why convergence depend on temperature gradient

daiga

Hi, I am solving a heat transfer through multidomain system (2D) in CFX. Temperature boundary conditions T1 and T2 are applied on 2 boundaries, remaining boundaries are adiabatic. All properties do not depend on temperature. The problem is that in case of large value T2-T1 there is good agreement between heat flux in and heat flux out but in case of smaller T2-T1 solution does not converge and heat flux in is different from heat flux out? Are there floating point values used by CFX during the calculation process (I hope)? What can be a reason for un-physical solution in case of small temperature gradients 0.0001 K /m ?