Posted By: Johnsdart
downflow vs. crossflow radiators - 12/15/11 02:12 AM
Are there distinct differences between the two types of radiators as far as one style is more efficient cooling over the other ?
downflow vs. crossflow radiators
Posted By: rhad
Re: downflow vs. crossflow radiators - 12/15/11 04:46 AM
no!
Posted By: Magnum
Re: downflow vs. crossflow radiators - 12/15/11 06:06 AM
I have zero research backing up my theory but here it is.
Tall radiators like our Mopars have and big trucks have downflows to keep the tubes long.
Short and wide radiators would have extremely short tubes if they flowed downwards.
Tall radiators like our Mopars have and big trucks have downflows to keep the tubes long.
Short and wide radiators would have extremely short tubes if they flowed downwards.
Posted By: DaytonaTurbo
Re: downflow vs. crossflow radiators - 12/15/11 10:10 AM
I don't think you'll see any real-world difference in the types of rads you'll use in our old cars. I run a crossflow and like it just fine.
Posted By: astjp2
Re: downflow vs. crossflow radiators - 12/15/11 11:45 AM
Posted By: dogdays
Re: downflow vs. crossflow radiators - 12/15/11 03:28 PM
I read it and didn't see a single thing about downflow or crossflow. Did I miss anything?
In general if the radiator is a single pass heat exchanger it doesn't really matter what direction the tubes run. I believe that radiators had vertical tubes because they fit in the grilles better and could have the radiator cap at the top where it was most easily accessed. When Detroit went to the "longer, lower, wider" mentality the radiators became lower and wider to fit under the hoods, thus the crossflow radiator.
R.
In general if the radiator is a single pass heat exchanger it doesn't really matter what direction the tubes run. I believe that radiators had vertical tubes because they fit in the grilles better and could have the radiator cap at the top where it was most easily accessed. When Detroit went to the "longer, lower, wider" mentality the radiators became lower and wider to fit under the hoods, thus the crossflow radiator.
R.
Posted By: can.al
Re: downflow vs. crossflow radiators - 12/15/11 04:10 PM
..a cross flow will lose cooling from the top few rows unless you have a coolant recovery tank.
Posted By: Dean_Kuzluzski
Re: downflow vs. crossflow radiators - 12/16/11 01:00 AM
Given the same area of fins and capacity of tubes the difference is neglible. What will make a difference is the style of fins.
What makes a HUGE difference and why I'd never get another downflow if I had the choice is that the downflow tubes will plug up a whole lot sooner than a crossflow will. The crossflow will lose one or two tubes at a time. The downflow is losing whole areas where sludge is gathering.
My 6 year old Dodge Durango lost major cooling ability last summer. If you put your hand on the rad. fins it was obvious that several sections of tubes were cooler and limited. In the span of owning at least 3 crossflow style rads in off brand cars.....I've NEVER had to replace a radiator due to blockage in 20+ years.
What makes a HUGE difference and why I'd never get another downflow if I had the choice is that the downflow tubes will plug up a whole lot sooner than a crossflow will. The crossflow will lose one or two tubes at a time. The downflow is losing whole areas where sludge is gathering.
My 6 year old Dodge Durango lost major cooling ability last summer. If you put your hand on the rad. fins it was obvious that several sections of tubes were cooler and limited. In the span of owning at least 3 crossflow style rads in off brand cars.....I've NEVER had to replace a radiator due to blockage in 20+ years.
Posted By: 471Magnum
Re: downflow vs. crossflow radiators - 12/16/11 01:50 AM
Don't know if this has been mentioned or not, but cross flows are more prevalent these days due to lower hood lines. Just can't make a down flow work in these situations.
In a "square" package though, there should be little difference in cooling capacity all else being equal. You will lose cooling capacity with a cross flow without an expansion tank that will keep it full and coolant flowing through all rows.
In a "square" package though, there should be little difference in cooling capacity all else being equal. You will lose cooling capacity with a cross flow without an expansion tank that will keep it full and coolant flowing through all rows.
Posted By: Junky
Re: downflow vs. crossflow radiators - 12/16/11 05:45 PM
How about we throw a 26" stock steel downflow radiator out of a late 60's B body and a 26" after market aluminum crossflow radiator into the mix. Which one is superior...?
Posted By: Fury Fan
Re: downflow vs. crossflow radiators - 12/16/11 08:15 PM
If the area of the exchanger (and other factors, of course) is held equal, a greater quantity of short tubes will outcool a smaller qty of long tubes.
Cooling occurs due to the difference in temp between tubes and airflow, so you will achieve greater heat exchange thru teh 1st 1/2 of a tube compared to the 2nd 1/2.
Cooling occurs due to the difference in temp between tubes and airflow, so you will achieve greater heat exchange thru teh 1st 1/2 of a tube compared to the 2nd 1/2.
Posted By: Dean_Kuzluzski
Re: downflow vs. crossflow radiators - 12/16/11 08:27 PM
Quote:
How about we throw a 26" stock steel downflow radiator out of a late 60's B body and a 26" after market aluminum crossflow radiator into the mix. Which one is superior...?
The one that is aluminum has the advantage.
Posted By: Fury Fan
Re: downflow vs. crossflow radiators - 12/16/11 08:42 PM
Copper/brass have better coefficients for heat transfer, but tube & fin design/layout in a modern radiator can make up for decreased heat transfer of aluminum (compared to an 'old' radiator).
Posted By: Dean_Kuzluzski
Re: downflow vs. crossflow radiators - 12/16/11 08:58 PM
Quote:
Copper/brass have better coefficients for heat transfer, but tube & fin design/layout in a modern radiator can make up for decreased heat transfer of aluminum (compared to an 'old' radiator).
Soooooo, that most likely makes now, 2 advantages that the newer styled aluminum rad. has over a "stock" unit.
I'm still not convinced that a longer tube has less efficiency over shorter, but numerically more, tubes.
Posted By: Fury Fan
Re: downflow vs. crossflow radiators - 12/16/11 11:08 PM
Quote:
I'm still not convinced that a longer tube has less efficiency over shorter, but numerically more, tubes.
I’ve read it in Corky Bell’s book, I understood it, I think I can explain it.
I suspect that you understand that hte greater the temperature difference, the greater (faster) that heat transfer will occur. It is therefore a non-linear event – with a constant ambient temperature of say 80°, hot coffee will cool faster from 150° to 145° than it will cool from 105° to 100°.
So, consider 1 tube 26" long. I’ll call heat removal ‘X’. Ambient temperature is constant for the whole radiator, so the 2nd section tries to exchange heat with a temperature differential that is lower/closer to ambient, so the 2nd section will not be able to exchange the same heat as the top half, so it will be less than ‘X’. Let’s just say perhaps 1.5 X for the top half and X for the bottom.
Now consider 2 tubes 13” long, and with all other conditions the same, we’ll have 2 times 1.5 X of heat removal. Without a bunch of coefficients, flowrates, and calculations we don’t know the difference between all the X’s, but mathematically/logically we see it.
The same principle explains why adding additional cores/thickness does not increase cooling by the same amount as the core before it. The first row of core receives ambient airflow, but the row of core tubes behind it receives warmer ambient air, and therefore does not exchange as much heat as core #1.
So now you say ’sure, we’ve got more heat rejection from teh 2 short tubes compared to the long one, but logically the overall temperature is lower at the end of the long tube’ (and I agree with that). But as heat rejection and temperature drop aren’t the same thing (there is more energy lost from 150-145 than from 105-100) I would say that as time goes on, the longer tube system would normalize to a higher temperature than it started, and higher than the 2 short tubes.
If anyone can provide a better/correct explanation of this, I'll be glad to edit/delete my wrong info.
Posted By: MasterDeBaTeR !
Re: downflow vs. crossflow radiators - 12/16/11 11:13 PM
Any new rads I buy in the future wil be ...crossflow DUAL PASS ! 
Posted By: Junky
Re: downflow vs. crossflow radiators - 12/18/11 01:11 AM
This spring I'm going to replace the stock type 26" radiator with an aluminum (Griffin) crossflow. This thread has been very informative.
Posted By: terzmo
Re: downflow vs. crossflow radiators - 12/18/11 01:57 AM
crossflow cools better.....looks uglier but cools better
Posted By: cudaman1969
Re: downflow vs. crossflow radiators - 12/18/11 02:23 AM
Are we forgetting one thing that heated water will flow to the top faster in vertical tubes. So. the bottom has cooler water for the engine.
Posted By: Strawdawg
Re: downflow vs. crossflow radiators - 12/18/11 04:04 AM
Cross flow units have the advantage of having the radiator cap on the low pressure end of tubes so that a high volume water pump that builds additional pressure in the block (which is a good thing as it raises the boiling point in the block thus minimizing localized steam points) will not blow the seal on the radiator cap.
Further wide rectangular aluminum tubes provide better heat transfer because more surface area is exposed to the air flow as opposed to the oval tubes that must be used in copper/brass units in order to maintain strength. In these units the air flow tends to skip across the high points of the tubes instead of following the contour.
And, the obvious, the wider tubes don't plug up with precipitates/sludge as easily as do the small tubes and the radiator weighs less as a bonus.
Further wide rectangular aluminum tubes provide better heat transfer because more surface area is exposed to the air flow as opposed to the oval tubes that must be used in copper/brass units in order to maintain strength. In these units the air flow tends to skip across the high points of the tubes instead of following the contour.
And, the obvious, the wider tubes don't plug up with precipitates/sludge as easily as do the small tubes and the radiator weighs less as a bonus.