Are more fans always better?
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bum_jcrules
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Sure. The better the airflow the cooler your components are. The less the internal resistance of the circiuts in those components and the closer the performance is to optimal. So sure go ahead. Equalized air in and out is best. Again flow is most important. The better the cool air is inducted <b>and</b> the warm air is expelled the high the flow through the case.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
This post is directed at everybody here.
Bum, you mention equalized pressure is best. Just wondering what your logic is.
I could certainly forsee that a negative case pressure might cause a dust buldup problem, but I've never been able to convince myself that either equalized or positive case pressure is better than the other.
PS I totally agree that the most important factor is how well the air is moving the heat out of the case.
Bum, you mention equalized pressure is best. Just wondering what your logic is.
I could certainly forsee that a negative case pressure might cause a dust buldup problem, but I've never been able to convince myself that either equalized or positive case pressure is better than the other.
PS I totally agree that the most important factor is how well the air is moving the heat out of the case.
bum_jcrules
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I am not talking down to you but to keep everyone reading up to speed. Sorry this is so long but it truely relays the point of equalized pressures.
Negative pressure in the case means that there is more air being forced out than in. Positive pressure is created when there is more air being forced into the case than is ourside the case.
Both are not optimal for a couple of reasons.
<b>1. Strain on the fan motors...</b>
If you have either positive or negative pressure, you put undue srtain on the fans. Extra force is pushing back on the blades of a fan that is forcing air into the case. There is extra force behind the the blades of the fans pushing air out of the case. For either fan, intake or exaust, there is extra strain on the motors. Negligable but still a real factor. Equalized or close to equalized pressure nearly eliminates this.
<b>2. Maximum Airflow...</b>
Looking at point #1, if the fans are running optimally than more air is flow through the case. The more air through the case the better. The optimal condition for air cooling is having as much new cooler air hitting components and picking up excess energy and then flowing out of the case to remove that energy. So the more air you have flowing through the better the cooling condition. Again I bring up through the case. One aspect of case design is airflow. Look at how they are designed today. Intake on the front bottom and exaust at the top rear. Cool in the bottom and hot out the top. Warm air is less dense and rises. This idea is utilizing the properties of a convection cell. The fans just help move the air in and out and sometimes to blow extra air at one component specifically.(Northbridge, GPU, and CPU coolers) The main point is maximum airflow. The more, new, cooler air you can get into the case and the more warm air out is all dependent on maximum airflow.
Equalized pressure is one factor in maximum efficiency. If the air does not need to be compressed to fit into the case, positive case pressure, the easier if flows into the case. If the case has negative pressure, the air needs to be compressed to flow out of the case. In either scenario the air needs to be compressed. Neither are efficient as having equalized pressures.
One sub point about positive and negative case pressures. If you hae more air air pressure on the inside than on the outside, some of you might say, well won't the excess air find it's ways out through the holes and cracks in the case? (Or vise versa with negative with air flowing in.)
The answer is yes it will but if hot air is trying to get out through cracks and holes it heats up the case. More latent energy will build up inside the case. For negative pressure the case will cool slightly. Either is a moot point. The real problem with drawing or blowing air out through small holes and cracks is inefficient airflow. It still has the same problem as above. Motors will still be overworked and the air will not travel in the most efficient direction.
Have you seen newer cases, Antec 1080 for example, which have a fan on the side panel? The air flow is two-fold. Air is drawn in from the bottom front towards the back of the case. The second fan in the side panel blow it in the direction of the components and adds cooler air, the rear fans and the PSU blow the warm air out the back and top of the case. Convection cell with extra help.
I hope that this helps explain why equalized pressure is optimal. Feel free to comment.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
Negative pressure in the case means that there is more air being forced out than in. Positive pressure is created when there is more air being forced into the case than is ourside the case.
Both are not optimal for a couple of reasons.
<b>1. Strain on the fan motors...</b>
If you have either positive or negative pressure, you put undue srtain on the fans. Extra force is pushing back on the blades of a fan that is forcing air into the case. There is extra force behind the the blades of the fans pushing air out of the case. For either fan, intake or exaust, there is extra strain on the motors. Negligable but still a real factor. Equalized or close to equalized pressure nearly eliminates this.
<b>2. Maximum Airflow...</b>
Looking at point #1, if the fans are running optimally than more air is flow through the case. The more air through the case the better. The optimal condition for air cooling is having as much new cooler air hitting components and picking up excess energy and then flowing out of the case to remove that energy. So the more air you have flowing through the better the cooling condition. Again I bring up through the case. One aspect of case design is airflow. Look at how they are designed today. Intake on the front bottom and exaust at the top rear. Cool in the bottom and hot out the top. Warm air is less dense and rises. This idea is utilizing the properties of a convection cell. The fans just help move the air in and out and sometimes to blow extra air at one component specifically.(Northbridge, GPU, and CPU coolers) The main point is maximum airflow. The more, new, cooler air you can get into the case and the more warm air out is all dependent on maximum airflow.
Equalized pressure is one factor in maximum efficiency. If the air does not need to be compressed to fit into the case, positive case pressure, the easier if flows into the case. If the case has negative pressure, the air needs to be compressed to flow out of the case. In either scenario the air needs to be compressed. Neither are efficient as having equalized pressures.
One sub point about positive and negative case pressures. If you hae more air air pressure on the inside than on the outside, some of you might say, well won't the excess air find it's ways out through the holes and cracks in the case? (Or vise versa with negative with air flowing in.)
The answer is yes it will but if hot air is trying to get out through cracks and holes it heats up the case. More latent energy will build up inside the case. For negative pressure the case will cool slightly. Either is a moot point. The real problem with drawing or blowing air out through small holes and cracks is inefficient airflow. It still has the same problem as above. Motors will still be overworked and the air will not travel in the most efficient direction.
Have you seen newer cases, Antec 1080 for example, which have a fan on the side panel? The air flow is two-fold. Air is drawn in from the bottom front towards the back of the case. The second fan in the side panel blow it in the direction of the components and adds cooler air, the rear fans and the PSU blow the warm air out the back and top of the case. Convection cell with extra help.
I hope that this helps explain why equalized pressure is optimal. Feel free to comment.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
Thanks for that detailed, and excellent explanation.
Now that you put it that way, I must agree. Equalized is best.
Now that you put it that way, I must agree. Equalized is best.
In theory, yes equalization is best, but there are a couple of environmental factors to consider:
1) The fans aren't the only place where air enters or exits the case. Air bleeds in around the slots and bays as well. Many cases also purposly have vent holes, usually in the bottom front of the case.
2) Compressed air will transfer heat more readily than uncompressed. This is because the air molecules in the compressed air are closer together, and thus more readilly "bump into" each other to transfer the heat energy. Anyone who has used a paintball gun knows that the compressed CO2 cylinder is usually cool to the touch.
3) Dust. Any dust on the components will have an insulating effect. This insulating effect can be quite high. Dust is also attracted to electrical devices because they tend to have a high static charge (check the back of your VCR and you'll see what I mean).
4) It's actualy not that easy to equalize the pressure. Sure you can use identical case fans, but what about the power supply fan? Sure you can find out the published CFM rating and try to match it, but published CFM rattings and actual CFM can vary widely.
For these reasons I would recommend a slight positive pressure. The positive pressure will push air out of the slots/vent holes and prevent dust from entering through these routes. Yes it will put slightly more wear on your case fans, but on the other hand it will not adversly affect to your CPU fan (on the heatsink) because the preasure INSIDE the case will not vary. You can survive losing a case fan, but losing a CPU fan will fry your AMD CPU.
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Knowan likes you. Knowan is your friend. Knowan thinks you're great.
1) The fans aren't the only place where air enters or exits the case. Air bleeds in around the slots and bays as well. Many cases also purposly have vent holes, usually in the bottom front of the case.
2) Compressed air will transfer heat more readily than uncompressed. This is because the air molecules in the compressed air are closer together, and thus more readilly "bump into" each other to transfer the heat energy. Anyone who has used a paintball gun knows that the compressed CO2 cylinder is usually cool to the touch.
3) Dust. Any dust on the components will have an insulating effect. This insulating effect can be quite high. Dust is also attracted to electrical devices because they tend to have a high static charge (check the back of your VCR and you'll see what I mean).
4) It's actualy not that easy to equalize the pressure. Sure you can use identical case fans, but what about the power supply fan? Sure you can find out the published CFM rating and try to match it, but published CFM rattings and actual CFM can vary widely.
For these reasons I would recommend a slight positive pressure. The positive pressure will push air out of the slots/vent holes and prevent dust from entering through these routes. Yes it will put slightly more wear on your case fans, but on the other hand it will not adversly affect to your CPU fan (on the heatsink) because the preasure INSIDE the case will not vary. You can survive losing a case fan, but losing a CPU fan will fry your AMD CPU.
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Knowan likes you. Knowan is your friend. Knowan thinks you're great.
bum_jcrules
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"1) The fans aren't the only place where air enters or exits the case. Air bleeds in around the slots and bays as well. Many cases also purposly have vent holes, usually in the bottom front of the case."
Why would the air want to if the case pressure is equalized. If the pressure inside was greater than outside then, yes the air would want to go out through cracks and holes. Why would the molecules want to go into a similar pressured area if they could just as easily go out in a direction they are flowing anyway?
"2) Compressed air will transfer heat more readily than uncompressed. This is because the air molecules in the compressed air are closer together, and thus more readilly "bump into" each other to transfer the heat energy. Anyone who has used a paintball gun knows that the compressed CO2 cylinder is usually cool to the touch."
True, however you are only partly correct in your thinking. Compressed air or anything-compressed more than at equilibrium as a matter of fact, will be at a higher energy state. {{Potential (PE) or Kinetic (KE)}} In your CO2 argument, the CO2 is compressed. When the volume decreases inside the cylinder the total amount of energy is decreased. Less molecules, less pressure, and thus less energy. This translates into a decrease in temperature. This is the same principle is used in refrigeration. Temperature is just the average KE. So the less KE the lower the temperature. Compress the air away from where you are trying to cool it. Less room for the molecules to bounce around in and they hit the walls of the container and the walls dissipate that KE. It is decompressed near the thing you are trying to refrigerate. More space for the molecules to travel in and thus less hitting the walls. The principle is the same air just at differing pressures. (<A HREF="http://www.rdoman.com/phy/gas/" target="_new">PV=nRT</A> which is the basic gas law in physics.)
So...If you compress the air, it will have a higher average KE level and thus a higher temperature. Why would you want to increase the temperature of the air you are drawing into the case? You would not have to think about increasing the KE level in a constant pressure enviroment.
"3) Dust. Any dust on the components will have an insulating effect. This insulating effect can be quite high. Dust is also attracted to electrical devices because they tend to have a high static charge (check the back of your VCR and you'll see what I mean)."
You are correct. However, if the flow of air in the front and back of the case and pressures are constant with the use of a filter this effect will be minimized. Also everyone should blast their components regularly to minimize dust buildup. Dust will attach itself to components regardless of airflow. The particles will be magnetically drawn to the components. Physics again... Ionic particles and electromagnetic devices. Dust buildup will happen reguardless of positive, negative, or equilized pressure enviroments. (Law of entropy or the 2nd law of Thermodynamics.) Maybe it might happen a little less, or better stated, at a lesser rate in your example but still will happen.
"4) It's actualy not that easy to equalize the pressure. Sure you can use identical case fans, but what about the power supply fan? Sure you can find out the published CFM rating and try to match it, but published CFM rattings and actual CFM can vary widely."
You are correct. No system will be 100% equalized. As closes as one can get to equilibrium the better the airflow and thus the better the transfer of KE. Each system will be different, but you can try to equalize the pressures. You are correct on CFM ratings. The are a Modal average at a specific voltage. The air pressure at that day of testing will be different that that in my house. So the figure won't be exact but the margin of error should be minimal.
Air flow again is key to keeping all components cool. Maximize the efficiency of moving the air and the better the flow will be. The better the flow, the more molecules you have hitting the components.
Back to you...
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
Why would the air want to if the case pressure is equalized. If the pressure inside was greater than outside then, yes the air would want to go out through cracks and holes. Why would the molecules want to go into a similar pressured area if they could just as easily go out in a direction they are flowing anyway?
"2) Compressed air will transfer heat more readily than uncompressed. This is because the air molecules in the compressed air are closer together, and thus more readilly "bump into" each other to transfer the heat energy. Anyone who has used a paintball gun knows that the compressed CO2 cylinder is usually cool to the touch."
True, however you are only partly correct in your thinking. Compressed air or anything-compressed more than at equilibrium as a matter of fact, will be at a higher energy state. {{Potential (PE) or Kinetic (KE)}} In your CO2 argument, the CO2 is compressed. When the volume decreases inside the cylinder the total amount of energy is decreased. Less molecules, less pressure, and thus less energy. This translates into a decrease in temperature. This is the same principle is used in refrigeration. Temperature is just the average KE. So the less KE the lower the temperature. Compress the air away from where you are trying to cool it. Less room for the molecules to bounce around in and they hit the walls of the container and the walls dissipate that KE. It is decompressed near the thing you are trying to refrigerate. More space for the molecules to travel in and thus less hitting the walls. The principle is the same air just at differing pressures. (<A HREF="http://www.rdoman.com/phy/gas/" target="_new">PV=nRT</A> which is the basic gas law in physics.)
So...If you compress the air, it will have a higher average KE level and thus a higher temperature. Why would you want to increase the temperature of the air you are drawing into the case? You would not have to think about increasing the KE level in a constant pressure enviroment.
"3) Dust. Any dust on the components will have an insulating effect. This insulating effect can be quite high. Dust is also attracted to electrical devices because they tend to have a high static charge (check the back of your VCR and you'll see what I mean)."
You are correct. However, if the flow of air in the front and back of the case and pressures are constant with the use of a filter this effect will be minimized. Also everyone should blast their components regularly to minimize dust buildup. Dust will attach itself to components regardless of airflow. The particles will be magnetically drawn to the components. Physics again... Ionic particles and electromagnetic devices. Dust buildup will happen reguardless of positive, negative, or equilized pressure enviroments. (Law of entropy or the 2nd law of Thermodynamics.) Maybe it might happen a little less, or better stated, at a lesser rate in your example but still will happen.
"4) It's actualy not that easy to equalize the pressure. Sure you can use identical case fans, but what about the power supply fan? Sure you can find out the published CFM rating and try to match it, but published CFM rattings and actual CFM can vary widely."
You are correct. No system will be 100% equalized. As closes as one can get to equilibrium the better the airflow and thus the better the transfer of KE. Each system will be different, but you can try to equalize the pressures. You are correct on CFM ratings. The are a Modal average at a specific voltage. The air pressure at that day of testing will be different that that in my house. So the figure won't be exact but the margin of error should be minimal.
Air flow again is key to keeping all components cool. Maximize the efficiency of moving the air and the better the flow will be. The better the flow, the more molecules you have hitting the components.
Back to you...
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
bum_jcrules
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They can add to the noise level but not necessarily increase it. That is where finding the best CFM to a low dBA comes in. There are plenty of ways to decrease noise and increase the flow.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
Well, yes... The biggest noisemakers are usually HSF, and possibly PSU (depends on quality). So, additional case fans might not really be "heard" - and that's of course the thing that matters, noisewise.
But, since P4user's thinking if he should put in fans just because there's room, he should also consider the quite possible increase in noise level. If he'd be replacing fans, that's another thing! Of course, if he's lucky enough and already has adjustable fans, then adding a couple of new ones might make it possible for him to slow down the current ones and lower noise.
But all this is academic, anyway. Since we don't know the system thoroughly, we can only speculate.
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But, since P4user's thinking if he should put in fans just because there's room, he should also consider the quite possible increase in noise level. If he'd be replacing fans, that's another thing! Of course, if he's lucky enough and already has adjustable fans, then adding a couple of new ones might make it possible for him to slow down the current ones and lower noise.
But all this is academic, anyway. Since we don't know the system thoroughly, we can only speculate.
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bum_jcrules
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I totally agree.
BTW: I really like the sig. I think you might have forgotten THECROSS.BAT, HEISRISN.COM, and RAPTURE.EXE
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
BTW: I really like the sig. I think you might have forgotten THECROSS.BAT, HEISRISN.COM, and RAPTURE.EXE
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
Thanks for all the information on case cooling. I definitely know alot more about it now. But the unfortunate thing is that the way my case is set up I don't have room for a front fan in the bottom. the power button and floppy drive are there. I do however have three empty drive bays for cdroms etc. If I was going to put a fan in the front of the case it would have to be here. But I don't know where I'd look for a fan that could fit in slots like these. Can anyone clue me in as to what kind of fan I should look for to fit in this large space? It would be nice to find one with a relatively low db level as well. Thanks.
bum_jcrules
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Just use an intake fan where the HDDs are. You can vent air to CD-ROM and Burners as well.
How would positive pressure(PP) decrease overall case temps and how would PP insure a lower HDD temp? If you have stagnate air around components, higher pressure would only increase the overall anount of energy. (That would equate to temperature, average KE.) More molecules of air means more latent energy. I still don’t see how higher pressures would improve the cooling of isolated and non-isolated components.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
How would positive pressure(PP) decrease overall case temps and how would PP insure a lower HDD temp? If you have stagnate air around components, higher pressure would only increase the overall anount of energy. (That would equate to temperature, average KE.) More molecules of air means more latent energy. I still don’t see how higher pressures would improve the cooling of isolated and non-isolated components.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
bum_jcrules
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Just use an intake fan where the HDDs are. You can vent air to CD-ROM and Burners as well.
How would positive pressure(PP) decrease overall case temps and how would PP insure a lower HDD temp? If you have stagnate air around components, higher pressure would only increase the overall anount of energy. (That would equate to temperature, average KE.) More molecules of air means more latent energy. I still don’t see how higher pressures would improve the cooling of isolated and non-isolated components.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
How would positive pressure(PP) decrease overall case temps and how would PP insure a lower HDD temp? If you have stagnate air around components, higher pressure would only increase the overall anount of energy. (That would equate to temperature, average KE.) More molecules of air means more latent energy. I still don’t see how higher pressures would improve the cooling of isolated and non-isolated components.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
bum_jcrules
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Classic THGC double post!!!
I love this server.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
I love this server.
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
The thing is it depends on the case design and the fan setup. In a normal fan setup with a intake at the bottom , and the psu and a out at the back, your drives and some other equibment are hardly ever given any air.
With a positive preassure you do get cool air to more of the case, and with the right openings you get rid of that air pretty quick, also it cuts down on dust alot.
With a limit of 2 fans on a system besides your HSF and your PSU I think positive preassure works well to cool your "entire system" vs just your cpu.
Ill present a small real life example to slightly back this. I have a fong kai 320 box that is running a server with some scsi drives. It has 1 120mm intake down at the bottom, and a 92mm intake from the back, the PSU is blowing out. With its normal setup(duron 900@1200 with a old volcano 2 HSF) 100% load averages around 45-50c. Case temp is normally around 23-27c. If i reverse the rear fan to blow out, my cpu temp goes down, but my case temp actually rises, and my scsi drives run hotter.
Of course i could add a harddrive fan, and add a side or pci slot cooler to cool some of the pci cards, and so on and i would achieve better temps, but instead I can settle for lower case temps, with higher cpu temps with only 2 fans and have all my componets receiveing some cooling.
With a positive preassure you do get cool air to more of the case, and with the right openings you get rid of that air pretty quick, also it cuts down on dust alot.
With a limit of 2 fans on a system besides your HSF and your PSU I think positive preassure works well to cool your "entire system" vs just your cpu.
Ill present a small real life example to slightly back this. I have a fong kai 320 box that is running a server with some scsi drives. It has 1 120mm intake down at the bottom, and a 92mm intake from the back, the PSU is blowing out. With its normal setup(duron 900@1200 with a old volcano 2 HSF) 100% load averages around 45-50c. Case temp is normally around 23-27c. If i reverse the rear fan to blow out, my cpu temp goes down, but my case temp actually rises, and my scsi drives run hotter.
Of course i could add a harddrive fan, and add a side or pci slot cooler to cool some of the pci cards, and so on and i would achieve better temps, but instead I can settle for lower case temps, with higher cpu temps with only 2 fans and have all my componets receiveing some cooling.
The truth is, I think 'positive air pressure' is just a myth. What you do want is air moving throughout the case, but that's all. The only reason for case cooling is to make sure that hot air does not collect inside of the case and gradually raise temperature. The air intake fans, even if they are 5000 RPM 120mm fans, just can't generate enough air flow to create that so-called 'air pressure' since the inside of a case is so large (and contains so much air). Again I will repeat myself, all you need is air moving in and out so that the hot air does not build up inside the case.
It's summertime here and last night when I wanted to cool my room using just a tiny high powered 250mm fan, all I had to do was open up a window on the far side of the room and put a fan right next to it blowing OUT the window. I'll try to make a text illustration of it
Pretend there are walls on the sides of these pictures and that there are no periods either (I had to use them because the forums don't allow more than 1 space in between characters
------- W I N D O W --------|
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.....air coming in....air being forced out by fan
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-DOOR (CLOSED)-------------|
CAPTION: THIS IS WHAT WORKS!
This is drawn just about to scale. You see at first what I did was put the fan pointing right outside my door and kept the window open to create the kind of airflow people try to create inside their PC cases, like this:
------- W I N D O W --------|
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............air coming in...........
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....fan blowing air out..........
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-DOOR (OPEN)---------------|
CAPTION: THIS DID NOT WORK AS WELL!
To summarize, basically what I found cooled faster was not necessarily about trying to get air to circulate more, but to simply get the maximum amount of cool air into the room as fast as I possibly could. Having a fan blow directly into the source of my cold air, in this case the window, even though it only caused air in the top half of my room to circulate, was more effective than trying to get it all to move.
Of course when it comes to computers, no one has a resevoir of cold air behind their case, so this can't really be done. But it certainly does make me think more about fan placement. What if a computer case was to have two fans in front and two in back, and instead of the two in front blowing in and two in back blowing out, have one of the fans in both front and back blow out and the other fan in both front and back blow in? Also, how much do fans placed on the sides or the top of the case help and how do they change airflow (and what about raising the case and cutting a hole in the bottom of it and putting a fan there?) What I'm illustrating here probably wouldn't help most people, but if someone here lives in a cold climate like Minnesota, it might be worthwhile to try this out.
Edit: I must note that the kind of cooling done in the first diagram does something that the second diagram doesn't do: It cools equally. In the first diagram, the whole room is cooled evenly, while in the second, the southeast corner of the room barely gets touched and stays generally at the same temperature. This is important to note because a lot of people have the Lian-li cases with blow holes on top, and that probably means that a lot of the air coming in simply goes out the top and does not pass through the CPU, the most important part! This means all of that noise from the intake fans may be in vain!<P ID="edit"><FONT SIZE=-1><EM>Edited by cakecake on 06/13/02 07:18 AM.</EM></FONT></P>
It's summertime here and last night when I wanted to cool my room using just a tiny high powered 250mm fan, all I had to do was open up a window on the far side of the room and put a fan right next to it blowing OUT the window. I'll try to make a text illustration of it
Pretend there are walls on the sides of these pictures and that there are no periods either (I had to use them because the forums don't allow more than 1 space in between characters------- W I N D O W --------|
............|............/\...........
............|.............|...........
............\/............|...........
.....air coming in....air being forced out by fan
.......................................
.......................................
.......................................
.......................................
.......................................
.......................................
.......................................
-DOOR (CLOSED)-------------|
CAPTION: THIS IS WHAT WORKS!
This is drawn just about to scale. You see at first what I did was put the fan pointing right outside my door and kept the window open to create the kind of airflow people try to create inside their PC cases, like this:
------- W I N D O W --------|
...................|...................
...................|...................
..................\/...................
............air coming in...........
.......................................
.......................................
.......................................
....fan blowing air out..........
......|................................
......|................................
.....\/................................
-DOOR (OPEN)---------------|
CAPTION: THIS DID NOT WORK AS WELL!
To summarize, basically what I found cooled faster was not necessarily about trying to get air to circulate more, but to simply get the maximum amount of cool air into the room as fast as I possibly could. Having a fan blow directly into the source of my cold air, in this case the window, even though it only caused air in the top half of my room to circulate, was more effective than trying to get it all to move.
Of course when it comes to computers, no one has a resevoir of cold air behind their case, so this can't really be done. But it certainly does make me think more about fan placement. What if a computer case was to have two fans in front and two in back, and instead of the two in front blowing in and two in back blowing out, have one of the fans in both front and back blow out and the other fan in both front and back blow in? Also, how much do fans placed on the sides or the top of the case help and how do they change airflow (and what about raising the case and cutting a hole in the bottom of it and putting a fan there?) What I'm illustrating here probably wouldn't help most people, but if someone here lives in a cold climate like Minnesota, it might be worthwhile to try this out.
Edit: I must note that the kind of cooling done in the first diagram does something that the second diagram doesn't do: It cools equally. In the first diagram, the whole room is cooled evenly, while in the second, the southeast corner of the room barely gets touched and stays generally at the same temperature. This is important to note because a lot of people have the Lian-li cases with blow holes on top, and that probably means that a lot of the air coming in simply goes out the top and does not pass through the CPU, the most important part! This means all of that noise from the intake fans may be in vain!<P ID="edit"><FONT SIZE=-1><EM>Edited by cakecake on 06/13/02 07:18 AM.</EM></FONT></P>
bum_jcrules
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"The truth is, I think 'positive air pressure' is just a myth."
For all intents and purposes I agree. It is hard to keep a "perfect seal" in any case. The movement of air through holes and cracks can and will happen when positive or negative pressures exist. The result will be the equalizing by the movement of air to the void. (Outside the case in a positive environment and into the case in a negative environment.)
When I talk about positive and negative environments I mean the stimulus that is the cause of a plus or minus. A fan by itself causes a negative environment. Air is forced away by the blade and air from the rear of the blade moves in to repressurize that area. No case will maintain a negative or a positive pressure. That would be too hard. (Unless you had a pump and a tight seal.)
Your example is actually negative pressure stimulus. You are using one fan to force hot air out of the room. The air outside the window is cooler and will flow into the room to replace the air that was forced out.
If you had two windows in your room on the back wall, one on the back left and one on the back right. (Door is in the front.) Put one fan facing out one of the windows. Have another facing into the room. (To be fair, I am talking about two smaller fans that equal the same CFM as the single large fan.) If the fans are of equal CFM, the pressure situation will ultimately go back to being neutral. Air is being forced into the room and out of the room at the same rate. Because there is a set of positive and negative pressures at different sides of the room the airflow will increase. Having the pressure change in two locations would add to airflow better than one large fan. (One large fan would most likely need more energy to function.)
"Edit: I must note that the kind of cooling done in the first diagram does something that the second diagram doesn't do: It cools equally. In the first diagram, the whole room is cooled evenly, while in the second, the southeast corner of the room barely gets touched and stays generally at the same temperature."
That might be the case but your conclusion for the first scenario is a little off. If you had a window in each of the corners of the back of the room, it would cool even more efficiently. The greater the circulation inside the convection cell, the better the transport of energy from hot to cold. (More efficient transfer of energy from high concentration to low.)
The airflow in the first might be better in the first tan in the latter. The door in your room most likely leads to some other part of you house. (Unless you live in a tent or hut.) The air going out your door was being forced into equal pressure situation, because it does not want to go to a higher energy state there will be resistance to the air flowing into the hall out the door.
With the door closed and the air being forced out of your room through the window, the only place for air molecules to go was primarily from outside back through the window. As you can see the flow was better in the first scenario. So again I say that flow is the best way to cool. Not positive nor a negative sustained pressure environment. Equalized force across the whole system will create maximum efficiency.
Back to you...
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
For all intents and purposes I agree. It is hard to keep a "perfect seal" in any case. The movement of air through holes and cracks can and will happen when positive or negative pressures exist. The result will be the equalizing by the movement of air to the void. (Outside the case in a positive environment and into the case in a negative environment.)
When I talk about positive and negative environments I mean the stimulus that is the cause of a plus or minus. A fan by itself causes a negative environment. Air is forced away by the blade and air from the rear of the blade moves in to repressurize that area. No case will maintain a negative or a positive pressure. That would be too hard. (Unless you had a pump and a tight seal.)
Your example is actually negative pressure stimulus. You are using one fan to force hot air out of the room. The air outside the window is cooler and will flow into the room to replace the air that was forced out.
If you had two windows in your room on the back wall, one on the back left and one on the back right. (Door is in the front.) Put one fan facing out one of the windows. Have another facing into the room. (To be fair, I am talking about two smaller fans that equal the same CFM as the single large fan.) If the fans are of equal CFM, the pressure situation will ultimately go back to being neutral. Air is being forced into the room and out of the room at the same rate. Because there is a set of positive and negative pressures at different sides of the room the airflow will increase. Having the pressure change in two locations would add to airflow better than one large fan. (One large fan would most likely need more energy to function.)
"Edit: I must note that the kind of cooling done in the first diagram does something that the second diagram doesn't do: It cools equally. In the first diagram, the whole room is cooled evenly, while in the second, the southeast corner of the room barely gets touched and stays generally at the same temperature."
That might be the case but your conclusion for the first scenario is a little off. If you had a window in each of the corners of the back of the room, it would cool even more efficiently. The greater the circulation inside the convection cell, the better the transport of energy from hot to cold. (More efficient transfer of energy from high concentration to low.)
The airflow in the first might be better in the first tan in the latter. The door in your room most likely leads to some other part of you house. (Unless you live in a tent or hut.) The air going out your door was being forced into equal pressure situation, because it does not want to go to a higher energy state there will be resistance to the air flowing into the hall out the door.
With the door closed and the air being forced out of your room through the window, the only place for air molecules to go was primarily from outside back through the window. As you can see the flow was better in the first scenario. So again I say that flow is the best way to cool. Not positive nor a negative sustained pressure environment. Equalized force across the whole system will create maximum efficiency.
Back to you...
<b>"Sometimes you can't hear me because I'm talking in parenthesis" - Steven Wright</b> :lol:
Thanks for your analysis, it was very informative. I didn't think of that the first time but I can see how the equal pressure environment outside my door (which is in fact a hall) could hinder air being pushed out. I've got another fan configuration in my head right now though. Hot air rises right? Most people have exhaust fans in the back pushing air out, but what if they instead had both the exhaust fan in back and intake fans in front push air INWARD, then have a fan (or fans) push air up from the top of the case, like a blowhole. Would this be any more effective than what we're currently doing? Also, would it make any difference if the processor was positioned flat on the ground (flip chip facing up) instead of being tilted on its side like it is now when it's in a mid-tower case standing up? In other words, what if we took our midtower cases and layed them sideways so that the processor heat would head upwards. Would the heatsink absorb more heat and cool the processor better?
Censorship makes us so much more creative.
Censorship makes us so much more creative.
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