Baffled Shell-and-Tube Exchangers

Film coefficients for turbulent flow that exist on the outside or shell side of the conventional baffled shell and tube exchanger are correlated for hydrocarbons, organic compounds, water, aqueous solutions, and gases by... 

In the common types of baffled shell-and-tube exchangers, the shell-side fluid flows across the tubes. The equations for predicting heat-transfer coefficients under these conditions are not the same as those for flow of fluids inside pipes and tubes. An approximate value for shell-side coefficients in a cross-flow exchanger with segmental baffles and reasonable clearance between baffles, between tubes, and between baffles and shell can be obtained by using the following correlation ... 

No. 83038 (1984) Baffled shell-and-tube exchangers Flow distribution, pressure drop and heat transfer on shellside. 

For a plate-baffled shell-and-tube exchanger, the temperature rise (or drop) per baffle pass is small compared to the overall temperature rise (or drop) of the shell fluid in the exchanger so that the shell fluid can be treated as mixed at any cross section. This implies that the number of baffles is large. 

Shell Fluid Bypassing. Various clearances are required for the construction of a plate-baffled shell-and-tube exchanger. The shell fluid leaks or bypasses through these clearances with or without flowing past the tubes. Three clearances associated with a plate baffle are tube-to-baffle hole clearance, bundle-to-shell clearance, and baffle-to-shell clearance. Various leakage streams associated with these clearances are identified elsewhere. 

These high velocities occur at the bundle entrance and exit areas, in the baffle windows, through pass lanes and in the vicinity of tie rods, which secure the baffles in their proper position. In conjunction with this, the shell side fluid generally will take the path of least resistance and will travel at a greater velocity in the free areas or by-pass lanes, than it will through the bundle proper, where the tubes are on a closely spaced pitch. All factors considered, it appears a formidable task to accurately predict heat transfer characteristics of a shell and tube exchanger. 

Shell-and-tube exchangers contain several types of baffles to help direct the flow of both tube-side and shelbside fluids. Pass partition baffles force the fluid to flow through several groups of parallel tubes. Each of these groups of tubes is called a pass, . since it passes the fluid from one head to another. By adding pass partition baffles on each end. the tube-side fluid can be forced to take as many passe.s through the exchanger as desired. 

Essentially, a shell and tube exchanger consists of a bundle of tubes enclosed in a cylindrical shell. The ends of the tubes are fitted into tube sheets, which separate the shell-side and tube-side fluids. Baffles are provided in the shell to direct the fluid flow and support the tubes. The assembly of baffles and tubes is held together by support rods and spacers, Figure 12.2. 

The construction of a condenser will be similar to other shell and tube exchangers, but with a wider baffle spacing, typically h = Ds. 

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