Pressure Drop Systems in Parallel 1

[bif]

I currently have an system that moves air and dust that is rated at 5000 m3/hr and the pressure drop through the sysem is measured at 20 m/barg.

I need to extend the system so that 5 of the 'units' above all operate in parrallel, all tying together just before a new fan that I need to specify.

Am I correct in thinking that the pressure drop through each system should be added together or not? ie the new fan would be rated at 2500 m3/hr(5x5000) and pressure drop 100 mbarg (5x20). I know I will need to add on a little for the ductwork after all 4 units combined at the high flowrate, but I am ignoring this for now.

 

[BigInch]

The pressure drop is not added, flow is. The first approximation of pressure drop in the parallel system will be equal to the highest pressure drop of any of the parallel lines.

Why ignore the chunk? You have to add that too.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[bif]

Thanks Big Inch,

It was the principal I needed to clarify.
That means its my 20 mbarg at 5000 mbar, which is my greatest drop at the split, plus my pressure drop in the pipework at 25000 m3/hr.

Thanks again

 

[BigInch]

Cheers.

Like I said, that's the first iteration. The pressure drop across all parallel branches combined will be less than the biggest drop during the first iteration since, if the drops are different during the first iteration, there must be a redistribution of flows amongst the parallel lines such that all parallel pressure drops come out equal. So, the maximum pressure drop would have a tendency to decrease while the minimum pressure drop would increase.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[zdas04]

BigInch,
It is a bit murkier than that. He has a blower on each leg so minor variations in hp, blower-efficiency, and conduit efficiency will allow pretty significant differences in the flow and dP down each leg.

David

 

[bif]

Just to clarify zdas04,
This is a system under suction - like a dust extraction system.
I am looking at 1 fan in the common part of the system and then splitting the upstream flow accross 5'units' in parellel. The plan is to crerate equal pd and hence flow through each common unit.

The way Big Inch has explained it seems to make sense.

 

[zdas04]

If you're happy, I'm happy. I took "units" to be a blower and associated pipe, otherwise how are you getting 20 m/barg pressure drop (i.e., if you started at atmspheric pressur you would be at absolute zero in 20 m)? Guess I didn't understand the question, good thing that BigInch did.

David