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Multi-bladed Pumps. Does the number of propellor blades affect the efficiency of a water pump?

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Pumps & Physics Research and Rationale What's new? When I was thinking about which aspect of physics to investigate for my investigation, I knew it was a good idea to choose something that really interested me. At the time I was becoming more and more fascinated by subatomic particles. I liked the fact that much of it was new and not understood properly, unlike the classical physics that everyone associates the subject with. Unfortunately, high energy physics does not translate into good practical coursework. However, while reading Six Easy Pieces, a book adapted from Richard Feynman's famous textbook The Feynman Lectures on Physics, I noticed that a very common everyday phenomenon is still not properly understood by physicists. Encouraged by the prospect of discovering something new, I read on. Chaotic ideas Feynman wrote (on page 66) "There is a physical problem that is common to many fields, that is very old, and that has not been solved...It is the analysis of circulating or turbulent fluids...No-one can analyse it from first principles" "Wow - something science can't explain" I thought. I looked on the internet for further details and I found a poster from World Maths Year 2000 (http://www.newton.cam.ac.uk/wmy2kposters/march/), showing just the type of unpredictable fluid motion that Feynman was writing about. It's a new and exciting branch of maths called chaos theory and it is just beginning to be understood mathematically. The main idea is that simple systems can show very complicated behaviour that seems to have no repeating pattern. The sums that describe these systems are difficult to get your head round and appear to be way beyond my abilities as an A-Level maths student. Despite this, I felt something chaotic was an excellent phenomenon to look into for this task - it's a chance to do some experimental work where there isn't a perfect formula or a flawless explanation in any textbook. I couldn't rely on distorting my results to fit a simple law, so my experimentation had to be rigorous. ...read more.


2.00 19.2 4 13 5 65 0.5 2 2 �10-3 2.00 19.1 Average 19.0 6 13 5 65 0.5 2 2 �10-3 2.00 8.6 6 13 5 65 0.5 2 2 �10-3 2.00 8.3 6 13 5 65 0.5 2 2 �10-3 2.00 8.4 Average 8.4 exact � 0.05 � 0.01 � 0.38 � 0.0005 � 0.05 � 5 �10-5 � 0.005 � 0.1 Results table 2: effect of number of blades at 35W input power Number of blades on propeller Voltage / V Current / A Power / W Height water raised / m Volume of water / L Volume water / m3 Mass of water / kg Time taken / s 2 7 5 35 0.5 2 2 �10-3 2.00 233.9 2 7 5 35 0.5 2 2 �10-3 2.00 232.3 2 7 5 35 0.5 2 2 �10-3 2.00 234.5 Average 233.6 4 7 5 35 0.5 2 2 �10-3 2.00 200.1 4 7 5 35 0.5 2 2 �10-3 2.00 202.0 4 7 5 35 0.5 2 2 �10-3 2.00 201.2 Average 201.1 6 7 5 35 0.5 2 2 �10-3 2.00 63.2 6 7 5 35 0.5 2 2 �10-3 2.00 62.5 6 7 5 35 0.5 2 2 �10-3 2.00 60.7 Average 62.1 exact � 0.05 � 0.01 � 0.32 � 0.005 � 0.05 � 5 �10-5 � 0.005 � 0.1 Observations from the graph Looking at the graph on the previous page, the most striking thing is how much the results for the 6-blade propeller differ from the 4- and 2-blade propellers. I first wondered if the 6-blade results were anomalous - but the experiment was repeated three times and error bars are included on the graph. I would normally repeat the test to confirm the results are not anomalous, but in this case there is no good reason to believe they are. Just because the difference in performance between 2 and 4 blades is small, why does that mean the difference in performance between 4 and 6 blades must be small? ...read more.


efficiency value incorporates the error in mass, gravity, time, change in height and power input, whereas the value of time only includes the error in time. Overall, the choice of equipment of appropriate accuracy and sensitivity has meant the data collected are reliable. The conclusions drawn about the relative efficiencies of the propellers are fully justified by the results, and the small percentage error in the results has lead to concrete conclusions. This is probably due to the large amount of time I spent developing the experiment, and the many modifications implemented. The explanations I have given for the behaviour of the propellers could be more detailed. I have found it difficult to use theory from the A-Level course because it does not go into much detail on fluid dynamics (with good reason - it's very complicated!). I have tried to be imaginative and provide some possible explanations. I researched fluid dynamics and the Bernoulli Effect quite thoroughly before starting the practical work, but I found it was not explained to any great depth in A-Level texts from other courses. Research on the internet led to much more quantitative theory on fluid dynamics, but the mathematics used to express it was beyond what I have learned. Suggested improvements This investigation was very difficult at times, but very interesting. I am sure it will crop up again at university in one form or another. The modifications I found most helpful were those that simplified the problem and allowed easy measuring. With that in mind, if I were to repeat the investigation or study this area in the future, I would design a simpler set-up with more prefabricated components used. As ever, if greater accuracy or sensitivity were required in the data, different measuring equipment could be used. Also, a greater change in height could be used to exaggerate the differences between results and make them more sensitive. The modifications made would almost certainly depend on how the results and conclusions were going to be used. ...read more.

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