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Fan Types - Why choose a forward curved centrifugal fan
FanManDan
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My background is in Mechanical & Production Engineering however working for ebm-papst that has expanded into electro-mechanical, some electronic and acoustic engineering. When it comes to acquiring and passing on knowledge, I try to keep it as simple and as least painful as possible. I am happy to receive feedback and if there are any questions that arise from anything that gets published. If I don't know the answer to your question immediately, I am sure that I know someone that can help.

Comments

June 15, 2020 08:12

Hi Dan,

I would like to ask why is that the number of blade of FC fan is always more than that of BC fan?

Thanks!

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May 25, 2020 15:20

Hello Dan,

My question is regarding small supply fans providing outdoor air to large air handler units. The fans used are propeller fans and they are not able to build up sufficient duct static and operate at 100% fan speed. Would a forward curve centrifugal fan be better for this application?

thank you,

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May 18, 2020 11:20

Hi Dan,

Thank you for your very informative article.

If I want to get more pressure (increasing a static head) from my existing blower, what particular modification can I do to accomplish the same? Thank you.

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May 22, 2020 08:59

@EdmundoF.Alvarez Hi Edmundo, without detail on the blower you have, the steps I would take would be as follows... 1) Consider if it is possible to reduce the system resistance by using rigid ducting instead of flexible, removing unneccesary bends or components. 2) If this is not possible then consider if a flared duct on the fan outlet to convert some of the dynamic pressure into static. Slowing the air down by reducing its velocity in a ducted system will lead to reduced system pressure. This will increase the static pressure output of the fan and will require the use of larger cross sectional ducting instead of smaller. 3) if this is not possible and the fan is being driven by belts and pulleys, changing the ratio between the pulleys may provide a higher speed. It is imperative that you check if the motor can handle the extra load! 4) Swap the motor/fan to use a brushless DC / EC motor. This will increase the speed capability and output performance. 5) Change the fan for one that has a higher pressure output. Hopefully this seems a logical process to follow however if you have more specific information on your application and need further assistance please let me know. Regards Dan

June 6, 2019 07:09

Namaste
I am planning to make a table top dust collector using backward curved centrifugal fan. Around 250 cfm free air delivery.
I will be using car air filter of 6"x 10" x2" size.
I will be making a cabinet of 18"x14" height and 14" depth. Open from front. The fan and filter will be fitted rear to this cabinet. The housing for this fan will be 7"x10" x 4" depth. And the filter housing will be attached to the rear of the main cabinet, of size 7"x10"x3" for filter.
Can you please tell me whether it is right or
not. Please advice. Thank you.

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August 27, 2019 08:35

@Umeshgep Hi Umeshgep, To start with a good source for research on this type of equipment would be to search Google images with the following search term - hobby box paint fume extractor A forward curved centrifugal fan has a steep characteristic curve which means as the filter becomes blocked, the flow rate remains relatively stable. Another area to research on design would be to look at Local exhaust ventilation (LEV). This tyopically uses a flexible hose positioned near the work piece that draws the particulates in like a vacuum cleaner. If you would like to send some shetches of what you are doing I will be happy to assist further.

May 22, 2019 13:27

Hello Roger, Sorry for the delay in responding.
In Effect of obstructions on the inlet side D refers to the outer diameter of the impeller. Te dimension used can be in any unit (mm, cm, m, in, ft etc.), however the units used must match.
e.g.
if the diameter of the impeller is 100mm a clearance of 30mm infront of the inlet of the fan satisfies the X/D = 30% condition
Similarly if the impeller diameter is 1 metre the 30% condition is met with a clearance of 0.3m or 300mm.
Hopefully this makes sense.

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May 7, 2019 07:21

What are the units for the Diameter "D" under mounting options?

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February 18, 2019 10:55

Thanks Brad,
Copy and paste errors are the enemy of us all!
I will correct the content now
Best regards
Dan

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February 15, 2019 11:24

Hello Dan,

Nice, informative article. I've saved a copy in my design tips library on my PC.

One little thing - shouldn't the summary heading be
Summary – Why Choose a forward curved centrifugal fan?
instead of
Summary – Why Choose a backward curved centrifugal fan?

(If it should, you'll want to fix the PDF version, too.)

-Brad

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February 15, 2019 09:10

Hello Moritz.A,
Firstly, sorry that this has taken a while to respond. I try to keep up to date with Design Spark but I have been working on other projects recently.
To keep it simple, the choice that you have when selecting a cooling fan is to decide if you want to provide general cooling for the area, or to provide focussed cooling for a localised hotspot.
A backward curved impeller will draw air in through the central inlet and spread it out in a radial direction, exiting out radially from the entire outer circumference of the impeller.
There are some small slimline impellers that are placed in a scroll (much like the fans in this article), and the purpose of the scroll can be for one of two reasons:
1) With a forward curved impeller, the scroll is required both to convert dynamic pressure energy into static pressure energy and to direct the air as it exits the scroll.
2) With a backward curved impeller, a scroll can both change the fan characteristic to deliver a higher pressure as well as direct the air as it exits the scroll.
In both cases, If there is a hot spot issue with your electronic application, it is advisable to direct the cooling airflow at the hot spot by pointing the scroll outlet directly at it rather than using the general uni-directional cooling that a backward curved impeller provides.
I hope that this helps.
Regards, Dan

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January 25, 2019 09:19

Hello Dan,
Thanks a lot for the very informative article.
I would like to ask a question concerning laptop fans. Based on what i have seen so far laptops prioritize backwards curved centrifugal fans, while blower style graphics cards use forward curved fans. Why does this difference exist and is there a reason backward curved fans are prioritized? The only reason I can see is the height limitation of often

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January 9, 2019 09:00

Hello Ali,
Sorry for the delay in responding, with what you have sent I can only give you my best estimate. What I could see in your photo is that you are restricting the flow of the fan using a glass shroud. This will cause a high pressure drop across the fan causing a low flow rate. Using a centrifugal fan may solve this issue however you need to consider how you wisgh to direct the flow around the incubator. From my experience, incubators use radiant heat however you appear to be also making use of convected heat to warm the eggs.
If the fan must be placed at the top of the incubator a backward curved motorised impeller will send air out in all directions around the circumference of the fan. Using a scroll will make the airflow directional. It is important that you know that forward curved motorised impellers only work when there is a scroll installed.
You may wish to consider repositioning the fan in a similar manner to how a fan assisted electric oven works. This is what I am attempting to describe in the lower line of sketches.
Hopefully this helps, let me know if I can assist further
Regards
Dan

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December 17, 2018 08:58

Hi
Is it reasonable to use a blower fan without its housing?
I want to use one in my chicken incubator for better thermal distribution. Previously, I had placed some axial fans but the result was not satisfying. It seems a centrifugal fan without housing is a better choice for air circulation. If it is, what about using backward or forward curved?
I posted a picture of my incubator.
Thank you very much

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December 17, 2018 11:17

Hi
Is it reasonable to use a blower fan without its housing?
I want to use one in my chicken incubator for better thermal distribution. Previously, I had placed some axial fans but the result was not satisfying. It seems a centrifugal fan without housing is a better choice for air circulation. If it is, what about using backward or forward curved?
I posted a picture of my incubator.
Thank you very much

0 Votes

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