As I have mentioned before I am a freshman at Florida Institute of Technology studying Mechanical Engineering. As all first-year engineering students, we have to take an intro course on whatever engineering we are majoring in. So for me, I was taking my “Intro to Mechanical Engineering” course. Now, the school puts a lot of emphasis on hands-on experience so our professor introduced us to our semester-long assignment. We had to build something based on a theme they give us and it had to be something tangible that actually worked. HOO HOO I was giddy when he told us that.
Let me tell you a little bit about why this made me giddy. In high school, I used to build things, it was my form of self-expression you could say. My brush was a soldering iron and my canvas was a circuit board. Yes, maybe I am being a bit dramatic, but being able to create something from just an idea was something that made me feel alive. I am very competitive in this sense though, if there was someone who could build something better, I made sure that I could build something even better than him next time. I think “competitive” would be an understatement actually. I built a lot of “things” in high school but some highlights were, a jet engine powered by a hydrogen gas generator, 3D Printer, assistive exoskeletal system(This was actually my biggest project of high school), and an AI-assisted laser targeting system. I built a lot of smaller things but those were my coolest ones. Ok anyway enough about me lets talk about the project, I won’t put any of the math in here and give a simplified account of the physics behind the project so anyone can understand it.
So our theme for this year and possibly every year after is “energy”, which makes sense given that energy is probably the biggest problem plaguing humanity as a whole. So as one does, why not put the next generation of engineers to work solving this problem. We were put into groups of five and I ended up becoming the team lead. So after several meetings, we settled on what we wanted to build, but we kind of took a different approach than the other teams. We decided we wanted to address the power problems that are running rampant across developing nations. So we built a device that we named “Lil’ Power Pump”, we thought it would be a good chuckle. So what is the purpose of this device you ask? Well, we wanted to milk as much renewable energy from as many sources as we could using only one device. So we built a modular system that can be inserted into the manual water pumps to generate power, but we wanted to use as many properties of water as possible to generate that power. In addition to power generation, we wanted it to be able to filter water, a little two birds one stone type situation. So let us talk specifications.
So which properties of water did we want to utilize? That’s a rhetorical question, I’ll answer that for you. We wanted to use the incompressible nature of water, the high specific heat capacity of water, and the density of the water. The goal was to be able to generate enough power through daily tasks such as pumping water to power lighting systems in homes thereby eliminating the need for these regions without reliable power to center their lives around the sun. We also wanted a decentralized power system for distribution of power. This is what is known as a micro-grid system and it works well in implementing in rural areas where the infrastructure for power is non-existent. In addition to power generation, we integrated a carbon filtration system to filter out fine particulates and output clean water. The next few sections will go over each method of power generation we used.
Method 1: The Archimedes Spiral
So this is where we leverage water’s high fluid density and incompressibility to generate power as efficiently as possible. The keyword there is “EFFICIENT”, in a developing country that is all that matters because that directly effects cost and we needed cheap power, not power for millionaires. Alright, that was a bit of a hyperbole but you get the idea. So after a lot of R&D on the matter of water generation, I finally designed a purpose-built turbine for pipe systems where we have a large lateral area but a small diameter. The turbine was based on a well known mathematical shape which also has some interesting hydrodynamic properties. The turbine was a tapered Archimedes spiral shape that is found everywhere in nature, I guess nature always does it best because it turned out to be the most efficient method of horizontally mounted power generation. So let’s talk about some of the properties of this turbine that made it so efficient. Although this turbine does not have a huge crossectional area compared to a traditional turbine, it made up for it by having a much larger surface area and geometric plane continuity (basically just means a spiral) to harness the water flow. So that pretty much meant we could make a thinner turbine to fit in long pipe systems without sacrificing power output and in some cases even increase it. So that’s all well and good but we need to make sure the flow within the pipe is laminar in a single upward vector so that it doesn’t cause an increase in net force input required to move the water. Well after some CFD analysis of the turbine the curious thing we found about this Archimedes spiral is that even though it can be considered a vortex generator when its inputting rotational energy into a fluid, it can harness that same energy without creating huge vortices in the aforementioned fluid. So why does this work the way it does? The key is the tip speed ratio of the turbine and this just means how fast the tips of the blades are spinning in relation to the fluid speed. If you compare tip speed ratios of different turbines what you will find that the larger the tangential velocity of the tip is in relation to the fluid velocity, the more turbulence or “noise” is created in the turbine wake. Additionally, the higher the tip speed, the more centrifugal forces are exerted on the turbine blades causing mechanical wear on the material. The Archimedes spiral really shines in that aspect as the tip speed ratio is really low and creates very little vortices in its wake. This also means in extremely large fluid velocities the turbine will fare much better than regular turbines. So that pretty much solves our flow issue, now how do we make it even more efficient? So this is where the tapered shape and the perfect fit of the turbine with the pipe comes into play. A basic law of physics, the same amount of water flowing in must flow out so I used this to mechanically manipulate the flow of water around the turbine to give us as much efficiency as possible. The turbine starts of very thin and gradually increases in area as it goes up the pipe. What does this mean? Well, the two variables that can change to maintain the rate of volume of water in and out is area and velocity. As the area decreases the velocity of the water must increase to maintain the volumetric flow rate and that’s exactly what the water did, it increased in velocity around the turbine itself. Since water is not compressible and has a high density ( 1000 kg/m^3) it meant we could harness a lot of power in a small volume without energy loss through fluid compression. So we know that velocity effects the amount of kinetic energy produced (KE = 0.5MV^2) and therefore the increase in fluid velocity was transferring more energy to our system without a noticeable increase in human input. As expected, this turbine was connected to a motor to generate power.
Method 2: Thermoelectric Tiles
In an effort to keep this article as brief as possible without missing information I won’t go into too much detail on the physics of these tiles but they utilize the Peltier-Seebeck effect to generate electricity. This just means that the tiles generate electricity by a thermal differential at the junctions of two dissimilar metals. The larger the temperature differential, the higher the voltage generated. So how does this play into our system? Well, water has a very high specific heat capacity, about 4.186 joule/gram °C and this just means that it takes 4.186 joules of energy to raise a gram of water by one degree. This is the highest specific heat of any everyday substance so this means water is very good at temperature regulation. So the whole system was pretty much turned into a cooling heatsink with a water flow to create even more efficient cooling. One side of the tiles were attached to a heatsink extension of the system and the other was facing the sun to be heated. The water very efficiently cooled one side of the tile while the sun heated the other creating a pretty sizable temperature differential on hot days. This was just our take on generating solar power, of course, solar panels were installed with it to harness the light energy part of the sun. Our solar power module can generate power from both the photoelectric effect and the Peltier-Seebeck effect all from the sun.
So now that we have our power generation set up we needed a way to reliably and intelligently distribute that power. In addition to making an integrated power generation unit, we also wanted to address the power distribution issues in developing nations as well. Our solution to that was a cheap and integrated power management computational system. To sum up our system without going into microelectronic physics it was multiple power regulation computers that charged a lithium-ion battery bank and distributed power to all connected systems and monitored power usage and prioritized high drain devices. This allowed the whole power distribution system to be automated and require minimal human intervention.
After we got all the power generation systems squared away it was time to tackle the filtration system. In many developing nations, power isn’t the only problem, access to clean water is also a problem. So this system solves that problem too, there is an integrated active carbon filtration system that filters very fine sediments and particulates for crystal clear water. Well, what about bacteria? The aforementioned thermoelectric tiles are actually mounted to the water filtration tank, so that means if we run a voltage through the tiles we can cause them to heat up and boil the water to kill bacteria. So the system can use the power that is generated and stored to output clean water when the pump is in use.
Even with our limited budget (<$100), we were able to create something that worked very well even from salvaged components. We were able to generate a regulated 12v at a maximum of 5 amps in non-ideal conditions. So already the system is efficient enough on a small scale to power an LED lighting system for a house at non-ideal conditions. With upgraded parts and manufacturing, it is capable of generating much more power. This could help a lot of rural areas get access to cheap, reliable, and sustainable power. As such I am working to refine the design, cut costs, and increase efficiency to ultimately deploy it to rural regions. The current course of action so far is to improve the design, perform long-term testing domestically, create an efficient and extensive micro-grid system, final testing, and finally deployment to test countries. It is my goal to help an immense amount of people in neglected areas and foster an ecosystem of development where we don’t just leave behind the less technologically advanced regions of the world. Mankind is moving to the space age, it would be criminal to exclude any part of mankind from technological innovation. Lets light up the world.