共查询到20条相似文献,搜索用时 187 毫秒
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利用计算流体力学(CFD)的方法,以高黏牛顿流体和假塑性非牛顿流体为研究对象,对错位六弯叶桨在层流域的搅拌流场特性进行了研究。结果表明:数值计算得到的功率值与实验测量值吻合较好,搅拌雷诺数对假塑性流体搅拌流场的量纲一速度和切应变速率影响较大,因此提高转速对改变流场的速度及切应变速率分布是一个有效的办法;而流体的流变性只对假塑性流体的量纲一速度有明显影响,对切应变速率影响较小,当流变指数n<0.3时与n基本无关。当流动由层流向过渡流转变时,搅拌桨的流量准数及泵送效率有显著提高;假塑性流体的流变指数降低时,其泵送效率显著下降。研究进一步认识了错位桨在不同流体中的搅拌流场特点,为高黏假塑性流体搅拌桨的设计、应用以及开发新型搅拌桨提供了参考。 相似文献
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研究了DEDS-12/AP-P4/Na2CO3三元复合体系(ASP)的流变行为以及盐的加入对其流变行为的影响。结果表明,在所研究的浓度范围内,DEDS-12起到无机电解质的作用,随DEDS-12浓度增加,溶液的表观粘度和剪切应力单调降低,稠度系数k下降,流性指数n增大,复合体系溶液流变行为遵循幂律流型;随体系中AP-P4和Na2CO3浓度的增高,虽然该三元体系的流变行为仍遵循幂律流型,但流性指数n增大,多在0.5以上,即与牛顿流体的差异减小;AP-P4浓度为2000 mg/L,Na2CO3浓度为1%,DEDS-12浓度为0.423 mmol/L,在NaCl浓度为1×104mg/L时,表观粘度上升3.88~8.11倍,随NaCl浓度增大,其流变行为由幂律流型逐渐表现出部分Bingham流体行为。 相似文献
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剪切稠化流体是一种典型的非牛顿流体,研究气泡在其中的运动特性对优化设备结构、提高反应效率具有重要意义。文中采用流体体积(VOF)法,通过改变Gallilei数(Ga)、E?tv?s数(Eo)与流变指数(n),对牛顿流体(n=1)及剪切稠化流体(n>1)内气泡的形状、尾涡、终端速度和气泡周围液相黏度分布的变化进行了深入的数值研究。结果表明:气泡变形程度和尾涡尺寸随着Ga数或Eo数的增大而增加;剪切稠化效应会阻碍尾涡的形成,减小气泡的尾涡尺寸;气泡周围剪切速率的差异会导致气泡上方及尾部产生高黏度区域,该高黏度区域会随剪切稠化效应的增加而增大;气泡终端速度随Ga数的增大或流变指数n,Eo数的减小而增大。 相似文献
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用毛细管流变仪研究了特性黏数([η])分别为0.631,0.705,0.808,0.898,0.978 dL/g的超有光聚对苯二甲酸乙二醇酯(PET)的流变性能,并计算得到黏流活化能(Eη)和非牛顿指数(n)。结果表明:不同[η]的超有光PET表观黏度(ηa)均随剪切速率(γ)和温度的升高而降低,且n小于1,均为切力变稀假塑性流体;在相同γ和温度时,[η]为0.705,0.631 dL/g PET的ηa,Eη和n较接近,而[η]为0.808,0.898,0.978 dL/g的PET的ηa,Eη,n变化明显。 相似文献
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根据气溶胶颗粒拟流体性质提出了气液交叉流界面捕集PM2.5的传质类比模型.分析了颗粒Schmidt数及其指数m对气溶胶流体传热传质类比的影响机理.以常用的横掠错排管束对流传热Nu方程为基础,导出了横掠错排降膜阵列PM2.5传质Sherwood数方程,由此建立了以m为模型参数的PM2.5捕集效率预测模型.用横掠20列×90排ø3 mm降膜阵列PM2.5捕集效率实测数据回归获得m值为0.808.在Reynolds数50~650的范围内,模型预测传质Sh与实测值误差在±20%之内. 相似文献
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Zoha Azizi Mohsen Rezaeimanesh Hossein Abolghasemi Hossein Bahmanyar 《Chemical Engineering Research and Design》2014
Mass transfer coefficients along a structured packed column were experimentally determined to obtain a new correlation for dispersed phase Sherwood number based on molecular diffusivity. Then in a comparative investigation, the correlation was re-established based on effective diffusivity. The applied chemical systems were toluene/acetic acid/water (T/A/W) and butyl acetate/acetic acid/water (B/A/W). The effects of droplet size and packing height on experimental Sherwood number were also discussed. It was shown that local Sherwood number could be increased up to 188% with increasing the droplet size from 6 to 9 mm in fixed dispersed phase flow rate. It was also observed that when height of packing increased from 10 to 40 cm, local Sherwood number decreased by almost 48% for constant dispersed phase flow rate. The results have shown that the proposed correlation based on effective diffusivity can estimate the experimental drop Sherwood number with high accuracy (error of less than 5%). Moreover, current research shows that replacing molecular with effective diffusivity in some theoretical models can correct their estimation. 相似文献
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Anjun Liu Jie Chen Moshe Favelukis Meng Guo Meihong Yang Chao Yang Tao Zhang Min Wang Hao-yue Quan 《中国化学工程学报》2022,41(1):230-245
This work systematically simulates the external mass transfer from/to a spherical drop and solid particle suspended in a nonlinear uniaxial extensional creeping flow.The mass transfer problem is governed by three dimensionless parameters:the viscosity ratio(λ),the Peclet number(Pe),and the nonlinear intensity of the flow(E).The existing mass transfer theory,valid for very large Peclet numbers only,is expanded,by numerical simulations,to include a much larger range of Peclet numbers(1 ≤ Pe ≤ 10 相似文献
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The advancing front theory is an approximate solution for mass transfer into a reactive fluid when the reaction can be assumed to be very fast. The theory has had considerable use in predicting mass transfer characteristics for reactive fluids flowing in conduits. In this paper, the mass transfer coefficient, in the form of the local, fluid-side Sherwood number, is derived for reactive flow in conduits with semi-permeable walls. The local, fluid-side Sherwood number is given as a function of the Graetz number, the wall Sherwood number, and a dimensionless reaction strength parameter. The limiting cases of both the constant wall concentration boundary condition (Shw?∞) and the constant wall flux boundary condition (Shw?∞)are investigated. Comparisons of the results with the classical Graetz and Leveque theories give conclusions about the accuracy of the advancing front theory for the worst possible case. 相似文献
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The effect of the viscosity ratio on mass transfer from a fluid sphere is examined in this paper. Numerical solutions of the Navier-Stokes equations off motion and the equations of mass transfer have been obtained for the unsteady state transfer from a fluid sphere moving in an unbounded fluid medium of different viscosity. The effects of the viscosity ratio and the flow on the concentration profiles were investigated for Reynolds number, viscosity ratio and Péclet number ranges of 0?Re?400, 0?κ?1000 and , respectively. The local and average Sherwood numbers are also presented graphically. The steady state results show that the average Sherwood number is increasing as Peclet number increases for a fixed viscosity ratio. However, for a fixed Peclet number, the average Sherwood number is decreasing as the viscosity ratio increases and reaches a limit value corresponding to the average Sherwood number for a solid spherical particle. From the numerical results, a predictive equation for the Sherwood number in terms of the Peclet number, the Reynolds number and the viscosity ratio is derived. 相似文献
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Piet J.A.M. Kerkhof 《Chemical engineering science》2007,62(7):2040-2067
The model for countercurrent steady state mass transfer between uniform dispersed phase particles and a continuous phase, both assumed to move in plug flow, with diffusion resistance inside the particles, and film resistance around the particles, is solved analytically for three particle geometries: infinite plates, infinite cylinders and spheres. In the solution, the direct relation between the local continuous phase concentration, and the average dispersed phase concentration is accounted for in the boundary condition. Concentration profiles in the mass exchanger are derived from the analytical solution, as well as asymptotic Sherwood numbers. The analytical solution requires the determination of roots of the characteristic equations, which is cumbersome for spherical particles. Correlations are provided for the asymptotic Sherwood numbers for easy computation. The model can easily be used for the analogous direct heat exchange problem. 相似文献
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Gas-phase controlled absorption of ammonia in foams made of solutions of sulphuric acid has been studied experimentally. Effects of gas-phase concentration of ammonia and type of surfactant on the performance of the foam-bed reactor are investigated. Gas-phase controlled absorption from a spherical bubble is anaylzed using the asymptotic value of Sherwood number (Sh = 6·58), for both negligible as well as significant changes in the volume of the bubble. The experimental data are shown to be in good agreement with the single-stage model of the foam-bed reactor using these asymptotic sub-models, as well as the diffusion-in-sphere analysis available in literature. Influence of effective diffusivity on the time dependence of fractional gas absorption has been found to be unimportant for foam columns with large times of contact. The asymptotic sub-models have been compared and use of the rigid-sphere asymptotic sub-model is recommended for foam columns of practical relevence. 相似文献
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P.W.A.M. Wenmakers M. MeeuwseM.H.J.M. de Croon J. van der SchaafJ.C. Schouten 《Chemical Engineering Research and Design》2010
This paper describes a model for gas–liquid mass transfer through thin liquid films present on structured packings for gas–liquid operations under dispersed gas flow regime. The model has been derived for two cases: the absorption (or desorption) of a gaseous component into the liquid film and the transfer of the gaseous component through the liquid film to the packing surface where an infinitely fast reaction takes place. These cases have been solved for three bubble geometries: rectangular, cylindrical, and spherical. For Fourier numbers below 0.3, the model corresponds to Higbie’s penetration theory for both cases. The Sherwood numbers for cylindrical and spherical bubbles are 20% and 35% higher, respectively, than for rectangular bubbles. In case of absorption and Fourier numbers exceeding 3, the effect of bubble geometry becomes more pronounced. The Sherwood numbers for cylindrical and spherical bubbles now are 55% and 100% higher, respectively, than for rectangular bubbles. In case of an infinitely fast reaction at the packing surface, the Sherwood number corresponds to Whitman’s film theory (Sh=1) for all bubble geometries. In this paper also practical approximations to the derived Sherwood numbers are presented. The approximations for both cases and all bubble geometries describe all the model data within an error of 4%. The application of the model has been demonstrated for three examples: (1) gas–liquid mass transfer for a structured packing; (2) gas–liquid mass transfer in a microchannel operated with annular flow; (3) gas–liquid mass transfer in a microchannel with Taylor flow. 相似文献
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Solutions for isothermal laminar flow diffusion with simultaneous heterogeneous and homogeneous reactions in a tube are extended to the case of non-Newtonian power-law fluids with arbitrary order reactions. Finite-difference methods are employed to yield the solutions. Special emphases are placed on the role of the reaction product characterized by two unique parameters, the diffusivity ratio and the stoichiometric coefficient ratio. Effects of reaction rate kparameters on the unique parameters, the diffusivity ratio and the stoichiometric coefficient ratio. Effects of reaction rate parameters on the system performance are also presented, showing a crossover behavior of the Sherwood number. The results are in good agreement with known solutions for systems of Newtonian fluids with first-order reactions. 相似文献