Shell and Tube Heat Exchanger Tube layout and Tube pitch

Tube layout is characterized by the included angle between tubes.

1. Two standard types of tube layouts are the square and the equilateral triangle.

•  Triangular pitch (30o layout) is better for heat transfer and surface area per unit length (greatest tube density.)
• Square pitch (45 & 90 layouts) is needed for mechanical cleaning.

1.  Note that the 30°,45° and 60° are staggered, and 90° is in line.

 For the identical tube pitch and flow rates, the tube layouts in decreasing order of shell-side heat transfer coefficient and pressure drop are: 30°,45°,60°, 90°.

Tube pitch

The selection of tube pitch is a compromise between a

• Close pitch (small values of Pt/do) for increased shell-side heat transfer and surface compactness, and an
• Open pitch (large values of Pt/ do) for decreased shell-side plugging and ease in shell-side cleaning.

Tube pitch PT is chosen so that the pitch ratio is 1.25 < PT/do < 1.5

• When the tubes are to close to each other (Pt/do less than 1.25) , the header plate (tube sheet) becomes to weak for proper rolling of the tubes and cause leaky joints.

Tube layout and tube locations are standardized for industrial heat exchangers.

•  However, these are general rules of thumb and can be “violated” for custom heat exchanger designs.