Re: Fan backwash problem - new parts to fix January 07, 2014 06:42AM |
Registered: 10 years ago Posts: 59 |
Re: Fan backwash problem - new parts to fix January 07, 2014 07:27AM |
Registered: 10 years ago Posts: 1,230 |
Re: Fan backwash problem - new parts to fix January 07, 2014 07:54AM |
Registered: 10 years ago Posts: 256 |
Quote
ormerod168
Andy
I'm so impressed by your scientific approach!
what I would do if I had your setup, make a quick and dirty static wing test
cut out a slice of aluminium width 10mm or so and roll it into a 40mm ring (maybe material from a beer can will do)
cut a disc of the thin aluminium diameter 40mm
cut out the profile of five wings toward the center
twist the five wings clockwise
put the D 40mm ring around
tape to end of fan
do the test
twist the five wings counterclockwise
do the test again
thank you for your time and great research
Erik
Re: Fan backwash problem - new parts to fix January 07, 2014 08:03AM |
Registered: 10 years ago Posts: 256 |
Quote
tim_h
Andy, nice work there. I'd be really interested to see the results from the duct design I'm using. It's very good at reducing the draft and is quieter, but I'd like to see how much the output is reduced.
The STL can be downloaded from here.
ps are you skyscraper on fpvhub forum?
Cheers, Tim
Re: Fan backwash problem - new parts to fix January 07, 2014 08:48AM |
Registered: 10 years ago Posts: 256 |
Quote
ormerod168
Andy
I'm so impressed by your scientific approach!
what I would do if I had your setup, make a quick and dirty static wing test
cut out a slice of aluminium width 10mm or so and roll it into a 40mm ring (maybe material from a beer can will do)
cut a disc of the thin aluminium diameter 40mm
cut out the profile of five wings toward the center
twist the five wings clockwise
put the D 40mm ring around
tape to end of fan
do the test
twist the five wings counterclockwise
do the test again
thank you for your time and great research
Erik
Re: Fan backwash problem - new parts to fix January 07, 2014 12:48PM |
Registered: 10 years ago Posts: 1,230 |
Re: Fan backwash problem - new parts to fix January 07, 2014 01:03PM |
Registered: 10 years ago Posts: 1,230 |
Quote
kwikius
Is this what you mean. Note that I have changed the sign of the camber. Is this something like it? Higher Reynolds numbers now!
regards
Andy
Re: Fan backwash problem - new parts to fix January 07, 2014 01:15PM |
Registered: 10 years ago Posts: 1,230 |
Re: Fan backwash problem - new parts to fix January 07, 2014 02:58PM |
Registered: 10 years ago Posts: 256 |
Re: Fan backwash problem - new parts to fix January 07, 2014 03:13PM |
Registered: 10 years ago Posts: 256 |
Quote
ormerod168
..and if one was to re-design the whole thing this blower or something like that might be a better choice
Farnell 1012796 - NMB TECHNOLOGIES - BM4515-04W-B30-L00 - FAN, BLOWER, 45X44X15MM, 12VDC
[uk.farnell.com]
Erik
Re: Fan backwash problem - new parts to fix January 07, 2014 03:24PM |
Registered: 10 years ago Posts: 14,672 |
Re: Fan backwash problem - new parts to fix January 08, 2014 03:57AM |
Registered: 10 years ago Posts: 256 |
Quote
dc42
You need to look at the fan specifications. This one, which looks similar to the one supplied in the kit, has a higher specified flow rate at zero pressure than either of those two. However, the NMB one linked to by ormerod168 can produce a higher static pressure, so might be more suitable in an application like this where the output is constrained.
Re: Fan backwash problem - new parts to fix January 08, 2014 04:54AM |
Registered: 10 years ago Posts: 94 |
Re: Fan backwash problem - new parts to fix January 08, 2014 01:54PM |
Registered: 10 years ago Posts: 135 |
Re: Fan backwash problem - new parts to fix January 08, 2014 02:01PM |
Registered: 10 years ago Posts: 1,230 |
Quote
kwikius
OK. So I just want the exact same shape as the fan blade but turned around.
I printed the last one as shown below before I saw your reply, but its a mirror image of the fan blade, which is incorrect?
Re: Fan backwash problem - new parts to fix January 08, 2014 02:12PM |
Registered: 10 years ago Posts: 1,230 |
Quote
Joar107
Just a thought how would it work with compressed air instead of the fan, it would be easy to regulate the flow and it would be very silent.... as long the compressor doesnt start
/Joar #25
Re: Fan backwash problem - new parts to fix January 08, 2014 02:27PM |
Registered: 10 years ago Posts: 1,230 |
Quote
dc42
You need to look at the fan specifications. This one, which looks similar to the one supplied in the kit, has a higher specified flow rate at zero pressure than either of those two. However, the NMB one linked to by ormerod168 can produce a higher static pressure, so might be more suitable in an application like this where the output is constrained.
Re: Fan backwash problem - new parts to fix January 08, 2014 02:33PM |
Registered: 10 years ago Posts: 14,672 |
Re: Fan backwash problem - new parts to fix January 08, 2014 03:28PM |
Registered: 10 years ago Posts: 94 |
Or water... no is not such a good ideaQuote
ormerod168
Quote
Joar107
Just a thought how would it work with compressed air instead of the fan, it would be easy to regulate the flow and it would be very silent.... as long the compressor doesnt start
/Joar #25
Yes, that would work just fine, a bit expensive in energy consumption though - and be very careful not to block the outlet if you feed it with 10bar :-)
..and make sure the air is clean, you don't want to spray oil on the bed :-)
Erik
Re: Fan backwash problem - new parts to fix January 08, 2014 03:55PM |
Registered: 13 years ago Posts: 1,611 |
Quote
ormerod168
Agreed, a centrifugal blower would be a better start, mounted top down, heat sink turned 90 degrees, close the hole from the old side mounted fan, what's not to like?
..and most importantly, implement a air activated micro switch in line with the heating element for safety in case the fan should fail
Erik
Re: Fan backwash problem - new parts to fix January 08, 2014 04:08PM |
Registered: 10 years ago Posts: 1,230 |
Quote
droftarts
Quote
ormerod168
Agreed, a centrifugal blower would be a better start, mounted top down, heat sink turned 90 degrees, close the hole from the old side mounted fan, what's not to like?
..and most importantly, implement a air activated micro switch in line with the heating element for safety in case the fan should fail
Erik
Haha, I suggested a very similar arrangement a few days ago...
Ian
RepRapPro tech support
Re: Fan backwash problem - new parts to fix January 08, 2014 05:17PM |
Registered: 13 years ago Posts: 1,611 |
Re: Fan backwash problem - new parts to fix January 09, 2014 03:25AM |
Registered: 10 years ago Posts: 256 |
Re: Fan backwash problem - new parts to fix January 09, 2014 03:53AM |
Registered: 10 years ago Posts: 14,672 |
Re: Fan backwash problem - new parts to fix January 09, 2014 04:22AM |
Registered: 10 years ago Posts: 94 |
@ Andy I followed your designs and like them but I can't open scad files can you export in a neutral format like step?Quote
kwikius
Regarding my previous tests. I tried redoing them but got different results. I guess to do it properly I should get a more sensitive differntial pressure guage, and drill a hole somewhere in the ducts and attach a nipple to get consistent readings. Someday I may get round to trying the different fan arrangements and even have a go at redesigning the part with a centrifugal fan.
Meantime I am quite pleased with my last fan deflector. This one is around 10 mm deep. There is no discernible backwash ( a piece of cotton on a wand, held nearby, is drawn in to the deflector at all positions on the open face); there seems to be very little restriction to the flow and, being a circular design, the effect should be uniform in all directions. All together I did 5 different versions in fact so now I had better move on to something else for a while.
[attachment 24351 Photo0025.jpg]
Unfortunately the stl is too big to attach, but here are the OpenSCAD files, though you need OpenSCAD version 2013.06 which allows scaling of an extrusion, else the blades are rendered without a taper
[attachment 24352 fan_deflector_v4.scad]
[attachment 24353 fan_deflector_v4_aerofoil.scad]
regards
Andy
Re: Fan backwash problem - new parts to fix January 09, 2014 04:35AM |
Registered: 10 years ago Posts: 14,672 |
Quote
Joar107
Unfortunately the stl is too big to attach, but here are the OpenSCAD files, though you need OpenSCAD version 2013.06 which allows scaling of an extrusion, else the blades are rendered without a taper
Re: Fan backwash problem - new parts to fix January 09, 2014 04:59AM |
Registered: 10 years ago Posts: 256 |
Quote
dc42
Nice work, Andy! I think I see what's going on here. The load on the fan is greater than the fan is designed for, which means that what the fan really needs is finer-pitch blades. Your deflector induces a rotation of the incoming air in the opposite direction to the rotation of the blades, so that when the air meets the fan blades, the angle between the two has changed to give the same effect as a finer blade pitch. So your mod should increase the efficiency of the fan, hence improve hot end cooling, as opposed to just deflecting the backwash out of the way like the louvre-style deflector.
Now I'm wondering whether a thinner (say 5mm) deflector might be effective enough? Or whether the gain in efficiency is enough to permit a 10mm or 15mm fan to be used?
Re: Fan backwash problem - new parts to fix January 09, 2014 05:01AM |
Registered: 10 years ago Posts: 256 |
Quote
dc42
Quote
Joar107
Unfortunately the stl is too big to attach, but here are the OpenSCAD files, though you need OpenSCAD version 2013.06 which allows scaling of an extrusion, else the blades are rendered without a taper
@ Andy I followed your designs and like them but I can't open scad files can you export in a neutral format like step?
Re: Fan backwash problem - new parts to fix January 09, 2014 06:24AM |
Registered: 10 years ago Posts: 14,672 |
Re: Fan backwash problem - new parts to fix January 09, 2014 06:34AM |
Registered: 10 years ago Posts: 14,672 |