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    8 out of 8 members liked this post. Yes Reputation No

    Intercooler Design

    Intercooler Design:

    I would like to talk about a subject matter that has been bothering me lately. My boss just got back from PRI and had this look on his face like "WTF MATE?".
    Why you ask?
    My boss is the kind of guy that likes to see numbers, real numbers, that make sense. He likes to see things engineered using real fundamental physical proof to design decisions which ultimately leads to a good performing device.

    At PRI he said, "no one engineers intercoolers, they don't do any analysis on intercoolers" and this struck me as NO SUPRISE.


    After you read this article you will understand where our frustration comes from. I perform CFD analysis and thermal analysis for a living. So when I see what's out there, I cry a little bit inside.

    I am not going to explain what intercoolers do, just what makes a good intercooler from a bad one; in theory.

    Here are the main parts of the intercooler:
    Inlet piping
    Expansion into endtanks
    Direction changes in endtanks (sometimes)
    Core flow


    The biggest concern I have with todays aftermarket intercoolers is endtank design. Before I talk about how you can $#@! up an endtank design we have to talk about what diffusion is and what makes for poor diffusion.

    Diffusion is when you need to slow the flow down to recover static pressure or when you need the flow to change
    direction while recovering static pressure. This occurs when a pipe dumps air into a large plenum-like chamber, sort of what we have in an endtank.

    Now, poor diffusion is when you dump TOO fast. Here is what happens.

    Click here to enlarge

    Notice in the picture above, the flow dumps out from a pipe into a sharp edged plenum. This will result in poor diffusion and a large pressure drop with poor flow distribution (more flow at the bottom vs. the top).



    Click here to enlarge

    Good diffusion takes place in rather simple geometric constraints, think of flow through this duct, the diffusion angle has to be 8 degrees or less for near perfect diffusion. This has been verified by Sovran and Klomp 1969.



    The problem with the above is you would need an endtank that is 10 feet long to be able to accomplish perfect diffusion. So there is a compromise to be made. Packaging need not suffer.

    What happens when it dumps out into a boxy endtank?
    You get flow detachment at the corners and lots of flow separation, some of the flow MAY NOT EVEN MAKE IT to the extremeties of the core flow.

    And that's a $#@!ty design.

    Click here to enlarge

    Here is an example of a $#@!ty end tank design.

    Click here to enlarge

    Here is an example of a good design.

    Click here to enlarge

    Now can you see which one was actually engineered and which one wasn't?

    Up until now we have not discussed core design or heat transfer effectiveness.
    We focued only on the endtanks and how to distribute the flow into the heat exchanger without compromising boost pressure drop.

    There are other techniques to aid flow into the core.

    Better:

    Click here to enlarge

    Best:

    Click here to enlarge



    The relationship between heat transfer effectiveness and pressure drop is inverse, most of the time. If you want good heat exchange, you will suffer with greater pressure drop.

    If you want to decrease pressure drop, your heat exchange will suffer. A well engineered core will offer good heat exchange with minimal pressure drop.

    What to avoid to reduce pressure drop:
    Weld flash exposed to flow
    Rough surfaces
    Abrupt changes in flow areas (sudden expansion or contractions)
    Forcing the flow to separate suddenly
    Air velocity too high (keep velocity below mach 0.3, pressure drop is proportional to V squared).

    Since a core has a very large internal surface area to volume ratio, one will have to live with the fact that a pressure drop is unavoidable in this device.
    We can only design to minimize it.

    Too big a core will produce too much of a pressure drop, so any gains you've captured from your big honkin heat exchanger in the form of gas cooling, you now lost because of boost drop through the core.

    At a later time, I will write an article about heat exchange effectiveness. This article will only serve as a basic means for designing a good flowing intercooler without taking into account core design, since good cores can typically be bought as an off the shelf item.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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  2. #2
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    Man this is a lot to soak in.

  3. #3
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Man this is a lot to soak in.
    Intended pun? lmao. Good info, it all makes sense.
    Burger Motorsports
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    Click here to enlarge Originally Posted by Sticky Click here to enlarge
    Man this is a lot to soak in.
    This^^
    Awesome to have a member like DBFIU! Thanks for sharing!

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    If anyone has any questions or comments don't be scared to ask and tell. A healthy discussion is always welcome.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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    So basically what i got from that was

    helix intercooler end tanks suck

    ams is teh wins?
    2006 AW/Black ZCP 6MT


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    1 out of 1 members liked this post. Yes Reputation No
    Click here to enlarge Originally Posted by folgrz Click here to enlarge
    So basically what i got from that was

    helix intercooler end tanks suck

    ams is teh wins?
    Pretty much.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


    Click here to enlarge

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    The worst part is there's no reason for the poorly designed end tanks. Well thoughtout and flow tested end tanks in all shapes and sizes are readily available for sale. The biggest reason for the lack of effort you describe is poorly informed buyers who want the biggest intercooler they can fit(not taking into account their needs) and people running eBay coolers with seemingly no ill result(which lowers peoples willingness to pay for a premium product)

  9. #9
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    Click here to enlarge Originally Posted by DBFIU Click here to enlarge
    Pretty much.
    hahaha just busting chops! Awesome post +1 rep for you Click here to enlarge
    2006 AW/Black ZCP 6MT


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    1 out of 1 members liked this post. Yes Reputation No
    Click here to enlarge Originally Posted by Jimefam Click here to enlarge
    The worst part is there's no reason for the poorly designed end tanks. Well thoughtout and flow tested end tanks in all shapes and sizes are readily available for sale. The biggest reason for the lack of effort you describe is poorly informed buyers who want the biggest intercooler they can fit(not taking into account their needs) and people running eBay coolers with seemingly no ill result(which lowers peoples willingness to pay for a premium product)
    A well designed intercooler takes a lot of time and money to develop, and this is what you pay for. It's not just a core slapped together with pipes.

    AMS used cast endtanks with very good flow characteristics. I have always been an advocate for their design because it was one of the only intercoolers on the market that passed my gut check.


    P.S. A lot of times people overlook the simplest components and wonder why they are feeling the turbo spool up at 5000+ RPM with huge lag between shifts, and they their IATs are 200F and their EGTS are 1500F???

    A well designed less powerful turbo system as a whole in my opinion is more preferred over a crappy system as a whole that makes more power.

    I like when devices work together and synergize. When a system as complex as a car engine is designed with parts that are just slapped together, you ruin every bit of the system, because all the parts need to work together.
    Last edited by DBFIU; 12-09-2011 at 03:03 PM.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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  11. #11
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    Nice post!

    The same stuff applies to Nitrous distribution.
    Rep Points > Posts since 2010

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    Click here to enlarge Originally Posted by PEI330Ci Click here to enlarge
    Nice post!

    The same stuff applies to Nitrous distribution.
    Yep, intake manifolds too.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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  13. #13
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    Click here to enlarge Originally Posted by PEI330Ci Click here to enlarge
    Nice post!

    The same stuff applies to Nitrous distribution.
    I think you might end up liking this forum section.

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    Sorta off topic but...

    What is standard velocity of air throughout the intake tract? Not in the intercooler as obviously this would change.

    You talk about diffusers and flow around angles had me wondering...most of what i know about airflow is in regards to gas turbines...specifically turbojets where intake velocity will be supersonic through at least some of the operating range...I don't think intake air in a turbo car is ever supersonic but that is why i am asking.
    Never thought I would see the day...
    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    Life is so much more fun with a nemesis. I miss Shiv. Click here to enlarge
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  15. #15
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    Click here to enlarge Originally Posted by Forced Air Click here to enlarge
    Sorta off topic but...

    What is standard velocity of air throughout the intake tract? Not in the intercooler as obviously this would change.

    You talk about diffusers and flow around angles had me wondering...most of what i know about airflow is in regards to gas turbines...specifically turbojets where intake velocity will be supersonic through at least some of the operating range...I don't think intake air in a turbo car is ever supersonic but that is why i am asking.
    The Mach # that most race engines try to stay under is around 0.7 in the port IIRC. (I'm really digging around the back of my foggy head on this one) Most head porters and intake manifold fabricators will target a theoretical 125/130 meters per second in the runner. (I'm more confident on this one, as I've been involved in the design process. You'd be surprised how often a port is reduced in size versus OEM to achieve this correctly.
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  16. #16
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    Here's a good calculator to help you play with flow velocities:

    http://not2fast.com/gasflow/velocity.shtml

    C
    ould be helpful looking at IC pipe sizing and IC flow.
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    I'm an idiot.

    You'd have to have some kind of miracle going on to see 0.7 mach....even the Pro Stock guys are well under that....and they are on the absolute edge of flow velocity IMO.
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    Click here to enlarge Originally Posted by Forced Air Click here to enlarge
    Sorta off topic but...

    What is standard velocity of air throughout the intake tract? Not in the intercooler as obviously this would change.

    You talk about diffusers and flow around angles had me wondering...most of what i know about airflow is in regards to gas turbines...specifically turbojets where intake velocity will be supersonic through at least some of the operating range...I don't think intake air in a turbo car is ever supersonic but that is why i am asking.
    Most of the air in the intake tract is not going past mach 0.3 on average. Compressibility effects of air take effect after about mach 0.25-0.3 where pressure drop starts to become very large. The intake valves can see sonic flow locally, but in the intake piping one should try and stay below 300 ft/s.

    Exhaust valves go sonic because you exceed the critical pressure ratio across the valve of about 1.98 for air (but mostly carbon dioxide in the exhaust so its close).
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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    Well crap. I guess it's time for be to throw the ol' Helix intercooler in the trash.

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    Yea...valves make sense...just wasn't sure about the rest. You read my mind, was thinking compressibility. So nowhere then do you have to worry about a divergent area becoming a nozzle then right. (except near the valves)
    Never thought I would see the day...
    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    Life is so much more fun with a nemesis. I miss Shiv. Click here to enlarge
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    Love info like this. No BS, just the facts ma'am.

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    Click here to enlarge Originally Posted by Forced Air Click here to enlarge
    Yea...valves make sense...just wasn't sure about the rest. You read my mind, was thinking compressibility. So nowhere then do you have to worry about a divergent area becoming a nozzle then right. (except near the valves)
    pretty much and I know what you are getting at. Converging diverging nozzle with transonic flow = possibility for flow to go super sonic. I am pretty sure that it does not go super sonic across the intake valve because it enters at about mach 0.7 and the area ratio may not be big enough.

    A over Astar... Where is that equation.. Gonna go do some calculations for fun.
    Some people live long, meaningful lives.

    Other people eat shit and die.

    I'm not racist, I hate everybody equally; especially fat people.


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    This thread makes my head feel things it hasn't for awhile...haha, love it
    Never thought I would see the day...
    Click here to enlarge Originally Posted by Terry@BMS Click here to enlarge
    Life is so much more fun with a nemesis. I miss Shiv. Click here to enlarge
    Click here to enlarge

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    Click here to enlarge Originally Posted by Jimefam Click here to enlarge
    The worst part is there's no reason for the poorly designed end tanks. Well thoughtout and flow tested end tanks in all shapes and sizes are readily available for sale. The biggest reason for the lack of effort you describe is poorly informed buyers who want the biggest intercooler they can fit(not taking into account their needs) and people running eBay coolers with seemingly no ill result(which lowers peoples willingness to pay for a premium product)
    This is so true...I tried explaining this to someone else on the other forum and I just ended up getting flamed and being told that I overpaid for intercooler...Now I remeber why I stooped visiting that forum. Anyways, you get what you pay for, I always believe that. Some people want to throw a $300 intercooler on a $55k BMW..that logic never made sense to me

    BTW DBFIU...what do you think about the Active Autowerk Intercooler...when I bought mine(almost 2 years ago) it was supposedly one of the best intercoolers on the market. From what I researched back then, that seemed to be true but you know much more about this subject than I do...are you familiar with this unit, and if so whats your opinion on it?
    Last edited by fast4door; 12-20-2011 at 02:11 PM.

  25. #25
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    So based on pressure drop and cooling efficiency, could you let us know which of these intercoolers are below par and which ones are decent?

    ETS, AMS, Helix, Big Tom, AA, HPF
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