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Corsair says stacking radiators is bad ?
- Thread starter Kenrou
- Start date
- Joined
- Jan 10, 2012
you don't use heated air to cool, EVER!!!!!
yes, we can get away with it and have been for years but, that does NOT make it right nor even good.
You've been cheating on your wife for all these years with the guy (to make our european friends happy) down the street, the fact that you have gotten away with it does NOT make it right.
The temp difference between the air passing through the cooler (radiators were used to heat houses) and the fluid within is what makes it work.
and just how do we get away with it day in and day out you might ask.
just look behind the grill of your car, the first thing you see is the a/c condensor, behind that is the radiator.
yes, we can get away with it and have been for years but, that does NOT make it right nor even good.
You've been cheating on your wife for all these years with the guy (to make our european friends happy) down the street, the fact that you have gotten away with it does NOT make it right.
The temp difference between the air passing through the cooler (radiators were used to heat houses) and the fluid within is what makes it work.
and just how do we get away with it day in and day out you might ask.
just look behind the grill of your car, the first thing you see is the a/c condensor, behind that is the radiator.
Airflow is boss in these scenarios. Also, we've all come to the agreemant that loop order doesn't matter(with exception to the pump/reservoir), and for the most part that is correct, but not always. If your heatsource (CPU/GPU) is placed just before your exhaust radiator then you will be expelling more heat than the intake radiator will be putting back into the case. In the end you will reach thermal equilibrium but placing both as exhaust will result in a lower TΔ. I believe this is what Corsair was eluding to.
- Joined
- Apr 29, 2010
- Location
- Central FL
Sorry couldn't make it through the video. Not sure why these youtube people feel the need to over-act like William Shatner in Star Trek but it just seems common sense not to blow hot air on something meant to cool. Might be just me though.
- Joined
- Jun 9, 2010
Makes sense to me, more surface area is better cooling. Under the "correct" conditions corsair is likely right, but for most people more radiators is better.
Pauls hardware is decent if you are looking to get away from linus' acting.
Pauls hardware is decent if you are looking to get away from linus' acting.
- Joined
- Dec 27, 2008
What's the difference between stacking two rads and using one thicker rad? Let's say you stack two 30mm x 240mm rads with the first in intake configuration and the second in exhaust configuration. And you compare that to one 60mm x 240 rad with a push/pull setup (to keep the same number of fans in both scenarios). Theoretically, these two setups should cool the same since in both scenarios, the second 30mm of rad surface is getting cooled by the pre warmed air passing though the first 30mm of rad surface.
What makes more sense to me is to assume that two stacked radiators of a given thickness, if both are set to intake so as to get fresh air from outside with only a push or pull fan, will outperform one twice as thick radiator with push/pull fan setup. What I'm saying is that it makes sense to me that exposed, external radiator surface of a given area should cool better than a radiator of the same volume but less exposed, external surface area with the same amount of outside air passing through.
What makes more sense to me is to assume that two stacked radiators of a given thickness, if both are set to intake so as to get fresh air from outside with only a push or pull fan, will outperform one twice as thick radiator with push/pull fan setup. What I'm saying is that it makes sense to me that exposed, external radiator surface of a given area should cool better than a radiator of the same volume but less exposed, external surface area with the same amount of outside air passing through.
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- Joined
- Jun 21, 2002
Some rads, like the Black Ice Nemesis GTX are actually two 30mm rads (I believe the fins are all connected but the tubes flow like two stacked rads), and the end tank connecting them.
I can tell you from my experience, I saw a massive improvement in performance adding a second radiator, using the bottom as intake and the top as exhaust. I saw a relatively minor improvement from switching to top and bottom intake. In this case the improvement from ambient vs warm air was more important than the already disrupted airflow with balanced intake / exhaust (did not work well in my case due to the GPU).
I can tell you from my experience, I saw a massive improvement in performance adding a second radiator, using the bottom as intake and the top as exhaust. I saw a relatively minor improvement from switching to top and bottom intake. In this case the improvement from ambient vs warm air was more important than the already disrupted airflow with balanced intake / exhaust (did not work well in my case due to the GPU).
- Joined
- Apr 29, 2010
- Location
- Central FL
You are still blowing warmer air over the second radiator in that situation. If I take two radiators one on top of the case as intake and one as intake on the front, both get cool air all the time. Why stack them and get warmer air on the second?
- Joined
- Jun 9, 2010
I think it isn't as simple as that. If you have enough air flow which most setups have, you will not be reaching temp saturation with the air as it flows through the first rad. So yes the second rad warmer air may not cool as efficiently as the first but will still add to the cooling capacity.
- Joined
- Dec 27, 2008
But I was proposing the scenario where the second thin radiator is exhaust on purpose to compare it to a single thick radiator being cooled by intake air from outside the case. Because of what you said, two thin rads stacked where one is intake and one is exhaust would seem to be provide the same cooling as one thick radiator of equivalent total volume being fed by fresh air from the outside. In other words, the finage toward the inside of the case would be less efficient than that toward the intake side of the radiator.
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Here is why its not a good idea to stack radiators.
First some very important basics:
-The radiator (or heat exchanger) transfers energy (heat) from high temperature water, through the highly conductive metal walls of the heat exchanger, to the relatively colder air.
-Per the never ever violated laws of thermodynamics, energy transfer only occurs when there is a temperature difference (Delta T) and that is, of course, between the high temperature water to a lower temperature air.
-The rate of heat transfer (eg. BTU/Sec) is always directly proportional the Delta T. The bigger the temp difference, the more energy is transferred per unit time.
So, if two radiators are stacked or placed in series, the first radiator sees good cool ambient air and that means a relatively high average Delta T (air to water) and therefore a high rate of heat transfer across it. The second radiator sees the hot exhaust from the first radiator so the heat exchange rate across it is much less (The Delta T between the water and the air is smaller so less heat gets transferred). There is still energy transfer but at a much smaller rate than what it could be if the second radiator was seeing fresh cool room air too. In other words, placing two radiators in series (stacking) means the second radiator does much less compared to the first radiator so why bother with it? Alternatively, placing two radiators in parallel, also doubles the heat transfer surface area (also directly proportional to the rate of heat transfer), but now both radiators equally see the coldest air available, so it is a much more efficient/effective system than two radiators in series.
This also ties into the frequent and stubborn misconception that lower flow rates of water and/or air is better because low flow rates allow the water and air to stick around longer so more heat is transferred before they flow out of the heat exchanger. This again goes back to needing as high a Delta T as possible. While passing through the heat exchanger the air progressively gets warmer. Therefore the Delta T between the air and water decreases during the air's travel through the heat exchanger. By speeding up the air flow, the average temperature of the air remains lower as it has less time in the heat exchanger to pick up energy but a higher Delta T is maintained, maximizing the rate of heat transfer. The same logic applies to the water side.
This all comes down to four principles with regard to heat transfer rate across a heat exchanger or radiator:
-The heat transfer rate is directly proportional to the average delta T between the hot fluid (water) and cold fluid (air).
-The heat transfer rate is directly proportional to the flow rates (actually called "mass flow rate"). The higher the flow rates the colder the cooled water will be when it heads back to the CPU.
-The heat transfer rate is directly proportional to the thermal conductivity of the heat exchanger material. Copper has better thermal conductivity than most other metals. If the heat exchanger is painted the heat transfer rate is reduced because paint has crappy thermal conductivity.
-The heat transfer rate is directly proportional to the heat transfer surface area so two radiator are better than one.
All four parameters above must be maximized for the most effective system and putting two heat exchangers in series does not maximize the average delta T between the hot fluid (water) and cold fluid (air). There are also other considerations like a water to water heat exchanger works better than a water to air but that is another topic that does not really apply to the type of CPU water cooling systems we use.
First some very important basics:
-The radiator (or heat exchanger) transfers energy (heat) from high temperature water, through the highly conductive metal walls of the heat exchanger, to the relatively colder air.
-Per the never ever violated laws of thermodynamics, energy transfer only occurs when there is a temperature difference (Delta T) and that is, of course, between the high temperature water to a lower temperature air.
-The rate of heat transfer (eg. BTU/Sec) is always directly proportional the Delta T. The bigger the temp difference, the more energy is transferred per unit time.
So, if two radiators are stacked or placed in series, the first radiator sees good cool ambient air and that means a relatively high average Delta T (air to water) and therefore a high rate of heat transfer across it. The second radiator sees the hot exhaust from the first radiator so the heat exchange rate across it is much less (The Delta T between the water and the air is smaller so less heat gets transferred). There is still energy transfer but at a much smaller rate than what it could be if the second radiator was seeing fresh cool room air too. In other words, placing two radiators in series (stacking) means the second radiator does much less compared to the first radiator so why bother with it? Alternatively, placing two radiators in parallel, also doubles the heat transfer surface area (also directly proportional to the rate of heat transfer), but now both radiators equally see the coldest air available, so it is a much more efficient/effective system than two radiators in series.
This also ties into the frequent and stubborn misconception that lower flow rates of water and/or air is better because low flow rates allow the water and air to stick around longer so more heat is transferred before they flow out of the heat exchanger. This again goes back to needing as high a Delta T as possible. While passing through the heat exchanger the air progressively gets warmer. Therefore the Delta T between the air and water decreases during the air's travel through the heat exchanger. By speeding up the air flow, the average temperature of the air remains lower as it has less time in the heat exchanger to pick up energy but a higher Delta T is maintained, maximizing the rate of heat transfer. The same logic applies to the water side.
This all comes down to four principles with regard to heat transfer rate across a heat exchanger or radiator:
-The heat transfer rate is directly proportional to the average delta T between the hot fluid (water) and cold fluid (air).
-The heat transfer rate is directly proportional to the flow rates (actually called "mass flow rate"). The higher the flow rates the colder the cooled water will be when it heads back to the CPU.
-The heat transfer rate is directly proportional to the thermal conductivity of the heat exchanger material. Copper has better thermal conductivity than most other metals. If the heat exchanger is painted the heat transfer rate is reduced because paint has crappy thermal conductivity.
-The heat transfer rate is directly proportional to the heat transfer surface area so two radiator are better than one.
All four parameters above must be maximized for the most effective system and putting two heat exchangers in series does not maximize the average delta T between the hot fluid (water) and cold fluid (air). There are also other considerations like a water to water heat exchanger works better than a water to air but that is another topic that does not really apply to the type of CPU water cooling systems we use.
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