The oil-lampblack technique was employed to reveal the patterns of fluid flow in a shell-and-tube heat exchanger. Flow patterns were visualized adjacent to the shell wall, to the baffle plates, and to each tube of the array. From the flow patterns adjacent to the shell, three recirculation zones were identified. The patterns adjacent to the baffles were similar to those for cross flow over a tube bank, with curvature-related deviations near the shell. The flow patterns adjacent to the tubes showed, typically, a stagnation line/circumferential flow system on the upstream face of each tube and a recirculation tone dominating the tee side. Turn-related deviations from these patterns were in evidence at the window region.