The pump does not use an active valve, instead it uses “bluff bodies”, which are hemispheres that provide more resistance to flow in one direction as opposed to the other, meaning theoretically that more fluid moves in one direction as opposed to the other.
Here’s the setup: The body of the pump is 3D printed, and the piezo disc is driven by a TI DRV8662 driver using an external PWM signal to control the frequency and amplitude of the driving signal. The driving signal is around 130V max p-p and resonance is achieved around 60-70 Hz as well as around 1.6 kHz.
The problem is that while I’m getting resonance of the fluid in the pump, the fluid is moving back and forth an equal amount, meaning no net displacement of the fluid. In other words, the bluff bodies are not working as a valve as intended.
I have attached a picture of the CAD model of the bluff bodies, and a video of achieved resonance . Please let me know if you have any ideas as to why the set up isn’t working as intended or if you have any alternative suggestions of valves etc.
Welcome to the forum, definitely not breaking any rules, this is a cool project!
I have a few thoughts that may help in debugging the pump:
You want to run it at the first resonance of the disk a so the higher order modes will not be the disk deforming up and down like in the diagram, it will instead be a much more interesting mode shape. The second eigenmode will probably be a symmetric and so there won’t be a change in volume in the chamber.
From the looks of the diagram the pumping mechanism seems to assume that the central chamber is full and that the vibrations are moving the water (air is compressible so ruins the efficiency). I cannot tell from your video but it looks like there is not much water in the system. (Of course filling it to the top with 130V going to the piezo is going to take some thinking about risk, some sort of dealing membrane may be worth considering)
I am not sure it will work pumping from the current containers, as unless the the output container is filled above the hole, air will seep into the system. What if you made the input chamber a bit larger, and gave it a lid. Then remove the output chamber so it is just a spout, and made it bit longer than in the current design. The aim would be to for the system to have the liquid in the input chamber not leaking out of the end by surface tension on the end of the spout, so it would probably require a fairly small hole. You would also need some clever way to tilt the system to purge all air from put pump container (hence the lid in the input chamber).
I assume the pumping force is pretty weak so you need to find another way to rely on surface tension. I Would not be surprised if it takes quite a lot of optimisation of the shapes and sizes of the components to get a noticeable force. The group that did this work seem to do a lot of simulations to get something with a pumping speed of a few uL/min.
Going to second Julian’s guess that there’s air in the system. And the volume of sound generated suggests the same conclusion. There may also be porosity in your print. The piezo disc may be leaking air where it attaches to the pump body.
If you’re going to pursue this angle, and you’re going to 3D print the device, you can also look into using a Tesla valve instead of “HSBB”.
On a pragmatic note, you can buy peristaltic pumps, some very small and suitable for microfluidics. These are metering pumps which may be useful for your application.
Some very good points by both of you. Yeah there is definitely more movement at the first resonance frequency.
I will definitely have a look at the suggestion of air in the system. I have some silicon tubing that I will use in the next design instead of the input and output chambers. This way, I can have the tubing submerged in another reservoir, and prime the pump by manually pulling liquid through with a syringe through the output tube. This should eliminate air in the system. I’ll update if there is any success.
Also excellent idea about the Tesla Valve, that will be my next attempt, thanks!
Some more notes: there doesn’t seem to be significant porosity in the print as the vessel holds water without leaks for a long period of time. There is also a thin layer of silicon between the piezo disc and the pump body so I don’t believe there are any leaks there.
Thanks for the suggestion Harold, I actually already have a working peristaltic pump for use with this project. What attracts me about the piezo pump is the size and the way it can be integrated into the pump body.
Again, the help is much appreciated and if anyone has anymore ideas, please share!
Just a quick update on this post, and a BIG thank you to both of the responders! I finally got some pumping.
So I changed a couple of things: As was suggested, I replaced the input and output chambers with silicon tubing. As Harold suggested, I ditched the HSBB and replaced it with a Tesla Valve. I also put hot glue over the edges of the piezo disc to improve the seal and safety.
Even with a Tesla valve with only one baffle, there is some decent flow rate (relatively speaking). The noise is also greatly reduced with a triangle wave instead of the previous square wave. There’s about 30 mm head pressure developed.
Please see the Cad Model of the new valve and a video of the pump working.
Once again, thanks so much for the suggestions from both of you, I would’ve still been scratching my head if I hadn’t come here :D.
Well I’m back with another question for you guys. I expected the most pumping to occur at the resonant frequency of the Piezo disc, which is 3.6 kHz. The actual best pumping frequency is much much lower at around 80 Hz.
Does anyone have any ideas as to why there’s such a big difference?
You said what I was thinking! it reflects what I’m seeing when the pump is in operation. At lower frequency (for example as low as 1 Hz), the fluid moves much more per stroke than at high frequencies.
But of course there is a balance between how many strokes per second and amount of fluid displaced per stroke to get the highest flow rate (which is what the 80 Hz seems to be). As the frequency goes much higher than 100 Hz, the water doesn’t seem to have enough time to react just like you said, before the next cycle begins.
I hadn’t thought of the fact that the resonant frequency of the disk changes when clamped, very good point. I was getting the resonance frequency of 3.6 kHz from the disc data sheet, but this is most likely when the disc is not fixed to anything, and in contact with air only…
Final note, that other papers that deal with piezo-pumps also mention optimum driving frequencies of around 100 Hz.
Hi Adrian, It’s working well after many changes to the design. I’m writing a paper on it at the moment which will be open source after publication. I’ll be happy to link to it here when that happens. In the meantime, if you, or anyone else, can think of some applications for a pump like this in microfluidics, please do mention it here, I’d appreciate it.
Hi, thanks for sharing this project. It is a very interesting! I could make the video running. Which 3D printing technologies did you use to manufacture the pump? Some technologies are more watertight and precise than others.
I am interested to read the paper when it will be published
best regards,
Tanguy
I do not know exactly what your design can do, but there is a major application in neuroscience, which is the administration of micro volumes directly into the brain, in the ventricles, or even in the parenchyma itself. This is crucial for screening candidate drugs, manipulating neural circuitry (by activating or inhibiting it), modeling neurological disorders, and others. Volumes would be around a tenth to a couple of microliters injected across a couple of minutes.
I can tell you more if you think this is a possible application.
Thank you for your reply and good luck with your paper. I was interested to use something like that to lyse and pump bacteria. I already bought some of those face moisturizers that practically pump a mist out of a container holding a liquid. I was hoping to find an already designed PCB that is in Open Source that would not require me open the moisturizers.
@Tanguy I am using FDM printing for the pumps, water tightness was an issue at the start but with the right print settings, a good seal can be made.
@vrcota That sounds very interesting. As of now, the pump is capable of delivering flowrates in the low mL/min range, so the flowrates you mentioned are much lower than what is currently capable, but I will look into it more, thank you very much for the suggestion.
@adrianMolecule Hi Adrian, that sounds like a perfect application for this. I tried the face moisturizers as well at one stage, but they work at much higher frequencies than what I need, in the one-hundred kHz range if i remember correctly, and the amplitude of vibration was a lot lower than what I needed.
The driver that we made uses off the shelf electrical components which together cost about 10$ to make. We’re planning to give away some pumps and drivers if you are interested? Thank you again for the application suggestion.
@tiberiusb Very interesting project, best of luck with it!
@rs98 Hi Ron, Yes I would be interested to try that for continuing the flow on my Open Source project (bioreactor Ottawa Bio Science - Bioreactor) to the the purification station (Proteopresso). An integrated and automated lysis feature will be really helpful especially for people that would not have an alternative. And certainly 10$ price tag would be acceptable.
Thank you,
Adrian
Hi Adrian, project sounds interesting. We will not be charging anything for the test units we’ll be giving away. I will be in touch when I have an update.
