Selecting Tube Inserts for Shell-and-Tube Heat Exchangers

Tube inserts are useful tools that improve tubeside performance in heat exchangers. The best insert type and design for a particular application depends on flow conditions and fluid properties. Inserts that augment single-phase heat transfer use one or more of the four distinct mechanisms to compensate for boundary layer effects, static mixing, boundary layer interruption, swirl flow, and displaced flow. Static mixing is the physical interchange of fluid particles to different locations in the flow stream by mechanical means. At higher Graetz numbers, the thickness of the laminar boundary layer can easily be reduced by boundary layer interruption inserts. It trips the boundary layer, causing it to thin to its minimum thickness, which enhances heat transfer. Displaced flow inserts increase heat transfer by blocking the flow area farthest from the tube wall, which creates higher velocities along the tube wall heat transfer surface.