scholarly journals Using tomography, CFD, and dynamic tests to study the continuous-flow mixing of yield-pseudoplastic fluids

2021 ◽  
Author(s):  
Dineshkumar Patel
Keyword(s):  
Yield Stress ◽  
Continuous Flow ◽  
Mixing Time ◽  
Mixed Volume ◽  
Dynamic Tests ◽  
Ideal Mixing ◽  
Flow Mixing ◽  
Batch Mixing ◽  
Pseudoplastic Fluids ◽  
2D And 3D

The major technological challenges faced by modern chemical industries are non-ideal flows such as dead zones and channeling encountered in the mixing of fluids with complex rheology. These cause sub-optimal mixing and lead to low quality products and high costs of raw materials. Therefore, the core objectives of this study were to develop methodology and tools to design an efficient continuous-flow mixing system for the fluids with complex rheology using electrical resistance tomography (ERT), computational fluid dynamics (CFD), and dynamic tests. The xanthan gum solution, which is a pesudoplastic fluid with yield stress, was used to study the dynamic behavior of the continuous-flow mixing process. The power consumption, cavern size, mixing time, and the extents of channelling and the fraction of fully mixed volume were successfully determined using dynamic tests, ERT tests, and CFD simulations and used as mixing quality criteria. A novel and efficient method was developed for flow visualization in the continuous-flow mixing of opaque fluids using 2D and 3D tomograms. A unique study on identifying the sources of flow non-ideality in non-Newtonian fluids with yield stress was done by visualizing the flow pattern inside the continuous-flow mixing vessel using 2D and 3D tomograms. The deformation of the cavern was analyzed and quantified in the continuous-flow mixing system for yield-pseudoplastic fluids using ERT. Moreover, the cavern volume was compared with the fully mixed volume and it was found that the latter was higher due to the extra momentum induced by the inlet-outlet flow. A novel study on exploring the effect of the rheological parameters of the pseudoplastic fluids with yield stress on the non ideal flows in a continuous-flow mixing system was performed using CFD. The CFD results revealed that the mixing quality was improved when the degree of the shear thinning was increased. The ratio of the residence time to the batch mixing time was evaluated to achieve ideal mixing for the continuous-flow mixing of yield-pseudoplastic fluids using dynamic tests and ERT. It was found that the ratio of residence time to the batch mixing time should be at least 8.2 or higher to achieve ideal mixing.

scholarly journals Using tomography, CFD, and dynamic tests to study the continuous-flow mixing of yield-pseudoplastic fluids

2021 ◽  
Author(s):  
Dineshkumar Patel
Keyword(s):  
Yield Stress ◽  
Continuous Flow ◽  
Mixing Time ◽  
Mixed Volume ◽  
Dynamic Tests ◽  
Ideal Mixing ◽  
Flow Mixing ◽  
Batch Mixing ◽  
Pseudoplastic Fluids ◽  
2D And 3D

The major technological challenges faced by modern chemical industries are non-ideal flows such as dead zones and channeling encountered in the mixing of fluids with complex rheology. These cause sub-optimal mixing and lead to low quality products and high costs of raw materials. Therefore, the core objectives of this study were to develop methodology and tools to design an efficient continuous-flow mixing system for the fluids with complex rheology using electrical resistance tomography (ERT), computational fluid dynamics (CFD), and dynamic tests. The xanthan gum solution, which is a pesudoplastic fluid with yield stress, was used to study the dynamic behavior of the continuous-flow mixing process. The power consumption, cavern size, mixing time, and the extents of channelling and the fraction of fully mixed volume were successfully determined using dynamic tests, ERT tests, and CFD simulations and used as mixing quality criteria. A novel and efficient method was developed for flow visualization in the continuous-flow mixing of opaque fluids using 2D and 3D tomograms. A unique study on identifying the sources of flow non-ideality in non-Newtonian fluids with yield stress was done by visualizing the flow pattern inside the continuous-flow mixing vessel using 2D and 3D tomograms. The deformation of the cavern was analyzed and quantified in the continuous-flow mixing system for yield-pseudoplastic fluids using ERT. Moreover, the cavern volume was compared with the fully mixed volume and it was found that the latter was higher due to the extra momentum induced by the inlet-outlet flow. A novel study on exploring the effect of the rheological parameters of the pseudoplastic fluids with yield stress on the non ideal flows in a continuous-flow mixing system was performed using CFD. The CFD results revealed that the mixing quality was improved when the degree of the shear thinning was increased. The ratio of the residence time to the batch mixing time was evaluated to achieve ideal mixing for the continuous-flow mixing of yield-pseudoplastic fluids using dynamic tests and ERT. It was found that the ratio of residence time to the batch mixing time should be at least 8.2 or higher to achieve ideal mixing.

scholarly journals Dynamic & CFD modeling of a continuous-flow mixer using fluids with yield stress

2021 ◽  
Author(s):  
Salwan Emad Saeed
Keyword(s):  
Yield Stress ◽  
Flow Rate ◽  
Continuous Flow ◽  
Air Entrainment ◽  
Mixed Volume ◽  
Solution Concentration ◽  
Impeller Speed ◽  
Feed Flow Rate ◽  
Tracer Injection ◽  
Ideal Flow

A continuous-flow mixer was designed and built in the Mixing Technology Lab, Chemical Engineering Department at Ryerson University to study mixing of xanthan gum solutions in water, a pseudoplastic fluid possessing yield stress. The extent of flow non-ideality was quantified using a dynamic model that incorporated the extent of channeling and the effective mixed volume within the mixing vessel. Dynamic tests were made using a frequency-modulated random binary input of a brine solution. The same experiments were simulated using Fluent, a Computational Fluid Dynamics (CFD) package. CFD flow fields were used to obtain the system dynamic response to a tracer injection applied at conditions indentical to the experimental conditions. The extent of channeling and effective mixed volume were determined and then compared with the parameters obtained experimentally. Experimental and CFD results show that the extent of non-ideal flow is significantly affected by impeller speed, impeller type, feed flow rate, fluid rheology, and exit location. The performance of continuous mixed vessels can be improved by increasing impeller speed, decreasing feed flow rate, and decreasing solution concentration. However, decreasing feed flow rate and solution concentration reduces the production capacity of the process. Increasing impeller speed may require modification to the motor and can cause air entrainment. Therefore, other remedies such as relocating the exit location and using the proper type of impeller may be taken into consideration. The results show that the extent of non-ideal flow was reduced using the bottom output and flow efficiency in the vessel was enhanced using A320 impeller.

scholarly journals Dynamic & CFD modeling of a continuous-flow mixer using fluids with yield stress

2021 ◽  
Author(s):  
Salwan Emad Saeed
Keyword(s):  
Yield Stress ◽  
Flow Rate ◽  
Continuous Flow ◽  
Air Entrainment ◽  
Mixed Volume ◽  
Solution Concentration ◽  
Impeller Speed ◽  
Feed Flow Rate ◽  
Tracer Injection ◽  
Ideal Flow

A continuous-flow mixer was designed and built in the Mixing Technology Lab, Chemical Engineering Department at Ryerson University to study mixing of xanthan gum solutions in water, a pseudoplastic fluid possessing yield stress. The extent of flow non-ideality was quantified using a dynamic model that incorporated the extent of channeling and the effective mixed volume within the mixing vessel. Dynamic tests were made using a frequency-modulated random binary input of a brine solution. The same experiments were simulated using Fluent, a Computational Fluid Dynamics (CFD) package. CFD flow fields were used to obtain the system dynamic response to a tracer injection applied at conditions indentical to the experimental conditions. The extent of channeling and effective mixed volume were determined and then compared with the parameters obtained experimentally. Experimental and CFD results show that the extent of non-ideal flow is significantly affected by impeller speed, impeller type, feed flow rate, fluid rheology, and exit location. The performance of continuous mixed vessels can be improved by increasing impeller speed, decreasing feed flow rate, and decreasing solution concentration. However, decreasing feed flow rate and solution concentration reduces the production capacity of the process. Increasing impeller speed may require modification to the motor and can cause air entrainment. Therefore, other remedies such as relocating the exit location and using the proper type of impeller may be taken into consideration. The results show that the extent of non-ideal flow was reduced using the bottom output and flow efficiency in the vessel was enhanced using A320 impeller.

scholarly journals Effect of Pre-Shear on Agglomeration and Rheological Parameters of Cement Paste

Materials ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2173
Author(s):  
Mareike Thiedeitz ◽  
Inka Dressler ◽  
Thomas Kränkel ◽  
Christoph Gehlen ◽  
Dirk Lowke
Keyword(s):  
Yield Stress ◽  
Mixing Time ◽  
Length Distribution ◽  
Chord Length ◽  
Rheological Parameters ◽  
Reflectance Measurement ◽  
Time Dynamic ◽  
Chord Length Distribution ◽  
In Situ Investigation

Cementitious pastes are multiphase suspensions that are rheologically characterized by viscosity and yield stress. They tend to flocculate during rest due to attractive interparticle forces, and desagglomerate when shear is induced. The shear history, e.g., mixing energy and time, determines the apparent state of flocculation and accordingly the particle size distribution of the cement in the suspension, which itself affects suspension’s plastic viscosity and yield stress. Thus, it is crucial to understand the effect of the mixing procedure of cementitious suspensions before starting rheological measurements. However, the measurement of the in-situ particle agglomeration status is difficult, due to rapidly changing particle network structuration. The focused beam reflectance measurement (FBRM) technique offers an opportunity for the in-situ investigation of the chord length distribution. This enables to detect the state of flocculation of the particles during shear. Cementitious pastes differing in their solid fraction and superplasticizer content were analyzed after various pre-shear histories, i.e., mixing times. Yield stress and viscosity were measured in a parallel-plate-rheometer and related to in-situ measurements of the chord length distribution with the FBRM-probe to characterize the agglomeration status. With increasing mixing time agglomerates were increasingly broken up in dependence of pre-shear: After 300 s of pre-shear the agglomerate sizes decreased by 10 µm to 15 µm compared to a 30 s pre-shear. At the same time dynamic yield stress and viscosity decreased up to 30% until a state of equilibrium was almost reached. The investigations show a correlation between mean chord length and the corresponding rheological parameters affected by the duration of pre-shear.

Sign in / Sign up

Export Citation Format

Share Document