共查询到19条相似文献,搜索用时 296 毫秒
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为了定量描述绕管式换热器壳侧降膜蒸发特性并进而优化换热器结构,建立了绕管式换热器壳侧降膜蒸发过程流动与传热的数值模型。首先对降膜流动过程中流型变化和传热传质机理进行分析;通过对降膜流动过程液膜所受表面张力、重力和剪切力的计算,实现层状流、柱状流和滴状流等不同流型的模拟;通过管壁面和气液交界面的组分守恒建立降膜蒸发过程的传质子模型,并基于传质速率计算得出潜热传热速率。将数值模拟结果与已有文献中实验数据进行了对比,结果显示89%的模拟数据与实验数据偏差不超过25%;模拟结果与实验数据吻合较好。基于提出的模型,对不同工况下的绕管式换热器壳侧降膜蒸发传热传质规律进行了分析。 相似文献
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非等温降膜流动在精馏过程中较为常见,其流动特性较为特殊,对填料表面的质量和热量传递有重要影响。本文搭建了可视化的实验装置,在保证液相室温进料的前提下升高填料温度,在规整填料表面构造液相被加热的非等温降膜流动,运用激光诱导荧光技术对液膜形态变化进行观测分析,对液体润湿面积、液膜厚度等参数进行比较。结果表明,随着填料温度的升高,液体润湿面积显著减小,波谷处液膜厚度显著增加,液膜逐渐收缩为沟流,填料表面的不规则液滴数目增多,干板现象越发严重。液体的聚并和分散轨迹消失,液相再分布及表面更新能力降低。因此,填料表面的非等温降膜流动液膜收缩现象十分明显,降低传热传质能力,需在工业生产中引起足够重视。 相似文献
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降膜式气液交叉流除尘系统中,布膜管表面液体受气流剪切力及壁面材质不均匀等因素的影响存在绕流和旋流的现象,该现象直接导致气液接触面积降低,不利于颗粒物的脱除。为解决此问题,采用非均匀式布膜管代替原有光滑管。数值模拟结果表明,模拟结果与实验数据吻合度较好,非均匀布膜管能够达到原有单元排75%的颗粒物脱除效率且有效降低实验液路用水量。通过对气液交叉流除尘能耗分析,得到液体输送过程能耗占据总能耗的90%以上。采用布膜管代替原有光滑刚性圆管达到相同颗粒物脱除效率时,降低了系统49%的能耗,提高了装置经济性且遏制了绕流和旋流现象。 相似文献
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在Harriott理论的基础上,提出一种新的垂直降膜吸收传质模型,将降膜过程中漩涡的作用点由一个几何点扩展到一个区域,将整个降膜流动过程划分为非湍流区和全湍流区.非湍流区内,波峰和波谷域采取了不同的Levich厚度处理方法.在全湍流区,对波动速度进行了修正.理论数据与氨水光管降膜吸收实验数据相比较,偏差在非湍流区不超过10%,在全湍流区不超过15%.扩散系数、Levich厚度及波动周期对传质系数的影响被表示为两个量纲1量之间的关系. 相似文献
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针对过程工业尾气中PM2.5治理难题,提出以废水-废气构建的气液交叉流降膜阵列系统,利用工业尾气冷凝组分冷凝捕集尾气中PM2.5。基于质量衡算和传质速率方程,得到以尾气湿含量为控制参数的气液交叉流PM2.5捕集效率模型。理论结果表明,进口尾气湿含量从0.28kg/kg增加到0.52kg/kg,单排降膜阵列PM2.5捕集效率从0.64%增加到1.26%。湿含量为0.52kg/kg时,预测182排降膜阵列组成长度为819mm的分离通道整体分离效率可达到90%。通过20列×90排降膜阵列进行实验验证,表明理论与实验结果基本一致。 相似文献
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本文提出了管壳式鼓泡阵膜塔的结构构思与操作工况.该塔的列管具有两种流体分布器,上端口的液体分配器与降膜塔相似,下端口的气体分布器与鼓泡塔相似,以实现列管内上半段降膜、下半段鼓泡的鼓泡降膜联合操作.文中阐述了在φ16—36mm单管和多管(塔径φ200mm)中水-空气系统的流体力学实验结果.实验表明,该塔具有良好的操作性能:气液负荷大,操作弹性大,两相流状态稳定,鼓泡层返混较小,兼具鼓泡塔和降膜塔的特点.实验并为这种新型反应器提供了必要的设计数据. 相似文献
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The coating of non-Newtonian liquids onto a vertical surface continuously withdrawn from the liquid bath is considered. An analytic treatment is presented for purely viscous non-Newtonial liquids using the Ellis and generalised Bingham models both of which may be reduced to a new theory for power-law fluids. The theories give a relationship between the dimensionless film thickness, T1, and the Capillary number, C1, as a function of the fluid physical properties and the parameters of the viscous model. The dimensionless groups have been generalised to allow for non-Newtonian behaviour. The power-law and Ellis model predictions are compared with previous theoretical studies and shown to be consistent with known limits. Experimental data are also presented for a wide range of non-Newtonian fluids and compared with the new theories. 相似文献
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Subhash C. Roy 《加拿大化工杂志》1971,49(5):583-589
The cylinder withdrawal theory for power-law fluids proposed by Tallmadge has been compared with continuous withdrawal data in this work. Calculated withdrawal speeds differ greatly from measured values, although Tallmadge's gravity-corrected theory for Newtonian fluids is in agreement with the present data on Newtonian fluids. Correlations similar to that of Goucher and Ward have been developed with the experimental data over a 400-fold range of dimensionless withdrawal speeds. These correlations are applicable for prediction of non-Newtonian liquid film thicknesses on vertical wires and also apparently for viscoelastic fluids like CMC solutions, but are not applicable for inelastic fluids like Carbopol 934. 相似文献
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Flow of non-Newtonian fluids in both the concentric and eccentric annuli is of great importance in extruders for molten plastics and wellbore fluid circulation for the removal of drilling cuttings. The steady laminar couette flow of non-Newtonian power-law fluids in eccentric annulus is employed in this study to analyze the problems of surge or swab pressures encountered when running or pulling tubular goods (pipes) in a liquid filled borehole. This is similar to the annular space created by two long co-axial cylinders with the inner cylinder in motion at a steady velocity, and a stationary outer cylinder. The solutions of the equations of motion are presented in both dimensionless form and as a family of curves for different pipe/borehole eccentricity ratios and power-law fluid index values for a more general application. The expected error in surge computation for concentric annulus as a result of eccentricity is evaluated. 相似文献
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Unsteady axisymmetric boundary layer equations for power-law non-Newtonian fluids are analyzed. A number of new exact solutions containing arbitrary functions and free parameters are constructed using generalized or functional separation of variables. The solutions are obtained using a Crocco-type transformation reducing the order of the equations examined and simpler point transformations. Along with the exact solutions to axisymmetric boundary layer equations, some new exact solutions to planar boundary layer equations for non-Newtonian fluids are constructed. Several properties have been discovered that allow the exact solutions of the unsteady axisymmetric boundary layer equations to be generalized by including additional arbitrary functions therein. All results refer to an arbitrarily shaped streamlined solid of revolution. 相似文献
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An analytical solution is presented for gas absorption with or without a first-order or zero-order chemical reaction in a laminar non-Newtonian power-l model falling liquid film. For physical absorption, the first ten eigenvalues, series coefficients and related quantities are computed accurately by a quasinumerical method which shows considerable improvement over previous investigations. The range of applicability of the penetration theory solution is also established to indicate in what regions will the finite film thickness and complete velocity profile be important in determining the absorption rate. It is found that the range of dimensionless axial contact length X* in which the penetration theory is valid diminishes rapidly with increasi values of the power-law index n. For chemical absorption, the solution can be obtained by a linear superposition principle in terms of a “transie part” in which the effect of hydrodynamics within the liquid film is of importance and a “steady part” in which the reaction rate is controlling. In the “transient part” solution, the first ten eigenvalues and related quantities are reported for a variety of values of n and the dimensionl reaction rate parameter kl* or k0*. Certain asymptotic solutions from the penetration theory are also given and their range of applicab estimated. For any given n, it is estimated that only when k1* or k0* is less than approximately 10 will the finite film thickness and velocity profile have any effect on the absorption rate as compared to that calculated from the penetration theory with chemical reaction. The non-Newt character of the liquid film also has a significant influence on the absorption rate. At a fixed X*, the absorption enhancement due to reaction is when n = ∞ and is smallest when n = 0. The solutions obtained in this work are useful either for predicting absorption rates or for deter molecular diffusivity (and reaction rate constant) of gases in non-Newtonian falling liquid films. 相似文献
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很多废水处理装置涉及非牛顿型流体中的多相流动和传质问题,研究其中的气液传质过程有助于实现装置的优化设计和高效节能运行。以鼓泡反应器内清水和不同质量分数的羧甲基纤维素钠(CMC)水溶液为实验对象,分别研究气相表观气速和液相流变特性对气泡尺寸分布、全局气含率和体积氧传质系数的影响。实验结果表明,液相的流变特性对其传质特性参数均有较大影响。与清水相比,CMC水溶液中气泡平均直径和分布范围更大;清水和CMC水溶液的全局气含率均随表观气速的增加而增大;CMC水溶液的体积氧传质系数随CMC水溶液质量分数的增加而减小。基于实验研究,得出修正的体积氧传质系数公式和适用于幂律型非牛顿流体流动体系氧传递过程的无量纲关联式,可很好地实现非牛顿流体流动的废水处理装置中气液传质参数的计算。 相似文献
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Mourad Yataghene Francine Fayolle Jack Legrand 《Chemical Engineering and Processing: Process Intensification》2009,48(10):1447-1458
Viscous dissipation plays an important role in the dynamics of fluids with strongly temperature-dependent viscosity because of the coupling between the energy and momentum equations. The heat generated by viscous friction causes a local temperature increase in the high shearing zone with a consequent decrease of the viscosity which may dramatically change the temperature and velocity distribution. These processes are mainly controlled by the Brinkman number, the rotating velocity and the thermal boundary conditions. This work analyses forced convection heat transfer including the viscous dissipation in a scraped surface heat exchanger (SSHE). In this study the increase of the temperature due to the viscous dissipation is analysed both experimentally and numerically for Newtonian and non-Newtonian fluids. Heat transfer simulations including viscous dissipation were carried out by means of the CFD code of the software Fluent, version 6.3, with solving momentum and energy equations. Two thermal boundary conditions were considered: pseudo-adiabatic wall and constant temperature on the stator wall exchange. In the case of Newtonian fluid (pure HV45), for both considered thermal boundary conditions, an important increase of the temperature was obtained. In the case of non-Newtonian shear thinning fluid (2 wt% CMC solution), viscous dissipation is neglected. The developed numerical model agrees well with experimental results. The validated numerical model was then used to study the effect of index and consistency behaviour of shear thinning fluid using power-law rheological behaviour on the viscous dissipation, and correlation using dimensionless analysis expressed with different dimensionless process numbers is proposed for Newtonian and non-Newtonian shear thinning fluid. 相似文献
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The falling ball method (FBM) is one of the well-established techniques for measuring the viscosity of Newtonian liquids at the room as well as at elevated temperatures and pressures. Owing to its simplicity and low cost, the possibility of extending its range of application to non-Newtonian systems including virgin and filled polymer melts, composites, polymer-solutions, and so forth, is explored here, In this work, theoretical results for the flow of power-law fluids past a sphere have been used to extract the values of the zero-shear viscosity and shear-dependent viscosity in the low-shear rate limit. The theoretical scheme outlined here has been validated by presenting comparisons with experimental results for scores of polymer solutions for which both falling sphere and rheological data are available in the literature. Indeed, the good correspondence obtained between these two independent data is encouraging and it is thus possible to use the FBM for shear-thinning systems when the resulting Reynolds numbers are such that the flow is viscosity-dominated, and the inertial effects are negligible. This implies that the Reynolds number should be ≤ ~1 for shear-thinning fluids and ≤ ~10−5 for shear-thickening fluids. 相似文献