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Mark February 13, 2004 08:14

heat flux question?
 
Hi,

I'm modelling combustion in a rotary kiln using two-step eddy dissipation model. In order to claculate the correct wall temperatures I conducted a number of simulations to obtain the correct heat flux from the flame to the walls. This took quite sometime.

I now want to repeat the simulation but with preheated combustion air to determine its effect on the heat transfer inside the kiln.

My question is, can I use the heat flux profile obtained earlier on the baseline simulation, which does not have preheated air, or should I try and find the correct heat flux for the preheated air simulation too. I want to save time by not doing this but I'm not sure what effect this will have on the result?

Regards,

Mark

Raja Banerjee February 17, 2004 12:18

Re: heat flux question?
 
Hi Mark,

Wall heat flux would depend on the temperature gradient at the wall. From your question, it is not clear whether you are trying to simulate a steady or an unsteady flow condition.

In case of unsteady simulation, you may like to capture the change in the termperature gradient at the wall and therefore, you would need to understand the heat transfer across the wall. This you might try to model by having a wall, define it as solid and give heat transfer coefficient on the other side of the wall and ambient temperature.

In case of steady state simulation, if the preheat temperature is not significant as compared to temperature that you achive after combustion, then you can safely use the heat flux profile that you had obtained previously. However, if the preheat is significant, then either you do the iteration that you had done previously, or model heat transfer across the wall as explained for the unsterady case.

Thanks Raja


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