The shell and tube heat exchanger includes a shell having a fluid inlet and a fluid outlet, and a plurality of tubes disposed inside the shell, the tubes having a fluid inlet and a fluid outlet. An impingement baffle having a plurality of perforations is disposed in the shell between the shell fluid inlet and the tubes. The impingement baffle is configured to guide a heat exchanger fluid from the shell fluid inlet to distribute the heat exchanger fluid uniformly around the tubes. The perforations prevent recirculation and stagnation of fluid flow behind the baffle, thereby preventing fouling and corrosion with subsequent thinning of the tube walls.