Transient simulation
 

I am analyzing heat generation by heated plates in an enclosed chamber. I have specified heat generation in the plates in cell-zone conditions in fluent. a steady state simulation shows a maximum temperature rise of upto 350K. However, when I run transient simulation the temperature after 1500 iterations is seen to rise only by 0.5K. What can be the reason for this? Can anybody shed a light on this matter..?

what about the time step? what about the estimated characteristic time to reach a steady state? I think that 1500 iterations can be just too few ...

my time step size is 0.005. As far as the characteristic time of my system is concerned, I don't have idea how to find it. Some mention, its the response time of the system. My case is actually natural convection in a closed cavity. The natural convection is setup by temperature change which is caused by heat generation in plates. How should I estimate the characteristic time?