Learning Forum

[Vanesa]

Hello,nnI have to do a simple flow analysis in a piping system. There are two blowers sending air flow into a 7 seven storage tanks which are connected through pipes and are modeled as outlets. Whole system is modeled as pipes only. Blower outlets are modeled by giving mass flow inlet boundary condition as the flow rate is known at blower exit. The geometry is such that flow from blower1 and 2 will be coming together through one pipe and then it is branched to a header where again it is branched into 7 different pipes.nSuppose the flow rate at blower exit is 10 kg/s each (so total flow rate = 20 kg/s). So at all the outlets it should be 20/7 = 2.85 kg/s each if we do not consider any friction losses. nWhen I am modeling all the outlets as pressure outlets, the flow distribution is such that outlet 1 is getting maximum flow rate and outlet two he minimum. Other 5 are in medium range. Outlet 1 is giving the value more than 2.85 and outlet 2 gives less than 2.85. nI thought I will restrict the flow at outlet1 and 2 by giving mass flow outlet boundary condition and then specifying the desired mass flow rate value. Results showed a very uneven distribution which was not acceptable. Then I tried by giving target mass flow rate condition nut for which the same thing is happening.nI want flow rates to be 2.85 or nearby this value at each outlet. I can limit all outlets and get the result but physically it is not possible.nHow can I solve this?nThank you.n

[peteroznewman]

nIt would be easier to follow your description if you inserted a sketch of the pipe network and labeled the inlets/outlets and the blowers.n

[Karthik R]

Hello,nJust to add to 's comments: irrespective of whether or not you have frictional losses in your plumbing, you will still have to conserve the overall mass. This means, as long as the flow is leaving only through these 7 outlets, the sum should add up to 20 kg/s in your case. nRegarding the variable flow rate from each outlet, this is expected (unless you have optimized your geometry to give an equal flow rate from each outlet). The problem is with the overall pressure drop through each flow path. Fluid tends to pick the path with the least resistance. Unless the pressure drop between your inlet and each outlet is the same, you will not be able to achieve this. If obtaining the same mass flow rate from each outlet is your final goal, then you will need to optimize your geometry.nKarthikn

[Vanesa]

Thank you so much for your reply. I understood where I was wrong and what has to be done.nThank you so much.nn

[Karthik R]

Excellent! Good luck!n