IC tank design and a second thought for me

[broxma]

So last weekend I was up at Bell Intercoolers getting my FMIC made for 379. I went with an API core 3.5 x 9.5 x 24 core. Corky and Trey estimated HP capability in the 425-475 range. When we got to building the pipes we ran into the conundrum. The hot side pipe off the turbo was going to hit the tank at a 90 degree angle. I have long been a proponent of not having a pipe do this as I know the energy loss in redirecting the airflow through the core after swirling in a 90 degree bend is huge, upwards of 10% or more. I always liked the straight flow, top to bottom design with the inlet up top and the outlet on the bottom. That setup basically demands the flow spread across the core without using a divertor. In absence of that, a straight flow, bottom/bottom or top/top with a divertor was my next best setup. The straight, bottom/bottom with a divertor was how we built my IC for my Evo. and it gained huge torque on the dyno. I wanted very much to mimic this on the hot side of 379 but quickly realized why the 90 degree into the tank configuration was a better design in this application.

Here is a picture of three possible scenarios with straight flow designs.

The top design is how my Evo IC is setup up. Divertor redirects some of the airflow to the upper portion of the core for better cooling. This is the optimal design for such straight through side to side flowing cores as the lack of a divertor basically means the channels right in front of the inlet will get the majority of the airflow and the top will basically go unused.

The middle design doesn't require a divertor since the air is forced to travel both across and down. This design is not possible on a factory GVR4 due to the interference of the bumper support, unless the IC is very low on the car and very short, maybe 6-8 inches tall.

The bottom design is the standard design for the GVR4 since the inlet pipe swings around the radiator and straight into the tank. It is possible on the GVR4 to build a short height tank and make a very sharp U-bend but that design is less efficient than the straight design. On the GVR4, the inlet is on the opposite side of the drivers tank. It is mirrored in the drawing.

So after talking with Trey, a designer for Bell IC, he gave me some new information about the straight inlet design. First, the straight 90 degree inlet design demands that once the airflow hits the back(front) of the tank, it spreads up and down. This means that while the energy loss is high, no complicated divertor is needed. In addition we discussed why companies use this design versus routing a pipe to meet the tank straight on. So while the energy loss is high in the 90 degree tank, it is generally lower than the numerous additional bends required to get the pipe to flow straight in. We counted no less than 5 simple or complex bends to route the IC from a down firing turbo outlet, under the frame rail, around the radiator support brace and back into the core. Each one of these bends would have energy losses between 3-5% for a combined loss much higher than simply running the pipe right into the tank at the 90 degree angle. So given the benefit of no divertor and less actual energy loss, the 90 degree inlet design is in fact the best possible inlet on the GVR4 given the obstruction of the frame rail and brace.

I'll take some pictures of my new IC once I find the battery charger, and hopefully better illustrate the data in the post.

/brox

 

[Barnes]

Personally, I would use whatever is cheapest/easiest.

Couple questions:
Where did the idea of this diverter come from? I was interested in reading some testing on how this affects things. I'm just surprised by the idea that the momentum of the air would cause half the intercooler to be 'unused'. Also, by the same rational you would need a diverter on the offset inlet/outlet design.

On your EVO, what were your torque gains? Was adding the diverter the only change to your setup? Other variables?

You could always calculate a pressure drop due to entering the IC at a 90 degree angle, see if the pressure drop is reasonable or not.

 

[Boostdtalon]

So after reading this, it makes me wonder how my IC is going to perform being that it's a short route with a 90 on both sides.

 

[broxma]

The inlet divertor is used on custom applications where the endtanks are custom fabricated. If you get an IC from a source that uses a cast endtank, you can be certain it won't have one. BIC uses divertors on any large frontal area application or if the customer requests one. For a top to bottom flow design, offset as you put it, the divertor is not necessary but I have seen them installed. A lot of data is out there representing pressure loss across the core itself, but very little in terms of actual even pressures inside the core.

As for a practical example, when speaking about airflow within a tube, it is best to think of it as a fluid. Even though it is simply air, for the sake of flow patterns it behaves very much like a fluid. Airflow turbulence through a curve is similar to water, with a high speed zone just off the outside bank, eddies on the inside track, etc. The engineers at BIC and I have discussed these intercooler elements for many hours on many occasions. The practical matter of airflow entering the core and generally following a straight line is based on Newton's Second law. When compressed air initially enters the endtank, it enters a volume of lower pressure, this forces it to expand unless the entire tank is at equal pressure. A turbo is generally able to fill the actually very small interior volume of the IC to boost pressure equally with a rise in manifold or compressor outlet pressure, meaning, the pressure in the core is generally the same as in the pipe before it at all times, if you ignore the effects of cooling and temperature, etc. Once the core is at a given pressure, the airflow will follow the path of least resistance which is through the channels directly in front of the inlet, unless a force (Divertor) is applied to it. The air at the top of the core, assuming a bottom/bottom flow inlet/outlet, does move, but not nearly at the same velocity as the flow rate directly in front of the inlet. What this means on most IC cores with cast endtanks, no divertors is the top half of the core is essentially being under utilized or unused. Only the bottom few channels will handle the majority of the flow. The 90 degree inlet eliminates this problem since when the airflow hits the flat surface directly in front of the inlet, it moves along a vertical axis in all directions. This evens the flow along the entire height of the endtank, at the expense of the energy loss of redirecting the flow into the core.

Here is another crude drawing to show the effects of the different styles. These are not close to accurate I assure you but cover the general principle as explained to me by the BIC engineers.

Air is represented by the red where a full channel is all red. The 90 degree inlet creates the rough pattern I show next to the IC design, where the air flows 90 degrees from its direction of flow in all directions. The square design of most 90 degree inlet tanks creates a lot of turbulence which is where the bulk of the energy loss is. Even this extreme amount of energy loss is not more than extra bends required to get a straight flow/divertor design to work on the GVR4 front end due to the chassis configuration. This is the key design element in deciding the specific tank design for the car. Even with the easy inlet access next to the radiator, if it were possible to bring the hotside pipe around the frame rail with only a single 180 degree turn and no vertical bends, the bottom/bottom/divertor design would be the better design. The limitations of the chassis configuration are what make the 90 degree inlet the better choice.

As for my custom Evo IC, I picked up 27 ft/lbs. of torque on an identical tune over the stock IC on a car making around 300WHP. The core was an API core 13.5 x 24 x 4.5. It had 17 or 18 internal channels and a flow rating of over 1800 CFM.

/brox

 

[Barnes]

Gonna try and save myself a protracted discussion on fluid* mechanics. Do these folks at BIC have test data where they measured pressure gradients? Or even better, temperature readings from the cores with and without the diverters? From my limited understanding of fluid mechanics, a diverter should not be needed. However that is just an educated guess. I'm curious what the data actually shows.

This is what it boils down to: I used to be VERY adamant about fancy end tank design and short IC pipes. I would always harp about pressure loses and stuff like that. I remember ripping the ETS endtank design because of this. However after spending a lot of time thinking about it, and lots of input from other folks, I realized something. It only matters if the pressure drops are significant. The big question is: are they significant? How do we know? We only know if we take actual measurements. To this day, I haven't seen any comparisons of end tank design and pressure drops using actual data. I think you said corky bell has this data in his book, but you weren't specific. If we spend a huge amount of effort to reduce pressure drop due to end tank design and piping and only reduce pressure drop 0.1psi, was it really worth it?? Point is, until we have *data* all this nit-picking of end tank design is essentially mental masturbation.

Same goes for what you and the BIC folks are saying about these diverters. What is the data showing the effect of these diverters? I'm not saying it isn't real, but is there a difference? How big is the difference? Finally is it worth getting ourselves tied up in knots over a few degrees of temp drop?

As for your example of switching intercoolers, it is unfortunately useless in illustrating anything. You are comparing an intercooler of different size, tube design, and end tank configuration. We have no way of knowing other than guessing which had the most effect and if other aspects (.e.g diverts) had any significant roll.

I don't mean to bust your balls, but this topic has come up a thousand times. We end up talking and talking and talking but NEVER get actual numbers. So in the end, we accomplish nothing.


BTW, for *everyone's* information, air is a fluid. Period. Water is a fluid. Honey is a fluid. Liquid nitrogen is a fluid. Anything that flows and conforms to it's container is a fluid. The only difference between any of these is compressibility. Which unless you are talking about super sonic flows is really irrelevant. (Yes, I know we have boosted applications running 30 psi gauge. Compressibility effects still don't matter until flows are super sonic which I doubt they are in our applications)

 

[brisvr4]

I hate to beat a dead horse but have a read here and see if it helps out.
A.R.E coolers

 

[4thStroke]

These fine details are really just nit picking. Small things do add up, but in the end, I'm not sure the payoff is worth the real world gains.

Brianawd has one of the highest 3052 numbers out there and has a 90* in, 90* out old school Spearco, the same one that 1051 has as well.

Would Brian's car see gains from a new core with baffles and a straight through design? Maybe some, but worth the few hundred to upgrade? At the same time, his piping is going to increase which will have adverse affects.

Then there is the headache of fitting the core to the car.

If we really want to get down and dirty, ditch the boxed end tanks and opt for tanks that are smooth (round).

Check out the fancy sheet metal end tanks Kevin Kiggley fabbed for his own car.



A core with little pressure drop will do a poor job cooling the air charge. There is a balance to be had between acceptable pressure drop and optimal cooling.

 

[broxma]

It is entirely nitpicking. Nothing more. I didn't start this thread to do any elaborate endtank design theory and my illustrations are not meant to be scientific, not meant to show any data, only the flow pattern relative to the general principle as told to me by people who do this for a living. I am making one claim. The reason the 90 degree inlet is the better option is because the combined energy loss of the pipe needed to get around the frame would be more. Source : click (First result) I don't believe anyone would argue against that position.

The mention of the divertor on the core of my Evo was in response to the specific question. The reason I mention it is to illustrate the point that given the stock Evo IC core is rated to handle the power my car was making, one might assume a change would have no/little effect. This is a common misconception when it comes to many things. A good example of this is the Subaru guys who all say that an intake is a waste of money until you're making 400 hp, since the stock intake can flow that much. My point is only that even given overhead on a part, changes in design to a higher efficiency part show an increase. In the case of my swap, 27 ft/lbs which is almost 10%, switching from a core I was not over running, to a different design. In my IC swap experiment the only change was the core. It most likely had an interior volume 4-6 times that of the stock core and was bar/plate not tube. It also had a divertor. I am sorry I forgot to build two exact cores, one with a divertor and one without to do a three way comparison test.

As for pressure drop. The guys assume the worst, and just say 10%.

/brox