heat exchanger in boiler
 

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

Re: heat exchanger in boiler
 

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

Re: heat exchanger in boiler
 

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?

Re: heat exchanger in boiler
 

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?

Re: heat exchanger in boiler
 

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?

Re: heat exchanger in boiler
 

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