Two Loops, One radiator

[3Z3VH]

Not really. The flow rate of the water and the air will determine how efficient the rad is, it will not be a wash, it will be very different at different flow rates.


Your first sentence here is misleading. Radiators are most efficient when there is a large liquid to air temp differential. If the rad's water is at 50C and so is the air, the rad won't be efficient at all. If the air was 25C it would be. The second sentence makes no sense. This would apply to serial rads where the first rad in the loop would be more efficient than the second because the first rad already cooled the water some.

Stop worrying about the flow rate of the air. We are assuming the air flow rate is a constant, because no matter how fast/slow the water is passing through the loop, it will not make your fans spin faster. So the air flow rate is a constant.

Also, my sentence isn't misleading. I agree with you, they get more efficient as the delta between ambient and water temps increases. Now, when you are given a constant value as your ambient temperature, what is the only variable that will increase the delta between ambient and water temps ? That's right, the temperature of the water... meaning, the hotter the water, the more efficient the radiator will be, since the ambient is considered a constant (for the purposes of this conversation). Now read my sentence again, considering that the ambient temp is a constant.... The hotter the radiator is (due to water temps) the more efficient it is. Seems true to me !

Your radiator, with a constant air flow over it, using a constant ambient temp, will give a predictable cooling capacity, represented by wattage, which will look like a curve on a graph of liquid temp vs. heat dissipated. The higher the temp of the liquid, the more capacity your radiator has to dissipate it.

Thus, my oversimplified statement "The hotter the radiator is, the more efficient it is" is true for purposes of this conversation. And you only proved my point by your statement about the differential... if you let the water sit in the rad for, say, an hour it should get pretty close to ambient temp... do you think the radiator is still radiating warm air ? Nope. That is because it is no longer removing as much heat from the water. If you let the water temp get too close to ambient, the radiator will not be as efficient. Thus, the slower the water, the more time it has to get closer to ambient, thus, the less efficient your radiator will be. All the water that is waiting to get pumped through the radiator is getting hotter and hotter waiting for its turn to go through the radiator at such a slow rate.

I'd tend to think that too, more turbulence in the radiator translates into better transporting of heat to the radiator fins. If you stir a pot of water, does it come to a boil much faster than if you just leave it sit? I live in a Dorm and can't test this.

Actually if you stir a pot, it will boil slower, but it is not due to turbulence. It is because you are letting ambient air into the liquid, which cools down what you are stirring. A pot that is not being stirred, still has natural convection to spread the heat around to all the liquid quickly.

I think you need to do some reading too. Step 1, reread what I wrote and what I was referring to. You asked me if I was kidding? Closed loop? Yes the assumption is a closed loop. And flow rate DOES make a difference in radiators. Please check your facts.

Please show us a benchmark of how flowrate through a radiator affects temps in a closed system.