Deciding the mesh element size in CFD
 

Could some one please let me know how to choose / decide on the element size for meshing in a CFD analysis

This FAQ discusses the issue a bit:
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

The reference has a much fuller description:
http://journaltool.asme.org/Template...umAccuracy.pdf

The key text book in the field is "Computational Fluid Dynamics" by Roache.