Efficiency: Parallel vs Sequential Radiator Coolant Flow
I had a fairly detailed discussion via PM's with another ApexSpeed member on this subject. Since I thought it was generally useful, I reworded it a bit, and here it is.
Efficiency: Parallel vs Sequential Radiator Coolant Flow
The science is basically two-fold:
1. Whether there is parallel flow or sequential flow, if the amount of heat transferred to the air is the same, the difference in coolant temperature from engine exit to engine entry will be the same. If that is true, then that difference occurs whether there is sequential or parallel flow. So, given the above, the temperature difference between the beginning and end of the radiator flow path would be the same in either case. So, that does not result in or explain any difference.
2. The major difference between the two setups is the coolant-flow velocity through the radiators. The sequential setup will have twice the flow velocity through the radiators compared to the parallel setup. This increased velocity increases turbulence and decreases boundary layer thickness, both resulting in increased heat transfer efficiency between the coolant and the radiator tubes. It also reduces “dead” (places where coolant is mostly stagnant) volumes in the radiators. Therefore, since the radiator metal will run warmer, and more heat will be transferred to the air, the sequential setup will give greater cooling capacity for the same size radiators and coolant flow.
In addition, if the two flows in the parallel setup are not equal, even more advantage will be shown by the sequential setup.
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Q&A
a) Wouldn't the additional distance for the coolant to flow in the sequential setup reduce the mechanical efficiency of the flow?
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Maybe slightly, but that is mostly controlled by the WP efficiency. With sufficient coolant pipe and radiator sizes, that is not usually significant.
b) Will what holds true for high-speed track racing hold true for low-speed autocross?
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Yes – in this case, it is all relative, and the same principles hold.
c) Is it true that maximum coolant temperature entering each radiator will result in more heat transfer?
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The temperature entering the radiator(s) is only one value at one point. What is important is the total area of radiator at each coolant-temperature level. With either system the radiator area at any given coolant temperature level is the same, not counting differences in total heat transfer that would change the difference between enter and exit temperatures. At the risk of being redundant, that means whether parallel flow or sequential, area times temperature differential between radiator and air is the same, except for any differences resulting from efficiency.
Thermodynamics by a dummy
Thermodynamics is such a complex subject matter and the many equations can be configured in a multitude of different ways to build the proper model of the "system."
Heat travels from hot to cold and there are three basic forms of heat transfer
- Conduction - the interaction of heat transfer on a molecular level - A hot cup of coffee in your hands.
- Convection - Heat transfer by a moving fluid. - A fan blowing during the summer time or cool water flowing over a hot object
- Radiation - Heat transfer by electromagnetic rays - sun burn
All three forms exist in every "system."
The most effective method for a automotive radiator is convection.
For a Solo car, I would think the most effective method to control the temperature between runs would be a combination of a continuously running electric fan and electric water pump, with a large battery.
Also you would need to size the electric water pump to produce a turbulent flow pattern. The electric water pump would address your low rpm and air flow.
One tiny update would make this perfect
Quote:
Originally Posted by
LJennings
Thermodynamics is such a complex subject matter and the many equations can be configured in a multitude of different ways to build the proper model of the "system."
Heat travels from hot to cold and there are three basic forms of heat transfer
- Conduction - the interaction of heat transfer on a molecular level - A hot cup of coffee in your hands.
- Convection - Heat transfer by a moving gas. - A fan blowing during the summer time or cool water flowing over a hot object
- Radiation - Heat transfer by electromagnetic rays - sun burn
All three forms exist in every "system."
The most effective method for a automotive radiator is convection.
For a Solo car, I would think the most effective method to control the temperature between runs would be a combination of a continuously running electric fan and electric water pump, with a large battery.
Also you would need to size the electric water pump to produce a turbulent flow pattern. The electric water pump would address your low rpm and air flow.
Your description of Convection should read, "Heat transfer by a moving fluid..." instead of moving gas. Since convection is also at play on the wet side of the thing we incorrectly call a radiator. Calling these heat exchangers "radiators" is a bad use of the word radiator. there is almost no radiation heat transfer going on in these systems, but somewhere a hundred or more years ago a mistake was made in choosing a name, and we still have it today
Steve.