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I've never experimented with minimal angles off perpendicular; those may not matter much. But at some point, you end up with a 'wedge' diffuser, and then the shape of the wedge becomes important. Finn, look at K&W chapter 12; section 12-2 deals with 'oblique flow'. BTW, figure 12-12 in that chapter doesn't seem to jive with real world experiments. Tracy found, and warned me about, the need to pinch the aft end of a wedge significantly to avoid the vast majority of the flow happening in the aft third of the core. It's impressive how much pinch is needed to keep flow even across the core.
Charlie
Rich. I said “if the airflow is there”. The question I was answering was about the angle of the heat exchanger. We do need to be sure we don’t trap air inside, and of course that there is actual airflow through. Many of our rotary installs would be helped by using manometers to check if the area behind the radiators are lower pressure. Motorcycles are another “special case” since most require the air to turn 90 degrees to exit the fairing. The only really excellent design on bikes was the Britten. I raced motorcycles in the past and the only different configuration I saw was the Honda RC 51. ( if I have the right number) with both radiators in the cheek position in the fairing. Bill Jepson Not totally true as I learned from overheating my norton rotary dragonfly. It makes sense that air flows from high pressure to low. But. Many times oh has a mind of its own counterintuitively. For example as the air exit the exchanger if it is not allowed to exit straight or gently deflected, independent of the delta the air will stagnate and not go where you expect. Pay as much attention to the exit as you do with the entry
Yrmv
Answer is nothing; provided the airflow is there. Also there needs to be a vent or tap to get all the air out of the inside. Bill Jepson Finn asks-
"BTW, what happens when you lay down (at a 20 degree) angle a radiator that is designed to be upright?"
I always wondered about that myself. The stock FD (3rd gen) radiator has to be at about a 45 degree angle (?) to the incoming airstream. And it has 2 "supplemental" staged electric fans (no pump fan), one is always on if the AC is on, the fans have different blades and different speeds controlled by ECU and temp sensor. I suppose the fins are canted or perhaps they are best tilted to airflow to create turbulence and help remove some heat..........don't know much about radiator design............
MW
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