It should come as no surprise to anyone that a high-performance Corvette engine produces heat — and a bunch of it. Today on our blog, we look back at a two-part article that appeared in the November and December 2018 issue of Vette Vues Magazine titled “High-Performance Radiators Are Not Created Equal.” You can read Part 2 Here.
Wayne Scraba shares some great technical information. Photos are courtesy and copyright of Wayne and DeWitts Radiator.
BOILING POINT – PART 1
It should come as no surprise to anyone that a high-performance Corvette engine produces heat — and a bunch of it. We’ve mentioned this before, but approximately one-half of the total heat energy produced by your Vette’s engine is transferred back to the cooling system. In a Corvette, the heat energy moves into the radiator and is then “radiated” back into the atmosphere. Taking this one step further, the liquid cooling system very simple. As the coolant (to keep things simple, let’s use plain water as an example) temperature approaches 212 degrees F, air pressure begins to build. Since the radiator is closed (with a cap), the pressure is allowed to build from within without any opportunity to “escape.” This air pressure actually expands, which in turn allows the water to reach a temperature higher than 212 degrees F before boiling. As the air pressure increases, so does the boiling point of the water. Basically, this is an efficient system that works well. Still, if the coolant temperature continues to increase (without leveling off), then the internal pressure will be too great for the radiator cap to handle. What happens next is pretty simple. Your Vette boils over.
The truth is the radiator in such a system is a huge tank that allows large amounts of hot coolant to come in contact with equally large amounts of cool air. The coolant is first forced into the radiator side tank (upper tank if you’re thinking of the old fashioned non-cross flow system). From this point, the coolant makes its way through rows of very small copper or aluminum tubes, finally returning to the adjoining side tank where it is returned to the engine. While the coolant passes through the tiny tubes, it is cooled by air flowing over and alongside the tubes. The primary purpose of the “fins” contained within the core (and surrounding the little tubes) is to direct airflow into the proper area of the radiator; however, there are secondary reasons for the fins, as you’ll soon see. FYI, the most common core construction is the tube-fin or the ribbon-cellular design.
Fin count plays an important role in cooling. As a rule of thumb, a radiator will normally have between eight and fourteen fins per inch. When the fin count number increases, the radiator can “radiate” more heat to both the surface airflow and the surrounding air.
What is the best type of Radiator? Copper? Aluminum?
When it comes to rad construction material, what’s the better choice for your Corvette — copper or aluminum? That’s a good question. Most recently, Detroit has embraced aluminum as the radiator material of choice. There’s a reason for this, aside from considerable vehicle mass reduction (aluminum radiators, on average, can be as much as 1/3 lighter than an equivalent copper-brass radiator). And that’s cooling capability.
Certainly, the choice of copper is a good one for radiators. It has better heat-dissipating properties than aluminum. But according to DeWitts Radiators, there are a couple of caveats: For example, the primary source of cooling in any radiator is the tubes. Heat dissipates from the coolant through the tube walls. This heat is then transferred to the fins that are in contact with the tubes. In turn, this provides a secondary source of cooling. As air passes through the fins, the heat is carried away. Radiator manufacturers know that wider tubes are more efficient because there is more “tube to fin” contact (in a typical modern aluminum radiator, the “tube-to fin” contact surface area is increased by 20% over an identically sized copper/brass unit – part of this is due to the fact the fins are both wider and closer together with a shorter fin height than a copper radiator). That improved tube-to-fin contact is what removes heat.
But that’s not the end of it. DeWitts also points out that while copper has better thermal conductive properties than aluminum, older copper radiators are made up of (4) four different materials, not just copper. The copper tubes are bonded to the fin with solder (lead), which has very (Very) poor heat transfer properties. The tanks are made of brass, and the side channels are steel.
Something you should keep in mind is today’s radiator business is extremely competitive. There are many elaborate words used to describe the technology, and unfortunately, some of it is misleading. More on this below:
People often ask DeWitts if they can build a radiator with 1-1/4-inch tubes? The answer is yes. Every model they build is available with 1-¼-inch tubes, and this option adds approximately 10% additional cooling. With that said, maybe a better question is, “do I need to get 1-1/4-inch tubes”? DeWitts notes that a double row core with 1.0-inch tubes is equal to a five (5) row copper unit and almost double the heat rejection of a single row aluminum unit. So, in most cases, the larger tubes are not necessary.
Increasing tube size isn’t always possible with a copper-brass design because of tube wall thickness limitations. Today’s radiator technology (which typically uses wider tubes inside aluminum rads coupled with multi-louvered fins) has allowed the aluminum radiator to cool efficiently. Just as important, aluminum rads are now as strong, if not stronger, than their older copper-brass relatives.
So, can you build a copper radiator the exact same way DeWitts makes the aluminum models? Yes, and it would likely work better than aluminum. The downside is, it would also weigh roughly 90 pounds! Not exactly high-performance Corvette friendly, we’d say.
Today’s Technology of Radiators
With today’s technology, an aluminum radiator will simply cool better. Tests from various sources document a 28% increase in performance over a brass-copper equivalent, provided both radiators are identical in size. The reality is the use of aluminum in radiator construction can lower engine temperature by 30 degrees. Any vehicle will benefit from an aluminum radiator, and that includes your Vette.
Here’s where things become interesting: There’s a lot of misleading information out there with regard to radiator technology. Case-in-point: At least one company (and maybe more) has claimed they’ve come up with a “revolutionary advancement in cooling technology using” Extruded Cooling Tubes (ECT).” Unfortunately, it’s not that revolutionary, and it’s not even new because this technology has been around for many years. ECT has been popular in high-pressure oil systems and Charge Air Coolers (CAC) coolers for more than a decade. Here’s how it works: Extruded cooling tubes are made by heating and pressing aluminum material through special dies to create a custom shape. It is very difficult to form these tubes with thin wall thicknesses. Typical wall thickness on this type of cooling tube runs between 0.020-0.040-inch, which is thick for cooling. The heavy tube wall thickness and internal trusses provide the strength that can hold higher pressures.
But that’s not the end of it. According to DeWitts Radiators: “Roll form tubes (RFT) are the gold standard in automotive cooling. Today, every major auto supplier uses RFT because the thinner wall will transfer heat better and reduce unnecessary weight. The typical wall thickness range for RFT is 0.010-0.015-inch (obviously, much smaller than the 0.020-0.040-inch tubing mentioned above). This design will hold pressures as high as 45 psi without tube distortion, providing a pressure safety factor of 300% when pressurizing the cooling system to 15psi.”
One company is making a claim that their ECT technology offers “more than triple the burst pressure of any other performance aluminum radiator in the world!” DeWitts Radiator LLC, amongst others, has resisted the industry tread to use thinner tubes and fin to save money on material. According to DeWitts: “We have stayed with proven (0.013-inch [26mm]) and (0.015-inch [32mm]) wall tubes when some companies are running 0.003-inch thinner material. We also continue with 0.005” fin material when others are using 0.003-0.004-inch fin. This may not sound like a big difference; however, our design will hold 60 psi without tube distortion and 100 psi without bursting.”
DeWitts adds: “Another misleading item is the “55mm Core with Twelve (12) 4mm Wide Tubes” feature. That statement is creative; however, they really only have one (1) tube that is 55mm wide. This tube is called a multi-port design with twelve 4mm paths for the coolant to flow. Due to the heavier tube wall thickness, the inside diameter is 25% smaller than a standard double row 26mm core.”
In comparison, a typical extruded cooling tube design will be heavier, run hotter, and have a higher pressure drop than a standard double row 26mm design radiator. The only clear difference of an ECT is the higher burst pressure. Since all automotive applications run in the 10-20 psi range, there is really no advantage and several disadvantages.
We’re done for this issue, but we’ll be back soon with more on high-performance aluminum radiators for your Corvette. We’ll look at double and triple pass radiators along with three-row rads along with “four core” radiators. Some of the findings might surprise you.
Radiator Photos and Information:
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