I have 3 exchanger in a boiler (rectangular duct). I created 3 zones for these heat exchangers. I defined them in user defined / heat echanger. I used a simple effectivness model with constant effectiveness. But when i am iterating i got this error message: macro .. has zero gas influx. This message appear for several macro and i dont get any change in my temperature profile. The energy equation is not resolving. Do you have an idea? Thank you

please can somebody experimented in heat exchanger modelling with FLUENT help me

I think first that we can not put one heat exchanger in two volumes which are not connected. That is one of my error. But i still dont get the convergence, so i think i got a problem as well with the setup of my heat exchanger model. I am using simple effectiveness model. My flow in flue gas is turbulent, i am using k epsilon model. I define the zone of the heat exchanger being porous and laminar. Somebody has an idea?

i actually succeed to converge the solution by using a SIMPLE C pressure velocity coupling and by decreasing the under relaxation coefficient. But with only one heat exchanger i dont have any significant change in temperature?

If i add manually a source term for energy equation in my boundary condition for the heat exchanger zone, i get a change in my temperature. So it looks like the heat exchanger model is not working properly with the inlet temperature of the auxiliary fluid constant?

i know why know. You CANNOT use a simple effectiveness model with a negative heat rejection. Using a NTU model works fine. Hope it will be usefull for somebody