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These cookies track visitors across websites and collect information to provide customized ads. Others Others. Other uncategorized cookies are those that are being analyzed and have not been classified into a category as yet. Since the solids volume is relatively low, the total water volume is assumed constant at 2. As an example: 0. There are 50 experimental points each for 6MFD and 6CB at every particle size range, while the Rushton had 10 experimental points for every particle size range.
The suspension of particles was observed with the naked eye, aided by a mirror located at an angle below the vessel and a halogen lamp shone from the side. Particle distribution with each impeller was observed and recorded. It was not easy to view the particles due to the black color of the solids rendering the whole tank completely dark. Nevertheless, it was still possible to distinguish the individual particles on the base for all the concentrations studied here. The use of a lamp was helpful to a certain extent.
The torque value displayed on the motor screen was recorded once the minimum speed for complete suspension was determined. Figures 5 a to 5 c show the minimum speeds for each impeller to achieve just-suspension over the range of PSAC concentrations.
The graphs also clearly show that higher speeds are required for the two radial impellers, the Rushton and curved blade compared to the downpumping mixed flow. To illustrate, at 1. In relation to the speed requirement, Figures 6 a to 6 c show the 6MFD requiring less power than the radial 6CB and 6DT at the suspension points of each solid concentration, while the power for both the 6CB and 6DT are close to each other.
Hence, as reported in previous work, the mixed flow impeller achieves suspension at speeds and power inputs lower than the radial impellers [ 17 ]. The same trend is observed with the three size ranges of activated carbon particles. Plots of specific power or power per unit mass versus concentration Figures 7 a to 7 c also show much lower values for the 6MFD compared to the radial impellers.
This observation may be so because of the range of solids concentrations used here. Nevertheless, the plots in Figures 7 a to 7 c do show the drop towards minima for all cases, and the differences between the radial and downpumping impellers getting less as the minima is approached.
It is also interesting to note that since power per unit mass decreases with increase in particle concentration, it is in fact more efficient to perform the solid suspension operation in the stirred tank at higher particles concentration, until the specific power increases again after the minimum.
Hence, there is an optimum concentration for slurry mixing [ 23 ]. Figures 8 a to 8 c show the effect of particle size to be less important especially for the 6MFD. The impeller geometry causes particles to be distributed at certain regions on the base before suspension occurs.
As reported earlier [ 17 ], for downward pumping 6MFD particles are divided in the centre and side as shown in Figure 9 with more being pushed to the side, since the impeller diameter is less than half the tank diameter [ 17 ]. As the speed of impeller increases, particles at the centre get suspended first followed by those around the side of the base.
There was tendency for some of the particles to get stuck behind the baffles. Figures 13 a to 13 c show the power consumption according to different particle sizes at different concentrations. In general the power increases with size and concentration. For the 6CB power for the largest size range is clearly higher than the lower two size range.
The 6DT shows increase from one size range to another, while the 6MFD has less difference among the different sizes, with fluctuations in power as particle concentration increased. Activated carbon with particle size 1.
Overall in this work, it is seen that in the lower size range, particle size does not have significant impact on the minimum suspension speed and power requirement, but with the larger size range from 1. The average values are given in Table 2 a. This could be due to the differences in experimental condition such as particle size and concentration, and the subjective nature of the visual technique. In this study, the suspension of porous activated carbon particles has been observed using 6-blade impellers of three geometries—downward pumping mixed-flow, Rushton disc turbine and curved blade.
The first objective is to evaluate the performance of the curved blade turbine as compared to the 6DT and 6MFD, which has often been reported. Werner, S. Maurer, and K. Rewatkar, K. Raghava Rao, and J. View at: Google Scholar L. Musil, J. Vlk, and H. View at: Google Scholar C. Chapman, A. Nienow, M.
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Small particles suspended, come to the top of the tank, results in vanishing interface while larger particles are still resting at the bottom. Variation of impeller power consumption by increasing the amount of solid suspended. Requires accurate measurement of power consumption, expensive for large scale vessels, the criteria are not clear. Requires accurate measurement of mixing time, not applicable for large-scale vessels, the criteria are not clear, in high solid loading or three-phase systems, accurate measurement of mixing time is challenging.
Decrease in count rate recorded from radioactive tracer inside the vessel by increasing impeller speed. Decrease in recorded count rate could be because of tracer dispersion not just off-bottom suspension The criteria are not clear.
Discontinuity in solid concentration close to the bottom of the vessel by increasing impeller speed. Peak in solid concentration measured close to the bottom of the vessel by increasing impeller speed. Applying the technique is challenging, ultrasound sensor must be installed inside the vessel otherwise signals are scattered by wall.
Change in the pressure recorded at the bottom of the vessel by increasing impeller speed. Proper selection of pressure recording port is important, method proposed to eliminate effect of dynamic pressure head is not accurate. Accuracy: 1: most accurate, 5: least accurate, Applicability: 1: easiest to apply, 5: most difficult to apply.
Energy necessary to suspend particles equals the energy dissipated by the particle moving at its terminal velocity in a still fluid. In a turbulent fluid, the settling velocity of a particle is different from that in a still fluid.
Very simple model, unable to precisely predict Assumptions are more likely similar to homogenous suspension rather than just-suspended conditions. Read more. Vehicle Inspection. Wheel Alignment. Get a free repair quote Write to us. Testimonials What other said about us. Robert Burton. John Doe. Gallery From the studio.
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