A novel supported tube bundle, useful for improving the shell fluid flow distribution in a shell and tube heat exchanger is improved by varying the number and position of rods that comprise the rod baffles in the heat exchanger. The number and position of rods are varied to provide fewer rods adjacent the inlet and outlet of the shell than at other portions of the shell so that flow of shell fluid through areas where the flow normally tends to channel is diverted to areas where flow normally tends to by-pass.