Maxblend Impeller Research Articles

Estimation of heat transfer coefficient in turbulent regime during agitation by two-blade wide paddle impellers

This work proposed a new equation to estimate heat transfer coefficients in a turbulent regime during the agitation by two-blade wide paddle impellers. The equation includes Nusselt number, Prandtl number, Reynolds number based on energy dissipation rate, a ratio of impeller diameter to vessel diameter, and a ratio of blade width to vessel diameter. The representative length related to the heat transfer, proposed by Hiraoka and Ito (1973), was adopted for the equation. The proposed correlation equation successfully estimated the heat transfer coefficient during the agitation by two-blade wide paddle impellers (Maxblend impeller, Fullzone impeller, Sanmeler impeller, MR210, and MR 203). The proposed equation is also applicable for the agitation by conventional impellers (disk turbine, flat paddle, and pitch paddle).

Large blade impeller application for turbulent liquid–liquid and solid–liquid mixing

AbstractApplication of large blade impellers to turbulent single‐phase and two‐phase mixing is investigated in this work in order to provide a quantitative basis for estimating the possible advantages in industrial mixing operations with respect to fast impeller types. The analysis is based on the discussion of three‐dimensional velocity fields collected in a single‐phase vessel stirred by a Maxblend impeller by stereoscopic particle image velocimetry and of dispersed phase distribution and liquid mixing time obtained in solid–liquid and liquid–liquid systems by electrical resistance tomography. The results highlight that turbulent two‐phase mixing can be efficiently performed in baffled vessels stirred by large blade impellers both in shear‐rate controlled and bulk‐motion controlled processes.

Friction Factor Distribution at the Side Wall of a Turbulent Agitated Vessel with Baffles Using a MAXBLEND Impeller

Friction Factor Distribution at the Side Wall of a Turbulent Agitated Vessel with Baffles Using a MAXBLEND Impeller

Effect of Baffle Clearance on Scale Deposition in an Agitated Vessel.

The material deposition in a mixing tank agitated by the MAXBLEND impeller in a turbulent state was quantified and compared between cases with and without baffle clearance. Magnesium hydroxide formed from the chemical reaction between calcium hydroxide and magnesium chloride was used as a model of scale formation. Flow velocity in the tank was investigated by employing computational fluid dynamics simulation and experimentally validated by an ultrasonic velocity profiler method. Results showed that the amount of scale decreased with the increase in the rotational speed of the impeller due to the erosion effect on the tank wall. In the case without baffle clearance, the smaller weight of the scale was deposited on the front of the baffle plate due to the flow impingement, which enhanced the removal of the scale deposition. However, the lower-velocity magnitude behind the baffles resulted in an enhancement in the formation of scale. Installation of baffle clearance caused a contraction flow in between the tank wall and baffles, and consequently, the higher flow velocity reduced the amount and thickness of the scale. Measurement of the torque showed that the baffle clearance did not affect the power consumption, so the installation of baffle clearance can be a promising approach to reduce scale deposition in terms of saving operational costs and increasing process efficiency and safety.

Effects of Scale-Up and Impeller Types on Spherical Agglomeration of Dimethyl Fumarate

Spherical agglomeration (SA) allows for intensifying a crystallization process through simultaneous particle size enlargement and process efficiency enhancement, without a compromise between bioavailability and processability of active pharmaceutical ingredients (APIs). Inefficient collision intensity may encounter during scale-up of an SA process, while mixing intensity and flow patterns do play critical roles especially in a batchwise stirred tank. In the present study, the scalability of an SA process by operating at all the same configurations of different scales, 0.5, 2, and 10 L, using a common one-layered impeller with four pitched blades was examined through the use of dimethyl fumarate as a model API. Insights into the guidelines for scaling up of the SA process are also given. Furthermore, the effects of impeller types, including the one-layered impeller, the two-layered impeller with four pitched blades, and the maxblend impeller, on the size, size distribution, and roundness of dimethyl fumarate agglomerates were investigated carefully.

A cleaner recovery of rare earth bearing minerals by Pickering emulsification: Improvement of processing conditions toward an economic operation

The production of rare earth elements (REE) is crucial in modern world. They are increasingly utilized in numerous applications, especially in clean- and high-tech sectors. The froth flotation is commonly considered for the concentrate production of REE, from their bearing ore, in the course of mine-to-metal production chain. However, various environmental drawbacks are present in conventional flotation processes such as large amounts of tailings, chemical reagents and surfactants all released in the surroundings of the operations. In our previous work, we introduced the Pickering emulsification as a novel approach, and cleaner alternative to the froth flotation, which potentially offers multiple ecologic and economic advantages, where we achieved a recovery of about 50% of REE, and an enrichment ratio of 2.9. Here, we investigated the effects of two essential process parameters such as mixing intensity (i.e., changing the impellers speed), and shear uniformity (i.e., comparing the performance of two hydrodynamically different impellers) to improve the process performance. We achieved an optimum rotational speed and energy consumption with a Maxblend impeller, where the size of the emulsion droplets showed much more uniform distribution. Thus, the recovery and the enrichment ratio rose up to 65% and approximately 3.85, respectively, after one single stage of emulsification. We have shown that such conditions outperform the froth flotation besides the environmental advantages.

Investigation of gas–liquid dispersion and mass transfer performance of wide-viscosity-range impellers in water solutions of xanthan gum

Wide-viscosity-range impellers have extensive demands and applications in process industry. The gas–liquid dispersion and mass transfer characteristics of wide-viscosity-range impellers including Large-double-blade (LDB) impeller, Fullzone (FZ) impeller and Maxblend (MB) impeller in water solutions of xanthan gum were investigated experimentally and compared. The influences of gas flow rate, impeller speed and polymer concentration of liquid on the power consumption, overall gas holdup εg and mass transfer coefficient KLa were also analyzed. On this basis, the appropriate operating parameters and impeller type were determined. The results indicate that with rising flow rate, the higher εg and KLa can be achieved with a drop in power consumption, and a relatively high flow rate is recommended on the premise of guaranteeing the complete dispersal condition in aerated vessel. Higher impeller speed provides better gas–liquid dispersion and mass transfer performance, but results in more power consumption simultaneously. The appropriate impeller speed should be just enough to meet the requirements of εg and KLa. It also is found that the increasing concentration of water solution of xanthan gum adds to the complexity of gas dispersion and mass transfer in aerated vessel. Under the same specific power consumption PV, the εg and KLa are positive and negative correlation with the polymer concentration of liquid, respectively. Specially, when the concentration of water solution of xanthan gum is relatively low, the FZ impeller exhibits the best gas dispersion and mass transfer performance under the same specific power consumption. Nevertheless, the mass transfer performance of FZ impeller deteriorates significant when the concentration of water solution of xanthan gum increases to 1.00 wt%, and the MB impeller becomes the most appropriate impeller type in this condition.

Designing of lab-scale anaerobic digester equipped with maxblend impeller to evaluate effect of mixing on anaerobic digestion

Operational parameters can be easily controlled at lab scale experiments for an anaerobic digestion process. Our aim is to design a lab-scale digester equipped with an impeller to investigate how the geometry of impeller and different mixing modes effect the biogas yield of digester. Further, the methods of measuring the gas volume, gas composition, mixing intensity, torque, temperature are discussed in this article. The assembling of 4 liters digester is described which can be operated at various operating parameters which control the anaerobic digestion process. Mixing is very important to enhance efficiency of an anaerobic digester. To attain mixing Maxblend impeller is used in this lab-scale digester due to its better performance for mixing and power consumption. Various design consideration has been described.

Designing of lab-scale anaerobic digester equipped with maxblend impeller to evaluate effect of mixing on anaerobic digestion

Designing of lab-scale anaerobic digester equipped with maxblend impeller to evaluate effect of mixing on anaerobic digestion

Using computational fluid dynamics to analyze the performance of the Maxblend impeller in solid-liquid mixing operations

Solid- liquid mixing is prevalent in several industries due to its wide range of utilization in various unit operations. The goal of this work was to examine the performance of the Maxblend impeller for the particle suspension in a slurry tank employing the computational fluid dynamics (CFD) technique. The CFD model was created using the Eulerian and Eulerian (E-E) method, standard k-ε turbulence model, and sliding mesh (SM) technique for simulating the two-phase fluid flow, turbulence effects, and stirrer rotation, respectively. The CFD model was validated by comparing and analyzing the results obtained from the generated model to the experimental data in terms of stirrer torque, just suspension speed, and degree of homogeneity obtained from the tomography technique. The validated model was utilized to obtain the particle concentration profiles and to determine the local particle distributions attained by the Maxblend impeller. The data were utilized to analyze the impacts of various important parameters such as the agitation speed, particle concentration, particle diameter, specific gravity of the particle, and the use of baffles on the mixing efficiency of the Maxblend impeller in terms of the extent of homogeneity. A new mixing index was adopted to understand the effect of both axial and radial concentration gradients on the mixing performance of the Maxblend impeller. The particle distribution in the slurry reactor furnished with a Maxblend impeller was also assessed through clouding height approach in this study.

Using tomograms to assess the local solid concentrations in a slurry reactor equipped with a Maxblend impeller

The solid-liquid mixing operation has extensive applications in many industrial processes. The aim of this investigation was to assess the mixing performance of a Maxblend impeller in a slurry reactor. The Maxblend impeller is one of the most efficient types of the new generation of the close clearance impellers with a unique geometry. The mixing efficiency of the Maxblend impeller for solid-liquid mixing operation was compared to those measured for the A200 (an axial-flow impeller) and the Rushton turbine (a radial-flow impeller). Electrical resistance tomography (ERT) as a non-intrusive/non-invasive visualisation technique was employed to quantify the degree of solid suspension within the vessel. The signals received from four ERT sensor planes (each plane containing sixteen electrodes) were used for the reconstruction of the tomograms through the non-iterative linear back projection algorithm. The tomography images were employed to assess the particles' distribution inside the slurry reactor. The particle concentration profiles were utilized to evaluate the extent of homogeneity and mixing index for the suspensions of the particles. The tomography data enabled us to examine the effects of several significant parameters such as impeller speed, particle size, solid loading, use of baffles, and impeller off-bottom clearance on the mixing performance of the Maxblend impeller. The results from this study showed that the use of baffles enhanced the extent of homogeneity attained by the Maxblend impeller. The extent of homogeneity and mixing index in the system enhanced with a raise in the agitation speed. Nonetheless, after attaining the maximum homogeneity level, further increment in the agitation speed had an adverse impact on the extent of homogeneity and mixing index. Hence, the assessment of the optimum impeller speed is extremely important to enhance the local mixing quality in the mixing vessel. The results also demonstrated that the maximum attainable homogeneity for the Maxblend impeller increased with a raise in solid loadings. The maximum homogeneity attained by the Maxblend impeller was higher than those of the A200 and the Rushton impellers.

Torque and Horizontal Load on an Agitating Shaft in an Eccentric Mixer with a MAXBLEND Impeller in a Turbulent State

Torque and Horizontal Load on an Agitating Shaft in an Eccentric Mixer with a MAXBLEND Impeller in a Turbulent State

Energy efficiency of different impellers in stirred tank reactors

The flow energy efficiency of different impellers for stirring rheologically complex fluids (yield stress fluids) in cylindrical tanks has been investigated in this paper. Four impellers have been used: a Maxblend, an anchor, a gate and a double helical ribbon impeller. Our investigations were achieved via numerical simulations with the help of a CFD (computational fluid dynamics) computer program CFX 13.0. It was found from the predicted results that the Maxblend impeller gives the best performance. The effects of some design parameters on the flow energy efficiency and the power consumption have been also studied; it concerns the Maxblend impeller: its grid size and its paddle curvature.

Experimental study on micromixing characteristics of novel large-double-blade impeller

Large-double-blade (LDB) impeller is a new type of agitator based on Fullzone (FZ) impeller and Maxblend (MB) impeller. To investigate its micromixing characteristics in rapid-reaction situations, we conducted experiments in a 380mm diameter stirred tank. The effect of feeding time, feeding location, agitating speed and viscosity on micromixing characteristics of the novel large-double-blade impeller was investigated, adopting the iodide–iodate parallel competing reaction system. The micromixing characteristics of the novel large-double-blade impeller were also compared with that of double helicon ribbon (DHR) impeller and FZ impeller, which were widely used in process industries. The results indicate that segregation index decreases with increasing feeding time, and won׳t stabilize until the feeding time is greater than its critical value, when macromixing effects can be neglected. In addition, it is favorable for micromixing effects to feed in the impeller regions with high local energy dissipating rate. Segregation index is negatively correlated with stirring speed, whereas the rate of decline tends to be smaller at higher stirring speed, which means that the strengthening effect of improving rotation speed on micromixing efficiency decreases. Moreover, whether the systematic viscosity is high or not, the novel LDB impeller has the advantage of better micromixing effects over FZ and DHR impellers with the same power consumption per unit volume (Pv ).

Power Consumption and Mixing Performance of an Eccentrically Located Maxblend Impeller

Power Consumption and Mixing Performance of an Eccentrically Located Maxblend Impeller

Pumping characterisation of the maxblend impeller for Newtonian and strongly non‐Newtonian fluids

AbstractThis paper examines the pumping mechanisms generated by the Maxblend impeller. Simulation results obtained with the lattice Boltzmann method (LBM) are presented for Newtonian fluids (Re = 2–140) and strongly shear‐thinning fluids (Reg = 0.1–50) obeying the Carreau–Yasuda model with a very small power index (n = 0.05). In the Newtonian case, the pumping numbers predicted by the LBM are shown to compare favourably to those obtained with the finite element (FEM) as well as to experimental data based on the decolourisation method. These results indicate a small pumping capacity in the deep laminar regime followed by its sharp increase in the transitional regime, a phenomenon which is explained by examining the flow field simulated with the LBM and the FEM and measured through PIV. In the case of the strongly shear thinning fluids, the impact of the rheology on pumping is investigated. The flow fields and so‐called pumping volumes predicted with the LBM reveal, similarly to the Newtonian case, a change in the structure of the axial and (secondary) radial flow when the Reynolds number is increased. Viscosity contours suggest that this phenomenon is in fact related to the occurrence of zones with very different apparent viscosities, which explains the problematic flow patterns observed experimentally with the PIV.

Investigation of the accuracy of the extrapolation method for the lattice Boltzmann simulation of viscous fluid flow in a Maxblend impeller system

This paper offers a thorough assessment on the performance of the extrapolation method for the lattice Boltzmann simulation of viscous mixing flows. This method appears to be well-suited for the treatment of the complex boundary conditions found in various mixing systems. Here, the ability to simulate accurate power consumption and pumping capacity is evaluated on several configurations of the Maxblend mixing system, which has proven efficient in a wide range of applications. First, the impact of the boundary conditions on the spatial convergence of the lattice Boltzmann method (LBM) is determined on the 3D Couette flow, clearly showing that small modifications of the boundary conditions may reduce the accuracy of the predicted shear rate and power. Second, a parallel LBM scheme was used to simulate fluid flow within a Maxblend mixing system. For the unbaffled configuration, the simulated power consumption and the pumping capacity are observed to be in good agreement with experimental data and finite element simulation results. The effect of the bottom clearance is also successfully evaluated, suggesting that the standard bottom clearance is not optimum in the transitional regime. Lastly, results for the most geometrically complex case (baffled configuration) indicate that the power consumption is affected by numerical perturbations appearing around the moving impeller. Overall, these results show that, when combined with the extrapolation method for the treatment of boundary conditions, the LBM is an efficient tool for the investigation of viscous flow in mixers of industrial relevance.

Using Tomography to Characterize the Mixing of Non‐Newtonian Fluids with a Maxblend Impeller

AbstractThe flow field inside a cylindrical mixing vessel was visualized by electrical resistance tomography (ERT), a non‐intrusive measurement technique. Six tomography planes, each containing 16 sensing electrodes, measured the mixing time in the agitation of pseudoplastic fluid exhibiting yield stress. The effects of various parameters such as impeller types, impeller speed, fluid rheology, power consumption, Reynolds number, and absence of baffles on the mixing time were investigated. The Maxblend impeller was able to improve the mixing performance of non‐Newtonian fluids in a batch reactor. The mixing quality could be further enhanced by decreasing the xanthan gum concentration and using baffles in the mixing vessel.

Experimental investigation of the flow dynamics of rheologically complex fluids in a Maxblend impeller system using PIV

The Maxblend® mixer is used in processes involving Newtonian, shear-thinning or viscoelastic fluids and, as for many impellers, little is known regarding the relationship between the rheological behavior and the flow and mixing properties. An experimental study of the hydrodynamics in the Maxblend was carried out using Newtonian and non-Newtonian fluids in laminar and early transitional regimes. Flow fields were measured by two-dimensional particle image velocimetry (PIV) to evaluate the effect of highly shear-thinning and viscoelastic behavior on the performance of the mixer. The experimental setup consisted of a 35-L tank equipped with two baffles. A total of 100 measurements were proven to be sufficient in order to attain convergence of the velocity components for all studied regimes. Isolated zones in the highly shear-thinning case were observed by means of a decolorization technique. Elasticity in the laminar regime produced a reversal of the flow and a solid body rotation in the bottom region of the tank. Fluid velocity magnitude and spread were observed to be reduced by the presence of elastic forces.

Hydrodynamic study involving a maxblend impeller with yield stress fluids

In the present study, the hydrodynamic characteristics of the Maxblend impeller have been investigated. A commercial CFD package (CFX 12.0) was used to solve the 3D hydrodynamics and to characterize the flow patterns at every point. A shear thinning fluid with yield stress was modeled in the laminar regime and transition regime. The study focused on the effect of fluid rheology, agitator speed, impeller clearance from the tank bottom and blade size on the fluid flow and power consumption. Predictions have been compared with literature data and a satisfactory agreement has been found.