mass flow

luckyboy · May 11, 2018, 00:03

In my case, I set a inflow boundary for injecting hydrogen. The boundary type I choose is mass flow, and the profile as attachment(mass_flow.png) shows.
In the result of mass_avg_flow is showed in attachment(mass_flow_rate.png), and it looks normal, but the total mass of hydrogen in species_mass.out is wrong. I caculated the mass of hydrogen if it is injected by the profile, theoretically,it should be 4.6mg. However, the result from CONVERGE is 4.1mg(mass_H2.png), and the error is 10.9%. It's abnormal, but I don't know why?
The follow is caculation procese:
engine speed=1500rpm, so crank angle speed is 1500*360/60=9000CA/s
massflow is 2235.98mg/s, equally 2235.98/9000=0.2484mg/CA
so total mass:0.2484*(17.5+19.5)/2=4.6mg

xieshengbai · May 14, 2018, 16:32

Hi,

May I know if it is a closed system, please? If you have outflow or backflow at the inflow, then the mass of H2 in the domain may not be the same as you injected. Also, may I know why it is 0.2484*(17.5+19.5)/2 rather than 0.2484*17.5=4.37mg, please?

If it is a closed system and the mass is not conserved, then we have to take a look at your case setup to determine why it is. Please send an inquiry to support@convergecfd.com.

Thank you.

luckyboy · May 14, 2018, 21:38

Because the injection profile is trapezoidal, so it's area is (a+b)/2*h
There is no outflow or backflow boundary. I have sent the case to support@convergecfd.com. Thank you.

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May 14, 2018, 16:32		#2
xieshengbai Member Shengbai Xie Join Date: Aug 2016 Location: Convergent Science, Madison WI Posts: 60 Rep Power: 9	Hi, May I know if it is a closed system, please? If you have outflow or backflow at the inflow, then the mass of H2 in the domain may not be the same as you injected. Also, may I know why it is 0.2484(17.5+19.5)/2 rather than 0.248417.5=4.37mg, please? If it is a closed system and the mass is not conserved, then we have to take a look at your case setup to determine why it is. Please send an inquiry to support@convergecfd.com. Thank you.

May 14, 2018, 21:38		#3
luckyboy Member liyong Join Date: Feb 2017 Posts: 66 Rep Power: 9	Because the injection profile is trapezoidal, so it's area is (a+b)/2*h There is no outflow or backflow boundary. I have sent the case to support@convergecfd.com. Thank you.