|
| Method proposed by | Concept | Advantages | Disadvantages | Applicability | Accuracy |
|
| Zwietering [3] | Visual observation of particles that do not rest at the vessel bottom for more than 1-2 sec | Simplicity, nonintrusive | Not applicable for opaque system, high uncertainty for high solid loading systems,
careful and skilled observation is necessary |
1 | 3 |
| Mersmann et al. [5] | Visual observation of the height of the slurry compared to the total height | Nonintrusive, Simplicity | Small particles suspended, come to the top of the tank, results in vanishing interface while larger particles are still resting at the bottom |
1 | 5 |
| Rewatkar et al. [6] | Variation of impeller power consumption by increasing the amount of solid suspended | Nonintrusive, can be used for opaque systems | Requires accurate measurement of power consumption, expensive for large scale vessels, the criteria are not clear |
3 | 5 |
| Rewatkar et al. [6] | Variation of liquid phase mixing time by increasing amount of solid suspended | Can be used for opaque system | 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 |
3 | 5 |
| Rewatkar et al. [6] | Decrease in count rate recorded from radioactive tracer inside the vessel by increasing impeller speed | Nonintrusive can be used in opaque system | Decrease in recorded count rate could be because of tracer dispersion not just off-bottom suspension
The criteria are not clear |
5 | 5 |
| Musil et al. [7] | Discontinuity in solid concentration close to the bottom of the vessel by increasing impeller speed | Can be used in opaque system | Intrusive, accurate measurement of concentration is challenging |
3 | 4 |
| Chapman et al. [8] | Peak in solid concentration measured close to the bottom of the vessel by increasing impeller speed | Can be used in opaque system | Intrusive
accurate measurement of concentration is difficult |
3 | 4 |
| Buurman et al. [9] | Use of Doppler effect at vessel bottom | Independent of material and scale, nonintrusive | Applying the technique is challenging, ultrasound sensor must be installed inside the vessel otherwise signals are scattered by wall |
4 | 2 |
| Micale et al. [10, 11] | Change in the pressure recorded at the bottom of the vessel by increasing impeller speed | Independent of material, nonintrusive | Proper selection of pressure recording port is important, method proposed to eliminate effect of dynamic pressure head is not accurate |
2 | 3 |
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