sweep problem

ado

Dear friends,

Solving a 2D (axial symetrical cylindrical geometry) unsteady heat conduction prob using a finite differences scheme, I am using TDMA as a solver. I noticed that if I use it in axial direction the solution is very fast. However if I use TDMA in radial direction, the solution obtained takes time and is almost 7 times longer to get than in axial direction. I think the main reason is due to the boundary conditions existing in those directions, since in axial direction both boundaries are at constant temperature. However such usfull information doesn't exist in radial direction. This order of selection is called by Patankar "the sweep". Is it true or I am wrong and there is another reason due to a serious problem in my program itself ???

Thank you for your contributions