Week 8 (Outside Lab) - Flow Rate Testing, Pt. II

At this meeting, the team continued to collect flow rate data and was able to create a standard curve for the end flow rate at one of the outputs. The team measured the time, in seconds, that was necessary for the output to reach volumes of 50 mL, 100 mL, 150 mL, 200 mL, and 250 mL, with three repeated trials for each. This data was put into Google Sheets and used to generate the standard curve shown in Figure 1. The curve is marked as "ideal" because the water level in the tank was kept relatively constant for all trials. The equation for the trendline is y = 0.126x + 0.512, with an R² value of 0.98.

Figure 1. Ideal standard curve for the time required to reach specified output volumes of water.

Using the standard curve equation, it was calculated that it takes 0.637 seconds to output 1 mL, which translates to 637 milliseconds per mL. This is the number that will go into the Arduino code as the multiplier for how long the pump needs to stay on.

Week 8 (Outside Lab) - Flow Rate Testing

At this meeting, the team started to collect empirical data on the end flow rate of the water as it is pumped. They set up the apparatus without the Arduino and breadboard and PC in between, to make it easier to turn the pump on and off (through plugging and unplugging it, rather than controlling it with the desktop application). One of the two output tubes was directed into a Pyrex glass measuring cup, which has metric measuring lines. When the team was ready, one member plugged in the pump as another member started a timer, and another kept an eye on the water level inside the cup - this third member called out for the timer to stop once the water reached the desired volume.

This process was repeated about ten times, at different volumes (the raw data is shown in Figure 1). In one of the later trials (Trial 9, below), the team realized that the flow rate actually changes depending on how much water is in the water container; when the water is low, the pump outputs a lower flow rate. This is something that will be tested further at the next meeting.

Figure 1. First flow rate data collection

Week 8 (In Lab) - Pump Modifications

In lab this week, Michelle and Le worked on modifying the pump, while Davina and Parm worked on further documentation of the project's progress, including updating the pages on this blog. The latter two also began to create the final presentation for the project.

Previously, the pump had exhibited unwanted behavior in that it continued to siphon water through the tubing while turned off. The team had conjectured that this was because stopping up one outlet and solely using the other had created a vacuum inside the pump: this meant that air pressure was sufficient to push the water through the whole pump apparatus. To remedy this, Michelle and Le tried several solutions:

1. Insert tubing system into the previously stopped-up outlet, and keep a small tube in the other outlet for aeration purposes.
• The tube was too smooth for hot glue to adhere correctly, so it had to be connected with electrical tape instead. This was an extremely weak and unstable connection.
• This solution was unsuccessful. Water was forced through both outlets rather than just through the one intended.
2. Put a cap on the water container to seal it off from the air, reducing air pressure on the water around the pump.
• This was Parm's and Davina's idea, but a cap for the container was hard to come by - they were only able to find a large piece of cardboard in the lab.
• This seemed like it wouldn't work, since several holes would have to be cut into the cardboard for the tubing and power cord, and this would let in the air anyway.
3. Use the original design, except make sure the ends of the tubes remain above the level of the pump.
• This was the simplest solution and the one that ended up working. It turned out that the problem was more related to gravity than to the presence of a vacuum. A diagram of the problem and solution can be seen in Figure 1. 

Figure 1. Diagram showing how position of tubing affects movement of water when pump is off.