Require help with proper fan hub management

ioverclockers said:
Was just my way of saying to simply let out the air that had been pushed in actively by the fans.
In my case, wouldn't it be beneficial to have a single exhaust fan at the back just opposite to the CPU cooler ? That way the Zalman would blow the hot air directly to the outlet, instead of having the hot air being "let out" by itself (probably by the top where it could still heat up the CPU a bit before it gets thru the grill and dust filter) ?

No problems with your nose :D. But I'm coming from OOB Macintosh land, where all the technical thinking and tinkering has been done for us ! As I said, this really is a first time build, so it's a journey full of discoveries ;)
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About as beneficial as having a fan on back of your CPU cooler .. or if you had a radiator putting fans on both sides of it. :D
 
doyll said:
Sorry I jumped at you. It's just that how airflow works is as plain to me as the nose on my face, and sometimes I loose patients with people who have no understanding of how airflow works. And yes, my nose is very plain. :D
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Its a lot more difficult to understand than spelling the words "lose patience". Loose patients are escapees from the loony bin ! :-)
 
Stil one thingy my stubborn preconceived ideas about airflow (that come from the Web :D) fail to grasp is how the fact that the exit airflow being partially obstructed by case grids and dust filters (and thus slowing down the exit ?) :
- doesn't imply that the hot air will stack up at least a while above or around the CPU before the same volume of air that got in 'unimpeded' will be able to passively exit (unless the continuous addition of colder air will somewhat lower the temps of that stacked hot air before it exits ?)
- it wouldn't help the speed of exiting the hot air by actively pulling it out thru a fan (sounds like a boo-boo word by now) like in the back of the case, especially when it sits in front of the CPU fans that come with the cooler...
 
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If you have filters on exhaust vents you are worse off than I thought. :D Generally our cases have 5+ vents so we end up with more exhaust vent airflow area than we have intake fans on vents airflow area.

- Can you 'stack up' the flow of water in a lake or pond? For air to move it has to displace/move the air in front of it, same as water in a lake or pond has to displace/move other water for it to move. FOR AIR TO FLOW INTO CASE THERE MUST BE THE SAME AMOUNT OF AIR FLOWING OUT OF CASE!!!! It's as simple as that. Simple physics of eqaul and opposite reaction. Air in must equal air out. And the difference in pressure between intake and exhaust side of a fan is almost nothing. If a fan is rated 1.47mm H2O of pressure (pressure with fan at full speed pushing air into a sealed box) that the differnce in pressure between intake side and exhaust side of fan. 1.47mm H2O pressure difference is the same as the difference in pressure against our feet and your chest while standing at sea level. Now do you get an idea of how little pressure an airflow our case fans can make?

- Air does not 'set' when it is being moved by fans. If your CPU cooler fan is running it is moving air (unless you have a plastic sheet on one side of fan). It is pulling air from a few inches in front of fan in and pushing air out through cooler toward rear vent.

Can you move water from one place in a pond to another without moving water in front and behind the water you are moving? Fill your kitchen sink with water. Fill a small jar and cap it in the sink full of water. Now move that jar around in the sink. Watch closely at how water in sink moves as you move the jar.
Sink full of water = room
Jar full of water = a volume of air moving around in room​
You can't move the jar / volume of air without moving water in sink / other air in the room.
 
Hi again. I think I get the idea of equal quantitative air displacement.
My question related to the unequal speeds of the intake and the outlet and its consequences on heat. If I follow your reasoning correctly, there couldn't be more air coming in than coming out. Follows from this that the next batch of fresh air won't be able to enter the case (even though being actively pushed by the fans) unless the previous batch has left. Is that correct ? So what happens when the speed of fresh air forcibly pushed in the case is different than the outlet capacities of the vents? I'm not talking about superior or inferior vent surface (and you do hint to the fact that the total surface area of exit vents may be bigger than the intake ones), but about the difference in speed of the former to effectively be able to let the air out (precisely because of the grids and dust shields that are obstacles and in fact reduce the capacities of equal speed unimpeded outlet).
At least this should in some way create some bigger air pressure inside the case, no (even if it's minimal) ?
Anyway, what are the consequences inside the case for de facto different speed ratios of air coming in and coming out ? Again, the air is being actively pushed in and passively exiting. It doesn't seem to be a simple case of communicating vessels to me (but I'm not a physician)...
 
ioverclockers said:
Hi again. I think I get the idea of equal quantitative air displacement.
My question related to the unequal speeds of the intake and the outlet and its consequences on heat. If I follow your reasoning correctly, there couldn't be more air coming in than coming out. Follows from this that the next batch of fresh air won't be able to enter the case (even though being actively pushed by the fans) unless the previous batch has left. Is that correct ? So what happens when the speed of fresh air forcibly pushed in the case is different than the outlet capacities of the vents? I'm not talking about superior or inferior vent surface (and you do hint to the fact that the total surface area of exit vents may be bigger than the intake ones), but about the difference in speed of the former to effectively be able to let the air out (precisely because of the grids and dust shields that are obstacles and in fact reduce the capacities of equal speed unimpeded outlet).
At least this should in some way create some bigger air pressure inside the case, no (even if it's minimal) ?
Anyway, what are the consequences inside the case for de facto different speed ratios of air coming in and coming out ? Again, the air is being actively pushed in and passively exiting. It doesn't seem to be a simple case of communicating vessels to me (but I'm not a physician)...
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Exacty!! Same in as out!

3 basic laws of motion;
  • First Rule: An object will remain at rest or in a uniform state of motion unless that state is changed by an external force.
  • Second Rule: Force is equal to the change in momentum (mass times velocity) over time. In other words, the rate of change is directly proportional to the amount of force applied.
  • Third Rule: For every action in nature there is an equal and opposite reaction.
Case flows same amount of air in as in flowing out.

The case can only flow as much air as the lesser volume of intake or exhaust.

You cannot force more air int than is coming out. At least not for more than a second or so. Remember the pressure fans make is extremely low, less than difference in air pressure on your chest vs your feet when standing up. Enogh difference to keep dusty air from leaking in if case does have a little more potential to flow in and does have a ittty-bitty-little bit higher pressure inside.

While there is a short delay between intake fans pushing air into case and it flowing out of case it's very quick. Not as quick as the speed of light, but only a few seconds. Then the exhaust vents (combined with other holes in case) will be flow exactly the same amount of air out of case as is flowing in.

If you have a sealed tank full of water and have 10 faucets on it, even if a faucet is open to let water out none can come out without something going into tank to fill the space of water that is coming out. If 4 faucets areflowing water into take and 6 letting water out, the maximum flow out is exactly the same amount as the 4 faucets are putting in.

If you completely sealed you case so nothing could leak out and are constantly pushing air into it it would eventually explode .. same as if you keep blowing up a balloon.

Just a wire grill made of 4 or 5 rings of round wire is enough resistance to limt a case fan by about 29%. A fancy front grill with filter restricts about 70-80% of air same fan would flow with no grill or filter.

Below link is to basic grill restriction as published by Silverstone computer case, cooler, fan, etc company:
https://www.silverstonetek.com/techtalk_cont.php?tid=wh_chessis&area=usa
 
doyll said:
A fancy front grill with filter restricts about 70-80% of air same fan would flow with no grill or filter.
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Yea, that was the point I was trying to make. The top vents in my case are falling in the latter case I guess, and the fan grill at the back really isn't optimized for airflow (I believe the dynamic xl was primarily conceived as a water-cooling case...).
I could have course remove the top filter. That wouldn't encourage dust to creep in too much right (especially as it's used for the main air exit...) ?
It would mean though that the hot air (albeit mixed with the incoming fresh air) would whirl around in the case for like 3-4 secs I'd say before being pushed out completely.
This is also the reason why I was thinking that maybe an active sucking fan on the back might speed up the process a bit. Wouldn't that be the case ?
 
I think you now are getting a grasp of how airflow works and how our fans are marginal at best. That said one with high pressure ratings do a good job of supplying needed airflow through grill and filter, so are definitely good enough.
In my experience top vents don't help with air cooling. In fact the ones on front half of case can hinder cooling more than help. Just leave filter in with no fans.

Hopefully your case airflow will be smooth, not swirling around. If it's being swirled around it is likely mixing with cool airflow and thus raising air temp into coolers. Every degree warmer air is going into coolers is same degree hotter component will be running same load and fan speed. So the closer to room temp we can keep air entering components the lower temps will be and the quieter system will be as well.

You can experiment with and without rear fan and see if it helps. Best way to get best cooling is to experiment, and best way to experiment is to monitor air temp entering coolers. Think I already give it to you, but just in case below link is basics of airflow and optimizing it.
https://forums.overclockers.co.uk/t...-i-put-my-temp-sensor.18564223/#post-26159770

You can pick up a remote sensor thermometer like for aquarium/terrarium, out/door indoor wired remote sensor digital thermometers off bay or river sites,
 
ok thanks for all the feedback ! It's surely more of a challenge than I had imagined for sure...
Waiting for the latest pieces to arrive and might post a thread for helping me building it the right way...:D
 
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