Non-Newtonian Fluids: The Weissenberg Effect Experiment. Sagir Kadiwala, Josh Mcbride, Joseph Mondok. University of California Merced

Transcription

1 Non-Newtonian Fluids: The Weissenberg Effect Experiment 1 Non-Newtonian Fluids: The Weissenberg Effect Experiment Sagir Kadiwala, Josh Mcbride, Joseph Mondok University of California Merced

2 Non-Newtonian Fluids: The Weissenberg Effect Experiment 2 Abstract Non-Newtonian fluids are fluids which exhibit properties unlike typical liquids. These fluids generally differ in terms of their viscosities which are inconsistent. In this experiment we examined the possible relationship between the density of a fluid and its ability to exhibit the Weissenberg Effect. This was done by measuring the volume and mass of the fluid then comparing those to the height of the weissenberg effect. Through our experiment, we found a relationship: the lower the density the higher the fluid will rise. Introduction

3 Non-Newtonian Fluids: The Weissenberg Effect Experiment 3 A Non-Newtonian fluid is a fluid that exhibits inconsistent viscosities and does not obey Newton's laws (Mool-Amart). The Weissenberg Effect is the effect created when a simple rod is put into a Non-Newtonian fluid and while the rod is spun, usually with a drill, the fluid rises up the rod. The thing to keep in mind is that this rod is smooth and is not a drill bit. The question then becomes is there a possible relationship between a fluid s density and its ability to rise up the rod. This question for us stemmed from the show called Mythbusters. In this specific episode The Mythbusters crew attempted to walk across water as it was depicted in many movies. These movies, usually depicting ninjas, led the mythbusters to believe that ninjas could walk across water. They tried various methods to walk across water, and, to be frank, none of them actually worked, except one. Some of the methods used some sort of floatation device attached to their feet to walk across water. These devices did not work; what did allow them to walk across water was a Non-Newtonian fluid: cornstarch and water. When these two are mixed, the properties of the new fluid allow the user to apply sudden amounts of force, making the fluid solid, but without such force it, the fluid remains liquid. After seeing this, we naturally became interested and began looking it up on youtube for more videos. Some of these videos consisted of people putting drills with rods into these fluids and watching the fluid rise up the rod. After seeing all this we wondered if there was some sort of relationship to predict the height of the fluid when it goes up the rod. Our experiment hopes to achieve a relationship between the height of the fluid and the density. Many household fluids are Non-Newtonian. These materials can include pancake mix, cornstarch and water, as well as ketchup, all of which are used in baking and cooking. This experiment is a way of showing why we use the stirring devices that we use to mix, cooking and baking, materials. Many devices used for mixing have some sort of cover so it does not get

4 Non-Newtonian Fluids: The Weissenberg Effect Experiment 4 messy. The actual object that is spinning in the fluid will have a different shape than a straight rod as well. Materials Drill Containers Cornstarch Water Ketchup Pancake Mix 2 Steel Rods ( half inch diameter and a fourth inch in diameter) Ruler Food Scale Methods It all began the week of April Fifteenth when we ordered a drill and a steel rod off of Amazon.com. We planned to meet on a saturday afternoon to do this experiment but when we discussed it the best day was sunday. Josh and Sagir met up on sunday afternoon at one in the afternoon and drove to his house where we then proceeded to go to target to get the last of the supplies. Those supplies being the fluid making materials. We got to Target where we would then be finding the materials. First Sagir had to buy an ice because it was quite hot out that day. after this we started looking for the items to use in the experiment. We were almost unable to find the borax but all the other supplies came very easily to us. Sagir talked to a target employee and he was very lazy and didn t offer much help to find the borax besides saying that it would be in the back corner. Josh found the cornstarch in the baking aisle while Sagir ventured to the back

5 Non-Newtonian Fluids: The Weissenberg Effect Experiment 5 of target to find the borax. Sagir came back empty handed. We then needed to go find some measuring devices. For this we bought a food scale to measure the mass and or weight of the fluids we were using. For the height of the fluid we used a simple ruler. We decided to take all our measurements in SI units. After finding the food scale we decided that we need to go look for the borax one more time we ahead towards the detergent area. We stood there for a good five minutes looking around then Josh looked down at the bottom shelf and found the borax. It was a relief and disappointment that it took two college students two hours to find simple household products for a science experiment. When Joseph finally called us back he was actually around the area we were in town so we were able to pick him up and take him back to Sagir s house. Getting hold of Joseph was a task that was very difficult because he does not have cell phone reception in his dorm. We met with Joseph at Raleys and took him back to Sagir s house. When we got to the house we were introduced to Sagir s housemates and ate some chicken and potstickers. Afterwards we set up a table in the garage to do the experiment. We acquired a few containers and measured their masses. The point of measuring the mass was to measure the volume as well as find the density so that we could see if there is a relation between the height and the density. Josh mixed the cornstarch and water into the container while Joseph and Sagir discussed the order of the materials to be tested. When mixing the materials we did not take exact measurements of the ratios because the density of the fluid should give an accurate description of the fluid. We decided to first demonstrate the concept by doing the experiment without measuring the height. When we did this the fluid did not rise up the rod. we knew that it was supposed to this is a well documented phenomena. At this point all of us were a bit on edge because we were thinking that our experiment would not work. We deduced that the reason was that the rod was too long. this

6 Non-Newtonian Fluids: The Weissenberg Effect Experiment 6 caused the rod to morph while it was spinning and ultimately ruin the test. Sagir walked to the house next to his house and asked his neighbor if he could cut the rod. He cut it about three eighths the way up. We also thought the drill may be too slow so the neighbor offered to let us use his drill. This drill was much faster and we felt that this would give the experiment the best chance of working. Unfortunately even with the shorter rod there was still some morphing of the rod and this led to not very concise data. Nonetheless we acquired the data. The cornstarch and water did not rise up the rod at all and this could be from the fact that the rod was not straight. After this we were getting worried so to simply see if it worked we used the ketchup and were able to measure the height that it rose. We did this by measuring the initial height on the rod by sticking it into the ketchup and pulling it out and measuring the amount of ketchup on the rod. We then put the drill and rod in and turned it on for a few seconds then pulled it out and remeasured. The residue on the rod should give a relatively accurate measurement. For the ketchup we found that the average initial height was lower than the final height. This was a good indication of the principle but it still seems that the rod was still too shaky even after cutting it so much. We also did the experiment for the pancake mix. The weissenberg effect was much more apparent for the pancake mix because it was actually visible. We found that the average height was also higher for the final height than the initial. We attempted to mix a substance made out of borax and PVA glue but unfortunately it did not work because the glue that we bought was not the right kind of glue. At the end of the first trial we decided that a second set of trials was necessary in order to make sure our results were accurate. We all agreed to meet at Sagirs House but unfortunately since no one had a car Joseph and Josh took the first bus possible to Sagirs house to start the trials. They took the 11:45 bus and they arrived at 12:45. Josh ordered a new rod which we are

7 Non-Newtonian Fluids: The Weissenberg Effect Experiment 7 expecting to give better results. Josh started setting up his drills and quickly realized that his drill didn t have enough torque to conduct the experiment. Sagir went over to his neighbor s to borrow his drill which is every man s dream to own. The neighbor was kind enough to let us borrow his drill again without his help we may not have been able to finish the experiment. Another reason we had to borrow a drill was because Josh s drill could fit ¼ inch of diameter of a rod while Sagir s neighbor s rod could be fit up to ½ inch. We didn t have enough cornstarch from our first trials but from our last trial we save our mixture of water and cornstarch. Interestingly enough when we opened the container out mixture had harden but also had mold growing in there which was unexpected. Sagirs house had extra cornstarch otherwise the experiment couldn t have gone ahead. We made our mixture and results were fantastic because we saw the liquid rise up the drill. The next fluid we chose to test was ketchup which we didn t have but Sagir decided to take his housemates ketchup by justifying that his housemate will never notice that the ketchup is gone. Joseph saw on our data charts that weight of the ketchup had more mass than last time but then we concluded that difference in mass should not affect on how the fluid would rise. Josh place the drill into the ketchup then came the hard part figuring out where to place the ruler to measure how much ketchup went up the drill. to do this we put the ruler into the ketchup and read the height directly from the ruler. We moved on to our last fluid which was pancake mix and then came the hard part deciding how much pancake mix we wanted to save so we could make pancake but then Josh dumped all the pancake mix into the container. Josh was having way too much fun mixing the pancake mix. It was very clear that the fluid was rising up the drill. We were debating if we wanted to use the pancake mix to make pancakes but then came to the conclusion it was for the best that we didn t use the pancake mix because there was mold in the container from the cornstarch. All the fluids we chose to measure demonstrated

8 Non-Newtonian Fluids: The Weissenberg Effect Experiment 8 that weissenberg effect but results weren t what we expected. We ran the experiments of the other non-newtonian fluids and as expect each fluid rose up the rod. In order for the second trials to have gone on many things were need to go right otherwise we could have been in mess that could not be fixed. Results Results from the first set of trials were fairly inconclusive. The failure of the Elmer's glue and borax mixture in making a non-newtonian fluid, instead making a solid rubbery mixture, limited the results to the other three fluids. Lack of a volume measurement also limited conclusions that can be made from the first trial; without volume, density cannot be calculated and only a comparison between final mass of the mixture and the height of the Weissenberg effect can be made. Each of the three viable fluids were tested three times; the results for each of trial can be seen in Table 2. The table includes the final masses of the fluids as well as the height of the Weissenberg effect of each of the trials. The only conclusion that can be made with the first set of results is that the fluid with the greater final mass was not affected by the drill at all while the other two with less mass had a notable Weissenberg effect.this did not affirm nor deny our hypothesis at all without the measurement of volume. The second set of trials yielded more conclusive results. In the second trials, the glue and borax mixture was completely removed due to its inability to create a fluid mixture; the other three fluids, however, yielded interesting results which can be seen in Table 3. As was in the first set of trials, the mass was appropriately weighed and calculated as well as the displacement of each of the three trials attempted on the three fluids. The difference was that the volume was actually determined as well as the density calculated (mass divided by volume). With the density actually calculated in this set of trials, a conclusion can be made on density correlation to the

9 Non-Newtonian Fluids: The Weissenberg Effect Experiment 9 Weissenberg effect. When examining the results in Table 3, the density of the fluid seems to have an opposite effect on the amount of displacement. The most dense fluid, ketchup at 1.22 g/cm 3, had the least average displacement, about 0.13 cm; the cornstarch, with a density at 1.08 g/cm 3, had a one centimeter displacement; and the least dense material at 0.68 g/cm 3, pancake mix, had the highest average displacement of a little more than 1.1 cm. With these results, one can conclude that the less dense a non-newtonian fluid, the greater the effect of the Weissenberg principle; this disproves our hypothesis that the more dense the fluid the greater the displacement created by the Weissenberg effect. Discussion Many factors could have led to the inconclusive evidence of the first trials. The most notable of these factors would be the materials used in the experiment. Proper materials for a glue and borax mixture had to be researched. The glue that we used was poly vinyl acetic glue as opposed to the one we wanted which was poly vinyl alcohol based glue. The two different containers could have been an issue; the only results with Weissenberg displacement were from the second container. Use of a universal or universally sized container could improve the results. Problems with both the drill and the rod might have affected the results. Two drills with different rotation speeds as well as two different rod lengths were tested before the experiment not leading to notably different visible results. However, drill speed and rod length could still be an issue. The biggest culprit that could have affected the Weissenberg effect was rod thickness; the thin rod used tended to wobble while drilling affecting how far the fluids could travel up the rod. A use of a thicker rod would improve the results in the second set of trials. Despite the more fruitful results of the second trials, possible factors leading to error should be considered. Many factors leading to problems in the first trials were fixed in the

10 Non-Newtonian Fluids: The Weissenberg Effect Experiment 10 second; the borax mixture was eliminated and both the faster drill and a thicker rod yielded results. However, the container was still not standardized in the second trials. The measurement of volume also revealed possible errors; to calculate volume, our group used basic geometry, length times width times height (container 1) and four times pi times radius squared (container 2). To eliminate this error more precise ways of measuring volume should be used. Finally, our experiment, due to time constraints and resource availability were only able to test three fluids; the use of more fluids could yield better or even different results.

11 Non-Newtonian Fluids: The Weissenberg Effect Experiment 11 Tables

12 Non-Newtonian Fluids: The Weissenberg Effect Experiment 12 Tables(cont.)

13 Non-Newtonian Fluids: The Weissenberg Effect Experiment 13 References Lentle, Tabitha, dir. "Episode 78: Walking on Water." Mythbusters. Discovery. 15 Apr Television. Lodge, A. S., Jay D. Schieber, and R. Byron Bird. "The Weissenberg Effect at Finite Rodrotation Speeds." The Journal of Chemical Physics 88.6 (1988): Print. Mool-Amart, Samart. "Non-Newtonian Fluids." KKU Engineering Journal 25. (1998): Print.