Selecting the Process Fluid Location

When fluid flows at a 90° angle across a tube, it creates turbulence, which is called vortex shedding. The swirls created when a river flows across a tree stump is a common example. The swirls destroy the film resistance to heat transfer created by laminar layers of fluid surrounding the tube. My experience indicates that a shell-side cross-flow velocity of 3 to 5 ft/s is sufficient to obtain this benefit. 

To calculate the cross-flow area, determine the open area between the tubes at the edge of the tube support baffles. For example  

In my book, Process Design for Reliable Operations, I ve given a vivid example of the terrible consequences of placing high-viscosity industrial fuel oil on the tube side of a water cooled exchanger. 

The second reason that shell-side flow is not subject to laminar flow is that the liquid only flows the diameter (several feet) of the shell, before its direction is reversed by the tube support baffles. That s not far enough to establish laminar flow. In the ordinary range of operations, there is no such thing as laminar flow on the shell side. 

Delta P varies with velocity squared (which has doubled) 

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