Intercoolers

[Unchained]

I'm not understanding the significance of a pressure drop caused by an intercooler.
It seems that when ever you cool the mixture there will be a pressure drop so it would be impossible to have one without the other.
Is pressure drop a negative thing or just an indicator of the effectiveness of the intercooler?
I hear the Turbo'ed import drag cars are running a dry ice mixture through the core at 35 +- degrees and that must cause a huge pressure drop.
To me, With the turbo's there is so much boost on hand that it's not like you're going to miss any amount of pressure drop.
There is no difficulty in making boost like there is with a roots blower.
Thought's ?
Mark

[Craig]

I might be off base here, but I think the pressure drop you hear about is the drop in actual boost pressure measured in the manifold. They say you'll loose a pound or so due to the physical interference of the intercooler core itself in the airstream. Not the pressure drop you see kust becuase you cool the air.
Craig

[Infomaniac]

I'm thinking the pressure drop is insignificant unless you are boost challenged so to speak.
Also just a way to measure intercooler performance.
Actually the hot air expanding above the intercooler helps push air through the intercooler.
I would think you need to measure the volume of air going through and the temperature decrease to compare intercoolers.
The Whipple intercooler is a very good one. You cannot see light when holding it up to look through.

[058]

The colder the air the denser the molecules are packed together that means less pressure for a given volume of air.

[Infomaniac]

Are you sure about that guys?
Pressure increases with density.
Normal atmosphere is greater pressure at sea level. Due to nothing but density. The actual weight of the atmosphere.
Any pressure drop across the intercooler is due to mechanical restriction.
The hot air above the intercooler has heat expanison. That pressure is different than density pressure.
On top of the intercooler is a device shoving air at it. Below the intercooler is a device drawing air away from it.
Ever see a dyno sheet from the good old days before intercoolers? Watch the power curve and boost curve. At one point the power will go down while boost goes up. This is due to heat expansion. More pressure but less power due to less dense air.
Edit: Found this with a quick search.
Pressure
Density depends on pressure, but what exactly is pressure? Pressure is simply the force experienced by an object divided by the area of the surface on which the force acts. Note that the force here is the force acting perpendicular to the surface.
Pressure : P = F / A (The force is applied perpendicular to the area A)
The unit for pressure is the pascal, Pa. Pressure is often measured in other units (atmospheres, pounds per square inch, millibars, etc.), but the pascal is the unit that goes with the MKS (meter-kilogram-second) system.
When we talk about atmospheric pressure, we're talking about the pressure exerted by the weight of the air above us. The air goes up a long way, so even though it has a low density it still exerts a lot of pressure:

[Havasu Hangin']

Like 058 said, ever stick a balloon in the freezer?
If you are talking about the same mass of air, once it cools, it will take up less volume, due to the denser properties (contraction). The balloon will be smaller.
Instead of a balloon, if you were to use a plastic jug (like a 2 liter bottle), there would be less pressure inside, as the walls would attempt to collapse around the now denser mass. To test it, open the cap, and the outside pressure will attempt to equalize.
I think atmospheric pressure due to gravity is different than thermal effects of expansion and contraction.
At least that's one thing I was semi-awake for in Physics...keep in mind I don't know anything about blowers.

[Infomaniac]

Very good discussion.
If I end up being full of shit - I will admit it openly. Then delete the topic immediately. :D
Fluid in motion is different than static fluid.
The bottle in the freezer is a good example of static fluid as well as my atmosphere example.
I guess the opinion I am trying to express is the pressure drop across the intercooler is not due to cooler air being more dense.
It is due to the mechanical restriction of the fluid in motion.

[Infomaniac]

Found this on a turbo site,
Heat Exchanger Theory and Intercoolers
by John Estill
Pressure Drop
Another aspect of intercoolers to be considered is pressure drop. The pressure read by a boost gauge is the pressure in the intake manifold. It is not the same as the pressure that the turbocharger itself puts out. To get a fluid, such as air, to flow there must be a difference in pressure from one end to the other. Consider a straw that is sitting on the table. It doesn't having anything moving through it until you pick it up, stick it in your mouth, and change the pressure at one end (either by blowing or sucking). In the same way the turbo outlet pressure is higher than the intake manifold pressure, and will always be higher than the intake pressure, because there must be a pressure difference for the air to move.
The difference in pressure required for a given amount of air to move from turbo to intake manifold is an indication of the hydraulic restriction of the intercooler, the up pipe, and the throttle body. Let's say you are trying to move 255 gram/sec of air through a stock intercooler, up pipe, and throttle body and there is a 4 psi difference that is pushing it along (I'm just making up numbers here). If your boost gauge reads 15 psi, that means the turbo is actually putting up 19 psi. Now you buy a PT-70 and slap on some Champion heads. Now you are moving 450 gm/sec of air. At 15 psi boost in the intake manifold the turbo now has to put up 23 psi, because the pressure drop required to get the higher air flow is now 8 psi instead of the 4 that we had before. More flow with the same equipment means higher pressure drop. So we put on a new front mount intercooler. It has a lower pressure drop, pressure drop is now 4 psi, so the turbo is putting up 19 psi again. Now we add the 65 mm throttle body and the pressure drop is now 3 psi. Then we add the 2.5" up pipe, and it drops to 2.5 psi. Now to make 15 psi boost the turbo only has to put up 17.5 psi. The difference in turbo outlet temperature between 23 psi and 17.5 psi is about 40 deg (assuming a constant efficiency)! So you can see how just by reducing the pressure drop we can lower the temperatures while still running the same amount of boost.
I have seen some misunderstandings regarding intercooler pressure drop and how it relates to heat transfer. For example, one vendor's catalog implies that if you had little or no pressure drop then you would have no heat transfer. This is incorrect. Pressure drop and heat transfer are relatively independent, you can have good heat transfer in an intercooler that has a small pressure drop if it is designed correctly. It is easier to have good heat transfer when there is a larger pressure drop because the fluid's turbulence helps the heat transfer coefficient (U), but I have seen industrial coolers that are designed to have less than 0.2 psi of drop while flowing a heck of a lot more air, so it is certainly feasible.
Pressure drop is important because the higher the turbo discharge pressure is the higher the temperature of the turbo air. When we drop the turbo discharge pressure we also drop the temperature of the air coming out of the turbo. When we do that we also drop the intercooler outlet temperature, although not as much, but hey, every little bit helps. This lower pressure drop is part of the benefit offered by new, bigger front mount intercoolers; by the Duttweiler neck modification to stock location intercoolers; by bigger up pipes; and by bigger throttle bodies. You can also make the turbo work less hard by improving the inlet side to it. K&N air filters, free flowing MAF pipes, removing a screen from the MAF, removing the MAF itself when switching to an aftermarket fuel injection system, the upcoming 3" and 3.5" MAFs from Modern Muscle, these all reduce the pressure drop in the turbo inlet system which makes the compressor work less to produce the same boost which will reduce the turbo discharge temperature (among other, and probably greater, benefits).
Here is the entire article (http://www.gnttype.org/techarea/turbo/intercooler.html)

[Unchained]

Originally posted by Infomaniac
Very good discussion.
I guess the opinion I am trying to express is the pressure drop across the intercooler is not due to cooler air being more dense.
It is due to the mechanical restriction of the fluid in motion.
Then the sq. in of the hole going through the intercooler core would be the over riding factor.
Maybe it was better that I made mine so that the air comes through the sides as well as the top.
http://www.***boat.com/image_center/data/504/220DSC01682-med.JPG
Now I'm curious as to what pressure drop I have.
I'll have to wait several months to find out.

[058]

300 deg/F air is less dense than 150 deg air regardless if its moving or not. Easy way to tell how effective an intercooler is, just shut the coolant off to the intercooler and compare boost levels. It will be higher with no coolant that with coolant flowing because of the less dense air. Like H.H. said about the balloon, take an empty soda bottle, cap it tightly and place it in the freezer. Check it in about an hour....is it as big as it was when you first placed it in the freezer? This is why I would rather have 10 lbs of boost at 150 deg/F than 15 lbs of boost at 300 deg/F....easier on the engine and the power will be about the same.

[MANIC MECHANIC]

I would think that the pressure drop would be due to a combination of both factors; the friction of moving the charge through the intercooler, plus the charge being cooled- thus making it more dense (more compact).
I would also assume that Higher boost whether from a blower or turbo would-
Increase the friction of forcing the charge thru the intercooler due to the fact that you are moving more air through the same size restriction.
And-
Due to the higher temps generated by producing a higher boost,
the drop in pressure from cooling the charge would be increased.
Just my thoughts on the subject.
Tim

[HeavyHitter]

It's all an energy balance. Some of the static pressure (pressure at turbo outlet) is converted to velocity pressure to move the air mass to the piston. The intercooler design plays into this fairly heavily. You need surface are to make the heat transer rate go up but if you get the fins too close the velocity of the moving air mass has to go up which reduces the static pressure. Faster moving air has less static pressure. That's what makes airplanes fly and F1 cars stick to the ground. Cooler air is less energetic so the pressure is lower. On a positive displacement device (belt driven blower) you would see a pressure drop due to cooling air as well. In the case of turbos the pressure drop is not realized since the compressor wheel is easier to turn so the turbine is able to spin faster, equalizing the pressure. That give you an increase in Hp. :eek: You've gotta love them turbos.

[superdave013]

Marc, I have a shit load of gauges to measure the differental pressure (pressure drop). I can send you one so you can measure it yourself if you want. You will only need an 1/8 NPT port on the top and bottom of the core.
A boost gauge is measuring static pressure.
A differentail pressure gauge will measure the difference in pressure from the top and bottom of your core.
click for da pic (http://www.iprocessmart.com/dwyer/dwyer_series2000_magnahelic_detail.htm)
Everything has some sort of pressure drop. There is a differental pressure drop across your screen door too if you want to be picky.
Our heat exchanges we build at work only have 13 inches of water collum of drop at full flow. That and 98% heat recovery is our claim to fame. The less drop, the less hp it takes to move the air through It's a big deal when it means some factory that runs 24 / 7 can use a 200 hp motor insted of a 250.
For a turbo that has wastegates dumping the extra pressure it's not that big of a deal I would not think. On a roots blower that's turned up all the way (say 40% over for example) and it's a bigger deal.
I think it's funny when I hear this or that cooler only have 1 pis of drop. Uh, that depends on the air flow. Say you have two engines that both make 25 pounds of boost. If it has one psi on a 350" engine @ 25 psi it will have more on a 600" @ 25psi for sure.

[Unchained]

[QUOTE]Originally posted by superdave013
[B]Marc, I have a shit load of gauges to measure the differental pressure (pressure drop). I can send you one so you can measure it yourself if you want. You will only need an 1/8 NPT port on the top and bottom of the core.
A boost gauge is measuring static pressure.
A differentail pressure gauge will measure the difference in pressure from the top and bottom of your core.
QUOTE]
SD, Thanks for the offer, I think I can pickup a gauge locally and install a check valve that will hold the pressure number above the core and I can datalog the manifold pressure. I plan on checking out that pressure drop just so I can see what efficiency I ended up with.
I would think that I would want to measure the pressure right at the compressor outlet and then under the intercooler so that I get a number that reflects the entire system pressure drop and not just the core.
Also I determined that I can install my EGT thermocouple at the compressor outlet and compare that temp to my manifold air temp.
Mark