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O.A. Asbjørnsen 《Chemical engineering science》1973,28(9):1699-1706
The Taylor diffusion model is applied to the interpretation of residence time distribution measurements in falling liquid films. In a range of Reynolds numbers from 40 to 1000, the application shows considerable systematic deviations. This indicates firstly, that the transverse transport mechanisms are not efficient enough to justify the application of the diffusion model, and secondly, that the transport mechanisms vary considerably through-out the film thickness. These observations are in full agreement with the theory at the wall by Spalding.The data used for this analysis are taken from frequency response measurements, where the Fourier transform is applied to the parameter estimation. By this transform, the effect of the mass transfer between streamlines in a velocity distribution is demonstrated by an interaction matrix from the differential equation for tracer dispersion. 相似文献
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采用高精度红外热成像技术研究固体平壁上加热和冷却液膜流动性能,比较了不同加热强度下液膜表面的温度场特征以及加热温差对固壁上液体分布的影响。传递过程中,界面上浓度和温度变化引起的表面张力梯度,驱使低界面张力处的液体流向高界面张力处(Marangoni效应),从而造成了液体特殊的流动现象与分布特征。在受热/冷却降膜过程中,由于流速和传热的差异,液膜表面存在一定的温度梯度。横向的温度梯度远大于流动方向的温度梯度,引起的Marangoni效应会造成受热液膜收缩和冷却液膜扩展,从而明显地影响液膜的相界面积及其传递性能。 相似文献
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Heat transfer characteristics for a falling turbulent liquid film flow over a fin are analyzed using the conjugate convection-conduction theory. Numerical results are obtained from a simultaneous solution of the energy equations of the fluid and the fin. Results are presented for the fin temperature distribution, dimensionless heat transfer coefficients, local heat fluxes, and fin efficiencies. 相似文献
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The collapsing liquid column phenomenon has been experimentally and theoretically studied. The experimental data demonstrated the development and travel of a shock wave. Point velocities within the flow regime were measured using a hot film probe. The numerical simulation was performed using a finite difference code similar to the Marker and Cell technique. The results were in good agreement with the experimental data. The numerical technique therefore promises to be a valuable aid in studying highly convective, incompressible flows. 相似文献
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Bedich ika Helena Bendov Ivan Macha
《Chemical Engineering and Processing: Process Intensification》2005,44(12):1312-1319
A procedure has been proposed for the estimation of the terminal falling velocity of non-spherical particles moving in a Carreau model fluid in the transition flow region. The procedure is based on a modification of the relationship formerly developed for the fall of spherical particles including the particle dynamic shape factor. The suitability of the proposed procedure has been confirmed by good agreement between experimental and calculated terminal falling velocity data. In the experiments, the terminal falling velocity of short cylinders and rectangular prisms in polymer solutions of different measure of shear thinning and elasticity has been measured. 相似文献
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对洗涤冷却管内垂直降膜的流动特性进行研究,采用超声波多普勒测速仪对管内不同周向以及轴向位置的液膜厚度和速度进行了无接触式的测量,液膜Reynolds数范围为1.0×104~3.1×104。结果表明:在0°周向位置上液膜厚度与速度均达到最大值,导致该位置局部液膜厚度过大而不能保持稳定,部分液体脱离液膜表面,此外还造成了8°和16°位置的液膜厚度激增。在轴向上,当Reynolds数小于2.0×104时,液膜速度在重力作用下随流动距离增加而增加,反之,液膜速度因为流动阻力会随距离增加而减小。随着Reynolds数的增大,液膜平均厚度和速度呈增大趋势。此外,Reynolds数的增大还会使得液膜更加不稳定。 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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Patricio Bohorquez 《American Institute of Chemical Engineers》2012,58(8):2601-2616
A finite volume method is proposed to study the dynamics of unsteady, falling liquid films carrying monodisperse spheres in Newtonian regime under the action of gravity. The Navier–Stokes equations were rewritten to implement a numerical scheme with interface capturing capability, able to compute discontinuities in the solid volumetric concentration and free surface flows. The interface capturing property is checked with simple benchmarks, showing that experimental data for a vertical settler and the dynamics of the wetting front in a thin liquid film are reproduced with success. Also, the numerical scheme computes with accuracy Kapitza instability or viscous roll waves. This work concludes illustrating the applicability of the model to study viscous resuspension phenomenon in a unsteady, falling suspension film. © 2012 American Institute of Chemical Engineers AIChE J, 58: 2601–2616, 2012 相似文献
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Cesar E. Meza 《Chemical engineering science》2008,63(19):4704-4734
Experimental data on the amplitude of large waves on vertically falling films are presented over a wide range of fluid properties and flow rates. Attempts are made to correlate the amplitude of these naturally excited and saturated waves to the Weber (We) and Kapitza numbers (Ka), the two dimensionless groups characterizing the film. For viscous fluids (with 2<Ka<200), the wave amplitude increases with the reciprocal of the Weber number and saturates at values around 3 (hmax/hN∼3) while the dependence on Ka is found to be weak. For less viscous fluids (200<Ka<3890), the waves are found to be much more dynamic with amplitudes saturating at much higher values of around 10. The film roughness, or more precisely, the standard deviation (r.m.s) of the film thickness is also found to be correlated with the reciprocal of the Weber number. Scaling arguments are used to explain the initial increase in wave amplitudes. A two-equation h-q model is used to study the spatio-temporal dynamics of waves on long domains with periodic inlet forcing. The model is used to examine the amplitude-celerity relation for three families of solitary waves: the slow moving γ1 family, the fast moving γ2 family and the very fast moving ‘tsunami (Γ2) family’ having Nusselt film as the substrate. It is found that the film profile at short distances depends on the forcing amplitude and frequency but once the wave amplitude exceeds a critical value, the amplitude-celerity relationship is linear for all solitary waves that exist on the film and is independent of the forcing frequency or amplitude. It is also found that for a fixed set of fluid properties and flow rate (We and Ka), the Γ2 wave has the largest amplitude and wavelength. Local bifurcation and computational results are used to explain the experimentally observed wave amplitudes on naturally excited films. 相似文献
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Junfei Tian 《Chemical engineering science》2009,64(14):3311-3319
This paper reports the development of a new experimental method suitable for the determination of the spreading velocity of surface active substances on a thin film of liquid substrate over a solid surface. Previous research showed that when oil and surfactants spread on the surface of a deep body of water, the spreading velocity is usually quite high, being in the range of several tens of centimeters per second. However, the spreading velocities of these substances on a thin water film are much slower. This is because that the spreading of an oil or a surfactant on water surface is not just a two dimension phenomenon, but a phenomenon involving the movement of water in a small depth below the surface. An additional process impeding oil or surfactant spreading in this situation is the interaction of the spreading molecules with the liquid/soild interface underneath water surface. The experimental method developed in this work uses a Wilhelmy balance to monitor the average spreading velocity of surface active substances on a thin water film over a porous solid substrate. The spreading of cellulose hydrophobization agents over wet paper web during the papermaking process is used as an example to demonstrate the capability of the method. 相似文献
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Nanometer-scale thick liquid films of poly(methylhydro-dimethyl)siloxane copolymer (PMDMS) deposited on hydrophilic and hydrophobic solid organic films have been studied using synchrotron X-ray specular reflectivity (XRR). The physico-chemical properties of liquid PMDMS at the interfacial level are controlled by the nature of the solid surface. Detailed analysis of the XRR-data revealed the formation of a low-density region in the liquid PMDMS film in the vicinity of the hydrophobic surface, whereas a densely packed molecular layer is formed at the liquid PMDMS-hydrophilic substrate interface. Non-covalent polymer chains are ‘frozen’ at the solid-liquid interfaces in the confined liquid films and interactions with the substrate surfaces (i.e. hydrogen bonding) are responsible for distinctly different density profiles. 相似文献