutions of acids and alkalis is considered using the example of two stagnant media (a liquid and a gas). It is shown that, in the general case, only two absorption modes are possible. In one of the modes, the resistance to mass transfer is concentrated in the gas phase, and, in the other, there is an instantaneous chemical reaction, in which the acceleration of two-phase physical absorption is constant. Conditions for each of these modes are found.Translated from Teoreticheskie Osnovy Khimicheskoi Tekhnologii, Vol. 39, No. 2, 2005, pp. 152–162.Original Russian Text Copyright © 2005 by Babak.  相似文献   

4.
An analytical solution for absorption of a gas with an accompanying first order reaction in a laminar falling film is developed. The gas flow is countercurrent to that of the liquid film. Change in the gas phase concentration because of the reaction, as it happens in practical situations, has been taken into account. Some computed results are presented to show the effects of the system parameters—namely, the reaction rate parameter, the Biot number, and the absorption factor— on the mass transfer enhancement factor and on the fractional removal of the feed gas over a given non-dimensional film length.  相似文献   

5.
Numerical results are presented for effects of latent heat transport associated with film vaporization on laminar mixed convection heat and mass transfer in a vertical channel with a half channel width b = 0.01 m. The influences of the inlet liquid mass flowrate and wall temperature on the film vaporization and the associated heat and mass transfer characteristics are examined for air-water and air-ethanol systems with gas Reynolds number Reg = 2000. Predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made in Lin et al. (1988) and Yan and Lin (1989) is only valid for systems having small liquid mass flow rates. Additionally, it is found that the interfacial heat flux is predominantly determined by latent heat transfer connected with film evaporation.  相似文献   

6.
Numerical simulations of turbulent flow have been used to determine the flow structure in a sudden pipe expansion, in order to explain the effects of disturbed flow on mass transfer controlled erosion–corrosion. Previously determined rates of mass transfer through the liquid boundary layer have been directly related to the predicted levels of near-wall turbulence. When rust films are present, the turbulent fluctuations affect both the mass transfer through the boundary layer and the removal of the film. The determining resistance to mass transfer, under the conditions examined, was that of the rust film.  相似文献   

7.
A numerical analysis was carried out to investigate the effects of film vaporization on natural convection heat and mass transfer in a vertical tube. Results for interfacial Nusselt and Sherwood numbers are presented for air-ethanol and air-water systems for various conditions. Predicted results show that heat transfer along the gas-liquid interface is dominated by the transport of latent heat in association with the vaporization of the liquid film. Additionally, the predicted results obtained by including transport in the liquid film are contrasted with those where liquid film transport is neglected, showing that the assumption of an extremely thin film made by Chang et al. (1986) and Yan and Lin (1990) is only valid for systems with small liquid mass flow rates. For systems with a high liquid film Reynolds number, Re10, the assumption of an extremely thin film is seriously in error.  相似文献   

8.
A novel experimental system was adapted to determine factors controlling selective absorption of hydrogen sulfide (H2S) from carbon dioxide (CO2). This work demonstrates that liquid film controlled mass transfer regime and a low value of the liquid side mass transfer coefficient favors selective removal of H2S from CO2. By identifying the factor controlling selective removal of H2S from CO2, this work lays the basis for the parameter optimization of a process for selective removal of H2S from CO2.  相似文献   

9.
Gas–liquid mass transfer of rotating disk reactor was studied in CO_2 absorption using 1,8-diazabicyclo-[5.4.0]-undec-7-ene(DBU)-glycerol solution as solvent. Effects of the rotating disk structure and various operation parameters on the CO_2 absorption rate and CO_2 removal efficiency were investigated. The rotating disk with optimal holes is conducive to mass transfer of CO_2 and the formation of thin liquid film at the opening increases the gas–liquid contact area. With the increase of rotating speed, the liquid flow pattern on the rotating disk surface changes from thin film flow to separated streams and creates extra liquid lines attached to the rim of the disk,which leads to a very complicated change on the CO_2 absorption rate and CO_2 removal efficiency. The overall gas-phase mass transfer coefficient increases 138% as the rotating speed increasing from 250 to 1400 r·min~(-1).Increasing temperature from 298 to 338 K can enhance the CO_2 absorption rate due to lowering the viscosity of the solvent. The rate-determined step for the absorption is focused on the gas side. The rotating disk reactor can effectively enhance the absorption of CO_2 with viscous DBU-glycerol solvents.  相似文献   

10.
This paper describes a transfer printing technique for directly patterning ordered TiO2 thin films onto Si substrates. Two- or three-dimensional TiO2 structures can be fabricated onto an Si substrate depending on the coating film thickness, which is controlled via the liquid phase deposition process parameters and attractive interaction forces between a poly(dimethylsiloxane) stamp and a polyelectrolyte layer during the transfer printing process. This additive transfer process is mediated by the presence of a thiol (SH)-terminated 3-mercaptopropyltrimethoxysilane self-assembled monolayer on the wafer surface. The transferred patterns are chemically bonded to the wafer surface, exhibiting strong adhesion. The attractive interaction forces between the stamp and the polyelectrolyte layer was weak enough to allow ready detachment of the patterns from the stamp during printing. Even the parts of a continuous TiO2 film that are not in contact with the substrate effectively transfer to form a free-standing structure. With long and short deposition times, three-dimensional structures and ordered two-dimensional round-hole grid structures, respectively, are obtained after the removal of the stamps.  相似文献   

11.
SIMULTANEOUS ABSORPTION OF H2S AND CO2 INTO A SOLUTION OF SODIUM CARBONATE   总被引:1,自引:0,他引:1  
The simultaneous absorption of H2S and CO2 has been studied both experimentally and theoretically. A model has been developed which predicts the absorption rates of H2S and CO2 into a sodium carbonate solution. The absorption rates are calculated according to the two-film theory. In the liquid film, the finite rate of the CO2 reaction was considered. Otherwise, in the liquid film as well as in the liquid bulk, equilibrium conditions for all reactions were assumed. Absorption experiments were performed on a packed column using a counter-flow strategy. In the experiments the influence of the initial carbonate concentration, the gas flow rate and the temperature on the removal efficiencies of H2S and CO2 and the selectivity of H2S were investigated. It is desirable to absorb the H2S but not the CO2. The agreement between the absorption model and the experimental results from the absorber tower was satisfactory. The mass transfer coefficients were determined by fitting the experimental data to the model with respect to the H2S and CO2 content in the outgoing gas. The H2S content was used to determine the gas side mass transfer coefficient and the CO2 content was used to determine the liquid side mass transfer coefficient, The effective contact area of mass transfer was taken from published data. With a constant packing height, both the experiments and the model indicated that high carbonate concentration benefits the removal efficiency of H2S. Higher gas flow rate also benefits the selectivity for H2S. However, the removal efficiency will decrease. At higher temperatures the selectivity and the removal efficiency of H2S decreased. Under the conditions investigated, the absorption of H2S was essentially controlled by gas-side mass transfer and the absorption of CO2 was controlled by liquid-side mass transfer  相似文献   

12.
李慧君  李东  王业库  彭文平 《化工学报》2021,72(5):2560-2569
基于双膜理论及边界层理论,建立了圆管、椭圆管、滴形管的管外气、液膜厚度及传热系数的数学模型。以圆管传热系数为依据进行了模型验证,计算结果与实验值的平均偏差约为6%,基本符合工程实际要求。在给定条件下,通过对不同曲率下各管型管外传热系数的计算,得到了气、液膜厚度的分布规律及换热特性。结果表明:在有效换热面积相同时,三种管型的气、液膜厚度,传热系数在一定角度下,随曲率的增大而增大;当曲率相同时,椭圆管传热系数最大,圆管最小。同时,分析了不同管型及其曲率对气、液膜排泄的影响机理和分离机理。为强化换热提供一定理论指导。  相似文献   

13.
赵清华  全学军  程治良  晏云鹏 《化工学报》2013,64(11):3993-4000
在一种新型高效的气液传质设备--水力喷射-空气旋流器(WSA)中,以Ca(OH)2料浆为吸收剂进行了模拟烟气湿法脱硫的实验研究。结果表明:脱硫率随进口气速增加而增加;随液体喷射速度增加先增加,增加到一定程度后几乎不变;随烟气中SO2的进口浓度增加而减小,存在一适宜的Ca(OH)2浓度和回流比。在气体流量24~72 m3·h-1、循环液体量0.4~0.8 m3·h-1、料浆中Ca(OH)2浓度7500 g·m-3时,对SO2浓度为1891~6373 mg·m-3的烟气进行湿法脱硫,脱硫率达88.9%~97.7%,且WSA的旋流气体和喷射液体在湿法脱硫中具有自清洁能力,未发现内部结垢和喷孔堵塞现象。总体积传质系数KGa、有效相界面积a均随进口气速uG增大而增大,而总传质系数KG随uG增加变化较小;当液体喷射速度 uL≤0.26 m·s-1时,KGa和KG随uL增加快速增大,之后增加缓慢,而a随uL几乎线性增加,KGa和KG随吸收剂中Ca(OH)2浓度cL增加有一最大值。结合实验数据拟合得到了相关的经验公式,这些关联式能较好地预测WSA的湿法脱硫传质性能。气体旋流场强度对总体积传质系数KGa和有效相界面积a起支配作用,脱硫传质过程同时受气膜和液膜阻力控制,但以液膜控制为主。  相似文献   

14.
The rapid advances in performance and miniaturization of electronic devices require a cooling technology that can remove the produced heat at a high rate with small temperature variations, as is obtained in flow boiling. To obtain insight in flow boiling, we performed numerical simulations in a 200 μm square microchannel using the local front reconstruction method. Besides validation with literature results, a parametric study shows an increasing heat removal rate and bubble growth rate with increasing wall temperature, liquid mass density, and liquid heat capacity and decreasing inlet velocity indicating the importance of phase change compared to convective transport. Finally, the heat transfer in the liquid film is studied using a Nusselt number defined with the film thickness, which is comparable to Nusselt number for falling films on hot surfaces. It is observed that convective effects are more pronounced at the bubble rear compared to the bubble front.  相似文献   

15.
Asymmetric transfer hydrogenation of acetophenone with isopropanol as hydrogen donor in the presence of a homogeneous catalyst was investigated in a rotating disc reactor. Initially, acetone stripping from binary mixtures acetone-isopropanol with nitrogen as inert gas was studied, since its removal is a key issue in improving reaction performance. The reactor consisted of a stainless steel disc mounted on a horizontal shaft, accommodated in a cylindrical shell. The disc was partially immersed in the liquid phase. Its rotation generated a thin liquid film on its upper part, which could be brought in contact with a gas phase used for stripping. A mathematical model was formulated to simulate the reactor and showed good agreement with experimental data for acetone stripping. It was observed that the efficiency of acetone removal from the liquid phase increased with the gas flowrate per initial liquid volume ratio. The effect of disk rotation was found to be small when the stripping gas was introduced in the liquid bulk. The reactor model agreed well with experimental data of the asymmetric transfer hydrogenation. An advantage of the rotating disk reactor is that the hydrodynamics of the phases can be decoupled and the gas flowrate can be increased without constraints in the liquid phase, unlike conventional agitated reactors that are limited by flooding. Simulations using high stripping gas flowrate per initial liquid volume, unachievable in stirred reactors, showed significant reduction of the residence time required to achieve >99% conversion.  相似文献   

16.
A volume of fluid method is developed in order to simulate reactive mass transfer in two-phase flows and is applied to study reactive laminar liquid film. The thermodynamic equilibrium of chemical species at the interface is considered using Henry's law. The chemical species concentration equation is solved using primitive variables and local fluxes are locally directly calculated at the interface. The present treatment of jump discontinuity of chemical concentration is consistent with a volume of fluid approach and the difficulty to calculate accurate local mass flux across interface is overcome. For plane interface, the precision of the numerical simulation is found to be very satisfactory while for curved interface a special procedure has been developed to reduce the development of spurious fluxes at the interface. The algorithm is validated for different cases by comparison with available solutions. The method is then applied to study non-reactive and reactive mass transfer in a falling liquid film. The results show that the liquid side mass transfer is well predicted by the Higbie (1935) theory when the transfer is controlled by the film advection provided that adequate parameters are considered, i.e. the actual velocity at interface and not the average liquid film velocity. For situations controlled by diffusion, the Sherwood number tends to a constant value characteristic of purely diffusive situations. For the reactive mass transfer, first and second order irreversible chemical reactions in the liquid phase are considered. The numerical results are compared respectively, with Danckwerts (1970) and Brian et al. (1961) solutions and good agreement is observed. The proposed Volume of Fluid method is shown to be well adapted to deal with interfacial reactive mass transfer problems.  相似文献   

17.
The problem of simultaneous heat and mass transfer associated with the vacuum distillation of a thin liquid film is solved by analyzing the system as a conjugated boundary value problem. The solution is developed in terms of well-known tabulated functions using a Green's function approach. The effects of heat transfer, liquid phase diffusion and effusion at the surface on the rate processes are elucidated, and separation efficiencies are predicted as functions of the length of the heated wall over which the film flows. The theoretical analysis is applied to calculate mass transfer rates for the separation of fatty acids from tall oil.  相似文献   

18.
Organic matter deposition on internal surfaces constitutes a drawback that impairs the efficiency of several industrial processes. To overcome this problem, sparging a train of bubbles could be useful since its presence strongly increases the wall shear stress. A detailed numerical mass‐transfer study between a finite soluble wall and the liquid around a rising Taylor bubble was performed, simultaneously solving velocity and concentration fields. The bubble passage throws solute backward and is responsible for radial dispersion. There is also an increase in the transfer rate with enhancements between 10 and 20% (depending on liquid average velocity and bubble length) compared to single‐phase flow. Mass‐transfer coefficients along the different hydrodynamic regions around the bubble nose, liquid film, and wake were characterized and their values compared with those from literature. The results suggest a promising potential of bubble train flow to enhance organic matter removal from walls in biological systems. © 2016 American Institute of Chemical Engineers AIChE J, 63: 2420–2439, 2017  相似文献   

19.
许闽  黄海  刘辉  雷志刚 《化工学报》2012,63(1):42-50
采用计算流体力学(CFD)的方法,研究了圆管中泰勒流的液侧传质特性,分析了泰勒气泡上局部传质特性,并研究了气泡上升速度、液膜长度和液栓长度对液膜处和气泡半球帽处平均传质系数的影响。结果表明,泰勒气泡表面局部传质系数存在3个峰值,液膜处的平均传质系数随气泡上升速度增大显著增大,随液膜长度增大而减小,而半球帽处的平均传质系数随气泡速度和液膜长度的增大变化较小,即膜接触时间增加时,液膜处的传质系数降低,而半球帽处传质系数变化较小。另外,引入场协同原则对单元胞内速度场和浓度场进行分析,解释了局部传质特性及强化机理。最后,给出了分别预测短和长膜接触时间下泰勒流液侧体积传质系数的关联式,该式在较宽的管径尺度范围(0.25~3 mm)内的预测误差在±20%以内。  相似文献   

20.
旋转填充床中伴有可逆反应的气液传质   总被引:2,自引:1,他引:1       下载免费PDF全文
钱智  徐联宾  李振虎  戴伟  郭锴 《化工学报》2010,61(4):832-838
应用CO2-MDEA气液吸收体系,对旋转填充床中伴有可逆反应的气液传质过程进行了定量的模型研究。在所有反应都可逆的情况下,根据Higbie渗透理论建立了旋转床中CO2-MDEA体系的扩散-反应传质模型。通过模型对传质过程的定量描述以及实验结果对模型的验证,超重力旋转床的强化作用可进一步被揭示为:由于不断更新的液膜使得可溶性气体在液膜内形成较大的浓度梯度,从而极大地增大了传质系数,强化了传质;旋转床的强化作用是在动态的传质过程中完成的,液膜的寿命越短则传质系数越大。在不同转速、温度、MDEA浓度和气液流量条件下进行了实验,本文模型的模拟值和实验结果吻合较好。  相似文献   

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