# Target Mass Flow Rate

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 June 8, 2007, 05:59 Target Mass Flow Rate #1 Brian Tang Guest   Posts: n/a Does anyone know if there is any real difference between using a pressure outlet with target mass flow rate specified and using a mass-flow inlet, but with the velocity specified in a direction that takes it out of the domain? As far as I can tell, both will merely adjust the static pressure each iteration to match the targetted mass flux. Thanks! Brian

 June 11, 2007, 09:11 Re: Target Mass Flow Rate #2 Xiana Guest   Posts: n/a Hi Brian, I have the same question!!! I donīt know why using a pressure outlet with target mass flow should adjust the static pressure to match the targeted mass flux.I did it and I saw that in the solution the outlet pressure is different as what I defined. What happens exactly in this boundary condition: pressure outlet + target mass flow??? Thank you very much Xiana

 June 20, 2007, 19:05 Re: Target Mass Flow Rate #3 red lemon Guest   Posts: n/a target mass flow rate dynamically adjusts downstream static pressure to meet the summed mass flux specified and the defined pressure is ignored. Fluent doesnt allow negative mass flow inlets (try it) so dont use with negative vector. Negative velocity inlets for outlets are ok for incompressible flow though. Always keep a bc as pressure to prevent overconstraining solution.

 June 21, 2007, 02:51 Re: Target Mass Flow Rate #4 Xiana Guest   Posts: n/a Thank you for your advice "red lemon", I will try with negative velocity inlet. I have another problem with the pressure outlet too. I used it without target mass flow and I noticed that the static pressure that Fluent achieved is not exactly what I defined (0 Gauge Pressure). It differs in some punts in a range of -1000 Pa. Does anybody know why? Kind regards Xiana

 June 21, 2007, 07:11 Re: Target Mass Flow Rate #5 red lemon Guest   Posts: n/a So you are specifying a 0Pa gauge pressure but youre seeing -1kPa. Could be that : - you have reverse flow and static is treated as total - you are reporting total instead of absolute If target mass flow rate is used though, the pressure condition is ignored as it cannot to conform to both a constant static pressure AND a fixed mass flux. Enabling one disables the other.