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Old 09-24-2015, 10:02 PM
Kwaz Kwaz is offline
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Default 120mm vs 140mm Fan Obstructions in 350D

Hello all,

I'm adding a DVD drive to my system and as a result I need to move a number of things around. I have some concerns about airflow and I'm hoping that you can help answer a few questions.

I have a Corsair 350D with an H100i. When I built this system, I removed the hard drive and SSD cages and moved the drives (one 3.5" WD Black and an SSD) to a 5.25" bay. I also cut a hole in the front panel of the case and added some mesh so that the intake fans aren't restricted and needing to pull air from around the front panel.

The current airflow path is as follows - Two 140mm intake fans are set up in the front to draw in fresh cool air where it meets the video card (open air type) and passes over the lower part of the motherboard, there is then a 120mm fan set up as rear intake on what is typically the rear exhaust. The air from this rear intake fan flows over the upper part of the motherboard and meets the air from the front intake which flows past the hard drives and is then drawn out the top mounted radiator by fans in a push configuration.

To make things easier, less jumbled together at the top of the case and possibly get better CPU temperatures, I've been thinking about mounting the H100i in the front of the case. The first problem, is that I've heard that due to the pump and block being one piece on the H100i, having the pump above the radiator can cause air to be trapped in the pump, raising CPU temperatures and shortening the life of the pump.

The other more concerning question that I have is dead space behind the fan on the radiator when using 140mm intake / push fans as intake. Using 140mm fans as intake in the front of the Corsair 350D also causes their airflow to be partially blocked as seen below.

140mm Front Intake Fans

120mm Front Intake Fans

My Concerns:
  • Is air getting trapped in the pump / waterblock a significant cooling or lifespan issue?

  • Will using 140mm Front Intake Fans cause less air to be pushed into the case? Due to the hub size in combination with additional blockage from the frame of the case - would 120mm Front Intake Fans be more efficient?

  • Would it be better to use a push / pull configuration to get more air into the case when setting the radiator up as front intake? Or is this a bad idea as this warmed air is then used to cool other components and therefor an inefficient setup?

  • As an a side - This particular PSU only spins the fan when its usage is above a moderate amount. I don't have the analog to digital adapter to hook up this RM series PSU to Corsair Link, so I cannot adjust the fan profile. I'd rather replace this PSU as I haven't read great things. I would imagine when the fan is off that heat would rise through the fan intake when flipped to the rest of the system. For when the system is at more than moderate use, would it be worthwhile to flip the power supply around so that the fan is drawing air from the inside of the case, drawing cool air under the video card to be used by the open air type cooler?
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Old 09-25-2015, 08:14 AM
c-attack c-attack is offline
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1) You can mount the cooler in any position regardless of hose orientation. If the pump couldn't push the water against gravity, it wouldn't work at all in any position. There may be a small number of pumps that didn't get filled up quite enough in the manufacturing process and as a result are more sensitive to certain positions. Most of the time the "bubbles" people refer to occur as a result of moving the cooler. Moving it again often works the trapped air out. There is no longevity issue with mounting position.

2) If you are going to put the H100i in the front, then you need to use 120mm fans. If there were no other recourse, you could try using 140 to 120mm converters, but that takes space and would make the install difficult. I love 140mm fans, but you shouldn't think of them as a upgrade to a 120mm fan -- just a different tool. Most 140mm fans have relatively low RPM limits. A higher spinning 120mm fan will move just as much air, although likely louder and at a different pitch. I don't see any reason not to use whatever is already on your radiator as front intake (SP120L?) or any other 120mm fan you like. Someone else asked about this yesterday, but 140mm fans tend to push air out in a more conical shape than a static pressure designed 120mm fan. Even a "more focused flow" fan like those Cougar's will spill half of its flow over and against the edges of the radiator. In regards to your current set-up, I also have small metal flanges that partially block my 2x140mm front intake. Whether you are better off with 2x120 or 2x140 for a normal (no radiator) intake likely depends on the individual fan in use. I have some 140's that produce a hum because of the blade proximity to the obstruction. Others are unaffected. Most 140mm fans move around 60-65cfm at 1000 rpm. A 120mm airflow fan usually needs 1500 to move that volume. So, 2x140@1000 or 2x120@1500? Again, it probably comes down to the fan, but for the most part we are talking about style and sound, not actual temperature differences.

3) If you have the space and want to run push-pull you can. Keep in mind it will not increase the maximum airflow you can move through the radiator, but it will increase the airflow at lower fan speeds. On a 120mm front intake, that may be an asset.

4) Don't use your power supply as a heat management tool. The fan on your PS won't make a bit of difference for anything in the system, but it can negatively impact the power supply. Your internal case air will certainly be warmer than the outside air your PS would normally draw and my preference would be to shield these passive fan models from any additional warmth. Besides, you GPU fans are more than capable of drawing their own air and on an ACX style card the air you really want to displace is right above the GPU.

Generally speaking, most people are going to wind up with worse over all system temperatures with a front mounting cooler in a single radiator system with air cooled GPU(s). You may gain a few degrees on your CPU temps by using it as front intake. However, you will then dump all that CPU heat into the case raising your internal temperature by 5-10-15C depending upon load and duration. Your GPU, memory, motherboard, drives, and any other components then operate in a 10C warmer environment for their lifespan. I don't know your intended uses for this system, but most people have 20-30C cap room on their CPU's for normal use and perhaps only 10C on their GPU before throttling kicks in. If this is a CPU workhorse with low graphics needs, then the priorities may be different. The physical location of the case can play a part too. If you need to shove it under a desk, in a corner, against a wall, etc., then other set-ups may be optimal over the standard front-in, top/rear out layout. All that said, you should feel free to experiment. You are not going to damage anything and all we can do is generalize about the possible results, unless we have the exact same case, hardware, fans, etc. and have tried the same thing. I just wouldn't go to any great expense until you've found an arrangement you like and then want to fine tune it.

Last edited by c-attack; 09-25-2015 at 08:25 AM.
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Old 09-25-2015, 12:30 PM
Kwaz Kwaz is offline
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Thanks c-attack,

Your thoughts are exactly in line with mine. As for the 140mm fans to 120x2 radiator, that is a great point. I hadn't thought about a lot of the air spilling over in some sense. The system is used for gaming sometimes, so yes, heating up the GPU isn't ideal. Nor is exhausting hot air into the system.
I think that the best solution overall would be to figure out a way to keep the radiator set up as top exhaust, with the 140mm fana in front. So far this setup has worked very well.
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