...
Our target expansion was 30% expansion, and we found to achieve this, the flow rate had to be 340 ml/min, or 8 mm/s. However, at this flow rate, the error between calculated and experimental was 110%.
We plotted the experimentally found measured fluidization velocity vs the calculated empirically predicted fluidization velocity as as target bed expansion was increased (see Figure 2). As expected, higher bed expansion required high fluidization velocity. However, the difference between calculated and actual velocity increased as the flow rate increased. therefore, the experimental and the calculated data had a roughly direct relationship with calculated data having a steeper slope.
Experiment results data.
Figure 2: Calculated Predicted Fluidization Velocity vs Actual Measured Fluidization Velocity
We believe there are two main sources for the error (more of which are discussed on the main on the Clear Well Filtration Page).
#1)Wall Friction: We can attribute the increase in error as flow rate increased due to the increase in wall friction on the test vial. We can minimize this by increasing the size of our bench scale experiments.
#2) Sand Properties Parameters: We might have used an incorrect D60 and porosity for the filter bed in our equations. We tested this in our Mathcad code and found that if we increased the porosity from 0.4 to 0.5, the graph changed to Figure 3, thereby decreasing the error at %30 expansion to only 30% error:
Figure 3: Fluidization Velocity Experiment-porosity change
Then we also found that if we instead increased the d60 from 0.55 to 0.9, the graph changed to Figure 4, thereby decreasing the error at 30% expansion to only 16.7% error:
Figure 4: Fluidization Velocity Experiment-d60 change
This shows that small errors in our d60 or porosity term could easily account for the major errors we have. Therefore, future experiments should carefully measure these properties before conducting experiments.
...