A Dan Horton question ?

[1001001]

Originally Posted by rv7charlie

The data I found for diffusers say max expansion is actually less than half that; 7 degrees from streamline. And for wedge diffusers (where the stream enters the diffuser at an acute angle to the face of the heat exchanger), one of my mentors told me (and I later verified with testing) that the far end of the diffuser needs to be pinched down radically, to preserve equal flow across the face of the heat exchanger. I haven't tested a typical a/c oil cooler, but I have checked a radiator. Unless the far end pinches down so it almost touches the core, virtually all the flow is through the last 1/3 of the core.

Yeah, the numbers I quoted are rules of thumb for large industrial ducts (like 20 or 30 feet diameter) where smoother transistions get to be so large that they are not economically justifiable. I probably should have mentioned that, and that smaller ducts can benefit from even more gradual transitions at lower cost.

[rv6ejguy]

Look at the Anequim project for an optimally shape oil cooler duct. You'll notice it is long with gentle transitions on the inlet AND exit sides of the HX.

We have enough good flying examples of efficient duct designs to know how to do it, the problem is that space is restricted in a typical RV. You can't build something as good as what a clean sheet design like the Anequim has.

Guide vanes are your friend when you have large divergent angles and short distances to the HX face. People seem to have an aversion to them though, preferring to use the crossed fingers method in their designs, hoping the large, square HX face will be fully wetted over a short distance by a 3 or 4 inch round hose feeding it, sans separation. Likely it won't, from my extensive tuft testing.

Cooling is one aspect, but we'd also like to minimize momentum loss (drag) while doing it.

[Snowflake]

...but we'd also like to minimize momentum loss (drag) while doing it.

In that case, shouldn't we use something a heck of a lot less draggy than scat tubing between the plenum and the cooler?

[rv6ejguy]

Originally Posted by Snowflake

In that case, shouldn't we use something a heck of a lot less draggy than scat tubing between the plenum and the cooler?

Yes, we should but SCAT is easy...

[AlexPeterson]

Originally Posted by Snowflake

In that case, shouldn't we use something a heck of a lot less draggy than scat tubing between the plenum and the cooler?

It depends on the flow regime (laminar or turbulent). Our short runs to the oil cooler aren't long enough in all likelihood to develop the flow regime, so it's probably mostly just chaotic...

[EXflyer]

Think I would worry more about the wiring laying across the motor mount and it appears one wiring clamp has some not protected by the clamps plastic cover too. Just something I noticed from the picture in the background.