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Old 11-09-2008, 05:40 PM   #26 (permalink)
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Originally Posted by ConnClark View Post
Actually it isn't from cooling. You can have hot air on one side of a room and cold air on the other side and they will be at the same pressure. If it indeed there is a 3 psi drop across the intercooler he should really consider looking at an after market intercooler to reduce this loss as it a serious loss in useful energy. I also don't know where he measured the the pressure drop from. If it was right before and right after the intercooler then the drop is all too the intercooler. If it was between the outlet of the turbo and the manifold the plumbing route could be a big contributing factor. Yet another factor is the velocity of the air at the two points of measurement as this will have different static and dynamic pressure if they are different.
Sorry ConnClark, but you are mistaken. In a closed system as we are discussing, temperature does effect pressure, and it is easily measured because it is constant. A room is not a closed system so it is harder to measure, but in fact if you suddenly cooled one end of a hot room there would be airflow to the cold end because of the pressure differential. True, the pressure would equalize as the air mixed, but so would the temperature. If you took 10 pressure readings in the room you are in right now they would all be slightly different - and all directly related to the slightly different temperatures at each sample point.

As for magnitude, it seems reasonable to me. Three psi is only 1/10 of an atmosphere, and reducing the temperature of air from 250F to 150F can easily induce a change of 0.10 bar (particularly when it is pressurized to begin with). Trust me on this - I spent a lifetime correcting air sample measurements to STP (standard temperature and pressure) for human exposure monitoring studies. Note that I made my biggest assumption in this paragraph - that the air was cooled about 100F by the IC. If this is way off let me know and I will recalculate the pressure drop that would be expected across the IC.

Static pressure and dynamic pressure (also known as velocity pressure, VP) are independent of each other. VP is a measurement used to measure the inertia of moving air (usualy in a duct), and has no purpose when determining the pressure drop across a restriction such as, say, a filter or IC. In this situation VP values do not complicate the situation because they are simply not applicable.

I read the post that he was getting a pressure drop measured across the IC, hence he blamed restrictive airflow in the IC. If the pressure measurements were taken other places it might change things, but those were not the parameters of the problem, and the pressure drop across the IC is almost surely due to the temperature drop.

Last edited by instarx; 11-09-2008 at 06:30 PM..
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