Semi-Welded Plate Heat Exchangers

Compressor oil is heavier than liquid ammonia and does not mix with it, so in a flooded or thermosiphon circuit it settles at the low point of the refrigerant side. The cassettes cannot be opened, which makes a drain at that low point and a regular draining routine the only way to keep oil off the plates. Tell us the system type so the connections and drain arrangement suit it.

Choose it on the secondary fluid and its temperature. EPDM is the usual pick for water and glycol, while NBR suits a secondary that carries oil. The welded cassettes keep the refrigerant away from the field gaskets between them, so water chemistry and temperature drive the decision. Tell us the glycol type and concentration too, since inhibitor packages vary in what they do to elastomers.

The working pressure depends on the frame and plate chosen within that span, so not every model is rated at the top figure. On ammonia condensing, the discharge pressure and the relief valve setting set the requirement on the welded side. Give us the refrigerant relief setting and the pump shutoff head on the water side, and the selection will be checked against both.

Cassettes can be added within the frame much as plates are on a gasketed unit, provided the carrying bar and tie bolts leave room. On refrigeration duty the charge matters too, since extra cassettes add internal volume and change how much ammonia a flooded circuit holds. If a plant expansion is planned, mention it at the start so the frame length and the charge are both considered.

A cassette leaking at the weld cannot be repaired in place, so it is replaced whole, or removed as a stopgap with the pack tightened to the shorter dimension. Pulling cassettes lowers capacity, so check the duty margin before running that way for long. On a critical refrigeration system, holding a spare cassette shortens the outage considerably.

Both share a 13.2 inch plate width and a 1-1/2 inch port. The difference is plate height, 34.9 inches against 45.2. A taller plate gives a longer thermal path per pass, which helps reach a close approach, while the shorter plate keeps pressure drop down at the same flow. The thermal rating decides between them, so send the refrigerant conditions and secondary flows rather than choosing by size.