Fan airflow - Page 1
Forum section: electronics / projects

author: akis
author_rank: Frequent Contributor
timestamp: February 22, 2019, 09:33:07 am
content: Is it possible to increase the airflow of a fan using only space? ie the fan stays the same, spins the same, but the airflow increases based on the shape/size/layout of the intake structure ?

author: johnkenyon
author_rank: Regular Contributor
timestamp: February 22, 2019, 10:03:39 am
content: Quote from: akis on February 22, 2019, 09:33:07 amRemove any obstructions upstream and downstream from the fan.Ensure that the cross-sectional area of any incoming and exhaust vents in the enclosure are sufficient.Ensure that any filtered air input is oversized to compensate for the resistance/restriction offered by the filterAvoid turbulent air flow in constricted areas (increases back pressure, decreases flow)

author: Berni
author_rank: Super Contributor
timestamp: February 22, 2019, 10:32:38 am
content: Its more about the other way around. Reducing the airflow as little as possible by removing obstructions.How much volume a fan can move is dependent on the RPM and the static air pressure between the front and back of the fan.Here is an example chart for a random fan:As you can see increasing the RPM increases the flow while increasing the static pressure reduces the flow. Static pressure is the difference in pressure between the front and back side of the fan. If you put a filter on the fan this causes resistance to air flow so the static pressure goes up until there is enough to push the given airflow trough the filter. The ideal case of 0 static pressure is typically where the CFM of a fan is specified (Fan hanging in free air with no obstruction). The other extreme case is blocking off the fan completely, this drops the airflow to zero but the fan will be producing the maximum air pressure it can. A realistic heatsink is somewhere in between like the filter from before.This characteristic curve is dependent on the fan design. The shape of the fan shroud and shape of the fan blades can optimize a fan for more air flow or more static pressure at a given RPM. A office fan is optimized for flow as it doesn't need pressure while a jet engine compressor turbine is optimized for pressure as it needs to produce a lot of pressure rather than just flow.

author: akis
author_rank: Frequent Contributor
timestamp: February 22, 2019, 06:08:33 pm
content: "Its more about the other way around. Reducing the airflow as little as possible by removing obstructions."OK. I was thinking about cooling the laptop. What if you could flip open half the base thus creating a wedge with the back raised. Then you could use larger fans in this extra space, but there are no "folding" fans, the blades are fixed. Maybe the input manifold then ? This was my thinking.

author: Berni
author_rank: Super Contributor
timestamp: February 22, 2019, 06:17:15 pm
content: Yes fixed veins before a fan are also a thing, but i think these veins are normally used to help it generate higher static pressure by flinging air into the moving blades more aggressively, as usually these blades point opposite of the moving blades. So they could potentially help if whatever the fan is blowing trough is very restrictive. Turbine compressors use these static vanes a lot.In terms of laptop cooling it usually helps quite a bit to lift a laptop off the table since there are often ventilation holes on the bottom. Moving the table farther away makes it easier for it to pull in air. But if a laptop is overheating it usually means that it needs to be taken apart to clean the dust out of it as-well as perhaps put fresh thermal paste on the CPU.