Radiator Confusion

[addo]

For about AUD$400, I have two options for my project.

1. A triple core radiator about 16" high, 20" wide, modded for the small outlet sizes. Slight trimming is needed to install it. Frontal area approx 320in².

2. A four core radiator about 16" high, 18" wide. Bolt in, frontal area approx 288in². This is 90% of the frontal area for Option 1.

Which will actually give the best cooling, if both are brass 14 fin-per-inch cores? Assume that throughflow is potentially equal on both. Manual tranny. The other curve ball is that I plan to fit aircon...

Thanks, Adam.

 

[CobraSix]

4 core. Even though it has less frontal area, it still has more cooling surface. It has approximately 33% more cooling area then a same sized 3 core. Now take into account the 10% drop in frontal area, you're looking at about a 15% increase in cooling area versus the larger 3 row.

Remember, it's all bout surfance area. basically, the cores are like rectangles (not circles). Say each rectangle has a length of 5, and the total width can only be 12 (that is governed by the total width of the radiator). use what ever units you want. calculate the perimeter of the two systems. 3 core, means each rectangle has a width of about 4. so perimeter of one core is 4*2+5*2, so you get 18. 18*3, you get 54 as the perimeter.

Now do it for 4 row: each rectangle still has a length of 5, but now has a width of 3. What is the perimeter: 16. total perimeter: 16*4, you get 64. An increase of about 16%. for the same width. Even if you decrease the width of the 4 row by 10%, you still end up (without showing all the math this time) an increase of 10% perimeter, which translate to 10% more cooling surface from the cores when you multiple in a given height. Since the height for both is assumed the same, then they have been divided out of both equations since they will cancel out and make the math easier.

Unless size is the issue, the 3-row will probably be more then enough cooling. I run mine all die, and it can idle in 95*+ (F) temperatures and still barely get above 175* (I have a 180* thermostat, so basically, it doesn't get above that temp). no granted, i do not have AC, so that may change, but I can't imagine needing a 4 row.

See...xecute isn't the only one who can do math.

Slade

 

[addo]

I've not seen any kind of dissipation gradient per row/core, that's why I was/am confused. Your theory stands 100% if rejection from a row is not influenced by the one(s) placed before it, but is that "interference" relevant? If it is, then the AC compounds that...

Being a wagon, I can't just shove the battery in the rear and whack in a stonking great triple core crossflow jobbie. (Good old Aussie fix.)

Adam.

 

[CobraSix]

You are right...the middle rows are not as effective, but that is one of the reasons you have the fins. The fins help distribute the heat from the parts of the cores that do not get nice flow.

Slade

 

[Anonymous]

You mention the 4 core filling up 90% of the area. You may want to place seals/baffles around the edge of the radiator so all air flow is directed through the radiator. This will help especially at idle.
Doug

 

[addo]

Doug, the 4 row fills up the original aperture. The wider three row would be cut in (that old-time mod; '68 302 radiator with smaller hose fittings).

I surfed around and found some interesting comments. From SEMA:

Stewart Components says, "We recommend using the largest radiator (as measured in square inch area) that will fit in your vehicle. Thicker radiators (cores) are better than thin radiators, but thickness is no substitute for surface area. The following comparison is commonly accepted: If the surface area is doubled, the potential thermal dissipation is doubled. If the thickness is doubled, heat dissipation increases approximately 25 percent."

From Eng-Tips (I know Whittey likes this bunch; they have experts on everything):

3 core copper/brass cooled well at speed, not well at idle

4 core copper/brass cooled better at idle, but worse at speed than the 3 core

Single (1.25") core aluminum, cooled OK at speed and not well at idle

2 core (1.25"X 2) aluminum cooled extremely well at speed, and a bit better at idle than the single core.

I would rate them this way:

At speed from best to worst 1. two core aluminum 2. 3 core copper/brass 3. tie between single core aluminum and 4 core copper/brass

At idle from best to worst 1. 4 core copper/brass 2. tie between 2 core aluminum and 3 core copper/brass 3. Single core aluminum

and:

In general, you can expect to see very little, if any, performance gain under vehicle operating conditions by adding the 4th row. The reason is that the cooling air has already almost reached its maximum temperature by the end of row 3, & there is then very little 'temp driving force' left for row 4...

Actually, there's "bulk" good info in that thread (including discussions on corrosion control), but it generates more questions than it answers! Also makes me very grateful for a mild climate. Some of the thermal and salt-related issues in that thread are frightening.

Cheers, Adam.

 

[Anonymous]

OK so assume you have 3 row 16 x 18 as the base option at 288 sq in. Going to a 16 x 20 represents an increase of 11%. And if the rule of thumb is correct and you get 25% more cooling with the fourth row, then it should perform like a 1.25 x 288 sq in = 360 sq in. Sounds like the 4 row may still be what you need. Your info also said the 4 row performed better at idle. So if you add on an air conditioner, you may need the better performance at idle which is typically where an A/C will contribute to cooling problems. Two other considerations would be that with 4 rows, there is more tube surface and the fouling of the tubes should take longer relative to a 3 row. Also the 4 row should be able to flow more fluid. Theoretically the reduced pressure drop would allow the coolant to flow a bit faster which aids heat transfer. (this would likely be of slight benefit in this application)

 

[Anonymous]

Even if the 3-core and 4-core radiators had the same cooling, if the 4-core will bolt in without trimming, I would go with it. It's safe to assume the 4-core cools at least as well as the 3-core.

 

[Lazy JW]

Without taking the time to do the math it seems that the four row will also hold more VOLUME which is a good thing too. And not needing to cut the opening out would settle the matter for me.
Joe

 

[rickwrench]

I hacked. Still looks great.
Rick(wrench)
I like to chop things up and put them back together a little different.

 

[Anonymous]

Speaking from experience with stationary engines (like generators and big industrial engines mounted to backs of big trucks, used in standstill operations), the thicker radiators are better in idle-to-slow-speed situations. One intersting thing we learned about this: if a 3-row radiator of a given thickness (say, 3" deep) is replaced by a 4-row radiator of similar size, but the same (3") thickness, there is NO CHANGE in the cooling in the stationary engines. However, as the engine ages and corrosion sets in, the 4-row units cool better for longer time, as measured in years.

My experience with my 2-row (old and new) Fairmont: I installed a 3-row that had 8 sq. in. less surface area, but was 3/4" deeper for the 3rd row. My idle temps (hot summer) are a little lower (like 10 degrees less), and it cools off better at low speeds (like 5-10 MPH) - which Denver has more than high speeds In the winter, though, it overcools severly with the 3-row: I have over 50% of it blocked off from September thru May.

Of course, Colorado only has 2 seasons - winter and the 4th of July.