Stacking TWO muffin fans ?

[DMOD]

That's just what Chuck/K1KW did with his two fans in his linear amp. His were about 10" X 10" and opposed. He said that was the way to do it, but it seems counter logical. IE, how does the air "know" which way to go?      Evidently the path with the back pressure is the way.

If you had two enclosed fans opposing (facing each other) in a "T" configuration, the outlet would certainly have more pressure and higher flow. Maybe this is what he meant.

By a "T" arrangement I mean two funs in a duct pointing at each other with a third duct at right angles to each fans exhaust. This third duct could be the one pressurinzing the tube bases in the RF deck.

Phil - AC0OB

[K5WLF]

If you had two enclosed fans opposing (facing each other) in a "T" configuration, the outlet would certainly have more pressure and higher flow. Maybe this is what he meant.

By a "T" arrangement I mean two funs in a duct pointing at each other with a third duct at right angles to each fans exhaust. This third duct could be the one pressurinzing the tube bases in the RF deck.

Phil - AC0OB

The two fans into a "T" sounds pretty promising to me, but I think some kind of ducting that would eliminate the fans blowing straight at each other, leaving the combined airflow trying to figure out where to go would be even better. Visualize the difference between a regular plumbing "T" and a "sanitary T" for wastewater. I think the sanitary T arrangement would yield better airflow by minimizing the turbulence as the outputs of the two fans meet and helping to blend the two airstreams.

ldb
K5WLF

[KD6VXI]

RF Parts sells a centrifigal blower for the 4CX250 tube.  It's their replacement for the Pride DX300.  It was a WELL abused amplifier, you may find it will move enough air for both your tubes....  I've seen a few of the single tube amps converted to dual tubes.....  And most kept the original blower.

Just a thought, it's pretty small.  And, as Bear stated, their is a 5 or 6 inch blower the size of a muffin fan....  Can't remember where I saw them, the bookmarks are on another (non-connected now) pc.

--Shane
KD6VXI

[W2PFY]

I have the answer, it does work on 120 volt AC, 5 inch fans. My son does it to cool LiPo batteries that he's using in his RC car. He's into RC racing  like we're into ham radio and has taught me a lot about charger controllers etc.

So anyhow I gave him two identical fans and he stacked them together and I have witnessed the affects of a much stronger air flow than just using one. No just stronger but impressive!

I still have six left and I'm going t stack two to cool an 833A at the camp. Right now I have a 220 volt fan running on 110 to quiet it down. It a bear on 220.

I don't know how this may work with DC fans with the permanent magnets in them? I suspect with the AC fans there is some self synchronization going on where as with DC types, there may be little slippage to have the (theoretical+) self synchronization going on.

I'm going to mount three more of them in a hard hat so I can cool my head from three sides.  One will go under this chair I'm setting on the cut down on BS

+ based on no facts.

[w3jn]

Tom, haven't done anything with that log yet.  I'm waiting for the right moment 

[WB2EMS]

I was thinking of those Russki bombers with all the counter-rotating props.  They seem to fly OK.

This had some interesting comments about that.

http://en.wikipedia.org/wiki/Contra-rotating_propellers

I wonder if it's not too applicable to the problem at hand because of the difference in Reynolds numbers?

[WBear2GCR]

The counter rotating props still BLOW in the same direction, yes??
Opposed stacked muffin fans do not...

centrifugal blowers:

http://www.allelectronics.com/make-a-store/item/CF-371/12VDC-50MM-BLOWER/1.html

http://www.allelectronics.com/make-a-store/category/220300/Fans/Blowers/1.html

Marlin P Jones might have some of these as well...

[Opcom]

Why dontcha just place 'em in water.... ..


klc

If is is flowing and not allowed to enter vapor phase that might work. The fin spacing is so small that bubbles could become entrapped in the radiator.

[Opcom]

It should be pointed out that noise is usually generated by turbulence and the generation of turbulence represents a loss of energy. When building up ducts and size transitions for airflow, it is best to fill corners with putty like 'DAP' and also create contours leading into and exiting any restrictions, even small ones. Case in point is an A/C evaporating unit I built for my previous M35 communications truck.

It was esssentially a box with a coffee-can-sized hole in one side for the inlet and the A/C evaporator making up one wall as the outlet. Inside was a 450CFM centrifugal blower from which I had removed about half the scroll. The remaining half supported the inlet airfoil and tube. It was just 1" diameter short of the same diameter as a large coffee can. Two such cans were used to bring outside air into the box and to the blower inlet. It was well-sealed. As-built, the noise from the intake was horrendous. The noise annoyance was reduced by 2/3 by building up a shape in the transition between the inlet and the coffee can diameter, getting rid of the square profile of the transition.

[KM1H]

Take a look at EBM-Papst fans. High quality, all metal, and tight tolerances. The LK-800 even with a full bore 5KW out mod uses one to move loads of air thru three 3CPX800A7's. At lower power a 330 Ohm series resistor is used. About $27 at Gopher Electronics but it may be too wide, check out their smaller ones on line.

Carl

[K1JJ]

Thanks for the suggestions, guys.

I ended up going back to a standard blower on a Variac. Seems the 4CX-250's have so much restriction that they aren't designed to flow lots of air like a big ext anode tube. I wasn't used to this.

But in the end, a muffin fan, in any configuration, is not as good as a standard squirrel cage blower when dealing with back pressure.

T

[The Slab Bacon]

Why dontcha just place 'em in water.... ..
klc

Tom,
       Kevin might just be onto something....................

I have seen 4CW250's pretty cheap at hamfests. They are exactly the same specs as a 4CX250, but have a water cooled anode. they were once popular for high powered VHF / UHF stuff but people got tired of futzing with the cooling plumbing. With a water cooled anode, you could really beat the snot out of them!! (and no fan noise!!)

Just a thought..............................

[w4bfs]

I've seen liquid cooling used on a 4cx250 .... used hv oil and no pump ....cooled by convection .... specific heat MUCH greater for liquids rather than air ... distilled water ok but must be changed fairly often due to ion buildup ... biggest problem is how to avoid leaks ...73...John