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Old 05-01-2016, 02:44 PM   #11
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Another phenomenon to keep in mind is "boundary layer". Boundary, as in the border between two things.
The air that is IMMEDIATELY next to the side of the bus travels with the bus. Then, perhaps one millimeter from the bus the air travels at a little less speed than the bus, and so on. This is why air intakes are often on top of a pedestal -- to get away from the boundary layer and get full ram effect.

Another way is the NASA or NACA (or some such) duct, which is recessed in the vehicle, so the boundary layer follows the bottom of the recess.

Some land speed record cars have the air intake sticking straight out ahead of the vehicle, so it encounters undisturbed air for the full ram effect.

This is a complex issue, but I think we can learn quite a bit from a few hours of Googling.
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Old 05-01-2016, 03:13 PM   #12
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You all have given me much to think about. I had hoped for an easy answer, but alas..

I wish I could just go hit the road and do a test. I generally like doing that. But as my bus is currently wearing only its floor and roof (no skin inside or out on the walls) its airflow behaviors would be entirely unrepresentative of real life!

cadillackid, you mentioned having a skirt-mounted condenser that sometimes got good airflow even with the fans turned off. Where was it located, and which direction did the air flow?
the skirt mounted condenser was located on the bus skirt, left side near the bottom.. right under the 1st and 2nd passenger windows...

im not sure whuch way the air flowed when the fans were turned off.. I only knew the coils stayed cool during that time.. when the unit was running with its fans, the air was sucked in from the grill in the skirt and discharged underneath the bus.

-Christopher
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Old 05-01-2016, 03:52 PM   #13
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A classic way to learn about air flow on a moving vehicle is to tape pieces of yarn or some such to the vehicle and photograph it as it drives by. Short pieces of "flag tape" might work well. This stuff is about one inch wide, in bright colors, and costs practically nothing. Any hardware store should have it. It is used by land surveyors and such.

You can also mount the camera on the vehicle.
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Old 05-01-2016, 03:53 PM   #14
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My bus came with a diesel generator hanging in a box in the underbelly.

the motor is reversed from what you'd think normal air flow is.

from the front tire, first is the battery box, then the generator head, the diesel motor, and last in the box is the radiator. just after the the radiator not shown in the picture is the exhaust from the generator, then the rear tire.




hope that helps
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Old 05-01-2016, 04:17 PM   #15
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Hmmm...have to wonder about that arrangement. Could it be that the airflow around the other items creates a draw through the rad at the rear? Or possibly slows the airflow down for more effectiveness?

Many air-cooled aircraft engines and old 2-stroke formula race bikes used what is called a "still air box" to aid in extracting heat. At speed, the air is not in contact with the cylinder heads long enough to take away adequate BTU's, so they enclosed the heads in a box that had a larger opening at the rear than the front. By slowing down the flow of air, it removed more heat. Maybe something like that effect?
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Old 05-01-2016, 04:47 PM   #16
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Maybe they just didn't want the radiator against the battery box?
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Old 05-01-2016, 07:18 PM   #17
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did not want the front tire throwing rocks into the generator radiator
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Old 05-01-2016, 07:22 PM   #18
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The concept of air or water moving too fast to pick up heat has always puzzled me. I am NOT convinced this phenomenon exists -- UNLESS it has to do with the boundary layer I mentioned earlier. Heat transfer, I expect, primarily takes place in the boundary layer. Possibly, the thickness of the boundary layer matters. I wold love to learn more about this!
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Old 05-01-2016, 07:34 PM   #19
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Like the experiment where they put golf ball dimples all over a car and found that it had less wind resistance.
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Old 05-01-2016, 08:30 PM   #20
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The concept of air or water moving too fast to pick up heat has always puzzled me. I am NOT convinced this phenomenon exists -- UNLESS it has to do with the boundary layer I mentioned earlier. Heat transfer, I expect, primarily takes place in the boundary layer. Possibly, the thickness of the boundary layer matters. I wold love to learn more about this!

my own personal OPINION on that is it is due to humidity.. If I raise the temperature of the water in the air that it continues to change states more and more to a gas it is going to transfer a LOT more heat than if the air simply goes through and no state change occurs..
-Christopher
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