Originally shared by Gert Galjoen
#FoldaRap first try for a fan (40x40x10) duct: easy closer to the nozzle…
Check the airflow on that design. I was trying to design one for my PrintrBot Simple (just a cone with a narrow outlet), and I got negligible airflow. I read somewhere that the outlet has to be at least 1/3 of the fan area for it to work (something about backpressure or some such).
Oh so much more then that. I am a retired Mining
Engineer with a specialty in mine ventilation. Some of the bioggest problems were caused by unfortunate duct designs. You could go under 1/3 of the fan inlet area but you would be looking at more of a multi-stage air compressor then a simple one-stage muffin fan. The several typoes of shock loss in your design made me twitch. With the fan and space constraints you have please consider a smooth a transition from the round outlet of the fan to the ( rectangular?) shape of your outlet.
The center-line of this duct transition piece would be inlikne with the axis of the fan and end inline with the direction you need the air to flow. I saw a very similar case at a tungsten mine just south of Sequoia Nat’l Park. After rebuilding the ducting power usage dropped and airflow nearly doubled. Let me know how it goes.
An inlet to the fan could help if you have an inch or so to spare on the fan inlet. I’ll hunt up a picture or two if you are interested.
With that amount of blockage on the fan, you might as well use a much smaller fan. Most of the air will be spinning with the blades as you are stalling it out. Very little energy is being used to push the air through the narrow passage. Use a smaller fan an move out further from your hot end assembly to allow a more gradual flow
@Kenneth_Cummings I’m interested! I’m attempting to design a fan duct for my printer too, though I’m using a far far smaller fan than this one. the 1/3 thing I didn’t know about, the smooth transition I did. any more tips you can give us on fan duct design would be most welcome. (and pictures are good! worth a thousand words apparently! )
The 1/3 thing is a rule of thumb, and is probably an absolute limit, which does not include other losses. Most fan data sheets have a fab curve but if not, they generally list the CFM and pressure (in-h2o, or in-hg) when you buy it. The cfm (cubic feet per minute) is listed at zero pressure drop, which means when the fan is in open air. So this is a theoretical best that will never be achieved. The pressure they list, on the other hand, is the pressure drop created when the fan is completely stalled and has no flow rate. So with these two values, you can estimate the fan curve by drawing a straight line between the two values. As a more scientific rule of thumb, I usually design cooling routes as efficiently as possible, with large fan vents and gradual transitions, and still assume that the flow rate offs no more than half the maximum. Usually this has served as a decent estimation.
As I started, it’s a “first try” with all its flip sides: the airflow is not in proportion to the generated free air flow. But a was aware of that. My back mount solution is limited in X and Z direction (X carrier dimensions), Y has extend possibilities. The end-tube (pass under) is max 7x11 mm. Good to have experts on board at G+, they can teach us the right way to build a well working fan duct. Love to hear/see more advice @Kenneth_Cummings Datasheet/curve available @Eric_Moy http://www.datasheetarchive.com/dl/Datasheets-UD1/DSAUD0013511.pdf
Appreciate the participation and support!
Thinking outside the box(fan) I’ve seen machining tools with a suction hose attached near the cutter head. We’re talking serious horsepower here. The dust intake and hose are dragged around by the tool and the hose leads to a suction fan and filters to one side. How about a fixed blower (blower - a high pressure fan) feeding a flexible hose attached to the hot end, discharging wherever you need it. About Jonathan’s set up I’d need to see it.
Realise that we don’t need much pressure output here at all, most times the fan is PID controlled and depending on the fan is normally only running at half speed, only time we really need more, is if we’re bridging.
the key things are: we don’t want to cool the heater block or nozzle, we don’t want to cool the bed or the rest of the print too much, we just want to get the extrude we just layed down to just below glass transition temp.
I do have a couple of blower fans on one of my printers, you can kind of see what I’ve done in this photo:
it’s the printer on the left, I’ve got two blower fans off to the side, blowing towards each other and a paper shroud around the hotend heaterblock to stop that getting cooled off. my idea here was air coming from two directions meeting in the middle slightly offset would cause a sort of whirlwind effect around the nozzle, giving an more even airflow on the part itself than just a single fan. it sort of worked, but not as well as I’d hoped, also pid control on that ended up me sticking a wire in different spots on a breadboard with different resistors o_O.
My new one (for the printer on the right in the above pic) I’m attempting something like this:
https://plus.google.com/u/0/101948760925084043079/posts/irRMkRhAoHo but with one of those small 30mmxX30mm fans that e3d use on thier hotends (I’ve a few spare 24v ones floating around)