# Thread: Formula for Blower Capacity

1. ## Formula for Blower Capacity

friends i need capacity of blower what i already have but how i can calculate theoritically,(Actually Capacity is 3500 CMH)
it's operated at 350 degree C.temperature at suction .having 5 HP motor.

2. Dear raj raval,

From your data, you must be referring to a centrifugal fan rather than a positive displacement blower.

A centrifugal fan has a volume pressure curve, which is very much depending on the geometry of the impeller vanes.
Therefore, it is almost impossible to calculate that curve, without knowing the geometry.

One point on that curve can be measured easily, by blinding off the outlet en measure the generated pressure.
That is the point on the curve, where the volume flow is zero.

The nameplate data can cause some confusion.
Assume that the nameplate data give the airflow at a certain pressure, then that is another point on the curve. (The working point)
However, some manufacturers give as performance data the maximum pressure at airflow is zero and the maximum airflow at open inlet and open outlet. All the energy is then used for dynamic pressure drop and internal losses.

Assuming your data as a “working point” on the curve gives the following approximation.
(pressure ratio for a fan is assumed almost 1)

pressure drop = Power / airflow

pressure drop = 5000 Watt / 0.972 m3/se = 5142 Pa # 51.4 mbar (dynamic pressure converted into static pressure)

Alternatively, measure the whole curve or ask the manufacturer for the required data.

If the fan is not performing as required, then replace the fan, according a new design specification.
It is a small fan after all.

Have a nice day
Teus

3. Hi there,

there is something seriously amiss here. Almost 60m3/min at 350C and only 5hp just does not sound correct. Please check the name plate data and see if you can find out more about the performance data or the manufacturer.