Centrigugal Blower

[arun17]

Hi friends,
I am posting this question about centrifugal blower because there is good similarity between a centrifugal pump and a centrifugal blower.

I want to select a blower for a gas which is about 36 times heavier than air at 1 atm. pr. The voulmatric flow rate for this gas is about 55 cfm and pr. drop in pipe line for this flow rate is about 18".

The problem is I don't know how the volumatic flow rate of a centrifugal blower changes with gas or fluid density.
Any suggestions??

"Knowledge is power"

 

[tonyh]

Power is proportional to density, so this device will need to be robust vs an atmospheric air machine. For low pressure ratio (I assume that it is v.low) gas properties are unlikely to be a major issue - and you should discuss this with the vendor in due course.

Flow rate is very low, and peripheral type fan or maybe a PD roots type blower would be the most likely sort of devices i would guess

 

[smckennz]

Hi arun 17

there is an excellent similarity between blowers and pumps.
For your purposes compressibility is not an issue.
A pump is a constant volume device; at a given speed it will deliver a given volume at a given head (in of fluid pumped)regardless of density. There are some minor issues about viscosity and the like but the effects are normally minor. If you have a pump at a given speed that delivers X m^3/s at a head of Y metres of water, then it will deliver approximately X m^3/s of gas at a head of Y metres of gas.
Alfred Buchi, the inventor of the turbocharger, used a cast iron water pump for his exhaust turbine, so you are in good company.
Now for the bad news; as tonyh implies, finding a suitably sized pump with suitable speed rating may take some doing.
A slow speed rootes or screw is probably easier to arrange.
Good luck

Cheers

Steve

 

[arun17]

Thanks tonyh and smckennz. But a little more clarification. I have mentioned the flow rate of 55 cfm and 18" pr. drop in pipeline( water column) or 12 m of process gas. If I select an air blower which can give 55 cfm and 18" water column, I should be able to use the blower without changing the motor.
Since Power =
density of gas* vol. flow rate* head( of the process gas)
= rho*Q*H
If i express the head in terms of water column, density is automatically taken care.
Kindly comment.

"Knowledge is power"

 

[Michael996]

The manufactures generally, publish performance maps for each of their blowers. If for some reason yours doesn't ask them to size the blower.