Hopefully I can get some input on this without too much of the inevitable "that won't work"

I'm cutting down a large tall radiator into a shorter one.. 1/3 the height to be exact. The 3 layers of radiator will be set up in a cross flow, sequentially. The hottest water will enter the rearmost later, travel across, then across again in the middle layer, and across yet again in the front layer. The idea is the hottest water gets the hottest air, and the coldest water gets the coldest air. This way delta T stays pretty constant.. I'm thinking of it as trying to heat the air as much as possible, which would cool the water as much as possible.

So I realize that cooling capacity will be reduced, as I will be dealing with 1/3 as much air. But then the cooling capacity must be more than 1/3, because it's 3 layers thick instead of 1. My question is what percentage of the original cooling capacity should I be expecting? Would it do me any good to do 5 layers instead of 3? (by adding 2/3 of a second radiator)

The original radiator cooled the same engine just fine, in a heavier car, with an AC condenser preheating the air. I will be running an electric pump, so I will have an advantage at idle.

I think by the time the air hits the 3rd layer, it's going to be too hot to cool anything and be pretty much useless....

When I worked on multiple heat exchangers, you'd always plumb in parallel...
You may try to plumb one, record temps and keep adding...Sometimes the best calculations did not match actuals.

Ask Seanery, he knows all about heat transfer.




M

So you are not in a hurry to finish your car and drive it huh? I would just pick up a Renegade setup and be done with it. But, thats just me.

"that won't work"

i think you're going to have a hard time getting any air through any layers...

you -can- heat up the air really hot by the simple expedient of reducing the airflow, but the object of the game is not to heat the air, it is to cool the water. hotter air does not equate to cooler water. (IOW - you are not as much interested in reducing temperature as rejecting heat. ( where heat == temp * mass ).

i understand your logic on the sequence, but i still think it is backward -- coolers are most efficient at higher delta-T. (still, i see in my mind a conventional coiled-tube lab distillery and we always plumbed those with the coldest inlet water at the exit - but that was not about efficiency, it was about achieving the lowest possible temperature - not the same thing...)

QUOTE

I will be running an electric pump, so I will have an advantage at idle.

will you also be running BIG electric fans to move some air?

QUOTE

So I realize that cooling capacity will be reduced, as I will be dealing with 1/3 as much air.

not just 1/3 as much air, 1/3 as much surface area exposed to the ambient temp freeestream air. i doubt that's a simple multiple (1/3 * 1/3 == 1/9) but i'm thinking it's on that order.

probably this technique has been documented in the HVAC and thermodynamics texts, none of which i have, but it is described in several references i do have on race car and aircraft plumbing, usually on the "don't" page of "do's and don'ts" ...

if you're determined to build such a thing, and if i were you i wouldn't count on my armchair analysis as a gospel, i'd put temperature sensors in front of each layer and behind the last, and in the water stream before and after each layer. and then test it.

i think that if reducing the frontal surface area is really your design goal, you would be better served finding one deep cooler than stacking multiple layers. but i'd take this as a hint: i have never seen any really deep coolers ...

just MHO, since you ask ...

QUOTE (Mueller @ Feb 2 2005, 12:10 AM)

I think by the time the air hits the 3rd layer, it's going to be too hot to cool anything and be pretty much useless....

The third layer gets the hottest water so the air that hits it will have to be cooler than the water going through it. BUT, it may not be enough cooler to do much good.

The reason I've come up with this idea is because of the tidbits I've managed to squeeze out of Scott (Renegade) regarding WHY 914 V8s have trouble staying cool. He says the water doesn't spend enough time in the radiator to lose heat. Thus my idea of the multipass design. I have since heard that Renegade's radiator is a multipass design (not 100% sure on this, I just read it here somewhere).

I will have big fans moving the air. They will be at the outlets instead of on the radiator.

If it doesn't work, it would be very easy to flip the whole thing over and do it the other way.. hottest water in the front. That would give a very good delta T for the first layer, but by the third layer the air may be as hot as the water.

The other option is to just run all 3 cores parallel in a conventional 3 core setup. The radiator construction would be easier, but I'm not sure it would be more effective.

As far as just buying Renegade's radiator, there's no way I'm spending $1000 on a radiator. I'm much to big of a CSOB for that

Hi
I recently replaced my custom 6 core radiator with a "Howe Racing" aluminum 2 core. My
car now runs aprox. 10 degrees cooler. Don't know if it was the change to 2 cores or the change to aluminum, but she does run cooler. I have also had good results with a Howe in my Monster Miata. In the 914 I am using a 16x27.5 (no fill-chevy) which cost
$190.
Bob

Rate of water flow thru a radiator is very important. On our water cooled race cars we used a 4 row crossflow aluminum radiator. To slow the water down, we used blanking sleeves in place of a thermostat. The one we ran was a plate with a 1/4" hole in it.

We also experimented with different ratio pulleys to slow the water pump speed down and found this to be the best solution.

That said, we were operating within a specific RPM range on the track (5500 to 8500 RPM). The only time the engine RPM was below 5500 was in the paddock.

I am not a thermodynamic engineer, nor a true HVAC person (spent a lot of time in that industry though). I have never seen heat exchangers plumbed in series...especially a fluid to air heat transfer. I do know that the effeciency is a relationship between the rate of fluid flow, material of heat exchanger construction and the surface area of the fins attached to the liquib bearing tube....break the bond between the fins/tube and effeciency immediately starts dropping radically.

Oh well, it's to early to make any sense

QUOTE (v82go @ Feb 2 2005, 08:50 AM)

Hi I recently replaced my custom 6 core radiator with a "Howe Racing" aluminum 2 core. My car now runs aprox. 10 degrees cooler. Don't know if it was the change to 2 cores or the change to aluminum, but she does run cooler. I have also had good results with a Howe in my Monster Miata. In the 914 I am using a 16x27.5 (no fill-chevy) which cost $190. Bob

Aluminum makes a big difference. The one I'm working on is aluminum, in case anyone was wondering.

I find this to be some interesting stuff and when it comes to 914 V8 conversions there's not a lot of real engineering available on what's an optimum cooling system design. I wish my co-worker mechanical engineer (PhD, specializing in thermal and numerous patents in cooling electronics packaging) was interested but he's not into cars.

I think that for a given engine and radiator setup there is an optimum coolant flow for the system, and this is independent of the power output of the engine. In other words, the flow rate should remain fairly constant and if the engine is dumping more heat into the coolant, then there should be a corresponding increase in the heat loss at the radiator (more air flow). There must be a rate of max. efficiency, if plotted it would peak out at some particular flow rate. Too low (or zero) obviously things would overheat. Increase the flow too much and the same thing happens. Would be interesting to attach a few thermocouples in a system and play around with this.

This is where an electric pump has an advantage as it can keep a constant flow independent of engine RPM and power output. Or its flow can be varied easily according to conditions. I've been very pleased with how mine is performing and I think I basically lucked-out finding a well-matched system. But I would like to understand it better as to why it works so well.

QUOTE (v82go @ Feb 2 2005, 07:50 AM)

Hi I recently replaced my custom 6 core radiator with a "Howe Racing" aluminum 2 core. My car now runs aprox. 10 degrees cooler. Don't know if it was the change to 2 cores or the change to aluminum, but she does run cooler. I have also had good results with a Howe in my Monster Miata. In the 914 I am using a 16x27.5 (no fill-chevy) which cost $190. Bob

Bob,

I have the same size AFCO Racing dual pass radiator. Is your's a single pass? Also, what size hoses did you run for the high and low sides?

andy

Ah, a topic dear to my heart, and a little within my realm of expertese.

Using counterflow you can get better heat transfer, and that is a good thing. However, by reducing your airflow down to 1/3 of the original design, your cooling will be reduced down to about 1/3 as well. You may be lucky and only lose 50% but I doubt you could get that lucky. Adding counterflow layers is an incremental effect, but having lots of airflow is crucial. The main thing here is that the heat is being dumped into the air. To reduce the airflow by two thirds would require a temperature rise three times greater, and that will not happen in your design. Sorry. It is difficult if not impossible to cheap out on the rad AND the hoses connecting it to the engine. You have to have the correct combination of airflow and waterflow.

Remember that the greater the waterflow, the greater the HP required for the pump, and that reduces the rear wheel HP. The HP used by the pump is transferred as heat to the water coolant, and that adds to the load on the rad. However, if the waterflow is too small, the engine will overheat because the circulation cannot take it away as fast as it is produced. If you want the engine to live, then you have to determine the heat dumped into the coolant by the engine under full load. Then the pump has to move that heat ( so much GPM times deltaT). Finally the rad and airflow must transfer that same amount of heat to the air. It is not trivial.

Ok, it looks like I'm looking at a couple different types of multipass radiator..

Correct me if I'm wrong..

The "typical" multipass radiator has everything in the same layer, but it divides the flow into top and bottom, so it flows one way across the top, and comes back across the bottom.

My idea has layers behind each other, which would obviously be less effective than the top/botom method, but would offer more cooling per frontal square inch.

I need to think more about this and maybe do some testing.

all this talk about water flow, air temp rise, delta what ever is great but i did it the easy way .... i am using a stock radiator that suby uses with the 2.5 engine. that way i know its is designed right by suby!

minor high jack
the radiator frame is welded up it goes in to the car today, tommarrow is shrouds and reinstall engine. then fun fun stuff starts, hooking up obd 2 wiring

high jack over

QUOTE (bondo @ Feb 2 2005, 12:34 PM)

My idea has layers behind each other, which ... would offer more cooling per frontal square inch.

"could," i think ...

and yes, multipass heat exchangers change directions in vertical (typically? exclusively?) zones. (almost?) exclusively hot water enters at the bottom and cooled water is extracted from the top. this allows the flow to work with convection and promotes the coalescing of air bubbles at the top rather than remaining trapped in the moving fluid.

testing is good...

i'm with Mike, i think you'll find the cooling will be no better, and possibly worse, with 3 layers rather than two. i think you'll gain more from increased airflow with 2 layers than you may lose from another incremental pass due to the preheat effect.

air is lazy, and at speed, will be happy to bypass the radiator core and go right over the car if internal restsrictions are too high. you can't blow air into a closed box. it's also more efficient to push air than pull it, and one problem with using extraction fans is that without really good sealed ducting, the air would much rather go around the core than through it. tends to preheat the fans too, although there are enough of them in service that the environment doesn't seem to adversely affect their life. (and it does have the plus that it does not shadow the core from incoming freestgream air...)

QUOTE (ArtechnikA @ Feb 2 2005, 10:56 AM)

QUOTE (bondo @ Feb 2 2005, 12:34 PM) My idea has layers behind each other, which ... would offer more cooling per frontal square inch. "could," i think ... and yes, multipass heat exchangers change directions in vertical (typically? exclusively?) zones. (almost?) exclusively hot water enters at the bottom and cooled water is extracted from the top. this allows the flow to work with convection and promotes the coalescing of air bubbles at the top rather than remaining trapped in the moving fluid. testing is good... i'm with Mike, i think you'll find the cooling will be no better, and possibly worse, with 3 layers rather than two. i think you'll gain more from increased airflow with 2 layers than you may lose from another incremental pass due to the preheat effect. air is lazy, and at speed, will be happy to bypass the radiator core and go right over the car if internal restsrictions are too high. you can't blow air into a closed box. it's also more efficient to push air than pull it, and one problem with using extraction fans is that without really good sealed ducting, the air would much rather go around the core than through it. tends to preheat the fans too, although there are enough of them in service that the environment doesn't seem to adversely affect their life. (and it does have the plus that it does not shadow the core from incoming freestgream air...)

Good point. I was thinking about it from a standpoint of: for every square inch of radiator, there is some peprcentage of open space for air to flow. Say that percentage is 50%.. So I was thinking of it like 3 plates with a 50% sized hole in them, would have roughly the same airflow as 1 plate with a hole that size. I didn't think about the turbulence and such of all those little fins. I was thinking about this from the standpoint of "more can't possibly hurt", but that only works up to the point where the additional restriction of airflow outweighs the increase in surface area.

Man, this is getting deep

QUOTE (bondo @ Feb 2 2005, 01:03 PM)

Man, this is getting deep

welcome to engineering...

the essence of engineering is one word: "enough." how much strength is enough? how much cooling is enough? how much power is enough?

like Dave said -- how much cooling is enough? it's enough when your worst-case combination of power output (usually high) and airflow (sometimes but not always low) creates a temperature no higher than the most sensitive component (often, the boiling point of the coolant at operating pressure) can take.

you can make some reasonable assumptions on some things (engine efficiency i.e. - how much waste heat is produced per HP) but sometimes the variable interact in unexpected ways (like a cooling system airflow restriction that works perfectly well at 60 mph but stalls at 80) and then, God help us, there are the nonlinearities ... where 2X of one thing gives you (or requires) 4X, or X**4, of something else...

we're not trying to poke holes in your design for the fun of it - there are innovations made every day.

we are trying to help you think through the design issues so your car can be (close to) working right, right out of the box.

Thanks for all the info and suggestions.. what a great group!

While I'm thinking about it, Scott had mentioned the other problem with cooling was thermostat delay/runaway. Apparently by the time the termostat opens, and the hot water runs up to the radiator, cools, and comes back to the engine, it can already be too late.

My idea to solve this problem (and the problem of firewall interference) is to place the entire LT1 water pump assembly in the front trunk, with an electric conversion on it. For those unfamiliar with the LT1 water pump, it has a 2 part thermostat valve. A typical thermostat blocks the cooling water, with a small bypass for the heater. The LT1 thermostat is mounted on the water pump and continiuously circulates the water throulgh the engine. Once it gets warm the thermostat opens and it adds the radiator to the loop. The way I plan to set it up will have water continuously flowing to the front of the car and back.

Question 1. Am I correct in thinking that the return hose (from the thermostat to the engine) should be as small as practical so the cool water gets to the engine quickly?

Question 2. Where should I put the reservior/filler? I'm thinking it should be on the cool side of the radiator, so it can store a quantity of cooler water that will be immediately available when the thermostat opens. There are basically 6 choices. Either end of the radiator, just before or after the thermostat/pump, or just before or after the engine.

I'm just full of crazy ideas! The fun part is that if my cooling system doesn't work, i won't have the foggiest idea which part isn't right... hooray for too many variables!

QUOTE (bondo @ Feb 2 2005, 02:22 PM)

Apparently by the time the termostat opens, and the hot water runs up to the radiator, cools, and comes back to the engine, it can already be too late. My idea to solve this problem (and the problem of firewall interference) is to place the entire LT1 water pump assembly in the front trunk

seems to me that when the thermostat opens sending hot water to the radiator, it is also opening the path that admits the ambient-temp water in the radiator and lines from the radiator to the engine. that oughtta produce an immediate cooling effect ...

but i am way outta my depth dealing with water-cooled plumbing issues ...
(however, that's the way it works with oil coolers with thermostats in the circuit...)

i do not like the idea of trying to suck a fluid. how many high-mounted water pumps do you see? you get one good bubble in there - steam pocket, leftover from filling, slosh from bumpy road, whatever - and you (theoretically at least) run the risk of cavitation and loss of prime.

also - pulling a vacuum on a liquid depresses its boiling point, but pressurising it by pushing it increases it.

maybe modern electric-drive water pumps handle all this stuff in stride nowadays.
but it would scare me ...

The pump will be mounted at the bottom of the front trunk, lower than its stock location, but probably about the same height as the belt driven pumps used on most conversions.

I agree about the ambient temp water from the radiator.. I was just thinking that since I need to add a reservior anyways, I might as well put it where it can assist that effect.

QUOTE (bondo @ Feb 2 2005, 02:43 PM)

The pump will be mounted at the bottom of the front trunk, lower than its stock location, but probably about the same height as the belt driven pumps used on most conversions.

it's still 10 feet of hose away from the engine.

i'd be concerned about (for instance) parking on a hill. but as i said - this is an area i don't claim to know much about. if it's not a problem, i'm not trying to make it one...

QUOTE (ArtechnikA @ Feb 2 2005, 12:47 PM)

QUOTE (bondo @ Feb 2 2005, 02:43 PM) The pump will be mounted at the bottom of the front trunk, lower than its stock location, but probably about the same height as the belt driven pumps used on most conversions. it's still 10 feet of hose away from the engine. i'd be concerned about (for instance) parking on a hill. but as i said - this is an area i don't claim to know much about. if it's not a problem, i'm not trying to make it one...

Hmm, hill. More variables I haven't though of. I think I'm getting to the "gotta try it and see" phase.

Just for fun, a couple of more variables to play with.....

1. Any bend in the piping system will create a resistance to flow and lower the gph capability of your pump.

2. The material you use for piping will have an effect on flow (frictional resistance).

Plumb it like a Fiat X1/9 with two copper pipes running under the car (they're placed there after the original thru body pipes rust out). Then we can bash you for being Vino oriented rather than rice oriented.

Another attribute that Scott discussed with me that seems to point to thinner cores is the fact that the heated air expands requiring more space to flow through. This is a real problem on 6 core rads, the flow is limited to the amount of expanded air that can fit through the last pass. It seems that cores that increase in area as you move farther back in the flow could help, but I have never heard of this being done. This concept is fairly new in car design, all my old trucks had 4 pass rads, but any of my recent cars or trucks have had only 2, at the most. Each of the new car rads that I've looked at have fairly large surface areas, so this trend may be a function of that.

Just more possible stuff to consider...
Eric
PS. The only thing that I could complain about my RH setup, is that it may cool too well. I guess it could be worse...

QUOTE (SLITS @ Feb 2 2005, 01:15 PM)

Just for fun, a couple of more variables to play with..... 1. Any bend in the piping system will create a resistance to flow and lower the gph capability of your pump. 2. The material you use for piping will have an effect on flow (frictional resistance). Plumb it like a Fiat X1/9 with two copper pipes running under the car (they're placed there after the original thru body pipes rust out). Then we can bash you for being Vino oriented rather than rice oriented.

Hmm.. ok, bends are bad, rough is bad. Good to know.

QUOTE (ewdysar @ Feb 2 2005, 01:19 PM)

Another attribute that Scott discussed with me that seems to point to thinner cores is the fact that the heated air expands requiring more space to flow through. This is a real problem on 6 core rads, the flow is limited to the amount of expanded air that can fit through the last pass. It seems that cores that increase in area as you move farther back in the flow could help, but I have never heard of this being done. This concpet is fairly new in car design, all my old trucks had 4 pass rads, but any of my recent cars or trucks have had only 2, at the most. Each of the new car rads that I've looked at have fairly large surface areas, so this trend may be a function of that. Just more possible stuff to consider... Eric PS. The only thing that I could complain about my RH setup, is that it may cool to well. I guess it could be worse...

Interesting.. My mustang has a 3 row radiator, and each row is about 1/2" deep. This radiator I'm hacking up for experimentation has a single row that's more like 1.25". I wonder if that's why.

Thanks to all this discussion I have some new ideas to try, if there's room.

QUOTE (bondo @ Feb 2 2005, 12:43 PM)

The pump will be mounted at the bottom of the front trunk

The best location for the water pump is low in the engine compartment. My electric pump is mounted on the engine mount bar. The reason for this is when you accelerate forward the water naturally pressurizes toward the rear and that assists the pump when you need it most. Having it at the lowest point in the system also helps somewhat, obviously, as compared to up high where air pockets could reside.

On my application I use aluminum condit instead of rubber hose under my car. I think this should also help get rid of alittle heat.

CONDUIT (yes I can't spell)

Bob,
The conduit looks good. Hell of a lot easier to work with than the steel pipe I used.

Nice, where do you get aluminum conduit? The stuff I've used (for electrical wiring) is all galvanized steel or PVC. Aluminum would be ideal.

Check with any electrical supply place. They also can supply you with long radius 90's.
The conduit also welds very nice.

v82go the fan and shroud look like they are from one of the first orginal Renegade brass and copper radiator setups. I also see a ac drier.
Does the car have AC? Also is this the car that was for sale in Orlando a couple of years ago. Looked real nice from the pictures.


Bob

Whenever I need to design something unusual I turn to... garage floor engineering!

Here's the latest idea... semi-paralell, semi series. Solves the air expansion problem as the rear layer has twice the area of the front layer. This still may not work, but I think it has a better chance.

Good thinking on the aluminum coduit v82go, definitely some added cooling vs rubber lines. Did you run the aluminum tubing all the way to the engine compartment? Which route, down the rockers?

Bondo I've seen and ridden in 2 914's that had junkyard radiators from a corvette and both of these cars ran cool in the heat of the summer. I really don't see a need for anything special.
I think the main thing is to have a expansion tank that will bleed the air from the system. If you look at the pictures of BOXSTR new yellow V8 914 you can see how it needs to be plumbed up with a larger hose from the bottom of the expansion tank to the low pressure side of the radiator(feed to the water pump) and then a feed line from the high pressure side(hot water from engine) of the radiator to a point about 1" from the top of the expansion tank.
This will bleed all of the air pockets from the system. On my V8 car all I do is put water in and bleed the air from the top of the radiator and drive.
If you look at most of the new cars this is the way they are plumbed. Here is a picture of the expansion tank I'm using on my new V8 car

Here is Boxstr new yellow 914 this is what I was trying to explain.

Bob

You guys are all wrong, the 914 is AIRCOOLED!!!



okay, back to your real conversation. I'll chime in after MAE 91 - intro to thermodynamics (should be next spring)

QUOTE (MattR @ Feb 2 2005, 06:56 PM)

You guys are all wrong, the 914 is AIRCOOLED!!!

Still is! Just moved the main heat transfer up to the front of the car

Here are some pics of my setup during the build. Here is how I built my system for under $200 (excluding pump).
84-89 corvette stock radiator, fan and shroud $125 (Used)
JC Whitney thermo switch: $25
copper pipe and such: $30
1 inch truck heater hose and alot of clamps: $15

The corvette is a bottom breather, as are the 914 V8 cars. The airflow should be about the same. I have a 305ci engine. Should run the same temp as a 350. The vette radiator is the shortest radiator for a v8 I could find.

I have put about 12000 miles on the car in a year and a half. It runs at 180 all day, even in traffic on a hot 90-100 degree day. The only time it gets over 180 is when the RPMS are sustained over 3300 for more than 15-20 minutes, then it can run 200-210. It has never exceeded 210. Now,with the money I saved from buying the Renegade radiator I had the trans regeared. With the new gearing, the revs rarely see over 3000 for more than 20 minutes.

Mark

Here is another, I have cutout the wheelwells since this stage.

Here are the hardlines under the car when I was test fitting them. Its good to have some bends so that when the pipes are attached, they do not twist. I hope this helps.
Mark

QUOTE (bondo @ Feb 2 2005, 12:22 PM)

Interesting.. My mustang has a 3 row radiator, and each row is about 1/2" deep. This radiator I'm hacking up for experimentation has a single row that's more like 1.25". I wonder if that's why.

simply the reason why the old radiator is 1.25 for a single row, is simple. look at it this way radiating the heat to the air is a surface area thing. the larger the fins the more heat each tube can give out. the more tubes the less the area of the fins. now in a modern radiator there are many tubes with less fin depth, but i would think that the tube surface area ( water side ) ratio to the fin surface area ( air side ) to the over all size works out to about the same for every maker, to engine size. with a modern radiator they have had years to figure the best cheapest stongest way to make the radiator.

With all this talk about too much flow of coolant there is something I don't understand.
Why is a cooling system less efficient when it has a smaller delta t with a larger flow of fluid, vs higher delta t with a smaller flow.
The total heat exchanged should be the same.
More water at slightly different temp or less water at large temp change?

I have an early renegade cooling system and they used a "lay down" set up, kinda like the early Corvettes.
I have noticed that two of the corners of the rad are hotter to the touch than the other corners. It is an old radiator and I suspect less water flow in the hot spots.
Any ideas?

George

Well there are two deltaTs. One is water to air, the other is engine to water. If you move a lot of water through the radiator but don't cool it as much, you may get the same amout of heat transferred to the air. But then that larger quantity of water is still pretty warm and can't take much more heat from the engine.. so the engine gets hotter and hotter until the deltaT is enough to reach a new equilibrium. If that point is above the boiling point of the coolant, you're in trouble

As far as the cooler corners of the radiator goes, it could be obstructions in the tubes, or just the way the radiator design works with the rest of the cooling system.