pitched blade turbine
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2021 ◽  
Author(s):  
Nasim Hashemi

This doctoral thesis addresses the mixing of highly viscous Newtonian fluids (corn syrup solutions) in a novel aerated reactor equipped with a central impeller (a pitched blade turbine in upward or downward pumping mode) and a wall scraping anchor. The non-intrusive electrical resistance tomography (ERT), dynamic gas disengagement method (DGD), design of experiments (DOE), computational fluid dynamics (CFD), and population balance model (PBM) were employed to characterize the performance of this novel aerated system. The performance criteria to be examined were mixing time, power uptake, gas holdup, and bubble size distribution. In this study, novel correlations were developed to estimate the gassed power drawn by the coaxial mixer, mixing time, and gas holdup. In addition, to obtain a master power curve, two new dimensionless correlations were proposed for the generalized power number and gas flow number by incorporating the equivalent rotational speed for the coaxial mixer, speed ratio (central impeller speed/anchor speed), and the central impeller power fraction into these two correlations. The experimental data demonstrated that gas flow affected the aerated anchor power consumption and central impeller power consumption in different manners. It was also found that at the higher fluid viscosity and beyond the critical speed ratio of 10, the anchor power consumption was increased by increasing the speed ratio (i.e. decreasing the anchor speed). It was shown that in the presence of gas, the anchor impeller in combination with the upward pumping pitched blade turbine in the co-rotating mode exhibited shorter mixing times and lower power consumption than the anchor-downward pumping pitched blade coaxial mixer. To enhance the efficiency of the aerated mixer, it is critical to investigate the influence of the gas-liquid flow within the vessel on the bubble size distribution (BSD) and the local and global gas holdup. To achieve this goal, the effects of the bubble breakup and coalescence on the BSD within the vessel were incorporated into the CFD model through the CFD-PBM coupling. The experimental and simulation results showed that beyond the critical speed ratio of 10, the volume fractions of the large bubbles decreased while the volume fractions of the small bubbles increased.


2021 ◽  
Author(s):  
Nasim Hashemi

This doctoral thesis addresses the mixing of highly viscous Newtonian fluids (corn syrup solutions) in a novel aerated reactor equipped with a central impeller (a pitched blade turbine in upward or downward pumping mode) and a wall scraping anchor. The non-intrusive electrical resistance tomography (ERT), dynamic gas disengagement method (DGD), design of experiments (DOE), computational fluid dynamics (CFD), and population balance model (PBM) were employed to characterize the performance of this novel aerated system. The performance criteria to be examined were mixing time, power uptake, gas holdup, and bubble size distribution. In this study, novel correlations were developed to estimate the gassed power drawn by the coaxial mixer, mixing time, and gas holdup. In addition, to obtain a master power curve, two new dimensionless correlations were proposed for the generalized power number and gas flow number by incorporating the equivalent rotational speed for the coaxial mixer, speed ratio (central impeller speed/anchor speed), and the central impeller power fraction into these two correlations. The experimental data demonstrated that gas flow affected the aerated anchor power consumption and central impeller power consumption in different manners. It was also found that at the higher fluid viscosity and beyond the critical speed ratio of 10, the anchor power consumption was increased by increasing the speed ratio (i.e. decreasing the anchor speed). It was shown that in the presence of gas, the anchor impeller in combination with the upward pumping pitched blade turbine in the co-rotating mode exhibited shorter mixing times and lower power consumption than the anchor-downward pumping pitched blade coaxial mixer. To enhance the efficiency of the aerated mixer, it is critical to investigate the influence of the gas-liquid flow within the vessel on the bubble size distribution (BSD) and the local and global gas holdup. To achieve this goal, the effects of the bubble breakup and coalescence on the BSD within the vessel were incorporated into the CFD model through the CFD-PBM coupling. The experimental and simulation results showed that beyond the critical speed ratio of 10, the volume fractions of the large bubbles decreased while the volume fractions of the small bubbles increased.


Author(s):  
Sotirios Nik Longinos ◽  
Mahmut Parlaktuna

Abstract This study investigates the effects of types of impellers and baffles on methane hydrate formation. Induction time, water conversion to hydrates (hydrate yield), hydrate formation rate and hydrate productivity are components that were estimated. The initial hydrate formation rate is generally higher with the use of Ruston turbine (RT) with higher values 28.93 × 10−8 mol/s in RT/RT with full baffle (FB) experiment, but the decline rate of hydrate formation was also high compared to up-pumping pitched blade turbine (PBTU). Power consumption is higher also in RT/RT and PBT/RT with higher value 392,000 W in PBT/RT with no baffle (NB) experiment compared to PBT/PBT and RT/PBT experiments respectively. Induction time values are higher in RT/RT experiments compared to PBT/PBT ones. Hydrate yield is always smaller when there is no baffle in all four groups of experiments while the higher values exist in experiments with full baffle. It should be noticed that PBT is the same with PBTU, since all experiments with mixed flow have upward trending.


Processes ◽  
2020 ◽  
Vol 9 (1) ◽  
pp. 68
Author(s):  
Jacek Stelmach ◽  
Czesław Kuncewicz ◽  
Szymon Szufa ◽  
Tomas Jirout ◽  
Frantisek Rieger

This paper presents an analysis of hydrodynamics in a tank with a 45° and 60° pitched blade turbine impeller operating while emptying the mixer and with an axial agitator working during axial pumping-down of water at different water levels above the impeller. Measurements made with the PIV method confirmed the change in direction of pumping liquid after the level dropped below the critical value, with an almost unchanged liquid stream flowing through the mixer. It was found that an increase in the value of the tangential velocity in the area of the impeller took place and the quantity of this increase depended on the angle of the blade pitch and the rotational frequency of the impeller. Change in this velocity component increased the mixing power.


Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6710
Author(s):  
Sotirios Nik. Longinos ◽  
Mahmut Parlaktuna

In the present study, the effect of different kinds of impellers with different baffles or no baffle was investigated. Up-pumping pitched blade turbine (PBTU) and Rushton turbine (RT) were the two types of impellers tested. The reactor was equipped with different designs of baffles: full, half and surface baffles or no baffles. Single (PBTU or RT) and dual (PBTU/PBTU or RT/RT) use of impellers with full (FB), half (HB), surface (SB) and no baffle (NB) combinations formed two sets of 16 experiments. There was estimation of rate of hydrate formation, induction time, hydrate productivity, overall power consumption, split fraction and separation factor. In both single and dual impellers, the results showed that RT experiments are better compared to PBTU in rate of hydrate formation. The induction time is almost the same since we are deep in the equilibrium line while hydrate productivity values are higher in PBTU compared to RT experiments. As general view RT experiments consume more energy compared to PBTU experiments.


Mechanika ◽  
2019 ◽  
Vol 25 (5) ◽  
pp. 370-376 ◽  
Author(s):  
BELHANAFI Abdelghani

This paper presents an numerical analysis influence of bottom shape on the hydrodynamic structure for cylindrical stirred vessel with bump. The turbulent flow generated in stirred tanks is numerically predicted by the resolution of the Navier-Stokes equation using standard k-ε turbulent model. Several parameters on the mixture efficiency has been investigated. Particularly, we have studied the bottom shape of the tank, which is the distance between the bump-turbine with down pumping direction  and impeller diameter.  The numerical obtained results of the CFD (computational fluid dynamics) code CFX V13.0 with the MRF (Multi Reference Frame) are presented in order to understand the flow structure. The three components velocity profiles and the turbulent kinetic energy dimensionless distributions obtained at bottom tanks with three different heights are analyzed and discussed. From these results, we can confirm that including a bump at the bottom center of the tank closer to the turbine improves significantly the operating conditions of stirring and mixing. Predictions have been compared with literature data and a satisfactory agreement has been found.


2019 ◽  
Vol 257 ◽  
pp. 10-18 ◽  
Author(s):  
Valaur E. Márquez-Baños ◽  
Aarón D. De La Concha-Gómez ◽  
José J. Valencia-López ◽  
Adrián López-Yáñez ◽  
Jorge Ramírez-Muñoz

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