Opinions on Intercooler Types...
03-11-2004, 03:24 AM
#31
Burning Brakes
Join Date: Aug 2001
Posts: 1,117
Likes: 0
Received 0 Likes
on
0 Posts
John,
I understand your concern about "loading" an A/W system. A valid point to be sure. You're right that it would be nearly impossible in an automotive scenario to "chill" an A/W system below ambient for any period of time. However, a properly designed and sized A/W does not thermo-load anymore than any other water radiator that is also properly dsigned and sized.
Old & New started down the road, I'm just continuing the drive, if you will...
Perhaps if you look at it like this, A/W will make more sense.
I believe we all know enough about thermodynamics to accept that water (or any liquid) will transfer more heat, faster than air (or any gas). Simple molecular density. If you doubt this, blow a 120F hairdryer at your hand. Then stick your hand in a 120F shower. Which one transferred more heat to your hand quicker?
That having been said, the goal of any intercooler ('aftercooler' if you're feeling pedantic) is to pull as much heat out of the intake charge as possible, while having the least impact on it's velocity and pressure.
The intake charge must flow over, or through, some sort of metal device. This metal device is the heatsink, it's function is to absorb the heat from the compressed air, then reject that heat to a cooler medium to move that heat elsewhere to be rejected again.
More heat is going to be rejected from the compressed air into a cooler surface than into a warmer surface. The latent heat (warmth) in the intercooler is a direct result of how quickly heat is transferred out of the same surface. So, it is way more effective to transfer the heat of the charge that has been shed into the intercooler body out of the intercooler with water.
Sure, but you've still got to get rid of the heat in the water, right?
True, true, true. But (this is the BIG but) you can do all sorts of things with the other end, the water to air heat exchanger, that you could never do with that same exchanger if you were trying to get the heat directly out of the charge. The radiator, shedding the heat from the water can have lots more passages, twists and turns. This allows the water greater contact time with the metal than is trying to dump heat into air. Velocity and presure losses become rather a moot point with the water - as long as the velocity is great enough to keep things moving, but not so great as to prevent adequate time to transfer the heat out, it's irrelevant.
The thing with trying to shed heat from a compressed charge directly into the atmoshere is that it takes a lot more time in contact with the metal to transfer the heat. This is because the ambient air is not able pull the heat out of the metal nearly as quickly as water is. So there is more latent heat in the device that's trying to pull heat out of the charge as quickly as possible.
In order to get the compressed charge in contact with the poorly heat transferring A/A long enough to move the heat, you nead a lot more contact time. Contact time = friction. Friction = more heat into the charge you're trying to cool, and lost velocity and pressure. Every time you call on air to change direction, you lose velocity - and one does a lot of direction changing plumbing an A/A intercooler. Frictional losses also cost precious velocity, as well as a great number of hardline to hose connections (required in most any non-OEM A/A setup) which also, will cost velocity.
But wait there's more. The charge, that has just been cooled off in an A/A, now has to work it's way back to the intake. More friction, more pressure loss, more chance to re-absorb ambient heat from the engine compartment.
The A/W can have it's intake heat removing plates ( or whatever) very close to the actual intake. The charge needs much less time in contact with the plates, because they absorb and reject heat faster. Because they can do this, they are designed much more efficiently. Transferring the heat to a large, slow moving rad up front and returning near-ambient water, can be accomplished with a coupla -12 AN (YMMV) hoses- a bit tidier on the engine compartment than a bunch of 3" silocone and aluminum tube. And far less able to pick up more ambient heat on the trip.
There still is the "extra parts" factor. Yup. But waterpump tech has advanced to the point where it's hardly an issue. But it's surely a point.
Race teams still use A/A? Yup. Sometimes it's rules restricting to a factory-esque A/A setup, but most often, it's like the Soviet Space program - it worked fine with minor tweeks for 40+ years, why change?
But, hey, ya gotta do what you are comfortable with. I have no desire to even try to talk somebody into something they will not be happy with later. Just depends on your priorities - efficiency or no moving parts?
Addendum: I would be inclined to focus even more on efficiency if I were doing a turbo setup. As I'm sure you know, turbos get really (red+) hot under any kind of sustained use, and put lots of additional heat into the intake equation. As a centrifugal blower, they are adiabatically very efficient, until they start glowing, then they aren't quite so great. Since the air isn't there very long, it's not terrible, but it adds some more degF to be removed just to get back to square one.
BTW- Like I said, don't get me wrong. The early stuff Reeves did was neat, and what I've driven still works nicely (for it's age). 435 RWHP was impressive for the time, and I trust that it's a nice drive.
Good luck and keep us posted either way,
Greg
I understand your concern about "loading" an A/W system. A valid point to be sure. You're right that it would be nearly impossible in an automotive scenario to "chill" an A/W system below ambient for any period of time. However, a properly designed and sized A/W does not thermo-load anymore than any other water radiator that is also properly dsigned and sized.
Old & New started down the road, I'm just continuing the drive, if you will...
Perhaps if you look at it like this, A/W will make more sense.
I believe we all know enough about thermodynamics to accept that water (or any liquid) will transfer more heat, faster than air (or any gas). Simple molecular density. If you doubt this, blow a 120F hairdryer at your hand. Then stick your hand in a 120F shower. Which one transferred more heat to your hand quicker?
That having been said, the goal of any intercooler ('aftercooler' if you're feeling pedantic) is to pull as much heat out of the intake charge as possible, while having the least impact on it's velocity and pressure.
The intake charge must flow over, or through, some sort of metal device. This metal device is the heatsink, it's function is to absorb the heat from the compressed air, then reject that heat to a cooler medium to move that heat elsewhere to be rejected again.
More heat is going to be rejected from the compressed air into a cooler surface than into a warmer surface. The latent heat (warmth) in the intercooler is a direct result of how quickly heat is transferred out of the same surface. So, it is way more effective to transfer the heat of the charge that has been shed into the intercooler body out of the intercooler with water.
Sure, but you've still got to get rid of the heat in the water, right?
True, true, true. But (this is the BIG but) you can do all sorts of things with the other end, the water to air heat exchanger, that you could never do with that same exchanger if you were trying to get the heat directly out of the charge. The radiator, shedding the heat from the water can have lots more passages, twists and turns. This allows the water greater contact time with the metal than is trying to dump heat into air. Velocity and presure losses become rather a moot point with the water - as long as the velocity is great enough to keep things moving, but not so great as to prevent adequate time to transfer the heat out, it's irrelevant.
The thing with trying to shed heat from a compressed charge directly into the atmoshere is that it takes a lot more time in contact with the metal to transfer the heat. This is because the ambient air is not able pull the heat out of the metal nearly as quickly as water is. So there is more latent heat in the device that's trying to pull heat out of the charge as quickly as possible.
In order to get the compressed charge in contact with the poorly heat transferring A/A long enough to move the heat, you nead a lot more contact time. Contact time = friction. Friction = more heat into the charge you're trying to cool, and lost velocity and pressure. Every time you call on air to change direction, you lose velocity - and one does a lot of direction changing plumbing an A/A intercooler. Frictional losses also cost precious velocity, as well as a great number of hardline to hose connections (required in most any non-OEM A/A setup) which also, will cost velocity.
But wait there's more. The charge, that has just been cooled off in an A/A, now has to work it's way back to the intake. More friction, more pressure loss, more chance to re-absorb ambient heat from the engine compartment.
The A/W can have it's intake heat removing plates ( or whatever) very close to the actual intake. The charge needs much less time in contact with the plates, because they absorb and reject heat faster. Because they can do this, they are designed much more efficiently. Transferring the heat to a large, slow moving rad up front and returning near-ambient water, can be accomplished with a coupla -12 AN (YMMV) hoses- a bit tidier on the engine compartment than a bunch of 3" silocone and aluminum tube. And far less able to pick up more ambient heat on the trip.
There still is the "extra parts" factor. Yup. But waterpump tech has advanced to the point where it's hardly an issue. But it's surely a point.
Race teams still use A/A? Yup. Sometimes it's rules restricting to a factory-esque A/A setup, but most often, it's like the Soviet Space program - it worked fine with minor tweeks for 40+ years, why change?
But, hey, ya gotta do what you are comfortable with. I have no desire to even try to talk somebody into something they will not be happy with later. Just depends on your priorities - efficiency or no moving parts?
Addendum: I would be inclined to focus even more on efficiency if I were doing a turbo setup. As I'm sure you know, turbos get really (red+) hot under any kind of sustained use, and put lots of additional heat into the intake equation. As a centrifugal blower, they are adiabatically very efficient, until they start glowing, then they aren't quite so great. Since the air isn't there very long, it's not terrible, but it adds some more degF to be removed just to get back to square one.
BTW- Like I said, don't get me wrong. The early stuff Reeves did was neat, and what I've driven still works nicely (for it's age). 435 RWHP was impressive for the time, and I trust that it's a nice drive.
Good luck and keep us posted either way,
Greg
03-11-2004, 05:20 AM
#32
Instructor
Join Date: Jan 2004
Location: Florida
Posts: 144
Likes: 0
Received 0 Likes
on
0 Posts
Originally posted by John..
Yes, but how often do you have the opportunity to add ice on say a 80 degree day on a 100+ mile trip. It can only offer below ambient if the water is below ambient.
For drag racing I would agree because ice can be added each time, but steady state all day performance I think my money would still be on the air to air.
Yes, but how often do you have the opportunity to add ice on say a 80 degree day on a 100+ mile trip. It can only offer below ambient if the water is below ambient.
For drag racing I would agree because ice can be added each time, but steady state all day performance I think my money would still be on the air to air.
Bob Norwood seems to prefer air-water.
Toyota MR2
Ferrari 308
Ferrari Testarossa
Kind of interesting that those twin Turbo Testarossa dyno charts show them making less power at 3,500 RPM or so and under than even a stock normally aspirated S4.
03-11-2004, 01:16 PM
#33
Three Wheelin'
Thread Starter
Join Date: Nov 2001
Location: Northern Kentucky
Posts: 1,446
Likes: 0
Received 0 Likes
on
0 Posts
Obviously rear engine Ferrari with air to air is a real chore. I have seen some photos of the Koenig F355 Twin turbo and it too has an air to water. Charge cooling air is probably really scarce on the TR that is for sure.
I still would prefer the air to air, but the temptation of the air to water still is there, mainly because of size and flow path to the throttle body. I simply can't deny these advantages and they may be enough to offset the complexity and less efficient transfer. Trust me, I know all about flow losses. If I showed you guys the 9 pipes to get the charges from my turbos to the intake you would be telling me it would never work. Fortunately it does, though I have not measured the pressure loss across the system.
I know I can make a clever air to water setup in place of the air cleaner that would have in integral storage tank, but this forces a cone style air cleaner and I don't particularly like those devices, but I can't deny they work. I have even considered a special airbox that will accept the stock 928 aircleaner, but mounted in a new location.
I have always liked the look of the stock 928 intake box and runners and at the onset of this project keeping that arrangement was part of the original goal.
Nonetheless, this has been a good thread with some informative information.
My goal is to come up with what will work best given the complexity and cost factors lumped into the equation.
I still would prefer the air to air, but the temptation of the air to water still is there, mainly because of size and flow path to the throttle body. I simply can't deny these advantages and they may be enough to offset the complexity and less efficient transfer. Trust me, I know all about flow losses. If I showed you guys the 9 pipes to get the charges from my turbos to the intake you would be telling me it would never work. Fortunately it does, though I have not measured the pressure loss across the system.
I know I can make a clever air to water setup in place of the air cleaner that would have in integral storage tank, but this forces a cone style air cleaner and I don't particularly like those devices, but I can't deny they work. I have even considered a special airbox that will accept the stock 928 aircleaner, but mounted in a new location.
I have always liked the look of the stock 928 intake box and runners and at the onset of this project keeping that arrangement was part of the original goal.
Nonetheless, this has been a good thread with some informative information.
My goal is to come up with what will work best given the complexity and cost factors lumped into the equation.
