Problem in solving radiation equations - CFX
 

I'm running CFX case that involves radiation and I've set the Thermal radiation control --> Iteration interval = 10

The solver is quite fast in running for the first 9 iterations , the 10 th iteration takes a lot of time.

Could some one please suggest me the ways of improving this.

Ummm - try Iteration interval = 20..... Isn't that obvious?

Obviously the issue is the radiation model is taking a long time. If your geometry is complex then this is to be expected. You can speed the radiation model up with various parameters, but it has been a while since I did radiation modelling so cannot tell you off the top of my head. But all the parameters are a compromise between accuracy and speed.