8.5.1 Tube support plates
From Figs 3.60 and 3.61, it will be seen that there is a divergence of design philosophy in the method of providing support for the tube bundles. The heater in Fig 3.60 has a vertically-disposed structure extending the length of the tube bundle, made of plate and hollow square-section tube which carries the tube support plates.
Attached to lugs on the periphery of the tube support plates are radial side support bars, which locate the tube bundle in the shell. The support plates also take the weight of the tube bundle while it is being inserted or withdrawn from the shell.
The heater shown in Fig 3.61 uses six stays, over which fit hollow cylindrical spacers to maintain the intended distance between baffle plates. The baffle plates are cropped at top and bottom, as shown in the section through the heater, to allow steam to flow transversely along the top of the shell and drains to flow along the bottom of the heater. The main steam and drain flow paths are indicated on the figure. Two guide rails are provided inside the shell to take the tube bundle weight via the baffle plates. They also support the tube bundle when it is inserted or withdrawn from the shell.
The distance between the tube support plates is determined by the following needs:
- To guide the steam across the tubes to provide efficient heat transfer.
- To support the tubes so that they are not damaged by the action of the steam flowing across them.
The rules used to determine distance between baffles is the same as those given in Section 6.4 of this chapter for HP heaters. The Thorngren  damage numbers are normally used to determine if the distance between baffles is such that flow-induced vibration damage is unlikely.