Plate and Frame Heat Exchangers

What a Gasketed Plate Unit Is

Each plate in the pack is pressed with a chevron or washboard pattern and carries a gasket in a groove around its edge and around two of its four corner ports. The gasket layout alternates from plate to plate, so seawater enters one pair of ports and can only flow through every second channel, while the fluid being cooled uses the other pair and the remaining channels. The whole stack is compressed between a fixed frame plate and a moving pressure plate by tie bolts.

The result is a great deal of heat transfer surface in a small box. The plates are thin, the channels are narrow, and the corrugations turn the flow turbulent at velocities a tube bundle would consider laminar. That is why a plate unit can be rated with the two fluids leaving only a few degrees apart, a closeness a shell and tube needs far more surface to match.

A plate is a fraction of the thickness of a tube wall and has no corrosion allowance to spend. Any pitting is a hole. Stainless steel in warm, stagnant or silted seawater pits and crevice-corrodes under the gaskets, and copper alloys are not pressed into plates for this duty. Titanium is immune to seawater pitting and crevice attack at the temperatures a cooler sees, and it shrugs off the turbulent, sand-laden flow that a plate pack is designed to run.

That immunity moves the life of the unit onto its gaskets, which is a manageable problem. Gaskets are a scheduled consumable, replaced when the pack is opened, with the choice between NBR and EPDM set by the temperature and the fluid on the other side. The plates themselves are cleaned and put back. Where the fluid on the other side is a refrigerant, ammonia or a high-pressure medium, the Semi-Welded unit takes it in a welded channel with no gasket in contact. More on the elastomers is on the Plate Packs and Gaskets page.