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-   -   a couple printed ideas (https://vansairforce.net/community/showthread.php?t=147771)

Steve Melton 07-14-2018 02:36 PM

added reinforcement to the thin bottom edge to keep it straight.

makes me wonder about adding a split line flange to separate these in halves but that is for a future time.


hendrik 07-15-2018 03:56 AM

I haven't followed the whole discussion, but if removing the mold is a concern: what about printing PVA instead of ABS? It's water-soluble, so you can make your fiberglass layup, let it cure, and put it in a bucket of water over night.

Paragon 07-15-2018 07:18 AM

A little follow-up on the vane discussion, I should have described the following:

If we look at the first CFD with no vanes, we might say, "the bottom 20% of the heat exchanger has no flow!". The CFD was completed with no heat exchanger blockage modeled.

However, the heat exchanger is a high blockage item. The blockage, if you think of it as (Aeffective/Atotal), is likely in the range of 40-60%. When the flow stagnates on the leading edges of the plates and fins, it will have higher pressure in the center of your profile, and lower pressure near the edges - this will cause the flow to migrate towards the edges.

Also, the heat exchanger core is almost like a thick block of the honeycomb material that is used as a flow straightener/flow conditioner in wind tunnels and in aero test rigs. The pressure loss in the long thru passages goes roughly as V^2, so if the flow in one area is 130% of the average, it's total pressure loss will be more like 170% higher than average - the end result is that the device blockage tends to drive the flow distribution towards more uniformity than whatever the inlet profile may indicate.

Finally, when we look at the heat transfer performance - in areas where the flow is higher than average, there is higher heat transfer. In areas where the flow is lower than average, there is lower heat transfer. (It goes a bit less than linear with velocity.) The net result is that even though we may have a distorted flow distribution upstream of the H/X, the actual heat transfer performance may only vary from the ideal uniform flow case by a rather small percentage.

It would be a reasonable bet that during flight tests, if one could replicate conditions exactly, it would be hard to measure the difference between the vaned configuration and the vaneless one.

Again, just my $0.02 worth - it may save the trouble of trying to manufacture a vane in there...


-Paragon
Cincinnati, OH

Steve Melton 07-15-2018 07:56 AM

wise words. the vane is an option for these. making both a 3 and 4 inch version. if your words are true, Charlie may be able to get by with the 3 inch scat tube version.

making the 3 inch version


walter 07-15-2018 08:50 AM

How will these attach to the oil cooler? On my home made duct I made flanges on two sides to bolt directly to the cooler. The flanges are sandwiched between a short section of angle and the oil cooler.


Steve Melton 07-15-2018 09:17 AM

that's artwork. any trouble with the scat becoming loose?

I need to refine my lofting techniques. that's my next learning with SW.

angle one the side.




3 inch version. now printing the 4 inch. this project is done.


walter 07-15-2018 09:29 AM

Don't know if it will come off or not as I haven't flown yet.

rocketbob 07-15-2018 09:58 AM

I've had good luck printing with Proto Pasta High Temperature Polycarbonate-ABS Alloy.

Suggest laying up a layer of fiberglass inside for insurance.

dtw_rv6 07-15-2018 10:27 AM

+1 for polycarbonate filament in areas like the engine compartment.

I've had luck with Polymaker PC Max - It is a modified PC that will print around 250C. For me it prints just as easily as ABS.

Gizmodorks PC is a more "traditional" PC that I prefer to print in a heated chamber and is much more finicky than ABS or PLA. I actually made exhaust hangar brackets out of this material.

Steve Melton 07-15-2018 06:44 PM

always keeping the plastic in a warm environment aids in printing.



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