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no fan curves

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henegg

Mechanical
Nov 2, 2007
15
hi
We have an old spray dryer. it has an inlet fan and an exhaust fan.
currently it pulls the inlet air from the the plant causing major air flow issues through out the plant.
The plan is to duct the inlet to the outside so it has its own air source.Then the plant air flow can be straightened out.

the problem is there is no name plate on the fans and no record of what these fans are.
We can get air flows of the inlet and amp reads of the motors.

how can I determine if the current inlet fan can handle the added duct work and merv 13 filters that will be added or if it needs a larger motor or it just won't work.

thanks
tom
 
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Can you install a damper on the outlet on a tempory basis and plot the pressure rise and amperage draw as you close the damper ?
Thereby generating your own fan curve.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor
 
What type of fan is it?

At any rate, this is a case where the fan laws can be nicely applied.

 
thanks guys great suggestions.
There is a damper on the inlet of the fan. It looks like it has not moved in decades. But maybe it is time to make it do some work.

these are centrifugal fans. and I will start digging into the fan laws to see if I can make heads or tails of them.

Do you have any recommendations of where to find the best explanation the fan laws, in laymans terms?
thanks again
Tom
 
Simple calculator here:
Assumed: You want to keep the same fan. You want to keep the same flow.

You are adding ductwork and filters, so you are adding pressure drop. You should be able to calculate the new total pressure drop.

That leaves you with speed to play with.

So to use the calculator:

Enter the known and needed air flow.

Enter your known current fan rpm.

Enter some new speed and calculate. Repeat until the calculation result returns the existing flow rate. Then note the new power requirement.
 
Spend some time also on different fan types (forward curved, backward inclined, radial, axial and etc) as they have different pressure/flow characteristics.

Then make your own curve using a manometer and a VOA meter.

Most fans with the same wheel design and size have similar flow characteristics. Fan laws are your friend.
 
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