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Question which fan should have higher rpm,exhaust fan or intake fan

THX_Buck

Prominent
May 15, 2019
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535
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Hey everyone.I have a corsair carbide spec 01 case and it comes with a intake fan of 120mm which runs around 1200rpm.i am also thinking about getting an exhaust fan of 120mm which has higher rpm than the current intake fan.so which fan should have higher rpm the exhaust one or the intake one.should i swap each other out?
 
Hey everyone.I have a corsair carbide spec 01 case and it comes with a intake fan of 120mm which runs around 1200rpm.i am also thinking about getting an exhaust fan of 120mm which has higher rpm than the current intake fan.so which fan should have higher rpm the exhaust one or the intake one.should i swap each other out?
Neither because rpm don't matter, only flow and pressure.
 

THX_Buck

Prominent
May 15, 2019
39
1
535
0
Neither because rpm don't matter, only flow and pressure.
the fan which i am going to buy has a airflow of 45 CFM and pressure of 2.56 mmH2O(it was written on the box and i dont know what tht means).i dont know the air flow and pressure of my current intake fan as it came with the cabinet
 

Paperdoc

Glorious
Ambassador
Based on the Corsair web pages, It appears the fan included with your case is their Air Series AF120 LED model, with a max air flow of 52 CFM. For case ventilation fans, the pressure spec does not matter much. (See below for more details if you want.) In actual use, the front intake fan SHOULD have a dust filter in front of it, and that reduces the intake fan's air flow a little. So for your situation, using the Corsair fan as front filtered intake, and the new fan at 45 CFM rated air flow for exhaust, would make sense.

Some notes to help understand those fan specs. AIR FLOW is the MAX air flow that fan can deliver when running full speed and with NO items in the air flow path to restrict them. But when there are restrictions (dust filters are minor, finned coolers and rads are big restrictions) the flow is reduced, and the fan experiences a back-pressure to blow against. As the restrictions get bigger, the backpressure increases and the flow is reduced, until at some backpressure (and above) the fan cannot deliver any AIR FLOW. That max back-pressure is the "pressure" spec of the fan. Between those two cases, the graph of actual air flow versus back-pressure is VERY roughly a straight line that begins at max air flow for zero backpressure, and drops down to zero air flow at the max pressure spec. All that is done assuming the fan is operating at max speed; at lower speeds, the air flow and max pressure specs will both be lower.
 

THX_Buck

Prominent
May 15, 2019
39
1
535
0
Based on the Corsair web pages, It appears the fan included with your case is their Air Series AF120 LED model, with a max air flow of 52 CFM. For case ventilation fans, the pressure spec does not matter much. (See below for more details if you want.) In actual use, the front intake fan SHOULD have a dust filter in front of it, and that reduces the intake fan's air flow a little. So for your situation, using the Corsair fan as front filtered intake, and the new fan at 45 CFM rated air flow for exhaust, would make sense.

Some notes to help understand those fan specs. AIR FLOW is the MAX air flow that fan can deliver when running full speed and with NO items in the air flow path to restrict them. But when there are restrictions (dust filters are minor, finned coolers and rads are big restrictions) the flow is reduced, and the fan experiences a back-pressure to blow against. As the restrictions get bigger, the backpressure increases and the flow is reduced, until at some backpressure (and above) the fan cannot deliver any AIR FLOW. That max back-pressure is the "pressure" spec of the fan. Between those two cases, the graph of actual air flow versus back-pressure is VERY roughly a straight line that begins at max air flow for zero backpressure, and drops down to zero air flow at the max pressure spec. All that is done assuming the fan is operating at max speed; at lower speeds, the air flow and max pressure specs will both be lower.
ok thank you dude for explaining.
 

Phaaze88

Illustrious
Ambassador
Also, because most manufacturers don't supply the fan curves for their products - save for be quiet! and Noctua(NF-A12x25), there's no real way to tell how the fan performs at rpms below max.
It's not linear, by the way. A fan run at 50% speed does not mean CFM, SP, and dbA are cut in half.
 
Reactions: CountMike
Jul 2, 2020
40
3
35
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Actually a good approximation is to use the three engineering fan laws to predict flow, pressure, and hp.
Fan Law 1: CFM2 = (RPM2/RPM1) x CFM1 (flow is linearly proportional to fan speed)
Fan Law 2: SP2 = (RPM2/RPM1)^2 x SP1 (static pressure is proportional to the square of the fan speed)
Fan Law 3: HP2 = (RPM2/RPM1)^3 x HP1 (power is proportional the cube of the fan speed)

Might not be exactly, but it's pretty close.
 

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