# Fan design and implementation

#### kalemaxon89

Joined Oct 12, 2022
217
Hi everyone! I don't know if this is the correct section of the forum to ask this question ... if it is not then I ask you to suggest the correct one and I will ask the question there.
Maybe it sounds like a stupid question, but I ask it anyway.

A friend of mine printed this object which is used to hold two small fans with the same characteristics.
I would like to know if the red fan will be less efficient than the green fan because of the "protuberance/tube" that is supposed to carry the air in another direction .. in other words I am wondering if (obviously with two same fans specs) the output of the red fan will be the same as that of the green fan. With "same" I mean for example: same air output speed etc.

I ask for a general opinion before trying to implement with some CAD the circuit.
If you can please argue the answer, even if it includes physical calculations etc.

Thanks!

#### Alec_t

Joined Sep 17, 2013
14,007
The red fan will be less efficient because (a) the ducting offers some air flow resistance and (b) its air flow is being redirected through 90° twice.

#### kalemaxon89

Joined Oct 12, 2022
217
The red fan will be less efficient because (a) the ducting offers some air flow resistance and (b) its air flow is being redirected through 90° twice.

Since I am very interested in the topic, I ask how can you prove what you said? Should I use a simulator? Any calculations? Or do you recommend me any books/articles where this is discussed?

#### Hymie

Joined Mar 30, 2018
1,228
To prove what Alec_t says, you could add a tube (of the diameter of each fan port) above each fan – and measure the airflow within each tube using a hot-wire anemometer.

#### Alec_t

Joined Sep 17, 2013
14,007
I ask how can you prove what you said?
It's due to the laws of physics. Whenever fluid (gas or liquid) flows there will be friction between the fluid molecules and the walls of whatever contains/contacts the flow. Try researching the subject of fluid dynamics.

#### Ya’akov

Joined Jan 27, 2019
8,521
I would like to know if the red fan will be less efficient than the green fan because of the "protuberance/tube" that is supposed to carry the air in another direction
To answer this question you have to define the what the fan is supposed to do.

Efficiency is always relative to the productivity of a mechanism. Productivity depends on the product, and that’s entirely up to you to define.

#### kalemaxon89

Joined Oct 12, 2022
217
It's due to the laws of physics. Whenever fluid (gas or liquid) flows there will be friction between the fluid molecules and the walls of whatever contains/contacts the flow. Try researching the subject of fluid dynamics.
Thank you very much, very kind!

#### kalemaxon89

Joined Oct 12, 2022
217
To answer this question you have to define the what the fan is supposed to do.

Efficiency is always relative to the productivity of a mechanism. Productivity depends on the product, and that’s entirely up to you to define.
To prove what Alec_t says, you could add a tube (of the diameter of each fan port) above each fan – and measure the airflow within each tube using a hot-wire anemometer.
Thank you both for your response.

The fan is to cool the extruder of a 3D printer.
Not having having a hot wire anemometer available, but knowing the maximum temperature reached with the fan originally arranged as it was in production ... now with this modification we will be curious to see if that maximum (critical) temperature will increase, given precisely the inefficient "design" built in XD

#### wayneh

Joined Sep 9, 2010
17,471
FWIW, the way (chemical) engineers estimate such things is to express each obstacle – any deviation from straight pipe – in terms of an equivalent length of straight pipe. There are tables of these equivalencies for just about any obstacle you can imagine. For instance a 90° elbow might cause as much head loss (pressure drop, energy loss) as four pipe diameters of straight pipe. A reducer might add 3.5 pipe diameters.

Of course in your case it looks like the obstacle, the convoluted path, is a complex shape not likely to appear in a table and there's really no way to estimate frictional loss except to collect your own data.

The anemometer wouldn't help you unless you add a long straight section to the output. The flow distribution is never uniform, and the measurement you make will depend on where exactly in the distribution you place the anemometer. I suppose if you can pipe all the flow through the anemometer, that might give the best estimate of the average.

#### Ya’akov

Joined Jan 27, 2019
8,521
Thank you both for your response.

The fan is to cool the extruder of a 3D printer.
Not having having a hot wire anemometer available, but knowing the maximum temperature reached with the fan originally arranged as it was in production ... now with this modification we will be curious to see if that maximum (critical) temperature will increase, given precisely the inefficient "design" built in XD