BFL Single air flow?

[eestimees]

Hi,

I've been looking at those single pictures (don't have one my own) and read about those whinigs about noise level... I was wondering are those two small fan's really nessesary ? I've made a drawing as I _think_ air flow goes.. and would be much quieter (if you replace those side plates):



I'm I wrong?

[dogie]

Yes they are. Without the small ones blowing directly through the fins, the majority of the air would just find the path of least resistance, which is around the sides of the heatsinks.

Arguably in an open case the two larger fans aren't required, but we don't know for sure the cooling requirements on the non-chip components.

[eestimees]

yes but when one has that blue airflow bracket, then the flow is forced to the sink and there would be a single continuous and effective air flow through the single (of-course case close not in open air)  ...?  that should be much quieter also.. in the original design air has multiple obstacles/high and low pressure points and different direction airflows collide.. all that is noisy and ineffective IMHO.

[dogie]

yes but when one has that blue airflow bracket, then the flow is forced to the sink and there would be a single continuous and effective air flow through the single (of-course case close not in open air)  ...?  that should be much quieter also.. in the original design air has multiple obstacles/high and low pressure points and different direction airflows collide.. all that is noisy and ineffective IMHO.

It would be inefficient, but not noisy. Get two case fans and hold them far apart and together, doesn't make much difference.

I didn't realise you had that as a bracket, but the design still doesn't work. You can't make an air tight seal around the heatsink, and so the air will still rather go around than through. There is a lot of flow resistance associated with high surface area.

[eestimees]

ok, thanks!

[rupy]

I think the best solution for sound here is remove the case and all fans, then place 2 singles next to eachother and put one big fan on top that covers all 4 heatsinks. Also why are all top mounted fans blowing DOWN?? Heat naturally goes UP!!

[eestimees]

I think the best solution for sound here is remove the case and all fans, then place 2 singles next to eachother and put one big fan on top that covers all 4 heatsinks. Also why are all top mounted fans blowing DOWN?? Heat naturally goes UP!!

you are joking, right? to cool them with one fan, it has to be a powerful and I doubt that it would be a quiet one, as the needed airflow (CPM) is a lot...

my main concern with this topic was, IMHO those fans inside case are working against each-other, I mean on the picture the left fan do not get much free air to blow down as the fan on the right has taken most of the incoming cool air away..

[bcp19]

I think the best solution for sound here is remove the case and all fans, then place 2 singles next to eachother and put one big fan on top that covers all 4 heatsinks. Also why are all top mounted fans blowing DOWN?? Heat naturally goes UP!!

The heat will go naturally up... the fins of the heat sink.  The narrowness of the fins combined with their height gives a lot of surface area for the radiation of heat off of the fins.  Many Jalapeno owners have already stated that the stock position of the fan (blowing up, thereby pulling air through the fins) results in the system running several degrees hotter than if the fan is blowing down into the fins.  It is much easier to get a uniform airlfow by pushing air than by pulling it. 

[k9quaint]

I think the best solution for sound here is remove the case and all fans, then place 2 singles next to eachother and put one big fan on top that covers all 4 heatsinks. Also why are all top mounted fans blowing DOWN?? Heat naturally goes UP!!

The heat will go naturally up... the fins of the heat sink.  The narrowness of the fins combined with their height gives a lot of surface area for the radiation of heat off of the fins.  Many Jalapeno owners have already stated that the stock position of the fan (blowing up, thereby pulling air through the fins) results in the system running several degrees hotter than if the fan is blowing down into the fins.  It is much easier to get a uniform airlfow by pushing air than by pulling it. 

When pulling air through a fan, it will take the path of least resistance into the fan. Thus it will not flow over the entire surface of the heat sink fins, but instead flow in along the top. Using the fan to push, thereby forcing air all the way down into every crevice of the heat sink creates airflow along the entire surface area of the heat sink which increases the amount of heat that can be transferred away.

[crazyates]

Problem: The 2 smaller fans don't blow down. They blow up, IIRC. People who have been running them out of their case have been reversing the direction so the fans blow down.

I feel like it's an interesting idea, but IDK how well it will work. The heatsink has a significant gap between the actual chip and the heatsink itself, so I don't feel it would be completely effective.

I've actually heard that the noise can be cut down significantly by running it outside of it's case, and with 2 quieter fans replacing the heatsink fans, but blowing down.

Still, you've got to remember: dissipating 200+Watts of heat is not an easy thing to do, although I do feel that 4 fans is a big overkill.

[ASIC-K]

the small fans blow UP not down.

i have a single, and this is how it works.

[chanberg]

I have 4 Jalapenos, and I arrange them in a stack of 2 open case (so two stacks, one on top of each other). If I leave it the way it is, it runs about 40C, if i put two fans next to them in a push pull manner, they drop 6C to about 34... So the two fans do make a difference believe it or not.. Also the push pull config fans are pointed in the direction of the heatsink grooves..

[dogie]

Cooling is much better when blowing through rather than sucking through a heatsink. As others have said, it takes a worse path when sucking through. This is because the pressure profile on either side of the fan isn't the same, its much stronger and compact on the blowing side.

Additionally, the rest of the PCB and components need airflow that a sucking arrangement wouldn't provide.

[eestimees]

Got my singles, today i moded one as i described, and it feels to me that it is more efficient. They are both side by side, hashing 61-63C. When i stop miner and start again, the modded single temp is much lower than original cooling setup. Within few minutes, they both are at the same temp again, but it feels like modded one's airflow is ligther = fans rotating slower.

Tomorrow i upload some pics of how i did it. I will try to get something to measure airflow and friend said he can borrow thermal cam to take pics.

[dogie]

Got my singles, today i moded one as i described, and it feels to me that it is more efficient. They are both side by side, hashing 61-63C. When i stop miner and start again, the modded single temp is much lower than original cooling setup. Within few minutes, they both are at the same temp again, but it feels like modded one's airflow is ligther = fans rotating slower.

Tomorrow i upload some pics of how i did it. I will try to get something to measure airflow and friend said he can borrow thermal cam to take pics.

tldr: You won't be able to get anything that measures airflow to any meaningful precision, unless you have a venturi arrangement.

[eestimees]

here it is



and still i'm pretty sure it is not only quieter but efficient too. still thermal imaging to be done to measure temp under the board and so.

[Bicknellski]

If it works great job.



Guessing the venturi effect is helping move that heat away nicely.

[dogie]

If it works great job.



Guessing the venturi effect is helping move that heat away nicely.

*Around the heatsink through the massive 0 resistance gap, yup. No way that is cooling better than before.

[Bicknellski]

If it works great job.



Guessing the venturi effect is helping move that heat away nicely.

*Around the heatsink through the massive 0 resistance gap, yup. No way that is cooling better than before.

Evidence to support your theory it doesn't work, possibly some models or math to prove that?

Basically calling the guy a liar, I am pretty much inclined to give him the benefit of the doubt at this point given the inelegant solution that was devised by BFL in the first place. Time for some numbers and proof cause dogie is calling you out eestimees.

[eestimees]

we'll see when i get the thermal cam in my hand, we'll see... I only need to figure out how to take pictures so that metal case would not block my "heat view".. I mean, I can't take pics when cover is taken off.. then the air will not tunnel through.. and taking pics with cover on I cant see single component heat.. I can only see heat spots on case.. maybe that is enough though...