共查询到20条相似文献,搜索用时 15 毫秒
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E. Klemm G. Mathivanan T. SchwarzS. Schirrmeister 《Chemical Engineering and Processing: Process Intensification》2011,50(10):1010-1016
A microstructured falling film evaporator made out of AlMg3 was used to evaporate a 50 wt.% aqueous hydrogen peroxide solution. Sufficient wetting with contact angles lower than 20° and a stable falling film was reached by a sealing procedure at elevated temperatures (about 100 °C). After a self-passivation procedure under operation conditions the relative decomposition related to the evaporated amount could be reduced to values of about 10%. From the experimental results it was concluded that the decomposition occurs mainly in the liquid phase during evaporation and not in the vapour phase by contacting the non-wetted surfaces of the evaporator and pipes. At an operation temperature of 130 °C 10 vol.% of hydrogen peroxide in the vapour could be reached which almost corresponds to the vapour/liquid equilibrium at the top of the evaporator. 相似文献
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The focus of this study is the investigation of the effect of liquid flow rate on partial evaporation, enhanced by convective nitrogen flow, in a falling film micro contactor. Experiments are performed at different flow rates and for a certain heating liquid temperature. The temperatures of the gas and liquid phases are measured at their exit points, and the evaporation rate is determined while the channels are monitored with a microscope.The channels do not appear fully wetted at low liquid flow rates, and the liquid temperature is relatively low. The bad wetting is attributed to liquid flow maldistribution that can cause temperature gradients and subsequently enhances the maldistribution by uneven evaporation. A heat transfer model is developed and solved for different numbers of wetted channels. According to the modelling results the low liquid temperatures, can be fully explained by liquid flow maldistribution and channel drying.These wetting effects are minimized by restricting the liquid flow at its exit point and increasing the amount of liquid maintained at the bottom of the contactor. This improves the temperature profile and prevents drying, as it is possible that capillary forces tend to drive liquid upwards when dry spots occur. 相似文献
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分子蒸馏器中加入刮膜器可以增强分子蒸馏过程中的传质效率。以辊筒式刮膜器作为研究对象,利用进料流量、液体浓度、刮膜电机转速以及蒸发器尺寸等主要因素之间的结构关系,建立刮膜式分子蒸馏的数学模型。通过将实验参数代入到该模型可以快速计算出分子蒸馏后流出浓度,并将计算出流出浓度与实际浓度相比较,误差范围缩小到1.5%~2.5%之间,为寻找最佳控制条件提供了参考。将该模型通过MATLAB依次调整每一个参数,研究每一个结构参数对分子蒸馏过程的影响,通过研究仿真图像的变化趋势,使分子蒸馏器的设计可以精确到具体数值,为刮膜式分子蒸馏器的设计提供了依据。 相似文献
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J. Prenosil 《Chemical engineering science》1973,28(9):1763-1764
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Grigori M. Sisoev Omar K. Matar Christopher J. Lawrence 《Chemical engineering science》2005,60(3):827-838
In this work, we present results of a study of gas absorption into a falling film on a vertical substrate. The film flow is accompanied by the formation of nonlinear waves which strongly influence the diffusion layer that develops from the film surface. As a result, significant enhancement of mass transfer has been observed in experiments. We use recent advances in modelling of the hydrodynamics and solve a two-dimensional convective-diffusion equation for the solute concentration. Numerical solutions for the finite-amplitude wave regimes and associated integral absorption rates are obtained for a range of flow conditions. Our results show clearly the influence of waves on the development of the diffusion layer and, in particular, the enhancement of absorption due to the waves; the existence of optimal conditions for maximizing the absorption rate is also demonstrated. 相似文献
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Paweł Sobieszuk Ryszard Pohorecki 《Chemical Engineering and Processing: Process Intensification》2010
Gas–liquid mass transfer in a falling film microreactor (FFMR) with 29 microchannels (0.6 mm width each) was investigated. CO2 was absorbed from a CO2/N2 gaseous mixture into a NaOH aqueous solution and the liquid-side mass transfer coefficient and the gas-side mass transfer coefficient were measured. The influence of gas concentration on the value of gas-side mass transfer coefficient has been discussed. 相似文献
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A gaseous reactant is absorbed in a liquid with a positive heat of absorption. It reacts with the liquid by an exothermic, irreversible first order reaction. Analysis of a CSTR for this process has shown that up to 5 steady state solutions may exist even though the system appears to be quite simple with only one reaction. The existence of an extraordinary large number of steady state solutions is explained by the coupling between absorption and reaction: A low temperature gives no reaction, a high temperature prevents absorption of the gas and hence leads to mass transfer control of the reaction, while an intermediate temperature may permit operation at a third (stable) steady state. In between the stable steady states one finds (as us two unstable steady states.We extend the analysis of the CSTR to the distributed system of a falling film reactor, and we treat both the transient situation in the entrance partAn eigenanalysis of the steady states shows that temperature rise across the gas film may lead to 3 stable steady states even if an isothermal model is 相似文献
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Sandra Schlögl Armin Temel Raimund Schaller Armin Holzner Wolfgang Kern 《应用聚合物科学杂志》2012,124(4):3478-3486
The photochemical prevulcanization of natural rubber (NR) latex via the thiol‐ene reaction is a new approach aiming at the replacement of noxious processing agents used in conventional sulfur vulcanization processes (e.g., accelerators) together with cost saving options. The crosslinking reaction involves the excitation of a selected photoinitiator with ultraviolet (UV) light which is followed by the formation of thioether links due to the thiol‐ene addition reaction. The photochemical process is carried out in a falling film photoreactor which provides not only a continuous prevulcanization process but also exhibits a technology which is already commercially well established. The main advantage of the falling film process lies in the short prevulcanization time and the mild reaction temperature. Following the idea of the manufacture of low‐allergenic surgical gloves made from NR latex without compromising on the glove quality by means of physical performance, crucial process parameters of the falling film process have been determined and characterized in this study. Surgical gloves were made from the photocured NR latex which was prevulcanized using selected process conditions. The physical properties including tensile strength, elongation, modulus, and crosslink density were examined together with the aging stability and the stability against high‐energy radiation (sterilization with gamma rays). It was found that the UV light intensity, the number of illumination cycles, the choice of photoinitiator, and the thiol crosslinker play an important part in the glove quality. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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Experimental studies of nitrobenzene hydrogenation in a microstructured falling film reactor 总被引:1,自引:0,他引:1
Nitrobenzene hydrogenation over palladium catalyst was performed in a microstructured falling film reactor at a range of flowrates (0.5-3 ml/min) and pressure (1-6 bar). Confocal microscopy was used to measure liquid film thickness. Comparison with film thickness prediction equations showed an overprediction of 10-30%. The kLa of this system was estimated to be 3-8 s−1 with interfacial surface area per reaction volume 9000-15000 m2/m3. Conversion was found to be affected by both liquid flowrate and hydrogen pressure, and the reactor operated between the kinetic and mass transfer controlled regimes. 相似文献
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The formation of calcium sulphate scale in Vertical Tube Evaporators (VTE) of the falling film type has been investigated in a single tube experiment using fluted tubes. It was found that the scaling threshold is dependent not only on the brine concentration and temperature, but also on the heat flux to the evaporating film. With normal sea water concentrations and a high heat flux, scale was observed at 240°F (115°C), whereas with a low heat flux scale-free operation was possible at 266°F (130°C). The effect of heat flux is attributed to the presence of local areas of high concentration in the falling film which form as a result of uneven evaporation from the film. A simple model has been developed to explain the results. 相似文献
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Arghya Samanta 《American Institute of Chemical Engineers》2020,66(5):e16906
A linear stability analysis of a three-dimensional shear-imposed fluid flowing down an inclined plane is studied based on the evolution equations for normal velocity and normal vorticity components. Both modal and nonmodal stability analyses are carried out. The modal stability analysis demonstrates that shear-imposed flow is more unstable to solo streamwise perturbation. On the contrary, the nonmodal stability analysis demonstrates that shear-imposed flow is more unstable to solo spanwise perturbation. There is evidence of existing transient energy growth in the wavenumber space that intensifies in the presence of imposed shear stress. Further, the boundary for the zone of transient growth appears far ahead of the boundary for the zone of exponential growth. This fact indicates that the onset of instability for the shear mode may occur before than that predicted from the eigenvalue analysis. A new critical surface parameter involving imposed shear stress is determined, which in fact reveals the existence criterion of instability for the surface mode. Moreover, we have found three different regimes of surface mode instability, shear mode instability, and transient growth phenomenon in the wavenumber space. The unstable region for the surface mode reduces while the unstable region for the shear mode enhances in the wavenumber space with the increasing value of surface parameter, or equivalently, with the increasing value of imposed shear stress. Finally, the unstable region for the surface mode disappears from the wavenumber space as soon as the surface parameter exceeds its critical value; instead, the wavenumber space is occupied by the regime of transient energy growth. In addition, the incident of pseudoresonance takes place on the response curve to external harmonic forcing. 相似文献
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Mass transfer data are presented for absorption of oxygen in a centrifugal film apparatus. The apparatus was designed to exclude the formation of foam by gas dispersion in liquid. Cells and micro-organisms are not subjected to high shear stress. Therefore, this equipment can be applied in fermentation processes. In the present work, experimental data and correlations were obtained on splitting of the liquid film and oxygen absorption into the film through a spiral ridge formed on the conical surface. The performance of the apparatus is found to be equivalent to those of other types of absorbers. 相似文献
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S. Ben Jabrallah A.S. Cherif B. Dhifaoui A. Belghith J.P. Corriou 《Desalination》2005,180(1-3):197-206
This article concerns the experimental study of heat and mass transfer in a distillation cell. This latter is a parallelepiped, of large form factor, whose active walls are vertical. The cell is fed with salt water, and pure water is evaporated from a thin film that falls along a heated wall while the opposite wall is maintained at a lower temperature and is used as a condensation surface. The experimental results show that the heat transfer in the distillation cell is dominated by the latent heat transfer associated with evaporation. A parametric study of the behavior of the distillation cell has been performed. A convenient choice of the operating parameters is suggested to optimize the distillation yield. 相似文献