The debate will rage on, which...
The debate will rage on, which is better,a single-pass radiator or a double-pass radiator?
Tech Editor John Gibson told me the story of how he was recently at a track in Georgia watching a Street Stock race. During the feature he noticed that several cars would come in under every caution and shoot the radiator with water to cool the engine. Then they would return to the track but wouldn't be able to get their track position back. He said he thought to himself, If these guys had the right radiator and fan they wouldn't have to lose valuable time and positions just trying to keep their engines cool.
In talking with one of these hose-happy Street Stockers after the race, he said that his reasoning for his low-buck radiator was exactly that . . . cost savings. The racer was under the impression that he couldn't afford a "fancy" radiator for his bomber. He didn't recognize the fact that a cracked head thanks to an overheating problem would cost way more than even the nicest double-pass radiator.
John's experience told us that it was time to revisit some critical cooling technology.
So without further ado, let's begin.
This is a worst case scenario....
This is a worst case scenario. There is significant fin damage, the housing is bent and it's highly likely that the tubes and cores have suffered severe damage. This radiator needs to be replaced.
Also known as heat exchange, thermal transfer is the very core of a radiator's function (pun intended). Obviously, radiators are designed to protect your engine from overheating by transfering that thermal energy away from fluid that circulates through the engine via the water jacket-a series of passageways cast into the block. As the fluid passes through the hot engine it absorbs the heat, thereby cooling the engine. Once the fluid leaves the engine, it passes through the radiator which is nothing more than a heat exchanger that transfers the heat from the fluid to the air blowing through the radiator.
That thermal transfer is the key to how the radiator functions, but it can only happen when the fluid is in direct contact with the aluminum of the radiator. Manufacturers achieve maximum thermal transfer through several design methods, one major one being by increasing the surface area of the tubing that carries the fluid through the radiator. Typically these tubes are very wide from front to back and slim from top to bottom. Dozens of these thin tubes can be stacked on top of one another leaving small air gaps between them.
Manufacturers will also make the wall of these tubes extremely thin which further increases thermal transfer. Think of it this way: Heat has to pass through the wall of these aluminum tubes away from the water or coolant. The thinner the tube wall, the quicker that process can take place. But that comes with a price since sealing narrow strips of thin-wall aluminum tubing in position can be a tricky proposition. Manufacturers such as C&R Racing have opted to TIG weld them in place and then follow it by furnace brazing, which essentially fuses all of the parts of the radiator together.
This is your basic design...
This is your basic design for a double-pass system. Note how the flow of the water crosses the radiator twice.
Most often these thin-walled tubes are mounted in a parallel arrangement. Separating the tubes are "Z" shaped aluminum fins which help radiate the heat from the tubes. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator.
In some radiators the tubes will have a type of fin inserted into them called a turbulator, which increases the turbulence of the fluid flowing through the tubes. If the fluid flowed very smoothly through the tubes, only the fluid actually touching the tubes would be cooled directly. The amount of heat transferred to the tubes from the fluid running through them depends on the difference in temperature between the tube and the fluid touching it. So the fluid that is in immediate contact with the tube cools down quicker than the fluid not in contact with the tube and less heat will be transferred. By creating turbulence inside the tube, all of the fluid has the opportunity to come in contact with the tubing wall and lose heat, thereby lowering the temperature of all of the fluid.