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Static pressure or airflow fans?

Y33
Go to solution Solved by wzrd,
3 minutes ago, ylst said:

I'm looking to add an intake fan to my case (NZXT S340) and have my eyes on the Corsair AF140 and Corsair SP140 fans. One is airflow optimised and the other static pressure optimised.

Which one should I get? There are no obstructions like drive cages in the case but there will be a dust filter in front of the fan.

Get the AF140s. Dust filter doesn't provide significant air resistance compared to a radiator - they are designed to provide as little air resistance as possible, and will run quieter at a given RPM because of their blade design. You can also run them at lower RPMs and get the same air flow, so your system will be quieter.

28 minutes ago, WoodenMarker said:

What's a derivation and not an actual measurement?

@WoodenMarker It means it doesn't directly measure the airflow, it measures the impact the airflow has on something else, and calculates the airflow using that impact. This is less accurate because it relies on calibration, which is affected by too many factors.

 

28 minutes ago, WoodenMarker said:

I asked earlier but you didn't provide the numbers. I was referring to your calculation here:

You assumed that the filter covered half of the fan and only provided a resistance of 0.00047619% 

Let's say 99% of the fan was covered by the filter's material. How much resistance would that provide using similar calculations?

You misunderstand me. When I assume the mesh is 50% material, I mean that 50% of the mesh itself is made up of actual solid material, and 50% is air holes, through which the air flows. 99% material would just be a solid piece of material, not a filter at all. I did the calculations assuming that 100% of the fan was covered by the filter's material. If you read back carefully, you will see that I assumed the area of the filter to be 0.0196m2, the same as the fan in question. The calculation you are looking for is the one you are quoting...

 

28 minutes ago, WoodenMarker said:

The dust filter is pretty much static and not malleable since it's mounted to the case. It's not moving out of the way for air.

I'm referring to elasticity and malleability on a molecular level. The impact of the air causes a reactionary force (Newton's third law), which contributes to air resistance. It is the reason density is a factor in calculating air resistance. Given that the size of a filter is always going to be the same size as the fan, volume is virtually constant, and so air resistance becomes directly proportional to mass, as density is a function of mass and volume.

 

28 minutes ago, WoodenMarker said:

The results from Puget are from fan grills. Dust filters are more restrictive. The heatsink itself would also inhibit airflow.

I used their value for a mesh dust filter, not the grill. It's in their chart.

 

28 minutes ago, WoodenMarker said:

Copper isn't necessarily a better scenario. A heatsink at copper at 90c contains more heat than an aluminum heatsink of the same size at 90c.

The more heat the heatsink contains, the more heat it has taken away from the CPU (Law of conservation of energy). The whole point is that the heat is taken away from the CPU and spread out over the heatsink. The more conductive the heatsink is and the more heat it can wick away, the cooler the CPU will be, so a copper heatsink is a better scenario. That's why every high-end waterblock is made of copper.

 

28 minutes ago, WoodenMarker said:

What does that 2.75c mean? It's not like the cpu doesn't stop producing heat.

It's the rate of constant heat dissipation per second, expressed in degrees. I changed it to degrees to make it more understandable for you.

 

To elaborate, we would be dissipating heat at a rate of 145W with a dust filter, or 130W without one, all other things being equal, meaning our rate of heat dissipation is approximately 10% lower with the dust filter. Increasing heat dissipation by 15W by removing the dust filter, would cause the temperature to drop by approximately 0.32C, which is a negligible change in real world performance.

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19 minutes ago, WoodenMarker said:

What's a derivation and not an actual measurement?

The airflow spec is in respect to zero static pressure. Any restriction will lower that amount of airflow and any fan with zero static pressure would fail to push air past any restriction.

 

I asked earlier but you didn't provide the numbers. I was referring to your calculation here:

You assumed that the filter covered half of the fan and only provided a resistance of 0.00047619% 

Let's say 99% of the fan was covered by the filter's material. How much resistance would that provide using similar calculations?

 

The dust filter is pretty much static and not malleable since it's mounted to the case. It's not moving out of the way for air.

 

Regarding your calculation here:

The results from Puget are from fan grills. Dust filters are more restrictive. The heatsink itself would also inhibit airflow.

1m² isn't insane. The 212 Evo for example has a bit over 1.1m² of fin surface.

Copper isn't necessarily a better scenario. A heatsink at copper at 90c contains more heat than an aluminum heatsink of the same size at 90c.

Seems extraneous and I don't get it.

What does that 2.75c mean? It's not like the cpu doesn't stop producing heat.

 

@WoodenMarker https://en.wikipedia.org/wiki/List_of_thermal_conductivities As you can see here, copper has a far better thermal conductivity than aluminium, which makes it a more efficient heatsink material, not less efficient.

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49 minutes ago, wzrd said:

You misunderstand me. When I assume the mesh is 50% material, I mean that 50% of the mesh itself is made up of actual solid material, and 50% is air holes, through which the air flows. 99% material would just be a solid piece of material, not a filter at all. I did the calculations assuming that 100% of the fan was covered by the filter's material. If you read back carefully, you will see that I assumed the area of the filter to be 0.0196m2, the same as the fan in question. The calculation you are looking for is the one you are quoting...

I'm referring to elasticity and malleability on a molecular level. The impact of the air causes a reactionary force (Newton's third law), which contributes to air resistance. It is the reason density is a factor in calculating air resistance. Given that the size of a filter is always going to be the same size as the fan, volume is virtually constant, and so air resistance becomes directly proportional to mass, as density is a function of mass and volume.

 

I used their value for a mesh dust filter, not the grill. It's in their chart.

 

It's the rate of constant heat dissipation per second, expressed in degrees. I changed it to degrees to make it more understandable for you.

I don't misunderstand you. That's exactly what I'm asking for. 99% material and 1% air holes using similar calculations.

That density you're referring to is meant to be applied to free moving objects like air molecules and not a static filter mounted to a case. Because you're treating the dust filter as if it isn't static, the resulting resistance becomes unrealistically low. I'm asking for this to show why this calculation isn't accurate.

 

If you mean the loose mesh, that's a fan grill and isn't very similar to standard case dust filters. They mention that it can double as a filter to some extent but it's not very effective.

 

If that's the rate of constant heat dissipation, what would the resulting temperature be after it equalizes?

Presuming that the heatsink is 90c doesn't tell how much heat is created by the cpu. I don't get how the example is relevant.

47 minutes ago, wzrd said:

@WoodenMarker https://en.wikipedia.org/wiki/List_of_thermal_conductivities As you can see here, copper has a far better thermal conductivity than aluminium, which makes it a more efficient heatsink material, not less efficient.

That wasn't my point. A heatsink of copper at 90c would contain more heat than an identically sized heatsink of aluminum at 90c. I'm referring to the resulting temperature and what that means due to the higher specific heat of copper. Using either copper or aluminum as a hypothetical isn't an issue--it was just a comment on how the copper heatsink would've contained more heat.

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7 hours ago, WoodenMarker said:

I don't misunderstand you. That's exactly what I'm asking for. 99% material and 1% air holes using similar calculations.

That density you're referring to is meant to be applied to free moving objects like air molecules and not a static filter mounted to a case. Because you're treating the dust filter as if it isn't static, the resulting resistance becomes unrealistically low. I'm asking for this to show why this calculation isn't accurate.

For a start, filters are far less than 50% material. That was just an arbitrary number. Obviously if you put something that is virtually a solid object over a fan it is going to completely choke it, so it's pointless. There is absolutely no difference in terms of calculations between air moving over something or the object itself moving. That is why wind tunnels exist, because the calculations are the exact same.

 

Calculations for airflow are the same for static objects, there is no difference. If you read a physics textbook, you will understand why.

 

For example, putting a car in a wind tunnel simulates the way the wind will move over the car when the car is moving at high speed, but the car itself isn't moving, the wind is. The calculations are identical.

 

7 hours ago, WoodenMarker said:

If that's the rate of constant heat dissipation, what would the resulting temperature be after it equalizes?

That depends on the TDP of the CPU, the cooler, the ambient etc. But I assumed the CPU to have a TDP of 150W (higher than most CPUs), and found the temperature would drop by a maximum of 0.35C, as I stated already. 

7 hours ago, WoodenMarker said:

Presuming that the heatsink is 90c doesn't tell how much heat is created by the cpu. I don't get how the example is relevant.

Actually, if you read what I actually said in my calculations carefully, I said we were assuming perfect efficiency of heat transfer between the CPU and the heatsink, which is best case scenario. 

 

The example would be the best, most efficient possible cooling situation, which is practically not possible. What you're misunderstanding is that I am giving the fan the best possible shot: the more efficient the transfer of heat from cpu to heatsink, the larger the impact the fan would have on CPU temperatures, because none of the heat dissipation it provides is lost in inefficient heat transfer.

 

In reality the transfer from the airflow, to the heatsink, to the CPU would be lesser, and the filter would have even less of an impact on temperatures. This would make less airflow LESS of an issue, because the heat transfer from CPU to heatsink would become MORE of a thermal bottleneck, meaning reducing fan airflow would have LESS of an effect, and cause an EVEN SMALLER rise in temperatures.

 

11 hours ago, WoodenMarker said:

A heatsink of copper at 90c would contain more heat than an identically sized heatsink of aluminum at 90c. I'm referring to the resulting temperature and what that means due to the higher specific heat of copper.

Copper has a HIGHER thermal capacity, which means it has a LOWER specific latent heat. It takes less energy to change the temperature of copper, which makes it a more effective heatsinkThe more effective the heatsink, the more effect the fan has on CPU temperatures.

 

My point is that I have given you calculations for a BEST CASE scenario, in which the interruption to airflow would be MOST NOTICEABLE and MOST MARKED. In reality, removing the filter would cause an even smaller drop in temperatures than I have demonstrated.

 

In the nicest possible way, I am happy to debate the merits of it, and it all comes down to whether or not you believe the demonstrated temperature delta is significant or not; personally I believe it isn't. However, in your last couple of replies, you haven't been contradicting me, you've just been demonstrating a lack of knowledge of thermodynamics. I don't mean this offensively, but while I am happy to explain how I derived the numbers, there is no point in basically explaining basic thermodynamics - it's a bit off topic. I would be happy to write a separate thread about how exactly heatsinks work on a thermodynamic level, but please read the calculations more carefully, and don't contradict the laws of thermodynamics themselves.

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7 hours ago, wzrd said:

For a start, filters are far less than 50% material. That was just an arbitrary number. Obviously if you put something that is virtually a solid object over a fan it is going to completely choke it, so it's pointless. 

All I'm asking for is the results using similar calculations where the arbitrary number is 99% as opposed to 50%. 

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Just now, WoodenMarker said:

All I'm asking for is the results using similar calculations where the arbitrary number is 99% as opposed to 50%. 

The result would obviously be extremely close to zero, because the area of the obstruction would be almost the same as the area of the draw radius of the fan itself, that doesn't require a calculation.

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Just now, wzrd said:

The result would obviously be extremely close to zero, because the area of the obstruction would be almost the same as the area of the draw radius of the fan itself, that doesn't require a calculation.

Intuitively, it would be zero. I would like the calculation to be done though since I think the result using similar calculations to before would result in a number far from zero.

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Just now, WoodenMarker said:

Intuitively, it would be zero. I would like the calculation to be done though since I think the result using similar calculations to before would result in a number far from zero.

If you insist, illustrated using algebra:

 

Fan area = A1

Filter area = A2

Filter density = p

Drag coefficient = k

Air velocity = v

Filter resistance = Fr

 

Fr = pkv2/2(A1-A2)

 

But A1 = A2 as filter covers ENTIRE fan

 

Therefore


Fr = pkv2/2(0)

 

= pkv2/0

 

= 

 

As air resistance is infinite when the grill is made of solid material.

 

Satisfied?

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Just now, wzrd said:

As air resistance is infinite when the grill is made of solid material.

Satisfied?

99%, not 100%

If you ever need help with a build, read the following before posting: http://linustechtips.com/main/topic/3061-build-plan-thread-recommendations-please-read-before-posting/
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24 minutes ago, WoodenMarker said:

99%, not 100%

OK.

 

If you insist, illustrated using algebra:

 

Fan area = A

Filter area = 0.99A

Filter density = p

Drag coefficient = k

Air velocity = v

Filter resistance = Fr

 

Fr = pkv2/2(A-0.99A)

Fr = pkv2/2(0.01A)

 

Subbing in our numbers from before:

 

Fr = (51.02)(0.42)(502)/0.01 (0.0196) = 2760822.51N

 

This is approximately 281429kg, or the weight of just over 9 aircraft carriers, i.e. pretty close to infinite when talking about computer case fans.

 

As I said, I am happy to explain the concepts, but I'm not going to continue doing equations to prove the laws of physics - they have been proven algebraically by people far smarter than me, a very long time ago :P

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@WoodenMarker I should also clarify that this accounts for air flow resistance, and not air flow dispersion.

 

Dispersion of airflow by the grill is what makes some of the tests questionable (as I described earlier), and could also effect performance, if say you were trying to direct linear airflow over a specific component, which could definitely affect performance in certain situations.

 

As I said I am not being confrontational - I fully accept that there are problems with dust filters for other reasons, but I'm not going to debate the laws of physics/thermodynamics, or the fact that they provide negligible air resistance, because that I can prove. Everything else is a matter of debate, which I am all for, though my personal views on them are probably quite obvious at this point :)

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5 minutes ago, wzrd said:

Fr = (51.02)(0.42)(502)/0.99 (0.0196) = 2760822.51N

This is approximately 281429kg, or the weight of just over 9 aircraft carriers, i.e. pretty close to infinite when talking about computer case fans.

As I said, I am happy to explain the concepts, but I'm not going to continue doing equations to prove the laws of physics - they have been proven algebraically by people far smarter than me, a very long time ago :P

Using the same numbers but swapping out 99% for 50% results in 1097658.857142857N

What am I doing wrong?

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7 minutes ago, WoodenMarker said:

Using the same numbers but swapping out 99% for 50% results in 1097658.857142857N

What am I doing wrong?

You have to account for dispersion of the mass, as is demonstrated here: http://ateam.lbl.gov/hightech/fumehood/students/su99/roberts/Roberts_Fume_Hood.pdf. I had to use windows excel to do so, it's not something you can do on a calculator. At least I can't, I'm an electronic engineer by trade, not a mechanical :P

 

EDIT: I would also like to leave this where it is, I think we have both our points more than adequately, and the thread could easily lead to confusion on what is essentially a moot topic. However I am more than happy to answer any further questions you have by PM.

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6 minutes ago, wzrd said:

You have to account for dispersion of the mass, as is demonstrated here: http://ateam.lbl.gov/hightech/fumehood/students/su99/roberts/Roberts_Fume_Hood.pdf. I had to use windows excel to do so, it's not something you can do on a calculator. At least I can't, I'm an electronic engineer by trade, not a mechanical :P

I don't get it. Your original result of 0.00047619% resistance and 1097658.857142857N seem inconsistent.

How did you come up with 0.00047619% in the first place? It seems like your using different calculations.

 

I can't help but think that you misunderstood the role of density in aerodynamics. Density of the fluid (air) is what matters in determining resistance and not the body (filter).

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Just now, WoodenMarker said:

I don't get it. Your original result of 0.00047619% resistance and 1097658.857142857N seem inconsistent.

How did you come up with 0.00047619% in the first place? It seems like your using different calculations.

 

I can't help but think that you misunderstood the role of density in aerodynamics. Density of the fluid (air) is what matters in determining resistance and not the body (filter).

As I said, if you want a full spectrum of calculations I am more than happy to take pictures of them and send them to you via email, if you want to PM me. I am not going to continually type out equations in detail because you can't follow them.

 

I didn't, you're misunderstanding how dynamics works. For the purposes of calculating air resistance of a static body while air flows over it, we use relative velocity regressions, and perform calculations as if the object itself was moving and the air is static. This is a very common practice, and a very basic principle of relative velocity. You can google it if you don't understand it, but I assure you that it is true. It is also often referred to as a 'wind tunnel calculation' in this field.

 

Liquid dynamics are a completely different field. Liquids and gases do not have even SLIGHTLY similar characteristics.

 

The density of an object is a massive factor in air resistance. Since you have such an aversion to maths and physics, here is a real world sample. If you drop a rock and ball of paper of equal volumes from the same height, they will fall at different speeds.

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Just now, wzrd said:

The density of an object is a massive factor in air resistance. Since you have such an aversion to maths and physics, here is a real world sample. If you drop a rock and ball of paper of equal volumes from the same height, they will fall at different speeds.

This is because of weight and inertia. Weight and inertia are irrelevant on a static dust filter mounted to a case.

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Just now, WoodenMarker said:

This is because of weight and inertia.

 

3 minutes ago, wzrd said:

If you drop a rock and ball of paper of equal volumes

Are you serious? Speed of free fall has nothing to do with either. Also:

 

Density = mass/volume

 

If volume is constant (equal)

 

Density  mass

 

3 minutes ago, WoodenMarker said:

Inertia

The principle of inertia is derived from Newton's first law, which states that a body remains at rest or constant speed when acted on by an outside force. When you allow an object to free fall there is no outside force apart from gravity and, wait for it, AIR RESISTANCE.

 

Therefore, as gravity is applied in the same way to both object, the only differentiating factor is density.

 

At this point you're just being stubborn. This is really really basic physics. I don't mind explaining it, but please don't act as if I'm wrong.

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Just now, wzrd said:

Therefore, as gravity is applied in the same way to both object, the only differentiating factor is density.

No, they have different weight and inertia because of their mass. If they have the same weight and inertia, they would fall at the same speed.

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4 minutes ago, WoodenMarker said:

No, they have different weight and inertia because of their mass. If they have the same weight and inertia, they would fall at the same speed.

Did you even read half of what I said? Inertia does not apply to objects in free fall. It is a derivation of friction and gravity. Friction with air is also known as AIR RESISTANCE. Gravity is constant.

 

Read my above post again please. WEIGHT AND DENSITY ARE DIRECTLY PROPORTIONAL. DENSITY IS A FUNCTION OF MASS (WEIGHT) AND VOLUME, BUT IN THIS CASE VOLUME IS CONSTANT. 

 

Raw weight is not a factor in air resistance. If it was, planes wouldn't exist.

 

You can't just say "no, I disagree with the laws of physics". They're not an opinion, they're a fact. This is getting ridiculous.

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Just now, wzrd said:

You can't just say "no, I disagree with the laws of physics". They're not an opinion, they're a fact. This is getting ridiculous.

I don't disagree with physics. The problem I see is that you are using a formula for determining resistance and swapping the body and fluid. 

Yes--In aerodynamics, air is assumed to be a Newtonian fluid. https://en.wikipedia.org/wiki/Fluid_dynamics

 

The example of a falling rock/paper is barely relevant.

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13 minutes ago, WoodenMarker said:

I don't disagree with physics. The problem I see is that you are using a formula for determining resistance and swapping the body and fluid. 

Yes--In aerodynamics, air is assumed to be a Newtonian fluid. https://en.wikipedia.org/wiki/Fluid_dynamics

 

The example of a falling rock/paper is barely relevant.

Do you actually know what a Newtonian fluid is, or are you just quoting Wikipedia? Like had you even heard of a Newtonian fluid before now?

 

Newtonian fluids and gases behave almost identically except at extremely high speeds (extremely high being supersonic-ish) A newtonian fluid is anything that exhibits linear scaling with shear force, which you clearly don't understand or you wouldn't have even mentioned fluid in the first place. The density of the fluid is already taken into account when calculating the density of the resistance, because air density is accounted for by the calculation of weight of the resistance (reactionary force), which is accounted for in the calculation of density.

 

EDIT: To be perfectly clear and concise, almost all gases act as Newtonian fluids at STP.

 

It's relevant because it illustrates how little you actually know about mechanics, and how unequipped you are for this discussion.

 

EDIT: Here is an explanation of why air is a Newtonian fluid http://www.glossary.oilfield.slb.com/Terms/n/newtonian_fluid.aspx.

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1 minute ago, wzrd said:

Do you actually know what a Newtonian fluid is, or are you just quoting Wikipedia? Like had you even heard of a Newtonian fluid before now?

 

Newtonian fluids and gases behave almost identically except at extremely high speeds (extremely high being supersonic-ish) A newtonian fluid is anything that exhibits linear scaling with shear force, which you clearly don't understand or you wouldn't have even mentioned fluid in the first place. The density of the fluid is already taken into account when calculating the density of the resistance, because air density is accounted for by the calculation of weight of the resistance (reactionary force), which is accounted for in the calculation of density.

 

It's relevant because it illustrates how little you actually know about mechanics, and how unequipped you are for this discussion.

You seemed to have an issue with me calling air a fluid. I wasn't bringing in liquid dynamics.

I don't need insults.

 

The links from PugetSystems, XtremeSystems, Reddit, and SPCR here seem to agree: http://www.silentpcreview.com/Case_Basics_and_Recommendations

'We've examined a handful of filters and their effect on both airflow and temperatures, and invariably find a negative effect; total airflow loss of >50% is not unusual.'

They don't seem anywhere near the 0.00047619% resistance you came up with.

 

My issue is with your statement that the density of the filter matters.

Please link a source that explains the density of the body making a difference in airflow.

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Just now, WoodenMarker said:

You seemed to have an issue with me calling air a fluid. I wasn't bringing in liquid dynamics.

I don't need insults.

 

The links from PugetSystems, XtremeSystems, Reddit, and SPCR here seem to agree: http://www.silentpcreview.com/Case_Basics_and_Recommendations

'We've examined a handful of filters and their effect on both airflow and temperatures, and invariably find a negative effect; total airflow loss of >50% is not unusual.'

They don't seem anywhere near the 0.00047619% resistance you came up with.

 

My issue is with your statement that the density of the filter matters.

Please link a source that explains the density of the body making a difference in airflow.

I did, because fluids in the general term, and Newtonian fluids are completely different things which you clearly didn't know. You're just brushing things under the rug every time I point out where you're wrong. I wasn't insulting you, I was just pointing out that you clearly don't actually have any knowledge of the subject. I apologise if I came across as offensive, it wasn't a slight on your personality.

 

The percentage of airflow loss, and the amount of physical resistive force it creates are vastly different things. As I went on to clarify in further calculations, slight reduction in airflow, even to the degree that they calculated doesn't have a significant effect on temperatures.

 

And my issue with your previous statements was that you didn't simply say "why does density matter?", you just blindly said "it doesn't matter". I will happily explain why density matters:

 

Density matters because of it's correlation to rigidity. Materials that are denser flex less. When something flexes, it absorbs the resistive force, slowing it down. However, when a material is significantly rigid, it allows the material to flow over it, as the hard material of an air filter would. However, if you were to use something less dense, like paper (again), it would flex rather than allowing the air to pass over it, and is also a factor in determining the amount of pressure applied by the filter to the air passing over it. A fixed multiple, called a drag coefficient is then used to account for the shape of the material, and different shapes have different drag coefficients. The reason F1 cars, for example, are shaped the way they are is because it minimises drag coefficient, and therefore minimises air resistance, all other factors being equal.

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5 minutes ago, wzrd said:

The percentage of airflow loss, and the amount of physical resistive force it creates are vastly different things. As I went on to clarify in further calculations, slight reduction in airflow, even to the degree that they calculated doesn't have a significant effect on temperatures.

 

Density matters because of it's correlation to rigidity. Materials that are denser flex less. When something flexes, it absorbs the resistive force, slowing it down. However, when a material is significantly rigid, it allows the material to flow over it, as the hard material of an air filter would. However, if you were to use something less dense, like paper (again), it would flex rather than allowing the air to pass over it, and is also a factor in determining the amount of pressure applied by the filter to the air passing over it. A fixed multiple, called a drag coefficient is then used to account for the shape of the material, and different shapes have different drag coefficients. The reason F1 cars, for example, are shaped the way they are is because it minimises drag coefficient, and therefore minimises air resistance, all other factors being equal.

What do you call a significant different in temps? Temps lowered by 2c when removing the front filter shown in the reddit thread. https://www.reddit.com/r/buildapc/comments/2c8oum/discussion_optimizing_case_airflow_10/

I don't see how calculations hold greater weight than actual results.

 

Paper wouldn't flex much either when mounted to a case. This demonstrates the relevance of density.

Can't find a link that explains how density is important?

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Just now, WoodenMarker said:

Paper wouldn't flex much either when mounted to a case. This demonstrates the relevance of density.

Can't find a link that explains how density is important?

Flex on a molecular level can't be seen by the human eye, so unless you've actually measured flex in a laboratory as I have, which I highly, highly doubt you have, you have no way of concluding that. At all. It demonstrates nothing, because you don't actually know what it is, apparently.

 

A. I really shouldn't have to provide links to illustrate really, really, really basic principles of physics.

B. If you had any mathematical knowledge whatsoever, you would see that it is a variable in the formula used to calculate air resistance, therefore making it a factor in determining air resistance.

C. The internet is not a scientific resource. The fact that someone writes something on the internet does not make it true, and so 'links' are not a scientific source of data.

D. Density is a factor in drag, drag is a factor in air resistance.

 

But I will humour you, here is the link you asked for. https://en.wikipedia.org/wiki/Drag_equation

3 minutes ago, WoodenMarker said:

What do you call a significant different in temps? Temps lowered by 2c when removing the front filter shown in the reddit thread. https://www.reddit.com/r/buildapc/comments/2c8oum/discussion_optimizing_case_airflow_10/

I call something outside of a margin for error. Scientifically, 5% is considered a fair margin for error in statistical analysis. 2/54 = 3.7%, which would be inside the margin for error of a study done using lab-grade equipment in a lab environment, which this reddit study is not. That said, I can see how you would consider it valid, and I accept your opinion as fair, though I disagree with it.

11 minutes ago, WoodenMarker said:

I don't see how calculations hold greater weight than actual results.

Results are only as accurate as the way they were measured. Handheld anemometers are not accurate, as I explained before. Calculations are always accurate and have virtually zero margin for error.

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