共查询到20条相似文献，搜索用时 0 毫秒
1.
High‐solids biomass slurries exhibit non‐Newtonian behavior with a yield stress and require high power input for mixing. The goals were to determine the effect of scale and geometry on power number P0, and estimate the power for mixing a pretreated biomass slurry in a 3.8 million L hydrolysis reactor of conventional design. A lab‐scale computational fluid dynamics model was validated against experimental data and then scaled up. A pitched‐blade turbine and A310 hydrofoil were tested for various geometric arrangements. Flow was transitional; laminar and turbulence models resulted in equivalent P0 which increased with scale. The ratio of impeller diameter to tank diameter affected P0 for both impellers, but impeller clearance to tank diameter affected P0 only for the A310. At least 2 MW is required to operate at this scale. 相似文献
2.
Based on experiments with single air bubbles rising in stagnant non‐Newtonian fluids, an innovative model containing the aspect ratio (E) and two parameters (α, β) was proposed and proved to be capable of characterizing the bubble shape from spherical/ellipsoidal to prolate/oblate‐tear with good accuracy. Several impacts on bubble deformation were investigated, involving the rheological properties of the fluids and different forces exerted on the bubble, which were quantified by multiple dimensionless numbers (e.g., Reynolds, Eötvös, and Deborah number). Within a wide range, the empirical correlations were obtained for parameter β, and between α and β. Together with the shape model, a complete system was set up for bubble shape characterization and prediction that will provide new ideas for future studies on bubble hydrodynamics. 相似文献
3.
Electrical resistance tomography (ERT) provides a non-intrusive technique to examine, in three dimensions, the homogeneity and flow pattern inside the mixing tank. In this study, a 4-plane 16-sensor ring ERT system was employed to study the shape and the size of cavern generated around a radial-flow Scaba 6SRGT impeller in the mixing of xanthan gum solution, which is a pseudoplastic fluid possessing yield stress. The size of cavern measured using ERT was in good agreement with that calculated using Elson's model (cylindrical model). The 3D flow field generated by the impeller in the agitation of xanthan gum was also simulated using the commercial computational fluid dynamics (CFD) package (Fluent). The CFD model provided useful information regarding the impeller pumping capacity, flow pattern, and the formation of cavern around the impeller. CFD results showed good agreement with the experimental data and theory. 相似文献
4.
Bubble formation from an orifice submerged in quiescent polyacrylamide aqueous solution was investigated numerically with a sharp‐interface coupled level‐set/volume‐of‐fluid method based on the rheological characteristics of the fluid. In both non‐Newtonian fluids and Newtonian fluids, the numerical approach was able to capture accurately the deformation of the bubble surface, validated by comparison with experimental results. The effects of orifice diameter, solution mass concentration, and gas flow rate on bubble volume and aspect ratio were evaluated. Both the instantaneous and detached volume decrease with the orifice diameter but increase with mass concentration and gas flow rate. The aspect ratio at the departing point tends to rise with the orifice diameter and mass concentration and falls with the gas flow rate. 相似文献
5.
6.
The study was carried out to simulate the 3D flow domain in the mixing of pseudoplastic fluids possessing yield stress with anchor impellers, using a computational fluid dynamics (CFD) package. The multiple reference frames (MRF) technique was employed to model the rotation of the impellers. The rheology of the fluid was approximated using the Herschel–Bulkley model. To validate the model, the CFD results for the power consumption were compared to the experimental data. After the flow fields were calculated, the simulations for tracer homogenization were performed to simulate the mixing time. The effects of impeller speed, fluid rheology, and impeller geometry on power consumption, mixing time, and flow pattern were explored. The optimum values of c/D (impeller clearance to tank diameter) and w/D (impeller blade width to tank diameter) ratios were determined on the basis of minimum mixing time. 相似文献
7.
Three‐dimensional simulations of bubble formation in Newtonian and non‐Newtonian fluids through a microchannel T‐junction are conducted by the volume‐of‐fluid method. For Newtonian fluids, the critical capillary number Ca for the transition of the bubble breakup mechanism is dependent on the velocity ratio between the two phases and the microchannel dimension. For the power law fluid, the bubble diameter decreases and the generation frequency increases with higher viscosity parameter K and power law index n. For a Bingham fluid, the viscous force plays a more important role in microbubble formation. Due to the yield stress τy, a high‐viscous region is developed in the central area of the channel and bubbles deform to a flat ellipsoid shape in this region. The bubble diameter and generation frequency are almost independent of K. 相似文献
8.
Regenerative liquid propellant guns (RLPGs) have been studied for many years. However, the presence of large pressure oscillations is observed in almost each RLPG firing. In order to push forward the liquid propellant application in guns, a low pressure firing system called regenerative liquid propellant mortar (RLPM) is developed. The multiphase multidimensional fluid-dynamics model is presented to research the interior ballistic properties of RLPM. A high-speed liquid sheet spray model is presented for the annular jet in RLPM based on the linear stability analysis and surface wave breakup theory. In addition to the jet atomization, the droplets secondary breakup is considered. The experiments on a 60 mm RLPM test fixture are carried out, and the results indicate that the liquid propellant combustion oscillations are effectively suppressed. The spray and combustion processes have been simulated for the 60 mm RLPM which are in agreement with the experimental data well. Numerical results indicate an important benefit for the RLPM that the muzzle velocity is improved by increasing the charge quantity while the maximum chamber pressure remains unchanged. 相似文献
9.
The computational fluid dynamics (CFD) approach was adopted to simulate benzoyl peroxide (BPO)‐initiated styrene polymerization in a laboratory‐scale continuous stirred‐tank reactor (CSTR). The CFD results revealed the effects of non‐homogeneity and the short‐circuiting of the unreacted styrene and initiator on the reactor performance. The study also investigated the effects of the impeller speed and the residence time on the conversion and the flow behavior of the system. The CFD simulation showed that intense mixing remained confined to a small region near the impeller. With increasing impeller speed, it was found that the perfectly mixed region near the impeller expanded, thus reducing non‐homogeneity. Different contours were generated and exhibited the effect of the mixing parameters on the propagation rate and styrene conversion. The monomer and initiator conversions predicted with the CFD model were compared to those obtained with a CSTR model. The CFD model accounts for the non‐ideality behavior of the polymerization reactor, and hence conversion predictions are more realistic. 相似文献
10.
Leszek Furman Zdzislaw Stegowski 《Chemical Engineering and Processing: Process Intensification》2011,50(3):300-304
The classical theory of RTD was applied to characterize a flow in a laboratory jet mixer using both numerical and experimental approaches. Detailed information about flow field in the reactor was obtained through computational fluid dynamics (CFD) simulations. Three different turbulence models have been tested: the standard k-?, RNG k-? and Reynolds Stress Model (RSM). The CFD models predicted slight yet relevant differences in flow patterns. The experimental RTD can be used to identify erroneous numerical results. This paper points out differences in the predicted flow velocities. Such discrepancy may have significant impact on the assessment of the reactor's performance. Thus, the role of experimental verification is emphasized. A dedicated experiment is proposed to resolve the potential validation problem. 相似文献
11.
An attempt has been made to study the mixing of yield‐pseudoplastic fluids with a Scaba 6SRGT impeller using electrical resistance tomography (ERT) and computational fluid dynamics (CFD). The ERT system with four sensor planes, each containing 16 equispaced stainless steel electrodes, was used to measure the mixing time. The multiple reference frames (MRF) technique and the modified Herschel–Bulkley model were applied to simulate the impeller rotation and the rheological behaviour of the non‐Newtonian fluids, respectively. To validate the model, the CFD results for the power consumption were compared to the experimental data. The validated model was then employed to obtain further information regarding the averaged impeller shear rate, impeller circulation, and pumping capacities. The CFD and ERT data were utilised to investigate the effect of the impeller power, fluid rheology, and impeller size on the mixing time. The mixing time results obtained in this study were in good agreement with those reported in the literature. © 2011 Canadian Society for Chemical Engineering 相似文献
12.
13.
Models commonly used in literature are evaluated versus 696 data points to predict the pressure drop of gas/non‐Newtonian power‐law fluids flow in horizontal pipes. Suitable models are recommended. A new correlation is developed by ignoring the pressure drop across the gas slug and adopting the liquid slug holdup of gas/non‐Newtonian fluid flow into the homogeneous model. The theoretical curves can capture the test data trends and the overall agreement of predicted values with experimental data is sufficient to be practically applied in industry. 相似文献
14.
Studies on hydrocyclones have evolved over recent years and various configurations of this device have been proposed in the literature for different purposes. Herein, an innovative geometrical configuration of hydrocyclones was developed by means of the response surface technique, combined with an optimization algorithm and supported by a computational fluid dynamics complementary study. The results obtained with these optimization techniques were validated by experimental data. The optimized hydrocyclone configuration is characterized by low energy consumption, i.e., low Euler number, with a small underflow‐to‐throughput ratio and can be used as a thickener hydrocyclone. 相似文献
15.
The radial multiple jets-in-crossflow mixing structure (RMJCMS) is extensively used in industrial manufacture. In this research, the effects of thickness of injection ring on mixing performance and factors influencing the mixing performance of RMJCMS were discussed based on the results of computational fluid dynamics. The simulation results showed that the dimensionless mixing distance, with the increase of the thickness of injection ring, drops from 1.1 to 0.18 first and then increases to 0.27 while the uniformity of flux monotonously improves, manifesting that the consistency of flux is not the single element determining the mixing performance. Analyzing the simulation results, a conclusion was drawn that the consistency of flux, penetration mode and interaction among injection flows which can be altered by adjusting the thickness of injection ring, determine the mixing performance of RMJCMS jointly. That is to say, in RMJCMS an injection ring with a suitable thickness can realize the function of injection and rectification simultaneously, which not only improves the mixing performance but also reduces the complexity of RMJCMS as well. 相似文献
16.
Modeling of non‐disperse solvent extraction of molybdenum(VI) with PC‐88A as extractant and a nanoporous hollow‐fiber membrane contactor as extractor was performed. Computational fluid dynamics was applied for modeling and simulation of molybdenum extraction. Concentration, pressure, and velocity distributions for molybdenum were determined. The extraction of Mo6+ was greatly influenced by the flow rate of feed solution. The extraction efficiency was reduced with higher feed flow rate and increased with the molybdenum content in the feed. The pressure drop along the shell side of the membrane extractor was found to be not significant, being one of the advantages of membrane extractors which assist in reducing the operational costs. The proposed simulation method is capable to prognosticate the performance of solvent extraction of molybdenum in membrane extractors. 相似文献
17.
Gas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients. 相似文献
18.
提升管三相流化床内的气液传质系数 总被引：3，自引：0，他引：3
采用溶氧电极法测定了以牛顿和非牛顿流体为液相的提升管三相流化床的气液传质系数（ｋｌａ）。证明其值受床层流动特性的影响显著，那些能提供高气含率和增大液体循环速率的操作条件也有助于ｋｌａ的提高。通过引入广义雷诺数得出了计算牛顿和非牛顿流体内ｋｌａ的关联式 相似文献
19.
Mixing in curved tubes 总被引：1，自引：0，他引：1
Vimal Kumar 《Chemical engineering science》2006,61(17):5742-5753
The mixing efficiency in a curved tube is a complex function of the Reynolds number, Schmidt number, curvature ratio and tube pitch, therefore, the relative effectiveness of a helical tube is quite complicated and challenging over a straight tube. A state of art review on mixing of two miscible liquids in curved tubes revealed that the mixing in coils of circular cross section has not been reported in the literature. In the present work a computational fluid dynamics study is performed in curved tubes of circular cross-section of finite pitch under laminar flow conditions to examine the scalar mixing of two miscible fluids using scalar transport technique. In the present study the phenomenon of mixing by convection and diffusion of two flow streams with inlet scalar concentrations of zero and unity in the two halves of a tube perpendicular to the plane of curvature has been reported. The mixing efficiency has been quantified with concentration distributions and unmixedness coefficient at different cross-sections and process conditions (Reynolds number, Schmidt number and curvature ratio) in the straight and curved tube of circular cross-section. The result shows that, in curved tube, for higher Schmidt number fluids, mixing is considerably improved at moderately low Reynolds numbers (Re∼10), but is not affected for Reynolds number of the order of 0.1. It is also reported that mixing in the curved tube is higher at low values of curvature ratio as compared to the higher curvature ratio. 相似文献
20.
A computational fluid dynamics (CFD) simulation is performed to investigate the influence of lateral flow on the orifice flow in a trough‐type liquid distributor. The discharge coefficients from the simulation are in good agreement with the experimental values, indicating that the CFD simulation is accurate in describing the outflow through orifices. The lateral flow near an orifice can change the velocity and pressure distributions of flow regions in front of this orifice, causing a decrease in the discharge coefficient. This phenomenon is supported by the theory of flow past a blunt body. An important implication derived from this finding is that the influence of lateral flow should be minimized in the design of a trough‐type liquid distributor, because the decrease in the discharge coefficient leads to non‐uniform outflow. The structure of a trough‐type liquid distributor is optimized to improve the liquid distribution performance by reducing the influence of lateral flow. 相似文献