time step and inner iteration loop

sagar gadkari

Hello all, Actually I am new to CFD. am using CFDesign to do a transient analysis for heating and cooling of a surface by forced convection using water. I tried using 10 iteration loops and it always gives divergence. I once tried with 2 iterations and it was kindoff stable. Can anyone tell or refer me to some nice explanatin of this. I want to know if it matters and why and how?

thank you