In designing a shell-and-tube heat exchanger, use a 30o triangular tube pitch if possible. This will lower the vortex shedding frequency which is a direct function of something called a Strouhal number. The Strouhal number is a constant composed of the vortex shedding frequency, shell side velocity and tube OD.
The 30o triangular tube pitch has a significantly lower Strouhal number than other tube pitch types. Using Barrington as a source, for 3/4 inch tubes on 30o triangular tube pitch the Strouhal number is 0.21. But for 60o rotated triangular tube pitch the Strouhal number is 0.81.Gulley