This week we began to take a more serious look at the math behind our device. Specifically, we are trying to discover (1) if the chlorine dosing is in fact linearly related to the flow rate of the water through the pipe, (2) which height differences matter in dosing, and (3) how much head changes dosing. We began tackling these question with Bernoulli’s equation. We will have a working excel model to test different parameters by next week. Hopefully with a better understanding of the physics of our situation, we will be able to make more informed design decisions.
So far this week, we tested our three current prototypes to see which one allowed the most consistent dosing of our water supply. Continuing our simplified testing setup from last week, we measured the ratio of water to chlorine taken up by the pump and aspirator, respectively. (Instead of volumetric measurements, we measured the distance each of these fluids travelled in their respective containers/channels.) From these preliminary results, we found that the tube-in-pipe concept actually provided the most consistent dosing.
Of course, we’ll have to repeat these tests to increase our sample size (and thus confidence) in these results. We’d also like to determine our ideal starting chlorine concentration by next week, which will depend on this dosing ratio we’ve been measuring. Additionally, we’ve been working on a model (based on Bernoulli’s equation) that will relate the flow-rate of the water entering our pump-system to the flow-rate of chlorine being drawn up by our aspirator.
We have a bit more work to churn out before Val & Yoshika head of to Dhaka to implement these technologies, but we’re excited about the progress so far, especially now that we’ve secured more funding to send additional team members to Dhaka in the near future. (Shout-out to the presenting team for blowing the judges away at the BASES Social-E Challenge!!)
This week we continued to test our three prototypes to evaluate the consistency and dosing of each. We are also working to define a mathematical model that describes the dosing of our device. We are interested in better understanding what variables affect dosing and which height differences are important. Next week we’ll continue to evaluate dosing to learn more about consistency and which prototype may make most sense moving forward.
This week the prototype team made a new prototype and began the pump corrosion test.
We made a new “T” prototype ready for testing. This prototype has the same set up as the venturi based device, but the difference is that instead of a venturi tube (with the narrowing and widening of the internal diameter) there is simply a straight tube. We are eager to test out this device and see if the “T” prototype doses about the same and at a similar consistency. If so, we will go with the “T” design because it reduces the cost because the “T” is more straightforward and simpler to manufacture. This “T” device needs a non return valve attached. We ordered a bunch of different types of non return valves to test out. One type we noticed has a metal spring inside which unfortunately would quickly corrode due to the chlorine. However, some of the other designs don’t have any metal parts! We discovered this by performing some “product surgery”. Fun.
Also this week the prototype team started the pump corrosion test. We cut off two small chunks from the pump (thanks, Keegan!). We placed on chunk in a beaker filled with 1.4ppm chlorine solution and the other in DI water as a control sample. We took a lot of pictures and also recorded the mass of each chunk. Over the course of the next 6 weeks we plan observe how the chlorine affects the iron from the pump by recording the change in mass, the iron content in the solution, and also making qualitative observations like changes in color or smell.
This week we simplified our testing setup to better understand dosing. Our plan is to fill the IV tube and straighten it on a plank. We then pump a number of times and mark the level of Cl dosed per pump. We can then also collect the volume of water coming out of the pump over the course of the few pumps and examine the ratio of Cl dosed to water coming out of the hand pump. This ratio will help us evaluate the consistency of our dosing easily. I’m looking forward to these tests.
There should also be two prototypes ready by next week or during the weekend, so we can test those too. Our business plan competition will conclude on 5/22.
Our latest development (largely thanks to Kara) has been a simplified testing approach for evaluating how consistently our device doses a given volume of water flowing past it. We assume that the volume of chlorine entering our water supply is directly proportional to the distance the chlorine travels through our IV tube. Therefore, we have been measuring the ratio of the distance the chlorine travels to the amount of water flowing out the pump. Over 5 trials, we found that this ratio is consistent within our +/- 25% error tolerance (based on our target dose of 1 +/- 0.25 ppm). However, we were concerned about the variability in dosing caused by variability in our manual pumping speed. Therefore, we plan to repeat our tests, except this time we will measure the volume of water taken up by the pump (instead of the volume flowing out of the pump). We think that the ratio of the water volume taken up to the chlorine volume administered will be a better indicator of our dosing consistency.
This week the we helped out with testing the new set up with non return valves on each side of the device. From this we discovered that a significant amount of back-flow actually came from leaking between the pump and pipe connection. We first tied towels around the pipe to soak up this leaking, but the towels would get saturated within 5 min. So, Yoshika fashioned a water catcher from a 2 liter soda bottle and that worked pretty well. For future testing, we plan to permanently attach a small section of pipe to the pump with putty to hopefully stop the leaking.
Among other tests, we tested the chlorine tank height effect on dosing. We did a very crude, very drastic test – we testing the dosing with the chlorine tank on the floor and then with the chlorine tank on top of the platform. We found that there was a difference in dosing so we know that height does effect dosing, but we will have to do more tests to determine exactly how much.