Fan flow

:eek: Hi guys.

I was running a few tests today and was just wondering what your speculations would be

Constants. Fan motor, pwr supply, air baffle, refrigerated space, ambient, test equiptment.

I start with a 20inch fan and matching cowl and measure Watts, Amps, M3/Hr and Rpm.

What will happen to these values if I increse firstly the blade and cowl diameter by 1 inch?

Then increase the pitch.

And decrease the pitch.


I have results but would like your speculation.:)

If you increase the diameter of the fan, the result depends on fan motor characteristics. If the motor didn't work on its limits, the m3/h, watts and amps will increase. If the motor had optimal load before increasing the fan diameter, the m3/h stay constant or decrease, the Watts and Amps stay constant or increase.

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Originally Posted by hybridjunction

:eek: Hi guys.

I was running a few tests today and was just wondering what your speculations would be

Constants. Fan motor, pwr supply, air baffle, refrigerated space, ambient, test equiptment.

I start with a 20inch fan and matching cowl and measure Watts, Amps, M3/Hr and Rpm.

What will happen to these values if I increse firstly the blade and cowl diameter by 1 inch?

Then increase the pitch.

And decrease the pitch.


I have results but would like your speculation.:)

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speaking from a speculative point of view, i think your fan may speed up or slow down. there is also the possibility that the volume of air moved by the fan may increase or decrease. further speculation leads me to believe that if you reverse the direction of the motor it may blow air in the other direction to the first direction in which it was directed.

It's simple , using the same fan but changing a parameter and see how this affects the other parameters, can be done by using the "Rateau" simulation (similitude) formulas (if you consider that the air density is unchangable between the inlet and the outlet of the fan).
If you need more information please let me know

Quote:

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Originally Posted by slingblade

speaking from a speculative point of view, i think your fan may speed up or slow down. there is also the possibility that the volume of air moved by the fan may increase or decrease. further speculation leads me to believe that if you reverse the direction of the motor it may blow air in the other direction to the first direction in which it was directed.

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That is very speculative slingbade thanks.;) :D

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Originally Posted by botrous

It's simple , using the same fan but changing a parameter and see how this affects the other parameters, can be done by using the "Rateau" simulation (similitude) formulas (if you consider that the air density is unchangable between the inlet and the outlet of the fan).
If you need more information please let me know

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Hi botrous, my tests were based working with the fan itself. I've not heard of the "Rateau" simulation formulas.
If you could elaborate, it would be appreciated.:)

I'm new to Refrigeration, yet to do second block of training. So These formulas would give great insight.

Regards

Hybridjunction:)

Anyway, It was found that increasing dia by 1 inch gave less air flow, slower revs, same amps and higher wattage; but when the pitch was increased 8 deg, wattage acually was lower than the former and air flow was greater.

When it came to a load test though, the larger fan with greater pitch failed.

It was put down to the air distribution characteristics.
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