Axial Flow Fans

Are you talking about stall/choke (end of curve high flow area), or surge (left hand side of curve - low flow)?

I am talking about stall (High flow area)

Then I do not understand your question. If the discharge pressure increases the fan will run further to the left on the curve, or am I misunderstanding something?

Dear Guest, Your understanding is correct, fan will run further on left hand side. But, the point is in manufacturer data maximum possible pressure is 80 Pa only. Also, since duty point shifted to left hand side air flow is reduced and I am not able to achieve required condition because of this (I think since airflow is reduced efficiency of evaporator is decreased) Regards, Keyur

With the fan running further to the left you will be entering the surge area. From what you say it would appear that you will not be "pumping" any air at all if the pressure that you are demanding is higher than the manufacturers curve can achieve.

You need to address this with the fan manufacturer - you have to trun it faster or increase the diameter. Motor power may limit these alternatives.

Dear Guest,

What happens if fan runs in surge area.

It breaks. In the surge area you get flow reversals when the fan can no longer "push the air forward". These reversal can be very severe and will cause bearing damage and possibly even lead to complete disintegration of the fan. Severity obviously is related to the energy input.

Dear Gueast,

Thanks for such a nice explanation. Also, it would be nice of you if you can explain some basics for fan selection. I mean to say I need to study how to calculate amount of air flow required and at what pressure to get the required heat dissipation in a condenser.

And what happens if we select a fan with higher or lower capacity.

Also, it would be nice of you if you can give your identity.

Regards,

Keyur