strange Temperature Increaing when using species Transport and negativ Species Source

tianxiao_tud · August 25, 2020, 10:34

Hallo every one,

i am having a problem at CFD-Simulation, hope i can get some useful infos from you.

I am now simulating a very normal flow in a duct, whoes inlet is fed by a Mixture (o2, n2, ar, co2 and h2o) with given concentrations. The special point in my simulation is that i have an Oxygenreduce through the duct (part of o2 will go through the duct wall), for which i use a negativ o2-Source to consider its effects. As i checked my results, i found that the temperature of the Mixture at the outlet is much higher than the inlet. I dont know how to explain this stange temperature increasing, because i dont have any heat source or thermal boundary conditions on the wall (such as T or q-boundary)

by the way, i have a pressure at inlet about 4.6 bar and temperature of 700 °C, the velocity is very small, about 0.5 m/s. For this problem i am using the incompressible ideal gas model.

viele Gruesse
tx

Eifoehn4 · August 25, 2020, 12:53

Some more information might help to answer your question. Note you can use Latex:

Mathematical model
Numerical method
Is the temperature only a passive scalar (incompressble flow)?
How is the temperature calculated?
Is the density allowed to change? Does the density change?
What heat capacity ratios or specific gas constants are considered for each pure species?

Ideal gas law (thermal):

$T=\frac{p}{\rho R_{mix}}$

Perhaps a loss of oxygen results in a decrease of $R_{mix}$ .

Regards

August 25, 2020, 10:34	strange Temperature Increaing when using species Transport and negativ Species Source	#1
tianxiao_tud New Member Tianxiao Xie Join Date: Nov 2018 Posts: 1 Rep Power: 0	Hallo every one, i am having a problem at CFD-Simulation, hope i can get some useful infos from you. I am now simulating a very normal flow in a duct, whoes inlet is fed by a Mixture (o2, n2, ar, co2 and h2o) with given concentrations. The special point in my simulation is that i have an Oxygenreduce through the duct (part of o2 will go through the duct wall), for which i use a negativ o2-Source to consider its effects. As i checked my results, i found that the temperature of the Mixture at the outlet is much higher than the inlet. I dont know how to explain this stange temperature increasing, because i dont have any heat source or thermal boundary conditions on the wall (such as T or q-boundary) by the way, i have a pressure at inlet about 4.6 bar and temperature of 700 °C, the velocity is very small, about 0.5 m/s. For this problem i am using the incompressible ideal gas model. viele Gruesse tx

August 25, 2020, 12:53		#2
Eifoehn4 Senior Member - Join Date: Jul 2012 Location: Germany Posts: 184 Rep Power: 13	Some more information might help to answer your question. Note you can use Latex: Mathematical model Numerical method Is the temperature only a passive scalar (incompressble flow)? How is the temperature calculated? Is the density allowed to change? Does the density change? What heat capacity ratios or specific gas constants are considered for each pure species? Ideal gas law (thermal): $T=\frac{p}{\rho R_{mix}}$ Perhaps a loss of oxygen results in a decrease of $R_{mix}$ . Regards __________________ Check out my side project: A multiphysics discontinuous Galerkin framework: Youtube, Gitlab.