Micro Pelton Turbine

air can be compressed and stored in tanks to later be used to power things such as air powered bikes and model aircraft but one thing i haven't tried is extracting this energy using a compressed air turbine this video is sponsored by kiwi co more about them later when building small scale air powered vehicles i like to store the compressed air in plastic drinks bottles as they can actually hold quite a lot of pressure and they're very lightweight the only problem is they can't store a whole lot of air for example if i want to power a turbine with the air in this bottle for more than 30 seconds the turbine must have an inlet diameter of one millimeter but there is one type of turbine which uses a very small diameter input nozzle called a says the turbine called a pelton wheel turbine pelton wheel turbines are used for extracting energy out of fast flowing water and at first glance might look like just a regular water wheel but they have a specially designed bucket to improve their efficiency this water is flowing at high speed from left to right so it has horizontal momentum but if i position a wall in its path the water is redirected through 90 degrees meaning it ends with zero horizontal momentum because force is equal to the change in momentum divided by time the force applied to the wall is proportional to the change in horizontal momentum the way a pelton bucket works is it redirects the water through a full 180 degree rotation creating a negative horizontal momentum this greatly increases the force on the bucket as the overall change in horizontal momentum is doubled i built a small test rig which attached a prototype pelton bucket to a load cell and held it in front of a high speed jet of water with a peak force of 0.46 newtons at 4 bar of pressure the performance wasn't looking very promising and i also realized how difficult it is to split a 1 millimeter jet of water down the center so i built a half pelton wheel known as a turbo turbine this works in the same way as a pelton wheel by redirecting the water through a 180 degree turn but the water is fed in through the top which makes it slightly more forgiving in terms of water jet alignment with the large propeller attached to the turbine the measured propeller speed is just 760 rpm i then tried the turbine with air and it spun a little faster at 780 rpm but it's still very slow maybe we need to add a gear ratio i recently purchased a resin 3d printer to help with these small projects and i'm absolutely fascinated with what it can print i don't do any 3d printer reviews and this wasn't a sponsored printer but the quality of these prints are so impressive i post the name of the printer i bought in the description below if you want to know more after a final uv cure the part was finished and as you can see i went back to the dual buckets pelton design as the bucket size relative to the nozzle should make it easier to align for scale this wheel is just 33 millimeters in diameter which when mounted on a bearing in front of the nozzle with four bar of pressure spins at 21 000 rpm however it will require a huge gear ratio to spin the propeller as it has very little torque here it has a 10 to 1 gear ratio and barely has enough torque to spin the propeller above 700 rpm which is worse than the first turbine so i decided to double the diameter of the wheel which almost exactly halves the speed at 10 600 rpm this way i can use a slightly smaller gear ratio of eight to one but gets a lot more torque to hopefully drive the propeller faster i then built a thrust test stand that held the turbine on a lever in the vertical position which might be a little hint of what i aim to use this on if it performs well this means the thrust can be measured by a load cell and we can try to improve its performance from there with 4 bar in the plastic bottle the turbine and propeller combo produced a peak thrust of 0.6 newtons which gradually reduced over a time period of 35 seconds i then tried reducing the gear ratio to see if it would use some of that extra torque to increase the propeller rpm which it did this produced 0.78 newtons of thrust meaning a 30 increase in performance just by changing the gears but why is this when compressed air inside of a tank exits through a small nozzle it converts the potential energy of the high pressure air into kinetic energy as the air exits at a really high velocity now the job of a turbine is to take this high velocity air and bring it to a complete stop in the most efficient way possible so that all of that kinetic energy is transferred into the turbine if we look at the earlier footage of the test turbine the water helps us visualize this you can see the water traveling around the curve of the bucket as it's designed to do but it also leaves the bucket at quite a high velocity meaning it still has some kinetic energy that could have been transferred to the turbine here is another shot with no propeller on the turbine and it's clear the water still has a lot of kinetic energy but in the other direction however if we balance the load perfectly there is a point where the water leaving the bucket is very close to being stationary meaning all the energy has been transferred so by changing the gear ratio of the turbine we essentially determine the speed it rotates under a given load and if it's perfectly matched to bring the high speed jet of air to a stop then we have a highly efficient turbine i found the most efficient gear ratio for this specific pressure and propeller to be five to one producing a peak thrust of 0.83 newtons which is a 38 improvement over the first version but i still think there is a lot to be improved my next thought was maybe the issue is that a pelton turbine is designed to be used with water and not air so maybe the air is hitting the bucket and spreading outwards instead of just following the curve shape of the bucket so here is my new design this turbine still works in the same way by redirecting the air through a near 180 degree curve but the blades are enclosed in a ring that spins with the turbine this should mean the air has no other direction to flow other than around the curve and out the other side hopefully increasing its efficiency with the exact same pressure and nozzle this new turbine produced a peak thrust of 1.37 newtons which is 65 percent more than the same size pelton wheel turbine so it's now clear why wheel turbines are almost completely exclusive to water flow also if we measure the area under the graph we get the turbine's impulse which is essentially a measurement of its efficiency this turbine produces an impulse of 15.7 newton seconds in comparison to my piston air engines the turbine produces a higher peak thrust but the efficiency is quite a bit less at least at these lower pressures this test was performed at 6.9 bar of pressure and almost maxed out my thrust test stand at 2.28 newtons which is equivalent to lifting a 228 gram mass which is impressive considering the turbine weighs just 51.6 grams and including the plastic bottle totals to 95 grams meaning the thrust to weight ratio is 2.4 and we can easily adjust the performance of the turbine by just changing the nozzle diameter this nozzle has half the cross-sectional area which means it produces about half as much thrust but for twice the duration i'm sure you're wondering surely the turbine has to be less efficient than just venting the air straight out the nozzle well fortunately we can easily test that the straight through nozzle at 4 bar produced a peak thrust of 0.34 newtons and an impulse of 3.7 newton seconds making the turbine four times more efficient than just the nozzle by itself i'll leave you to figure out why in the comments down below there's still lots of things i need to test on this turbine to try and improve its performance further and prototype testing these projects are the best way to learn which is why kiwico creates super cool hands-on projects designed to expose kids to concepts in science technology engineering art and math each monthly crate is designed by experts and tested by kids to make sure they are both fun and educational like this magazine that contains more information about the project especially as this one shows how gas is compressible but water is not which is partly why the pelton wheel didn't perform well when powered by air it's the small lessons like these that lead to world-changing ideas in the future and kiwico is teaching the skills of innovation creativity and problem solving today in the hopes that kids are equipped to better the world tomorrow also the crates include everything you need to complete each project so there's no need to worry about going out for extra supplies and since a new crate can be delivered every month there is a wide range of topics to learn from month to month viewers of my channel can get 50 off their first month of any crate by going to kiwico.com forward slash tom50 the link will be down in the description below so that's it for this video i want to do a lot more optimizations with this turbine i've spoken mostly about the velocity of the air and also the water but with air the faster it travels the lower pressure is so you need to take into consideration the pressure as it flows around the turbine and i feel like with this kind of turbine the only way i'm going to improve that is to just trial an error try different shapes of blades more or less blades stuff like that but that's something that i'm going to do in a future video and if you haven't guessed why i've got it mounted in a vertical position i eventually want to make an air-powered helicopter and i think we're getting closer to that um goal with this higher thrust to weight ratio versus the previous air engines but that's it for this video i'd like to thank you very much for watching if you enjoyed the video be great if you could leave a thumbs up down below and if you're new to my channel and want to see other crazy projects like this please click subscribe down below a huge thanks to all of my supporters over on patreon.com for making these videos possible i honestly couldn't do without your support so thanks once again thanks again for watching and i'll see you in the next video goodbye

Channel: Tom Stanton

Views: 943,158

Rating: 4.959374 out of 5

Keywords:

Id: zXEnXEfVBA8

Length: 9min 44sec (584 seconds)

Published: Wed Feb 17 2021

Reddit Comments

[u/Hugo_Stiglitz_88]

Tom Stanton has some really awesome videos

[u/Itz_M4X77]

I was shocked to se Stanton heat great kid