Experiments 1 and 2 - Replicates of the Previous Fluidized Bed Experiments

Parameters:

For both Experiment 1 and Experiment 2, the [general procedure] had been followed using specific parameters. The parameters used in each experiment are listed and compared below:

Results and Discussion:

Data from both experiments were analyzed using the method outlined below:
For each sand grain size, the experiment was run for a certain amount of time, throughout which it completed several data collection periods. Each data collection period ("run") represents a time period during which the water level in bubble collector gradually falls down from its maximum to the set minimum point. In Figure 1. and Figure 2. this period is represented on the graph when the line slants downward. Once the minimum water level is reached, the bubble collector has to refill with water in order to continue the runs. For this reason, the water outflow valve is closed until the water level reaches the set maximum point. This period is represented on the graph by the vertical lines. More detailed information on the bubble collector setup can be found here.
Once the change in water level in the bubble collector was recorded, we added the linear fit line to each of the runs to see the rate of change of the water level inside the bubble collector with respect to time. Figure 3. and Figure 4. show the linear fit line for the second data collection period in both experiments, and more detailed graphs can also can be found here.
The value of the linear fit is very close to 1, indicating that the data can be modeled accurately using a linear relationship. Once the slope of the fitted line was known, we calculated the content of gas removed per liter of water sent through the sand filter using the formulas:

where the radius of the bubble column was 1.9 cm.

The calculations for the amount of gas removed during each data collection periods gave us the results summarized in Table 2 and Table 3 below:

For further reference, please click here to download the experimental data logs from [Experiment 1.|^Data and Calculations, Experiment 1.xls] and [Experiment 2.|^Data Analysis and Graphs1.xls].
The data from Experiment 1. shows that the content of the gas removed is very similar to the result from the Fluidized Bed Experiment done last semester, when the measured content of gas removed was 5.07 mL/L. While the data from the second run are comparable to the results from last semester, the data for each subsequent runs show gradual decrease in the content of air removed. These decreasing rates of gas removal probably resulted from a clogging problem in the sand filter. Clogging in the filter occurs because of the diameter of the sand column is relatively small. Large bubbles form in the sand bed and push segments of sand up to the top of the filter. While we did not directly observe this problem during the experiment, sensor data collected through Process Controller indicates that clogging occurred.
The data from Experiment 2. show consistent amount of gas removed for each run. The uniform results might indicate reliable functioning of the components of the system. However, the amount of removed gas is still a bit lower than the result from the Fluidized Bed Experiment done last semester, when the measured content of gas removed was 3.23 mL/L. The fluidized bed experiment involved the same sand parameters: Sand 30, depth = 60cm, bed expansion = 50%, aerator air pressure = 100kPa, except for the flow rate, which was 345 mL/min. The cause of the difference in results might be the experimental setup, which has been modified since last semester. The modifications include replacing the aerator with a new one. Perhaps the current aerator is not producing water that is supersaturated enough. That might affect the environment in which bubbles are formed, and thus indicate why only 2.00 mL/L of gas is removed. For further observation, we measured the dissolved oxygen content at three various points in the system. Detailed information can be found here.