Andy.F

OK, its just that its difficult to measure pressure in a fast flowing stream due to the low pressure (suction) created when a high speed gas or fluid passes over a surface/tube end etc

Andy

911

So a hot wire sensor would be better and very fast to respond?
Graham

Andy.F

That would be better for measuring actual mass flow for sure.
DP measurement is only accurate in a pipe of known diameter with an orifice plate fitted.

Andy

911

If you measure flow in the scoop and flow in the gearbox areas or elsewhere then that indicates 'pressure differentials'?
The TMIC 'trousers' (such a good way to describe the item!) crossed my mind when looking to put high speed fans on the TOP of the TMIC, continuously running in a hill climb, water spray up-stream of them so the fans speed up the water flow and maybe 'atomises' the dropplets too (?)
A thought was to mount the fans in each (or the one) trouser leg, and draw the TMIC air by the fan down to the lower front wishbone area under the starter motor side.
This is however very restrictive if you look down there and try to sight a clear 'tube' passing down... The turbo side is silly..far to blocked up with the hot D/P!

When you consider all the thread's (good) points of view which have been bullsh!t free (I hope I qualify) a simple FMIC with a clear inlet/grill opening, 'sealed' to the water rad so the twin rad fans are effective for drawing cool air through at slow speeds and chilling the FMIC core/end tanks, coupled with a wide open lower engine bay would fix it all! ( cracking open the rear edge of the bonnet or removing the bonnet seal front and back also)

Now then...isn't that what the Lateral Performance FMIC is?

Shall I get my coat immediatly and leave?

Graham

Andy.F

Door is to your left

The problem with estimating mass flow based on DP in 2 different CSA's is that you can't ! Not without knowing the velocity.
Air or fluid will flow from low to high pressure as well as from high to low. Think of how a carburetor works.

Andy

911

Can't read this thread from out here!
What i'm trying to say is if the flow grows or diminishes with speed it indicates the changes happening in different/chosen zones around the car.

Still think a FMIC vented well will simply work from any reasonable speed, and better than a TMIC with a stationary car because of limited heat soak from the surroundings and exposure of the FMIC core to cold air rather than hot constantly rising engine bay air.

Catching the bus now....

Graham

RB5_245

Actually you could if you also measured temperature and plotted on a pv graph, but i very much doubt it would be accurate enough to be of any use

In this case as the intercooler is finned and both sides are under pressure natural flow must be from high to low. After all you wouldn't expect air to flow INto a leaking boost hose at full boost

only way you can get from low to high is through a venturi or mechanically force it.

Andy.F

Scoop inlet = venturi

Andy

jaytc2003

iTrader: (1)

what about measuring the flow at the scoop with the bonnet vent blanking plates removed. What effect does this have on the general flow under the bonnet etc and would it help with the temperatures?

silent running

I'd agree with this quote in general. But either I've not done enough thinking about venturis or I'm missing something...I can't see how pressure can ever flow from low to high. So in the 'no bull****' spirit of this thread, someone please explain this to me. My understanding of the venturi efffect is where you have a restricted area of high velocity fluid flow which causes a low pressure area relative to its surroundings e.g. a venturi tunnel effect under a well designed, very low race car which will increase downforce. It's not immediately obvious to me how the scoop is a venturi...the flow towards and into it is not particularly controlled or channelled...help!

silent running

Very good question. I've got an adapter on the way so I can take proper differential pressure readings from any two points I choose. Damn thing is 1/8 NPT fitting so it's a pain in the **** to get from my local hardware store and had to resort to Demon Tweeks. See the lengths I go to to get you results?

I like the idea of the 'trousers' with a fan in each leg. Clunky and probably impossible to rig up practically, but a cool idea nevertheless.

Andy.F

If you blow across the top of a straw, it will pull up water. Just like a paint spraygun uses high pressure air to pull up paint which is at low (atmospheric) pressure.
The entry area to the tmic could work like a venturi as the area increases after the entry point, in turn slowing down the airflow and increasing its pressure.
I'm not suggesting the airflow is reversing out the scoop or even that I have any idea what is actually happening to the flow at this point. I'm just saying that pressure measurement in this area is highly likely to be misleading.

Andy

RB5_245

I wasn't actually going to post this but since you ask

Imo the scoop entry to intercooler surface acts as a volute, ie converting pressure into flow. As the scoop can be seen as a sealed volume from the high pressure high velocity small csa scoop the flow reduces in pressure and increases in volume in the same way as a cenrifugal pump does. I don't think it can be described as a venturi as it doesn't create an area of pressure lower than it's outlet pressure, with the exeption of a pocket of air on the sharp side of the bend (which should be reduced as much as poss with a splitter).

By reducing the volume of a tube and hence the pressure of the flow, allowing a inlet feed then expanding the tube you can create a very good vacuum in the line which is obviously at much lower pressure than the outlet of the venturi. Hence you are flowing from low to high pressure in a cheating sort of way. I'm not the best at descriptions but have a look at this link

It should help.

but I think this is going to far into theories rather than that which is practically measurable to us.

Dave

silent running

Andy - yes that's pretty much what I thought of as a venturi effect - an area of low pressure created by a zone of fast moving or expanding air. But surely in that example of the straw, it's not doing anything that surprising - the blow across the top of the straw is simply creating a low pressure area which the liquid rises towards because at the opposite end it's pushed by the relatively higher atmospheric pressure.

So I can see how there's a possibility that the scoop MIGHT have a venturi effect going on, but I can't see how it could possibly be significant enough to make any difference to flow in that area.

I think I can follow what you're saying Dave, and it seems to make sense.

Andy.F

Ok, I realise I'm kind of taking things off topic based on theory here regards the validity of dp measurement.
If anyone has use of a basic data logger or even a multimeter, I have a used maf I could give them. It could be cable tied in position, powered up from a lead to the battery and the output (proportional to mass flow) at various speed monitored.
A definative measure of actual airflow through the intercooler.

Andy

ZEN Performance

The exit of the scoop, is about double the area of the entry. Argument over, Bernoulli wins, pressure will increase as you go inside the scoop, pressure is decreased over the surface of the bonnet due to increased velocity.

Andy.F

Yea, we know that Paul, thats why I was saying beware of measuring pressure differential and be carefull where you measure it.
It would be easy to measure the low pressure in front of the scoop, high pressure inside the scoop and conclude (incorrectly) that there was no flow into it !

ZEN Performance

I was merely backing up what you had said. maybe I should put a cherry on top next time to keep you quiet!

Measureing the pressure say at the surface of the fins at the top and bottom would be a more valid way of doing it, as the CSA is effectively the same. I like the idea of a maf sensor, but it doesn't give an idea of direction of flow, although if it reversed you would see it pass through zero.

silent running

OK so to rule out the problems of any other effects, I'll just measure differential pressure directly above and below the I/C. I'll do it today if I get the chance.

vindaloo

<cough>

Any news?